Confocal microscopic observations of stromal keratocytes during extended contact lens wear

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Abstract
The aim of this study was to monitor changes in keratocyte density during extended contact lens wear and to explore the possible role of hypoxia and oedema in any changes observed. Twenty-three neophyte myopic subjects wore a high Dk/t lens (PureVision) in one eye and a low Dk/t lens (Acuvue 2) in the other eye on an extended wear basis for six months. Slit-scanning confocal microscopy and ultrasonic pachometry were performed on both eyes at baseline (before lens wear), after three and six months of lens wear, and one week after cessation of lens wear (the 'post-cessation' visit). No differences were established between the two lenses or between the three study visits for anterior stromal keratocyte density (KD). Posterior stromal KD was similar for the two lenses throughout the study. However, there was an overall drop in posterior KD of 14 per cent in both eyes at the six-month visit, compared to the initial visit. Posterior KD at the six-month visit was no different from that at the post-cessation visit. Corneal thickness was similar for the two lenses at the initial and post-cessation visits, but was three per cent greater for the eye wearing the Acuvue 2 lens at the six-month visit. Extended contact lens wear causes a loss of keratocytes; this loss cannot be attributed to contact lens-induced hypoxia and/or oedema, or to an artifact of confocal microscopy relating to presence of residual oedema. It is postulated that lens-induced keratocyte loss may be related to the physical presence of contact lenses creating some mechanical effect.