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Corneal Hysteresis and Intraocular Pressure Measurement in Children Using the Reichert Ocular Response Analyzer
Abstract
To examine corneal hysteresis in children with normal eyes and congenital glaucoma and assess intraocular pressure (IOP) measurement with the Reichert Ocular Response Analyzer (RORA).
Observational, cross-sectional study.
setting: Clinical practice. patients: Corneal hysteresis and intraocular pressure (Goldmann correlated [IOPg] and corneal compensated [IOPcc]) were recorded with RORA. IOP was also measured by Goldmann applanation tonometry.
Mean corneal hysteresis of 12.5 mm Hg was recorded in 81 [corrected] normal eyes of 42 children. It was markedly lower (mean 6.3 mm Hg) in 11 eyes of eight children with congenital glaucoma. No correlation was found between age and corneal hysteresis (r = -0.08). IOPg did not differ significantly from Goldmann applanation tonometry (P = .27). IOPcc was statistically significantly greater than IOPg (P = .014). RORA measurement was not possible in the presence of nystagmus but was possible with applanation tonometry. Cooperation with IOP measurement was much higher with RORA (89.8%) compared with applanation tonometry (78.7%).
Corneal hysteresis in children is similar to that reported in adults. No correlation was found with age. In the presence of nystagmus, IOP measurement was possible with Goldmann applanation tonometry but not RORA. Cooperation with IOP measurement was better with RORA than with Goldmann applanation tonometry.
... The mean age of the group of healthy control patients was 38.7 years, similar to that of other published studies [11,14,20,21]. The standard deviation of 15.54 in the age range (9-84 years) shows an age range of the control group subjects greater than that of other published works [10,22]. Mean values of CH (10.75 mmHg), CRF (10.75 mmHg), CCT (556.8 µ), IOPg (15.63 mmHg), and IOPcc (15.72 mmHg) hwere obtained. ...
... In the context of corneal biomechanical parameters of patients with glaucoma, we previously observed a significant decrease in CH when compared to healthy subjects [39,40]. This coincides with the results of other authors [14,[41][42][43] who also found a significant decrease in CH in glaucoma, which was particularly evident in cases of congenital glaucoma [22]. The published results of CRF values are not consistent, as some have obtained low values [37] and others have obtained high values [35]. ...
... Regarding CCT, in the DG group we found no differences in the CCT of DG patients compared to those of the control group, which coincides with the results of other authors [14,22,38,42]. Although low CCT influences an underestimation of IOP by GAT [16], our glaucoma patients did not present different CCT values from those of the normal population, and the underestimation of IOP by GAT (IOPcc higher than IOPg) in the DG group could be related to other corneal biomechanical conditions, such as CH. ...
Purpose:
To evaluate and compare corneal hysteresis (CH), corneal resistance factor (CRF), and central corneal thickness (CCT), measurements were taken between a healthy population (controls), patients diagnosed with glaucoma (DG), and glaucoma suspect patients due to ocular hypertension (OHT), family history of glaucoma (FHG), or glaucoma-like optic discs (GLD). Additionally, Goldmann-correlated intraocular pressure (IOPg) and corneal-compensated IOP (IOPcc) were compared between the different groups of patients.
Methods:
In this prospective analytical-observational study, a total of 1065 patients (one eye of each) were recruited to undergo Ocular Response Analyzer (ORA) testing, ultrasound pachymetry, and clinical examination. Corneal biomechanical parameters (CH, CRF), CCT, IOPg, and IOPcc were measured in the control group (n = 574) and the other groups: DG (n = 147), FHG (n = 78), GLD (n = 90), and OHT (n = 176). We performed a variance analysis (ANOVA) for all the dependent variables according to the different diagnostic categories with multiple comparisons to identify the differences between the diagnostic categories, deeming p < 0.05 as statistically significant.
Results:
The mean CH in the DG group (9.69 mmHg) was significantly lower compared to controls (10.75 mmHg; mean difference 1.05, p < 0.001), FHG (10.70 mmHg; mean difference 1.00, p < 0.05), GLD (10.63 mmHg; mean difference 0.93, p < 0.05) and OHT (10.54 mmHg; mean difference 0.84, p < 0.05). No glaucoma suspects (FHG, GLD, OHT groups) presented significant differences between themselves and the control group (p = 1.00). No statistically significant differences were found in the mean CRF between DG (11.18 mmHg) and the control group (10.75 mmHg; mean difference 0.42, p = 0.40). The FHG and OHT groups showed significantly higher mean CRF values (12.32 and 12.41 mmHg, respectively) than the DG group (11.18 mmHg), with mean differences of 1.13 (p < 0.05) and 1.22 (p < 0.001), respectively. No statistically significant differences were found in CCT in the analysis between DG (562 μ) and the other groups (control = 556 μ, FHG = 576 μ, GLD = 569 μ, OHT = 570 μ). The means of IOPg and IOPcc values were higher in the DG patient and suspect groups than in the control group, with statistically significant differences in all groups (p < 0.001).
Conclusion:
This study presents corneal biomechanical values (CH, CRF), CCT, IOPg, and IOPcc for diagnosed glaucoma patients, three suspected glaucoma groups, and a healthy population, using the ORA. Mean CH values were markedly lower in the DG group (diagnosed with glaucoma damage) compared to the other groups. No significant difference was found in CCT between the DG and control groups. Unexpectedly, CRF showed higher values in all groups than in the control group, but the difference was only statistically significant in the suspect groups (FHG, GLD, and OHT), not in the DG group.
... Lower CH has emerged as a potentially significant factor in the development and progression of glaucoma, and CH of <10 mmHg has been found in glaucomatous patients when compared to normal controls. [7][8][9][10][11][12][13] Low CH indicates a stiffer cornea, which suggests it is unable to disperse the internal force (i.e., stress) created by raised IOP within the anterior segment. This undispersed stress could potentially be transmitted posteriorly to the optic nerve head (ONH), 14 contributing to optic nerve cupping and neuronal cell death. ...
... CH in normal controls has been shown to be between 10.2 and 12.6 mmHg, [42][43][44] with little variation in CH over a 24-h period. 44 13,45,[49][50][51] Mean CH among children has been found to be between 11.78 and 12.5 mmHg. 13,49 The European Prospective Investigation of Cancer (EPIC)-Norfolk Study 50 found a mean CH of 9.35 mmHg in men and 9.74 mmHg in women over 80 years of age. ...
... 44 13,45,[49][50][51] Mean CH among children has been found to be between 11.78 and 12.5 mmHg. 13,49 The European Prospective Investigation of Cancer (EPIC)-Norfolk Study 50 found a mean CH of 9.35 mmHg in men and 9.74 mmHg in women over 80 years of age. Ortiz et al. 51 found CH in those 60-80 years of age was 10.0 -1.2 mmHg and significantly lower when compared to a younger group (children 9-14 years of age, CH = 11.1 -1.1 mmHg, P = 0.01). ...
Biomechanical properties of the cornea have recently emerged as clinically useful in risk assessment of diagnosing glaucoma and predicting disease progression. Corneal hysteresis (CH) is a dynamic tool, which measures viscoelasticity of the cornea. It represents the overall deformability of the cornea, and reduces significantly with age. Low CH has also been associated with optic nerve damage and progression of visual field loss in glaucoma. The extracellular matrix (ECM) constituents of the cornea, trabecular meshwork (TM), sclera, and lamina cribrosa (LC) are similar, as they are predominantly made of fibrillar collagen. This suggests that biomechanical changes in the cornea may also reflect optic nerve compliance in glaucomatous optic neuropathy, and in the known increase of TM tissue stiffness in glaucoma. Increased collagen cross-linking contributes to tissue stiffening throughout the body, which is observed in normal aging and occurs at an accelerated rate in systemic conditions such as fibrotic and cardiovascular diseases, cancer, and glaucoma. We reviewed 3 ECM cross-linking proteins that may have a potential role in the disease process of increased tissue stiffness in glaucoma, including lysyl oxidase (LOX)/lysyl oxidase-like 1 (LOXL1), tissue transglutaminase (TG2), and advanced glycation end products. We also report elevated messenger RNA (mRNA) levels of LOX and TG2 in glaucoma LC cells to support our proposed theory that increased levels of cross-linking proteins in glaucoma play a role in LC tissue stiffness. We highlight areas of research that are needed to better understand the role of cross-linking in glaucoma pathogenesis, leading potentially to a novel therapeutic strategy.
... Corneal biomechanics has become a hot topic related with keratoconus, corneal ectasia and other ophthalmopathy. However, there are still many controversies existing regarding the relationship between corneal biomechanical properties and age [6][7][8][9]. While some studies showed the CH and CRF decreased with advancing age [9], a few articles reported that there was no statistical difference between corneal biomechanical properties and age [6,7]. ...
... Narayanaswamy et al. [9] reported that CH and CRF were significantly negative associated with age. Meanwhile, Kirwan et al. [8] reported that there was no statistical difference in children and adults. We found that the lower mean values of CH and CRF in adults group compared with those in children group. ...
Purpose
To investigate potential impact factors associated with corneal biomechanical properties in Chinese myopia and further to investigate quantifying corneal biomechanics in clinical work.
Methods
Three hundred fifty-five eyes from 181 healthy myopic subjects with a mean age of 25.1 ± 9.4 were recruited in this study. Each patient carried out a comprehensive ophthalmic examination, including corneal hysteresis(CH), corneal resistance factor(CRF), central corneal thickness(CCT), axial length(AL), intraocular pressure(IOP), spherical equivalence(SE) and corneal curvature (K). CH and CRF were measured with the ocular response analyzer(ORA). To analyze the corneal biomechanical characteristics of myopia patients and their association with other parameters.
Result
The multiple linear regression analysis showed that CH was positively associated with CCT, and corneal curvature (all with P < 0.05) and negatively associated with SE and AL)(all with P < 0.05); CRF was positively correlated with CCT, corneal curvature and IOP(all with P < 0.05), but negatively correlated with SE and AL(all with P < 0.05). The CH and CRF values in children group were both higher than adults group (≥ 18 years old) (P < 0.05), but it attributed to that the CCT of children was thicker than adults. Excluding factor of CCT, there was no significant difference in CH and CRF between children group and adult group. Excluding factor of CCT, there was no significant difference in CH and CRF among different stage of age (age 18–48).
