New Research- Binocular Vision Therapy faster and better results in Amblyopia Treatment

When it comes to modern treatment of eye disease there is a strong emphasis in the current literature and continuing education on the latest and most advanced methods for quality patient care.

Surely, are there any ocular diseases or visually impairing conditions, such as cataracts, glaucoma or dry eye disease, where a doctor’s prescribed treatment approach centers around a method developed 100+ years ago?

The answer is none, except…Amblyopia. 

Amblyopia, otherwise known as Lazy Eye, is the most common form of monocular visual impairment affecting approximately 3% of the population worldwide. This condition is one that Dr. Leonard Press and I have blogged about extensively over the last 10 years on the VisionHelp Blog. Many of our posts on this topic describe, to some degree, our frustration with the persistence of  many doctors to solely prescribe the conventional 100+ year old treatment approach involving occlusion (eye patching) or penalization (atropine drops) of the fellow eye, when more modern and efficacious treatments are available. The modern treatment methods for amblyopia involve binocular vision therapy which treats the etiology of amblyopia beginning with a dysfunction of binocular vision causing suppression in the amblyopic eye. This has been documented extensively by the research of Dr. Robert Hess and many others during the last 20+ years. 

And now we have more new research that supports the premise that the best results for those with amblyopia is to prescribe binocular vision therapy along with traditional methods. To better explain, published on January 31, 2022 in the Open Access BMC Ophthalmology Journal, is the research paper entitled: Efficacy of vision therapy for unilateral refractive amblyopia in children aged 7-10 years. 

The author’s Conclusions state: “Vision therapy combined with conventional treatment (optical correction and part-time patching) is more effective than conventional treatment alone in children aged 7-10 years with unilateral refractive amblyopia. The treatment results in not only greater vision gain, but also in shorter duration of treatment.”

One particularly impressive aspect of this research paper was the thoroughness of the Discussion Section. Here the authors did an excellent job of addressing elements of the research design, for example, why this was a retrospective study vs a prospective study and how their conclusions were valid with this treatment group. 

Other examples outlined in the discussion had to do with emphasizing that their research design  was not a binocular vs monocular strategy in treatment, but rather a combination of the two compared to only a  monocular “patching strategy” in treatment. Once again, their research  evidence clearly showed  that better outcomes occur when the treatment targets the cause of amblyopia, that being a failure of binocular vision, with an emphasis to rehabilitate the binocular dysfunction as a vital component of the amblyopia patients treatment plan.


With more evidence now showing that the best method for patients with unilateral amblyopia is with binocular vision therapy as the foundation;  we are long overdue in placing a priority in modern patient care on the role of incorporating binocular vision therapy as the new “gold standard” in amblyopia management. The time has come.

Dan L. Fortenbacher, O.D.,FCOVD

Function Influencing Structure in Amblyopia

It’s the ultimate example of neuroplasticity: the ability of amblyopia therapy to improve the retinal microvasculature in the vicinity surrounding the foveal avascular zone. A new study published in JAAPOS shared with us from Dr. Curt Baxstrom, who was alerted to it by Dr. John Tassinari, supports this concept.

From the article, here was the treatment protocol: “Treatment spanned 6 months. For the first 3 months, mild amblyopic subjects underwent optical correction, moderate amblyopic subjects completed optical correction and 2 hours of daily patching, and severe amblyopic subjects completed optical correction with 6 hours of daily patching. After 3 months of treatment, we remeasured all patients’ refraction without cycloplegia and visual acuity. Based on the improvement that each patient experienced at this timepoint, we adjusted our treatment protocol for the next 3 months of treatment. For patients whose amblyopic eye visual acuity improved significantly (ie, ≥1 line of improvement), treatment remained unchanged. However, for those who experienced little or no improvement in their amblyopic eye visual acuity, we increased daily patching by 2 hours.”

It matters much less that the treatment approach here involved patching, absent any of the more contemporary optometric approaches to therapy. The important point is that results suggest the existence of retinal microstructural deficits in unilateral amblyopia, with the foveal avascular (FAZ) shape more irregular in amblyopic eyes. Above all, FAZ shape became more regular after amblyopia treatment, along with improved best-corrected visual acuity (BCVA) in the amblyopic eyes.

