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Increased Corneal Thickness Simulating Elevated Intraocular Pressure
Abstract
A 17-year-old girl had intraocular pressure readings of 30 to 40 mm Hg in both eyes, with normal visual fields and optic nerve heads. Medical treatment was unsuccessful in lowering the IOP measurements substantially. The central corneal thickness was 0.90 mm in each eye in the absence of corneal edema. Cannulation of the left anterior chamber revealed an IOP of 11 mm Hg, while the Perkins' and Schiŏtz' tonometers gave readings of 35 and 34 mm Hg, respectively. Previously, elevated tonometry readings had been obtained by Goldmann's, Perkins', Schiŏtz', MacKay and Marg's, pneumatic tonometer and air puff tonometer. This suggested that measurement of central corneal thickness be performed in cases in which IOP recordings do not correspond to other clinical findings.
... Numerous studies have shown that patients diagnosed with ocular hypertension have significantly thicker corneas than normal subjects. (16,17) But in our study, the respondents did not have a positive history of glaucoma. From 360 eyes in the TG with refractive anomalies, the highest IOP values were found in the astigmatic group (20.6 mmHg) and the lowest values in the myopic group (15.3 mmHg) (P<0.001) and were statistically higher compared to the CG (P<0.001 in both cases) ( Table 3). ...
... Regarding the relationship between IOP and refractive errors, a study conducted in Wisconsin (16) showed that myopes were 60% more likely to develop glaucoma than emmetropes. A study by Nomura et al. (19) found a positive relationship between IOP and increasing degrees of myopia; unlike our results, a correlation was found between IOP and the myopic group, regardless of the degree of myopia. ...
Background: The aim of this study was to determine the relationship between central corneal thickness (CCT) and intraocular pressure (IOP) in patients with refractive anomalies and emmetropes.
Methods and Results: This retrospective study was conducted in the Department of Ophthalmology at the University Clinical Center. The study included 330 respondents, with a total of 660 eyes, divided into two groups. The test group (TG) included 180 respondents with refractive anomalies (65 respondents with hypertropia, 65 with myopia, and 50 with astigmatism); the control group (CG) included 150 respondents with uncorrected visual acuity – 6/6 in both eyes. All respondents included in the research were aged 18–40, with an average age of 22.9 years. The values of CCT in TG was around 499.3–577.1 μm. From 360 eyes in the TG with refractive anomalies, the highest IOP values were found in the astigmatic group (20.6 mmHg) and the lowest values in the myopic group (15.3 mmHg) (P
... However, subsequent studies have not been consistent in their findings about how, and indeed whether at all, CCT should be corrected. Whilst a number of studies have found variations in IOP with CCT [19][20][21][22][23], correction factors have varied [14,23] and the use of any correction factor for the healthy adult cornea has been questioned [24,25]. Paucity in the understanding of the rheological properties of the cornea prevents definitive conclusions from being made about the effect of CCT on IOP measurements in the adult eye. ...
... For the Caucasian ('white') group alone, the average CCT was 564 ± 28 μm, which is very close to the mean value found in this study (563 ± 30 μm). The IOP for controls (Caucasian and African) was found to be 14.9 ± 2.7 mmHg for the Goldmann and 15.1 ± 2.4 mmHg for the Tono-Pen [19]. This compares to 14.7 ± 2.9 mmHg (GAT) in this paper. ...
Purpose To evaluate the influence of central corneal thickness (CCT) and radius of the corneal curvature (R) on IOP measurements obtained with the ICare rebound tonometer and the Goldmann applanation tonometer (GAT).
Methods Eighty four eyes of 48 subjects (65 eyes of glaucoma patients and 19 eyes of healthy volunteers) were examined with ICare and Goldmann tonometers. Central corneal thickness was determined by ultrasound pachymetry. Corneal radius of curvature was determined using corneal topography.
Results There was no significant difference between IOP readings with ICare and GAT. Intraocular pressure measurements were found to be higher with the ICare tonometer, both in glaucoma patients (15,3±4,0 mmHg) and normal subjects (14,4±3,0 mmHg). ICare‐GAT mean difference was 1.1±3.6mmHg (95% CI, ‐6.1‐8.3mmHg) for glaucoma patients and 1.8±3.2mmHg (95% CI, ‐4.6‐8.2mmHg) for healthy volunteers. Using CCT patients were divided into 2 groups: 1) thinnest corneas ‐ CCT<556 μm (mean CCT 531±23 μm), 39 eyes and 2) thickest corneas ‐ CCT >556 μm (mean CCT 578±17 μm), 45 eyes. In the group of thinnest corneas there was no correlation between IOP, CCT and R. In thickest corneas there was significant correlation between IOP readings obtained by ICare and CCT (r=‐0.4, p<0.01), and mean radius (R) (r=0.5, p<0.001).
Conclusion Measurements of IOP using the ICare rebound tonometer are in good agreement with Goldmann applanation tonometer in glaucoma patients and normal subjects, although influenced by CCT.
... (1) Responsável pelo Setor de Glaucoma do Departamento de Oftalmo-Otorrinolaringologia do Hospital das Clínicas -UFPR. (2,3,4) Acadêmicos do 6° ano do Curso de Medicina -UFPR. (5) Residente do 1° ano de Oftalmologia do Hospital das Clínicas -UFPR. ...
... (5) Residente do 1° ano de Oftalmologia do Hospital das Clínicas -UFPR. ( (2) Ana Cecília Pedriali Guimarães (3) Artur José Schmitt (4) Luciana Scapucin (5) Luis Guilherme Rego Barros (6) Nara Delai (7) RESUMO Palavras-chave: Pressão intra-ocular; Espessura corneana central. ...
Purpose: To evaluate the distribution of the central corneal thickness (CCT) and its relationship with the intraocular pressure (IOP) in a group of patients and to demonstrate the usefulness of the pachymeter to evaluate IOP in selected cases. Methods: The central cornea thickness of 167 patients over 40 years old (319 eyes) was determined using ultrasonic pachymetry. The intraocular pressure was measured by the "Goldmann" applanation tonometer. Results: The CCT average of the 319 eyes was 0.5173 + 0.0377mm, the maximum value being 0.656mm and the minimum value 0.430mm. The IOP average was 16.44 + 3.88 mmHg; the maximum pressure 30 mmHg and the minimum pressure 8 mmHg. A linear regression of 0.13677 of the analyzed variables (p=0.0145) was observed, with no difference between sex and age. The observations were divided in to two groups: group I - IOP ≤ 21 mmHg ? with 285 eyes which presented a CCT average of 0.517 + 0.0376 mm; and group II ? IOP ≥ 21 mmHg ? with 34 eyes which presented a CCT average of 0.519 + 0.0393 mm. Conclusion: A linear regression between IOP and CCT was observed, meaning that the higher the CCT the higher the IOP will be. The usefulness of corneal pachymetry for IOP evaluation was shown in those patients where it was falsely increased or decreased on applanation tonometry, directing therapy towards patients really with glaucoma.
