Slow Binocular Reading in Children With Amblyopia is a Fellow Eye Deficit

The authors previously conducted two studies in which they found that children with amblyopia tended to read more slowly than those without a history of amblyopia. In the present study, they now investigated whether the slower reading speed among children with amblyopia could be attributed to binocular inhibition or a deficit in the fellow (non-amblyopic) eye. This was accomplished by comparing the reading rates during silent reading of 100-word passages using the ReadAlyzer computer-assisted infrared eye tracking system between children with anisometropic or strabismic amblyopia and age-matched controls and further comparing the reading rates of the amblyopic children when reading binocularly versus when reading with the amblyopic eye occluded.

The study participants were children aged 7 to 13 years; those with strabismus >4 prism diopters were excluded owing to ReadAlyzer's technical limitations. Amblyopia was defined by an interocular difference in visual acuity of ≥0.2 logMAR, with the amblyopic eye having a best-corrected visual acuity of ≥0.2 logMAR and the fellow eye having a best-corrected visual acuity of ≤0.1 logMAR. Age-matched controls without a history of visual disorders and with normal visual acuity and stereoacuity were also recruited. All participants had English as their primary language. The amblyopic and non-amblyopic pools were matched for socioeconomic status and reading comprehension. The analyzed samples included 38 children with amblyopia (mean age, 10.0 ± 1.5 years) and 36 control children (10.3 ± 1.7 years). There were no significant differences between the two groups in terms of the last grade completed or binocular or fellow-eye reading comprehension.

As in their previous research, the authors found that children with amblyopia read more slowly, with average binocular reading rates of 176 ± 60 words per minute (wpm) versus 217 ± 83 wpm for non-amblyopic children. Additionally, they found that amblyopic children read more slowly than their age-matched peers when the amblyopic eye was occluded, at 173 ± 53 wpm. To directly compare this monocular situation for non-amblyopic children, the control group was evaluated with their left eyes occluded, resulting in a mean reading rate of 213 ± 75 wpm. The authors also examined other key metrics of reading eye movements measured using the ReadAlyzer, including the number of forward saccades, regressive saccades, and fixation duration. The amblyopic group exhibited more forward saccades than the control group, indicating that the amblyopic children in this study had smaller spans of recognition and had to make more saccades to complete the 100-word passages than the non-amblyopic children. This finding was consistent whether the amblyopic children were reading with both eyes open or with the amblyopic eye occluded. Interestingly, there were no differences in fixation duration; thus, the slower reading speed for amblyopic children appears to be a direct result of them having to make more saccades, not taking longer for each fixation.

This study and the prior studies published by Kelly and co-authors are important because they demonstrate that, on average, children with amblyopia have visual deficits that exist and impact major life activities, such as reading, regardless of whether the amblyopic individual is reading with both eyes open or when the amblyopic eye is occluded. Therefore, it is incumbent on all eye care practitioners to carefully evaluate visual functioning that may have an impact on reading or other occupational or academic activities in all individuals with amblyopia. If an individual with amblyopia objectively demonstrates slower reading speed, as is shown to be possible in this study and the authors’ prior studies, accommodations for test taking and other reading-related tasks should be considered.