Why effective Amblyopia treatment requires binocular vision rehabilitation

Recognized as a significant vision problem that affects millions of people worldwide, one of the “hot topics” of  advocacy at the recent 2019 VisionHelp Annual Meeting  was Amblyopia. 

Amblyopia/Lazy eye is a serious neurodevelopmental vision problem that causes vision loss in approximately 2-4% of the population or 1 in 30 people. Neuroscience has shown that Amblyopia occurs when there is a unilateral failure in binocular vision, occurring early in life typically infancy or toddlerhood.

When the binocular system is broken at a young age, a neuroadaptation occurs, known as suppression where the signal from one eye is “shut down” by the brain to counteract the confusion created by the broken binocular system. As a result of this unilateral failure of binocular function a cascade of delayed visual function occurs leading to the following:

  1. Reduced visual acuity (eye sight) in one eye
  2. Reduced, or no stereo acuity (depth perception)
  3. Poor saccadic eye movement 
  4. Poor visual processing ability
  5. Poor eye hand coordination

Thus, due to a failure in binocular vision, a spiral of visual problems occurs that is much more involved than visual acuity of one eye. But, because visual acuity is reduced in one eye even with best correction, Amblyopia is one condition in optometry and ophthalmology that should never be misdiagnosed or overlooked.

The issue presented at VisionHelp 2019 was, in spite of the obvious hard to miss diagnosis of Amblyopia, as well as the impact of a failed binocular visual system on a patient’s life that supersedes the visual acuity loss in one eye, there is a need to improve professional and public understanding for effective Amblyopia management.

Indeed, even though patching for Amblyopia has been around for 300 years, it still is touted on many notable sources to be the treatment of choice for amblyopia. In fact, patching the non-amblyopic eye, either part-time or full-time, is evidence-based and outlined in various PEDIG Amblyopia Treatment Study (ATS) research clinical trials. These ATS clinical trials have shown a moderate amount of improvements in the visual acuity function of the amblyopic eye with occlusion therapy. However, what the PEDIG ATS research doesn’t show is that patching has a multitude of negative side-effects that are outlined in several other research papers. In addition visual acuity gains often regress when the treatment ends, plus and even more important, patching does not repair the broken binocular visual system which is the underlying cause for patient’s amblyopia.

It should seem fairly obvious that you can not repair a broken binocular system by patching an eye. Patching only re-enforces the failure of binocular vision. Therefore, 3-D, depth perception, ie stereo acuity, which is a measure of the quality of binocular vision, is ignored when a patient is sent home to wear an eye patch.

Therefore, using an occlusion-based model of treatment, stereo acuity does not develop nor do the related other conditions involving poor micro eye movement, poor visual processing and poor eye hand coordination.

Additionally, while there have been recent studies that have tried to explore binocular vision treatment for amblyopia, (PEDIG ATS-18) due the treatment design centered around a home-based model with once a month office monitoring (for 16 weeks), compliance by the patient was very poor resulting in less than optimal outcomes. Even though previous clinical trials exploring the best modality of delivery of care has proven that home-based models are no more effective than a placebo, the investigators of the recent PEDIG ATS-18 study presumably made the assumption that  a home-based model of treatment, with once every 4 weeks office monitoring, would somehow substitute for the professional guidance of an office-based model and get better compliance presumably because the binocular activity was an iPad game.

So, it was no surprise that with only once a month visits to the clinic over 16 weeks,  the compliance results for the two age categories being studied with the binocular video game were substantially below the required time to get results. For the two groups studied, age 5-12 year old, the compliance was 22% and for the 13-18 year old the compliance dropped to 13%.

Yet, instead of showing that the research subjects did not follow the prescribed dosing time, based on guidelines set by previous cohort studies, they simply concluded that binocular vision therapy was not effective. 

In conclusion, it’s important for professionals and patients to understand that the loss of monocular best corrected eyesight in Amblyopia is due to a broken binocular system. Due to this failure in binocular vision, effective treatment must include the vision rehabilitation of visual processing, oculomotor/saccadic eye movement, eye-hand coordination that begins with vision rehabilitation of the binocular visual system. The progress in vision rehabilitation should be measured not just based on visual acuity, but also stereo acuity and specific tests of visual processing and eye-hand coordination. Furthermore, research shows that effective developmental vision rehabilitation must be office-based with home support that is closely monitored and altered as needed to get consistent compliance and results. 

The VisionHelp Guidelines show that for treatment to be most effective, the following is recommended:

  1. To establish the diagnosis and various elements of treatment, the patient must have a comprehensive developmental vision evaluation including eye health, refraction, establishing optimal lenses for best corrected visual acuity,  binocular vision assessment, including measure of stereo acuity, oculomotor assessment, visual perceptual evaluation, and visual motor integration evaluation.
  2. Prescribed treatment should be 45-60 minutes office-based vision therapy, 1-2 times per week, with 1 hour per day of home activities that require close support by the supervising doctor and/or vision therapist.
  3. Home activities must have sufficient novelty and high level binocular stimulation including stereo acuity development. (examples: virtual reality in vision therapy
  4. Weekly progress on visual acuity, sensory fusion, suppression zone, stereo acuity. When these areas are not making expected progress the treatment activities and compliance must be carefully analysed with proper adjustments made to bring about improvements. 

Only when the complexity of Amblyopia is addressed with a comprehensive developmental vision rehabilitation delivery of care model, will patients have the chance to have successful outcomes in their amblyopia treatment. We must begin to realize that the best care for patients with amblyopia goes beyond patching.

For more information, the VisionHelp Amblyopia Project provides treatment protocols for most effective results.

Dan L. Fortenbacher, O.D.,FCOVD

3 thoughts on “Why effective Amblyopia treatment requires binocular vision rehabilitation

  1. Agreed, the PEDIG conclusion should have underscored the importance of office-based treatment under professional supervision, rather than labeling it an ineffective treatment.

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