AMBLYOPIA

Overview

Visual impairment in children is caused by amblyopia commonly known as “lazy eye”. In the early developmental stage of an infant, the vision of one eye or rarely both the eyes are reduced or blurred. This mainly occurs when one eye becomes weaker. Automatically the brain favors the eye with a better vision which allows the other eye to become weaker over time. Nearly 3 out of 100 children are affected by amblyopia under six years of age and 2% adults overall. There are three main common causes for amblyopia namely:

1. Refractive Error- In this type, there is the problem with the shape/length where one eye cannot focus as well as the other. Length abnormal-Nearsightedness, farsightedness, and when the curvature of the eye is abnormal- astigmatism.
2. Strabismus- In this type both the eyes are not aligned in one direction.
3. Deprivation- In this type, the cataract or similar structural phenomena deprive the vision leading to opacity.

Early detection is the key factor in curing and getting treatment through the proper channel precisely. Some common treatments are patching the eye, wearing glasses, getting proper eye drops, and in the extreme scenario surgery.

Definition

Abnormal vision development in infants or childhood reduces the vision of one or both eyes and is called Amblyopia. In other words, it is the loss of the ability to see clearly through one or both eyes. It is often called a “lazy eye”, but it is a serious condition that becomes worst with an increase in age if it goes untreated and, in some cases, leads to loss of vision.

(Image resource: American association of ophthalmology)

The illustration above clearly defines the lazy eye where one eye has a clear vision and the other has a blurred one.

Symptoms

Many people go unnoticed until advanced age with mild symptoms which are then tested in their old age, this happens particularly when one vision of the eye is way stronger than the other. In some cases, may it be children or adults only after the clinical examination amblyopia is diagnosed. So, every child must undergo a test at the age of three to five years. Following are the symptoms of the amblyopic condition in the child at an early stage,

1. Favor one side of the body.
2. Have crossed eyes.
3. Eyes do not work together.
4. Shutting of one eye or squinting of an eye a lot.
5. Tend to bump on the things on a particular side.
6. Wandering of the eye inward or outward.
7. Encountering a large difference in nearsightedness or farsightedness between the two eyes.
8. Head tilting- head is tilted particularly to one side.
9. Eyes tend to have droopy eyelids.
10. Poor depth perception.
11. Abnormal results of the screening.

With these characterized abnormalities amblyopia shows the above symptoms which, if diagnosed at an early stage can be corrected.

Causes

When a child is born, he/she has poor vision which gradually develops over the time as the vision center of the brain develops. If the child does not properly use the eyes or does not understand their use at early life, the vision center of the brain does not develop properly which leads to a decrease in vision of a particular eye and in rare cases both the eyes. Amblyopia can happen, even though the eyes are structured properly with absolute zero abnormality. Abnormal visual experience at an early stage in life changes the nerve pathway between the thin layer of tissue (retina) at the back of the eye and the brain. As a result, the weaker eye receives fewer visuals eventually the brain ignores the visuals from the weaker eye suppressing the vision.

Precisely there are three main causes of amblyopia as shown below figure:

1. Strabismic Amblyopia

The most common cause of strabismic amblyopia is muscle imbalance which positions the eyes erratically. It is developed when the eyes are not straight. One of the eyes can turn up, down, inward, or outward. Depending upon these positions it is further classified into four categories as follows:

• Hypertropia- when the eye turns upwards
• Hypotropia- when the eye turns downwards
• Exotropia- when the eye turns outwards
• Esotropia-when the eye turns inwards

(Position of eyes in strabismic amblyopia)

(Image resource: https://almunireyecenter.com/)

Each eye is surrounded by six muscles that work together as a compatible team which allows the eye to function properly. In majority of the children with the strabismic disorder the cause is unknown whereas in one-half cases out of them the problem peeps out shortly after birth which is known as congenital strabismus. Two percent of adults suffer from strabismic amblyopia caused due to diabetes, injury to the eye, traumatic brain injury, graves’ disease, stroke, botulism. If strabismic amblyopia is not treated well, the eye that the brain ignores will never tend to see well as a result it will develop a “lazy eye” i.e., “amblyopia”. In some cases, the lazy eye is seen first and then the strabismus is noticed.

1. Refractive Amblyopia

A large or unequal amount of refractive error between a child’s eyes leads to refractive amblyopia. As a result of which child develops blurred vision. The picture below shows the normal view through the normal eye and the blurred view through the eye which has a refractive error.

