Amblyopia Treatment Part 2 -
A Binocular Approach
In last month's newsletter, we looked at how the treatment of amblyopia is changing from a monocular to a binocular approach. In this edition, we will explore the binocular approach in more detail.
Amblyopia is a neuro-developmental disorder of binocular vision and is the most common form of reversible blindness. The condition results in reduced eyesight in one eye and thus, reduced depth perception and delays in visual processing and visual-motor coordination. Untreated amblyopia can also negatively impact a child's self-esteem, his/her work and school life, and his/her relationships with friends and family members due to the physiological impact that occlusion therapy (patching) can have on the individual. Amblyopia is a result of the individual's coping mechanism to an inability for him/her to use the two eyes efficiently and effortlessly together. This is why the treatment needs to be a binocular solution.
As discussed last month, the treatment protocol of occlusion therapy is an outdated and largely ineffective approach to a complex and serious binocular vision disorder. The conventional treatment protocol which advises a full spectacle correction of refractive error in the amblyopic eye, and either full- or part-time direct occlusion, is now considered an outdated approach as it does not address the underlying binocular nature of the condition. Developmental optometrists have advanced amblyopia treatment far beyond just refractive and passive occlusion methods. One goal of vision therapy in the treatment of amblyopia is to develop equal monocular skills first, which will then aid in the development of efficient binocular vision. Robert Hess, director of vision research at McGill University, showed in a 2011 study that, "...amblyopes possess cortical cells with binocular connections, but that under binocular viewing suppressive mechanisms render their cortex functionally monocular. The consequence is that amblyopia is an intrinsically binocular problem and not the monocular problem on which current patching treatment is predicated."
In order to work the amblyopic eye but continue to encourage the development of binocularity in amblyopic patients, vision therapists use a concept called MFBF - monocular fixation in a binocular field. These procedures work one eye at a time - monocular - but at the same time, the procedure only works if both eyes are open and seeing at the same time -in a binocular field. This is accomplished by using anaglyphic (red/green or red/blue) filters so both eyes are used to see the activity, but only one eye at time is actually seeing the target. One eye sees the central target/detail while the other eye sees the background in the same space. Successful use of this technique encourages accurate perception of details with one eye and the perception of the background with the other eye. A range of activities from accommodation and fixation, to pursuits and saccades can be worked with MFBF therapy techniques. If the patient is unable to see the target or the target starts fading, this is an indication that the amblyopic eye is being suppressed. From the same study mentioned above, Hess notes, "...that prolonged periods of viewing during which information from the two eyes is combined leads to a strengthening of binocular vision...and eventual combination of binocular information under natural viewing conditions. Concomitant improvement in monocular acuity of the amblyopic eye occurs with this reduction in suppression and strengthening of binocular fusion. Furthermore,...stereoscopic function is established." This advanced amblyopia treatment paradigm, which is based on the latest neuroscience about the visual brain and amblyopia, yields better and faster results than conventional monocular (patching) treatment protocols, and is also more enjoyable to the patient which eliminates compliance concerns.
Once MFBF is established, vision therapy treatment for patients with amblyopia moves on to establish equal monocular skills (including oculomotor, accommodative, visual spatial awareness, and visual processing skills), contrast sensitivity development, binocular skills (including fusion and stereopsis) and finally, an expanded range of fusion.
A 1995 article written by Israel Greenwald, OD, FCOVD, FAAO describes a binocular approach to the correction of strabismic amblyopia developed by Frederick Brock, OD. In it, he includes this quote from Brock, "We should never lose sight of the fact that an amblyopic eye has its greatest usefulness in combination with the good eye when their planes of orientation coincide." Thanks to the latest neuroscience research available, developmental optometrists are creating a more current and accurate way to treat amblyopia - one that yields better results and affords amblyopic patients the chance to become truly binocular.