Effects of Lubricants on Ocular Surface Functions

Abstract

Abstract: : Purpose: Certain lubricants increase tear film stability in humans. However, the effects of such lubricants on ocular surface functions are not well characterized. The effects of various lubricants on tear film stability and corneal epithelial integrity as well as the precorneal residence times of these agents were determined in experimental animals. Methods: All experiments were conducted in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. Eyedrops containing 0.1% hyaluronan (HA, 3.74 mPas ), 0.2% hydroxyethylcellulose (HEC, 3.68 mPas), 0.25% hydroxypropylmethylcellulose (HPMC, 3.44 mPas), 0.5% carboxymethylcellulose (CMC, 5.36 mPas), 1.0% dextran 70 (1.11 mPas), or saline (control) were tested. The corneal surface regularity index (SRI) was determined with a corneal topographic modeling system as an index of tear film stability after the instillation of eyedrops in anesthetized rabbits. Corneal epithelial damage was evaluated from fluorescein staining after repeated instillation of eyedrops in a rat model of dry eye. Precorneal residence time of each eyedrop containing 0.002% fluorescein sodium as a tracer, was evaluated with an anterior fluorophotometer in anesthetized rabbits. Results: Instillation of saline, HPMC, or CMC, but not that of HA, dextran, or HEC, in rabbits resulted in a time–dependent increase in the corneal SRI, representing a decrease in tear film stability. Instillation of HA, but not that of HEC or dextran, reduced the extent of fluorescein staining in the rat cornea compared with that observed after instillation of saline. With regard to precorneal residence time, the area under the fluorescein intensity time curve from 0 to 30 min (AUC_0–30) for HA or HEC was significantly greater than that for saline. Conclusions: The lubricants tested manifested different effects on ocular surface functions, with no correlation apparent among the stabilizing effect on the tear film, amelioration of corneal epithelial damage, and precorneal residence time. The amelioration of corneal epithelial damage may be due to a direct effect of each lubricant, whereas the precorneal residence time may be related to eyedrop viscosity. The effect on tear film stability may be attributable to multiple factors.

Keywords: cornea: tears/tear film/dry eye • cornea: basic science • pharmacology