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Original Article Comparison of central corneal thickness of primary open angle patients with normal controls in South India

Maya Natarajan, Krishna Das1, Jayakumar Jeganathan2

Consultant Ophthalmologist, Vasan Care Hospital, Mangalore, 1Chief of Glaucoma Services, Aravind Eye Hospital and PG Institute of , Madurai, 2Department of Medicine, Kasturba Medical College, Mangalore (Manipal University), India

Background: Studies mainly in the western population compared using Wilcoxon two sample test and the have compared central corneal thickness in primary signed rank test. open angle glaucoma and normal individuals have found variable results. We did this study to compare Results: The mean central corneal thickness in the central corneal thickness of primary open angle the control group was 536 µm (462‑608 µm) and in the primary open angle glaucoma group was glaucoma patients with normal controls in a south 531 µm (476‑609 µm). Indian population. Conclusion: There was no significant difference in the Materials and Methods: This was a masked, central corneal thickness between primary open angle cross‑sectional study undertaken in a tertiary care glaucoma patients and the normal controls. center in South India. A total of 50 controls and 50 primary open angle glaucoma patients were studied. Keywords: Central corneal thickness, open angle Central corneal thickness between the two groups was glaucoma, ocular tonometry

Introduction comparable central corneal thickness in primary open angle glaucoma and normal individuals,[3,4] some studies have found One of the most important risk factors for primary open that central corneal thickness in primary open angle glaucoma [5] angle glaucoma is an elevated intra‑ocular pressure whose patients is significantly lesser than in the normal population. This may lead to the misclassification of many patients as normal measurement by Goldmann applanation tonometry has been tension glaucoma. This has led us to do this study to see if there found to be influenced by the central corneal thickness (CCT) of was any significant difference in the central corneal thickness the individual. The variation in central corneal thickness was not between primary open angle glaucoma patients and normal taken into account as Goldmann applanation tonometry assumes controls in south India. a standard 520 µm for all .[1] The normal range in most studies was between 427‑620 µm.[2] The central corneal thickness in primary open angle glaucoma has been studied, but mostly Materials and Methods in the western population. Though most studies have quoted Aim To compare the central corneal thickness of primary open angle Access this article online glaucoma patients and normal controls. Quick Response Code: Website: Objectives www.ojoonline.org To see if there were differences in the central corneal thickness with respect to age and sex in the two groups. DOI: 10.4103/0974-620X.111907 The design of this study was masked cross‑sectional study. The study was approved by the local ethics committee. Informed

Copyright:  2013 Natarajan M, et al. This is an open‑access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Correspondence: Dr. Jayakumar Jeganathan, Department of Medicine, Kasturba Medical college, Mangalore (Manipal University), Karnataka, India. E‑mail: [email protected]

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Natarajan, et al.: Central corneal thickness comparison

consent was obtained from all participants before including them value, which would also be the median value. As the distributions in the study. A total of 100 patients were enrolled in the study of the measurements were non‑normal and badly skewed, taking during a period of one year as per the inclusion and exclusion the median value was found to be more appropriate. A histogram criteria, which is given below. There were two groups of patients, was constructed with the measured values. The distribution of the control group and the primary open angle glaucoma patients the central corneal thickness measurements in controls and group. All patients were aged 40 and above keeping in mind the primary open angle glaucoma had a non‑normal or an asymmetric age distribution in primary open angle glaucoma. distribution. Wilcoxon two sample test and the signed rank test were the two non‑parametric tests used in this study to compare Control group the central corneal thickness measurements in primary open Consisted of people who had intra‑ocular pressures <21 mm. angle glaucoma and controls. of Hg. in both the measured by Goldman’s applanation tonometer, had normal optic discs, open angles on , no Results suspicion of any form of glaucoma, no family history of glaucoma, and did not have any other eye disease. Studying the age distribution in the two groups, it was found that the maximum numbers of patients in the control group were Fifty primary open angle glaucoma patients were enrolled in the between the ages of 40‑50 years while in the primary open angle study during the same one year period after written informed glaucoma group, they were between the ages of 50‑60 years. The consent. Individuals with primary open angle glaucoma had mean central corneal thickness for each patient was calculated by untreated intra‑ocular pressures of 22 mm of Hg or higher, an open, averaging the right and left eye values. This was done because we normal angle, a glaucomatous optic disc, and glaucomatous visual did not find any statistically significant difference in the central field defects. The subjects were chosen randomly from the glaucoma corneal thickness values between the right and left eye. This was services department of our hospital. Both newly diagnosed cases of done using non‑parametric testing. In the controls, the difference primary open angle glaucoma and those on treatment were included. in the central corneal thickness between the two eyes was not significant (signed rank test, P = 0.62). In the primary open People who had the following characteristics were excluded: angle glaucoma group also, the difference in the central corneal Persons with evidence of any anterior segment pathology including thickness between the two eyes was not significant (signed rank corneal opacities, history of previous intraocular or corneal test, P = 0.49). The distribution of the difference in the right and surgery, people with diabetes mellitus, people using contact lenses left eye central corneal thickness in both the groups showed that or any other condition that may affect corneal thickness, corneal most of the values were within ‑12 to +12 µm. The mean central edema, corneal astigmatism >2D and sphere >4D, any optic nerve corneal thickness in the control group was 536 µm with a range or cranial disease, and people with evidence of pseudoexfoliation. of 462‑608 µm. In the primary open angle glaucoma group, the mean was 531 µm with a range of 476‑609 µm. Thus, the mean All patients enrolled in the study underwent the following tests. central corneal thicknesses in the two groups were comparable. Their best corrected visual acuity, bio microscopy to By non‑parametric testing using the Wilcoxon two samples test, exclude corneal pathology, applanation tonometry, gonioscopy, it was found that there was no statistically significant difference dilated fundus examination and stereoscopic examination of the in the mean central corneal thickness measurements in primary optic discs and the nerve fiber layer using + 90D lens with the slit lamp. All glaucomatous patients underwent automated perimetry prior to dilation using the 24‑2 program of the Humphrey field Table 1: Distribution of central corneal thickness Analyzer. Central corneal thickness was measured in both the Central corneal Controls (No.) Primary open angle thickness (µm) glaucoma (No.) eyes. The readings were taken using the PACSCAN 300p model 450‑460 1 0 of SONOMED Inc. The corneal velocity was preset at 1636 ms. 461‑470 1 0 A calibration check was performed before performing actual 471‑480 2 4 measurements. A measurement accuracy test was also performed 481‑490 7 3 periodically to ensure the functionality of the PACSCAN. This 491‑500 2 3 performs an internal calibration check, which should generate a 501‑510 9 13 reading of 500+/‑ 1 µm. Topical proparacaine 0.5% was instilled in 511‑520 18 14 both the eyes. The patients were seated, erect, and were all asked to 521‑530 6 8 look at a target fixed 1 m. away when the measurements were made. 531‑540 9 23 541‑550 12 6 Three consecutive readings were taken for each eye by a single 551‑560 5 8 observer, an ophthalmologist, who was masked to the diagnosis. The 561‑570 8 12 numerical value of the readings taken was recorded by a technician. 571‑580 7 2 581‑590 7 1 Statistics 591‑600 4 1 The median of the three values was noted. If two out of the three 601‑610 1 1 readings were similar, then the mode was taken as the working 611‑620 1 1

