title: Estimating a just-noticeable difference for ocular comfort in contact lens wearers.
abstract: OBJECTIVE
  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 (ΔC) between the right and left eyes were determined for each Likert scale preference criteria. The distribution of group ΔC 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 ΔC 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 ΔC 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.
authors.affiliation: Brien Holden Vision Institute, Sydney, New South Wales, Australia. e.papas@brienholdenvision.org
authors.forename: Eric B
authors.initials: EB
authors.lastname: Papas
authors.forename: Lisa
authors.initials: L
authors.lastname: Keay
authors.forename: Blanka
authors.initials: B
authors.lastname: Golebiowski
mesh_terms: D000328:Adult; D003261:Contact Lenses / Q000592:standards*; D004056:Differential Threshold / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017060:Patient Satisfaction; D012030:Refractive Errors / Q000503:physiopathology / Q000534:rehabilitation*; D012189:Retrospective Studies; D014785:Vision, Ocular; D055815:Young Adult