Chances are by now you’ve heard about the new paradigm in amblyopia treatment emphasizing a binocular approach to therapy, as reviewed extensively in The Amblyopia Project.
A new article in the August issue of Investigative Ophthalmology & Vision Science adds to that body of evidence, and reinforces that vision in the fellow eye is negatively impacted by amblyopia. The amblyopic or “lazy” eye tends to get all of the attention because visual acuity through that eye is clearly not as sharp as through the other eye. In fact, that’s how most people still conceive of amblyopia despite all the evidence showing that reduced visual acuity is only the tip of the iceberg.
The new article we’re talking about in IOVS is titled Impaired Fellow Eye Motion Perception and Abnormal Binocular Function. It notes that binocular discordance due to strabismus, anisometropia, or both may result in not only monocular visual acuity deficits, but also in motion perception deficits. The specific deficit studied here is called motion-defined form perception, or MDF – the ability to identify a two-dimensional shape defined by motion rather than luminance contrast.
The idea here involves a coherent motion display, in which the subject has to judge the direction of moving dots or squares, a fixed proportion of which are moving in a specified or coherent direction. The display in the IOVS paper includes the following figure and explanation.
Top: MDF stimulus showing a horizontal rectangle defined by 100% coherently moving dots moving upward inside of a central horizontal rectangular area and 100% coherently moving dots moving downward outside of the rectangular area (i.e., a long spaceship). Bottom: The stimulus appearance when motion coherence is reduced to 75%; 25% of the dots are moving in random directions both inside and outside the rectangular area. Yellow dotted lines are not present on the display during testing; they have been added to the figure only to highlight the rectangular borders of motion contrast.
The bottom line of the study is that fellow eye MDF deficits were common in 7- to 12-year-old children with residual amblyopia, occurring in 23% of the cases, and to a similar extent through the amblyopic eye when treatment was limited to patching. When stereoacuity was present, the percentage of children with MDF deficits in the amblyopia and fellow eye went down considerably, between 4 and 7%. When stereoacuity was absent, the presence of MDF deficits rose dramatically, to 36%. This is not surprising when we conceive of amblyopia as a binocular vision deficit.
The article concludes as follows: “Fellow eye MDF deficits were significantly more common among those treated with patching than among those who had binocular amblyopia treatment. We were also able to observe that binocular amblyopia treatment was associated with a reduction in mean fellow eye MDF threshold and a higher proportion of children with fellow eye MDF thresholds within the normal range. These data support the effectiveness of binocular amblyopia treatment, designed to decrease or eliminate suppression and provide binocular visual experience in rehabilitating fellow eye deficits.”