Objective: To investigate the effects of the ocular torsion on horizontal fusion and stereopsis in normal adults and to probe the effects of the torsion on peripheral fusion, macular fusion and foveal fusion.
Methods: Twenty-five normal adults aged 30-38 years were enrolled in this study. Using synoptophore test, the break points (BP) and recovery points (RP) of convergent fusion (CF) and divergent fusion (DF) and random-dots stereopsis (RDS) were measured and analyzed at objective intorsion and extorsion 3 °\5 °\ 7 °\9 °. According to the different sizes of the retinal areas simulated by the synoptophore slides, the fusional functions are divided into three categories: peripheral fusion (p-F), macular fusion (m-F) and foveal fusion (f-F). The p-F, m-F and f-F were analyzed and compared at the same torsional angle.
Results: For p-F, BPCF, RPCF, BPDF and RPDF decreased at objective extorsion and intorsion 5 °, 7 ° and 9 °, compared with those without objective torsion (P < 0.05). For m-F, the BPCF, RPCF, and BPDF at intorsion and extorsion 7 ° and RPDF at intorsion and extorsiont 9 ° decreased significantly, compared with those without objective rotation (P<0.05). For f-F, the BPCF and RPCF at extorsion 7 ° and 9 ° decreased significantly (P<0.05). Comparing among p-F, m-F and f-F, there were significant differences in BPCF at intorsion 3 °, extorsion3 ° and no torsion and in RPCF at extorsion 3 °. RDS was gradually damaged with increasing torsion (Spearman correlation, P = 0.018).
Conclusions: The ocular torsion in the normal range of cyclofusion affects the horizontal fusion and stereopsis. Torsion≥5 ° could decrease peripheral fusion and torsion≥7 ° could decrease macular fusion and foveal fusion.