title: Normal values for a clinical test of letter-recognition contrast thresholds.
abstract: OBJECTIVE
  To investigate the contrast thresholds (CTs) in normal subjects using a high-luminance, letter-recognition task under clinically relevant testing conditions.
  
  
  METHODS
  Texas Tech University Health Sciences System, Lubbock, Texas, USA.
  
  
  METHODS
  Sixty normal subjects aged 20 to 49 years with a best corrected visual acuity of 20/20 or better in both eyes participated. M & S Technologies software was used to display black-on-white Sloan letters at contrast levels of 25%, 20%, 15%, 12%, and 10% through 1% in 1% decrements. The effects of age, sex, optotype size, eye dominance, ambient illumination level (bright = 625 - 630 lux; dim = <3 lux), and direction of approach to threshold were analyzed using a multivariate, ordinary, least-squares analysis.
  
  
  RESULTS
  Age and sex did not influence CTs. Ascending versus descending testing was not statistically significant (P>.5). The effects of room illumination and eye dominance were significant (P<.01). Significant differences were found between 20/30 and 20/50, 20/30 and 20/70, and 20/50 and 20/70 optotype sizes (P<.01 for all comparisons).
  
  
  CONCLUSIONS
  A commercially available, computer-based test of CTs was easy to administer and apparently easy for inexperienced subjects to perform. The results suggest criteria for detecting visual problems concerned with familiar but complex spatial-image shapes. This information might be used to assess the effects of treatments such as laser refractive surgery on recognition contrast. Further study is warranted.
authors.affiliation: Department of Ophthalmology and Visual Sciences, Texas Tech University Health Sciences Center, Lubbock, TX, USA.
authors.forename: Arshad M
authors.initials: AM
authors.lastname: Khanani
authors.forename: Sandra M
authors.initials: SM
authors.lastname: Brown
authors.forename: Ke Tom
authors.initials: KT
authors.lastname: Xu
mesh_terms: D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012684:Sensory Thresholds / Q000502:physiology; D014787:Vision Tests / Q000295:instrumentation / Q000379:methods; D014792:Visual Acuity