Crossed and uncrossed stereoacuity at distance and the effect from heterophoria.
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.
Lam
Andrew K C
AK
Department of Optometry and Radiography, The Hong Kong Polytechnic University, Hong Kong SAR, China. orkclam@polyu.edu.hk
Tse
Patrick
P
Choy
Emily
E
Chung
Magic
M
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