Related Experiment Video
Updated: May 22, 2026
Assessing Binocular Central Visual Field and Binocular Eye Movements in a Dichoptic Viewing Condition
Published on: July 21, 2020
Impact of Viewing Distance on the Occurrence Rate of Intermittent Exotropia Revealed by Ambulatory Eye Tracking
John R Economides1, Jonathan C Horton1
1From the Program in Neuroscience, Department of Ophthalmology, University of California, San Francisco, San Francisco, California, USA.
Purpose:
Eye tracking in ambulatory patients permits measurement of the occurrence rate of intermittent exotropia. This information is useful for deciding which patients need surgery. However, viewing distance can influence the occurrence rate, creating a potential confound. To address this issue, an approach was devised to break down the overall occurrence rate into separate components, compiled during either near viewing or far viewing.
Design:
Prospective cross-sectional study.
Subjects:
This study included 35 patients with intermittent exotropia, ranging in age from 3 to 79 years, with a median of 10 years.
Methods:
Eye-tracking glasses were used to record each eye's horizontal position while subjects engaged in their customary daily activities. Scene video was reviewed to parse the data into epochs of near viewing vs far viewing.
Main Outcome Measures:
Four exotropia occurrence rates were calculated: (1) overall rate before segmentation by viewing distance, (2) overall rate after segmentation by viewing distance, (3) rate during near viewing only, and (4) rate during far viewing only. In addition, eye positions during near viewing and far viewing were compared to assess convergence effort during exotropia.
Results:
In participants with a low occurrence rate, exotropia occurred mostly during distance viewing. As the occurrence rate increased, exotropia became more common during near viewing. For 28 of 35 patients, segmentation of data into near vs far viewing had a negligible impact on the overall occurrence rate. However, in 7 patients, this process revealed a near exotropia peak partially hidden in the orthotropia far peak, which resulted in a higher overall exotropia occurrence rate after segmentation by viewing distance. Comparison of exotropia amplitude during near vs far viewing showed that convergence effort varied widely among deviated subjects and, surprisingly, bore no relationship to the overall rate of exotropia occurrence.
Conclusions:
Partitioning of data recorded with eye-tracking glasses into near viewing vs far viewing allows a more accurate assessment of the overall rate of exotropia occurrence. A major advantage is that the impact of viewing distance associated with various activities is neutralized because separate exotropia occurrence rates are provided for near vs far viewing. Incorporation of range-finding capability into currently available mobile eye trackers would enhance their utility for the evaluation of patients with exotropia.
