Pupil measurement using the Colvard pupillometer and a standard pupil card with a cobalt blue filter penlight

Abstract

Purpose: To compare scotopic pupil measurements obtained with a Colvard pupillometer with measurements taken with a printed pupil gauge and penlight with a cobalt blue filter attachment in mesopic and scotopic luminance.

Setting: The Illinois Eye Institute, Chicago, Illinois, USA.

Methods: Pupil measurements were taken of both eyes of 38 patients (76 eyes). Any subject presenting with anterior segment disease, fixed or dilated pupils, iris abnormalities, or a history of eye disease or eye trauma was excluded. At a mesopic luminance of 2.11 foot-candles, pupil measurements were taken with a Bernell pupil card and penlight with a cobalt blue filter attachment. At a scotopic luminance of less than 2.00 foot-candles, pupil measurements were taken with the Bernell card system and the Colvard pupillometer.

Results: In mesopic luminance, the mean pupil diameter was 5.17 mm (range 3.0 to 7.5 mm) with the Bernell card method. The mean difference between the Colvard in scotopic luminance and the Bernell card system in mesopic luminance was -0.04 mm (P = .0831). In scotopic luminance, the mean pupil diameter was 6.32 mm (range 4.0 to 8.0 mm) with the Bernell card method and 5.13 mm (range 3.0 to 7.5 mm) with the Colvard pupillometer, with a mean difference of -1.18 mm (P<.0001). The limits of agreement between the mesopic Bernell card system and the Colvard pupillometer were small (-0.32 to 0.24), whereas the limits of agreement between the scotopic measurements of both techniques were large (-2.18 to -0.18).

Conclusions: Under both illuminance conditions, the Bernell card system with the cobalt filter measured a larger pupil size than the Colvard pupillometer. The measurement differences between the techniques were most pronounced at the lower illumination. The limits of agreement were larger under the lower illumination, indicating more variation between techniques. This study suggests that the Bernell card system with cobalt illumination provides a generous measurement of the pupil size compared with the Colvard pupillometer, which makes it an appropriate and cost-effective screening tool for refractive surgery evaluation.