A Quantitative Evaluation of the PowerRef 3 for Measuring Gaze Position

PURPOSE: To evaluate the quality of gaze position measurements from the PowerRef 3 photorefractor and assess the impact of gaze position on the PowerRef 3 refractive measurements. METHODS: Monocular right-eye gaze was recorded in 20 adults (16 female, 4 male; 25.0±7.4 years) using the PowerRef 3 photorefractor (50 Hz). Participants fixated a target at 120 cm in 39 randomised locations (±24° horizontally [h], ±14° vertically [v]; 2° steps from centre). At each location, spatial accuracy, precision (root mean square of distances between samples and mean fixation [RMS-mean] and between successive samples [RMS-S2S]) and data loss were assessed. The impact of gaze position on refractive measurements was also examined. Gaze position data were also recorded using the EyeLink 1000 (500 Hz) to provide reference quality metrics. RESULTS: The PowerRef 3 had spatial accuracy of h = 1.45° ± 0.41° and v = 1.29° ± 0.15° and variable precision (RMS-Mean: h = 1.37° ± 0.12°, v = 1.32° ± 0.11°; RMS-S2S: h = 1.96° ± 0.16°, v = 1.90° ± 0.18°). Reference metrics obtained using the EyeLink showed slightly higher accuracy and precision (accuracy: h = 0.53° ± 0.09°, v = 0.52° ± 0.09°; RMS-Mean: h = 0.17° ± 0.02°, v = 0.19° ± 0.03°; RMS-S2S: h = 0.08° ± 0.01°, v = 0.07° ± 0.01°). Notable data loss for the PowerRef 3 was primarily observed at eccentric horizontal locations (0°-±16°: ≤30% of participants; ±20°-±24°: 35-70%; EyeLink 0°-±24°: ≤5%). PowerRef 3 data loss was also greater for lower vertical targets (≥30%) than for higher ones (≤20%). Relative to the pupillary axis, refractive measurements were more hyperopic beyond +10° horizontally (rightward gaze; 0.36-0.62 D) and beyond -6° vertically (downward; 0.59-1.44 D) and more myopic (≤1.29 D) between -10° to -18° horizontally (leftward). CONCLUSION: The PowerRef 3 can record gaze positions within ±8° horizontally and -4° (downward) to +10° (upward) vertically without a significant impact on both gaze and refractive measurements.