By Dr Raghuram Y.S. MD (Ay) & Dr Manasa, B.A.M.S
Amblyopia is a condition of reduced vision in one eye. It develops when there is a breakdown in how the brain and the eye work together. As a consequence the brain fails to recognize the sight from one eye. Over a period of time the brain relies more and more on the stronger eye. On the other hand the vision in the weaker eye gets worse. Some kids are born with this condition and some others will develop it later. (Read more)
The weaker / lazy eye often wanders inward or outward. The one eye which is not developed properly seems to be lazy in comparison to the other normal eye and hence the name.
This condition starts in childhood. It is caused by abnormal visual development early in life. It is the most common cause of vision loss among kids. It generally develops from birth up to 7 years of age. We also have reference that it usually occurs between 6 and 9 years of age. The best chance of correcting this condition is to identify and treat it before 7 years of age.
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Table of Contents
Signs and symptoms of amblyopia
Parents often notice their children struggling to see clearly and also observe squinting, tilting of head and shutting of one eye. Below mentioned are the symptoms of amblyopia –
- Wandering eye – one eye that wanders inward or outward
- Non-alignment of eyes – the eyes appear to not work together, there is no synchronization
- Poor depth perception – the patient finds it difficult to tell how far or near something is
- Shutting / squinting of one eye
- Tilting of head
- Abnormal results – will be obtained in vision screening tests
Sometimes a thorough examination is mandatory to identify and diagnose a lazy eye.
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The causes are not clearly known in most cases of amblyopia. Sometimes a different vision problem can lead to amblyopia. When present and identified, the causes of amblyopia include –
Abnormal visual experiences – happens early in life is one of the causes. This changes the nerve pathways between retina and the brain. In this condition the weaker eye receives fewer visual signals. This eventually decreases the ability of both eyes to work together. The brain suppresses or ignores the inputs from the weaker eye. Lazy eye is an effect of anything that blurs a child’s vision or causes the eyes to cross or turn out.
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Refractive errors – This is a condition wherein one eye will have a better focus than the other eye. The other eye will have a problem. It could have one of the below mentioned conditions –
- nearsightedness – have trouble seeing far away
- farsightedness – have trouble seeing things close up
- astigmatism – blurry or distorted vision
In this condition the brain gets both – a blurry image from the problematic eye and a clear image from the normal eye. Here the eye starts to ignore the blurry image and will accept a clear image. If this continues for months or years, the vision in the blurry eyes would get worse. These problems are easy to fix with glasses or contacts. If they are not treated, the brain may start to rely more on the stronger and healthier eye.
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Strabismus – This is a condition the eyes are mutually misaligned. The patient cannot focus his eyes together on an image. This is the reason they see the images double. The brain will ignore the image from the misaligned eye.
Deprivation and occlusion – This happens when the ocular media becomes opaque as in congenital cataract or corneal haziness. It is a condition wherein a cloudy lens inside the eye can make things look blurry. The vision in the afflicted eye is not good since it hasn’t developed in the way it should.
The opacities will prevent adequate visual input and disrupt development. Drooping of eyelid / ptosis can physically occlude vision. This condition can also be a complication of a hemangioma that blocks some part of the eye or the entire eye.
Ptosis / Droopy Eyelid – Here there is sagging of eyelid. This will block your vision.
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Amblyopia is a developmental problem in the brain. It is not any intrinsic or organic neurological problem in the eyeball. The part of the brain which receives images from the affected eye is not stimulated properly. It also doesn’t develop to its full visual potential. This aspect has been confirmed by direct brain examination. (Read more)
Common types based on the causes of lazy eye
Strabismus Amblyopia / Muscle imbalance – In this the muscles that position the eyes are put into imbalance. This will eventually cause the eyes to turn out or cross in. This would further prevent both eyes from working together.
Refractive Amblyopia / Difference in sharpness of vision between the eyes – often due to farsightedness, but is also sometimes due to nearsightedness or astigmatism can cause this condition. To correct these refractive errors contact lenses or glasses are used. A combination of strabismus and refractive problems sometimes cause lazy eyes in some children.
Deprivation Amblyopia – clear vision can be prohibited when there is a problem like cataract in one eye. In infancy this condition requires urgent treatment to prevent permanent vision loss. It is most often the most severe type of amblyopia.
