The use of a focused light beam to cauterise the retina has been practiced for several years and the value of this treatment has been confirmed by extensive clinical trials for both proliferative disease and some types of maculopathy. The exact mode of action is not known but it has a b a b been suggested that the photocoagulation of ischaemic areas prevents the release of some, as yet unidentified, vasoformative factor in proliferative disease. The treatment must be applied promptly in the early proliferative stage or sometimes before. About 2500-3000 burns (of 500 mm spot size) are needed in an eye with proliferative retinopathy. This might require several treatment sessions (Figure 21.8). The laser treatment of focal and diffuse maculopathy involves application of small number of burns (of 100200 mm spot size) to the leaking area, avoiding the fovea. Ischaemic maculopathy generally is less amenable to laser treatment.
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