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Natarajan, et al.: Central corneal thickness comparison

Table 2: Age‑wise distribution of central corneal thickness Age group Controls Primary open angle glaucoma P value No. Mean CCT* (µm) Range No. Mean CCT* (µm) Range 40‑50 29 542 (462‑608) 8 531 (502‑569) 0 .17 51‑60 18 526 (467‑597) 23 529 (497‑562) 0.42 61‑70 2 553 (511‑554) 12 531 (476‑609) 0.35 71‑80 1 506 (506‑506) 5 535 (516‑570) 0.12 81‑90 0 ‑ ‑ 2 552 (550‑555) *CCT: Central corneal thickness

open angle glaucoma and the control group (P = 0.16). The found in a studies by Casson RJ et al. and Bron AM et al.,[15,16] central corneal thickness was sub‑grouped using a range of 10 µm whereas other studies found the central corneal thickness in males for each subgroup, and the number of controls and primary open to be significantly greater than females.[17,18] We did not find any angle glaucoma patients falling into each group was assessed significant differences in the central corneal thicknesses between as showed in Table 1. The maximum number (i.e., eighteen the two eyes. Similar findings were noted by La Rosa Fa et al.[19] We patients) in the control group belonged to the subgroup of central did not find any significant trend in the central corneal thickness corneal thickness between 511‑520 µm. In the primary open with increasing age in our study. Noche CD et al. in their study angle glaucoma group, the maximum number (i.e., 23 patients) also did not find any significant effect of age on the central corneal belonged to the subgroup of central corneal thickness 531‑540 µm. thickness,[20] whereas a few studies showed a tendency for the By non‑parametric testing using the Wilcoxon two sample test, central corneal thickness to decrease with age.[21,22] P value was 0.16, and thus, there was no statistically significant difference between the two groups. The mean and the range of Conclusion central corneal thickness in the various age groups were studied and depicted in Table 2. There was no statistically significant We did not find any significant difference in the central corneal difference in the central corneal thickness among the various age thickness between primary open angle glaucoma patients and groups between the control group and the primary open angle normal individuals. The mean central corneal thickness found in glaucoma group. We also did not find any significant trend in our study was comparable to that of western populations. the central corneal thickness as the age advanced. Among the controls, 28 were males and 22 females. Among glaucoma group, Limitation there were 40 males and 10 females. Non‑parametric testing This study was done on patients in a tertiary care center, and the revealed no significant statistical difference in the distribution results may not necessarily be applicable to that of the general of central corneal thickness between males and females in the population, for which a population‑based study will be needed. control group (P = 0.20) and the glaucoma group (P = 0.21). Acknowledgement Discussion We would like to thank Mr. Kannan Mahadevan and Ms. Mahalakshmi for In our study, we found a central corneal thickness of 536 um in their immense help in the statistical analysis. We would also like to record the normal control group. A meta‑analysis of corneal thickness our sincere thanks to Dr. George Varghese puthuran, from glaucoma services literature done previously had found that the mean central corneal and Dr. N. V. Prajna, chief of medical education, for their constant guidance. thickness in normal white adults was 535 um,[6] whereas a study done in rural central India found a mean central corneal thickness References of 514 um, which was thinner compared to our values.[7] Studies done on this topic previously have found significant inter‑racial 1. Goldmann H, Schmidt T. Applanation tonometry. Ophthalmologica variation in central corneal thickness.[8,9] Some studies have even 1957;134:221‑42. found intra‑racial differences in the central corneal thickness 2. 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