A 48-year-old woman is admitted to a general medical ward presenting with a progressive, painless decline in her vision over the past month, affecting both central and peripheral fields in her right eye, and more recently, a subtle blurring in her left eye. She reports no ocular pain, redness, or photophobia. Her medical history is significant for HIV infection, diagnosed approximately 15 years ago, which she admits has been poorly controlled due to intermittent adherence to antiretroviral therapy. She has a documented CD4+ T-lymphocyte count of 35 cells/µL from a recent outpatient visit. On physical examination, her vital signs are stable. Ophthalmic examination reveals an unreactive relative afferent pupillary defect (RAPD) in the right eye. Fundoscopy of the right eye shows extensive yellow-white retinal opacification with perivascular hemorrhages, giving a characteristic 'cottage cheese and ketchup' appearance, particularly prominent along the vascular arcades. The left eye shows early peripheral granular opacities. Based on these findings, what is the most appropriate initial diagnostic approach and subsequent definitive management strategy?