Fellow Eye Deficits in Amblyopia

Abstract

Amblyopia is a neurodevelopmental disorder of the visual system, as a result of discordant visual experience during infancy or early childhood. Because amblyopia is typically defined as monocularly reduced visual acuity accompanied by one or more known amblyogenic factors, it is often assumed that the fellow eye is normal and sufficient for tasks like reading and eye-hand coordination. Recent scientific evidence of ocular motor, visual, and visuomotor deficits that are present with fellow eye monocular viewing and with binocular viewing calls this assumption into question. This clinical update reviews the research that has revealed fellow ocular motor and visual deficits and the effect that these deficits have on an amblyopic child's visuomotor and visuocognitive skills. We need to understand how to prevent and rehabilitate the effects of amblyopia not only on the nonpreferred eye but also on the fellow eye.

Keywords: Amblyopia; fellow eye; motion perception; motor skills; ocular motor.

Figure 1

Unpublished monocular viewing data from the cohort described in Kelly et al showing larger mean fellow eye instability for 85 amblyopic children (light gray bars) and 55 nonamblyopic children with strabismus or anisometropia (white bars), compared with 43 normal control children (dark grey bars). Error bars represent ±SE. *significantly different than controls (p<0.01).

Figure 2

Mean fellow eye instability and vergence instability during binocular viewing for 98 amblyopic children (light gray bars), 62 nonamblyopic children with strabismus or anisometropia (white bars), and 46 normal control children (dark grey bars). Amblyopic and nonamblyopic children exhibited larger fixation and vergence instability compared to controls. Error bars represent ± SE. *significantly different than controls (p<0.01).

Figure 3

Left: global motion stimuli with 100% coherence (top) and 75% coherence (bottom). Right: motion-defined form stimuli with 100% coherence (top) and 75% coherence (bottom). Arrows were added to illustrate the direction of motion of each dot. The dotted-line boxes were added to illustrate the target shape. Neither the arrows nor the boxes were present in the actual stimulus displays.

Figure 4

% of children with amblyopia who had a deficit in perception of global motion direction (left) or motion-defined form orientation (right) when viewing with their fellow eye, compared with controls. Thresholds for both tasks were measured by the minimum percentage of coherently moving signal dots required for accurate discrimination.

Figure 5

Mean reading rate (words per minute) and number of forward saccades (per 100 words) assessed with the Readalyzer ® during binocular viewing (grey bars) and fellow eye viewing (white bars) for 49 amblyopic children No differences were found (ps≥0.50). Error bars represent ± SE. The dashed line represents previously published control data for binocular reading.

Figure 6

Mean standard scores for manual dexterity tasks completed during binocular viewing for 129 amblyopic children (light gray bars), 47 nonamblyopic children with strabismus (white bars), and 40 normal control children (dark grey bars). Amblyopic children had lower scores for all three tasks compared to controls. Nonamblyopic children with strabismus had lower scores on the bimanual and drawing trail tasks compared with controls. Error bars represent ± SE. *significantly different than controls (p<0.01).

Figure 7

% of amblyopic children who have a fellow eye deficit for motion-defined form perception in subgroups with randot stereoacuity of 1.6–2.9 log arcsecs (Yes) vs nil stereoacuity (No), with macular/foveal fusion by Worth 4-dot test (Yes) vs peripheral/no fusion, and with prior binocular amblyopia treatment (Yes) vs no prior binocular treatment (No).