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Krista R Kelly, Christina Cheng-Patel, Reed M Jost, Eileen E Birch; Fixation instability during binocular viewing in strabismic and anisometropic children. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5796.
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Strabismus or anisometropia disrupts binocularity and results in fixation instability, which is amplified by amblyopia. Fixation instability has typically been assessed for each eye individually. Recently, vergence instability was reported in exotropic adults and monkeys when binocularly fixating. We evaluated fixation instability during binocular viewing in children with surgically corrected esotropia or anisometropia.
174 children age 3-13 years with treated esotropia and/or anisometropia (111 amblyopic [0.2–1.2 logMAR], 63 nonamblyopic) were compared to 46 age-similar controls. Fixation instability was recorded during binocular fixation of a 0.3 deg dot for 20 seconds using a 500 Hz remote video binocular eye tracker (EyeLink 1000; SR Research) at a viewing distance of 115 cm. The bivariate contour ellipse area (BCEA; log deg2) for fixation instability was calculated per eye and for vergence instability (left eye position – right eye position). Best-corrected visual acuity (BCVA), Randot Preschool stereoacuity, and extent of suppression scotoma (Worth 4-Dot) were also obtained.
When binocularly fixating, children with strabismic amblyopia had greater nonpreferred eye instability, greater preferred eye instability, and greater vergence instability than controls (ps<0.001). Children with strabismic nonamblyopia also had greater nonpreferred eye instability (p<0.001), greater preferred eye instability (p=0.018), and greater vergence instability (p<0.001) than controls. Children with anisometropic amblyopia had greater nonpreferred eye instability (p=0.029), and greater vergence instability (p=0.005), but similar preferred eye instability (p=0.037) compared to controls. Children with anisometropic nonamblyopia did not differ from controls on any measure. Nonpreferred eye instability was related to poorer stereoacuity (p=0.001) and a larger suppression scotoma (p<0.001). Preferred eye instability was related to a larger suppression scotoma (p=0.027). Vergence instability was related to poorer stereoacuity (p=0.036) and a larger suppression scotoma (p=0.001). No relationships were found for BCVA.
Fixation instability during binocular viewing suggests that a disruption in binocularity interferes with ocular motor development, especially for strabismus. Vergence instability may limit potential for recovery of binocular vision in these children.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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