Amblyopia

Amblyopia is a condition in which the desired level of vision cannot be obtained even when corrected with spectacles or contact lenses. Normally, eyesight and vision develop as children grow. Babies have a low visual acuity when they are born, and their visual acuity improves to around 0.2 at 1 year of age and to about 1.0 at 3 years of age. It’s important to note that if the vision stops improving during childhood, as this may result in the child developing amblyopia.

This article describes following topics.

・Types and causes of amblyopia
・How to check for amblyopia
・What kind of treatment and measures are effective

The medical term “amblyopia” refers to a condition where most often one eye had reduced visual acuity due to vision development being hindered. Visual acuity cannot be improved to the desired level even when it’s corrected with spectacles or other means.
A condition in which visual acuity is poor due to eye disease is called “low vision” and is different and separate to amblyopia. Amblyopia can often be fully treated if it’s detected early.

More than half of children achieve visual acuity of 1.0 at age 3.

Immediately after birth, babies can only perceive bright light but by the time they are three months old, they are far sighted their visual acuity is only 0.01 to 0.02. Just as children develop in their language and gross motor skills as they grow, so do their eyesight and vision.  Generally, by the age of three, more than half of all children have the same level of vision as adults, around 1.0.

However, during these growth periods, if the vision stops improving, this can lead to “amblyopia,” a condition which makes it difficult to see even with spectacles.

Early treatment is critical.

Even if vision growth is temporarily halted, resumption of visual growth and improvement in visual acuity can be expected if the factors interfering with growth are removed and early treatment is initiated.
The critical period is commonly described as the first 6-9 years of a child’s life hence the sooner the treatment is started the better. It’s difficult for very young children to convey their symptoms. General vision screening is possible after the age of 3 or 4.

In Japan, children’s eyes are examined for 3 years of age, so if the possibility of amblyopia is detected at this point, early treatment can begin.
The treatment goal is to achieve a corrected visual acuity of 1.0 with spectacles.

Types of amblyopia are classified into the following four categories according to cause.

・Refractive Amblyopia
・Anisometropic amblyopia
・Strabismic amblyopia
・Deprivation amblyopia

The difficulty in treating amblyopia is excluding other eye diseases. Therefore, it’s difficult to determine that a child has amblyopia until the child reaches age of 4, when vision tests can be performed.
Amblyopia diagnosis is done comprehensively, including refraction and strabismus tests. If a diagnosis of “high possibility of developing amblyopia” is made, preventive treatment is initiated.

Refractive Amblyopia

In eyes with severe refractive error, such as high hyperopia, high myopia, or high astigmatism, the retina is not in properly focused. This reduces the stimuli to the brain, which leads to amblyopia.
The most common type of refractive error in children is hyperopia. At birth, children are slightly far sighted  which improves with age, but in cases of severe hyperopia, retina cannot be focused, which prevent children from developing normal vision. Similarly, strong astigmatism can also cause amblyopia.

Amblyopia is suspected from the following behavior.
・Squinting
・Approaching and looking objects at near

Amblyopia can also be detected at 3-year-old child’s health checkup or at medical checkup in school entrance.

Anisometropic Amblyopia

Anisometropic amblyopia occurs when visual development is impaired in one eye due to a significant difference in hyperopia, myopia, or astigmatism between the left and right eyes.
When there is a large difference in refractive power between the left and right eyes, anisometropic amblyopia is a visual impairment that occurs in the eye with the stronger refractive error. The eye that has difficulty seeing is less likely to be used, resulting in poor vision development and reduced vision.
Because vision development is impaired in only one eye, while the other eye’s vision develops normally, so there is almost no inconvenience to the child in daily life. Because of this, it’s difficult for parents to notice if their children having difficulty seeing when they observe them.
However, it’s usually picked up during a visual acuity and refraction tests where one eye is tested at a time. There are many cases of amblyopia being detected during 3-year-old and school age health checkups.

Strabismic Amblyopia

Strabismus is a condition in which one eye looks straight ahead but the other eye looks in a different direction. The strabismic amblyopia occurs because the misaligned eye, called the strabismic eye, doesn’t see the object using their central part of retina, and therefore visual acuity doesn’t develop.
Because it’s unilateral amblyopia, the vision in the fixating eye is often good and can be determined by a visual acuity or refractive examination. In cases of mild strabismus, the eye deviation may not be apparent. Therefore, if the visual acuity test results aren’t good in only one eye, a detailed examination is performed to determine whether the patient is using their central vision or not. Strabismic amblyopia can co-exists with anisometropic amblyopia.