Conclusion
The CCT played the most important role of affecting the CH and CRF. The SE, corneal curvature, AL and IOP had a certain influence on corneal biomechanics. Whether the CH and CRF values of individual patient are normal in clinical work, it should refer to the CH and CRF values corresponding CCT sectional range and SE.
... [10][11][12] More speci cally, CH has been shown to be predictive of early changes in parts of the retina, i.e. thinning of peripapillary retinal nerve ber layer and ganglion cell complex, both of which are rst affected in glaucoma. 13 19,20 However, when comparing these two studies the measurements for CH for patients with congenital glaucoma were not consistent (6.3 ± 1.58 vs. 9.1 ± 1.6) suggesting the need for further investigation. Investigations into other forms of secondary glaucoma including neovascular, uveitic, and traumatic have yet to be studied. ...
... Furthermore, the other two studies that have analyzed CH in patients with secondary glaucoma report similar total sample sizes of both 26 patients (40 eyes) and 42 patients (91 eyes), only 11 of which were con rmed with congenital glaucoma, suggesting the di culty that comes with enrolling patients these patients into these types of studies. 19,20 Another limitation was the racial demographics of our patient population. For all study groups, the majority of patients were black or ...
Purpose
To investigate and compare the association of corneal hysteresis (CH) in patients with secondary glaucoma to those with primary open-angle glaucoma (POAG). Additionally, to determine the consistency of CH measurements in patients with secondary glaucoma.
Methods
A total of 84 patients (121 eyes) were prospectively included in this study. 23 patients (46 eyes) were healthy controls, 24 patients (40 eyes) were diagnosed with POAG, and 27 patients (35 eyes) were diagnosed with a form of secondary glaucoma. CH and intraocular pressure (IOP) were measured using the Ocular Response Analyzer. Three measurements per eye were performed and used for the analysis and to determine fluctuations in CH data. One-way ANOVA with post-hoc Bonferroni analysis and Chi-Squared testing was done to determine differences between groups.
Results
All patients were matched for age. Patients in both POAG and secondary glaucoma groups were matched for age and IOP. All groups had similar sex and racial compositions as well as similar proportions of diabetes, hypertension, and hyperlipidemia. CH was lower (p < 0.05) in patients with POAG (9.32 ± 1.64) and secondary glaucoma (7.89 ± 3.18) when compared to healthy controls (11.16 ± 1.60). Fluctuations in CH measurements were minimal in all groups. Further analysis of the secondary glaucoma group revealed no differences in CH between different types of secondary glaucoma (p > 0.05).
Conclusion
Patients with secondary glaucoma have lower CH when compared to POAG or control groups. The ORA exhibits precision of CH measurements for control, POAG, and secondary glaucoma groups.
... However, no significant difference in keratoconus clinical findings was found in the reports of Mahmoud et al. (19) similar to the present series. The distribution of pediatric keratoconus in different age groups can possibly be attributed to the effects of geographic location, ethnicity, sex hormones, corneal viscoelasticity, and corneal stiffness (34,37,38). Among sex hormones, two major classes are androgens and estrogens that peak after puberty in both sexes and then decline with age (34,35). ...
... Among sex hormones, two major classes are androgens and estrogens that peak after puberty in both sexes and then decline with age (34,35). Kotecha et al. (37) reported a negative correlation between corneal viscoelastic properties and advancing age, and the progressive alteration of the keratoconic corneal shape may be caused by elastic deformation (38). Several experimental studies have shown age-related changes in corneal collagen fibril properties, contributing to an increased corneal stiffness with age (39,40). ...
Purpose
To evaluate the distribution of pediatric keratoconus patients and the disease severity based on different age and gender groups in China.
Materials and methods
A total of 446 keratoconus eyes in 266 pediatric patients from January 2019 to January 2022 were included in the cross-sectional study. The clinical findings and severity of keratoconus were recorded and Kruskal–Wallis test, chi-squared test, and Cochran-Mantel-Haenszel (CMH) test were used to compare the parameters between different gender and age groups.
Results
The male/female ratio was 353/93 (3.8:1), and the median age was 16 years (range: 6–17 years). Male patients were statistically younger than female patients ( P = 0.041). The male/female ratio decreased with age ( P for trend = 0.011). The distribution of the topographic keratoconus classification (TKC) stage was significantly different between gender and age groups (all P < 0.05). Male patients had a higher ratio of advanced keratoconus eyes (TKC ≥ 3) than female patients ( P < 0.001), and CMH analysis indicated that being a male was a risk factor for advanced keratoconus after controlling for age (odds ratio: 2.581, P < 0.001).
Conclusion
Male keratoconus patients were younger, with a higher ratio of advanced keratoconus than female patients in the Chinese pediatric patients evaluated. Multicenter studies with larger sample sizes are necessary in the future.
... Participants had to pass a complete ophthalmic examination including slit lamp biomicroscopy, GAT, and fundus biomicroscopy. GAT measurements were taken as one reading performed by an experienced investigator according to standard protocols [22,23]. Consecutive measurements by DCT, ORA, and CST were done. ...
... From the differences of the acting pressures to achieve defined corneal deformation states, the device calculates and provides four variables: the Goldmanncorrelated IOP (IOPg), the corneal-compensated IOP (IOPcc), the corneal resistance factor (CRF), and the corneal hysteresis (CH). Details are described elsewhere [18,23,28]. In the present study, for every eye, three consecutive measurements were obtained and the average (calculated by the ORA software) was used for further analysis. ...
Purpose:
To compare intraocular pressure (IOP) measurements with Goldmann applanation tonometry (GAT), ocular response analyzer (ORA), dynamic contour tonometer (DCT), and Corvis ST (CST) in healthy subjects.
Methods:
In a prospective, observational study, IOP measurements with GAT (GAT-IOPc), ORA (IOPcc), DCT (DCT-IOP), and CST (bIOP) were performed and analyzed in 94 healthy subjects.
Results:
Mean age of the participants was 45.6 ± 17.2 years (range 18 to 81 years). Mean GAT-IOPc was 12.9 ± 2.4 mmHg, mean DCT-IOP was 16.1 ± 2.6 mmHg, and mean IOPcc was 15.6 ± 3.3 mmHg. DCT-IOP and IOPcc were significantly higher than GAT-IOPc (P < 0.001). Mean bIOP was 13.5 ± 2.4 mmHg that was slightly higher but not significantly different from GAT-IOPc (P=0.146). Correlation analysis of IOP values and central corneal thickness (CCT) revealed a negative correlation between GAT-IOPc and CCT (r = -0.347; P=0.001). However, IOPcc, DCT-IOP, and bIOP showed no significant correlation to CCT. Only bIOP revealed a weak but significant age dependency (r = 0.321, P=0.002).
Conclusion:
All tonometry devices showed a good agreement of biomechanical corrected IOP values with GAT-IOPc. As no influence of CCT on IOPcc, DCT-IOP, and bIOP was detectable, the used correction algorithms appear to be appropriate in these tonometers in the clinical setting. The highest agreement was found between GAT-IOPc and bIOP. However, bIOP weakly correlated with participants' age. Further studies are needed to elucidate the role of bIOP for IOP measurement.
... The ocular response analyzer measures CH as a reflection of the viscoelastic properties of the cornea, and CRF as a reflection of the elastic properties of the cornea. It also measures a cornea-adjusted IOP with consideration to the influence of corneal biomechanics on IOP measurements [25,26]. Corneal biomechanical properties and corneal thickness can be affected by many disorders that can cause corneal stromal lamellae changes [23]. ...
... Corneal hysteresis and CRF reflect the combined effects of corneal thickness, hydration, rigidity, curvature, and IOP [25]. Central corneal thickness was found to be positively correlated with the CH and CRF in some reports [38,39]. ...
Purpose:
The aim of this study was to evaluate the corneal biomechanical parameters in patients with ankylosing spondylitis (AS) and to compare them with the healthy subjects.
Methods:
Sixty patients with AS (study group) and 60 healthy subjects (control group) were enrolled in this prospective study. The study group was further classified as active (n:30) and inactive (n:30). After detailed ophthalmological examination including intraocular pressure (IOP) measurement with Goldmann applanation tonometer (IOPGAT), corneal hysteresis (CH), corneal resistance factor (CRF), corneal-compensated IOP (IOPcc), and Goldmann-correlated IOP (IOPg) were measured with the Reichert Ocular Response Analyzer (ORA). Central corneal thickness (CCT) was measured with the Spectral-Domain Optical Coherence Tomography (SD-OCT).
Results:
The study group's mean CH, CCT, IOPg, and IOPGAT values were lower than the control group (p < 0.05 for all variables). The mean CH, CRF, CCT, IOPg, and IOPGAT values were higher in active patients when compared to the inactive ones (p < 0.001, p < 0.001, p = 0.013, p = 0.021, and p = 0.002, respectively).
Conclusions:
AS patients have lower CCT, CH, IOPg, and IOPGAT when compared with healthy subjects. In the active stage of AS, patients present with higher levels of corneal biomechanical parameters with thicker corneas. IOPcc is a more accurate measurement than IOPGAT or IOPg in AS patients.
... Therefore, corneal biomechanical properties, such as corneal hysteresis (CH) and corneal resistance factor (CRF), play important roles in maintaining eye integrity and corneal transparency. Moreover, CH predominantly reflects the viscous properties of the cornea, and CRF is a synthetic measure of corneal elastic properties 23,24 . Numerous studies have shown that corneal biomechanical properties are influenced by different factors, such as central corneal thickness (CCT), spherical equivalence (SE), corneal curvature (K), axial length (AL), intraocular pressure (IOP) and age 25,26 . ...
