The Initiation of Smooth Pursuit is Delayed in Anisometropic Amblyopia

Abstract

PurposeSeveral behavioral studies have shown that the reaction times of visually guided movements are slower in people with amblyopia, particularly during amblyopic eye viewing. Here, we tested the hypothesis that the initiation of smooth pursuit eye movements, which are responsible for accurately keeping moving objects on the fovea, is delayed in people with anisometropic amblyopia.MethodsEleven participants with anisometropic amblyopia and 14 visually normal observers were asked to track a step-ramp target moving at ±15°/s horizontally as quickly and as accurately as possible. The experiment was conducted under three viewing conditions: amblyopic/nondominant eye, binocular, and fellow/dominant eye viewing. Outcome measures were smooth pursuit latency, open-loop gain, steady state gain, and catch-up saccade frequency.ResultsParticipants with anisometropic amblyopia initiated smooth pursuit significantly slower during amblyopic eye viewing (206 ± 20 ms) than visually normal observers viewing with their nondominant eye (183 ± 17 ms, P = 0.002). However, mean pursuit latency in the anisometropic amblyopia group during binocular and monocular fellow eye viewing was comparable to the visually normal group. Mean open-loop gain, steady state gain, and catch-up saccade frequency were similar between the two groups, but participants with anisometropic amblyopia exhibited more variable steady state gain (P = 0.045).ConclusionsThis study provides evidence of temporally delayed smooth pursuit initiation in anisometropic amblyopia. After initiation, the smooth pursuit velocity profile in anisometropic amblyopia participants is similar to visually normal controls. This finding differs from what has been observed previously in participants with strabismic amblyopia who exhibit reduced smooth pursuit velocity gains with more catch-up saccades.

The functional impact of amblyopia

“…While amblyopic eyes show poorer fixation stability than control eyes during both monocular and binocular viewing, fellow eyes have fixation stability comparable to that of controls, both when fixating or under binocular viewing . However, the initiation of tracking pursuits is delayed and saccadic latency of the non‐amblyopic eye can be less accurate than in age‐matched controls …”

“…Oculomotor deficits including inaccurate or unsteady fixation, delayed and more variable initiation of saccades, and inaccurate tracking pursuits have been recorded in amblyopic subjects . While amblyopic eyes show poorer fixation stability than control eyes during both monocular and binocular viewing, fellow eyes have fixation stability comparable to that of controls, both when fixating or under binocular viewing .…”

Visuomotor Behaviour in Amblyopia: Deficits and Compensatory Adaptations

“…In contrast, individuals with anisometropic amblyopia show relativity fewer deficits. Specifically, a recent study showed that the mean pursuit gain of both eyes was comparable to visually normal controls; however, pursuit initiation was slightly delayed (~20 ms), and the gain was more variable in the amblyopic eye [107].…”

Simplified updates on the pathophysiology and recent developments in the treatment of amblyopia: A review

“…Moreover, recovery from amblyopia is expedited by tasks requiring coordination of hand and eye movements, such as having patients manipulate objects during visual training as reviewed in Daw, in 2013. Several researchers have pointed out that patients with amblyopia exhibit oculomotor impairments including problems with saccadic eye movements,[80] smooth pursuit,[81] fixation stability,[82] hand--eye coordination,[83] thus suggesting that targeting visuomotor circuits during treatment may help to alleviate some of these deficits. [84]…”