The morphology of corneal endothelial cells in long term soft contact lens wearers in Kuala Lumpur

https://doi.org/10.1016/j.clae.2020.06.007Get rights and content

Abstract

Purpose

To analyse and compare the alterations in corneal endothelium morphology induced by different materials and durations of wearing soft contact lenses (CL) among young adults living in Kuala Lumpur.

Methods

Healthy soft CL wearers were invited to participate in this study. Visual acuity (VA) was measured using the Snellen chart, and subjective refraction was performed using cross-cylinder technique. Standard ocular assessments were conducted using a slit lamp biomicroscope and morphology of corneal endothelial cells (endothelial cell density, ECD, coefficient variation, COV, hexagonality, HEX and central corneal thickness, CCT) were evaluated using a non-contact specular microscope. Statistical analysis was conducted using ANOVA and data from the right eye only is included.

Results

A total of 72 subjects (32 SiHy and 40 HCL wearers) and 24 non-CL wearers (control) participated in this study. The gender distribution for study subjects was 13 males and 59 females, with a mean age 22.15 ± 1.84 years old. The mean refraction was −1.86 ± 1.25DS. The duration of wearing CL ranged from 1 to 9 years. Subjects were later divided into 2 groups following duration of CL wear: Group 1 (<5 years) and Group 2 (≥5 years) for analysis purposes. Statistical analysis showed significant alterations in ECD, COV and HEX of CL wearers (p < 0.05), with more changes found in HCL and Group 2 wearers. No significant change was found in CCT.

Conclusion

This study concludes that soft CL wear induced alterations in the morphology of corneal endothelial cells. Contact lens material and duration of CL wear (in years) are factors that affect the alterations. Optometrists are recommended to regularly evaluate the morphology of corneal endothelial cells in CL wearers and provide necessary intervention when required.

Introduction

Corneal endothelium is a single thin cellular layer that covers the posterior cornea and primarily regulates stromal hydration, which is related to the transparency of the cornea. Its morphology status are usually described in three aspects: endothelial cell density (ECD), which is the number of corneal endothelial cells per square millimetre (mm2); coefficient of variation (COV), which is the mean cell area divided by the standard deviation (SD) of cell area; and percentage of six-sided hexagonal cells (% HEX). When some endothelial cells die, the remaining cells enlarge and spread to maintain the intact mosaic monolayer. Nevertheless, not all cells grow to the same degree, thus increasing the variations in cell shapes and sizes. An increased COV is known as polymegethism, and a decreased HEX is known as pleomorphism.

Alterations in the morphology of corneal endothelium are indicators of corneal stress or instability [1]. Several factors, such as age, contact lens (CL) wear, ocular diseases, diabetes mellitus, race and ocular surgery influence the morphology of corneal endothelial cells [[2], [3], [4]]. However, CL wear is often associated with morphological changes in the corneal endothelium of young healthy adults [5]. All CLs reduce the amount of oxygen reaching the epithelial layer of the cornea to some degree. In the open eye state, oxygen level is primarily dependent on CL oxygen transmissibility. A mathematical model of oxygen diffusion across the cornea has identified the minimum requirement of 125 × 10−9 (cm2/sec) mL O2/mL × mmHg) oxygen transmissibility for extended wear CL to prevent alterations [6]. Thus, the changes in the morphology of corneal endothelial cells during CL wear must be monitored.

Conventional hydrogel CL (HCL) is found to substantially alter the morphology of corneal endothelial cells due to inadequate oxygen supply or corneal hypoxia [7,8]. Lee et al. found an important correlation between the morphology of corneal endothelium and the duration of HCL wearing periods [7]. CL wearers have remarkably greater COV in cell size than non-CL users. Individuals using HCL for more than 6 years have substantially lower percentages of HEX and ECD than the control group. Chang et al. reported a remarkable correlation between the morphological changes of corneal endothelium and the duration of daily wear HCL [8]. With the increasing hours of HCL wear per day and the duration of HCL wear in >5 years, HEX substantially decreased, but ECD was not changed. COV is more closely correlated with increased hours of HCL wear per day than with the duration of HCL wear in years.

Mohidin et al. compared the morphology of corneal endothelial cells between silicone hydrogel (SiHy) and spectacle wearers after a 24-month intervention and found no important differences in ECD, COV and HEX due to the high oxygen permeability of SiHy and the short CL wearing period of approximately 11 h per day for majority of the subjects [9]. Ahmad et al. compared the morphological alterations of corneal endothelium in neophyte wearers before and after 6 months of wearing HCL and reported insignificant changes in all the parameters (ECD, COV, HEX and CCT) due to the high oxygen permeability of the CL used, the short duration of CL wear and good patient compliance [10].

This study aims to analyse and compare the alterations in corneal endothelium morphology induced by different CL materials and wear durations among young adults living in Kuala Lumpur. Hamano et al. suggested substantial difference between Asian and non-Asian eyes with regards to corneal response towards oxidative stress [11]. Their study showed that Asian eyes have remarkably higher degree of endothelial bleb formation during closed eye conditions than non-Asian populations. Additionally, Doughty examined the morphology of corneal endothelium in Asians and concluded that polymegethism is uncommon in healthy young adults [12]. Therefore, ethnicity is a potential factor in determining corneal response towards CL wear, but the reports on this topic are limited. This study examined the morphological changes of corneal endothelial cells induced by different materials and CL wear durations among young adults living in Kuala Lumpur were analysed and compared.

Section snippets

Materials and methods

This retrospective study was conducted at the Optometry Clinic, Faculty of Health Sciences, UKM, Kuala Lumpur. This study was approved by the Universiti Kebangsaan Malaysia (UKM) Research Ethics Committee (UKM 1.21.3/244/NN-2017-121) and followed the tenets of the Declaration of Helsinki regarding experiments using human subjects. Young and healthy soft CL wearers who have worn CLs for ≥12 months and have no history of ocular disease, serious CL complications, diabetes mellitus or ocular

Subjects

In addition to the 72 soft CL wearers (13 males and 59 females) that participated, 24 non-CL wearers were included as controls. The mean age of subjects was 22.15 ± 1.84 years, and the mean refraction and VA were −1.86 ± 1.25 DS and 6/6, respectively. The CL wear duration for all subjects ranged 1–9 years. Subject distribution regarding the CL material type is summarized in Table 1.

Measurements

Corneal morphology measurements in relation to CL material type are as follows: for SCL and SiHy, the mean ECD

Discussion

Corneal endothelium regulates stromal hydration and thus maintains corneal transparency. This study analysed and compared the morphological alterations of corneal endothelium induced by different CL materials (hydrogel versus SiHy) and wear durations (<5 years versus ≥5 years) among young adults living in Kuala Lumpur. Overall results showed significant morphological alterations in the corneal endothelial cells (with the exception of CCT) of soft CL wearers compared with the control group, with

Conclusion

This study concludes that the corneal endothelial cells are substantially altered by CL wear, and the CL material type and wear duration in years are factors affecting this change. Optometrists are recommended to regularly evaluate the morphology of corneal endothelial cells in CL wearers to ensure that they can provide suitable intervention when necessary.

Funding

This work is supported by Universiti Kebangsaan Malaysia [grant number NN2017-121]

Declaration of Competing Interest

Both authors have no competing interest in the study.

Acknowledgements

Both authors would like to acknowledge the teachers and students who were involved in this study.

References (16)

There are more references available in the full text version of this article.

Cited by (0)

View full text