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A comparison of three different scales for rating contact lens handling
Rènée du Toit1, Nicola Pritchard, Sonia Heffernan
1Cornea and Contact Lens Research Unit, University of New South Wales, Sydney, Australia. r.dutoit@cclru.unsw.edu.au
Purpose:
To compare the validity, responsiveness, and reliability of three subjective rating scales applied to soft contact lens (SCL) handling.
Methods:
Fifty-four adapted SCL wearers handled three different types of lenses on two occasions and rated the handling with each scale: visual analogue scales (VAS), 20-interval visual analogue scales with descriptors (VAD) and Likert rating scales with five intervals (LRS).
Results:
There were significant differences between the scales (p < 0.01) and between the subjective ratings of lens handling (p < 0.001). VAS showed the least variability, exhibited the highest construct validity, were the most responsive, and were the most reliable: interclass correlations (0.63), coefficient of repeatability (27.5), and correlation between test and retest (Spearman r = 0.65, [all p < 0.05]). Higher repeatability, because of the fewer intervals of LRS, was not demonstrated and, generally, LRS was the least satisfactory scale. Handling was rated as easiest using VAD and most difficult using LRS.
Conclusions:
Although all three scales can be used to provide measures of lens handling, VAS may provide a simple and repeatable tool for measuring subjective responses.