To analyze the changing trend of CH and CRF values under different influencing factors in T2DM patients. A total of 650 patients with T2DM were included. We discovered that the course of T2DM, smoking history, BMI, and FBG, DR, HbA1c, TC, TG, and LDL-C levels were common risk factors for T2DM, while HDL-C levels were a protective factor. Analyzing the CH and CRF values according to the course of diabetes, we discovered that as T2DM continued to persist, the values of CH and CRF gradually decreased. Moreover, with the increase in FBG levels and the accumulation of HbA1c, the values of CH and CRF gradually decreased. In addition, in patients with HbA1c (%) > 12, the values of CH and CRF decreased the most, falling by 1.85 ± 0.33 mmHg and 1.28 ± 0.69 mmHg, respectively. Compared with the non-DR group, the CH and CRF values gradually decreased in the mild-NPDR, moderate-NPDR, severe-NPDR and PDR groups, with the lowest CH and CRF values in the PDR group. In patients with T2DM, early measurement of corneal biomechanical properties to evaluate the change trend of CH and CRF values in different situations will help to identify and prevent diabetic keratopathy in a timely manner.
... en niveles bajos y la subestiman en niveles altos 9 El iCare® tiende a dar mayores niveles que el Goldmann El Pascal® tiende a dar mayores niveles que el Goldmann, pero muy similares a la manometría 9 . El ORA® tiende a marcar mayores niveles que el Goldmann 10 . Bajo maniobras que inducen Valsalva, como llorar, contener el aire o pujar la P.I.O. ...
Resumen El glaucoma en niños es una entidad poco frecuente, con gran impacto sobre la función visual y calidad de vida para el paciente y su familia. Por esta razón es prioritario identificar y diagnosticar correctamente esta entidad. Los tratamientos que requieren éstos pacientes son costosos, a menudo con la necesidad de varios eventos quirúrgicos, y es crucial hacer diagnóstico diferencial para operar solo a los niños que realmente tienen glaucoma. La finalidad de ésta revisión es hacer una síntesis comprehensiva de las condiciones que se presentan en niños y que los hacen así, sospechosos de glaucoma. Abstract Childhood glaucoma is an unusual entity, with a high impact on visual function and quality of life on the patient and family. For this reason, it is a priority to identify and accurately diagnose it. Treatments are usually expensive, with several surgical events, so a proper diagnosis is crucial so we only operate patients who need surgery. The purpose of this article is to present a comprehensive review of the conditions that make children become glaucoma suspects. Introducción: Los glaucomas infantiles se presentan con una frecuencia de 1:2000, y pueden ser primarios o secundarios. Cuando un niño tiene glaucoma tenemos que actuar de manera pronta, precisa y adecuada, ya que la enfermedad impacta su función visual de manera irreversible. El tratamiento adecuado puede lograr que el niño tenga buena visión para el resto su vida, mientras que la falla del tratamiento puede derivar limitaciones visuales importantes, por esa misma cantidad de tiempo. Criterios de sospecha de glaucoma en niños •Nervio óptico sospechoso o excavaciones sospechosas. •Presión intraocular (P.I.O.) arriba de 21 mmHg en al menos dos ocasiones. •Aumento del diámetro corneal o longitud axial con P.I.O. normal. • Campos visuales sospechosos de glaucoma. Tabla 1: La definición W.G.A. de sospecha de glaucoma en niños incluye UNA de las siguientes condiciones por si misma.
... In normal tension glaucoma (NTG), low CH has a statistically significant correlation with a high cup-to-disk ratio and a low volume and surface of the neuroretinal rim, while in advanced NTG, CH and CRF are lower (47). Several studies have shown that CH was significantly lower in pseudoexfoliative glaucoma than POAG (48) (49), similarly in congenital glaucoma (50,51). In primary angle closure glaucoma (PACG) several studies reported a lower CH, while others identified no correlations between corneal biomechanics and PACG evolution (9). ...
Corneal biomechanical properties reflect the capacity of the cornea to respond to applied mechanical forces. They are an increasingly important domain in ocular pathology, correlated to the diagnosis and evolution of eye diseases such as refractive errors, glaucoma or corneal ectasias. Refractive errors constitute a significant etiology of decreased vision worldwide, with a particular impact in children. Myopic eyes significantly differ from emmetropic eyes in terms of morphology and biomechanics, with differences being reported in both adults and children. In the latter, corneal hysteresis (CH) and the corneal resistance factor (CRF) are significantly lower in myopic individuals, and both biomechanical parameters correlate with the central corneal thickness and axial length. Glaucoma is a progressive optic neuropathy that leads to thinning of the nerve fiber layer and specific visual field loss, in which intraocular pressure (IOP) is an important risk factor. There is an inverse correlation between IOP and CH - a low hysteresis is associated with a high IOP. Furthermore, CH is on average lower in primary open angle glaucoma (POAG) compared to ocular hypertension (OHT) for the same IOP. Significant correlations between CH and the thickness of the ganglion cell layer (GCL) and retinal nerve fiber layer (RNFL), in both POAG and OHT, have been described. Keratoconus is the most frequent corneal ectasia, which leads to a progressive thinning and protruding of the cornea. Biomechanical parameters are severely affected in keratoconus - usually, both CH and CRF are lower compared to normal eyes. The biomechanical behavior of the cornea modulates the evolution of several ocular pathologies. As research is ongoing, more data will enable us to apply this knowledge in diagnosing disease more efficiently and targeting the right treatment for the right patient, including refractive surgery.
... Based on the results of this study, it can be assumed that the pressure applied to the cornea differs significantly from the piston chamber pressure in magnitude and shape. Studies on healthy eyes showed a high variation in those parameters [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52]. The difference between the piston chamber pressure and the airflow pressure at an 11 mm distance can be one of the major factors contributing to such a diversity. ...
(1) The aim of the study was to investigate the spatial and temporal characteristics of the airflow created by two commercially available non-contact tonometers: the CorvisST and the Ocular Response Analyser (ORA). (2) The airflow pressure was measured using a microelectromechanical system (MEMS) pressure sensor to investigate the spatial and temporal distribution. The airflow from the CorvisST and Ocular Response Analyser were mapped to a 600 µm and a 1 mm resolution grid, respectively. (3) Central airflow pressure of the CorvisST (96.4 ± 1.4 mmHg) was higher than that of the Ocular Response Analyser (91.7 ± 0.7 mmHg). The duration of the air-puffs also differed, with the CorvisST showing a shorter duration (21.483 ± 0.2881 ms) than that of the ORA (23.061 ± 0.1872 ms). The rising edge of the CorvisST airflow pressure profile demonstrated a lower gradient (+8.94 mmHg/ms) compared to that of the Ocular Response Analyser (+11.00 mmHg/ms). Both had similar decay response edges: CorvisST −11.18 mmHg/ms, Ocular Response Analyser −11.65 mmHg/ms. (4) The study presents a valid method to investigate the physical dimensions of the airflow pressure of non-contact tonometers. Novel findings relating to the magnitude, duration and spatial characteristics of the respective airflow pressures are reported. It is anticipated that this information will better inform clinical studies and theoretical models relating to ocular biomechanics.
... e NCT utilizes an air jet to achieve corneal flattening based on the same principle that GAT applies to measure IOP [22]. e main advantages of an NCT over GAT include that it is noninvasive and more convenient, thus facilitating patient cooperation, and no direct contact with the cornea occurs, which decreases its consequences [23,24] and lessens any influence on tear film instability in GO patients [25]. In addition, many studies have reported no significant differences between IOP measurements obtained by GAT and an NCT [24,26]. ...
Background:
To investigate the clinical characteristics of Graves' orbitopathy (GO) with elevated intraocular pressure (IOP) using the European Group of Graves' Orbitopathy (EUGOGO) system.
Methods:
In this retrospective study, the clinical data of GO patients with elevated IOP (≥21 mmHg) were collected in Sun Yat-sen Memorial Hospital from January 2010 to June 2016. The demographic characteristics, clinical history of thyroid disease and GO, and ocular examination data were evaluated, and the activity and severity of GO were classified.
Results:
Data were collected from 58 eyes of 39 patients. The durations of thyroid disease and GO were 15.9 ± 18.9 months and 7.5 ± 6.2 months, respectively. The average IOP was 24.8 ± 5.3 mmHg (range: 21-55 mmHg). No significant difference in IOP was observed between active and inactive eyes. Eight eyes (13.8%), 29 eyes (50.0%), and 21 eyes (36.2%) were graded as mild, moderate-severe, and sight-threatening disease, respectively, according to the EUGOGO classification. The IOP was not significantly different among the three EUGOGO grades. No glaucomatous optic nerve damage or visual field defects were found.
Conclusion:
Increased IOP was evident for every grade of GO severity and activity of the EUGOGO system. IOP, glaucomatous optic nerve damage, and visual fields must be evaluated regularly during follow-up evaluations, regardless of the degree of activity and severity of GO.
... Recent studies carried out with ORA have shown that age can cause a reduction in CH and CRF [12][13] , proving that with age the cornea would be less resistant to deformation, that is, "softer". However, another study, also carried out with ORA, has not found a relationship between corneal biomechanical properties and age [14] . In contrast, the study carried out by Valbon et al [15] , where corneal biomechanical properties were measured with Corvis ST, as in our study, showed that only the value of the highest concavity time (HC-time) was correlated with age, proving that the corneas of older patients are more resistant, that is, stiffer. ...
Aim:
To study of corneal biomechanical properties and intraocular pressure (IOP) measured with Corvis Scheimpflug Technology (ST) in patients with childhood glaucoma (CG).
Methods:
Cross-sectional study in which 89 eyes were included 56 of them with CG. Only one eye per patient was included. The following variables were obtained from the clinical history and the ophthalmological examination: age, sex, IOP, number of surgeries, and the cup/disc ratio (CDR). The following parameters were recorded using Corvis ST: corrected by biomechanics IOP (bIOP), not corrected IOP (nctIOP), central corneal thickness (CCT), maximum concavity [radius, peak distance (PD) and deformation amplitude], applanation 1 and 2 (length and velocity). The mean age was 23±14.55 and 33±19.5 years old for the control group and CG group, respectively. Totally 36 were males and 53 were females. In the CG group, 7 patients were controlled only with medical treatment. Sixteen had at least one previous goniotomy, 19 had at least one trabeculectomy, and 11 had an Ahmed implant.
