Polarized light biomicroscopic observations on the pre‐corneal tear film. 3. The normal tear film of the cat

Abstract

ABSTRACT Polarized light biomicroscopy was used to examine the pre‐corneal tear film in 14 normal cats. Blink rates were also determined. The normal range of surface morphology of the feline tear film was established. Two principal categories of surface patterning of the lipid layer of the tear film were identified. These occurred in all eyes examined and were: (a) a wave‐like pattern, and (b) a pattern of variable character resembling the polished surface of granite. Over most of the area of the tear film, the thickness of its lipid layer between blinks was under 0·089 μm in all cats examined. However, narrow streaks of thicker lipid (up to 0·511 μm) were occasionally observed. The mean total blink rate was 2·4/min. Overall, incomplete blinks constituted approximately 50 per cent of the total blink rate. The tear film of the cat is compared with that of man and the dog.