Krista Kelly¹ (), Dorsa Mir Norouzi², YiZhong Wang²; ¹University of Waterloo, ²Retina Foundation of the Southwest

Introduction: Children with amblyopia silently read paragraphs 28% slower than their peers during binocular viewing, which is associated with ocular motor dysfunction (i.e., fixation instability, increased forward saccades). We previously reported slow reading even when the need for inter-word saccades is removed using rapid serial visual presentation (RSVP) (Mir Norouzi VSS 2022). Yet, this does not necessarily rule out a role for ocular motor dysfunction in slow reading. Here, we report on fixation instability during RSVP reading in amblyopic children compared to controls. Methods: Amblyopic (n=33) and control (n=30) children ages 8-12 years silently read grade-appropriate sentences presented in RSVP (single word presentation at screen center) during binocular viewing. Exposure time per sentence changed using a descending adaptive 2 down-1 up staircase method. The child’s reading speed threshold in log words per minute (WPM) was obtained. Eye movements were tracked simultaneously with the EyeLink 1000 binocular eye tracker to determine fellow eye (FE) and amblyopic eye (AE) fixation stability (log BCEA) during reading. Results: Compared to controls, amblyopic children read slower (2.8±0.5 log WPM vs 3.1±0.4 log WPM, p=0.009), and had increased AE fixation instability (0.21±0.39 log BCEA vs −0.20±0.18 log BCEA, p<0.001) and increased FE fixation instability (−0.03±0.34 log BCEA vs −0.20±0.15 log BCEA, p=0.012) during RSVP reading. Reading rate in amblyopic children with good FE stability (n=11) did not differ from controls (p=0.63) and was faster than those with poor FE stability (p=0.026). Amblyopic children with poor FE stability read slower than controls (p=0.001). Conclusions: Amblyopic children read slower than control children, even when the need for inter-word saccades is removed (i.e., RSVP reading). The direct relationship of slow RSVP reading with poor FE fixation stability during binocular viewing provides support for fixation instability as a source of slow natural reading in children with amblyopia.

Acknowledgements: National Institutes of Health – National Eye Institute EY028224