 Foveal avascular zone (FAZ) circularity changes after 6 months of amblyopia treatment. FAZ circularity at baseline (before treatment) in amblyopic eyes (A) and in the fellow eyes (B). After optical correction and patching therapy for 6 months, FAZ circularity in amblyopic eyes increased to (C), and fellow eyes remained stable.

Take a look at our original post about structure vs. function in amblyopia in 2012, and at the follow-up post on structure vs. function in amblyopia in 2018.

Egocentric Distance Perception Disorder in Amblyopia

This article, Egocentric Distance Perception Disorder in Amblyopia, is intriguing from a variety of angles, not the least of which is its origin of publication in Psychologica Belgica – the journal of the Belgian Association for Psychological Science. After describing amblyopia as a neurological disorder in the visual cortex due to a mismatch between the two eyes, the authors cite evidence that quality of life is significantly reduced for individuals with amblyopia. This includes not only a propensity toward the visual factors of blur, diplopia, decline in distance judgement, and other functional disorders, but also psychological distress, such as lack of self-confidence, depression, and family tension.

The authors explain that egocentric distance perception is a psychological process in which observers use various depth cues to estimate the distance between the target and themselves that plays an important role in quality of life. Approximately 40% of the items tested on the main quality of life scales such as the Amblyopia and Strabismus Questionnaire (ASQE); the 20-item Adult Strabismus questionnaire (AS-20); and the Amblyopia Treatment Index (ATI) are related to egocentric distance perception including estimating distance, going down stairs, or parking a car.

A graphic is produced to depict three regions of visual space that can be differentially affected in amblyopia: personal space (there is a typo in the graphic), action space, and vista space. Pesonal space or egocentric distance within a meter or two is heavily influenced by accommodation, convergence, and motion. Beyond that, and out to about 30 meters is action space which is heavily influenced by visual angle and binocular disparity. And beyond that is vista space heavily laden with the cues of aerial perspective and relative size.

All this sounds remarkably similar to the partitioning of visual space consistent with Rourke’s neuropsychology of personal, peripersonal, and extrapersonal space, and embodied cognition as we have discussed relative to Brock’s String and Sanet’s Space Fixator (see here). It also reinforces the importance of emphasizing binocular tasks in amblyopia, rather than getting hung up on monocular visual acuity as the be-all and end-all of impairment or success. In particular, stereopsis and stereo-motion play an important role in real world visuomotor tasks such as walking, grasping objects, and driving, as noted in the review paper they cite by Grant and Moseley. A type of dyskinesis occurs in amblyopia in which motor planning and execution in impaired particularly when tasks are novel or speed-related.

Another interesting study reviewed in this article is by Ooi and He on Space Perception of Strabismic Observers in the Real World Environment. Looking at their research paradigm, one is reminded of principles inherent in Space Fixator and Marsden Ball procedures, in contrasting monocular to binocular performance, and in guiding visual judgment through lenses, prisms, and movement in 3D space. As Ooi and He write: “Poor stereopsis as a result of childhood disorders of strabismus and/or amblyopia persists into adulthood, and affects everyday perception and actions in the near and intermediate visual space. It is notable that at the time of testing none of our observers would be classified as amblyopic when referenced to the American Academy of Ophthalmology’s guideline for visual acuity deficit.”

Amblyopia/Lazy Eye – novel interview provides greater understanding for doctors and patients

When it comes to explaining Amblyopia, few doctors do it better than Dr. Leonard Press. As one of the world’s leading experts on developmental vision, Dr. Press answers questions with Dr. Paul Freeman, Eye Care Editor and Chief for Practice Update, on the topic of Current Concepts in Amblyopia Management. This video is one of a series of  interviews produced by Practice Update as a free online resource for healthcare professionals. The uniqueness of Dr. Press is his ability to explain this complex condition so that is understandable not just to doctors, but also to those patients, or parents of patients with Amblyopia.

