Momeni-Moghaddam H, Yekta AA, Kundart J, Etezad-Razavi M, Askarizadeh F. Effect of Induced Vertical Disparity on Horizontal Fusional Reserves.
Strabismus 2017;
25:195-199. [PMID:
29235886 DOI:
10.1080/09273972.2017.1396351]
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Abstract
PURPOSE
The aim of this study was to investigate the effects of induced vertical disparity on horizontal fusional reserves at near.
MATERIALS AND METHODS
In 170 healthy subjects wearing best corrective refraction, the negative and positive horizontal fusional reserves were measured with base-in (BI) and base-out (BO) prisms, respectively, in the presence of 0.5 prism diopters (∆) and 1∆ vertical prisms placed in trial frames in front of the right eye. The prism power was slowly increased step by step until the subject reported sustained blur, break, and recovery. These were compared to horizontal fusional reserves in the same subjects without a vertical prism. Data were analyzed in SPSS.17 software using a repeated measures ANOVA.
RESULTS
Induced vertical disparity decreased negative fusional reserves (NFR) horizontally and was more significant with 1∆ vertical disparity (P<0.001). There were significant differences between the blur (P<0.001), break (P<0.001), and recovery (P<0.001) for NFR before and after induced vertical disparity and no significant difference between blur (P=0.173) and recovery points (P=0.261) with a marginal difference for break points (P=0.045) for the positive fusional reserves (PFR).
CONCLUSION
Inducing vertical disparity even with small magnitudes affects all 3 aspects (blur, break, and recovery) of horizontal negative fusional reserves while only break is affected in positive fusional reserves. These changes are statistically significant but do not seem to be clinically significant except for cases accompanied by symptoms.
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