Answer
C: Optic neuritis
Educational Objective
Diagnose optic neuritis.
Critique
This patient with acute vision loss and eye pain unassociated with trauma has signs and symptoms suggestive of optic neuritis, including pain with eye movement, loss of color vision out of proportion to the vision loss, and an afferent pupillary defect. Two thirds of optic neuritis cases occur in women. The average age of onset is between 20 and 40 years, and it is often associated with multiple sclerosis. Most of these patients have a normal optic disc on funduscopy, but one third may have a swollen disc or papillitis. An urgent evaluation by an ophthalmologist is required; treatment usually involves high-dose intravenous glucocorticoids.
Corneal abrasion can cause sudden onset of pain and foreign-body sensation. It is classically seen in patients who sleep without taking out their contact lenses and then awaken with eye pain and photophobia. If the abrasion is in the central area of the visual axis, visual acuity may be diminished. Corneal abrasion cannot explain the loss of color discrimination and the afferent pupillary defect in this patient.
Herpes simplex keratitis typically presents with acute onset of pain, blurry vision, and watery discharge. The absence of discharge and ciliary flush in this case make keratitis unlikely. Ciliary flush is characterized by erythema that is most marked at the limbus, which is the junction of the sclera and cornea. Keratitis would not be associated with loss of color discrimination or an afferent pupillary defect.
Orbital cellulitis often presents with eye pain as well as eyelid swelling and erythema, although some cases present without erythema. In the case of inflammation of the extraocular muscles and fatty tissue in the orbit, the patient may experience pain with eye movement. When the condition is severe, visual acuity may be impaired. Orbital cellulitis, however, is more likely to be associated with fever and chemosis, which are not present in this patient, and it would not explain the patient's other findings related to optic nerve damage.
Key Point
The hallmarks of optic neuritis are acute vision loss, eye pain with movement, color perception change, and afferent pupillary defect; results of a funduscopic examination may be normal.
Bibliogrpahy
Balcer LJ. Clinical practice. Optic neuritis. N Engl J Med. 2006;354:1273-80. [PMID: 16554529]