Hypoxia, overnight wear, and tear stagnation effects on the corneal epithelium: data and proposed model.

PURPOSE : To explore the possible mechanisms that may lead to overnight contact lens-associated corneal morbidity by examining data from several corneal epithelial permeability experiments obtained under different environmental and lens fitting paradigms. METHODS : Epithelial permeability was assessed by using fluorometry to determine the fluorescein penetration rate from the tear film into the corneal stroma. Changes in this rate provide an index of the corneal epithelial status; increased permeability leads to decreased barrier function. RESULTS : Hypoxia and tear stagnation during overnight lens wear play a significant role in altering the corneal epithelial barrier function (P<0.05). However, eliminating lens-induced hypoxia alone does not ameliorate changes in epithelial status (P<0.05). CONCLUSIONS : Based on data from these experiments, it is suggested that hypoxia and tear stagnation should be eliminated to minimize alteration of the corneal epithelium associated with overnight contact lens wear.