A 56 year old woman came to the emergency room 3 hours after visual loss in the right eye. Visual sensitivity limits to light perception in the right eye. Examination reveals pupillary defect whereas anterior surface of both eye are normal. Fundus examination shows a red lesion with pale retina. Probable diagnosis
**Core Concept**
The underlying principle being tested is the diagnosis of sudden vision loss, specifically the identification of **central retinal artery occlusion (CRAO)**. This condition involves the sudden blockage of the central retinal artery, leading to ischemia of the retina. The clinical presentation typically includes sudden, painless loss of vision in one eye.
**Why the Correct Answer is Right**
Given the symptoms of sudden visual loss, limited to light perception, and the presence of a pupillary defect, along with the fundus examination findings of a red lesion with a pale retina, the most likely diagnosis is **central retinal artery occlusion (CRAO)**. This condition is characterized by the abrupt cessation of blood flow to the retina, resulting in severe visual impairment. The "red lesion" described is likely the fovea, which appears cherry red due to the thin retina and the intact choroidal circulation, while the surrounding retina appears pale due to edema.
**Why Each Wrong Option is Incorrect**
**Option A:** Without specific details on Option A, it's challenging to provide a precise reason for its incorrectness, but in general, other causes of sudden vision loss (like optic neuritis or retinal detachment) would have different clinical findings.
**Option B:** Similarly, without specifics, if this option suggested a condition like glaucoma, it would be incorrect because glaucoma typically presents with pain and other specific symptoms not mentioned here.
**Option C:** If this option proposed a diagnosis of a transient condition like amaurosis fugax, it would be incorrect because, despite both being vascular, CRAO leads to more severe and persistent vision loss.
**Option D:** If suggesting a condition outside vascular occlusion, it would not align with the acute onset and specific fundus findings described.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that **central retinal artery occlusion (CRAO)** is a medical emergency, similar to a stroke, and prompt treatment (within 24 hours) is crucial to attempt to restore vision. The presence of a **cherry-red spot** in the fovea is a classic sign of CRAO.
**Correct Answer:** D. Central Retinal Artery Occlusion