Progression of ²²⁶Ra-Induced Ocular Alterations in Beagles (with 1 color plate)

Abstract

The temporal progression of ocular injury involving the iris and tapetum lucidum in beagles injected with ²²⁶Ra was quantitated by assigning subjective numerical indices. Concentration of radium in melanotic ocular tissue was measured by an auto-radiographic technique. The observed changes consisted of iris hyperpigmentation, de-pigmentation and progressive tapetal loss. Each change was dependent on the injected radium activity and on the time after injection. At higher radium levels iris depigmentation progressed centrally and peripherally, exposing fibrillar structural elements. Tapetal alteration progressed initially from a granular or finely stippled pattern to pigmented foci interspersed between hyporeflective tapetum and finally to a complete loss of tapetum and exposure of the choroidal vasculature. The average radiation dose from injections of 28.1 and 83.6 μCi ²²⁶Ra to ocular pigmented tissues integrated for 5 years was estimated at 150 and 460 rad, respectively. An injection of 0.18 μCi ²²⁶Ra did not induce an ocular alteration within 10 years of follow-up.