Comparison of patient-reported visual outcome methods to quantify the perceptual effects of defocus

Patient-reported subjective responses have become increasingly popular in describing contact lens visual performance and discriminating between designs. The purpose of the current study is to evaluate the ability of patient-reported measures of vision to quantify the perceptual effects of defocus.

Ten young (18-35 years) subjects rated their subjective visual performance monocularly on 3 scales following wear of their optimal monocular distance correction and nine different blurring lenses (-0.50 to +1.50 in 0.25 D steps) in a trial frame. The three scales used were a 0-100 numeric rating scale (NRS), a 100 mm visual analog scale (VAS), and a 5 point ("Poor", "Fair", "Average", "Good", "Excellent") categorical rating scale (CRS).

Mixed linear modeling results found no significant effects either for eye or trial number, but did find a significant effect due to blurring lens power (p<0.0001), with ratings decreasing with increasing levels of blur for all scales. Results were not significantly different between the NRS and VAS at any level of blur, with limits of agreement falling within 22% of the measurement scale. CRS ratings were about 15 units lower than the other scales on average, with limits of agreement that varied with lens power and were roughly 3 times as large. Across scale internal consistency was 0.94.

The NRS and VAS yield virtually identical rating responses, but both differing slightly, however from the CRS. Each scale successfully discriminated levels of blur smaller than 0.25 D with only a single measurement.