Measuring Exotropia

Rod Foroozan, MD


April 25, 2008


Exotropia may be constant or intermittent.[1,2] When exotropia is intermittent, it may be asymptomatic for periods, during which the patient has fusional control, and then may cause episodes of blurred or binocular double vision. A common method to judge the severity of exotropia is to measure the angle of ocular misalignment.

The authors of this prospective case series studied 25 patients with intermittent exotropia to determine the change in fusional control (as determined with a 6-point scale) over the course of 1 day and to evaluate potential changes in the degree of ocular misalignment as measured over time. In addition, interobserver variability was determined.

Variability of Control in Intermittent Exotropia

Hatt SR, Mohney BG, Leske DA, Holmes JM
Ophthalmology. 2008;115:371-376.e2


In 17 patients who were assessed for interobserver variability, the agreement between observers was high. (Greater than or equal to a 2-point difference on the scale was used to indicate a change.) There was a high level (24%) of minute-to-minute variability. Of the 13 patients studied over 1 day, 6 (46%) showed a change in fusional control of the exotropia. Two of these were at distance fixation only, 3 at near only, and 1 at near and distance.


Although a particular measurement of exotropia may be a sensitive measure of ocular deviation, the study authors noted that control of intermittent exotropia was variable, not only throughout the day, but minute-to-minute as well. These findings suggest that because of the variability, single measures of exotropia may be inadequate to fully judge the severity of intermittent exotropia. The study authors suggest that for important clinical decisions, such as whether to perform surgery, it may be necessary to perform multiple measurements of exotropia.

A commonly presumed finding in intermittent exotropia, and strabismus in general, is that fusional control worsens with fatigue as the day progresses. The findings of this study did not substantiate this notion because none of the patients who were studied over a 1-day period had the greatest amount of exotropia measured at the last timepoint. In addition, the level of fusional control did not completely correlate to the amount of ocular misalignment. The study authors admitted that their study population was small, but still concluded that a single measurement is likely inadequate to determine the severity of intermittent exotropia for an individual patient.



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