Aspects ultrastructuraux des mécanismes de la rudimentation rétinienne chez l'Anoptichthys adulte, forme cavernicole aveugle de l'Astyanax mexicanus (Characidae, Pisces)

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Abstract
Degeneration of the retina and retinal pigment epithelium operates by necrosis, phagocytosis, and also by vacuolization, the processes causing the retinal layers to shorten. The residual cells are transferred in a necrotic center that probably represents the persistance of a transitory event in normal eye development.In this case, the lack of vascularization cannot be the cause of rudimentation. The progressive degeneration of the outer segment of the photoreceptor can eventually be explained by an inhibition of the proteic synthesis or by another cytological disturbance. When the cell degenerates the renewal process slows and stops, the shedding and the phagocytosis of the pigment epithelium continues, and the outer segment gradually disappears. The comparison of the eyes of adult animals reared in darkness or light indicates only that the light effects are not long detectable as aging and degeneration progresses.The cytological characteristics of the main occular rudimentation mechanisms indicate that retinal rudimentation of blind cave Astyanax (or Anoptichthys) obeys previously described rules of occular degeneration as defined for other cave vertebrates.