Can unequal focusing between your eyes make reading uncomfortable without slowing you down?

Details

This experiment investigated how simulated refractive imbalance affected binocular vision, reading performance, and vision-related reading difficulty symptoms after short periods of reading under different ophthalmic lens power conditions in expert adult readers.

Eighteen adults aged 18–35 years participated. They were defined as expert readers because they were currently studying toward, or had previously studied to, at least a bachelor's degree level in tertiary education. In a within-participant experiment, refractive imbalance was simulated by placing ophthalmic lenses of -2.00, -1.00, 0.00, +1.00, and +2.00 diopters (D) in front of the dominant eye, over each participant's full refractive error correction. For each condition, participants read sets of three paragraphs from the background section of an academic journal paper. After each set, reading comprehension, reading speed, symptoms, visual acuity, and binocular vision status were assessed across the refractive imbalance conditions.

Binocular visual acuity decreased significantly for distance viewing in the +2.00 D condition and for near viewing in the ±2.00 D conditions. The greater the refractive imbalance stimulus applied to the dominant eye alone, the more underfocused the binocular accommodative response became. Simulated refractive imbalance did not affect reading speed or comprehension. Stereoacuity and subjective vision-related reading difficulty symptoms worsened as the absolute refractive imbalance increased.

The researchers concluded that simulated refractive imbalance did not affect performance on this short reading task, but produced statistically significant reductions in clarity, increased binocular difficulties, and visual discomfort. They concluded that full correction of refractive imbalance during reading is beneficial and recommended it.