Which of the following is NOT associated with optic nerve pallor?

• A. Leber's optic neuropathy
• B. Stargardt's disease
• C. Vitamin B12 deficiency
• D. Ethambutol toxicity

Answer: (B)

Optic nerve pallor indicates damage to the optic nerve itself, a sign ofoptic neuropathy that often becomes apparent as the nerve head looks pale as the retinal nerve fiber layer thins. Conditions that primarily injure the optic nerve—such as Leber’s hereditary optic neuropathy, vitamin B12 deficiency–related optic neuropathy, and ethambutol toxicity—can produce this pallor as the nerve fibers degenerate. Stargardt's disease, on the other hand, is a retinal dystrophy that affects the macula and the retinal pigment epithelium, not the optic nerve. Its pathology is retinal, leading to central vision loss, but it does not cause pallor of the optic disc. So, Stargardt's disease is not associated with optic nerve pallor.