Changes in Corneal Subbasal Nerve Morphology and Sensitivity During Orthokeratology: Onset of Change.

Purpose: To investigate changes in corneal subbasal nerve fiber density and orientation during a 3-month orthokeratology (OK) lens wear period and their relationship with concurrent changes in corneal sensitivity.

Methods: Sixteen subjects wore overnight OK lenses for 90 days and were assessed at baseline, Day 30, and Day 90. Nerve images at the corneal apex and temporal mid-periphery were captured from the right eye only using in vivo confocal microscopy and analyzed to calculate nerve fiber density (NFD) and global nerve fiber orientation (GNFO). Corneal sensitivity was measured using the Cochet-Bonnet aesthesiometer at similar corneal locations. Control groups of non-lens (NL) wearing and conventional rigid gas-permeable (GP) lens-wearing subjects were also examined.

Results: Significant changes in NFD, GNFO and corneal sensitivity were observed during OK lens wear over the study period. In the central cornea, both NFD and corneal sensitivity decreased by Day 30, with further reductions at Day 90. Reduced NFD was associated with reduced corneal sensitivity. In the mid-peripheral cornea only, GNFO was rotated in a clockwise direction at Day 30, with further rotation at Day 90. Corneal sensitivity reduction plateaued by Day 30. In the GP lens-wearing subjects, only corneal sensitivity decreased by Day 30 at both corneal locations. No changes were observed in the NL control subjects.

Conclusions: Alterations in corneal nerve morphology occur rapidly with commencement of OK lens wear and appear to underpin functional sensitivity loss. Nerve fiber orientation can provide a useful index for changes in corneal nerve morphology.