The recovery of corneal sensitivity and nerve morphology changes in orthokeratology

Abstract

Purpose: To investigate the recovery of changes in corneal sensitivity and nerve morphology in orthokeratology (OK) following lens wear discontinuation, over a 3-month period.

Methods: Sixteen myopic subjects (age 28±9 yrs) who wore OK lenses during sleep for 3 months discontinued lens wear for 3 months. Corneal sensitivity and nerve morphology were assessed 3 hours after waking on the right eye only at the pre-lens wear baseline (BL), after 3 months of OK lens wear (Day0), and 1 month (Day30) and 3 months (Day90) after lens wear discontinuation. The threshold to sensation at the corneal apex and temporal mid-periphery (2.5mm from the apex) was measured using the Cochet-Bonnet aesthesiometer. Corneal nerve morphology was assessed by sampling a 1mm² area of the sub-basal nerve plexus at the same corneal locations using the Heidelberg Retinal Tomographer with Rostock Corneal Module. Nerve fiber density (NFD) was calculated by measuring total nerve fiber length per mm² using Image J with Neuron J plugin (National Institutes of Health, MD). Measurements over time and between corneal sites were compared using two-way repeated-measures ANOVA and post hoc paired t-tests with Bonferroni correction. A p-value <0.05 denoted statistical significance.

Results: There was a significant change in sensation thresholds over the 3 months of lens wear and the subsequent 3-month discontinuation period (RM-ANOVA, p<0.01). Central threshold at BL (0.63±0.51g/mm²) was significantly different from Day0 (2.10±1.32g/mm²; p<0.001), but not significantly different from Day30 (0.91±0.71g/mm²; p>0.05) or Day90 (0.79±0.86g/mm²; p>0.05). Mid-peripheral threshold did not change significantly over time (ANOVA, p>0.05). There was also a significant change in NFD over the lens wear and subsequent discontinuation periods (RM-ANOVA, p<0.01). Central NFD at BL (19.2±3.8mm/mm²) was significantly different from Day0 (12.1±2.8mm/mm²; p<0.001), Day30 (15.5±3.4mm/mm²; p<0.01) and Day90 (17.0±3.5mm/mm²; p<0.05). Mid-peripheral NFD did not change significantly over time (ANOVA, p>0.05).

Conclusions: OK lens-induced reduction in corneal sensitivity recovers with cessation of lens wear, returning to pre-lens wear levels shortly after lens wear discontinuation. Changes to central NFD, however, do not recover fully within 3 months, which suggests that a longer non-lens wear period is required for a return to pre-lens wear levels.

Keywords: 477 contact lens • 610 nerve fiber layer • 565 innervation: sensation