(Image resource: Google images-

https://eyevision2020.net/uncategorized/1284)

Refractive error is nothing but the strength of the glasses or the conditions of how the light passes through the eye required seeing a clear vision. This type of amblyopia may not be detected because the child does not complain of blurred vision. In addition, the eye does not look different from the affected eye. This type of amblyopia develops because of the following causes:

• Myopia is also known as nearsightedness which is trouble seeing far away.
• Hyperopia is also known as farsightedness which is trouble seeing close things.
• Astigmatism is caused due to altered curve of cornea.

There are mainly two forms of refractive amblyopia as shown below.

• Anisometropic Refractive Amblyopia- It is caused by a distinct refractive error of each eye which is unilateral
• Isometric Refractive Amblyopia- It refers to both eyes with similar refractive error.

In some cases, a combination of strabismic and refractive error leads to amblyopic conditions too.

1. Deprivation Amblyopia

It is also known as Amblyopia Ex Anopsia. The most common cause for this type of amblyopia is congenital cataracts or haziness in the cornea leading to opaque or cloudy vision. In infants, it is urgent to treat to prevent permanent vision loss. It is one of the serious amblyopia and sometimes can affect both eyes. The visual axis of the eye is obstructed which results in deprivation amblyopia over the period, it is the least common but most severe amblyopic condition.

Risk Factors

A risk factor is nothing but a chance to get a condition compared to individuals without risk factors. Moreover, having a risk factor does not mean that one will get the condition. Some risk factors identified are more important than others. However, an individual without risk factors also can be affected by amblyopia. To sum up, there are no specific factors that can state if a person can be affected or not. Few risk factors which are determined over the period are as follows,

• Premature birth
• Low birth weight
• Family history of amblyopia
• Cornea Opacity/Refractive error
• Absence of lens in one or both eyes
• Congenital Cataract
• Developmental Disability

Diagnosis and Tests

It is difficult to diagnose amblyopia. Early detection between three and five years of age is more precise through vision examination by a pediatric or ophthalmologist during routine checkups. Test and exams are necessary to find out the underlying cause which leads to proper treatment. Many other conditions can cause vision loss in an individual after birth or by birth thus, amblyopia is not the only one. Thorough diagnosis through the expertise and observations by the guardians would be beneficial in treating such cases. A typical diagnosis may involve following tests or exams.

General eye examination

• Medical history evaluation of the family (includes congenital condition such as cataract)
• Assessing symptoms like wandering eye, eyes turning, the difference between eyes, etc.
• Corneal light reflex test
• Neuronal receptive fields
• Sensitivity of contrast objects
• Snellen chart (visual acuity test)
• Refractive studies by using various instruments
• The fundoscopic examination helps to examine the back part of the eye known as the fundus.
• Slit-lamp examination
• Imaging studies include CT scans and MRI which scans the head and neck region which is useful to determine neural disorders related to the eye.
• Normally in the USA and European countries, a pediatrician in a school vision program tests a child’s vision for amblyopia. They perform the following things,
  • To make the pupil bigger in an eye they put drops
  • They cover one eye at a time and test the other which should follow the moving object
  • Shine light in each the eye
  • Older children are asked to read letters on the chart on the other side of the wall of the room.
• Vision screening is carried on newborn babies almost all over the world to detect amblyopia at the early stage and to have a successful treatment. They check for congenital or cataract problems. Infants are precisely checked for strabismic amblyopia (misalignment of eyes) and the tendency to fix and follow the object. Electronic tests mentioned above may be used for toddlers to check for refractive amblyopia. Once the child can read, they are tested the same way as adults. In nutshell typical vision exam addresses the following questions,
  • Do both the eyes see equally?
  • Are the eyes aligned properly?
  • Are the eyes moving together?
  • Are the eyes moving correctly?
  • Is there any visual difference between the two eyes?
  • Does the eye allow the light all way through?
  • Does anyone eye wanders or drifts?
  • Are any cataracts visible when seen with the help of magnifying tools?

Thus, early diagnosis and by defining the underlying causes one has a higher chance of full recovery.

Treatment

Early start in treatment is a more effective strategy in curing amblyopia. It is effective while the connection between the brain and eyes is still developing. The main agenda is to make the child’s brain use the weaker eye without reverse amblyopia occurring. Treatment varies on the type of amblyopia that happened to one’s eye.

