title: Crossed and uncrossed stereoacuity at distance and the effect from heterophoria.
abstract: BACKGROUND
  Previous studies have found that crossed disparities give better stereoacuity than uncrossed. When near phoria is considered, exophores had a better crossed stereoacuity and esophores had a better uncrossed stereoacuity. The current study investigated the effect of heterophoria on distant crossed and uncrossed stereoacuity.
  
  
  METHODS
  Seventy-two subjects were recruited and their distant heterophoria measured. Heterophoria within two prism dioptres was considered as orthophoric. Esophoric group had esophoria greater than two prism dioptres. Exophoric group had exophoria greater than two prism dioptres. There were 40 orthophores, 23 exophores and nine esophores. Their stereoacuity was measured with a three-rod apparatus at 6 m.
  
  
  RESULTS
  The mean crossed stereoacuity was 4.8" and uncrossed stereoacuity was 7.2" (t = -3.03, p < 0.01). The mean stereoacuity for orthophoric subjects was 5.31", 6.02" for exophores and 8.91" for esophores. The distant crossed stereoacuity is better than uncrossed stereoacuity in all three groups but the difference is only significant for the exophores. Exophoric subjects demonstrated a significant difference between crossed (4.10") and uncrossed (7.95") stereoacuity.
  
  
  CONCLUSIONS
  Orthophores have the best stereoacuity, followed by exophores and esophores. Exophoric subjects have a better crossed than uncrossed stereoacuity. More esophoric subjects should be recruited to confirm the difference between crossed and uncrossed stereoacuity.
authors.affiliation: Department of Optometry and Radiography, The Hong Kong Polytechnic University, Hong Kong SAR, China. orkclam@polyu.edu.hk
authors.forename: Andrew K C
authors.initials: AK
authors.lastname: Lam
authors.forename: Patrick
authors.initials: P
authors.lastname: Tse
authors.forename: Emily
authors.initials: E
authors.lastname: Choy
authors.forename: Magic
authors.initials: M
authors.lastname: Chung
mesh_terms: D000293:Adolescent; D000328:Adult; D003867:Depth Perception; D005260:Female; D006801:Humans; D008297:Male; D013285:Strabismus / Q000503:physiopathology / Q000523:psychology*; D015357:Vision Disparity / Q000502:physiology; D014787:Vision Tests / Q000379:methods; D014792:Visual Acuity