... In some cases the effect on measured IOP is clinically significant. [3][4][5] It also became apparent that central corneal thickness is more variable among clinically normal individuals than Goldmann and Schmidt recognized. ...
Objective
Central corneal thickness influences intraocular pressure (IOP) measurement. We examined the central corneal thickness of subjects in the Ocular Hypertension Treatment Study (OHTS) and determined if central corneal thickness is related to race.
Design
Cross-sectional study.
Participants
One thousand three hundred one OHTS subjects with central corneal thickness measurements.
Intervention
Central corneal thickness was determined with ultrasonic pachymeters of the same make and model at all clinical sites of the OHTS.
Main Outcome Measures
Correlation of mean central corneal thickness with race, baseline IOP, refraction, age, gender, systemic hypertension, and diabetes.
Results
Mean central corneal thickness was 573.0 ± 39.0 μm. Twenty-four percent of the OHTS subjects had central corneal thickness > 600 μm. Mean central corneal thickness for African American subjects (555.7 ± 40.0 μm; n = 318) was 23 μm thinner than for white subjects (579.0 ± 37.0 μm; P < 0.0001). Other factors associated with greater mean central corneal thickness were younger age, female gender, and diabetes.
Conclusions
OHTS subjects have thicker corneas than the general population. African American subjects have thinner corneas than white subjects in the study. The effect of central corneal thickness may influence the accuracy of applanation tonometry in the diagnosis, screening, and management of patients with glaucoma and ocular hypertension.
... Central Corneal Thickness (CCT) Groups with Mean IOP and Statistical Analysis for the Normal IOP Group(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) ...
Purpose: The factors associated with the increased risk of glaucoma include intraocular pressure (IoP), central corneal thickness (CCT), vertical cup-to-disc ratio, visual field index, age, and diabetes mellitus. We have investigated the relation of IoP with CCT in normal, healthy pre-presbyopic persons. Methods: A total population of 698 normal patients (1396 eyes), aged 4 to 40 years, were evaluated in two separate clinics, one in Houston, Texas, USA and the second in oakville, ontario, Canada. IoP was measured using a noncontact tonometry (nCT 20 Topcon). In Houston, CCT was determined by using the Pentacam (occulus Pentacam – Belinea) and an optical pachymetry that utilized optical low-coherence reflectometry (oLCR) technology, and in oakville, a Hagg-Streit slit lamp–mounted pachymeter was used. Results: of the total number of eyes tested, 1226 eyes had IoP of 21 millimetres of mercury (mm Hg) or lower and 134 eyes had IoP greater than 21 mm Hg. For the normal IoP group (n = 1226 eyes), the overall IoP mean was 15.63 +/– 2.87 mm Hg; the overall CCT mean was 550.21 +/– 39.64 micrometres (µm). In the normal IoP group, for every 10 µm change in CCT, IoP changed a statistically significant amount of 2.49 mm Hg (p <0.05 to <0.001), except for the 10 nm CCT bins above and below the 550 µm mean. Conclusions: Although many investigators have described a positive correlation between IoP and CCT, this relationship has not been demonstrated in normal, healthy pre-presbyopic persons. There is a significant change of IoP with CCT (2.49 mm Hg IoP change per 100 µm of CCT). These normative data allow primary eye care clinicians to accurately determine normal and abnormal IoP and refine the index of suspicion for identifying patients who need to be worked up for glaucoma.
... Central corneal thickness (CCT) was one of them. 1 2 Later on some groups reported thicker corneas in patients with higher intraocular pressure (IOP) compared with thinner corneas in patients with lower IOP. [3][4][5][6][7][8][9][10] Varying corneal rigidity was claimed to be responsible for false applanatory IOP readings with diVerent CCT. Some authors recommended a recalculation of the IOP depending on the CCT with a correction factor ranging from 1 to 6.8 mm Hg per 0.1 mm CCT. ...
... Hokin [1] 1953 Garfield 579 S 1 = 3323 Leakey [2] 1964 Tobias 335 S 1 = 408 Scott [3] 1973 Ohba& Nakao 345 S 1 = 363 De Rujula [4] 1977 Li 201 S 1 = 808 Johnson [5] 1978 Ohba&Nakao 157 S 10 = 172 Ackermann [6] 1980 Glänzel et al. 55 S 10 = 346 Edwards [7] 1980 Glänzel et al. 296 S 1 = 1033 Gitter [8] 1980 Glänzel et al. 89 S 10 = 178 Lis [9] 1980 Glänzel et al. 793 S 1 = 1000 Ogino [10] 1980 Glänzel et al./Braun et al. 506 S 1 = 1099 Vanderzee [11] 1980 Glänzel et al. 320 S 1 = 410 Waite [12] 1980 Braun et al. 166 S 10 = 187 Romans [13] 1986 Van Raan 363 S 1 = 758 ...
In this study we investigate if articles suffering delayed recognition can at the same time be under‐cited influential articles. Theoretically these two types of articles are independent, in the sense that suffering delayed recognition depends on the number and time distribution of received citations, while being an under‐cited influential article depends only partially on the number of received (first generation) citations, and much more on second and third citation generations. Among 49 articles suffering delayed recognition we found 13 that are also under‐cited influential. Based on a thorough investigation of these special cases we found that so‐called authoritative citers play an important role in uniting the two different document types into a special citation chimera. Our investigation contributes to the classification of publications.
... 12 In our study, though the difference in IOP measurement between the two methods was statistically significant (P<0.05) for the entire group and in the subgroup with central corneal thickness more than 575 µm, the reliability indices for the noncontact tonometer considering the Goldmann applanation tonometer as gold standard are highly correlating as coefficient of correlation is near to +1 in all the subgroups. There we have found a positive correlation between CCT and IOP (as the CCT increases, IOP measured by GAT and NCT increases) in the groups of >513 µm of CCT corroborating with the study done by Johnson M et al. 13 We suggest that if the IOP measured with a noncontact tonometer is significantly different from that taken with an applanation tonometer, the patient's corneal thickness to be measured. Central corneal thickness is indirectly important in the diagnosis and follow up of glaucoma as it may lower the incidence of misdiagnosis. ...
