Evaluation of anterior segment parameters in keratoconic eyes measured with the Pentacam system
To evaluate the alteration in anterior chamber parameters with the progression of keratoconus using a rotating Scheimpflug camera.
Inonu University, Turgut Ozal Medical Center, Ophthalmology Department, Malatya, Turkey.
Two hundred sixteen eyes of 123 patients diagnosed with keratoconus and 224 eyes of 112 normal subjects were evaluated with a Pentacam Scheimpflug camera (Oculus Inc.). Keratoconic eyes were divided into 3 groups according to mean keratometer (K) readings: mild (K = less than 47.0 diopters [D]), moderate (K = 47.0 to 52.0 D), and severe (K = 52.0 D or higher). The following parameters were obtained: thinnest corneal thickness (TCT), anterior chamber depth (ACD), corneal volume (CV), anterior chamber angle (ACA), and anterior chamber volume (ACV).
One hundred twenty-nine eyes had mild keratoconus, 59 had moderate keratoconus, and 35 had severe keratoconus. There were no statistically significant differences between the keratoconus group and control group in age, sex, or eye distribution (P>.05). With the progression of the disease, TCT and ACD were statistically different between all groups (P<.05). There were statistically significant differences in ACA and CV measurements between the mild keratoconus and severe keratoconus groups (P<.05). Also, CV readings were significantly different between the control group and all keratoconus groups (P<.05), although there was no significant difference in ACA measurements (P>.05). Despite a progressive increase in the ACV with disease progression, the differences between groups were not statistically significant (P>.05) except between the severe keratoconus group and the control group (P<.05).
Anterior segment parameters of the eye showed significant alterations with the progression of keratoconus.
Available from: Lei Tian
- "Corneal hysteresis and the corneal resistance factor are the main biomechanical parameters measured by the Ocular Response Analyzer. Several studies [10–12] have compared the biomechanical properties of normal and keratoconic corneas and found that the latter have lower corneal hysteresis and resistance. However, these parameters are derived from a proprietary algorithm applied to the measured waveform, and the ORA cannot display the dynamics of the deformation process in real time. "
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ABSTRACT: Purpose. To compare the corneal biomechanical properties of keratoconic patients and age-matched controls using corneal visualization Scheimpflug technology (Corvis ST). Methods. Sixty keratoconic eyes from 47 keratoconus patients and 60 normal eyes from 60 controls were enrolled in this prospective study. Tomography and biomechanical parameters of all eyes were obtained with the Pentacam and Corvis ST, respectively. Intraocular pressure was measured using a Goldmann applanation tonometer.
Results. The tomography and biomechanical parameters of the keratoconic corneas were significantly different from those of the normal corneas except for the anterior chamber angle, first applanation length, the highest concavity time, and peak distance. The deformation amplitude was the best predictive parameter (area under the curve: 0.882), with a sensitivity of 81.7%, although there was a significant overlap between keratoconic and normal corneas that ranged from 1.0 to 1.4 mm. In both the keratoconus and control groups, the deformation amplitude was negatively correlated with intraocular pressure, central corneal thickness, and corneal volume at 3 and 5 mm. Conclusions. Corvis ST offers an alternative method for measuring corneal biomechanical properties. The possibility of classifying keratoconus based on deformation amplitude deserves clinical attention.
Available from: Khalil Ghasemi Falavarjani
- "The Pentacam system may be used for the diagnosis of keratoconus, monitoring post-surgical corneas, calculating the keratometric index, intraocular lens power, and assessment of intraocular lens implants.45678910 Despite several reports on corneal thickness (CT),5 anterior and posterior corneal curvature and elevation,124 anterior chamber depth (ACD) and anterior chamber angle (ACA),31112 and corneal volume (CV) measurements,512 little is known about the distribution of these measurements in the normal population and its relation to the refractive status. We evaluated the distribution of the anterior segment measurements in a population of normal Iranian subjects with different types of refractive errors. "
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ABSTRACT: The purpose of this study was to evaluate the anterior segment measurements according to refractive status in a sample of the Iranian population.
Rassoul Akram Hospital, Tehran University of Medical Sciences.
IN THIS STUDY, REFRACTIVE SURGERY CANDIDATES WERE ASSIGNED ACCORDING TO THE REFRACTIVE ERROR TO ONE OF THREE GROUPS : emmetropia, myopia, and hyperopia. Myopic eyes were further divided to four subgroups : simple myopic group, simple myopic astigmatism group, high myopic group, and high myopia with astigmatism group. Anterior segment measurements with the Pentacam Scheimpflug system were performed in the right eye of all subjects.
The study sample was comprised of 283 subjects with a mean age of 29.1 ± 7.5 (standard deviation) years. Mean keratometry reading, Anterior chamber depth (ACD) and volume measurements were significantly higher in the myopic group and mean keratometry reading and anterior chamber angle measurements were significantly lower in the hyperopic group (P < 0.05, all comparisons). Maximum anterior elevation (AEmax) and maximum posterior elevation (PEmax), Q value, progression index, minimum corneal thickness, and corneal volume measurements were similar for all groups (P > 0.05, all comparisons). In the myopic subgroups, AEmax and PEmax and maximum keratometry (Kmax) were significantly higher, and ACD was lower in the astigmatic groups (P < 0.05, all comparisons). The Q value was less negative in low myopia (P < 0.05).
Myopic eyes had steeper corneas than hyperopic eyes and anterior chamber measurements were significantly higher in the myopic eyes. In myopic eyes, AEmax and PEmax and Kmax measurements were higher, and ACD measurements were lower in the astigmatic groups.
Available from: Seyed Mahdi Ahmadi Hosseini
- "There were no significant correlations between the mean K-reading with ACV and ACA nor between PCC with ACV and ACA in this study. In contrary, statistically significant positive correlations between mean K-readings with ACV and ACA were indicated in a previous study . It was supposed that with keratoconus development, central cone protrusion is compensated by peripheral corneal flattening and a decrease in ACA. "
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To assess changes in anterior segment parameters of keratoconus eyes at different stages of the disease in a sample of the Asian population.
Files of 32 patients (48 eyes) diagnosed as clinical keratoconus were assessed and the following parameters noted: central corneal thickness (CCT), thinnest corneal thickness (TCT), location of thinnest pachymetry, anterior chamber depth (ACD) at the centre from posterior corneal surface, ACD at 1, 2 and 3mm inferior-paracentral, ACD at thinnest pachymetry, anterior chamber volume (ACV) and anterior chamber angle (ACA). For analysis, keratoconus eyes were classified into 3 subgroups according to mean keratometry readings (mild: K≤47.0D, moderate: 47.0<K<52.0D, and severe: K≥52.0D). Forty-five subjects (45 right eyes) were recruited as a control group. They underwent Pentacam tomographic evaluation. The same parameters were recorded for control subjects as in the keratoconus patients.
Each keratoconus subgroup comprised of 16 eyes. CCT, TCT, ACD at centre, ACD at 1, 2mm inferior-paracentral and ACD at thinnest pachymetry were statistically different between mild and severe keratoconus groups (P<0.05). There were also significant differences between normal with each of the moderate and severe keratoconus groups (P<0.05). Non-significant differences were found in ACV (P=0.84) and ACA (P=0.71) between all measured groups.
With the exception of ACV and ACA, parameters that include CCT, TCT, ACD at centre, thinnest pachymetry and 1, 2 mm inferior-paracentral were significantly altered with progression of keratoconus. These findings may be useful in monitoring and management of keratoconus patients.
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