Long-term corneal morphology after PRK by in vivo confocal microscopy

To examine human corneal morphology and nerve recovery 5 years after photorefractive keratectomy (PRK).

Fourteen eyes of 14 patients (ages, 27-53 years) who underwent 6-mm diameter PRK for low to moderate myopia (spherical equivalent [SE] -2.5 to -8.0 D) were examined once 5 years after surgery. Nine healthy individuals served as control subjects. Standard biomicroscopy, manifest refraction, and visual acuity tests were performed. The morphology of the corneas was examined by in vivo confocal microscope. Thicknesses of the epithelium and stroma, as well as the density of corneal opacity (haze) were obtained from digital image analysis of the confocal microscopy through-focusing (CMTF) scans.

Confocal microscopy revealed increased reflectivity in the subepithelial extracellular matrix, keratocyte nuclei and processes in all patients. The mean objective haze estimate was 166.7 U (range, 50-390) in control corneas compared with a mean of 225.9 U (range, 125-430, P = 0.15) in the post-PRK corneas. The density of the subbasal nerve fiber bundles in post-PRK corneas (mean, n = 4.2; range, n = 1-7 per field of view) was not significantly lowered from that in control subjects (mean, n = 4.9; range, n = 3-6; P = 0.56). Bowman's layer was undetectable in all post-PRK corneas. Clinically, slit-lamp-observed trace of haze in four corneas correlated positively with the ablation depth (P = 0.016) and the thickness of the haze area (P = 0.006) in the confocal microscope.

In vivo confocal microscopy demonstrates the presence of morphologic alterations even 5 years after PRK. However, these alterations are overcome by cellular and neural recovery and do not seem to interfere with visual performance.