Introduction to amblyopia


lazy eye, amblyopia statisticAmblyopia or "lazy eye" is weak vision or vision loss in one eye that cannot be fully corrected with lenses.

It usually develops in children before age eight and is best treated if caught early. It becomes more difficult to treat amblyopia after age eight and if untreated it can lead to total blindness in the affected eye.  However, new studies on the  neuroplasticity of the brain hold out hope for older people with amblyopia who have not been treated.  A recent study by the National Eye Institute concluded that patients as old as 17 may benefit from treatment.

Amblyopia involves the "wiring" of the nerve impulses from the eyes to the brain. Treatment typically includes vision therapy (vision training, perceptual learning, dichoptic training), eyeglasses and contact lenses, or a patch. Surgery alone is not sufficient. 

Amblyopia is rarely obvious to parents and teachers.  An eye doctor should be consulted to diagnose the condition.  If amblyopia is not caught and treated early, permanent vision loss may result.


Patching alone is not good enough

Patients must ensure that they are being treated not just to improve the acuity of the affected eye but also to improve binocularity (both eyes working together).  Neglecting the latter may result in depth perception problems and difficulties reading.  Doctors who advocate patching alone may not be aware of the latest scientific research that shows that amblyopia is not just a problem with one "lazy eye" - it is a binocular problem, which means that it is a problem of both eyes working together.  This point was made in a recent study published in the September 2010 issue of the journal Optometry & Vision Science:

amblyopia is an intrinsically binocular problem and not the monocular problem on which current patching treatment is predicated. Thought of in this way, the binocular problem involving suppression should be tackled at the very outset if one is to achieve a good binocular outcome as opposed to hoping binocular vision will be regained simply as a consequence of acuity recovery in the amblyopic eye, which is the current approach and which is often not found to be the case.

Hess, Robert F.; Mansouri, Behzad; Thompson, Benjamin, A Binocular Approach to Treating Amblyopia: Antisuppression Therapy. Optometry & Vision Science:September 2010 - Volume 87 - Issue 9 - pp 697-704

A famous case of treatment that ignored binocularity (although for strabismus rather than amblyopia) is that of Susan Barry who was unable to see in three dimensions until she was treated with vision therapy in her 40's.

Amblyopia: the full picture

The most cutting edge research into amblyopia is confirming that the way developmental optometrists treat the disease, using office-based binocular vision therapy, neuro-ocular (eye-brain) rehabilitation and perceptual learning to achieve functional binocular vision is at the cutting edge of science.

The old way was to place an eye patch over the good eye in the belief that the weak amblyopic eye would be forced to work better. Not only does patching not work very well, it ignores the sometimes serious social and psychological impacts that wearing a patch has on a young, vulnerable, developing child. Patching without integrating other treatment approaches also ignores the necessity to achieve functioning binocular vision (both eyes working together).

The standard test for amblyopia is to have a patient read the eye chart. When one of the eyes can’t read the chart clearly (this is called poor visual acuity) even with corrective lenses, the patient has amblyopia.  Because lenses cannot fix the vision in the weak eye, we know that there is a problem with the eye-brain connection: the eye is not communicating images to the brain properly. 

However, when treating a patient with amblyopia, it is critical for the doctor to understand that there is often more going on than simply low visual acuity. That is why effective treatments for amblyopia address much more than visual acuity. In fact, visual acuity is only the tip of the iceberg. 

Other visual functions that contribute to the inability to read an eye chart clearly include the stability with which the patient is able to focus, the nature of a patient’s eye movements and the patient’s ability to fix his or her vision at a specific point. How well the eyes can track letters and read across a line of print can also prevent a patient from reading the eye chart clearly. When some people with amblyopia read, the letters spill over into one another and crowd one another out. Developmental optometrists are trained to look for and treat all the causes of amblyopia. 

Some of the recent cutting-edge research into amblyopia has been completed by the Pediatric Eye Disease Investigator Group (PEDIG), a group of eye doctors that includes both ophthalmologists and optometrists. Because of the work of PEDIG, we now have reliable evidence that amblyopia can probably be treated much later in life than doctors once believed. 


New research in amblyopia

Doctors used to believe that there was a “critical period” in early childhood development beyond which the brain is to hard-wired for amblyopia to be treated. It was thought that this it was not possible to treat amblyopia after about age 7. The PEDIG studies disproved this old medical dogma and found that amblyopia can be treated successfully even in 17 or 18 year-olds.1 As a result, doctors should not tell parents that their child is too old to obtain a benefit from amblyopia vision therapy. 

The second important research study published by PEDIG was on patching. Patching has been the traditional treatment for amblyopia for decades. In contrast, developmental optometrists have been advocating active vision therapy approaches to treating amblyopia combined with a limited amount of patching. That approach makes sense because active therapy is more stimulating to the brain and therefore more effective and it avoids the need to wear a patch all day – something most children detest. The PEDIG studies proved that targeted, or focused, patching for as little as an hour or two a day consistently can be as effective as all-day patching. 

PEDIG also showed that for some types of amblyopia, we can use a drug called atropine which comes in the form of eye drops instead of patching. A drop of atropine is placed in the good eye several times a week to fog it or penalize it; this way the better eye does not see as well, which serves the same function as an eye patch. This approach is a benefit to those children who have certain types of amblyopia and who will not patch because of social pressure, teasing at school or other reasons. 

