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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 25  |  Issue : 2  |  Page : 90-94

Central corneal thickness: Important considerate in ophthalmic clinic


1 Department of Ophthalmology, Dr Mohan Lal Memorial Gandhi Eye Hospital, Aligarh, Uttar Pradesh, India
2 Department of Ophthalmology, PMMM Shatabdi Hospital, Mumbai, Maharashtra, India

Date of Submission02-May-2018
Date of Acceptance24-Feb-2020
Date of Web Publication15-Dec-2020

Correspondence Address:
Dr. Sneha Thakur
Department of Ophthalmology, PMMM Shatabdi Hospital, Mumbai - 400 088, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jmgims.jmgims_18_18

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  Abstract 


Aim: The aim of this study was to evaluate the relationship of central corneal thickness (CCT) with age, sex, refractive status, and keratometry (KM). Materials and Methods: In our cross-sectional study, 1000 eyes of 500 patients from the outpatient department were randomly selected between July 2014 and December 2015. CCT was measured with a Humphrey ultrasonic pachymeter. Horizontal and vertical curvatures of the cornea were measured with a Bausch and Lomb keratometer, and its mean was calculated. Refractive state was measured with a Priestley-Smith retinoscope and converted to spherical equivalent (SE). The patients were divided into three age groups (Group A [16–30 years], Group B [31–45 years], and Group C [46–60 years]), and the data were analyzed statistically by the Statistical Package for the Social Sciences programme. Results: The mean SE, KM, and CCT of the patients under the study were(-) 0.47 ± 2.26, 43.79 ± 1.18D, and 528.41 ± 19.1 μm. The mean CCT was higher in age Group C (46–60 years) than other groups (P = 0.008), but we found that an increase in age has no impact on CCT after regression analysis. CCT was not affected by sex (p = 0.168). The mean CCT for myopic patients was 522.87 ± 18.03 μm, which was less compared to 536.39 ± 17.753 μm in hypermetropic patients (p ≤ 0.001). Positive correlation was found between CCT and SE (r = 0.520,P≤ 0.001). KM showed negative correlation with CCT (r = −0.288,p≤ 0.001). Conclusion: From our study, we concluded that CCT was related to age, refractive status, and KM, but not to sex.

Keywords: Age, central corneal thickness, keratometry, refractive state, sex


How to cite this article:
Thakur S, Saxena AK, Bhatnagar A. Central corneal thickness: Important considerate in ophthalmic clinic. J Mahatma Gandhi Inst Med Sci 2020;25:90-4

How to cite this URL:
Thakur S, Saxena AK, Bhatnagar A. Central corneal thickness: Important considerate in ophthalmic clinic. J Mahatma Gandhi Inst Med Sci [serial online] 2020 [cited 2021 Aug 5];25:90-4. Available from: https://www.jmgims.co.in/text.asp?2020/25/2/90/303415




  Introduction Top


The cornea occupies one-third of the ocular tunic and forms the anterior meniscus-shaped transparent portion of the ocular globe. It serves as the principal refractive element in the eye, while maintaining a highly impermeable barrier between the eye and environment.

It serves as a transparent window of the eye that allows the entry of light. The maintenance of corneal shape and transparency is critical for light refraction, with the cornea accounting for more than two-thirds of the total refractive power of the eye. Central corneal thickness (CCT), one of the important corneal parameters, plays an important role in planning various intraocular procedures, refractive surgeries, and corneal transplantation. Recently, there has been an increased interest in corneal thickness.[1] Different aspects such as a correlation between CCT, intraocular pressure, and progressive thinning in the cornea have been well documented in many studies.[2],[3],[4],[5],[6]

The CCT is an important diagnostic and prognostic factor in determining whether a patient is suitable for refractive surgery and also to determine the required procedure. It also helps in classification as well as diagnosis of glaucoma.

A pachymeter measures corneal thickness, which is now routine and increasingly important in ophthalmic practice in avoiding postoperative complications. Other uses of corneal pachymetry include determining the “health” of a corneal transplant, evaluating a patient with keratoconus, and monitoring the degree of stromal edema. In contact lens wearers, corneal edema and hypoxia can be assessed in daily wear, extended wear, or therapeutic lens patients.

Uncorrected refractive error is increasingly recognized as a significant cause of avoidable visual disability worldwide and has been included as one of the priority areas of Vision 2020.[7] In-depth knowledge of ocular biometric parameters is required in understanding the risk factors and determinants of ammetropia[8],[9],[10],[11] and in formulating appropriate preventive and treatment strategies. The most important factor in refractive errors is the relationship to the ocular components.[9]

Linke et al.[2] evaluated 4600 eyes to study the relationship between the thinnest point in corneal thickness and the refractive state, keratometry (KM), age, sex, and the ocular side. They concluded that refractive state, mean KM, and age had statistically significant, although marginal impact, on the thinnest point in corneal thickness. Sex and the ocular side had no correlation.

