Afferent Pupillary Defects

When a light is shone into a normal eye, the pupil responds by getting smaller. The latency and amplitude of the pupillary contraction depend on a number of factors. The intensity and location of the test light, the level of background illumination, the size of the pupil, the age of the patient, and the level of alertness of the patient all play a role. Both intra- and inter-individual variability of the pupil response are high. With a given stimulus the latency of contraction is less variable than the amplitude, but latency is still susceptible to conditions that affect efferent pupillary pathways. Measurement of pupillary latency requires sophisticated equipment, and even then the definition of onset of pupillary contraction poses difficulties.