01938nas a2200157   4500000000100000008004100001100001400042700001300056700001900069245008700088250001500175300001100190490000700201520152600208020004601734       2011                            d1 aKeay Lisa1 aPapas E.1 aGolebiowski B.00aEstimating a just-noticeable difference for ocular comfort in contact lens wearers  a2011/04/19  a4390-40 v523 a<p>
Purpose. To estimate the just-noticeable difference (JND) in ocular comfort rating by human, contact lens-wearing subjects using 1 to 100 numerical scales. Methods. Ostensibly identical, new contact lenses were worn simultaneously in both eyes by 40 subjects who made individual comfort ratings for each eye using a 100-point numerical ratings scale (NRS). Concurrently, interocular preference was indicated on a five-point Likert scale (1 to 5: strongly prefer right, slightly prefer right, no preference, slightly prefer left, strongly prefer left, respectively). Differences in NRS comfort score (DeltaC) between the right and left eyes were determined for each Likert scale preference criteria. The distribution of group DeltaC scores was examined relative to alternative definitions of JND as a means of estimating its value. Results. For Likert scores indicating the presence of a slight interocular preference, absolute DeltaC ranged from 1 to 30 units with a mean of 7.4 +/- 1.3 (95% confidence interval) across all lenses and trials. When there was no Likert scale preference expressed between the eyes, absolute DeltaC did not exceed 5 units. Conclusions. For ratings of comfort using a 100-point numerical rating scale, the inter-ocular JND is unlikely to be less than 5 units. The estimate for the average value in the population was approximately 7 to 8 units. These numbers indicate the lowest level at which changes in comfort measured with such scales are likely to be clinically significant.
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