"No signs of cataractous changes were observed during the follow-up period in control rats; nor were they seen at the lowest dose of naphthalene used (0.10 g/kg). Cataractous changes were observed in all rats given naphthalene 0.50 to 1.5 g/kg. Two of the rats fed 1.5 g/kg were prematurely excluded from the study because of their poor general condition.

The first signs of cataractous changes (i.e. water clefts) appeared after two and a half weeks and were only visible in RI photographs. In the SI photographs, the first signs of cataractous changes were seen three weeks after the start of naphthalene treatment in rats administered 1.0–1.5 g/kg, and one week later in rats administered 0.50 g/kg. A hazy spherical zone developed, circumscribing the adult nucleus in the lens, i.e. a diffuse epinuclear opacification, easily seen in the SI photographs (Fig. 3). In rats administered 1.5 g/kg, the cataractous changes were seen as several spherical layers in RI photographs during the last week."

"When cataractous changes were quantified in RI photographs, no significant difference was found between automatically and manually set threshold values. However, the manually determined threshold value was selected in subsequent analyses in this study, because the EAS–1000 threshold estimation occasionally failed to adjust the tangent to normal lens peaks. Cataractous areas partly hidden behind the iris were also common in the RI lens photographs. These photographs could not be excluded due to their high prevalence. Photographs were excluded if the software could not distinguish between cataractous changes and opacities located in other parts of the optical media, such as particles in the vitreous body.

The quantitative results obtained from RI photographs were different from the quantitative results obtained from SI photographs, because the more subtle initial changes could be quantified in RI photographs (Fig. 4). Thus, the degree of the cataractous changes was less correlated to both duration and dosage when RI photographs were evaluated."

Female Brown Norway Rats