Morphology and time-course of defined photochemical lesions in the rabbit retina

The present study demonstrates an experimental set-up to study light injury with defined parameters including retinal irradiance levels and spectral composition of the damaging light. The time-course of acute morphological changes at constant light intensity and increasing exposure durations (from 5-30 minutes) was evaluated, the wavelength of the damaging light being 400-550 nm. Pigment epithelial lesions appeared already after 5 minutes, and rod outer segment membrane disruptions after 15-20 minutes of light exposure. Striking was the observation of disruption and vesiculation of disk membranes at the base of rod outer segments. This "clear zone" was consistently observed beginning after twenty minutes of light exposure. The comparison of morphological changes in pigmented and albinotic eyes revealed no essential differences. This result confirms the observations of other laboratories that pigment epithelial melanin neither protects against nor promotes light damage to a significant extent. Long-term changes after light exposure revealed pigment epithelial lesions and rod outer segment disruptions, followed by macrophage invasion and pigment epithelial proliferation with subsequent loss of photoreceptor cells.