Purpose: Mucin balls appear to cause spherical indentations in the corneal epithelium during silicone hydrogel extended contact lens wear. The purpose of this report is to describe and quantify these spherical indentations, as examined in the human cornea by in vivo confocal microscopy and by in vitro immunocytochemistry in the rabbit cornea.
Methods: Confocal images of full-thickness corneal epithelium were taken from three human patients participating in a 1-year extended contact lens-wear trial. Diameter and depth of the indentations were determined and measured. Two rabbit corneas showing identical indentations were stained with propidium iodide (nuclear stain) and Ki-67 (proliferation marker) and were examined using a laser scanning confocal microscope.
Results: The diameter of the spherical indentations is largest on the epithelial surface, ranging from 33.9 to 78.8 microm. Indentations form spherical sections whose depth variably extends into the corneal epithelium, reaching as far as the basal lamina. The rabbit model showed no epithelial nuclei within the indentation. Furthermore, stromal cells localized immediately beneath the indentations were positive for Ki-67 (proliferation).
Discussion: Spherical indentations of the corneal epithelium induced by mucin balls appear to be gaps or holes that can extend deep into the corneal epithelium. Indentations may potentially open a pathway for infectious microorganisms to penetrate the cornea. Surprisingly, stromal cells immediately beneath the holes were stimulated to proliferate, and there seemed to be an increase in localized cell density.