title: Aniseikonia associated with epiretinal membranes.
abstract: OBJECTIVE
  To determine whether the computerised version of the new aniseikonia test (NAT) is a valid, reliable method to measure aniseikonia and establish whether aniseikonia occurs in patients with epiretinal membranes (ERM) with preserved good visual acuity.
  
  
  METHODS
  With a computerised version of the NAT, horizontal and vertical aniseikonia was measured in 16 individuals (mean 47 (SD 16.46) years) with no ocular history and 14 patients (mean 67.7 (14.36) years) with ERM. Test validity was evaluated by inducing aniseikonia with size lenses. Test reliability was assessed by the test-retest method.
  
  
  RESULTS
  In normal individuals, the mean percentage (SD) aniseikonia was -0.24% (0.71) horizontal and 0% (0.59) vertical. Validity studies revealed mean (SD) 0.990 (0.005) horizontal and 0.991 (0.004) vertical correlation coefficients, 0.985 (0.111) horizontal and 0.989 (0.102) vertical slope. Repeatability coefficients were 1.04 horizontal and 0.88 vertical. Aniseikonia in patients with ERM ranged from 4% to 14%. Eight patients showed 2% or more size difference between horizontal and vertical meridians.
  
  
  CONCLUSIONS
  The aniseikonia test used in this study can be considered a simple, fast, valid and reliable method to measure the difference in image size perceived by each eye. Aniseikonia does occur in symptomatic patients with ERM. The effect of ERM on image size is heterogeneous across the retinal area affected.
authors.affiliation: Department of Ophthalmology, St Thomas's Hospital, London SE1 7EH, UK. mugarte@doctors.org.uk
authors.forename: M
authors.initials: M
authors.lastname: Ugarte
authors.forename: T H
authors.initials: TH
authors.lastname: Williamson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000839:Aniseikonia / Q000175:diagnosis* / Q000209:etiology* / Q000503:physiopathology; D003936:Diagnosis, Computer-Assisted; D019773:Epiretinal Membrane / Q000150:complications* / Q000503:physiopathology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012029:Refraction, Ocular; D015203:Reproducibility of Results; D014787:Vision Tests / Q000379:methods; D014792:Visual Acuity