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Fixation disparity in binocular stress.
L D Pickwell1, T C Jenkins, A A Yetka
1School of Studies in Optometry, University of Bradford, U.K.
Summary
Reading in low light can increase visual stress and alter fixation disparity, particularly in near vision. This study found that inadequate illumination, when combined with other visual stressors, significantly impacts binocular vision function.
Area of Science:
- Optometry
- Vision Science
- Ophthalmology
Background:
- Fixation disparity is a known indicator of stress on binocular vision.
- Prism-induced stress reliably creates fixation disparity.
Purpose of the Study:
- To investigate the impact of visual stress from reading in inadequate illumination on fixation disparity.
- To determine if reduced illumination alone or in combination with other stressors affects binocular vision.
Main Methods:
- Subjects read under reduced illumination conditions.
- Fixation disparity and associated heterophoria were measured.
- Changes in fixation disparity curves and reported symptoms of stress were analyzed.
Main Results:
- Reduced illumination alone did not immediately alter fixation disparity magnitude.
- An increased mean slope in the central fixation disparity curve was observed.
- Reading in reduced light for 30 minutes increased mean associated heterophoria and symptoms of stress in over half of subjects.
Conclusions:
- Visual stress from reading in inadequate illumination can alter fixation disparity in some individuals.
- Near vision fixation disparity tends to increase towards exo-disparity under these conditions.
- The majority of this increase occurs within the first ten minutes of exposure.