Dan L. Fortenbacher, O.D., FCOVD

Adults with Amblyopia/Lazy Eye… effective treatment now

Amblyopia/Lazy Eye is a vision problem that affects both children and adults. This neurodevelopmental loss of vision, typically in one eye, begins in childhood and causes loss of eyesight, poor or no depth perception and many other problems including poor eye hand coordination and reduced reading speed and fluency. 

The cause of Amblyopia is clearly understood from decades of research to be a failure in binocular vision (both eyes working together), known as Suppression, that begins in infancy or early toddler-hood, normally due to strabismus (crossed or turned eye), known as Strabismic Amblyopia and/or refractive imbalance, known as Refractive Amblyopia or deprivation caused by congenital cataracts. But, regardless of cause, Amblyopia impacts the lives of all of those who suffer with it at all ages. 

The reason for the emphasis of focus on children historically has been because the standard treatment for Amblyopia, occlusion therapy (patching) has been determined to be effective up until approximately age 10. In fact, this is true when you look at the clinical trials that evaluate the efficacy of occlusion as the treatment. However, what new research  shows is that age is not a barrier to treatment for Amblyopia when the patient, even an adult patient, is participating in visually interesting techniques that are engaging and designed to decrease the suppression and “turn-on” the function of both eyes working together. This method of turning on both eyes working is known as binocular vision therapy.

Even though occlusion therapy has a host of negative side effects it is routinely prescribed because the volume of clinical research shows visual acuity can improve in young childhood.  But, what about the impact of patching on suppression? And does treating the problem of vision loss due to the origin of the amblyopia by “attacking” the suppression from a binocular vision therapy model work better than patching, regardless of age?

The answer to these questions and many more are addressed in a new paper, published in Frontiers in Neuroscience, January 2020, Volume 13,  entitled: Patching and Suppression in Amblyopia: One Mechanism or Two?, authors: Yiya Chen, Zhifen He, Yu Mao, Hao Chen, Jiawei Zhou and Robert F. Hess. 

The authors conducted a clinical trial to study the following:

  • The effect of occlusion therapy on patients’ visual acuity
  • The effect of occlusion therapy on patients’ suppression
  • The relationship between changes in visual acuity and suppression.

What the researchers concluded was that their findings were consistent with other studies regarding visual acuity and occlusion therapy. That is about 50% of patients’ visual acuity improved with occlusion therapy. But, they also concluded that even in those who had improved in visual acuity from occlusion therapy,  the problem with suppression did not change significantly. Therefore, those who did occlusion therapy still had a failure in binocular vision.

The authors further stated, “The notion that monocular occlusion therapy and binocular therapy might involve different neural mechanisms is in line with several other notable differences between the effects of these two therapeutic approaches.”

Now the reader may wonder, what does any of this have to do with adults with Amblyopia? The answer to this question can be found on page 8 of their paper. The authors went on to summarize, based on their own research and that of multiple other cited studies the following five conclusions:

  1. Occlusion therapy is only effective in children, but ineffective in adults. However, binocular vision therapy has been shown to be effective in adults and children with similar effectiveness.
  2. Better binocular outcomes have been achieved through binocular vision therapy than occlusion.
  3. The treatment duration is approximately 3-6 times faster with binocular vision therapy vs occlusion.
  4. The recurrence rate of amblyopia is high with occlusion but low with binocular vision therapy.
  5. Studies that have examined children who failed to improve in visual acuity after occlusion therapy actually showed improvement in their visual acuity after binocular vision therapy.

Given the fact that binocular vision therapy has been shown in research to be more effective at the cause of amblyopia, ie suppression, than occlusion therapy and given that binocular vision therapy is effective both in adults and children with similar effectiveness, plus is 3-6 times faster than occlusion therapy, what might we expect if the quality of the binocular vision therapy is advanced into a highly stimulative, visually engaging and enjoyable experience?