Deprivation Amblyopia

If light stimuli cannot reach the retina, vision will not develop. The main causes are drooping eyelids (ptosis), clouding of the surface of the eye (corneal opacity), and cataracts.
Deprivation is a condition that prevent the light stimulus from reaching the retina. Sometimes surgery is needed to remove causes that are interfering with the retina’s ability to receive stimuli.
In addition to diseases, there are also known cases of amblyopia caused by using only one eye for a while, for example, with an eye patch.

To determine if a child has amblyopia, a detailed examination is necessary, not just results of poor visual acuity. If a parent notices something “a little strange” at home, please see an ophthalmology as soon as possible.

Points to be observed by parents at home

If you notice that your child is having trouble seeing things, you should pay more attention.
Children with visual impairments have the following characteristics:

・Watching TV at near.
・Squinting (narrowing their eyes to see things)
・Tilts head when looking at things

Amblyopia can be particularly difficult to detect when vision in one eye is fully developed. It may be detected by asking a person to read a clock or calendar at a distance with one eye covered.
In many cases, parents do not notice the child’s poor vision, especially when the symptoms are mild. If you notice any abnormalities, please visit an ophthalmologist as soon as possible.

Examination by Ophthalmologists

In addition to visiting an ophthalmologist for a direct diagnosis, there are many cases where suspected amblyopia is discovered during a 3-year-old health check or a health check at the time of school entry.
The ophthalmologist will then conduct a visual acuity test, a refraction (power) test, and a strabismus test to determine if the child has amblyopia.
In some cases, it may be necessary to test the eyes following instillation of eye drops. This is because a child’s eyes had significant accommodative power, so a normal eye examination alone cannot accurately determine the condition of the eye. Eye drops are used to relax the muscles involved in eye accommodation.

Treatment for amblyopia varies depending on the type and onset of the condition, but the basic treatment is correction with glasses. In some cases, occlusion training may also be performed at the same time.

Wearing Spectacles

In cases of amblyopia with refractive error, it is important to wear spectacles to focus on the fovea of the retina. This is because the development of visual acuity is stimulated when a clear image is formed.
Spectacles should be worn all the time except when bathing or sleeping. Also, check regularly to make sure that the spectacles fit properly. Since a child’s vision often changes with age, it is essential to treat amblyopia with the best pair of spectacles that will promote vision development.

Patching

When vision doesn’t improve sufficiently with the use of spectacles, patching is also performed. This involves attaching a patch or other shielding device to the better eye to encourage the patient to see with the eye with poor vision. If the patient already wears spectacles, it is also effective to use a cloth shielding device over the spectacles.

Eliminate the cause of Deprivation Amblyopia

If the child is developing deprivation amblyopia because of some disease, the priority is to remove the cause. In the case of congenital cataracts, depending on the degree of lens opacity, lens removal surgery is performed. Refractive correction and patching are usually performed in conjunction with the surgery during the postoperative follow-up.

Appropriate age for treatment

It has previously been suggested that there is a limit to the age at which amblyopia can be treated, generally considered to be up to about age 8. The critical period is commonly described as the first 6-9years of a child’s life hence the sooner the treatment is started the better.
However, it has been reported that anisometropia and refractive amblyopia can be effective up to about age 12. It’s also clear that the earlier it’s detected and treated, the better the outcome of the treatment.

My child is unwilling to wear spectacles. Is it necessary?

It’s natural for young children to feel uncomfortable wearing spectacles. It’s also understandable that parents may feel sorry for their children having to wear spectacles all the time, but regular use of spectacles is essential for the treatment of amblyopia.
Generally, the younger the child is, the more effective the treatment is, so please make sure that the child wears spectacles regularly. In addition, since children’s vision changes regularly, it’s necessary to check regularly whether the spectacles are appropriate for them.

Internal link: Why does myopia occur? How eyes and vision work and the relationship between heredity and environment

Can amblyopia be cured?

Amblyopia varies from person to person, depending on the age of onset and the manner in which it’s discovered. However, there’s a good chance that amblyopia can be fully treated if it’s detected early and treated appropriately. It’s thought that 95% of amblyopia cases can be treated (vision improved to the desired level) if treatment is started by the age of 4, and more than 75% by the age of 7. Treatment isn’t difficult if the improvement of vision can be promoted.

What is amblyopia? How does it differ from low vision?

The World Health Organization defines low vision as visual acuity worse than 0.05 to 0.3. Amblyopia in the medical sense refers to a condition in which normal development of vision is inhibited during childhood. Amblyopia can often be corrected with spectacles or other means from childhood, and vision can often be improved with the necessary intervention and treatment.