Results:
A significant and positive intraclass correlation coefficient was found between Goldman IOP and the IOP measured by Corvis in both groups. No differences were found between the IOP measured with Corvis and Goldman using a student t-test. Regarding biomechanical parameters, there were differences in the applanation length 2 (A-L2), in the applanation velocity 2 (A-V2) and in the PD. By sex, only the applanation length 1 (A-L1) was found to be different in control group. A positive and significant Pearson correlation was found between CDR and the A-L1.
Conclusion:
Corneal biomechanical properties have shown differences between CG and healthy subjects and also between men and women.
... However, we found that SSI was basically stable before the age of 35. In previous studies, Kirwan used ORA to measure corneas of normal children aged 4 to 18 years, and found that CH was not correlated with age 24 . Another study found that there was no signi cant correlation between biomechanical parameters and age in healthy Chinese adolescents at 4-18 years of age 25 . ...
Background: To investigate the new cornea Biomechanical parameter stress-strain index (SSI) in Chinese healthy people and the factors associated with SSI.
Methods: A total of 175 eyes from 175 participants were included in this study. Axial length was measured with the Lenstar LS-900. Pentacam measured curvature of the cornea and anterior chamber volume (ACV). Cornea biomechanical properties assessments were performed by corneal visualization Scheimpflug technology (Corvis ST). Student’s t-test, one-way ANOVA, partial least square linear regression (PLSLR) and linear mixed effects (LME) model were used in the statistical analysis.
Results: The mean (±SD) SSI was 1.14 ± 0.22 (range, 0.66–1.78) in all subjects and affected by age significantly after age of 35 (P < 0.05). In LME models, SSI was significantly associated with age (β=0.526, P<0.001), axial length (AL) (β=-0.541, P<0.001), intraocular pressure (IOP) (β=0.326, P<0.001) and steepest radius of anterior corneal curvature (RsF) (β=0.229, P<0.001) but not with ACV, biomechanical corrected intraocular pressure (bIOP), flattest radius of anterior corneal curvature (RfF) or central corneal thickness (CCT) (P>0.05 for each).
Conclusions: SSI increased with age after the age of 35. In addition to age, SSI was positively correlated with RsF and IOP, while negatively correlated with AL.
... However, we found that SSI was basically stable before the age of 35. In previous studies, Kirwan used ORA to measure corneas of normal children aged 4 to 18 years, and found that CH was not correlated with age 24 . Another study found that there was no signi cant correlation between biomechanical parameters and age in healthy Chinese adolescents at 4-18 years of age 25 . ...
Background: To investigate the new cornea biomechanical parameter stress-strain index (SSI) in Chinese healthy people and the factors associated with SSI.
Methods: A total of 175 eyes from 175 participants were included in this study. Axial length was measured with the Lenstar LS-900. Pentacam measured curvature of the cornea and anterior chamber volume (ACV). Cornea biomechanical properties assessments were performed by corneal visualization Scheimpflug technology (Corvis ST). Student’s t-test, one-way ANOVA, partial least square linear regression (PLSLR) and linear mixed effects (LME) model were used in the statistical analysis.
Results: The mean (±SD) SSI was 1.14 ± 0.22 (range, 0.66–1.78) in all subjects and affected by age significantly after age of 35 (P < 0.05). In LME models, SSI was significantly associated with age (β=0.526, P<0.001), axial length (AL) (β=-0.541, P<0.001), intraocular pressure (IOP) (β=0.326, P<0.001) and steepest radius of anterior corneal curvature (RsF) (β=0.229, P<0.001) but not with ACV, biomechanical corrected intraocular pressure (bIOP), flattest radius of anterior corneal curvature (RfF) or central corneal thickness (CCT) (P>0.05 for each).
Conclusions: SSI increased with age after the age of 35. In addition to age, SSI was positively correlated with RsF and IOP, while negatively correlated with AL.
... However, we found that SSI was basically stable before the age of 35. In previous studies, Kirwan used ORA to measure corneas of normal children aged 4 to 18 years, and found that CH was not correlated with age [24]. Another study found that there was no significant correlation between biomechanical parameters and age in healthy Chinese adolescents at 4-18 years of age [25]. ...
Background
To investigate the new cornea biomechanical parameter stress-strain index (SSI) in Chinese healthy people and the factors associated with SSI.
Methods
A total of 175 eyes from 175 participants were included in this study. Axial length was measured with the Lenstar LS-900. Pentacam measured curvature of the cornea and anterior chamber volume (ACV). Cornea biomechanical properties assessments were performed by corneal visualization Scheimpflug technology (Corvis ST). Student’s t-test, one-way ANOVA, partial least square linear regression (PLSLR) and linear mixed effects (LME) model were used in the statistical analysis.
Results
The mean (±SD) SSI was 1.14 ± 0.22 (range, 0.66–1.78) in all subjects and affected by age significantly after age of 35 (P < 0.05). In LME models, SSI was significantly associated with age (β = 0.526, P < 0.001), axial length (AL) (β = − 0.541, P < 0.001), intraocular pressure (IOP) (β = 0.326, P < 0.001) and steepest radius of anterior corneal curvature (RsF) (β = 0.229, P < 0.001) but not with ACV, biomechanical corrected intraocular pressure (bIOP), flattest radius of anterior corneal curvature (RfF) or central corneal thickness (CCT) (P > 0.05 for each).
Conclusions
SSI increased with age after the age of 35. In addition to age, SSI was positively correlated with RsF and IOP, while negatively correlated with AL.
... Paletta Guedes [32] in their longitudinal study on PCG eyes, found that the mean CCT in PCG was thicker before surgery and became comparable to the mean CCT in a normal population after surgical treatment. Kirwan et al. [33] found CH to be lower in majority of congenital glaucoma patients. ...
Intraocular pressure (IOP) is currently the only modifiable risk factor in glaucoma. Since all our efforts are directed towards maintaining a stable IOP to halt glaucoma progression, proper understanding about the science behind IOP measurement and biomechanics of cornea becomes paramount. In this paper, we address the basics of corneal biomechanics, recent developments and its impact on glaucoma diagnosis and management. An extensive literature search was done using PubMed and Google Scholar with the search terms such as biomechanics, hysteresis, and glaucoma. Relevant articles published in English language were reviewed.
... Previous studies have shown that older patients present lower values of CH and CCT. 33,34 Although children present a mean CH of 12.5 mmHg, 35 normal adult populations show a mean CH lower than 11 mmHg in all studies. 9,20,30 Therefore, it is possible that the effect of aging on glaucoma damage may be partially related to its effect on ocular biomechanical characteristics. ...
Purpose:
To investigate the incidence and risk factors for glaucomatous visual field progression in eyes with well-controlled intraocular pressure (IOP).
Design:
Prospective cohort.
Participants:
A total of 460 eyes of 334 patients with glaucoma under treatment.
Methods:
Study subjects had a mean follow-up of 4.3±0.8 years. Patients were classified as well controlled if all IOP measurements were less than 18 mmHg. Rates of visual field progression were calculated using ordinary least-squares linear regression of standard automated perimetry (SAP) mean deviation (MD) values over time. Progression was defined as a significantly negative MD slope (alpha = 0.05).
Main outcome measures:
Rates of SAP MD change; mean and peak IOP, and IOP fluctuation; and corneal biomechanics: corneal hysteresis (CH), central corneal thickness (CCT), and corneal index.
Results:
Of the 179 eyes with well-controlled IOP, 42 (23.5%) demonstrated visual field progression. There was no significant difference between progressing and stable patients in baseline MD (-6.4±7.1 decibels [dB] vs. -6.0±6.2 dB; P = 0.346), mean IOP (11.7±2.0 mmHg vs. 12.1±2.3 mmHg; P = 0.405), IOP fluctuation (1.6±0.6 mmHg vs. 1.6±0.5 mmHg; P = 0.402), or peak IOP (14.3±1.9 mmHg vs. 14.6±2.1 mmHg; P = 0.926). Progressing eyes had significantly lower CH (8.6±1.3 mmHg vs. 9.4±1.6 mmHg; P = 0.014) and thinner CCT (515.1±33.1 μm vs. 531.1±42.4 μm; P = 0.018, respectively) compared with stable eyes. In the multivariate analysis, a 1 standard deviation lower corneal index, a summation of normalized versions of CH and CCT, resulted in a 68% higher risk of progression (odds ratio, 1.68; 95% confidence interval, 1.08-2.62; P = 0.021).
Conclusions:
Approximately one-quarter of eyes with well-controlled IOP may show visual field progression over time. Thin cornea and low CH are main risk factors.
... Ocular diseases, such as keratoconus, Fuch's endothelial dystrophy and open angle and normal tension glaucoma were found to reduce CH and CRF values. 6,8,10,13,14 There is an ongoing debate as to the influence of age on CH, few studies have demonstrated insignificant influence of age on CH while establishing a tendency to a lower CH in the elderly. 13,15 Others demonstrated a reduction in CH as we age. ...
Introduction
Laser surgeries are effective and safe, however, over the years data has accumulated about several complications of the procedures, particularly corneal ectasia. Various studies demonstrated the importance of the front layers of the cornea to keep its structure fixed. In order to correct various degrees of myopia, different thicknesses of tissue have to be removed. Therefore, it is conceivable that the risk of developing ectasia might increase depending on the depth of corneal tissue removed.
In the last few years, the Reichert Ocular Respond Analyzer (ORA) for measuring the biomechanical parameters of the cornea has been introduced. Studies demonstrated a decrease in the corneal biomechanical parameters after Laser Assisted Sub-epithelial Keratomileusis (LASEK) surgery. However, the, relation between the depth of tissue removed and the amount of change in the biomechanical parameters had not been tested yet.
Purpose
To evaluate the relationship between corneal biomechanical parameters and corneal tissue ablation thickness.
Methods
Data was retrospectively collected from patient's files that underwent LASEK in private medical center – Hadassah Optimal in Haifa between January 2009 and May 2010. All patients were operated by same surgeon (AB). In our study we included patients that had at least three ORA measurements at three set periods of time; before the operation, up to 3 months postoperative and more than 3 months postoperative. We divided the patients into 3 groups depending on the refractive error and tested the effect of variable factors (Age, Total depth ablated-TDA, percent of total depth ablated-%TDA, sex, refraction). The data was analyzed by descriptive statistics and student t-test to find the relation between LASEK and the corneal biomechanical parameters.
