MEDizzy - A 74-year-old man with a history of well-treated

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Cardinal Manifestations and Presentation of Diseases 2

A 74-year-old man with a history of well-treated hypertension presents with painless blurry vision on one side. You perform the “swinging fashlight” test. Panel A shows the patient sitting in a dim room; panel B shows him with the fashlight shining in his right eye; and panel C shows the f ashlight shining in his left eye. Which defect is present and is appropriately matched to a likely cause?

ExplanationThis is a classic representation of a left relative aferent pupillary defect, or the Marcus Gunn pupil. In this case, the left eye does not perceive the light stimulus as strongly. Thus, when the light is shined in the left eye, the bilateral constriction stimulus is less than when the light is shined in the right eye. This fnding is sometimes the only clue to the presence of an optic neuritis, which can subsequently uncover neurodemyelinating disease. The patient has equally sized pupils in dim light, ruling out Adie tonic pupil, where anisocoria is present due to parasympathetic denervation of the iris ciliary muscle in the afected eye. Thus, the anisocoria would worsen in bright light (the afected eye would be unable to constrict). Curiously, while the pupillary response to light in this condition is poor, the response to near stimulus is often relatively preserved. This can be due to oculomotor nerve palsy or be idiopathic. A similar light–near dissociation can be seen in the Argyll-Robertson pupil of neurosyphilis with involvement of the midbrain. The opposite dissociation (where a pupil reacts to light but does not accommodate to near stimulus) does not occur. Likewise, Horner syndrome would present with anisocoria with miosis (constriction) of the afected eye due to sympathetic denervation, which is not present in this patient. In this condition, the anisocoria would worsen in dim light, and the unafected eye is free to dilate, while the afected eye is miotic. Often, concomitant ptosis and anhidrosis are seen in Horner syndrome. A homonymous hemianopsia is a defect in visual felds and cannot be assessed with the swinging fashlight test.