This is discussed extensively in our chapter published in the August 2018 3rd Volume, Issue 1 of Advances in Ophthalmology and Optometry entitled: Vision Therapy and Virtual Reality Applications, Drs. Fortenbacher, Bartolini, Dornbos, Tran where we present the latest developments in technology coupling the clinical research in neuroscience and brain neuroplasticity. This modern frontier of new therapeutic applications of highly motivating, patient-engaging binocular vision therapy brings into the next generation, even for adult patients, effective treatment for amblyopia with properly prescribed and supervised virtual reality (VR) in vision therapy.

Now bringing this into practical applications, for the last 5 years we have provided office-based vision therapy, utilizing Vivid Vision Virtual Reality as an integral element for our adult patients with amblyopia treatment with excellent outcomes. Our patients have gained dramatically improved depth perception, as well as visual acuity.

What’s more, during the last 2 years, we have dispensed home Vivid VR as a new addition to our at-home vision therapy regimen used in conjunction with our doctor and vision therapist guided office-based vision therapy sessions. In the home units, the patient can use their VR equipment anywhere they have access to WiFi where they literally toggle into our office computer, working on the same VR programs, just as if they were physically in our office. 

The advantages of these new technologies in vision rehabilitation and vision therapy have positioned adult patients, just as much as children, to now obtain effective treatment for their Amblyopia.  

Dan L. Fortenbacher, O.D., FCOVD

Levi’s Gems in Rethinking Amblyopia

Finally got around to the pleasure of watching Dr. Dennis Levi’s thoughtful iHeartVT lecture on Rethinking Amblyopia.

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There will be no difficulty in reflecting on this year to realize that we’ve lost much more than 2020, and that is a good way to think about amblyopia.  Although it is still characterized in the public eye as poor vision in one eye, amblyopia reflects much more than a loss of 20/20 visual acuity.  This of course has been known for many years, stipulated very clearly in a book that Levi co-authored with Ciuffreda and Selenow on the subject nearly 30 years ago (1991).  Yet somehow that message has been slow in getting through to eyecare practitioners at large, yet alone the public.

Amblyopia Book

One of Dr. Levi’s slides in his iHeartVT lecture noted that for many years, the mainstay of amblyopia treatment has been occlusion of the better eye, which dates back to Compte de Buffon in 1743.  For a number of reasons, which we’ll get to shortly, occlusion as the primary treatment approach to amblyopia is quite outdated.  It is a curious slide, however, on which Donald Trump makes an appearance modeling a pirate patch.  (Or perhaps something about de Buffon reminded Dennis of Trump, but to see if that’s that case you’ll have to tune in to the lecture.)

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Another point that Dr. Levi makes is that the critical period isn’t so critical, and at best should be termed a sensitive period although in underdeveloped countries congenital cataract is more common which can present more of a true critical period with regard to amblyopia.  But in most cases the potential for improvement in amblyopia exists well beyond the age at which “Entwicklungspotenz” or what we now call neuroplasticity is lost, as originally suggested in this graphic from Bangerter in 1959.

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Dr. Levi proceeds to make the point that amblyopia results in abnormal visual-motor behavior, and illustrated this with a brief video clip showing the challenges of trying to do something as basic inserting a peg in a hole when binocular vision is compromised through amblyopia.  As an aside, Agnes Wong and colleagues in Toronto recently did a nice summary on the subject, which you can access through this link on Visuomotor Behaviour in Amblyopia: Deficits and Compensatory Adaptations.  Dr. Levi suggested that reduced or absent stereopsis is one of the most common abnormalities in amblyopia.  In fact, reduction in stereo vision may be the main deficit that amblyopes actually encounter in everyday vision and is more responsible for abnormal visuomotor behavior in amblyopia than strabismus or reduced acuity per se.

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Rounding out the importance of of stereo vision, Dr. Levi put up a slide with a quote from “Stereo Sue” Barry, gleaned from a presentation she made in 2007.  I had the pleasure of sharing the podium with Drs. Levi and Barry at that meeting on amblyopia, organized by the New York Academy of Sciences in concert with the James McDonnell collaborative network for Critical Period Re-examination (Brain CPR) titled Critical Periods Revisited: Plasticity of Sensory Systems.

