It’s Friday afternoon, and the last opening on the schedule gets filled with a “red eye walk-in”…the dreaded, all-too-familiar scenario. In this case, a 48-year-old Caucasian male arrived complaining of seasonal allergies, a non-productive cough for the past 10 days, and a one-day, unilateral red eye. The immediate thought was “Yes! Slam-dunk viral conjunctivitis…topical steroid and out the door.” But, after further questioning, the patient recalled having a brief episode of painless vision loss that occurred in his left eye the night before as well as a worsening headache over the past week.

Biomicroscopy revealed mild ptosis,1+ inferior tarsal follicles, and 3+ diffuse bulbar injection with mild corkscrewing of the subconjunctival vessels of the left eye. The patient had 20/20 monocular acuity, and aside from minor arteriolar attenuation and venous engorgement of the posterior segment (OS>OD), all other exam findings, including blood pressure, ocular motility, intraocular pressures, pupils, and visual fields, were completely normal.

Digging Deeper

The patient was started on prednisolone acetate 1.0% q.i.d. OS for conjunctivitis and 81mg aspirin by mouth q.d. for stroke prophylaxis while a complete blood workup was ordered. He was also referred to a nearby imaging center for magnetic resonance imaging (MRI) and a magnetic resonance angiogram (MRA) of the head and neck, with and without contrast.

MRA imaging showed complete occlusive internal carotid artery dissection at the level of the petrous region (Figure 1). Thankfully, the patient had patent and healthy anterior cerebellar and posterior communicating artery collaterals to compensate for the reduced blood supply.

Figure 1. (A) Axial 3D time-of-flight MRA image of the head demonstrates a left internal carotid artery dissection with complete occlusion (arrow). (B) Contrast-enhanced MRA coronal image showing the extent of occlusion beginning at the cervical (C1) level of the left internal carotid artery (circle).

The patient’s internist and neurologist began 10mg pravastatin q.d. as well as a five-day course of 4mg oral dexamethasone b.i.d. An echocardiogram was scheduled, and he was ordered to keep a blood pressure log, continue daily aspirin therapy, and avoid excessive exertion for six to eight weeks. Although the exact cause of the dissection remains unclear, his team of specialists are looking into collagen tissue disorders, cardiovascular issues, or the persistent, non-productive coughing as possible explanations.

Don’t Forget the Zebras

The majority of red eye cases that we encounter each day typically fall into the allergic, infectious, inflammatory, or traumatic categories. Some of these may have a mixed presentation at onset, which make it easy to reach for that “combination drop,” especially when signs and symptoms don’t necessarily point to a specific cause.

However, this case reminds us to not get overly comfortable with routine diagnoses and to keep our differential list open to all possible etiologies. Although the old adage “when you hear hoofbeats, think horses, not zebras,” should still apply to our daily practice, we must remember that any patient in the chair could be that one-in-a-million case. We need to listen to our intuition and not let the seemingly “straightforward” red eye (or the fact that it is 5 o’clock on a Friday) distract us from treating the patient as a whole. CLS