... Of course numbers are too small to accord any meaning to this percentage. First author [number in Table 2] PY Discussed as sleeping beauty by the following author(s); see Table 3 Received citations Sparking index Hokin [1] 1953Garfield (1989) 575 S 1 = 3307 Leakey [2] 1964 Tobias 310 S 1 = 358 Scott [3] 1973 Ohba & Nakao 320 S 1 = 343 De Rujula [4] 1977 Li 191 S 10 = 210 Johnson [5] 1978 Ohba &Nakao 153 S 10 = 164 Ackermann [6] 1980 Glänzel et al. 55 S 10 =338 Edwards [7] 1980 Glänzel et al. 295 S 1 =950 Gitter [8] 1980 Glänzel et al. 88 S 10 =176 Lis [9] 1980 Glänzel et al. 763 S 1 = 966 Ogino [10] ...
In this study we investigate if sleeping beauties, also known as articles suffering delayed recognition, can at the same time be under-cited influential articles. Theoretically these two types of articles are independent, in the sense that being a sleeping beauty depends on the number and time distribution of received citations, while being an under-cited influential article depends only partially on the number of received (first generation) citations, and much more on second and third citation generations. Among 49 sleeping beauties we found 13 that are also under-cited influential.
... In our study population, there was a significant positive correlation between CCT and uncorrected IOP in agreement with numerous studies [7,[19][20][21]. Even though the impact of CCT on IOP is clear, there is no universal consensus on the formula for IOP With regards to the CCT adjusted IOP values, we defined outcomes as defined by Shih et al [9]. ...
Aim: To test if central corneal thickness (CCT) and intraocular pressure (IOP) are related in patients with glaucoma and normal IOPs. Methods: A prospective descriptive study which took place from September 1 to December 31, 2014 at the Presbyterian Eye Clinic Acha-Douala, Cameroon. Consenting patients who were newly diagnosed with glaucoma and had a normal IOP included. IOP was measured using applanation tonometry. CCT was measured in both eyes of all patients and a correction factor for IOP was read from the chart provided for by the manufacturer based on the CCT. Results: Fifty-three consenting patients (106 eyes) were included, comprising 24 males (45%). The mean age was 34 ± 16 years. The mean CCT in all eyes was 529 ± 36 µm (range: 433 to 594 µm). The mean CCT for the right and left eyes were 526 ± 36µm and 528 ± 37 µm, respectively. The mean uncorrected IOP for all eyes was 16 ± 3 mmHg. The mean corrected IOP for all eyes was 17 ± 3 mm Hg. The difference between the uncorrected and corrected IOP for all eyes was found to be statistically significant (P < 0.0001). Conclusion: Measured IOP in most glaucoma patients with 'normal' IOP needs to be corrected. We suggest that the measurement of CCT be part of the routine workup of patients with glaucoma in order to permit a more precise estimation of IOP, hence target pressure in order to assure a better follow up.
... 18,33 Although there is no consensus among investigators about the magnitude of IOP measurement bias for each micrometer of CCT change, numerous correction factors ranging from 0.19 to 0.7 mm Hg for each 10 µm difference in CCT have been proposed. [33][34][35][36][37] We found that in our study, mean change of IOP was 0.21 to 0.22 mmHg for per 10 µm CCT with Icare and GAT, respectively. ...
Purpose: This clinical study was conducted to compare the performance of a rebound tonometer with that of the Goldmann applanation tonometer (GAT) in the measurement of intraocular pressure (IOP) and to evaluate the effect of central corneal thickness (CCT) on IOP measurement with both devices.
Materials and Methods: One hundred and sixty-five healthy subjects were tested using rebound tonometer and GAT by two observers. The patients were divided into 3 groups according to CCT measurement and OHTS criteria as follows: group 1 with CCT<555 μm; group 2 with CCT 555-584 μm; and group 3 with CCT≥585 μm. Correlation analysis was performed to compare the 2 devices; paired sample t test, Bland and Altman analysis were used. Results: The mean IOP levels measured by rebound tonometer and GAT were 13.9±2.3 and 13.5±2.5 mm Hg in Group1 (p=.587), 15.76±2.7 and 15.3±3.1 mmHg in Group 2 (p=.563), and 17.76±2.6 and 18.42±3.03 mm Hg in Group 3 (p=.878), respectively. Rebound tonometry and GAT readings were strongly correlated in terms of IOP measurement in all CCT groups (r=0.78, p<.0001).
Conclusions: The use of rebound tonometer is effective and safe in comparison to GAT readings. In eyes with a healthy cornea, the IOP measurements from the rebound tonometer and the GAT seemed to be similarly affected by CCT.
... IOP may be underestimated in eyes with thin corneas and overestimated in eyes with thick corneas. [2][3][4][5] A report of the landmark Ocular Hypertension Treatment Study(OHTS) showed that central corneal thickness (CCT) was found to be a powerful predictor of development of primary open-angle glaucoma among ocular hypertensive eyes. 6 Eyes with CCT of 555 µm or less had a threefold greater risk of glaucoma developing than participants who had CCT of more than 588 µm. ...
... 9 The error could be as much as 24 mmHg with the Goldmann applanation tonometer. 10 Although some correction algorithms for IOP considering CCT values have been suggested, 11 these studies have been performed on adult eyes with normal corneal structure, and may not be generalizable to eyes of children with glaucoma. Collagen fibers are softer and more elastic in children less than 3 years of age as compared to older individuals. ...
... Goldmann applanation tonometry (GAT) is considered to be the gold standard among intraocular pressure (IOP) measurement methods. However, GAT measurements are affected by corneal thickness, corneal astigmatism, and corneal rigidity (1)(2)(3)(4)(5)(6). This has led investigators to search for a tonometry that will measure IOP without being affected by central corneal thickness (CCT). ...
Objective: To evaluate factors affecting measurement quality of dynamic contour tonometry (DCT). Material and Methods: Three hundred patients took part in this prospective clinical study. For each patient, measurements for one eye were included in the study. Of the participants, 116 had ocular hypertension, 114 had glaucoma, and 70 had normal eyes. We used automatic refractokeratometry, ultrasonic pachimetry, Goldmann applanation tonometry, and DCT measurements to investigate the effects of age, corneal astigmatism, refractive error, central corneal thickness (CCT), intraocular pressures (IOP), and ocular pulse amplitude (OPA) on DCT measurement quality (Q). Logistic regression analysis was used for statistical analysis. Results: For 159 patients, the DCT Q score was 1 (group 1). For the remaining 141 patients, the Q score was 2-3 (group 2). The following values were determined for the two groups, respectively: mean age 58.9 +/- 9.9 and 61.4 +/- 10.6; mean corneal astigmatisms -0.78 +/- 0.67 and -0.92 +/- 0.77 diopter; mean spherical equivalents 0.33 +/- 1.87 and -0.01 +/- 2.02 diopter; mean CCT 547.0 +/- 35.2 and 549 +/- 38.7 mu m. Measurements with DCT provided mean IOPs of 18.5 +/- 3.70 and 21.27 +/- 6.19 mm Hg and mean OPA 3.5 +/- 1.4 and 3.2 +/- 1.2 mm Hg. By logistic regression analysis, we determined that the parameters affecting measurement quality were age, DCT measurement level, and OPA (p=0.015, p=0.000, and p=0.000, respectively). Conclusion: High IOP values, advanced age, and low OPA values can lead to decreased DCT measurement quality.
