QUVID is a patient-reported outcomes questionnaire that collects responses from the subject about vision-related experiences. A halo is a circular spreading of light around a light source, such as car headlights at night. Question 2 of QUVID asked the subject, "In the past 7 days, have you experienced halos?" Subjects responding "No" were automatically imputed as reporting, "0=Not bothered at all." Subjects responding "Yes" were then asked Question 2.3: "In the past 7 days, how much have your halos bothered you?" Subjects responded on a 5-point scale: 0=Not bothered at all; 1=Bothered a little bit; 2=Bothered somewhat; 3=Bothered quite a bit; 4=Bothered very much. Percentage was calculated as number of subjects with score of 0 divided by number of subjects with data regardless of response, times 100.