Use of a digital infrared pupillometer to assess patient suitability for refractive surgery

PURPOSE: To assess the role of binocular infrared dynamic pupillometry in measuring and recording the pupil size in scotopic, low mesopic, and high mesopic illumination prior to refractive surgery. SETTING: The Rosen Eye Surgery Centre, Alexandra Hospital Victoria Park, Manchester, United Kingdom. METHODS: In this prospective study, the pupil sizes of 58 patients (mean age 46 years +/- 11.7 [SD]) presenting for refractive surgery assessment were evaluated using the P2000 SA pupillometer (Procyon Instruments Ltd.). Each patient was measured at 3 illumination levels: 0.02 lux (scotopic), 0.15 lux (low mesopic), and 10.6 lux (high mesopic). At each level, 10 images were acquired by the system at 5 images per second. Both eyes were imaged at the same time, with a spatial accuracy of 0.03 mm per pixel. RESULTS: Pupillary unrest (PU) occurred at all levels of illumination. Some degree of PU amplitude was observed in both eyes of all patients. The median PU was 0.12 mm (95% confidence limits [CLs], 0.11, 0.14) in the scotopic range, 0.34 mm (95% CLs, 0.28, 0.38) in the low mesopic range, and 0.28 mm (95% CLs, 0.23, 0.30) in the high mesopic range. The degree of anisocoria varied among individuals. The median value was 0.28 mm (95% CLs, 0.21, 0.39) in the scotopic range, 0.32 mm (95% CLs, 0.26, 0.37) in the low mesopic range, and 0.16 mm (95% CLs, 0.12, 0.19) in the high mesopic range. Because of PU and anisocoria, single versus multiple binocular measurements demonstrated the possibility of errors greater than 1.0 mm in some patients. CONCLUSIONS: Patients showed an appreciable degree of pupillary motion during measurement at all levels of illumination; the motion was largest under low mesopic illumination. The 2 pupils were rarely identical. Multiple-measurement binocular pupillometry is better than single monocular measurement to gain a precise description of pupil behavior before refractive surgery.