Purpose: The accuracy and agreement of intraocular pressure (IOP) measurements using a noncontact self-measuring tonometer, TONO-i, compared with the Goldmann applanation tonometer (GAT).Methods: A total of 35 healthy participants and 42 primary open angle or normal tension glaucoma patients were enrolled in this study. TONO-i and GAT measurements were obtained and the mean difference in IOPs was analyzed using a paired t -test. IOP agreement was calculated using the two-way random effects model. Bland-Altman analysis and simple linear regression were used to estimate the disagreement between IOP measurements.Results: The mean IOPs measured using the TONO-i and GAT were 15.9 ± 3.3 mmHg and 16.4 ± 5.1 mmHg, respectively. In glaucoma patients, the mean values measured using the TONO-i (16.7 ± 4.1 mmHg) were lower than those measured using the GAT (17.9 ± 6.1 mmHg; p < 0.001). However, there was no significant difference among the healthy participants ( p = 0.273). The intraclass coefficients (95% confidence interval) for all participants, normal participants, and glaucoma patients were 0.847 (0.702-0.920), 0.882 (0.804-0.941), and 0.828 (0.742-0.887), respectively, indicating good agreement between the IOP measurements. The mean difference and limits of agreement were not statistically significant. As IOP increased, the absolute difference between the GAT and TONO-i measurements also increased.Conclusions: The TONO-i, a novel tonometer, may be used reliably for IOP self-measurement and detecting IOP elevations. However, caution must be exercised because of the possibility of underestimating high IOPs.
This work presents results from numerical simulations of optic nerve head’s (ONH) biomechanical behavior during exposure to elevated intraocular (IOP) and/or intracranial pressure (ICP) for ocular hypertension conditions. At the same time, a range of geometric and material properties of the eye structure and their interrelation with elevated IOP and ICP values are investigated. These simulations are performed on a generic model of the eye, which allows parametrical modification of geometric and material properties. Our main interest is in measuring ONH’s potential damage in ocular hypertension due to intracranial pressure. Simulation results indicate a significant role of ICP in post-laminar neural tissue failure and a possible role of central corneal thickness (CCT) and scleral modulus in clinical assessment and treatment of patients with ocular hypertension (OHT). Specifically, CCT was found to affect ONH at early stages of damage in ocular hypertension conditions, and high scleral modulus seems to result in reduced shear failure in lamina cribrosa in a similar OHT state. These findings suggest that CCT could be a risk factor for glaucoma in OHT patients at initial stage along with cornea stiffness.
Graphical abstract
Introduction: Intraocular pressure (IOP) is one of the basic and most important investigations. Central corneal thickness influences IOP measured by various devices. Objective: In this study, we attempt to determine the agreement and influence of the central corneal thickness in the measurement of IOP obtained by Goldman applanation tonometer, Airpuff tonometer and tonopen. Methodology: A cross-sectional analytical study of Central corneal thickness (CCT) was done using Ultrasonic pachymetry. IOP was adjusted using Ehler's formula. Mean and the standard deviation was measured using the observed and predicted values for each instrument for its accuracy irrespective of the CCT. Results: 200 eyes of 100 patients were included in the study. Mean IOP measured was 16mmHg (SD 4). Tonopen was found to have closer observed values when compared with the predicted values to IOP obtained by Goldmann's applanation tonometer after CCT adjustments with Mean difference of 0.0134 mmHg with SD of 0.814. Air Puff tonometer was found to be the least accurate with Mean difference -2.08mmHg and SD of 4.704. Linear regression analysis also predicted that while the tonopen tend to underestimate the IOP levels by 5 %, Airpuff tonometer had a tendency to overestimate the IOP by 13%.(p<0.05). Conclusion: Tonopen had the greatest agreement and significant correlation with the GAT over a range of IOP and CCT and replicate measurements that are closest to the values obtained by using GAT after CCT adjustments. CCT adjustments may not even be required or has very little influence on IOP when using Tonopen.
Research is conducted into variation in the stress-strain state of the corneoscleral shell of the human eye under loading by a flat base stamp of varying weight. A three-dimensional finite-element model of the contact problem of loading of the corneoscleral shell in the ANSYS program package is presented. Cornea and sclera are modeled as conjugated transversely isotropic spherical shells. The cornea is modeled as a multilayer shell with variable thickness in which all modeled layers have their own individual elastic properties. The research deals with the numerical calculation of the diameter of the contact zone between the shell and the stamp. Values of correction coefficients for intraocular pressure are obtained depending on the thickness of the corneal shell in its center, allowing the true intraocular pressure to be determined more accurately.
Purpose
To determine the magnitude of ocular hypotony and the length of recovery time to 6 and 10 mm Hg IOP following anterior chamber (AC) cannulation.
Methods
Bilateral IOP was recorded 500 times per second via telemetry immediately before, during, and immediately after AC cannulation with a 27-G needle in 10 different sessions at least 2 weeks apart in four male rhesus macaques (nonhuman primates; NHPs) aged 3- to 6-years old. Bilateral IOP was recorded continuously using a proven telemetry system while the NHPs were under general anesthesia during IOP transducer calibration experiments involving manometric control of IOP via AC cannulation, then continuously after the AC needles were removed until IOP recovered to precannulation levels. The change in IOP from baseline to AC cannulation was tested using the signed-rank test. The times necessary for IOP to recover to 6 and 10 mm Hg, respectively, were calculated.
Results
Average precannulation IOP was 11.5 mm Hg and significantly decreased to an average of 2.3 mm Hg immediately following AC needle removal (P = 0.0156). On average, IOP recovered from 2.3 to 6 and 10 mm Hg in 32.4 and 63.7 minutes, respectively. Recovery times of IOP were not affected by repeated AC cannulations every 2 weeks.
Conclusions
Generally, IOP recovers relatively quickly after repeated AC cannulation, and did not result in extended duration hypotony. It is important to consider hypotony in animal experiments and clinical procedures involving AC cannulation and paracentesis when consideration of IOP or its effects is important.
