Relative Afferent Pupillary Defect Measurement

Principles of Measurement

• The relative afferent pupillary defect (RAPD) is evaluated using the swinging-light test, where a pupillary defect is manifested as pupillary dilation when the light is directed at the affected eye, according to the American Academy of Ophthalmology 1

Technique of Evaluation

• The evaluation is performed in a darkened room using a bright light source, with the patient fixing their gaze on a distant object, as recommended by the American Academy of Ophthalmology 1
• The light is directed alternately at each eye for less than 5 seconds, and the direct and consensual pupillary responses are observed in each eye, according to the American Academy of Ophthalmology 1

Interpretation of Results

• A RAPD of 0.3 or more log units is not typical in amblyopia and should alert clinicians to possible optic nerve or retinal pathologies, as stated by the American Academy of Ophthalmology 2, 3
• A significant RAPD should prompt an investigation for compressive optic neuropathy or other causes of visual impairment, according to the American Academy of Ophthalmology 2, 3

Special Considerations

• Pupillary evaluation in children can be challenging due to hipus, poor fixation, and/or rapid changes in accommodative state, as noted by the American Academy of Pediatrics and the American Academy of Ophthalmology 2, 4
• Confusing anisocoria (difference in pupil size) with RAPD (difference in pupillary response to light) should be avoided, as warned by the American Academy of Ophthalmology 1