The Wills Eye Hospital Neuro-ophthalmology Service was asked to evaluate a 57-year-old female inpatient with a complaint of new-onset double vision. The patient was admitted to the Thomas Jefferson University Neurology Service two days prior with a chief complaint of dizziness.
The double vision was described as horizontal, side-by-side images, worse at distance than at near. When either eye was covered, visual acuity was at baseline. Symptoms were noticed acutely while watching television. She denied any prior episodes of double vision.
Her initial complaint of dizziness was described as “feeling unbalanced.” Review of systems was notable for decreased hearing and sensation of right ear fullness. She denied numbness, weakness, headache, vertigo or other neurologic complaint.
Past medical history was significant for borderline hypertension, obesity and one episode of vertigo two years prior. She was on no chronic medications. She reported a recent episode of bronchitis two weeks prior to admission, treated with oral doxycycline. Family history was noncontributory.
Vital signs were stable and within normal limits. Ocular examination revealed visual acuity of 20/30 in both eyes. Color plates were 12 out of 12 briskly in each eye with normal Amsler grids bilaterally. Pupils were equal and reactive, with no afferent pupillary defect. Visual fields were full to confrontation. No mass or proptosis was observed.
Extraocular motility was notable for a right abduction deficit, measured at 6 prism D in primary gaze, 12 D in right gaze, 3 D in left gaze, 1 D in up gaze, and 3 D in down gaze using alternate cover testing. All other ductions and versions were full.
Slit-lamp exam was white and quiet in both eyes. Dilated fundus exam was normal with no optic disc edema in both eyes.
What is your differential diagnosis? What further workup would you pursue?