title: Repeatability of mesopic visual acuity measurements using high- and low-contrast ETDRS letter charts.
abstract: OBJECTIVE
  To determine the repeatability of mesopic high-contrast (HC) and low-contrast (LC) visual acuity (VA) measurements made at distance and near in healthy young individuals. While the repeatability of photopic VA is well-known, there is a lack of information with regard to the repeatability of VA measured under low luminance conditions.
  
  
  METHODS
  In two different sessions 1 week apart, best-corrected monocular VA was determined using HC (96 %) and LC (10 %) ETDRS charts under mesopic luminance conditions (0.75 cd/m(2)) at distance (HCD, LCD) and near (HCN, LCN) in 47 healthy subjects aged 22.9 ± 6.8 years. Repeatability was estimated by the Bland and Altman method, whereby the mean difference (MD) and the 95 % limits of agreement were determined as the coefficient of repeatability (COR).
  
  
  RESULTS
  Mean logMAR VA values were HCD = 0.09, LCD = 0.44, HCN = 0.21, and LCN = 0.57. Mean differences in measurements between sessions 1 and 2 were not significant, and low in clinical terms (≤1 letter). Repeatability was better for the distance measurements at both high and lowcontrast (COR HCD ±0.11 and COR LCD ±0.11 logMAR vs COR HCN ±0.15 and COR LCN ±0.16 logMAR), and MDs were also slightly closer to zero for the distance measurements. Similar repeatability was observed between HC and LC VA, both at distance and near.
  
  
  CONCLUSIONS
  In mesopic conditions, ETDRS charts offer repeatable best-corrected monocular VA measurements. The criterion for a significant change in logMAR VA was 1 line at distance and 1.5 lines at near.
authors.affiliation: Applied Vision Research Group, Faculty of Optics and Optometry, Complutense University of Madrid, Av. Arcos de Jalón 118, 28037, Madrid, Spain, arbarrio@ucm.es.
authors.forename: Ana
authors.initials: A
authors.lastname: Barrio
authors.forename: Beatriz
authors.initials: B
authors.lastname: Antona
authors.forename: María C
authors.initials: MC
authors.lastname: Puell
mesh_terms: D000293:Adolescent; D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D055255:Mesopic Vision / Q000502:physiology*; D015203:Reproducibility of Results; D014787:Vision Tests / Q000295:instrumentation*; D014792:Visual Acuity / Q000502:physiology*; D055815:Young Adult