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And with that, I’ll leave you in some suspense until we get to Part 2 …

The Three Opias: Hyperopia + Anisometropia + Amblyopia

Not to be confused with The Threepenny Opera, The Three Opias of hyperopia, anisometropia, and amblyopia can present a daunting clinical challenge when co-occurring.  In the new paradigm for amblyopia therapy we address the binocular aspect of the problem while de-emphasizing punitive measures such as occlusion, penalization, and anti-suppression, something that Bob Sanet, Pilar Vergara and I will present in detail at COVD 2020 in Toronto.  This places a premium on deriving the optimal lens Rx, for which opinions are many and varied.

Fundamental to deriving the Rx is the interrelationship between hyperopic refractive profiles, visual acuities, and indices of binocular function such as stereopsis.  To some extent this is a chicken vs. egg question in considering whether the brain has orchestrated anisometropia at higher levels resulting in amblyopia, or if there is some fundamental difference in the refractive properties of the eyes that resulted in amblyopia.

chicken vs. eggIt is interesting to note a basic difference between hyperopic anisometropic amblyopia in contrast to its myopic counterpart.  In my experience, it is unheard of to find high unilateral hyperopia (I’ve personally never seen hyperopic aniso exceed four diopters other than in unilateral aphakia) whereas the same cannot be said for high unilateral myopia.  This argues against axial length asymmetry as a precipitating factor for hyperopic aniso and associated amblyopia.  If that assumption is correct, then guiding the patient functionally toward isometropia by re-balancing binocular vision is possible and desirable.  On the other hand, high myopic aniso is likely caused by axial length being too long in the highly myopic eye, and efforts to attain binocular balance are often futile.  Those cases, as well as unilateral aphakia, are exceptions to the new paradigm, and  typically do require occlusion, penalization, or anti-suppression measures.

I’d like to share another clinical observation, one that I find very useful in prescribing for hyperopic aniso in the presence of amblyopia.  While I realize that clinicians adept with a spot retinoscope can qualitatively observe what I’m about to relate, comparing a printout of the manifest autorefractor finding to the cycloplegic autorefractor finding can help considerably in prescribing for The Three Opias, as well as for demonstrating to parents what is happening.

Here is a representative set of findings, showing three consecutive readings for each eye, in a six year-old child with unaided VA of 20/20(-) OD and 20/30 OS:


OD: 1) 0.00 – 0.50 x 107    2) +1.25 – 0.50 x 113    3) +0.50 – 0.50 x 105

OS: 1) +1.50 – 0.75 x 85     2) +2.00 – 0.50 x 80      3) +2.00 – 0.50 x 88


OD: 1) +1.50 sphere         2) +1.50 – 0.25 x 100     3) +1.25 sphere

OS: 1) +3.25 -0.50 x 85     2) +3.25 sphere             3) +3.25 sphere

When you see fluctuating plus sphere, latent hyperopia lurks.  Even the eye with less plus, in this case the right eye, often lacks a clean 20/20 acuity due to hyperopic flux.  The eye with higher plus on manifest is almost guaranteed to have amblyopia when the anisometropia exceeds +0.50.  The more the aniso, the greater the amblyopia.

Clinical Pearls Cover

In Clinical Pearls, when I originally wrote the chapters addressing intelligent use of cycloplegia as well as autorefraction, I leaned toward pushing plus in these cases.  In the ensuing years I’ve evolved toward Rxing just enough plus to jump start the system, with an eye toward minimizing the anisometropia even if adding extra plus to the (more) amblyopic eye initially results in better acuity.  Seeing the amount of latent hyperopia on cycloplegia can still be a useful tool, particularly with helping parents understand how hard the child is working to maintain focus.  (As an aside, it also helps clear up “but why did the other doctor say …”).

I blogged previously about the suite of subjective binocular vision tests that I rely on most heavily in conjunction with stereopsis.  For binocular balance at near I use the Bernell slide #553.   Its Duochrome Test is a sensitive gauge for the amount of plus that provides the best accommodative balance between the right and left eyes.