Results
Ninety-eight patients participated in our study, which included 98 separate eye operations. A statistically significant decrease (p < 0.001) was found in CRF, CH, IOPg after LASEK. In group 1 (refraction −0.5 to −2.99): on CH – there was a statistically significant (p < 0.05) weak-moderate effect of TDA and %TDA (Pearson coefficient of 0.4, 0.39 respectively), statistically significant (p < 0.05) effect of age. On CRF — we found a statistically significant (p < 0.05) weak-moderate effect of TDA and %TDA (Pearson coefficient of 0.36 for both factors), statistically significant (p < 0.05) effect of age. In the second group (refraction value −3 to −5.99) only on IOPg a statistically significant (p < 0.05) weak effect of TDA (Pearson coefficient of 0.33) was demonstrated. In the third group, we did not find any effect of the variable factors on the change in biomechanical properties characteristics after LASEK.
Importance
Corneal biomechanical properties influence corneal behavior in certain eye diseases. Moreover, it has been noted that operations and procedures affect these biomechanical properties of the cornea. Hence, it is of great importance to reveal factors that could affect and change such parameters.
How to cite this article
Barbara R, Nassar A, Zadok D, Barbara Corneal Biomechanical Properties Post-LASEK for the Correction of Myopia. Int J Kerat Ect Cor Dis 2014;3(1):23-28.
... Thus, we could analyze corneal deformation parameters independent of these confounders. [18,19] which reported a change in corneal biomechanics with age, and this difference may be explained by the close age distribution in our study group being of adult and middle age ctegories without children and elderly population. A statistically significant moderate correlation was found between CCT and preoperative levels of deformation amplitude and A1 time, supporting findings in other studies [11,12,20]. ...
... 79 It has additionally been demonstrated that eyes with lower CH seem to be associated with altered optic nerve head compliance during the adjustment of IOP. 79 Multiple studies have demonstrated 71,72,[80][81][82][83][84][85][86] Sullivan-Mee and co-workers 70 assessed CH, CCT and IOP in patients with OH and POAG and found that only CH was cantly lower CH in the POAG group. Consequently, the measurement of corneal hysteresis in OH patients can provide additional information that can help the optometrist when assessing the risk of conversion. ...
Increased intraocular pressure is arguably the most important, and currently the only modifiable, risk factor for glaucomatous optic neuropathy. Ocular hypertension is often encountered by clinicians in daily practice and is expected to be seen with increasing frequency as the population ages. Awareness and understanding of the extensive research performed on this subject, with particular focus on the work of the Ocular Hypertension Study Group, are critical for comprehensively assessing the risk of conversion to glaucoma. Although management decisions can be complex, they can be aptly handled by the well-informed optometrist in consultation with their patients.
... 11 The ORA provides the following variables: the corneal-compensated intraocular pressure (IOPcc), the corneal resistance factor (CRF), and the corneal hysteresis (CH). 12 The ORA also provides a keratoconus score based on normative data that represent the probability of existing keratoconus. 13 In the present study, three consecutive measurements for each eye were obtained and the average (calculated by the ORA software) was used for further analysis. ...
Purpose:
To investigate corneal biomechanical parameters in healthy and keratoconic eyes using the Ocular Response Analyzer dynamic bidirectional applanation device (ORA) and the Corvis ST dynamic Scheimpflug analyzer (CST).
Setting:
Department of Ophthalmology, Carl Gustav Carus University Hospital Dresden, Germany.
Design:
Prospective, monocentric, case-control study.
Methods:
Corneal biomechanical parameters were obtained in 60 eyes of 60 healthy participants (Group I) and 60 eyes of 60 keratoconus patients (Group II) with different grades of severity using the ORA and the CST. Participants were matched by age (Group I: 38.3 years ± 12.8 [SD], Group II: 37.3 ± 11.2 years) and intraocular pressure (Group I: 13.7 ± 1.7 mm Hg, Group II: 13.6 ± 1.5 mm Hg).
Results:
For the ORA, the receiver operating characteristic curve analysis showed an area under the curve (AUC) of 0.950 for the keratoconus score, a sensitivity of 87% and a specificity of 93%. The AUC for the corneal resistant factor and corneal hysteresis was 0.930 and 0.868 with a sensitivity of 87% and a specificity of 87%, and sensitivity of 80% and a specificity of 80%, respectively. For the CST, the corneal biomechanical index showed the highest AUC (0.977) with a sensitivity of 97% and a specificity of 98%. The AUC of integrated radius (0.974; 90% sensitivity, 93% specificity) was followed by maximum inverse radius (0.962; 92% sensitivity, 93% specificity). Most parameters were able to discriminate healthy eyes from different keratoconus stages and early stages of keratoconus from moderate stages.
Conclusion:
Both devices allowed for good differentiation between healthy eyes and keratoconic eyes and between different severity grades of keratoconus. Several parameters of ORA and CST revealed high sensitivity and specificity values for keratoconus detection.
... It is possible that the phenomenon reflects the changes in elastic properties of the cornea associated with age, but the authors also note the potential influence of other parameters (intraocular pressure and anterior-posterior axis length) that were disregarded in the study [48]. The comparison of CH and CRF in children and adults did not reveal any age-related differences [49]. ...
... Kirwan et al. concluded that CH in children is like that found in adults [14]. Kotecha et al. found that the effect of age on biomechanical properties of the cornea decreased with older age [15]. ...
The correct estimation of Intraocular Pressure (IOP) is the most important factor in the management of various types of glaucoma. Primary congenital glaucoma is a type of glaucoma that can cause blindness in the absence of control of the IOP. In this retrospective observational study, 95 eyes, including 48 healthy eyes and 47 eyes with Primary Congenital Glaucomatous (PCG) were studied. Two groups were matched for age, gender, and Goldman Applanation Tonometry (GIOP). Corneal Hysteresis (CH), Corneal Resistance Factor (CRF), and Goldman intraocular pressure were measured by ORA (IOPg), and corneal compensated Intraocular Pressure (IOPcc) was measured for each patient using the Ocular Response Analyzer (ORA). Central Corneal Thickness (CCT) was measured by ultrasonic pachymetry. For each patient, one eye was selected randomly. Student's t-test and analytical regression were used for statistical analysis. The two groups were matched for age (P = 0.34), gender (P = 0.47), and GIOP (P = 0.17). Corneal hysteresis and CRF were significantly lower in PCG than in normal eyes (P < 0.0001), yet CCT was significantly thicker in PCG than normal eyes (P < 0.0001). The regression equation on the effect of CH, CRF, and CCT on GIOP in the PCG group showed that CH and CRF (P-value = 0.001 and P-value<0.0001) also had a significant effect yet CCT did not (P-value = 0.691). A significant decrease in CH and CRF was found in the PCG group compared to the normal controls. In the PCG group, the CCT was greater than normal. These results showed the usefulness of biomechanical properties (CH, CRF) in order to interpret IOP measurements. Furthermore, GIOP measurement may not be confined to consideration of CCT alone. A low CH and CRF value could be responsible for under-estimation of GIOP in the PCG group, in comparison to the normal controls.
... Yaş ortalaması 11.39±3.18 yıldı (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16). Sferik eşdeğer -0.34±1.28 ...
ABSTRACT Purpose: To compare the intraocular pressure (IOP) measurements obtained with ocular response analyzer (ORA) and non-contact tonometer (NCT) in the pediatric age group. Material and methods: One hundred forty one eyes of 74 patients were included in the study. IOP measurements of all patients were performed with the Nidek NT 510 NCT. Corneal hysteresis (CH), corneal resistance factor (CRF), corneal-compensated IOP (IOPcc) and Goldmann-correlated IOP (IOPg) were measured with the ORA. Results: The mean age was 11.39±3.18 years. The mean central corneal thickness (CCT) was 547.51±36.95 μm. The mean IOP, IOPcc and IOPg were 17.96±3.29 mm Hg, 17.06±4.14 mm Hg, and 17.72±4.03 mm Hg respectively. The mean CH and CRF were 11.16±2.18, 11.73± 2.25 respectively. There was no statistically signifi cant difference between IOP and IOPg (p= 0.564). IOPcc values were found to be lower than IOP and IOPg values (p=0.021 and p=0. 003, respectively). There was no difference between IOP, IOPcc and IOPg values in patients with CCT less than 540 μm. There was no difference between IOP-IOPcc and IOP-IOPg values in patients with CCT between 540-580 μm. IOPg value was higher than IOPcc (p=0.008). IOP and IOPg values were higher than IOPcc in patients with CCT greater than 580 μm (p=0.01, p=0.00, respectively).
... CH was also found to be significantly lower in eyes with OH, normal tension glaucoma, primary angle-closure glaucoma, and childhood glaucoma compared with normal eyes. 37,[83][84][85][86][87] Assessment of corneal biomechanical properties may be particularly useful in cases of pseudoexfoliation syndrome (PXF) and pseudoexfoliation glaucoma (PXG). PXF is known to cause keratopathy, probably through deposition of pseudoexfoliative material on the corneal endothelium. ...
... Ayrıca BH, dokuda büyüme etkisini hücre apoptozisini önleyerek de sağlamaktadır.12 KH ve KRF gibi korneanın biyomekanik özellikleri korneal hastalıkların sınıflandırılması, refraktif cerrahi, glokom tanı ve takibinde önem taşımaktadırlar.[13][14][15][16][17][18] KH'nin azalmasının ve KRF'nin artmasının glokom ile ilişkili olduğu gösterilmiştir.15,16 ...
... Kirwan C et al. found a lower CH in the majority of congenital glaucoma patients (approximately 6.3 mm Hg) included in their study compared to normal eyes (approximattly12.5 mm Hg) and found no correlation between age and CH [50]. ...
