Retinal vaso-occlusion in sickling hemoglobinopathies.

Sickle cell retinopathy, in all of its manifestations, represents the effects of arteriolar and capillary occlusions. Increased viscosity of circulating whole blood plus the microembolic action of individual sickled erythrocytes contribute to vasoocclusion. Decreased oxygenation and increased acidosis develop and lead to further sickling -- and further vaso-occlusion. The cycle of erythrostasis that characterizes sickling throughout the body is also applicable to the retina. The transparent media of the eye permit direct visualization of vaso-occlusions which occur preferentially in and about the macula and in the far periphery of the retina. Many of the occlusive episodes are transient. There dynamic events are simultaneously occurring elsewhere in the body but can only be visualized in the eye. The net effect in the retina is a remodeling of its vasculature, as some vessels close and others reopen. After the onset of arteriolar closure in the retina, affected blood vessels embark on a spontaneous, naturally evolving course of events leading to arteriolarvenular anastomoses, neovascular proliferations, vitreous hemorrhages, and retinal detachment. The advanced stages of proliferative sickle retinopathy are most commonly observed in SC disease and in Sthal, possibly because these two forms of sickling have significantly higher than normal whole blood viscosity. Retinal vaso-occlusions can also lead to blow-out hemorrhages which may evolve into salmon patches, iridescent spots, schisis cavities, and black sunbursts. In some respects sickle retinopathy is unique, but many of its manifestations are similar to those of retinopathies found in diabetes mellitus, AC hemoglobinopathy, Takayasu pulseless disease, sarcoidosis, chronic myelogenous leukemia, branch retinal vein occlusion, retrolental fibroplasia, and Eales disease.