Measurement of scotopic pupils: comparison of scotic pupil measurements using a colvard pupilometer and the slitlamp green light test

Abstract

The aim of the study was to compare the accuracy and the reproducibility of scotopic pupil measurements using two different methods. We developed a simple test to measure scotopic pupil diameters using a narrow slit of light through a green filter of the Haag-Streit slitlamp. A total of 100 eyes from 50 refractive surgery candidates were prospectively examined by 2 independent investigators using both the Colvard pupilometer (Oasis/USA) and Sekundo's slitlamp green light test. Results were compared using all pairwise multiple comparison procedures (Student-Newman-Keuls method, SigmaStat/Jandel Scientific). The mean age of the patients was 36.3 years with a male:female ratio of 16:34. The colour of the iris was considered blue for 36 individuals and brown for the remainder. Reproducibility: the right eye mean pupil diameter using Sekundo's method was 6.4 mm (+/-0.9) measured by both the first (Slit 1R) and the second (Slit 2R) investigator. The left eye mean pupil diameter was 6.5 mm (+/-1) (Slit 1L) and 6.35 mm (+/-1) (Slit 2L), respectively. The following measurements were obtained with the Colvard pupillometer: (Colv1R)=6.25+/-0.85 mm, (Colv2R)=5.99+/-1 mm, (Colv1L)=6.15+/-0.91 mm, (Colv2L)=6.05+/-0.9 mm. There were no statistically significant differences between the two investigators within the same method of examination. Comparability:The data of both investigators were combined to form 4 groups: (Slit R)=6.4+/-0.96 mm, (Slit L)=6.4+/-1 mm, (Colv R)=6.05+/-0.9 mm, (Colv L)=6.1+/-0.93 mm. There was a significant difference ( p=0.024) between the two methods for both right and left eyes. Particularly for large pupils, the slitlamp green light measurements were significantly higher (up to 0.35 mm) than those with Colvard's device. The slitlamp green light test provides similar reproducibility for the measurement of the scotopic pupil diameter as the commercially available Colvard pupilometer.