The Effect of Induced Vertical Prism On Reading Related Parameters In Normal Subjects

Background: The study evaluated the effect of induced vertical prism on reading efficiency, speed, and comprehension in a group of young adults. Reading efficiency, speed, and comprehension were evaluated using The Visagraph 3 which provides an objective measurement of ocular movements as the subject reads through a paragraph. Vertical deviations were induced by introducing prisms before one eye after controlling for any natural heterophoria.
Methodology: A sample of students (N=46) between the ages of 21-30 were included. All subjects were initially screened with a Modified Thorington test to elicit any vertical phorias. If a vertical phoria was present, correcting prism was given to neutralize the phoria. Visagraph testing then ensued with induced prismatic powers of the following strengths: 0 PD, 1 PD, 2 PD & 3 PD (or the prism of highest magnitude which does not disrupt fusion). Testing was randomized to minimize the effects of fatigue and learning.
Results: We found vertically induced prism caused significant differences on the following reading related parameters: fixations, reading speed, and grade level equivalent.
Conclusion: We found that vertically induced prism caused significant differences on the following reading related parameters – a) Fixations, b) Reading Speed, c) GLE. These differences could be the effect of the increased vertical vergence demand created by the induction of prism and could have clinical implications for prismatic prescribing practices. However, we cannot discount the effect of confounding variables such as subject psychology, criterion, and familiarity with content – all of which may have influenced our results.