Glaukomchirurgie soll erhöhten intraokularen Druck normalisieren. Da Drucksteigerungen unterschiedliche Ursachen haben, kann auch Drucksenkung nur auf verschiedenen Wegen erreicht werden. Am häufigsten geht es darum, den Kammerwasserabstrom aus dem Augapfel zu erleichtern. Oft müssen Hindernisse beseitigt werden, die den Durchfluß des Kammerwassers im Augapfel ventilartig hemmen. Wenn dementsprechende, prinzipiell unterschiedliche Eingriffe zur Verbesserung der Kammerwasserzirkulation den Augendruck nicht senken können, bleibt nur die Möglichkeit, die Kammerwasserproduktion zu drosseln. Nicht immer ist leicht zu erkennen, welche dieser Aufgaben vorliegt, und nicht selten müssen Maßnahmen kombiniert werden, da verschiedene Pathomechanismen gemeinsam einwirken können.
The aim of this work was to analyse the pressure inside the eyes anterior chamber, namedintraocular pressure (IOP), in relation to the biomechanical properties of corneas. The approach used was based on the constructal law, recently introduced in vision analysis. Results were expressed as the relation between the temperature of the ocular anterior chamber and the biomechanical properties of the cornea. The IOP, the elastic properties of the cornea, and the related refractive properties of the eye were demonstrated to be dependent on the temperature of the ocular anterior chamber. These results could lead to new perspectives for experimental analysis of the IOP in relation to the properties of the cornea.
Variations in central corneal thickness (CCT) influence the accuracy of all tonometry techniques to some degree.
PurposeTo evaluate the ability of baseline clinical, morphological, and functional factors to predict the conversion to primary open-angle glaucoma (POAG) in ocular hypertensive (OHT) patients.Methods
This single-center prospective longitudinal observational study included 116 eyes of 116 OHT patients followed for a 10-year period. All patients had intraocular pressure (IOP) ≥24 mm Hg in one eye and >21 mm Hg in the other eye, normal visual fields (VFs) and normal optic disc (OD) appearance in both eyes at baseline. All OHT patients were untreated at baseline with subsequent treatment upon need according to clinical judgement. Only one eye per subject was randomly selected. Patient age, gender, IOP, central corneal thickness (CCT), and ibopamine test results were collected at baseline. All patients underwent standard automated perimetry, short-wavelength automated perimetry (SWAP), frequency-doubling technology, confocal scanning laser ophthalmoscopy (CSLO), and scanning laser polarimetry (SLP) at baseline and every 6 months thereafter. Main outcome measure was the conversion to POAG, defined as the development of reproducible VF and/or OD abnormalities attributable to glaucoma. Cox proportional hazards models were used to identify the baseline factors predictive of POAG conversion.ResultsDuring the 10-year follow-up, 25% of eyes converted to POAG. In multivariate Cox models, baseline factors that were significant predictors of POAG development included: older age (hazard ratio (HR) 1.0, 99% confidence intervals (CIs) 1.0-1.2, per 1 year older); SWAP Glaucoma Hemifield test 'outside normal limits' (HR 4.3, 99% CIs 1.2-17.9); greater SLP 'Inter-eye Symmetry' (HR 1.1, 99% CIs 0.4-3.0, per 1 unit lower); lower CSLO Rim Volume (HR 1.1, 99% CIs 0.3-3.2, per 0.1 mm(3) lower); and greater CSLO cup-to-disc ratio (HR 6.0, 99% CIs 3.6-16.8, per 0.1 unit greater).Conclusions
The baseline parameters that proved to be useful in assessing the likelihood of an OHT patient to develop POAG included age, functional variables provided by SWAP, and structural variables provided by SLP and CSLO. In this cohort of patients, baseline IOP, CCT, and ibopamine provocative test results were not significant predictors of POAG conversion.Eye advance online publication, 13 May 2016; doi:10.1038/eye.2016.86.
To evaluate the influence of increased and decreased corneal thickness and corneal curvature on applanation tonometry, 91 controls (167 eyes) and 45 patients (79 eyes) after keratomileusis were examined. Pressure readings and findings of corneal thickness and curvature were correlated. It could be shown that thin corneas produce an underestimation and thick corneas an overestimation of the intraocular pressure. Further, in flatter corneal curvatures the applanation diameter is achieved earlier; thus, the intraocular pressure is underestimated. Based on these findings, the following correction schedule is suggested: for each increase or decrease of corneal thickness of 0,05 mm from the physiological value (0,54 mm) one may add or sub-stract 1 mm Hg: for each increase or decrease of corneal curvature (7,7 mm = 43 dpt) of 1 mm one may add or substract 1,5 mm Hg from the obtained IOP.
Purpose
From the literature it is known that after PRK on myopic eyes, the Goldmann tonometer readings are reduced incorrectly. There are different studies on the amount of this reduction. The purpose of this study was to observe the intraocular pressure on our PRK patients.
Material and methods
Sixty five patients underwent Goldmann tonometry before and after (1 month, 3 months, 6 months and 12 months) PRK. Twenty nine patients underwent corneal pachymetry before and after surgery. Tonometer readings, ablation, and spherical equivalent was correlated with the t-test for paired samples (p<0.05). The clinical results (reduction in corneal thickness and change of the curvature) were compared with the experimental findings obtained by means of dynamic mechanical analysis (DMA) and discussed.
Results
There was a mean reduction in tonometry readings of the intraocular pressure of 2.54 mm Hg 12 months after PRK (preoperative: 17.86 mm Hg, postoperative: 15.32 mm Hg; p=0.0001). The mean spherical equivalent was reduced by −4.71 dpt by reducing the corneal thickness by 59.6 pm. Corneal pachymetry showed a reduction of 57.0 pm on average (preoperatively 545 µm, postoperatively 488 µm). The amount of ablation correlated with the intraocular pressure readings (p=0.0001). With increased ablation, the intraocular pressure readings were reduced. We found a 0.5 mm Hg reduction in tonometry readings associated with a 11.7 pm reduction in the corneal thickness equivalent to a −0.92 dpt refractive changing following PRK.
Discussion
This study shows, that corneal thickness has a significant influence on the accuracy of Goldmann-style applanation tonometry. In recent studies, the mean error of deviation in tonometry readings was approximately 0.5 mm Hg for 7 m to 23 µm change in corneal thickness. This could be confirmed by our study (0.5 mm Hg per 11.73 µm or 0.92 dpt). The influence of the corneal thickness and curvature on tonometry were discussed.
Conclusion
Tonometry readings as a screening tool in the evaluation of glaucoma might delay the recognition in patients after PRK. PRK-patients with slightly elevated IOP should be observed more closely and treated as glaucoma suspects.