Purpose:
to familiarize the public with the role of corneal biomechanics in glaucoma patient management.Methods:Ocular Response Analyzer (ORA) is the only device that measures in vivo corneal biomechanics. Recent studies regarding "corneal biomechanics and glaucoma" were reviewed and the obtained data were compared in order to present a better understanding of the corneal biomechanical properties involvement in glaucoma care.Results:According to the studies reviewed, in primary open angle glaucoma (POAG) the mean corneal hysteresis (CH) and the corneal resistance factor (CRF) were approximately 2 mmHg lower than in normal eyes. In ocular hypertension (OH), the mean CH was about 1mmHg higher than in POAG patients and 1mmHg lower than in the control group, while the mean CRF was about 2mmHg higher than in POAG and 1mmHg higher than in the control group. Regarding the normal tension glaucoma (NTG), there were studies that showed that the mean CH and CRF were approximately 1mmHg lower than in POAG and studies that showed similar values between the POAG and NTG groups. The mean CH did not differ much between POAG and angle closure glaucoma (ACG), being lower than in normal individuals, while CRF appeared to be higher in the ACG than in normal individuals. Concerning congenital glaucoma (CG), both CH and CRF were about 2mmHg lower than in normal eyes.Conclusions:Corneal biomechanics influenced the IOP measurement and have been proven to be of a great significance in glaucoma patients regardless of the central corneal thickness (CCT). Lower values of CH and CRF could suggest an alteration in the corneal response associated to glaucoma.
... These 2 facts suggested a significant variation in rabbit corneal 8 BioMed Research International viscoelasticity from 3 to 7 months because of the corneal development. CH was relatively stable from 7 to 18 months; this result is not different from Kirwan's result on the children aged 4-18 years old [36]. Another significant decrease in CH from 18 to 24 months needs to be further investigated. ...
Purpose
To study the variations in corneal clinical biomechanical parameters (CCBP) and corneal geometrical parameters of rabbit in relation to age.
Methods
Rabbits aged 3, 7, 12, 18, and 24 months were enrolled. Each eye of the rabbits was tested with Ocular Response Analyzer (ORA), Optical Coherence Tomography (OCT), and Pachymeter to obtain the intraocular pressure (IOP): Goldmann-correlated IOP (IOPg) and Corneal Compensated Intraocular Pressure (IOPcc); CCBP: Corneal Hysteresis (CH) and Corneal Resistance Factor (CRF); corneal geometric parameters: corneal curvature radius (CCR) and central corneal thickness (CCT).
Results
The IOP of the rabbits changes slightly from 3 to 7 months of age, while it significantly decreases from 7 to 18 months of age and increases from 18 to 24 months of age; CH and CRF decrease with the increase of age; CCT increases from 7 to 18 months and decreases from 3 to 7 months of age and from 18 to 24 months of age; CCR presents an upward trend from 3 to 18 months and a significant decrease between 18 and 24 months of age.
Conclusion
CH and CRF are negatively correlated with age. CCT and CCR are positively correlated with age.
... Corneal biomechanical parameters in patients with glaucoma have been evaluated by ORA in some studies and have shown that glaucomatous eyes have reduced CH (Streho et al. 2008;Abitbol et al. 2010;Cankaya et al. 2012). Few studies have evaluated ORA parameters in patients with PCG and reported reduced CH and CRF in eyes with PCG (Kirwan et al. 2006;Gatzioufas et al. 2013;Perucho-Gonz alez et al. 2016); our findings are in accordance with these studies. Reduced CCT and high axial length have been reported to be associated with decreased CH (Altan et al. 2012). ...
Purpose:
To investigate biomechanical and ultrastructural corneal parameters and ocular biometrics in the affected eyes of patients with unilateral primary congenital glaucoma (PCG) as compared to unaffected fellow eyes and age-matched healthy controls.
Methods:
A total of 12 patients with treated unilateral PCG and 10 normal subjects were evaluated. LENSTAR was performed to determine biometric parameters; the ocular response analyser was employed to determine biomechanical properties and slit-scanning confocal microscopy was used for evaluation of corneal ultrastucture.
Results:
Axial length was significantly higher and mean keratometry in affected eyes was significantly flatter in affected eyes as compared to fellow eyes and normal controls (p < 0.05), and a negative correlation was present between axial length and mean keratometry (p < 0.05). Mean aqueous depth and anterior chamber depth were increased in affected eyes as compared to fellow eyes and normal controls (p < 0.05). There was no significant difference in central corneal thickness (CCT) among affected eyes, fellow eyes and normal controls. Corneal hysteresis (CH) was significantly reduced in affected eyes (p < 0.05) and corneal resistance factor (CRF) was also reduced in the affected eyes as compared to fellow eyes and normal controls, although not statistically significant. Mean endothelial cell density was reduced in the affected eyes compared to fellow eyes and normal controls (p < 0.05).
Conclusion:
Corneal biometrics, biomechanical parameters and ultrastructural features are altered in eyes affected with PCG despite clinically normal and clear corneas. These findings should be considered in the preoperative assessment of intraocular or corneal surgery in these patients.
Over the last two decades, there has been growing interest in assessing corneal biomechanics in different diseases, such as keratoconus, glaucoma, and corneal disorders. Given the interaction and structural continuity between the cornea and sclera, evaluating corneal biomechanics may give us further insights into the pathogenesis, diagnosis, progression, and management of glaucoma. Therefore, some authorities have recommended baseline evaluations of corneal biomechanics in all glaucoma and glaucoma suspects patients. Currently, two devices (Ocular Response Analyzer and Corneal Visualization Schiempflug Technology) are commercially available for evaluating corneal biomechanics; however, each device reports different parameters, and there is a weak to moderate agreement between the reported parameters. Studies are further limited by the inclusion of glaucoma subjects taking topical prostaglandin analogues, which may alter corneal biomechanics and contribute to contradicting results, lack of proper stratification of patients, and misinterpretation of the results based on factors that are confounded by intraocular pressure changes. This review aims to summarize the recent evidence on corneal biomechanics in glaucoma patients and insights for future studies to address the current limitations of the literature studying corneal biomechanics.
Worldwide, glaucoma affects about 3% of the population over the age of 50 years and is a leading cause of irreversible visual impairment among older people. Because glaucoma is asymptomatic in its early stages and can be challenging to diagnose clinically, it often remains undiagnosed until substantial vision loss has occurred. Efficient methods of glaucoma screening are therefore warranted for early detection of disease. Identification of risk factors for glaucoma – family history of glaucoma, older age, African or Asian ethnicities, raised intraocular pressure, and thin corneas — have helped inform guidelines on the recommended age at commencement and frequency of glaucoma screenings. A genetic predisposition or family history of glaucoma is one of the most important risk factors for the disease. However, an accurate family history cannot always be ascertained. Genetic testing for genes such as myocilin could help to identify high-risk individuals and, with further research, could even provide insight into individual patients' response to treatment. With the ongoing discovery of glaucoma-associated genes and the advent of polygenic risk scores to identify individuals at high risk of glaucoma, gene-based screening for glaucoma is becoming closer to realisation. In the meantime, regularly screening family members of people with existing glaucoma is an efficient way of detecting early glaucoma. Raising public awareness of glaucoma is also necessary to educate the general public on the key role of routine eye examinations and early disease detection. Future studies should be undertaken to explore efficient public health campaign methods for improving glaucoma awareness.
There are many ways to measure the intraocular pressure (IOP) and all are influenced to some degree by the individual characteristics of the eye. Ocular rigidity (OR) is a familiar concept used in ophthalmology to describe the relationship between pressure and volume changes in the eyeball. This concept partly explains why IOP measurements vary between different types of tonometers. Some tonometers are more heavily influenced by OR than others, due to different amounts of corneal deformation, and volume of fluid displaced during tonometry. More recent tonometers either produce less corneal deformation and less fluid displacement or, attempt to compensate for variations in the biomechanical characteristics of the cornea. Surgical intervention can influence the true IOP but, additionally modify the OR and therefore differentially influence the results from different tonometers. Clinicians should be aware of these effects when interpreting IOP measurements, especially in eyes that have had surgery or have other characteristics that may affect OR. A deeper understanding of the factors that influence OR might lead to the development ofmore accurate instrumentation that is less influenced by OR.
In the past few decades there has been a constantly increasing interest in the biomechanical properties of the cornea. The cornea is comprised of tissue with elements of both elasticity and viscosity [1, 2]. Any elements that change the structure of the cornea may impact its biomechanical properties. The 3-dimensional meshwork of transversely oriented collagen fibers plays a dominant role in giving the corneal stroma its specific visco-elastic configuration and is a significant factor in the determination of corneal shape [3].
Glaucoma is a multi-factorial disease often associated with elevated intraocular pressure and increased rigidity of the trabecular meshwork (TM). Stiffening of inner wall endothelial cells of the Schlemm’s canal (SC) has also been documented with glaucoma. Such stiffening is often associated with changes in the extracellular matrix and thus plays a critical role in maintenance of aqueous outflow homeostasis. Considering that biomechanics and topographical cues from the matrix significantly influence cellular responses, it is imperative to understand the biomechanical attributes of the TM. Here, we review relevant studies that have measured the elastic moduli of the TM from humans and a variety of non-human animal models including the various methods used. The reported elastic moduli vary from kilopascal to megapascal range depending on the method utilized in excised tissues. Multiple attempts are currently underway for in vivo quantifications which would significantly be beneficial for diagnosis of the disease. We conclude the chapter by discussing briefly the cellular consequences to the dynamically changing matrix stiffness and its implication in disease etiology and progression.
Background:
Rebound tonometry (RBT) can be used to measure intraocular pressure (IOP) in children unable to tolerate measurement with applanation tonometry (AT) while awake. RBT readings are often 2-3 mm Hg higher than AT. We have experienced children with a repeatedly higher difference between RBT and AT measurements (≥6 mm Hg). The purpose of this study was to identify demographic and ocular characteristics that contribute to this artifactuous discrepancy.
Methods:
The medical records of pediatric patients with IOP measured by RBT followed by AT within 6 months without intervening surgery or change in medical management were retrospectively reviewed to identify potential predictors of greater difference between RBT and AT readings.
Results:
A total of 123 eyes of 65 patients were included. In patients with normal IOP (≤24 mm Hg), 18.5% had a ≥6 mm Hg difference between RBT and AT, with RBT being higher. Risk factors for this included presence of persistent fetal vasculature (PFV), increased corneal diameter, and higher initial RBT value (>20). In patients with elevated IOP (>24 mm Hg), 77% had ≥6 mm Hg difference, with larger corneal diameter being the sole predictor. Eyes were less likely to have significant RBT-AT difference if there was corneal opacity or iris abnormalities in eyes with elevated IOP (>24 mm Hg).
