Morphologic changes in cat epithelium following continuous wear of orthokeratology lenses: a pilot study

To investigate the sequence of morphologic changes over time in cat epithelium during continuous wear of orthokeratology lenses.

Four 2-year-old female cats were used; one served as a no lens wear control and three wore custom designed Paragon CRT lenses for myopic and hyperopic correction in the right and left eyes, respectively. Lenses were worn continuously and animals were euthanased after 4h, 8h and 14 days. Corneal tissue was fixed then stained with hematoxylin and eosin for histologic evaluation and measurement of epithelial thickness.

Average epithelial thickness of control eyes in the centre (38+/-1 microm) and mid-periphery (3.0 mm from the centre, 38+/-2 microm) of the cornea was similar. Epithelial thickness in myopic corrected eyes showed progressive thinning in the centre and progressive thickening in the mid-periphery with increased lens wearing time. Hyperopic corrected eyes showed the opposite pattern of progressive epithelial thickening in the centre and thinning in the mid-periphery with lens wearing time.

The epithelium appears to play a major role in the changes induced by orthokeratology lenses. The epithelial effects were dependent on time and lens design. Further studies are needed to determine the mechanisms responsible for these changes.