[Purpose] Corvis ST (CST, Oculus Co.) is a tonometer that uses the Scheimpflug images for its intraocular pressure (IOP) measurement. The purpose of this study was to compare the IOP measurement in healthy eyes and repeatability among 3 devices: the CST, the noncontact tonometer (NCT; TX-F, Canon), and the Goldmann applanation tonometer (GAT). [Subjects and Methods] The study included 20 eyes of 20 participants without any ocular diseases other than refractive error. The mean age was 35.0±12.9 years (range, 20-60 years). Subject's IOP was measured five times each by the three devices. The average IOP, coefficient of variation (CV), and the intraclass correlation coefficient (ICC) were assessed and compared among the three devices. In addition, correlation coefficient was obtained for the measurements by each pair of the three devices. ANOVA with post-hoc Tukey-Kramer test was performed and a significant level < 0.05 was considered statistically significant.[Results] The average (± standard deviation) IOP measurements by the CST, GAT, and NCT were 12.5±2.7 mmHg, 15.6±2.8 mmHg, and 13.6±2.6 mmHg, respectively. A significant difference was observed among all three devices (P < 0.01). The average CV (± standard deviation) for the CST, GAT, and NCT were 9.8±5.1%, 6.3±4.5%, and 8.7±3.6%, respectively. The CV for the CST was significantly higher than that for the GAT (P < 0.01). However, the CV for the NCT did not significantly differ from those for the CST and GAT (P > 0.05). The correlation coefficients were 0.865 (P < 0.0001) between the CST and NCT, 0.865 (P < 0.0001) between the CST and GAT, and 0.845 (P < 0.0001) between the NCT and GAT. The respective ICC values for the CST, NCT, and GAT were 0.792, 0.812, and 0.876. [Conclusion] Although the IOP measurements by the CST highly correlated with the measurements by the NCT and GAT, the values appeared to be lower. This might be due to the difference in the measurement principle of the instrument. The repeatability of the CST was equivalent to that of the NCT.
Bei der Diskussion des Glaukombegriffes könnte der Augeninnendruck als „normal“ bezeichnet werden, der nicht zu einem Glaukomschaden des Sehnerven führt. Leider kann eine derartige Definition nicht präzise numerisch abgegrenzt werden, da nicht alle Augen in gleicher Weise auf ein gegebenes Augeninnendruckniveau reagieren. Man kann lediglich die Häufigkeitsverteilung des Augeninnendruckes in der allgemeinen Bevölkerung darstellen und mit Patientengruppen mit einem manifesten Glaukom vergleichen, um den verschiedenen Augeninnendruckbereichen ein gewisses Glaukomrisiko zuzuordnen. Im folgenden Kapitel sollen deshalb die Häufigkeitsverteilung des Augeninnendruckes in der allgemeinen, scheinbar augengesunden Bevölkerung und nichtglaukomatöse Einflüsse auf den Augeninnendruck besprochen warden.
7.1. Differential diagnosis information from other assessments
7.2. Examination of the anterior segment and ocular adnexa
7.3. Tear film & ocular surface assessment
7.4. Assessment of the lacrimal drainage system
7.5. Anterior chamber angle depth estimation
7.6. Gonioscopy
7.7. Tonometry
7.8. Instillation of diagnostic drugs
7.9. Pupil light reflexes
7.10. Fundus Examination, particularly the posterior pole
7.11 Optical Coherence Tomography
7.12. Fundus examination, particularly the peripheral retina
Objectives: The European Glaucoma Prevention Study seeks to evaluate the efficacy of reducing intraocular pressure (IOP), with dorzolamide to prevent or delay patients affected by ocular hypertension from developing primary open-angle glaucoma. Design: Randomized, double-blinded, controlled clinical trial. Participants: Patients (age :30 years) were enrolled from 18 European centers. The patients fulfilled a series of inclusion criteria including the measurements of IOP (22-29 mmHg), two normal and reliable visual fields (VFs) (on the basis of mean defect and corrected pattern standard deviation/corrected loss of variance of standard 30/II Humphrey or Octopus perimetry), and normal optic disc as determined by the Optic Disc Reading Center (vertical and horizontal cup-to-disc ratios; asymmetry between the two eyes less than or equal to0.4). Intervention: Patients were randomized to the treatment with dorzolamide or a placebo. Main Outcome Measures: End points are VF and/or optic disc changes. A VF change during the follow-up must be confirmed by two further positive tests. Optic disc change is defined by the agreement of two out of three independent observers evaluating optic disc stereo-slides. Results: One thousand seventy-seven subjects were randomized between January 1, 1997 and May 31, 1999. The mean age was 57.03 +/- 10.3 years; 54.41% were women and 99.9% were Caucasian. Mean IOP was 23.6 +/- 1.6 mmHg in both eyes. Mean visual acuity was 0.97 +/- 0.11 in both eyes; mean refraction was 0.23 +/- 1.76 diopters in the right eye and 0.18 +/- 1.79 diopters in the left eye. Previous use of medication for ocular hypertension was reported by 38.4% of the patients, systemic hypertension by 28.1%, cardiovascular diseases by 12.9%, and diabetes mellitus by 4.7%. The qualifying VFs were normal and reliable according to protocol criteria. Conclusions: The mean IOP of the patients enrolled in the European Glaucoma Prevention Study is consistent with the estimated mean IOP (within the range of 22-29 mmHg) found in a large sample of the European population. The European Glaucoma Prevention Study should be able to better address the clinical question of whether pharmacological reduction of IOP (by means of dorzolamide) in ocular hypertension patients at moderate risk for developing primary open-angle glaucoma effectively lowers the incidence of primary open-angle glaucoma.
Ever since the recognition that glaucoma was associated in many patients with a firm eye, ophthalmologists have been attempting to measure intraocular pressure (IOP) clinically. Prior to the introduction of Goldmann Applanation Tonometry (GAT) in the 1950s, tonometry techniques were inconvenient and unreliable. Professor Goldmann’s tonometer rapidly gained widespread acceptance following its introduction – it was reasonably-priced, based on easily-understood physical principles, fitted seamlessly into the workflow of the slit-lamp exam, and appeared to provide accurate, reproducible measurements. GAT’s status as a tonometry “Gold standard” went largely unchallenged for 50 years, even though Professor Goldmann himself drew attention to various potential sources of error for the device in his first description of his tonometer [1]. In particular, Goldmann and Schmidt acknowledged that their design assumptions were based on a central corneal thickness (CCT) of 0.5 mm (500 µm) and that the accuracy of their device would vary if CCT deviated from this value – “Under conditions which differ considerably from our measurement conditions (abnormally thick or thin cornea, for example…), errors of several millimeters are to be expected” [1]. Given the paucity of published data at the time, 500 µm seemed a reasonable assumption for the “average” patient. We now know CCT varies greatly among the general population, to a degree that impacts the accuracy of GAT in daily practice.
