title: Further validation of the Daily Living Tasks Dependent on Vision: identification of domains.
abstract: OBJECTIVE
  To examine the Daily Living Tasks Dependent on Vision (DLTV), a visual function questionnaire for domain structure, and redundancy.
  
  
  METHODS
  235 subjects underwent full ophthalmic assessment and completed the DLTV questionnaire by interview. Principal component analysis with varimax rotation and item response theory (IRT) were used to assign the items to domains. The internal consistency of each domain was examined using Cronbach's alpha. Redundancy was assessed by regressing each item in a domain against the remainder of items in that domain.
  
  
  RESULTS
  Four domains were identified. Domain 1 was formed by nine items, which after applying IRT were seen to be among the most difficult questions in the instrument. Domain 2 contained eight items, all of which fell in the easier half of the instrument on applying IRT. Domain 3 contained only three items, all of which were among the easier questions and appear to deal with peripheral vision function. Domain 4 consisted of two items dealing with adaptation to light and dark conditions. Cronbach's alpha for each domain was 0.96, 0.93, 0.73, 0.66. Redundancy was found to be present in domain 1, which was therefore reduced by two items, with little effect on internal consistency.
  
  
  CONCLUSIONS
  The authors believe using the domains identified in this report will optimise the information provided by patients on their ability to function on visually demanding tasks.
authors.affiliation: Department of Ophthalmology and Vision Science, The Queen's University of Belfast and Royal Group of Hospitals, Grosvenor Road, Belfast BT12 6BA, UK. pat.hart@royalhospitals.n-i.nhs.uk
authors.forename: P M
authors.initials: PM
authors.lastname: Hart
authors.forename: M R
authors.initials: MR
authors.lastname: Stevenson
authors.forename: A-M
authors.initials: AM
authors.lastname: Montgomery
authors.forename: K A
authors.initials: KA
authors.lastname: Muldrew
authors.forename: U
authors.initials: U
authors.lastname: Chakravarthy
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D000369:Aged, 80 and over; D004185:Disability Evaluation; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008268:Macular Degeneration / Q000523:psychology*; D008297:Male; D008875:Middle Aged; D025341:Principal Component Analysis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D011795:Surveys and Questionnaires; D019987:Persons with Visual Disabilities