This condition is mentioned separately because of the severe and devastating effect it can have on the vision. The sickle-cell haemoglo-binopathies are inherited and result from the affected person having one or more abnormal haemoglobins as recognised by the electro-phoretic pattern and labelled alphabetically. Haemoglobins S and C are the most important ophthalmologically. Thalassaemia (persistence of foetal haemoglobin) can also cause retinopa-thy. The abnormal haemoglobins occur either in combination with normal haemoglobins resulting in AS (sickle-cell trait) or in association with each other: SS (sickle-cell anaemia or disease) or SC (sickle-cell haemoglobin C disease) and S thal (thalassaemia). Individuals with cell trait usually lead a normal life and do not have any systemic or ocular complications. The red blood cells in patients with sickle-cell (SS, SC, S thal) disease adopt abnormal shapes under hypoxia and acidosis. These abnormal red cells are less deformable compared with normal, leading to occlusion of the small retinal blood vessels especially in the retinal periphery.
Sickle-cell retinopathy can be divided into two types: (1) nonproliferative and (2) proliferative. In nonproliferative sickle retinopathy there is increased venous tortuosity, peripheral choriore-tinal atrophy, peripheral retinal haemorrhages, peripheral haemosiderin deposits, which appear refractile,and peripheral arterial occlusion. These lesions are usually asymptomatic. When central retinal arterial or venous occlusion, macular arteriolar occlusion or choroidal ischaemia occurs, there is significant visual deficit.
When significant ischaemia is present, retinal neovascularisation occurs. This is generally in the retinal periphery. Such peripheral neovas-cularisation can respond to laser photocoagulation or cryotherapy of the retina. Occasionally vitrectomy is required.
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