Pre–Excimer Laser and Post–Excimer Laser Refractive Surgery Measurements of Scotopic Pupil Diameter Using 2 Pupillometers

Abstract

To compare a digital infrared pupillometer with a handheld light amplification pupillometer for measuring scotopic pupil size and to evaluate if the postoperative refractive changes of the cornea can influence pupil measurements. Prospective noncomparative interventional case series. One hundred eyes, 50 myopic (mean spherical equivalent [SE] refraction [+/- standard deviation], -4.32+/-2.44 diopters [D]) and 50 hyperopic (mean SE refraction, +2.95+/-0.99 D), of 50 otherwise healthy subjects underwent photorefractive keratectomy or LASIK. The preoperative and postoperative scotopic pupil sizes were measured by 2 examiners (E1, E2) with both a handheld light amplification pupillometer (Colvard, Oasis Medical, Glendora, CA) and a digital infrared pupillometer (Eye World Pupillometer [EWP], Oculus Keratograph, Oculus Opikgerate GmbH, Wetzlar, Germany). The agreement and interrater repeatability were determined using the comparison method described by Bland and Altman. The paired Student's t test was used to evaluate the difference between the preoperative and postoperative measurements. Scotopic pupil diameter, topographic corneal refractive power, uncorrected visual acuity (VA), best spectacle-corrected VA, and manifest spectacle refraction. The preoperative mean scotopic pupil diameter was 6.12+/-0.90 mm with the EWP and 6.18+/-0.91 mm with the Colvard. After the surgery, mean SE refractions were -0.22+/-0.98 D (myopic patients) and +0.19+/-0.40 D (hyperopic patients). Postoperative mean scotopic pupil diameters were 6.12+/-0.89 mm (EWP) and 6.17+/-0.90 mm (Colvard). There was no statistically significant difference between preoperative and postoperative mean scotopic pupil sizes in either patient group. The limits of agreement between the 2 devices ranged from 2.24 mm (E1) to 2.12 mm (E2) preoperatively and from 2.27 mm (E1) to 2.08 mm (E2) postoperatively. The coefficient of interrater repeatability ranged from 0.56 mm (EWP) to 1.12 mm (Colvard) preoperatively and from 0.62 mm (EWP) to 1.14 mm (Colvard) postoperatively. The digital infrared pupillometer showed better preoperative and postoperative repeatability than the handheld light amplification pupillometer. In the present study, a mean correction of <3 D of the corneal refractive power did not seem to modify the preoperative scotopic pupil size measurements.