Effects of Age on the Sensitivity of the Rat Lens to Hexanol in Vitro

The Draize eye irritation test involves the injection of 0.1 mi of a test material into the conjunctival sac of young adult rabbits. A numerical scale is used to determine if the chemical is an irritating or nonirritating substance. This is the standard eye irritancy test used today. Aside from ethical concerns, and concerns related to the subjectivity of the measures, the Draize test fails to acknowledge whether there is a change in sensitivity of the eye to irritation as the subject ages. Some chemicals, particularly cosmetics and shampoos, are used throughout a human lifespan. A rat lens model of young (2.5-month) versus older (16-month) animals was used to show that there is a change in the sensitivity to a known irritant, hexanol, with age, and that recovery (repair of incurred damage) is also age dependent. The optics of the in vitro lens, tested using a specially developed Scanning Lens Monitor, are sensitive enough to show small variations in hexanol damage with various aged lenses. Lenses from 2.5- and 16-month-old rats showed 100% increases in focal length variability (optical focus), respectively, at 0.6 +/- 0.7 and 10.0 +/- 5.3 h after removal from a 2 h exposure to 100% hexanol. Recovery was seen only with the younger lenses at 46.8 +/- 5.5 h.