Effects of repeated photic exposures on the monkey macula
J. Borges, Z. Y. Li and M. O. Tso
Department of Ophthalmology, H.S. Joao/Oporto Medical School, Porto, Portugal.
The posterior pole of the eyes of rhesus monkeys was exposed to the light
of an indirect ophthalmoscope. The tissue changes caused by repeated (three
to five) photic injuries were compared with those produced by a single
photic insult. The ophthalmoscopic and angiographic examinations showed a
progressive involvement of the foveal area after multiple exposures to
light. Histopathologic study showed that after one exposure the retinal
pigment epithelium appeared focally atrophic. Plaques of proliferated
retinal pigment epithelium could also be seen, and on the anterior surface
of these plaques a layer of relatively cuboidal hypopigmented retinal
pigment epithelial cells was present. With multiple exposures, focal areas
of total absence of retinal pigment epithelium were seen in these eyes. The
eyes that received only one exposure showed partially regenerated
photoreceptor outer segments. After repeated photic exposures, the
photoreceptor outer segments failed to regenerate even 6 to 8 months after
the last exposure. In one eye exposed five times for 60 minutes, areas of
total absence of photoreceptor cells could be seen, and the inner nuclear
layer was directly apposed to Bruch's membrane. These experimental
exposures to the light of an indirect ophthalmoscope were 60 to 120 minutes
long and were not comparable to clinical exposures of the ophthalmoscope in
patient examination. Our observation highlighted the cumulative effects of
repeated light injury to the retinal pigment epithelial and photoreceptor
cells and also showed the similarity between this animal model of photic
maculopathy and the changes present in the eyes of human patients with
atrophic agerlated macular degeneration.
