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Fixation Preference in Intermittent Exotropia Quantified Using a Wearable Eye Tracker
John R Economides1, Jonathan C Horton1
1From the Program in Neuroscience, Department of Ophthalmology, University of California San Francisco, San Francisco, California, USA.
Purpose:
To measure eye fixation preference in patients with intermittent exotropia using a wearable binocular eye tracker that records the position of each globe within the orbit.
Design:
Prospective assessment validity analysis.
Subjects:
Forty patients referred to a single pediatric ophthalmologist for evaluation of intermittent exotropia.
Methods:
Ambulatory patients wore eye tracking glasses for up to 12 hours to monitor their ocular alignment while carrying out their usual daily activities. Histograms were prepared of each eye's horizontal position as a function of vergence angle. Epochs of exotropia were extracted and replotted to show each eye's horizontal position as a function of relative time. The centration of each eye's horizontal position profile, relative to 0°, provided a quantitative index of eye fixation preference. This result was compared to eye fixation preference, determined previously in the clinic, to gauge the accuracy of clinical assessment.
Main Outcome Measures:
Clinical assessment of eye fixation preference compared with data provided by the eye tracker.
Results:
Eye fixation preference ranged between 53% and 100%, with a mean value of 72%. There was no correlation between the strength of eye fixation preference and exotropia occurrence rate or amplitude. Clinical examination usually found a stronger eye fixation preference than measured by the eye tracker. In 9 patients rated as having a strong eye fixation preference by cover/uncover test, the eye tracker detected none. In 4 cases, clinical examination assigned eye fixation preference to the wrong eye.
Conclusions:
In addition to occurrence rate, eye tracking glasses can be used to quantify eye fixation preference in patients with intermittent exotropia. Such data show that clinical examination is often inaccurate in determining eye fixation preference. Information from eye tracking about which eye deviates most frequently is particularly important if a unilateral recess-resection operation is planned to correct exotropia.
