Capturing the Moment of Fusion Loss in Intermittent Exotropia.
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ABSTRACT: To characterize eye movements made by patients with intermittent exotropia when fusion loss occurs spontaneously and to compare them with those induced by covering 1 eye and with strategies used to recover fusion.Prospective study of a patient cohort referred to our laboratory.Thirteen patients with typical findings of intermittent exotropia who experienced frequent spontaneous loss of fusion.The position of each eye was recorded with a video eye tracker under infrared illumination while fixating on a small central near target.Eye position and peak velocity measured during spontaneous loss of fusion, shutter-induced loss of fusion, and recovery of fusion.In 10 of 13 subjects, the eye movement made after spontaneous loss of fusion was indistinguishable from that induced by covering 1 eye. It reached 90% of full amplitude in a mean of 1.75 seconds. Peak velocity of the deviating eye's movement was highly correlated for spontaneous and shutter-induced events. Peak velocity was also proportional to exotropia amplitude. Recovery of fusion was more rapid than loss of fusion, and often was accompanied by interjection of a disconjugate saccade.Loss of fusion in intermittent exotropia is not influenced by visual feedback. Excessive divergence tone may be responsible, but breakdown of alignment occurs via a unique, pathological type of eye movement that differs from a normal, physiological divergence eye movement.
<h4>Purpose</h4>To characterize eye movements made by patients with intermittent exotropia when fusion loss occurs spontaneously and to compare them with those induced by covering 1 eye and with strategies used to recover fusion.<h4>Design</h4>Prospective study of a patient cohort referred to our laboratory.<h4>Participants</h4>Thirteen patients with typical findings of intermittent exotropia who experienced frequent spontaneous loss of fusion.<h4>Methods</h4>The position of each eye was recorde ...[more]
