A 69-year-old man comes to the emergency department because of the sudden onset of painless vision loss in his right eye that he noticed upon awakening this morning. He describes the loss as a shadow over the bottom half of his vision. His medical history is significant for hypertension, type 2 diabetes mellitus, and obstructive sleep apnea. On physical examination, visual acuity is 20/100 in the right eye and 20/20 in the left eye. Visual field testing reveals an inferior altitudinal defect in the right eye. A relative afferent pupillary defect is present on the right. Funduscopic examination of the right eye shows a swollen, pale optic disc with several small, flame-shaped peripapillary hemorrhages. The left optic disc is small with a cup-to-disc ratio of 0.1. Erythrocyte sedimentation rate and C-reactive protein are within normal limits.
Which of the following is the most likely diagnosis?
The correct answer is:
D) Non-erteritic anterior ischemic optic neuropathy
This patient is presenting with the classic features of non-arteritic anterior ischemic optic neuropathy (NAION). NAION is the most common cause of sudden optic nerve-related vision loss in patients over the age of 50 years. It is caused by ischemia to the posterior ciliary arteries that supply the anterior portion of the optic nerve. Risk factors include crowded optic discs (a small cup-to-disc ratio, often called disc-at-risk), hypertension, diabetes, and sleep apnea. The classic presentation is sudden, painless, monocular vision loss which is often discovered upon awakening and an altitudinal visual field defect (loss of either the upper or lower half of the visual field). Fundoscopy reveals a swollen, pale optic disc, often with splinter (flame-shaped) hemorrhages.
Answer choice A: Amaurosis fugax, is incorrect. This refers to transient, curtain-like vision loss that typically lasts seconds to minutes and resolves completely. It is usually an embolic phenomenon from the carotid artery. This patient’s vision loss is persistent.
Answer choice B: Central retinal artery occlusion, is incorrect. Central retinal artery occlusion (CRAO) presents with sudden, profound, painless vision loss. However, fundoscopy typically reveals a pale retina with a cherry-red spot at the macula, rather than a swollen optic disc with altitudinal defects.
Answer choice C: Central retinal vein occlusion, is incorrect. Central retinal vein occlusion (CRVO) presents with sudden, painless vision loss, but the funduscopic appearance is often described as "blood and thunder," characterized by diffuse, widespread retinal hemorrhages in all four quadrants and a severely engorged, tortuous venous system.
Answer choice E: Optic neuritis, is incorrect. While optic neuritis also presents with an afferent pupillary defect and vision loss, it typically occurs in younger patients ages 20–40 years and is almost always associated with pain that worsens with eye movement.
Key Learning Point
Non-arteritic anterior ischemic optic neuropathy (NAION) presents as sudden, painless, monocular vision loss, typically with an altitudinal visual field defect. It is associated with a crowded optic disc (small cup-to-disc ratio) and cardiovascular risk factors. It is distinguished from the arteritic form (giant cella arteritis) by the absence of systemic symptoms and normal inflammatory markers such as ESR and CRP.
