title: Normative reference ranges for binocular summation as a function of age for low contrast letter charts.
abstract: OBJECTIVE
  Binocular summation (BiS), defined as the superiority of binocular over monocular viewing on visual threshold tasks, is most often studied in laboratory settings. Few studies have evaluated BiS with readily available clinical tools. Low contrast acuity (LCA) charts are increasingly popular in clinical research, yet their utility in detecting BiS has not been evaluated.
  
  
  METHODS
  129 normal subjects aged 3 to 85 years were prospectively enrolled and underwent monocular and binocular testing using 2.5% and 1.25% Sloan LCA charts and Pelli-Robson (PR) contrast sensitivity (CS) charts at an academic institution. Subjects also underwent similar testing with Early Treatment Diabetic Retinopathy Study (ETDRS) VA charts. BiS was calculated as the difference between the better eye and binocular scores.
  
  
  RESULTS
  Monocular and binocular scores decreased with increasing age for all metrics. The mean (±SD) BiS scores for 2.5% and 1.25% Sloan LCA were 6±4.5 and 3±5 letters, respectively. BiS score was 4.5±7 letters for PR charts and 2±3 letters for ETDRS VA. There was a significant effect of age on BiS for the low contrast metrics (P≤0.001 for all), but not for high-contrast ETDRS VA. Linear regression revealed significant associations between increased interocular difference (IOD) in acuity and decreased BiS for all tests, and associations between increasing age and decreased BiS for the LCA tests.
  
  
  CONCLUSIONS
  Of the clinical tests evaluated, 2.5% and 1.25% Sloan LCA charts most readily demonstrated BiS in young normal subjects. BiS declined with increasing age and increased IOD. Median values presented in this study may be useful for future clinical studies utilizing LCA.
authors.affiliation: Jules Stein Eye Institute and Department of Ophthalmology, University of California , Los Angeles .
authors.forename: Stacy L
authors.initials: SL
authors.lastname: Pineles
authors.forename: Federico G
authors.initials: FG
authors.lastname: Velez
authors.forename: Fei
authors.initials: F
authors.lastname: Yu
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Demer
authors.forename: Eileen
authors.initials: E
authors.lastname: Birch
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D002648:Child; D002675:Child, Preschool; D015350:Contrast Sensitivity / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D014787:Vision Tests / Q000295:instrumentation*; D015348:Vision, Binocular / Q000502:physiology*; D014792:Visual Acuity / Q000502:physiology*
keywords: Binocularity; binocular inhibition; binocular summation; low contrast acuity