1. In 1908 Coats published his classical paper on a comparatively rare form of external retinopathy with massive exudation, in which he divided the condition into three groups. Since that date Groups I and II, as originally described by him, have borne his name and are conventionally known as "Coats's disease". Group III was somewhat different; in addition to the external retinopathy and massive exudation, it was characterized by large capillary angiomata in the retina with demonstrable arteriovenous communications. This condition had previously been described, was later recognized to be a different clinical entity, and is now known as the von Hippel-Lindau disease. This Group III is not concerned in the present discussion
2. In the consideration of possible aetiological factors, Coats discussed syphilis, tuberculosis, and bacterial metastasis, but discarded these as highly improbable causes. Acting on the premise that "with the exception of the lens, the presence of cholesterin crystals in a tissue is almost to be regarded as diagnostic of a preceding haemorrhage", Coats came to the conclusion that the organization of haemorrhage was probably the true explanation for the subretinal mass. He admitted, however, that the haemorrhage might well be secondary to some infectious process. This same view he maintained in a later paper (Coats, 1912) in which he reported four additional cases
3. Coats's clear and convincing paper at that time established his Groups I and II as recognized clinical and histological entities. Since this time, however, there have been numerous additions and embellishments, and other aetiologies have been suggested. In his classical textbook, Duke-Elder,1940
4. What is the role and the pathogenesis of the telangiectasis and other vascular changes which are so often such a prominent feature?
5. What is the origin and role of the foam cells in the pathogenesis of the disease?