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- premature birth
- child smaller than average at birth (smaller birth size)
- family history of amblyopia or other conditions
- developmental disabilities in child
Amblyopia occurs in between 2-5% of the population in Western countries. About 90% of visual health appointments sought out for the children in U.K. concern amblyopia. About 1-4% children suffer from amblyopia depending on what criterion has been chosen to make its diagnosis.
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The examination done to check –
- the eye health overall
- that nothing blocks the light coming into their eyes
- poor vision in one or both eyes
- a difference in vision between the eyes
- presence of a wandering eye
- visual field and visual acuity in one or both eyes – reactions of the patient when one eye is covered, includes patient’s ability to follow objects with one eye and being able to read words of different sizes on Snellen’s Chart
Other tests –
Binocular retinal birefringence scanning
Screening for amblyopia is highly recommended to all people between their 3-5 years of age.
As per some experts any kid should undergo an eye test at 6 months of age for the first time, then at 3 years and later during the ‘schooling years’ eye examination should be done every year.
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Vision loss – There may be permanent loss of vision if treatment is delayed.
Most children will regain vision if the condition is diagnosed and treated at the earliest.
Right time to see the doctor
When the parents notice the eye of their child wandering after the first few weeks of life (post birth) the parents should immediately see the doctor. If there is a family history of crossed eyes, childhood cataracts or other eye conditions a thorough vision check can be done.
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This condition should be diagnosed and treated in childhood itself. It is found that the results are promising when the treatment of lazy eye has been initiated before age 7. About half children respond well when treatment is done between 7 and 17 years of age.
Treatment most often depends on the cause of the lazy eye and how much the disease is affecting the vision. The recommendations would include –
Correction – of underlying vision problems including near and farsightedness or astigmatism should be primary approach. Corrective eyewear – glasses, contact lenses would correct far and nearsightedness or astigmatism.
Eye patches – are done to stimulate the weaker eye. It shall be done on the normal eye. This will force the brain to use the weaker eye. In spite of having initial difficulties in seeing the child’s vision would get better in a few weeks or months. Using the patch will be temporary until the vision gets right. While using both eyes in later time the kids might feel loss of vision or the vision reduced to certain extent in the weak eye. In this case the patch needs to be reused.
Bangerter filter – a special filter placed on the eyeglass lens of the stronger eye, it blurs the vision and compel the child to use the weak eye.
Eye-drops – like atropine blurs the stronger eye and enables one to use weaker eye, alternative to eye patch.
Surgery – is the option to treat cataract and strabismus causing amblyopia . It is also an option if droopy eyelids are causing deprivation amblyopia.
Treatment of lazy eye in teenagers and adults is successful to an extent but once the vision has been developed completely in the child the treatment may not work.
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Other treatment options
Activity based treatments – encouraging drawing, solving puzzles, playing computer games etc. The effectiveness of these inclusions into the mainstream treatment lineup is not proved. Many research works into new treatments for this condition are in progress.
Proper and timely treatment improves vision in most children within a few weeks to months. The treatment might also last for about 6 months to 2 years.
The child should be regularly monitored for symptoms indicating recurrence of lazy eye. Recurrence happens in about 25% of children. If it happens the treatment for the same shall be restarted.
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Reverse Amblyopia – If the good eye is subjected to over-patching as a part of the treatment, a condition called ‘reverse amblyopia’ can result. Therefore eye patch is usually done for about 4-6 hours a day. As long as the vision improvements are seen the treatment is continued. If no improvements in vision are noted, it is better to discontinue ‘use of patches’.
Treatment of Deprivation Amblyopia – This condition is treated by removing the opacity as soon as possible followed by patching the good eye. The earlier it is done, the lesser the damage to the vision. If the treatment is initiated at the earliest, there are chances of achieving 20/20 vision.
Perceptual Learning / Training – This can be used as a measure to treat individuals age 9 and above.
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- In Amblyopia the neurons establish functional connections with only one retina (Read more here)
Next gen devices to test for ‘lazy eye’ in children developed using computer gaming technology (Read more)
Electronic shutter eyeglasses may be alternative treatment for amblyopic children in future (Read more)
Abnormal vision in childhood can affect development of brain areas responsible for attention (read more)
2013 study – playing a popular game Tetris that is modified in a way such that each eye sees separate components of the game may help in treating this condition in adults. Effects of such therapies may be further enhanced by noninvasive brain stimulation.
Master Sushruta has explained a condition afflicting the vision i.e. among the ‘vision related disorders’ named ‘Pitta Vidagdha Drishti’. Here the vision is destroyed by vitiated pitta.