I also discuss the functional relevance of pupil responses, that is, how pupil responses help us to better see the world. In this review, I describe these three pupil responses, how they are related to high-level cognition, and the neural pathways that control them. In the elderly, this same presentation could be Giant Cell Arteritis, which if not caught and treated carries a high risk of having a stroke or causing vision loss in the other eye by the same mechanism.Pupils respond to three distinct kinds of stimuli: they constrict in response to brightness (the pupil light response), constrict in response to near fixation (the pupil near response), and dilate in response to increases in arousal and mental effort, either triggered by an external stimulus or spontaneously. In a young patient without any recent trauma, a mass or tumor compressing on the optic nerve is amongst the most concerning causes of painless vision loss with an RAPD. Accompanied pain suggests an optic neuritis while painless vision loss with an RAPD are concerning for ischemic optic neuropathies. If present, this typically localizes to the optic nerve, though widespread retinal diseases are also a possibility. In summary, patients presenting with eye pain or unilateral vision loss need a careful pupillary exam, looking for an RAPD. This typically presents acutely with pain with eye movements and in a young patient, often female. A subacute onset of days to months has a larger differential such as asymmetric glaucoma, severe macular degeneration or a mass in the orbit compressing on the optic nerve.Īn RAPD is almost always correlated with some visual loss, however some patients with optic neuritis may retain 20/20 vision. An acute onset of visual loss of hours to days points to inflammation or infection of the optic nerve, such as optic neuritis. In these cases, an urgent ophthalmic consultation is warranted because immediate intervention may preserve vision. A hyperacute onset of seconds to minutes points to a traumatic or vascular cause such as a fracture compressing the optic nerve, a large retinal detachment or ischemic optic neuropathy from something like a central retinal artery occlusion. If visual loss is present (which is almost always the case with an RAPD), the speed of onset is an important clue. The first step is to take a careful history that focuses on the timing of visual changes, prior eye diseases, eye pain and any recent trauma. Because of its potential urgency, it is important to determine the etiology of the RAPD. Spend about 3 seconds on each eye and then switch to the other eye so that the light exposure remains equal between the two eyes.Īlthough an RAPD is almost always a result of an asymmetrical defect of the optic nerve or retina, any pathology that decreases the amount of light sensed by one eye relative to the other will result in this finding. Repeat these steps several times to confirm your findings – be careful not to overexpose one eye and induce an RAPD.Quickly swing the light back to the first eye.If RAPD is present in that eye, both pupils will dilate. If that eye is normal, both pupils will constrict slightly.Quickly swing the light to the other eye and observe pupil diameter.Shine a light in one eye and allow pupil diameter to stabilize, shining the light directly into their eye for about 3 seconds.In a dim room, have the patient fixate on a distant point.This exam finding is best assessed with the swinging light test: The disease or condition causing the RAPD has to be asymmetric because if both eyes are equally affected than the pupillary reaction is symmetric. It is most commonly a sign of asymmetric optic nerve disease or damage but can also present in widespread asymmetric retinal disease. Title: Relative Afferent Pupillary Defect (RAPD)Īuthor: Marshall Huang, 4th Year Medical Student, University of PittsburghĪ Relative Afferent Pupillary Defect is an examination finding in patients who have an asymmetric pupillary reaction to light when it is shined back and forth between the two eyes. Home / Basic Ophthalmology Review / Pupillary Exam Relative Afferent Pupillary Defect (RAPD)
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