title: Consistency between visual acuity scores obtained at different test distances: theory vs observations in multiple studies.
abstract: OBJECTIVE
  To investigate the consistency of visual acuity (VA) scores measured at 2 different distances in patients with or at risk for choroidal neovascularization.
  
  
  METHODS
  Best-corrected VA scores measured at 2 distances for the same eyes at the same examinations were collected from 4 sets of randomized clinical trials among patients with or at risk of choroidal neovascularization. Within each trial, the pairs of VA scores were compared and their relationship was explored.
  
  
  RESULTS
  After adjustment for test distance, VA scores obtained at the closer distance were found to be systematically lower than those obtained at the farther distance in all data sets. In the Submacular Surgery Trials pilot study, the average discrepancy between 2- and 0.5-m VA scores was 7.5 letters. In an ancillary study of the Macular Photocoagulation Study, the discrepancy between 10-ft and 5-ft VA scores was 3.1 letters. In the Laser to Drusen Trial pilot study, the discrepancy between 3.2- and 1-m VA scores was 7.3 letters. In the Treatment of Age-Related Macular Degeneration With Photodynamic Therapy Study, in which the VA scores at the closer test distance were censored, the estimated discrepancy between 2- and 1-m VA scores was 8.2 letters. Reduction in visual angle at closer test distance did not explain the discrepancy completely. Features of the macular lesion, poor accommodation of the elderly population with age-related macular degeneration, or the test charts did not account for the discrepancies.
  
  
  CONCLUSIONS
  The VA scores at distances less than 2 m were lower than expected in all 4 studies. The observed discrepancy was consistent with findings from a study among healthy young subjects, suggesting that the phenomenon is real and common.
authors.affiliation: Wilmer Clinical Trials and Biometry, 550 N Broadway, Ninth Floor, Baltimore, MD 21205-2010, USA.
authors.forename: Li Ming
authors.initials: LM
authors.lastname: Dong
authors.forename: Barbara S
authors.initials: BS
authors.lastname: Hawkins
authors.forename: Marta J
authors.initials: MJ
authors.lastname: Marsh
mesh_terms: D000465:Algorithms; D020256:Choroidal Neovascularization / Q000503:physiopathology / Q000628:therapy; D006801:Humans; D017075:Laser Coagulation; D013508:Ophthalmologic Surgical Procedures; D010778:Photochemotherapy; D010865:Pilot Projects; D014787:Vision Tests / Q000295:instrumentation / Q000379:methods*; D014792:Visual Acuity