Reading Individual Words in Sentences in Infantile Nystagmus

Purpose: Normal readers make immediate and precise adjustments in eye movements during sentence reading in response to individual word features, such as lexical difficulty (e.g. common or uncommon words) or word length. Our purpose was to assess the effect of infantile nystagmus (IN) on these adaptive mechanisms. Methods: Eye movements were recorded from 29 participants with IN (14 albinism, 12 idiopathic and 3 congenital stationary night blindness) and 15 controls when reading sentences containing either common / uncommon words or long / short target words. Parameters assessed included: duration of first foveation / fixation, number of first-pass and percentage second-pass foveations / fixations, percentage words skipped, gaze duration, acquisition time (gaze + non-gaze duration), landing site locations, clinical and experimental reading speeds. Results: Participants with IN could not modify first foveation durations in contrast to controls who made longer first fixations on uncommon words (P<0.001). Participants with IN made more first-pass foveations on uncommon and long words (P<0.001) to increase gaze durations. However, this also increased non-gaze durations (P<0.001) delaying acquisition times. Participants with IN re-read shorter words more often (P<0.005). Similar to controls, participants with IN landed more first foveations between the start and center of long words. Reading speeds during experiments were lower in IN participants compared to controls (P<0.01). Conclusions: People with IN make more first-pass foveations on uncommon and long words influencing reading speeds. This demonstrates that the ‘slow to see’ phenomenon occurs during word reading in IN. These deficits were not captured by clinical reading charts.