Interactions between Ocular Surface Fluid and Cornea Related to Contact Lenses

Purpose To improve the quantification of damage to the ocular surface, metabolite levels, electrolyte concentrations, and enzyme activities were assayed in corneal epithelium, stroma and tears. Methods In rabbits, rinsing or contact lenses were used to induce microtrauma. For more severe trauma, experimental injuries were induced with 1 N NaOH. Human accidents included epithelial lesions and mild chemical burns. Enzymatic test systems and electron dispersive X-ray analyses (EDXA) were employed. Corneal hydration was assessed by wet and dry weights. Interleukins were analysed with ELISA. Results In contrast to normal eyes, in ocular surface trauma the interaction between tear fluid and cornea played an important part. After wearing contact lenses or rinsing, glucose and lactate levels in the cornea and in tears increased, and ATP and glycogen in the cornea decreased. After epithelial lesions, N-acetylglucose aminidase (NAcGA, E.C.3.2.1.50) was released into the tears. Epithelial defects alone and – much more – rinsing the denuded stromal surface produced an increase of lactate and glucose in tears and a dramatic fall in Na, Cl, and S levels in the stroma. Rinsing with phosphate induced corneal calcification. IL-1 and IL-6 were increased in human corneal buttons from patients with trauma and inflammation. Conclusions Biochemical analyses may be useful to quantify trauma to the ocular surface.