An 18 year-old cat presents with a two day history of acute…

An 18 year-old cat presents with a two day history of acute blindness and widely dilated pupils. Abnormal physical examination findings include: a 2/9 body condition score, 2.5% dehydration, slightly pale mucous membranes and bilaterally small, irregularly shaped kidneys. On ophthalmic examination, Schirmer tear tests, fluorescein staining and intraocular pressures are within normal limits. Both pupils are markedly dilated and using a penlight to retroilluminate the patient, the presence of a vascular membrane within the vitreous, abutting on the posterior aspect of the lens is visible OU. Based on your physical and ophthalmic examination findings, you correctly make what clinical diagnosis and first recommend which of the following diagnostic tests?