Assessing the contribution of eye movements to slow binocular reading in children with amblyopia

Introduction: Previous research has shown a relationship between slow silent reading in amblyopic children and ocular motor dysfunction (i.e., fixation instability, increased forward saccades) during binocular viewing (1,2). Here, we investigated the hypothesis that children with amblyopia will read at a similar speed as controls if the need for inter-word saccades is removed during binocular reading. Methods: Silent reading was assessed during binocular viewing in amblyopic children aged 7-12 years and compared to an age-similar control group. Children silently read grade-appropriate sentences presented in rapid serial visual presentation (RSVP; single word presentation at screen center). Participants were asked a ‘yes/no’ question after each sentence. Words in each sentence had the same exposure time. Exposure time per sentence changed based on a descending adaptive 2 down-1 up staircase method to determine the child’s reading speed threshold in log words per minute (WPM). Results: A total of 16 amblyopic children (mean age±SD=9.6±1.3 years, mean amblyopic eye visual acuity±SD=0.4±0.2 logMAR) and 14 control children (10.1±1.2 years, 0.0±.00 logMAR) were enrolled. During binocular viewing, amblyopic children read slower than age-matched controls (2.6±0.5 log WPM vs 3.0±0.4 log WPM, U=64, p=0.044). Conclusions: Amblyopic children read slower than control children, regardless of whether the text is presented in a fixed location (i.e., RSVP reading) or if the reader has to scan the text in a conventional manner (i.e., paragraph reading). Removing the need for inter-word saccades during silent, binocular reading does not help amblyopic children to read at a similar speed as controls. However, this finding does not rule out a role for other types of ocular motor dysfunction such as fixation instability in slow reading. Other possible factors to slow reading in amblyopia may be crowding and reduced visual span. Slow reading in children with amblyopia may hinder academic success.