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Purpose: To describe a simple technique that detects a subtle relative afferent pupillary defect., Design: Observational report., Methods: With the patient seated at a slit lamp and the slit illumination turned off, a transilluminator light is swung back and forth between the eyes. The examiner observes the direct pupil light response and the consensual light response under slit-lamp magnification., Conclusion: Using slit-lamp magnification, the examiner may observe small amplitudes of pupillary movement in the evaluation of a relative afferent pupillary defect.

The aim of this study was to investigate variables that influence the degree of pupillary constriction to dilute pilocarpine eyedrops in healthy control subjects. The pupillary response to 50 microliter of pilocarpine 0.0625% in darkness, dim light, and bright light was measured photographically in 15 healthy adults. Constriction to pilocarpine was greater in darkness and in dim light than in bright light, indicating that the pupillary-light reflex masked the constrictive effect of pilocarpine. In ten other subjects pupillary constriction to 50 microliters of pilocarpine 0.04%, and to 50 and 100 microliters of pilocarpine 0.0625%, was measured on separate occasions. Pupillary constriction increased in proportion to the volume and concentration of pilocarpine. Data for pupillary constriction to 50 microliters of pilocarpine 0.0625% in dim light were determined in all 25 subjects.

We compared the direct light response of both eyes in 90 patients who had anterior visual pathway disease using two different testing methods. We measured Kestenbaum's number in millimeters of pupillary diameter. Kestenbaum's number (K) is the difference in the pupil size attained in each eye under direct illumination while the other eye is occluded. We then measured the relative afferent pupillary defect (RAPD) in log units using neutral density filters. The two tests gave similar results (K = 0.88 x RAPD). Kestenbaum's number is the less precise measure, but it can be quickly and cheaply estimated even in dark brown eyes. The filter test requires a set of filters and at least one well-innervated iris sphincter. Kestenbaum's number can be measured without filters, but the iris sphincter and dilator muscles in both eyes must be normally innervated.