Differences between overnight and long-term wear of orthokeratology contact lenses in corneal contour, thickness, and cell density.

PURPOSE: To investigate changes in corneal topography and morphology in human eyes wearing orthokeratology (OK) lenses for overnight and over a 5-year period.

MATERIALS AND METHODS: Fifty-six adults with moderate myopia were assigned to 2 groups based on age matching: 5-year lens wear (n = 26, 51 eyes) and 1-night lens wear (n = 30, 60 eyes). All subjects wore reverse-geometry OK lenses with the eyes before 1-night lens wear serving as a control to both the groups. Visual acuity, slit-lamp biomicroscopy, confocal microscopy, and corneal topography were assessed before and after lens wear.

RESULTS: Visual acuity was improved satisfactorily with flattening of the central cornea in both lens wear groups. Corneal thickness increased extensively in the 1-night lens wear group but only paracentrally in the 5-year lens wear group. Central epithelial thinning with a decreased density of the basal cells was only observed in the 5-year group. Keratocyte density was reduced throughout the entire corneal thickness for the 2 groups. Endothelium was normal in density and morphology for the 2 groups.

CONCLUSIONS: Short-term and long-term OK lens wear can effectively correct myopia by flattening the cornea. The flattened cornea in the short-term lens wear is mainly because of the thickening of the midperipheral cornea. In the long-term lens wear, however, this change is associated with thickening of the midperipheral cornea and thinning of the central corneal epithelium.