A 33 year old woman presents to the emergency department with loss of vision in her right eye over the past few days. She describes the vision loss as a dark patch right in the middle. She is only able to see objects clearly if she looks out of the corner of her eyes. She also complains of some pain during eye movement. She has no other significant medical history besides hypothyroidism for which she takes levothyroxine. When the penlight is moved from the left to the right eye, the right pupil appears to dilate. Visual acuity testing reveals left eye 20/20 and right eye 20/60. What is the most likely finding on fundoscopic examination?
a) Normal optic disc
b) Increased cup-to-disc ratio
c) Optic disc pallor
d) Hyperemic optic disc
e) Flame-shaped hemorrhages
Correct answer: A
This patient most likely has optic neuritis. The combination of monocular central vision loss, pain on eye movement, and a relative afferent pupillary defect make this the most likely diagnosis. Optic neuritis is also commonly the first manifestation of multiple sclerosis. Optic neuritis can present very differently on the fundoscopic exam depending on location of the inflammation. The two most common sites are retrobulbar and the optic nerve head. Because the inflammation in retrobulbar is behind the globe, there is no evidence of disc swelling on examination.
B) This finding is commonly seen in glaucoma, but glaucoma is less likely as it more commonly causes peripheral vision loss. There is also no other relevant ophthalmic history.
C) Optic disc pallor can be seen weeks to months after initial presentation from axonal loss but would not be expected acutely.
D) Although papillitis is seen in optic nerve head inflammation, this is less likely than retrobulbar neuritis. It is estimated that about ⅔ of cases are retrobulbar compared to ⅓ being papillitis.
E) These are commonly seen in retinal vascular occlusions which are typically painless with vision changes happening more acutely making this unlikely.
Beck RW, Cleary PA, Anderson MM Jr, Keltner JL, Shults WT, Kaufman DI, Buckley EG, Corbett JJ, Kupersmith MJ, Miller NR, et al. A randomized, controlled trial of corticosteroids in the treatment of acute optic neuritis. The Optic Neuritis Study Group. N Engl J Med. 1992 Feb 27;326(9):581-8. doi: 10.1056/NEJM199202273260901. PMID: 1734247.
Osborne B & Balcer LJ. Optic neuritis: Pathophysiology, clinical features, and diagnosis. In: UpToDate, Connor RF (Ed), Wolters Kluwer. (Accessed on June 11, 2026.)