Immunostaining of initial choroidal biopsy from the right eye (a, b, and c) followed by immunostaining of choroid from the enucleated right eye after 6 months (d, e, and f). (a) Choroid immunostained for CD20 (brown, peroxidase technique), demonstrating extensive infiltration by medium-sized B lymphocytes. BV, blood vessel; R, retina. (b) Choroid immunostained for CD5, demonstrating very variable expression of CD5 by the B lymphocytes, although a bone-marrow trephine in 2004 confirmed a diagnosis of the B-cell lymphoma/leukaemia, CLL with cells that were uniformly CD20 þ CD79a þ CD5 þ and cyclin D1-negative. (c) Choroid immunostained for the proliferation marker, Mib-1, giving a very variable proliferation index that appeared to be up to 50% in places. However, overall it did not definitely exceed 30%, the World Health Organization-defined minimum for diffuse large B-cell lymphoma. 4 Because of the small size of the biopsy, it was difficult to give a definitive diagnosis of CLL or to determine whether transformation to diffuse large B-cell lymphoma might have occurred. (d) Area of extensive lymphoid infiltration in choroid from enucleated right eye immunostained for CD20, demonstrating extensive infiltration by large pleomorphic B lymphocytes. (e) Enucleation specimen immunostained for CD5, showing very little CD5 expression, as sometimes occurs during high-grade (Richter) transformation of CLL to diffuse large B-cell lymphoma. 4 (f) Enucleation specimen immunostained for the proliferation marker Mib-1, demonstrating a proliferation index of 90%, confirming the diagnosis of diffuse large B-cell lymphoma.