Altinok et al.[12] and Prasad et al.[13] found no correlation between for age, sex, and refractive status and CCT.

Phakic intraocular lenses are increasingly being used to correct refractive errors[14] which require different ocular parameters to consider. Effective visual rehabilitation after cataract surgery also depends on accurate intraocular lens power calculations which are primarily derived from normative ocular biometric data.[15],[16],[17],[18],[19] Therefore, it is important to understand the factors that have an influence on the CCT.

In our study, we had analyzed different biometric ocular factors and investigated the possible influences of age, sex, refractive state, and KM on CCT.


  Materials and Methods Top


This cross-sectional study was conducted at a hospital. Approval for this study was obtained from the ethics committee of the hospital. Informed consent was obtained from patients in their own language in a prescribed bilingual format. Five hundred patients (1000 eyes) who fulfilled the inclusion criteria were selected from the outpatient department.

Patients ≥16 years of age, and <60 years of age, of either gender, with visual acuity 6/6 by Snellen's Chart or Landolt's C Chart were included. Patients below 16 years and above 60 years, with history of any ocular surgery, ocular trauma, pre-existing eyelid disease, anterior segment pathology such as conjunctivitis, keratitis, uveitis, glaucoma, corneal dystrophy, corneal degeneration, keratoconus, congenital corneal disease (keratoglobus), with systemic disease such as diabetes mellitus, and hypertension, and patients using contact lens were excluded from the study.

The patients were divided into three age groups: Group A (16-30 years), Group B (31-45 years) and Group C (46-60 years).

Visual acuity

Visual acuity of both the eyes was recorded by Snellen's Chart or Landolt's C Chart, and refractive state determined by a Priestley-Smith retinoscope. Spherical equivalent (SE) was calculated as a sphere plus half-cylindrical power for the left and right eyes. Refraction subgroups were formed with respect to SE as follows: Myopia SE <0 D and hypermetropic as SE >0 D.

Slit-lamp examination

A Haag-Streit 900 slit lamp (Haag Streit INC Mason Ohio, USA) was used for examination. Both the eyes were examined under diffuse, focal, and retro illumination on the day of examination. The cornea was examined carefully for any abnormality such as corneal opacity, corneal dystrophy, corneal degeneration, keratitis, corneal ulcer, and stromal thinning as in keratoconus. The anterior chamber, lens, and pupillary reactions were examined to rule out any abnormality. Slit-lamp biomicroscopy 90 D was done to rule out fundus abnormality.

Pachymetry

CCT was measured with a Humphrey ultrasonic pachymeter for the left and right eyes. Three consecutive readings were taken, and the mean was calculated for the left and right eyes.

Keratometry

The curvature of the cornea was measured with a Bausch and Lomb Keratometer. Vertical and horizontal curvatures of the cornea were measured. Three consecutive readings were taken and the mean KM was calculated for the left and right eyes.

Data were tabulated and statistically analyzed by the Statistical Package for the Social Science program, version 17.0 (IBM Inc., New York,USA). Continuous variables were presented as mean ± standard deviation (SD), and categorical variables were presented as absolute numbers and percentages. Data were checked for normality before the statistical analysis. Normally distributed continuous variables, KM values, and CCT were compared between male and female using the unpaired t-test. One-way analysis of variance was used to evaluate the significance of the differences of KM values and CCT among age group and further paired comparisons were done using Tukey test. Pearson correlation was also used between SE, CCT, and KM. For all statistical tests,p< 0.05 was taken to indicate a statistically significant difference.


  Results Top


About 41.2% of the patients were under 16–30 years of age, 29.8% were under 31–45 years, and 29% were under the age group of 45–60 years. The mean age was 36.09 ± 13.05 years with a median of 35 years. It was observed that 53.2% of the patients were male, whereas 46.8% were female.

The mean SE was (-) 0.47 ± 2.26 with a median of 0.50, whereas the mean KM was 43.79 ± 1.18 D with a median of 43.88D. The mean CCT was 528.41 ± 19.1 μm with a median of 530 μm [Table 1].
Table 1: Mean, Median, Minimum-Maximum for SE, KM and CCT

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The mean CCT was 527.20 ± 19.30 μm for Group A, 526.94 ± 20.86 μm for Group B, and 531.66 ± 16.43 μm for Group C as shown in [Table 2]a. Further, it was observed that there was a significant difference in the mean CCT among the various age groups (p = 0.003). Further post-hoc analysis witnessed a significant difference in the mean CCT between Group A and Group C (p value=0.006), and between Group B and Group C (p=0.008).


