Which of the following is NOT a typical cause of unilateral disc edema?

• A. CRVO
• B. Diabetic papillopathy
• C. Papilledema
• D. NAION

Answer: (C)

Unilateral disc edema usually points to problems affecting one optic nerve or the retina on that side, rather than a global increase in pressure affecting both nerves. Papilledema, by contrast, is swelling from raised intracranial pressure and tends to involve both optic nerves, presenting as bilateral disc edema. That bilateral pattern makes papilledema not a typical cause of swelling in just one eye.

In practice, a unilateral disc edema can be seen with retinal vascular or optic neuropathies such as central retinal vein occlusion, which causes edema in the affected eye along with possible hemorrhages; nonarteritic anterior ischemic optic neuropathy, which presents with sudden, painless vision loss and an edematous optic disc in one eye; and diabetic papillopathy, which can produce disc edema in diabetics and may be unilateral. Because papilledema is classically bilateral, it is the least fitting cause for unilateral disc edema.