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.