Distribution of calcium and sulphur in the blue-light-exposed rat retina

Background: Blue-light exposure inhibits cytochrome oxidase and may therefore inhibit retinal metabolism. The reduced metabolism decreases the extrusion of calcium from the photoreceptor cell. Overload of calcium is proposed as one of the factors that lead to photoreceptor degeneration after light exposure. The light-induced photoreceptor degeneration can be ameliorated by calcium overload blocker. In the present study the calcium concentration was measured in the inner and outer segment layer of the rat retina. Methods: Six eyes were exposed to blue (404 nm) light at a retinal dose of 380 kJ/m². Five eyes served as the control group. The calcium and sulphur distributions were measured with a nuclear microprobe in the freeze-dried rat retina. The proton beam size was 12 × 12 m and the energy of the protons was 2.55 MeV The calcium concentration was calculated using sulphur as a reference. Results: The level of calcium per milligram sulphur was 21 g (range 17–23 g) in the inner segment of the control retina. It increased to 62 g/mg sulphur (range 52–67 g) and 61 g/mg sulphur (range 58–66 g) 1 h and 12 h after blue-light exposure, respectively. Conclusion: The findings of the present study support the idea that accumulation of calcium in the inner segment layer is one of the factors that cause photoreceptor degeneration.