A 52-year-old man from Delhi presents with sudden loss of vision in the superior half of the visual field of the left eye. He reports the vision loss occurred 2 hours ago while reading the newspaper. On examination, visual acuity is 6/9 in the affected eye. Fundoscopy reveals a pale, whitish appearance of the inferior retina with a cherry-red spot at the macula. Carotid auscultation reveals no bruits. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Central Retinal Artery Occlusion (CRAO) ### Pathognomonic Findings **Key Point:** The classic triad of CRAO is: (1) sudden, painless, monocular vision loss; (2) diffuse pale/whitish retina due to ischemic edema; and (3) cherry-red spot at the macula. This triad is pathognomonic for CRAO and is described in this patient. **High-Yield:** The cherry-red spot occurs because the macula (fovea) is thin and the underlying choroidal circulation (which is NOT supplied by the central retinal artery) shows through as a red spot, contrasting with the surrounding pale, edematous retina. This finding is a hallmark of CRAO, NOT BRAO. ### Why This Is CRAO, Not BRAO | Feature | This Patient | CRAO | BRAO | |---------|-------------|------|------| | Cherry-red spot | **Present** | **Yes — pathognomonic** | Absent (macula spared) | | Retinal pallor | Inferior retina pale | Entire retina pale | Sectoral pallor only | | Visual acuity | 6/9 (relatively preserved) | Typically CF/HM, but can vary | Often preserved | | Visual field | Superior field loss | Can be altitudinal or complete | Altitudinal/sectoral | **Clinical Pearl:** The presence of a cherry-red spot is the single most important distinguishing feature here. In BRAO with macula sparing, the cherry-red spot does NOT appear because the macula retains its blood supply. The cherry-red spot is exclusively seen when the central retinal artery (supplying the entire inner retina) is occluded, leaving only the choroidal supply visible at the fovea. ### Why the Other Options Are Incorrect - **Retinal migraine with aura (A):** Typically transient, bilateral, and associated with headache; fundoscopy is usually normal during the episode. - **Amaurosis fugax (C):** Vision loss is transient (minutes), resolves completely, and fundoscopy is normal. This patient has persistent loss with fundoscopic changes. - **BRAO — inferior branch (D):** Would cause superior field loss and sectoral retinal pallor, but critically would NOT produce a cherry-red spot, as the macula would retain its blood supply. ### Pathophysiology of CRAO Occlusion of the central retinal artery (branch of ophthalmic artery from internal carotid) causes ischemia of the inner retinal layers. The retinal ganglion cells and inner nuclear layer swell (cytotoxic edema), producing the white/pale appearance. The fovea, nourished by the choriocapillaris, remains red — the "cherry-red spot." **Common causes:** Embolism (carotid atherosclerosis, cardiac), thrombosis in situ, giant cell arteritis, hypercoagulable states. [cite: Harrison's Principles of Internal Medicine, 21e, Ch. 28; Kanski's Clinical Ophthalmology, 9e]