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Keeping the Rx power and the aniso to a minimum while maximizing binocular balance is an effective way to counteract amblyopia.  When the Rx is worn consistently by the patient, and the binocular balance is monitored by the doctor at regular intervals and the power adjusted accordingly, the lenses have a therapeutic effect.  You’ll ultimately be able to achieve better endpoint acuity and higher levels of binocularity than the old-fashioned way of focusing on maximum Rx for best monocular acuities.

(Part Two follows here.)

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

Stereo Acuity as the Dow Jones Index of Binocular Function in Amblyopia

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In the current issue of Vision Development & Rehabilitation, Bob Sanet, Pilar Vergara and I have a Perspective piece in which we review a Paradigm Shift in the Treatment of Amblyopia.  The article resurrects a formula proposed by Dr. Arnold Sherman to provide a more accurate measure of the extent of treatment success in amblyopia, now that current research has squarely positioned the condition as a binocular problem in which visual acuity is simply one monocular sign.  Sherman notes that Mayer and colleagues proposed an Amblyopia Success Index (ASI) based on visual acuity as follows:

ASI = (Initial VA – Final VA) / (Initial VA – Test Distance) x 100. As an example, if the initial acuity was 20/60 and improved to 20/30, the ASI = (60- 30/60-20) = (30/40) x 100 = 75%.

Given the significance of amblyopia as a binocular problem, Sherman proposed an analogous Binocular Success Index (BSI) using Wirt Circle Stereopsis (WS) in seconds of arc as a guide. A maximum value in most commercially available tests of 20 seconds of arc is the constant. His formula is: BSI = (Initial WS – Final WS) / (Initial WS – Maximum WS) / x 100.

As an example, if initial stereo acuity was 100 seconds of arc and improved to 30 seconds of arc, the BSI = (100-30) / (100-20) = (70/80) x 100 = 88%. He suggested that the more appropriate index of success in amblyopia would be the average of the ASI and BSI, in this instance (75 + 88) / 2 x 100 = 82%.

While the numbers in Sherman’s example don’t seem significant when differentiating between a 75% level of success and an 82% level of success, combining ASI and BSI obviously becomes more significant when stereopsis improves to a considerably greater extent that visual acuity. For example, using the formula for ASI, a patient who improves from 20/50 to 20/40 would be assigned a success index of only 33%. But if that patient improved from 100 seconds of arc to 20 seconds of arc, BSI is 100% which doubles the overall success index to 67%.

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For many years we have routinely conducted the Wirt Circle test on all of our patients (with or without amblyopia).  In all of our patient reports I have included this phrase: “Stereopsis is a sensitive index of binocular function.  On the Wirt Circle Test, ________ scored at the level of X% accuracy.”   In other words, if 5 out of 10 are correct, the patient is assigned a score of a 50% level of accuracy.  While I realize this isn’t as sophisticated or technically as accurate as Dr. Sherman’s index, it is a justifiable simplification of the test result.  That way, when we re-test with a suitable lens/prism Rx, or after vision therapy, we can say that the patient improved from X% level of accuracy to Y% level of accuracy.

Nearly 30 years ago, in an article in the Journal of Behavioral Optometry, Dr. Selwyn Super pointed out some of the nuances of stereopsis testing.  He made the observation that speed of the stereopsis response may prove to be just as valuable as the stereo acuity measure in seconds of arc.  When taking visual acuity measures, the patient with amblyopia takes longer to respond, particularly as we approach the limit of their visual resolution, so this lag in the speed of stereo acuity responses is not entirely surprising.  Although he introduced a test for the speed of stereopsis based on Wirt Circle responses that was distributed by OEPF, it was ahead of its time and removed from the market. There is reference to this test in a master’s thesis on file with Pacific U. College of Optometry.  It remains a valuable concept, and would be another potentially useful metric in differentiating amblyopia and documenting response to treatment.

