Retinal light-damage in albino rats: lysosomal enzymes, rhodopsin, and age

The damaging effects incurred during a light-insult on the albino rat retina are studied separately from the resultant loss of visual cells which occurs. Groups of rats, 5-20 weeks of age, are exposed to 48 hr of 80 lux illumination, maintained in the dark for various lengths of time, and then killed. Beginning at light-off and continuing throughout 3 days of darkness, assays are made of (i) outer nuclear layer thickness; (ii) whole retina rhodopsin levels; and (iii) activities of lysosomal proteases known to be important in the degradation of retinal and ocular tissue. It is found that (a) having been given the light-insult, most of the visual cells that will die and disappear do so during the dark, postexposure period; (b) the retinas of all the animals show a limited capability for regenerating rhodopsin after the light-insult but younger animals are somewhat more successful at sustaining this than are older ones; (c) proteolytic enzyme activity is greatest in older animals which are also the ones that lose the most cells.