Purpose: To identify differences in applanation tonometry between retreated and nonretreated eyes (primary LASIK eyes) 6 months after hyperopic laser in situ keratomileusis. Methods: In a prospective study 100 eyes (100 patients) underwent conventional hyperopic laser in situ keratomileusis under a 160-μm flap. Central Goldmann applanation tonometry was determined before and 6 months after surgery in 78 (78%) primary LASIK eyes and before surgery and 6 months after the retreatment date in 22 (22%) retreated eyes. Results: Preoperative mean tonometry was 14.96 ± 1.96 mm Hg and 15.30 ± 1.95 mm Hg in primary LASIK and retreated eyes, respectively. Six months after surgery it was 12.99 ± 2.03 mm Hg (P < 0.001) and 12.67 ± 2.20 mm Hg (P < 0.001), respectively. No significant differences in mean tonometry were found between retreated and primary LASIK eyes 6 months after surgery (P = 0.537). Decreased tonometric values were found in 20 retreated eyes (90.91%) and in 62 primary LASIK eyes (79.48%). Increased tonometric values higher than 1 mm Hg were found in 3 primary LASIK eyes (3.84%), but no retreated eyes showed increased values 6 months after surgery. Two retreated eyes (9.09%) and 10 primary LASIK eyes (79.49%) presented the same tonometric values before surgery and at the end of the study. Conclusions: After hyperopic laser in situ keratomileusis there was no significant difference in Goldmann applanation tonometry between retreated and primary LASIK eyes.
To compare the level of accuracy of intraocular pressure (IOP) measurements of a rebound tonometer (RT) Icare®, and non-contact tonometer (NCT), using Goldmann Applanation tonometer (GAT) as a reference to evaluate the influence of central corneal thickness (CCT) on IOP readings in the Korean population.
We measured the central corneal thickness and the applanation intraocular pressure (IOP) on 45 Hong Kong Chinese. There was no obvious relationship between these two parameters, as different from other literatures. It could be due to either a limited number of subjects with a high IOP level (only six subjects with IOP ⪰ 22 mmHg), or Chinese has a thicker central cornea in general. The mean central cornea of our subjects was thicker (566 ± 36 μm) than some previous findings. Thirty subjects had their intraocular pressure further increased by adopting a 40 ° head-down posture. Their IOP and topographic corneal thickness were measured again. There was no significant change in the central corneal thickness even though the IOP was elevated by 11.7 mmHg. However the nasal cornea demonstrated a thinning effect (by some 18 μm) during the IOP elevation but it returned to the pre-inverted level after returning to a sitting posture for 5 min. Further investigation with more corneal regions being measured would be valuable to evaluate the in vivo effect of IOP elevation from glaucoma attack on corneal thickness.
To compare the intraocular pressure (IOP), retinal nerve fiber layer (RNFL) thickness and central corneal thickness (CCT) in healthy individuals and patients with chronic renal failure (CRF) undergoing hemodialysis, and to evaluate the changes in each parameter before and after hemodialysis in patients with CRF.
OBJECTIVES: To compare the intraocular pressure figures obtained with Goldman applanation tonometer and with Pascal dynamic contour tonometer, as well as the central corneal thickness variation before and after the refractive surgery with LASIK, and to set the relationship between both tonometers. METHODS: Seventy four patients (140 eyes) aged over 21 years, with stable myopia (-1 to -10 dioptres), cylinder defect lower than-3 dioptres and central corneal thickness under 480 microns. The patients were operated on using Excimer laser (LASIK technique) at the Refractive Surgery Service of "Ramón Pando Ferrer" Cuban Institute of Ophthalmology in the period from December, 2006 to March 2007; then they were followed up for one year, even though the variables were estimated one month after surgery. RESULTS: Females slightly predominated; the 21-39 years age group represented 81 % of cases and moderate myopia present in 74 eyes accounted for 52.6 % of the total number. The intraocular pressure value taken with the dynamic contour tonometer was higher than that of the Goldmann tonometer by 2 mm Hg in the preoperative phase and by 3.7 mm Hg in the postoperative phase. The corneal thickness variation after surgery with LASIK and the intraocular pressure according to the used tonometer were correlated. CONCLUSIONS: The figures of intraocular pressure measured with Pascal tonometer are more reliable than those obtained with Goldmann applanation tonometer, whenever the central corneal thickness is not within the set normal value range.
Diferentes estudios han observado que los ojos con espesor corneal central menores poseen mayor riesgo de desarrollar pérdidas en el campo visual en sujetos con glaucoma normotensivo. También se ha señalado a los de espesor corneal central bajos como un factor de riesgo para el desarrollo de glaucoma. Por ello, el espesor corneal central se ha convertido en un factor biométrico importante y es una parte esencial de la evaluación del paciente glaucomatoso. El objetivo nuestro fue comparar los resultados de la paquimetría (medición del espesor corneal) en pacientes normales, sospechosos de glaucoma e hipertensos oculares. Se seleccionaron de forma prospectiva, longitudinal y comparativa, 31 ojos normales, 152 sospechosos de glaucoma y 67 ojos hipertensos oculares. De los ojos sospechosos de glaucomas 98 presentaron corneas inferiores a 555 micras representando el 64,9% de la muestra. El grupo de hipertensión ocular se comportó similar a los sospechosos de glaucoma 46 ojos con espesor corneal central de 555 o menor. La mayoría de los ojos sospechosos de glaucoma presentaron corneas inferiores a 555 micras. El grupo de hipertensión ocular se comportó similar a los sospechosos de glaucoma.Different studies have stated that eyes with less central corneal thickness are in a higher risk of developing losses in the visual field in subjects with normotensive glaucoma. Low central corneal thickness has been identified too as a risk for developing glaucoma. That is why central corneal thickness has become an important biometric factor and is an essential part of the glaucoma patient's evaluation.
Purpose
To evaluate repeatability within and between examiners and to assess agreement in corneal thickness measurements obtained by anterior segment optical coherence tomography (ASOCT) and ultrasonic pachymetry (USP).
Methods
This was a prospective, observational study. Fifty-one patients who visited a glaucoma service with suspected glaucoma, glaucoma, or cataract were enrolled. Patients with a history of corneal surgery or abnormalities and those who were uncooperative for examinations were excluded. Each patient underwent ASOCT followed by USP, with each test performed by two different examiners. Measurement repeatability was evaluated using intraclass correlation coefficient (ICC) values. Agreement in corneal thickness measurements was evaluated by the Bland and Altman plot method. Linear regression analysis was used to assess the relationship between ASOCT and USP measurements.
