The Effects of Refractive Imbalance on Binocular Vision Status, Reading Performance, and Vision-Related Reading Difficulty Symptoms in Expert Readers.

Purpose: To investigate how refractive imbalance affects binocular vision parameters, reading performance, and vision-related reading difficulty symptomatology after short periods of reading with different simulated ophthalmic lens power conditions in expert adult readers. Methods: Eighteen adult participants (18-35 years of age) were recruited. They were expert readers, defined as currently studying, or previously studied to, at least a bachelor's degree tertiary education level. Refractive imbalance conditions were simulated by placing -2.00, -1.00, 0.00, +1.00, and +2.00 diopters (D) ophthalmic lenses in front of the dominant eye over their full refractive error correction. For each condition, participants were required to read sets of three paragraphs from the background section of an academic journal paper, after which reading comprehension, reading speed, symptomatology, visual acuity, and binocular vision status were assessed for each set through refractive imbalance conditions. Results: A significant reduction of binocular visual acuity was observed for distance (+2.00 D condition) and near (±2.00 D conditions) viewing distances. The greater the refractive imbalance stimulus provided to the dominant eye monocularly, the more underfocused the binocular accommodative response. Simulated refractive imbalance did not affect reading speed and comprehension. Stereoacuity and subjective vision-related reading difficulty symptoms worsened with increased absolute refractive imbalance. Conclusions: Simulated refractive imbalance did not affect reading performance for the short reading task but resulted in statistically significant reductions in clarity, increased binocular difficulties, and visual discomfort. During reading, full correction of refractive imbalance is beneficial and recommended.