The test light affects quantitation of the afferent pupillary defect.

Nineteen patients with afferent pupillary defects (APDs) from a variety of lesions were examined using a brighter and dimmer test light. A denser neutral density filter was required to balance the afferent defect using the brighter test light in every case. For quantitation of an afferent defect to have meaning, the test light used must be specified. An indirect ophthalmoscope set to 6 V and held 1 foot from the eyes will allow easier detection of subtle relative APDs than it will if set to 3 V.