Conclusions:
In some children, RBT readings are ≥ 6 mm Hg higher than AT readings. Caution should be taken when interpreting RBT values in patients with PFV, increased corneal diameter, and higher initial RBT values.
Purpose:
To determine the agreement between intraocular pressure (IOP) measurements obtained using the handheld version of the Goldmann applanation (Perkins; Clement-Clarke, Haag-Streit, Harlow, United Kingdom), rebound Icare-Pro (Icare, Tiolat Oy, Helsinki, Finland), and Tonopen XL (Reichert Inc., Depew, NY) tonometers in children with childhood glaucoma and to identify factors that may affect those measurements.
Methods:
Ninety-one eyes of 46 children with early-onset childhood glaucoma were included in this cross-sectional study in which IOP, ocular axial length, anterior chamber depth, lens thickness, vitreous length, and central corneal thickness measurements were obtained under general anesthesia. Agreement between tonometers was evaluated using intraclass correlation coefficients (ICCs) and the Bland-Altman method. The influence of ocular biometric parameters and central corneal thickness on IOP measurements was analyzed using multiple linear regression analysis.
Results:
The mean age of the children in the current study was 29.1 months (range: 13 to 31 months). The Icare-Pro and Tonopen XL overestimated IOP measurements compared to the Perkins tonometer (Icare-Pro-Perkins mean IOP difference: 2.2 ± 3.4 mm Hg, P < .0001, 95% confidence interval [CI]: 1.5 to 2.9 vs Tonopen XL-Perkins mean IOP difference: 6.7 ± 7.1 mm Hg, P < .0001, 95% CI: 5.2 to 8.2). The Icare-Pro showed greater agreement with the Perkins tonometer than the Tonopen XL (ICC: 0.789, 95% CI: 0.697 to 0.856, P < .0001 vs 0.453, 95% CI: 0.272 to 0.603, P < .0001). Ocular axial length affected IOP measurements the most, finding increased impact on Tonopen XL (slope: 0.086, 95% CI: 0.013 to 0.16, P = .022 vs 0.997, 95% CI: 0.369 to 1.625, P = .002 vs 1.571, 95% CI: 0.541 to 2.602, P < .0001 for Perkins, Icare-Pro, and Tonopen XL IOP measurements, respectively).
Conclusions:
Ocular axial length affects IOP measured by the Perkins, Icare-Pro, and Tonopen XL devices in patients with childhood glaucoma. The Icare-Pro shows more agreement with the Perkins tonometer than the Tonopen XL; therefore, it seems to be a more suitable option for these patients. [J Pediatr Ophthalmol Strabismus. 2020;57(1):27-32.].
Background
To determine four‐year changes of corneal biomechanical parameters in Iranian children aged seven to eleven years and their correlation with optical components.
Methods
In this four‐year prospective cohort study, 468 children aged seven to eleven years who were initially evaluated in 2012 were re‐evaluated in 2016–2017. Multi‐stage stratified cluster sampling was applied. Cycloplegic refraction, biometry using LENSTAR/BioGraph, and corneal biomechanical assessment using Ocular Response Analyzer (ORA) were undertaken for each participant. The corneal biomechanical parameters assessed were corneal hysteresis (CH), corneal resistance factor (CRF), areas under the peaks 1 and 2 (p1 and p2 areas) and irregularity indices (A and B indices).
Results
All biomechanical parameters except A index decreased in phase 2. The mean changes of CH and CRF were 0.68 ± 0.16 mmHg (for both parameters) during four years. The mean difference in CH and CRF was 0.23 ± 0.23 and 0.24 ± 0.23 mmHg in females and 1.03 ± 0.23 and 0.96 ± 0.23 mmHg in males, respectively. Different age groups showed varying amounts of decrease in all parameters except for A index. The age group ‘ten years’ experienced the smallest decrease in CH (0.02 ± 0.48 mmHg) and CRF (0.20 ± 0.47 mmHg) and the age group ‘eleven years’ showed the greatest decrease in CH (1.41 ± 0.35 mmHg) and CRF (0.99 ± 0.34 mmHg). According to linear regression analysis, CH and CRF had a significant direct relationship with corneal power and an inverse relationship with axial length (p < 0.001).
Conclusion
Age and sex are influencing factors on the ORA parameters. Older age is associated with reduced biomechanical parameters and reductions are more significant in males than females. Axial elongation and corneal flattening decrease CH and CRF.
Objective
To determine the characteristics of children who were likely to progress rapidly and gain the greatest benefit from orthokeratology (ortho-k) treatment.
Methods and analysis
The files of 113 children who participated in two myopia control studies and wore either ortho-k lenses (n=62) or single-vision spectacles (SVS) (n=51) were reviewed. Baseline cycloplegic subjective refraction, central corneal thickness, axial length, keratometry, intraocular pressure, corneal biomechanical properties and 24-month axial length data were retrieved and analysed.
Results
Multivariate analysis showed that there was significant negative correlation between axial elongation and baseline age and corneal hysteresis (p<0.05) in the SVS group. In the ortho-k group, only baseline age was significantly and negatively associated with axial elongation (p<0.01).
Conclusion
Corneal biomechanical properties and baseline age can predict the rate of axial elongation in myopic children. It may be beneficial for younger myopic children with low corneal hysteresis to commence ortho-k treatment as early as possible.
Purpose:
To assess the relationship between the corneal biomechanical parameters and the anterior segment parameters in Caucasian children.
Methods:
This study included 293 eyes from 293 healthy children aged between 6 to 17 years. Corneal hysteresis (CH) and corneal resistance factor (CRF) were evaluated with the Ocular Response Analyzer, axial length (AL) with IOLMaster and the anterior segment with Pentacam. Anterior segment parameters obtained were the following: central corneal thickness (CCT), corneal volume (CV), anterior chamber depth (ACD), anterior chamber volume (ACV) and mean anterior and posterior keratometry. Two multiple linear regression models were constructed to assess the association between CH and CRF with anterior segment parameters. A p-value of <0.05 was taken as the criterion for statistical significance in all analyses.
Results:
The mean CH and CRF were 12.12 ± 1.71 and 12.30 ± 1.89 mmHg, respectively. Multiple linear regression revealed that CH and CRF were associated negatively with AL in both models, and positively with CCT and CV in the first and second model, respectively. Meanwhile ACD, ACV or mean keratometry did not correlated with CH and CRF. Moreover, when CCT was in the model, it explained more variability for both CH (22.1%) and CRF (30.9%) than when CV was included (16.2% for CH and 16.5% for CRF).
Conclusions:
CH and CRF were correlated positively with CCT and CV, and negatively with AL in healthy Caucasian children. Moreover, corneal parameters were the most contributory variables to CH and CRF changes.
Purpose: To determine the effect of aging on corneal biomechanical parameters measured via ocular response analyzer in a homogenous healthy Caucasian population.
Methods: A total of 2039 Caucasian adults were consecutively recruited and divided into seven groups according to decades of age. The difference in mean corneal hysteresis (CH), mean corneal resistance factor (CRF), mean Goldmann-correlated intraocular pressure (IOPg), and mean corneal-compensated IOP (IOPcc) between decades of age were investigated. The strength of the correlations between corneal biomechanical parameters, and between each biomechanical parameter and age were evaluated. The effect of age on each corneal biomechanical parameter was analyzed.
Results: Mean age of the participants (1173 female and 866 male) was 43.30 ± 14.64 years. Mean CH, CRF, IOPcc, and IOPg were 11.49 ± 1.89 mmHg, 11.40 ± 2.30 mmHg, 15.01 ± 3.11 mmHg, and 15.72 ± 3.80 mmHg, respectively. There were significant differences in mean CH, CRF, IOPcc, and IOPg between groups (p < 0.001 for all parameters). There was a significant negative correlation between age and CH (r = –0.067 and p = 0.003), and a significant negative correlation between age and CRF (r = –0.053 and p = 0.017). There was a significant positive correlation between age and IOPg (r = 0.25 and p < 0.001), and between age and IOPcc (r = 0.20 and p < 0.001). Linear regression analysis showed that for every 1-year increase CH decreased 0.011 mmHg, CRF decreased 0.004 mmHg, IOPcc increased 0.053 mmHg, and IOPg increased 0.047 mmHg.
Conclusions: Aging can cause significant changes in corneal biomechanical parameters. Corneal biomechanical parameters were correlated with each other, and each was correlated with aging.
Background
Ectasia development occurs due to a chronic corneal biomechanical decompensation or weakness, resulting in stromal thinning and corneal protrusion. This leads to corneal steepening, increase in astigmatism, and irregularity. In corneal refractive surgery, the detection of mild forms of ectasia pre-operatively is essential to avoid post-operative progressive ectasia, which also depends on the impact of the procedure on the cornea.
Method
The advent of 3D tomography is proven as a significant advancement to further characterize corneal shape beyond front surface topography, which is still relevant. While screening tests for ectasia had been limited to corneal shape (geometry) assessment, clinical biomechanical assessment has been possible since the introduction of the Ocular Response Analyzer (Reichert Ophthalmic Instruments, Buffalo, USA) in 2005 and the Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany) in 2010. Direct clinical biomechanical evaluation is recognized as paramount, especially in detection of mild ectatic cases and characterization of the susceptibility for ectasia progression for any cornea.
Conclusions
The purpose of this review is to describe the current state of clinical evaluation of corneal biomechanics, focusing on the most recent advances of commercially available instruments and also on future developments, such as Brillouin microscopy.
Aim:
to analyze corneal hysteresis (CH) and corneal resistance factor (RF) readings obtained with the Reichert Ocular Response Analyzer (ORA) before and after hyperopic femtolaser-assisted laser in situ keratomileusis (FS-LASIK) in children with anisometropia as well as to establish factors that may cause changes in these parameters.