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I just did a quick survey of ODs on Facebook, a community of primary care optometrists, posing this question:  Does your office routinely test stereopsis on all pediatric patients? Please indicate “yes” or “no”.  Realizing that this isn’t a scientific survey since it wasn’t “anonymous”, and the people who don’t do the test tend not to answer in a forum of that nature, it was still encouraging to note that among the first 200 respondents there were 197 yes and 3 no.  Although I didn’t ask respondents to indicate how many considered themselves primary care optometrists, it would be reasonable to expect that the high majority are.  A public word of thanks to all those who responded.

If our premise regarding amblyopia is correct, that stereo acuity is a sensitive index of binocular function, most primary care optometrists have a tool at their disposal that they’re already using that will help facilitate the paradigm shift in amblyopia from a monocular emphasis to a binocular balance.

Dichoptic Treatment of Amblyopia in a Clinical Setting

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This is a relatively brief post to bring to your attention a continuing education article now available online through Clinical & Refractive Optometry titled Dichoptic Treatment of Amblyopia in a Clinical Setting – a Retrospective Study, authored by Giovanni M. Travi, MD, Seyedbehrad Dehnad, and Behzad Mansouri, MD, PhD, FRCSC.  Dr. Travi is an ophthalmologist and biomedical engineer; Dr. Mansouri is a neuro-ophthalmologist; and Seyedbehrad Dehnad is their research assistant at the University of Manitoba in Winnipeg, Canada.  If Dr. Mansouri’s name seems familiar, it is likely because he is a co-author of the paper in Restorative Neurology and Neuroscience, along with Hess and Thompson at McGill University in Canada in 2010, that introduced dichoptic training of amblyopia into the literature.

I like the authors’ description of amblyopia, contained in the introduction to this paper:

Amblyopia is an abnormal development of the visual system secondary to its inadequate (i.e. anisometropia and deprivation amblyopia) or erroneous (i.e. strabismic amblyopia) binocular stimulation during early visual development. It is usually unilateral, and it occurs due to a mismatch of information between the two eyes. Beyond affecting the visual acuity, amblyopia affects contrast sensitivity, spatial integration, global motion perception, and depth perception.  Moreover, it may impact negatively the quality of life, either due to the low vision in the amblyopic eye, weak depth perception or because of the social burden of the most widely used treatment, i.e. occlusion therapy.  Recently, the understanding of unilateral amblyopia physiopathology has evolved and the concept that the visual loss is related uniquely to an abnormally developed visual system has given place to the one based on an anomalous binocular interaction.


Here is the authors’ abstract:

Purpose: Dichoptic visual stimulation has been evolving as a promising treatment for amblyopia. We aimed to assess the visual outcomes of Dichoptic Amblyopia Treatment (DAT) in a clinical setting for patients who had completed all conventional amblyopia treatments and did not have any other clinical treatment options. The primary outcome was the improvement of visual acuity (VA) in children and adults. The secondary outcomes were improvement in stereo acuity (SA) and reduction of suppression.

Methods: We performed a retrospective chart review of amblyopic patients who received DAT from 2014 to 2016 in an eye care practice. DAT consisted of playing “Falling Cubes” game on an iPod, using dichoptic presentation.

Results: 23 patients with a median age of 12 years-old (Interquartile range (IQR) = 9-30) met the inclusion criteria. 3 patients were excluded on the final VA analysis due to non-completion of treatment. The median for pre- and post- treatment VA was 0.54 (IQR=0.41-0.84) and 0.19 (IQR=0.09- 0.28) logMAR, respectively. Mean improvement in VA was 0.33 ± 0.18 logMAR (IQR=0.25-0.41) (p<0.001). Patients showed an improvement in SA (p=0.002) and a decrease in suppression (p=0.003). Age group, presence of SA at baseline, previous treatment, amblyopia type and severity did not correlate with VA improvement. There was no adverse effect such as double vision or VA reduction in the sound eye.

Conclusion: To the best of our knowledge we showed for the first time that DAT is a plausible amblyopia treatment at a clinical environment. The results demonstrate that DAT is effective in improving VA and SA, and reducing suppression in amblyopia. We emphasize the importance of an active follow-up regarding game monitoring and frequent patient’s reassessments.