Results
USP and ASOCT corneal thickness measurements revealed high intraexaminer and interexaminer repeatability (ICCs ≥ 0.978). ASOCT corneal thickness measurements of a central 2-mm zone showed higher intraexaminer (ICC = 0.999) and interexaminer (ICC = 0.999) repeatability than USP measurements or ASOCT measurements of the vertex. The 95% limit of agreement (LoA) between the vertex-centered ASOCT and the USP scan was between 3.68 and 24.76 μm. The 95% LoA between the central 2-mm zone ASOCT and the USP scan was between 3.75 and 23.39 μm. Average ASOCT corneal thickness was less than USP measurements, but ASOCT thickness could be converted to USP thickness through linear regression equations.
Conclusion
Both devices have good intraexaminer and interexaminer repeatability, though ASOCT has slightly better interexaminer repeatability. ASOCT accurately and reliably measures corneal thickness in a noninvasive manner.
To identify delayed recognition publications, or ‘Sleeping Beauties’ (SBs), that are scarcely cited in the years or decades following their publication, but then go on to become highly cited, we screened citation histories of 184,606 articles in 52 ophthalmology journals using the Science Citation Index-Expanded (Thomson Reuters). Nine articles were identified as SBs, which accounted for 0.005% of basic materials. The SBs were published in Archives of Ophthalmology (n = 3), American Journal of Ophthalmology (n = 3), Acta Ophthalmologica (n = 1), Investigative Ophthalmology and Visual Science (n = 1), and Japanese Journal of Clinical Ophthalmology (n = 1). For citation histories according to the conjuring SB from the fairy tale, the sleep duration ranged from 7 to 59 years with mean of 19.7 years, the depth of sleep as evaluated by the average citations per year during the sleeping period ranged from 0.09 to 0.82 with mean of 0.45 citations, and the awake intensity as determined by the average citations per year during the first 5 years period following awakening ranged from 3.60 to 17.80 with mean of 8.51 citations. The number of total citations up to 2010 ranged from 109 to 375 with mean of 176.3 citations. Topics of the SBs covered description of new clinical diseases including acute retinal necrosis syndrome, cancer-associated retinopathy, and polypoidal choroidal vasculopathy, correlate of central corneal thickness with intraocular pressure readings, inadvertent eyeball perforation in retrobulbar anesthesia, pharmacologic weakening of extraocular muscles, amniotic membrane graft for ocular surface reconstruction, and refractive surgery. These data provide a perspective of rare but interesting delayed citation articles in ophthalmology.
PurposeTo determine the relationship between dynamic contour tonometry (DCT), Goldmann applanation tonometry (GAT) and pneumotonometry (PNT) in ocular hypertension patients (OHT) and their relationship to central corneal thickness (CCT) and ocular pulse amplitude (OPA).Methods
Sixty patients (101 eyes) with intraocular pressure (IOP) ≥21 mmHg using GAT and normal appearing optic nerve heads and normal visual fields were included. The following tests were performed simultaneously during a single visit: IOP using DCT, GAT and PNT, OPA using DCT and CCT using ultrasound pachymetry. We studied the difference IOP between these 3 tonometers using Wilcoxon non-parametric test and the effect of CCT on IOP and OPA, as well as the relationship between OPA and IOP using Spearman correlation coefficient.ResultsThe median PNT IOP was 24 mmHg (Inter-quartile range [IQR]: 22-26), median GAT IOP was 22 mmHg (IQR: 22-24), and median DCT IOP was 28.2 mmHg (IQR: 24.1-30.7). PNT and DCT had higher IOP values than GAT (median 2 mmHg and 6.2 mmHg, respectively). Mean CCT was 594.5 μm (SD 30.0). GAT IOP and DCT IOP showed an increase with increased corneal thickness (r: 0.209; P = .036 and r: 0.195; P = .051, respectively). PNT IOP did not change with CCT (r: 0.15; P = .12). The median OPA was 4.8 mmHg (IQR: 3.6-6.1), and significantly increased with GAT IOP (r: 0,38; P < .001) and with CCT (r: 0.287; P = .004). This association was unclear with IOP PNT and IOP DCT (r: 0.067; P = .50 and r: 0,17, P = .08, respectively).ConclusionsDCT and PNT IOP values were higher than GAT IOP measurements in ocular hypertension patients. GAT IOP showed a significant increase with increased corneal thickness. Increased OPA seems to correlate with increased CCT and IOP, particularly if GAT is used.
Zusammenfassung Der Augeninnendruck ist nach wie vor der wichtigste Risikofaktor für die Entstehung eines glaukomatösen Schadens. Neuere Studien weisen darauf hin, dass auch die Hornhautdicke ein Risikofaktor für die Entstehung einer glaukomatösen Schädigung darstellt. Eine mögliche Ursache hierfür könnte sein, dass die Hornhautdicke die Messung des Augeninnendruckes beeinflusst. Es konnte gezeigt werden, dass bei der Applanationstonometrie nach Goldmann die Messwerte mit der Hornhautdicke korrelieren. Dicke Hornhäute führen zu einer falsch hohen Messung des Augeninnendruckes und dünne zu einer falsch niedrigen. Ob es sich bei der Hornhautdicke als Risikofaktor für das Glaukom um einen reinen Messfehler oder einen Ausdruck biomechanischer Besonderheiten der Glaukomaugen handelt, ist nicht mit Sicherheit geklärt. Ein großer Teil des Hornhauteffektes beruht sicherlich auf dem Messfehler bei der Augeninnendruckmessung. Durch die Nichtberücksichtigung der Hornhautdicke können Messfehler entstehen, die zu Fehldiagnose und fehlerhafter Behandlung führen können. Aus diesem Grund sollte die Messung der Hornhautdicke bei Patienten mit einem Glaukom oder Glaukomverdacht nicht fehlen.
Introducción: Se ha construido un nomograma práctico para representar los resultados del Ocular Hipertensión Study (Gordon et al. Arch Ophthalmol 2002;120: 714-720) que relacionan la presión intraocular y el espesor corneal con el riesgo de evolucionar de hipertensión ocular a glaucoma en un plazo de 6 años. Material y Métodos: Se ha aplicado una regresión logarítmica múltiple a los 9 datos mostrados en la figura 1 del trabajo señalado anteriormente. Resultados: Un coeficiente de correlación de 0,91 (p<0,001) permite definir la siguiente ecuación:
To assess the performance of the dynamic contour tonometer (DCT) in eyes undergoing excimer laser photorefractive keratectomy (PRK).
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