Doctors now know that the brain displays considerable neuroplasticity for most of our lives. This means that as long as a patient and a doctor are willing to work at amblyopia therapy, there is probably no age-limit to treating amblyopia successfully and effectively. However, it is important to realize that the younger the patient, the easier it is to treat him or her because the visual system is more plastic the younger you are. Parents should not delay in commencing amblyopia therapy. 

Some patients have anisometropic amblyopia (sometimes called anisometropia). This is when there is a difference in power between the two eyes. PEDIG showed that with this condition, wearing the correct lens prescription consistently is probably the single most important factor in improving amblyopia and maintaining the improvement. This should be the first treatment approach before patching, atropine penalization, or active vision therapy is commenced. When the amblyopia is more severe, it is necessary to be more aggressive and use occlusion therapy, atropine penalization, or active vision therapy. 

Some patients have strabismic amblyopia, where weak eyesight is caused by a misalignment of the eyes. For these patients, wearing the correct glasses in conjunction with keeping the eyes aligned with vision therapy treatment is very effective. 

Research is now bringing to light the way in which amblyopia affects visual performance such as reading, eye–hand coordination, depth perception and spatial judgment. For doctors to properly help a person with amblyopia, they must take a broader view it than a simplistic eye chart focused measurement of visual acuity and examine dynamic human factors and visual performance. 

The best approach to treating amblyopia is to wear a patch for fewer hours, and, during those patched periods, carry out aggressive vision therapy that accelerate the rate of improvement of that eye. At our office we use computerized and non-computerized activities that enhance compliance with therapy.

Dr. Randhawa's approach to amblyopia treatment

Dr. Randhawa’s approach to treating patients with amblyopia starts with the principle that a patient is never too young to receive and benefit from therapy. However, the earlier, the better. We do not make value judgments about the utility of treating adults or older patients. As long as the patient desires improved vision and is willing to follow the doctor’s instructions, we are willing to help them. 

The first requirement in treatment is getting the appropriate lens correction on the patient and having them wear it as much as possible. 

The second requirement in treatment is to integrate both eyes together to achieve functional binocular vision. Sometimes we recommend that patients wear contact lenses rather than glasses. Contact lenses help a patient achieve better binocular vision than glasses. This is supplemented by active vision therapy that is specifically targeted to help both eyes work together better. 

Dr. Randhawa uses the full arsenal of treatment approaches to help both eyes work together, such as glasses, contact lenses, patching, active vision therapy. For many children, especially those who will not wear a patch or those who don’t like drops in their eyes (or parents who would rather not use prescription drugs if it can be avoided), the best option is in-office vision therapy where patients come to our office regularly and take part in the fun activities that also help their eyes. To the patient, it may seem like they are playing, but the activities are deeply therapeutic, because they train the brain to use both eyes together. 

This optometric approach to amblyopia treatment has been studied. See the study titled "A binocular approach to treating amblyopia: Antisuppression therapy", published in Optometry and Vision Science in 2010,  which is a study by researchers at McGill University in Montreal, Canada. Other researchers have found that therapy that works like a video game can be a helpful part of amblyopia treatment, even for adults (see Li RW, Ngo C, Nguyen J, Levi DM. Video-game play induces plasticity in the visual system of adults with amblyopia. PLoS Biol. 2011;9(8):e1001135.) 

In the 21st century eye doctors are lucky to have so many effective tools to treat amblyopia in children and adults. Dr. Randhawa takes advantage of all of them to design a therapy program that is best for a particular patient, at a particular age, at a particular time in their life and that fits best with their personality and life.

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Amblyopia infographic



"[A]mblyopia is an intrinsically binocular problem and not the monocular problem on which current patching treatment is predicated. Thought of in this way, the binocular problem involving suppression should be tackled at the very outset if one is to achieve a good binocular outcome as opposed to hoping binocular vision will be regained simply as a consequence of acuity recovery in the amblyopic eye, which is the current approach and which is often not found to be the case."

Hess, Robert F.*; Mansouri, Behzad*; Thompson, Benjamin, A Binocular Approach to Treating Amblyopia: Antisuppression Therapy. Optometry & Vision Science:September 2010 - Volume 87 - Issue 9 - pp 697-704


Vision Therapy appears to be more effective than patching alone.

A 1999 study published in the Journal of the American Optometric Association showed that amblyopes treated with vision therapy had better depth perception than patients treated with patching and glasses only.

A 2002 study published in the journal, Optometry, showed that only 50% of patients who had initial improvement following treatment maintained their improvement at a 1-2 year follow-up.  However, 100% of those patients who had vision therapy maintained their improvement after a 1-2 year follow-up.

Amblyopia quotes

“Use of perceptual learning and video games has helped by increasing activity and attention as the therapy is done. Many of the principles have been employed by pediatric vision therapists for some time, but the publicity generated by “Stereo Sue” and others has helped to broadcast them.”

Vision Development by Dr. Nigel Daw, Professor Emeritus of Ophthalmology and Neuroscience at Yale University


Amblyopia risk in preschoolers


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