• Strabismic Amblyopia can be merely treated with eyeglasses, contact lenses, prism lenses, vision therapy, and in extreme conditions eye surgery. Vision therapy assists in helping the brain and eye work as a team together helping the weaker eye to develop the vision.
• The main purpose of the treatment in refractive amblyopia is to eliminate the dominant eye advantage which is used for vision. The eye which doesn’t participate to see the vision more is compelled to process the vision because of which, the severity of symptoms and signs decreases. It corrects the refractive error in the eye or both the eyes.
• Deprivation amblyopia treatment measures include treating and managing underlying disorders or conditions.

Some of the common treatments for all types of amblyopic conditions are almost the same in the primary approach wherein it gets more specialized if complications occur or the condition worsens. Common treatments are as follows,

• Glasses/lens or prism lens –

This type of treatment is more common and a primary approach to treat amblyopia. The power lenses normally help to correct the nearsightedness, farsightedness, and cross eyes.

• Eye-patch –

Wearing an eye patch for the stronger eye is also one of the common treatments in which the brain is re-trained and forced to use the weaker eye eventually making that eye too stronger. This patch is like a bandage. Wearing this normally lasts up to continuously during waking hours in severe amblyopia, depending on age. Good eye is patched for some time(Refer to table given below). This effective treatment can last for months or even years.

Usage of eye drop in the stronger eye is normally recommended in mild cases or probably younger children as they pull off the patch easily as play. This type of drop (atropine) normally blurs vision in the stronger eye which forces the weaker eye to develop the vision. Daily atropine administration is not necessary; a twice-per-week schedule is also effective. Parent education regarding atropine penalization for the treatment amblyopia:

Drop Administration	Administer in morning; if problematic, instill drop before child wakes
Sun Protection / Comfort	Wear brimmed hat and sunglasses when outside, particularly if sunny
Storage	Store securely out of reach of children
Systemic Reaction	Discontinue and call if facial flushing, fever, dry mouth, irritability, or confusion
Other Health Care Visits	Inform of atropine use at office visits, particularly if at emergency room

(Table 1 resource https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5396957)

Amblyopia treatment approaches: Historical versus current evidence-based approach-

	Historical Dogma	Current Perspective
The mainstay of amblyopia treatment	Patching	Optimal refractive correction
Timing of refractive correction and occlusion (patching or atropine)	Simultaneous	Occlusion prescribed after gains from optical treatment effect
Patching dosage for moderate amblyopia	Generally, the more the better; usually ≥5–6 hours	Start with 2 hours; can increase dosage if needed
Patching dosage for severe amblyopia	Full-time or most waking hours	Start with 6 hours; 2 hours is effective in some cases
Atropine penalization use	Patching failures only	First-line treatment as alternative to patching or for patching failures
Atropine penalization guidelines
Amblyopia severity	Only for moderate amblyopia	Both moderate & severe cases
Age of child	Only in young children	Younger and older children
Age after which amblyopia can no longer be treated	Approximately 6–9 years of age	Upper age limit not established; albeit generally greater VA gains if <7 years of age
Recurrence of amblyopia after treatment cessation in 9 to <13- year-old children	High likelihood of regression	Vast majority (>90%) do not regress.

(Table 2 resource- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5396957)

Treatment Approach–

*Alternative treatments include atropine penalization of the sound eye 2 times per week or full-time wear of a Bangerter filter over the sound eye.

**Intense treatment is ≥ 6 hours of daily patching.

(Image resource https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5396957)

 

Today’s era is of virtual reality where many people are working from home. In such an age treatment are also developed likewise. Virtual-reality-based vision therapy is an exciting program to treat amblyopia. In this program, virtual reality is combined with a video game which has allowed them to experience three-dimensional depth perception. It is specifically designed for patients with amblyopia and strabismic patients of younger age.

(Virtual reality-based vision therapy)

(Image resource – https://www.ferris.edu/optometry/extern/WOW-Vision-Therapy/index.htm)

 

Once the treatment is started the vision starts to get better within a few weeks and may take months to get the best results. To completely stop amblyopia from affecting again one needs to use these treatments on a timely basis. To avoid lifelong vision problems early detection and treatment is mandatory.

Complications

A significant complication of amblyopia is complete vision loss if it is untreated. Other common complications are as follow:

• Inability to read, play, drive or even perform simple tasks
• Social life disturbances lead to embarrassment due to poor eye contact.
• Development of negative self-image.
• Low self-esteem is an individual.
• Quality of life is decreased due to loss of stereoscopic vision which increases the risk of vehicular or operational accidents.
• Employment opportunities are reduced eventually.
• Complications from the ongoing treatment.
• Strabismus development
• Reverse amblyopia after treating the previous amblyopic condition.

