Tablet App halometer for the assessment of dysphotopsia

PURPOSE: To assess the validity and repeatability of the Aston Halometer. SETTING: University clinic, United Kingdom. DESIGN: Prospective, repeated-measures experimental study. METHODS: The halometer comprises a bright light-emitting-diode (LED) glare source in the center of an iPad4. Letters subtending 0.21 (similar to 0.3 logMAR) were moved centrifugally from the LED in 0.05 degree steps in 8 orientations separated by 45 degrees for each of 4 contrast levels (1000, 500, 100, and 25 Weber contrast units [C-w]) in random order. Bangerter occlusion foils were inserted in front of the right eye to simulate monocular glare conditions in 20 subjects (mean age 27.7 +/- 3.1 years). Subjects were positioned 2 meters from the screen in a dark room with the iPad controlled from an iPhone via Bluetooth operated by the researcher. The C-Quant straylight meter was also used with each of the foils to measure the level of straylight over the retina. Halometry and straylight repeatability was assessed at a second visit. RESULTS: Halo size increased with the different occlusion foils and target contrasts (F = 29.564, P<.001) as expected and in a pattern similar to straylight measures (F = 80.655, P<0.001). Lower contrast letters showed better sensitivity but larger glare-obscured areas, resulting in ceiling effects caused by the screen's field-of-view, with 500 C-w, being the best compromise. Intraobserver and interobserver repeatability of the Aston Halometer was good (500C(w): 0.84 to 0.93 and 0.53 to 0.73) and similar to the straylight meter. CONCLUSION: The halometer provides a sensitive, repeatable way of quantifying a patient-recognized form of disability glare in multiple orientations to add objectivity to subjectively reported discomfort glare. (C) 2015 ASCRS and ESCRS