The diagnosis is clinical and based on the observation of the ocular fundus: venous dilation and tortuosity, flame-shaped retinal hemorrhages, retinal edema, and cotton-wool exudates affecting all the retinal sectors (in CRVO) or the sector of the retina drained by the affected vein in BRVO. Oxygen supply and nutrition from the choroidal vascular bed to the thinner peripheral retina help in its much longer survival and the maintenance of peripheral visual fields. CRAO studies have shown that the ischemic retinal whitish opacity and swelling are essentially located in the perifoveolar region of the macula.

164 Central retinal artery occlusion (CRAO) results in sudden, catastrophic visual loss, and branch retinal arteriolar occlusion (BRAO) causes sudden segmental visual loss and may recur to involve other branch retinal arterioles. RVO is typically due to external compression or disease of the vein wall, such as is seen in vasculitis. 163 RVO represents an obstruction of the retinal venous system that involves either the central retinal vein or a branch retinal vein. RVO is the second most common sight-threatening retinal vascular disorder after diabetic retinopathy. Occlusion of large retinal blood vessels is a common occurrence, which results in retinal hypoxia. Schachat MD, in Ryan's Retina, 2018 Retinal Vein Occlusion (RVO) 22,34,35 A good prognostic sign of retention of central acuity is electroretinography (ERG) amplitudes remaining quite large (e.g., greater than 100 µV). Patients with X-linked RP are usually blind (acuity 20/200 or worse) by 30–40 years of age. 22 Marmor, in his study of visual loss in adRP and arRP, 33 found that when visual acuity began to fail, it generally dropped to 20/200 within 4–10 (median 6) years. Patients with autosomal dominant RP (adRP) are more likely than patients with autosomal recessive (arRP) or X-linked RP to retain good acuity beyond 60 years of age. Patients with regional (“sector”) RP may retain good visual acuity all their life. To a considerable extent, the likelihood of retaining “good vision” (central acuity) to a given age in life depends on the specific inheritance type of RP. Macular edema is the topic of a section on treatment of RP later in this chapter. 42.4), and retinal pigment epithelial (RPE) defects in the macula or fovea 31,32 can occur early in the disease. 27 Cystoid macular edema (CME), 28 diffuse retinal vascular leakage, 29 macular preretinal fibrosis 30 ( Fig. Central visual function can, however, be seriously affected early in typical RP, while significant peripheral field remains. There is a common misconception in RP (documented in older texts) that the central vision will remain good until most, if not all, the peripheral field is lost. Schachat MD, in Ryan's Retina, 2018 Central Vision Loss

Scotoma evolution optic neuritis