Preoperative measurement of scotopic pupil dilation using an office pupillometer

To describe a light-amplification pupillometer designed for office evaluation of refractive surgical candidates and compare its usefulness with that of a millimeter ruler and a standard pocket-card pupillary gauge.

Center for Ophthalmic Surgery, Encino, California, USA.

The pupil sizes of 100 patients with a mean age of 28 years (range 18 to 50 years) were measured at 2 levels of illumination: 15 and 3 lumens. Pupil size was measured with a Rosenbaum pocket-card pupil gauge, a millimeter ruler, and the pupillometer at approximately 15 lumens. This level of illumination was chosen by 3 technicians as the lowest at which the pupil of a brown eye could be measured with confidence using the Rosenbaum card. Pupil size was then measured using the light-amplification pupillometer at approximately 3 lumens. This illumination level was chosen to simulate that of night-driving conditions.

At 15 lumens, mean pupil diameter was 5.1 mm (range 2.5 to 8.0 mm). There was no difference in the measurements taken with the 3 instruments at this illumination level. At 3 lumens, the pupil diameter could not be measured with confidence using the Rosenbaum card or the millimeter ruler. Using the pupillometer, mean pupil size was 6.2 mm (range 3.0 to 9.0 mm). The mean difference in pupil diameter measured at 15 and 3 lumens was 1.1 mm (range 0.0 to 3.0 mm).

This evaluation suggests that it would be difficult for clinicians to reliably predict the level of pupil dilation at 3 lumens by measuring pupil size at 15 lumens. The light-amplification pupillometer provides a tool for measuring pupil size at an illumination level that simulates night-driving conditions. The use of this device may help surgeons identify refractive surgery candidates who are more likely to be dissatisfied with their postoperative vision at low illumination levels.