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After the linear regression analysis, it was found that increase in age had no impact on CCT (B = 0.103, SD = 0.065,p= 0.114) as shown in [Table 2]b.

The mean CCT was 529.19 ± 18.38 μm for females and 529.19 ± 18.38 μm for males. Further, it was observed that there was no significant difference in the mean CCT when compared between the two genders [Table 3].
Table 3: Correlation between central corneal thickness and sex

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The mean CCT was 522.87 ± 18.03 μm for myopic patients and 536.39 ± 17.753 μm for hypermetropic patients. Further, it was observed that there was a significant difference in CCT between myopic and hypermetropic patients (p < 0.001) [Table 4].
Table 4: Comparison of central corneal thickness between myopic and hypermetropic eyes and its correlation with spherical equivalent and mean keratometry

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[Table 4] shows that there was a significant positive correlation between CCT and SE (r = 0.520, P < 0.001) and negative correlation between KM and CCT (r= −0.288).


  Discussion Top


The cornea is an important refractive element in the eye. The maintenance of the corneal structure is crucial for the physiological role of this tissue in refraction and biodefense. The widespread application of corneal surgery including keratoplasty and refractive surgery has necessitated a more detailed understanding of recent advances in cellular and molecular biology of the cornea.

CCT measurements are important when monitoring glaucoma and ocular hypertensive patients. Corneal pachymetry abnormalities include both thinning disorders such as keratoconus and pellucid marginal degeneration and thickened cornea with endothelial compromise.

Various studies have been conducted to evaluate the relationship between CCT, refractive error, age, sex, and KM, and statistically significant results have been found.

Nangia et al.[20] conducted a population-based study in rural area and found that CCT was associated significantly with younger age, male gender, and lower corneal refractive power. CCT was not associated significantly with refractive error. In accordance with the above study, we found that CCT was associated with age (p = 0.003) and had negative correlation with the mean KM values (r = −0.88). However, we found no association with gender of the patient with CCT.

Tomidokoro et al.[21] conducted a population-based cross-sectional study to study CCT and related factors in Japan. They found that CCT was thicker in men than in women and was correlated with age (right eye only) and corneal curvature. In accordance with the above study, we found that CCT significantly correlated with age (P = 0.003) and KM (p < 0.001). However, no correlation with sex was seen (p = 0.168).

Chen et al.[22] found that CCT has no association with age, while its significance was less in females than in males. It also showed that CCT has no significant association with refractive error. They found that CCT was significantly less in females than in males. Finally, he concluded that there was no correlation between CCT and degree of myopia among the Taiwanese population, and CCT of myopia and emmetropia did not differ significantly. In contrast to the above-mentioned study, we found no correlation between CCT and sex (p = 0.168). However, we found statistically significant correlation of CCT with age (p = 0.003) and refractive status (p < 0.001).

Touzeau et al.[23] studied the correlation between subjective refraction and biometry parameters. They found that corneal biometric parameters did not correlate with subjective SE and showed no differences between the refractive groups except for the CCT. High myopic group (-6D) had thinner corneas. In accordance with the above study, we found that CCT was thin in myopic individuals (mean CCT = 522.87 ± 18.034 μm) than hypermetropic ones (mean CCT = 536.39 ± 17.753 μm). However, we also found a statistically significant correlation between mean KM and CCT with SE.

Chang et al.[24] found that the mean corneal thickness was 533 (SD 29) μm and was thinner in more myopic eyes (p = 0.021). Similarly, in our study, we found that CCT was significantly thinner (p < 0.001) in myopic individuals that in hypermetropic individuals.

Chen et al.[1] found no significant correlations between CCT and refractive error, corneal curvature, anterior chamber depth, and axial length. They concluded that CCT is an independent factor unrelated to other ocular parameters. In contrast, we found that CCT correlated significantly with the mean KM (p < 0.001) and refractive error (p < 0.001).


  Conclusion Top


From our study, we found a significant correlation between different ocular biometric parameters. CCT was found to be increased in elderly individuals, but an increase in age has no impact on CCT. Furthermore, CCT was thinner in myopic individuals than hypermetropic ones. Hence, it is important to do a detailed preoperative workup for such patient undergoing refractive and cataract surgery to avoid future complications. Due to the sudden increase in the use of various contact lenses, it has become utmost important to consider different corneal parameters. As already mentioned in ocular hypertension study, CCT plays an important role in the assessment of glaucoma; therefore, its value should be predetermined to measure intraocular pressure, especially in elderly and myopic groups.

CCT correlated positively with SE, but no correlation with sex was seen. A significant negative correlation between mean keratometric values and CCT was seen. Hence, in extremes of keratometric reading, it is always better to measure CCT to explain the visual prognosis following various refractive and intraocular surgeries. From the above study, we concluded that CCT was related to age, refractive status, and KM, but not to sex.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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