REPEATABILITY AND COMPARISON OF VISUAL ANALOG AND NUMERICAL RATING-SCALES IN THE ASSESSMENT OF VISUAL QUALITY

The repeatabilities of both the visual analogue scale (VAS) and numeri cal rating scale (NRS) as methods of assessing visual quality (VQ) wer e estimated by obtaining three replicated responses from each of a gro up of nine normal subjects who viewed a standardized scene under condi tions of controlled refractive blur. In both cases, repeatability was highest in the absence of blur but fell markedly as increasing amounts of visual decrement were induced. Coefficients of reproducibility ran ged from 4.1 to 36.0 for VASs; and from 1.2 to 34.9 for NRSs. Except w here VQ was high, both types showed generally poor repeatability. When the data were used to compare the two methods, no consistent bias was found and agreement was good for high VQ levels. The NRS offers a rea sonable alternative to the VAS as a method of assessing subjective VQ. Copyright (C) 1997 The College of Optometrists. Published by Elsevier Science Ltd.