Light scattering in normal and cataractous lenses of farmed Atlantic salmon (Salmo salar): A slit lamp and Scheimpflug photographic study

To investigate normal light scattering and cataract formation, the anterior eye segments of farmed Atlantic salmon (Salmo salar) reared in fresh water and sea water were documented in vivo for the first time with a Topcon SL- 45 Scheimpflug camera. A total of 40 fish from the fresh-water-rearing peri od, obtained from 2 groups of identical age but showing a different growth rate, and 24 fish from the sea-water-rea ring period, sampled from 2 groups with identical age but being fed different food brands, were included in t his study. The fish were anaesthetized before examination. Due to the natur ally wide pupil, no mydriatic compound was applied. All fish were removed f rom the water for photography, which was performed for each eye in 0 degree s = vertical slit position. Images were recorded on Kodak Tmax 400 black-an d-white film. Microdensitometric image analysis of all negatives was perfor med using a Joyce-Loebl online microdensitometer. In spite of the virtual a bsence of an anterior chamber gap between cornea and lens and very little l ight scattering in the normal fish lens, a small number of distinct layers could be reproducibly identified in the lens. While there was little abnorm al light scattering which could point to cataract development in young fish from the fresh water period, the evaluation of the lenses from the 2 sea w ater groups showed the presence of specific forms of cataract especially in the cortical and supranuclear layers. There were significant differences b etween the groups fed different food brands at the sea water site. In concl usion, Scheimpflug photography proved to be applicable to eye research in f ish in vivo. It is suggested that this method should be employed for reprod ucible documentation as an extension to slit lamp monitoring in experimenta l research to reveal causative factors for cataracts in farmed fish. Copyri ght (C) 2001 S. Karger AG, Basel.