Epithelial permeability reflects subclinical effects of contact lens wear

Recently, it was reported by the authors that a single drop fluorophotometric technique for estimating corneal epithelial permeability (Pde) to fluorescein is not sufficiently precise for monitoring permeability changes in individual patients., but may be useful for evaluating mean differences in Pdc in population based research. To determine whether this technique provides a more sensitive index of epithelial integrity compared with conventional clinical assessments, the effects of mild corneal trauma on Pdc, the slit lamp appearance of the cornea, and corneal thickness (CT) were assessed.

After baseline slit lamp examinations (SLE) and CT measurements, one randomly chosen eye of each of 32 normal subjects underwent 1 hour of closed eye soft contact lens (CL) wear while the fellow eye served as a control (no CL). After removing the CL, the SLE and CT measurements were repeated. Then, Pdc to fluorescein was assessed using a single drop fluorophotometric method refined to enhance feasibility, precision, and accuracy.

The mean (95% confidence interval) difference in natural log (Pdc) between 32 pairs of eyes (CL minus no CL) was 0.341 (0.069, 0.613), p = 0.016. By contrast, none of the 32 subjects exhibited corneal epithelial disruption upon SLE with white light following the closed eye period. Also, no substantial differences were apparent in the corneal swelling response between paired eyes, mean delta CT (95% CI) = -2.31(-7.53, 2.91) microns, p = 0.37.

Pdc measurements, used in studies of modest sample size, appear capable of detecting average differences in corneal barrier function that remain undetectable by SLE or pachymetry.