Prevention

There is no known prevention method for any type of amblyopia today.  However, to prevent symptoms from getting worse early detection and early treatment are the key. Efforts are taken to reduce the risk of developing amblyopic conditions one must have regular eye examination in infants, younger children, and adults with predetermined conditions like diabetes, stroke. The undertaking of the early and adequate treatment of ocular conditions like eye tumors, cataracts, corneal opacity is vital. Along with the treatment, it is mandatory to find a doctor with a specialization in Optometric Vision Therapy and Visual Perceptual learning techniques to prevent further complications and delays.

Exercise

To do the exercises one must have a proper diagnosis and recommendation from the doctor. It can cause vision problems if not done under proper supervision. Better communication can be generated between the brain and eye with the help of eye exercise which strengthens the weaker eye. These exercises eventually lead to working of eyes together and improve vision. However, the effectiveness of exercises is undetermined but when combined with other therapies or treatment it has shown proven results. Medical experts may recommend glasses or patches or drops, in addition, to exercise which depends upon the underlying causes of amblyopia.

Effective exercises are shown in image given below:

(Image resource: https://www.verywellhealth.com/lazy-eye-exercises-5089336)

The exercises shown in the images are enjoyable tasks that can be performed while wearing a patch over the eye with stronger vision. Exercises in the above images are as follows:

• Reading
• Dot-to –dots
• Puzzles
• Coloring in the lines
• Computer games (Tetris, virtual reality)

These exercise does not need many materials they are simple to implement and allocate also cost-effective except computer games/virtual reality. A medical provider may prescribe specific vision therapy eye exercises. In such types of exercises, it is also necessary to relax eyes in between by closing the eyes for a few minutes or looking at an object which is far away which would help from straining the eyes.

Outcomes

Severity, age, underlying condition, and treatment purpose are the depending factors on which the resolution of Amblyopia is decided. Treatment given on time for the specific condition is important. If the condition is not treated properly then in some of the cases amblyopia may present even after the correction of ocular media. Typically, before age of ten if the conditions are well treated or corrected the better are the outcomes. In case it is not detected and treated at an early age the vision may be permanently affected in the long term which may lead to vision loss.

Tips to care for children with amblyopia

One needs to support the child morally, emotionally, and physically by all means to overcome the lazy eye disease. This will help to develop their fine motor and gross skills even with the hindrances and boost their self-esteem. Three major keys need to be followed-

• Eye care- The child should be taken to regular eye examination or undergo routine checkups once at six months age and the other at three years age and follow up all the appointments.
• Stick to the treatment- One should always encourage the child to wear eyeglasses, patches even if it’s against their wishes. Convince them by giving some fun examples or stories to make them understand why it should do that way.
• Strengthen the eye-Work together with the child as a team to read or do puzzles or virtual-reality-based games encouraging them to use lazy eyes while wearing the glasses or eye patch.

Epilogue

The prevalence rate of Amblyopia is two to three percent in infants globally. According to the global survey, there are nearly 36 million visually impaired around the globe. Recently insurance companies have also started covering treatment for amblyopic disease in the European region.

The sooner the better is the only chant to treat and get rid of Amblyopia over time. Diagnosed in routine checkups or a special visit to an ophthalmologist, Amblyopia can be detected. In addition, underlying cause identification also plays a key role. Observe the child, seek advice, follow, and stick to the treatment is the process to follow. Every child has a right to live joyfully and grow with confidence in society it is you who are responsible to boost the child to overcome Amblyopia. Everything is possible with the right actions along with proper caution.

Reference

1. Wikipedia- https://en.wikipedia.org/wiki/Amblyopia#:~:text=Amblyopia%20is%20the%20most%20common,with%20focusing%20during%20early%20childhood.
2. Google -https://www.google.com/search?q=google+images+of+amblyopia&sxsrf=APq-WBtJKGPa2obVm8eUei2H7thb0z5qKQ:1643982362790&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjy2YDGl-b1AhXJs1YBHbOiDy4Q_AUoAXoECAEQAw&biw=1366&bih=568&dpr=1
3. NIH, National Institutes of health-https://www.nei.nih.gov/sites/default/files/health-pdfs/FactsAbout_AMBLYOPIA_2015.pdf
4. American Academy of ophthalmology- https://www.aao.org/
5. Medclinic- https://www.mayoclinic.org/diseases-conditions/lazy-eye/symptoms-causes/syc-20352391
6. Dovmed- https://eyewiki.aao.org/Amblyopia