A 26-year-old man was seen in the Neuro-Ophthalmology Clinic because of blurred vision and discomfort in the right eye. Approximately 8 days earlier, vision in the right eye became hazy, and periorbital pain developed. Six days earlier, he was evaluated in the emergency department. He had recently had an upper respiratory infection and nasal congestion.During the next 5 days, visual acuity in the right eye gradually decreased, and the patient felt mild discomfort with movement of the eye. Nasal congestion and headache persisted.

On examination, there was decreased visual acuity, loss of color vision, a swollen right optic nerve, and visual-field abnormalities. Computed tomography of the orbits and sinuses revealed sinusitis with erosion of the optic canals.

When a patient such as this one presents with blurred vision, the first and most important task is to determine whether the vision loss is

(1) refractive

(2)related to an ophthalmic disorder

(3)neurologic disorder.

In this case, pinhole testing raised the possibility that the vision loss was of retinal or neurologic origin. The next step is to localize the defect within the visual pathway.