Clinical Reasoning: An unusual pattern of optic disc swelling and visual loss

A 9-year-old boy was seen for bilaterally decreased vision.The patient noted gradual decrease in his visual acuity over a few months with difficulty seeing the blackboard.Otherwise, he was asymptomatic with no headaches.His examination showed visual acuities of 20/60 in his right eye and 20/400 in his left eye.For color vision, pseudo-isochromatic plates were 15/16 right eye and 0/16 in the left eye.There was a left relative afferent pupil defect.Ocular motility was normal.Funduscopy showed swelling of both optic discs affecting mainly the upper and lower aspects with sparing of the horizontal part of the disc, suggesting band atrophy.Maculae were normal (figure 1). Questions for consideration:1. What is the differential diagnosis?2. What initial investigations would help you in narrowing the differential?GO TO SECTION 2 Figure 1 Fundus photographs and Goldmann visual field (A) Bilateral optic disc swelling affecting the upper and lower aspect of the optic discs (arrows).There is a horizontal band of atrophy that shows no swelling.Note the blurry margins of the upper and lower pole in contrast with the clear margins on the nasal and temporal aspects of the discs.(B) Goldmann visual field showing complete bitemporal hemianopia, with some involvement of the nasal field and macular region in the left eye, in keeping with the reduced acuity.