A 45-year-old female with a long history of progressive myopia develops sudden patchy loss of vision in her right eye. She is very alarmed and rushes to her family doctor. Funduscopic examination reveals a large retinal detachment in the right eye. The retina in the left eye is normal. When the pupillary light reflex is tested by shining a light in the right eye, the physician would likely note?

This patient is exhibiting the Marcus-Gunn phenomenon. When light strikes the retina, the pupillary light reflex is automatically triggered, leading to simultaneous constriction of both pupils. In the absence of adequate light entering the eye, for example following retinal detachment or optic neuritis, paradoxical dilatation of the pupils occurs. The retina receives far less light than it normally would, and the pupils dilate in order to absorb as much light as possible.