Material and methods:
CH and RF were evaluated before and 1.5 years after FS-LASIK performed on amblyopic eyes of 28 patients aged 6-14 years. Preoperatively, there was a correlation between CH and RF (r=0.41, p=0.03). No correlation was found between CH and age (r=-0.02, p=0.82) or between CH (r=0.00, p=0.98), RF (r=0.04, p=0.83), and cornea thickness.
Results:
The mean preoperative CH was 12.56±1.21 mmHg, RF 12.31±1.57 mmHg. Postoperatively, a statistically significant change occurred to both CH (by 0.97±1.51 mmHg, p=0.002) and RF (by 1.42±1.55 mmHg, p=0.000). No correlation was found between CH before and after surgery (r=0.11, p=0.57) as well as between the ablation depth and changes in CH (r=0,04, p=0.83) and RF (r=0.21, p=0.28). Regression analysis showed that the extent of CH (r2=0.52, p=0.00) and RF (r2=0,48, p=0.00) changes was closely related to their preoperative values.
Conclusion:
The statistically significant relative change in CH and RF after hyperopic FS-LASIK was 8% and 12%, respectively. CH and RF changes correlated with their preoperative values, but not with the ablation depth or cornea thickness.
An understanding of normal structural and functional development of the eye and adnexa assists in the identification of abnormal departures reflecting disease processes. Normal data for visual acuity, refractive error, and globe size are presented along with specifications for the anatomic development of the cornea, anterior chamber, iris, lens, ciliary body, vitreous, retina, sclera, optic nerve and sheath, vasculature, extraocular muscles, eyelids, orbit and sinuses. Normal values for intraocular pressure and visual fields are also discussed.
[Purpose] To compare intraocular pressure (IOP) in normal eyes using two different non-contact tonometers to correct corneal properties.
[Subjects and Methods] Using an FT-01 tonometer (TOMEY, Nagoya, Japan) that corrects IOP from measurements of corneal thickness and a 7CR tonometer (Reichert, NY, USA) that corrects IOP from measurement of corneal rigidity, we measured normal eyes at the same time with sufficiently long intervals between measurements. The study evaluated 109 normal eyes in 71 healthy subjects. We compared results before and after correction and also the correction rate of both devices, and examined which background factors may influence the correction rate for the 7CR.
[Result] Mean values before and after correction were 16.0±3.0 mmHg and 16.2±2.7 mmHg for the 7CR, and 15.1±3.4 mmHg and 16.5±3.0 mmHg for FT-01, respectively. We only found significantly higher correction of measured values for 7CR results compared to before correction (multiple comparison Scheffe's method, p<0.05). Median correction rate was significantly higher for the 7CR (11.2%) than for the FT-01 (1.8%; Wilcoxon rank sum test, p<0.01). Furthermore, only corneal thickness influenced the result (multiple regression analysis partial regression coefficient, -0.26; p<0.01).
[Conclusion] IOP corrected by corneal thickness showed no significant differences, but IOP increased significantly with correction by corneal rigidity in normal eyes. Knowing which device most accurately reflects the actual IOP is difficult. However, further examination should be performed. A possible correlation was suggested between thickness and rigidity. We found that the IOP correction by rigidity increased as corneal thickness decreased. Further examination of how corrections by each device are influenced under conditions of glaucoma and other diseases appear warranted.
Purpose:
To evaluate corneal biomechanical changes induced by trabeculectomy and their impact on intraocular pressure (IOP) measurements.
Materials and methods:
In total, 35 eyes of 35 consecutive glaucoma patients undergoing first-time trabeculectomy with mitomycin C were enrolled in this prospective interventional case series. Goldmann applanation tonometry (GAT) IOP, central corneal thickness, axial length, and Ocular Response Analyzer measurements [Goldmann-correlated IOP (IOPg), corneal-compensated IOP (IOPcc), corneal hysteresis (CH), and corneal resistance factor (CRF)] were assessed before and 6 months after uncomplicated trabeculectomy. Linear mixed models were used to compare the parameters before and after surgery.
Results:
IOP, central corneal thickness, and axial length showed a strong correlation with CH and CRF preoperatively and postoperatively. After adjusting for these influencing factors, CH changed from 7.75±1.46 to 7.62±1.66 mm Hg (P=0.720) and CRF from 8.67±1.18 to 8.52±1.35 mm Hg (P=0.640) after trabeculectomy, but these changes were not statistically significant. IOP decreased statistically significantly with all IOP measurements (P=0.001). IOPcc was statistically significantly higher than GAT (4.82±5.24 mm Hg; P=0.001) and IOPg (2.92±1.74 mm Hg; P=0.001) preoperatively and postoperatively (GAT, 3.29±3.36 mm Hg; P=0.001; IOPg, 3.35±1.81 mm Hg; P=0.001). The difference between IOPcc and GAT (P=0.5) and IOPcc and IOPg (P=0.06) did not change significantly before or after trabeculectomy.
Conclusions:
Despite a marked IOP reduction and a possible weakening of the ocular walls after trabeculectomy, corneal structural tissue properties are not altered, and therefore, the accuracy of IOP measurements is not changed postoperatively. It seems likely, however, that Goldmann-correlated IOP measurements are underestimated in glaucoma patients before and after surgery.
Measuring the intraocular pressure (IOP) in children can be difficult. We compared the accuracy of IOP measurements in pediatric patients using three tonometers: Perkins, Schiötz, and Tono-pen. Seventy-seven children (132 eyes; average age, 1 year, 7 months; range, 1 month to 60 months), mainly afflicted with retinopathy of prematurity (107 eyes), were evaluated. A good correlation (r = 0.867) was found between the Tono-pen and the Perkins tonometers. No statistical difference was found between the mean difference of IOP values obtained with the Tono-pen and the Perkins (P > .05). The Schiötz measurements were significantly higher than those obtained with the Perkins and the Tono-pen tonometers (P < .05). We concluded that the Tono-pen tonometer has a higher correlation coefficient, comparable to the Perkins tonometer, and can be used reliably to assess IOP in pediatric patients.
To study the results of an ocular response analyzer (ORA) to determine the biomechanical properties of the cornea and their relationship to intraocular pressure (IOP).
Reichert Inc., Depew, New York, USA.
The ORA (Reichert) makes 2 essentially instantaneous applanation measurements that permit determination of corneal and IOP effects.
Measurements of several populations indicate that corneal hysteresis, a biomechanical measure, varied over a dynamic range of 1.8 to 14.6 mm Hg and was only weakly correlated with corneal thickness (r(2)=0.12); this is related to the observation that some subjects with relatively thick corneas have less-than-average corneal hysteresis. Corneal hysteresis changes diurnally, presumably as a result of hydration changes. Keratoconus, Fuchs' dystrophy, and post-LASIK patients demonstrated low corneal hysteresis.
The corneal hysteresis biomechanical measure may prove valuable for qualification and predictions of outcomes of refractive surgery and in other cases in which corneal biomechanics are important.
We sought to compare intraocular pressure (IOP) measurements by Perkins tonometer and Tono-Pen in young children with primary congenital glaucoma (PCG).
This was a retrospective comparative case series. We reviewed the clinical records of all children with primary congenital glaucoma who underwent examinations under general anesthesia at Soroka University Medical Center between January 1999 and July 2002. Our main outcome measures were IOP with Perkins hand-held tonometer and Tono-Pen tonometer.
A total of 28 eyes of 16 children were examined under general anesthesia. The mean IOP was 18 +/- 6 mm Hg with the Perkins tonometer and 22 +/- 8 mm Hg with the Tono-Pen. In 18 eyes, IOP was less than 21 mm Hg with the Perkins tonometer; these eyes had already undergone surgical procedures. The other 10 eyes with IOP greater than 21 mm Hg with the Perkins tonometer underwent surgery at the end of the examination under anesthesia. In eyes with IOP greater than 16 mm Hg (Group A, n = 18), a significant difference (P < 0.001) was found between the Perkins and Tono-Pen measurements, even although the values were strongly correlated (r = 0.60). In contrast, in eyes with IOP less than 16 mm Hg (Group B, n = 10) no statistically significant difference (P = 0.28) and good correlation (r = 0.78) were obtained. A difference of 5.8 +/- 3.8 mm Hg and 0.6 +/- 1.7 mm Hg between Perkins and Tono-Pen readings, respectively, was found in Groups A and B.
Tono-Pen readings disagree with Perkins tonometer measurements for measuring IOP in children with PCG who present with IOP greater than 16 mm Hg and tends to overestimate IOP. A further study with a similar population is necessary to confirm these results.
The ICare (Tiolat Oy, Helsinki, Finland) is a new portable tonometer that measures intraocular pressure (IOP) with a new rebound method, in which a very light probe is used to make momentary contact with the cornea in slow motion. The purpose of this study is to assess the accuracy of the ICare IOP measurements by comparing them against other portable tonometers: Perkins applanation tonometer and Tono-Pen XL digital tonometer (Medtronic Solan, Jacksonville, FL).
Sixty-five young subjects were assessed with each of the tonometers. ICare tonometry was performed first, followed by Perkins applanation tonometry and Tono-Pen XL in a random order. Regression analysis was used to evaluate the relationship between the Perkins tonometer and the remaining tonometers used in this study. Tonometers were also compared by plotting the difference between the methods against the mean. The hypothesis of zero bias was examined by a paired t test and the 95% limits of agreement (LoA) were calculated.
ICare and Tono-Pen XL significantly overestimate IOP when compared with Perkins applanation tonometry. The mean of the difference between Perkins and ICare and Perkins and Tono-Pen XL was (mean +/- standard deviation) -3.35 +/- 2.28 mm Hg and -2.78 +/- 2.53 mm Hg, respectively. The 95% LoA between Perkins tonometry and ICare tonometry were between -7.81 and +1.12 and between Perkins tonometry and Tono-Pen XL tonometry between -7.74 and +2.18.
Compared with Perkins tonometry, the ICare tonometer allows clinicians to estimate IOP with a portable, rapid, and noninvasive method with similar reliability to that offered by Tono-Pen XL. Clinicians should be aware of the systematic overestimation of IOP with the ICare. Further research is needed to evaluate the performance of rebound tonometry in populations with higher IOP and assess the reliability of this technique in the early detection and follow up of glaucomatous patients.