Toxoplasmosis, Cryptococcis, Bartonella,
Feline infectious peritonitis,
feline immunodeficiency, and
feline leukemia virus often present as anterior and posterior uveitis, chronic uveitis, retinal detachment, and secondary glaucoma, which just means that systemic diseases can result in ocular disease such as sudden onset of blindness. Your cat did test neg for feline leuk. but your cat should be tested for these other common diseases.