Shong Min Voon1, Logan Mitchell1,2, Gina Wilson1
Aim: Investigating the vertical prism fusion ranges (VPFR) of a cohort of subjects with BCVA > 4/8, normal stereopsis, and no past history of strabismus or amblyopia. Previous papers have noted normal VPFR of 2.0? to 10.0? , which is greater than the ranges listed in current textbook guidelines.
Method: The break point and recovery point of each subject’s vertical prism fusion ranges were measured with a vertical prism bar while fixating at a near (33cm with a letter on a fixation stick) and distant (4m with a Snellen chart) target.
Results: Sixty participants (19 – 31 years old) were measured and their VPFR ranges were between 2.0? and 11.0? (Mean 5.4?) for near and 1.5? to 12.0? (Mean 5.1?) for distance. Thirty-seven participants had phorias, however the VFPR ranges were not significantly different compared to normal subjects.
Conclusion: Vertical fusion ranges in normal subjects were recorded to have a slightly higher mean at near compared to distance, and agrees with the previously noted normal range of 2.0? to 10.0?, which reinforced the findings of previous research, and is different from current prescribed textbook guidelines.