What is amblyopia ?

Amblyopia means reduced vision in a normal anatomical eye.

When does amblyopia develop?

Amblyopia develops due to any of the following?

• Squint/strabismus (eyes not positioned straight)
• There is great difference in power of both eyes(one eye focussing differently from the other)
• Cataract (clouding of lens)
• Severe ptosis (droopy eye lids)
• Premature birth
• Heredity (parents with amblyopia or strabismus)
• Any disease that affects the eye.

Amblyopia develops during childhood. Children under 9 years of age whose vision is still developing are at a highest risk for amblyopia. Generally, the younger the child, the greater the risk.

Why does amblyopia develop?

Amblyopia develops because when one eye is turned as in squint, two different images are sent to the brain. In a young child, the brain learns to ignore the image of the deviated eye and see only the image of the better eye. Similarly when there is difference in power of both eyes, the blurred or defocused image formed by the eye with more power is avoided by the brain. For the retina to capture the object, it needs adequate light and visual stimulus. This being absent in presence of cataract either in one or both eyes result in amblyopia. High or moderate degree of refractive power present in both eyes when not corrected early and adequately also results in amblyopia.

How is amblyopia treated?

The most effective way of treating amblyopia is to make the child use the amblyopic eye. Covering or patching the good eye to force use of the amblyopic ye may be necessary to ensure equal and normal vision. This can achieved by

• Prescribing proper spectacles if the patient is found to have refractive error.
• Removal of cataract when indicated.
• Occluding the normal eye.
• Surgery when amblyopia is accompanied by strabismus.

Occlusion means closure of normal eye with a patch and this makes the child use the amblyopic eye. Occlusion is done from few hours to few days depending upon the age of patient, type and severity of amblyopia. In case having less severe amblyopia partial occlusion by making one glass translucent, may be sufficient. Elder children can do reading exercises with patching of the normal eye at home. Those patient who are doing patching need periodic follow up, which is decided by an optometrist/ ophthalmologist. Duration of treatment may extend from months to year. Once the vision is improved up to the level of normal eye, it has to be maintained by occluding the normal eye for few hours during critical years of the age. The optometrist / ophthalmologist will decide whether or how long the occlusion should be continued. Loss of vision from amblyopia is preventable if treatment is begun early.

Facts on patching.

• Patching is not a pleasant thing for a child, so initially the child will be reluctant to undergo it.
• In a young child, it is done for shorter periods initially and gradually the duration is increased to get better compliance.
• Acceptance is good as soon as vision is increased in amblyopic eye.
• Method of patching should be according to the interests of the child.
• Patch should be stuck directly on to the face over the eye.
• If the child wears glasses, the patch should still be placed on the face, not on the glasses.
• Glasses can also be used as an occluder only in elder children. Refractive errors in children to be corrected or ignored?
• Failure to correct refractive error leads to decreased vision and also hampers the academic activities of the child.
• Children found with symptoms of refractive errors should be brought to an Optometrist/ophthalmologist for necessary correction.
• Parents should encourage their children to wear glasses. Wearing glasses is not a stigma.
• Loading children with vitamin-A may neither help in preventing nor correcting refractive errors.
• Spectacles perse do not increase or decrease or decrease the power.

Normal vision

In normal vision light rays from an object focus on the retina.

Fig.

Refractive error is said to exist when the light rays get focused in front or behind the retina causing blurred vision. Causes

Causes

• The eyeball being larger or smaller than the normal size.
• Changes in the crystalline lens.
• Flat or steeper corneal curvature.

Types of Refractive Errors?

->The common types of refractive errors that occur in children are myopia (near sightedness),

->Hyperopia (far sightedness) and astigmatism.

Hyperopia?

In hyperopia or farsightedness, the light rays from an object from an image behind the retina because of the small size of the eye ball

Myopia?

The light rays from an object from an object from an image in front of the retina. The occurs when the cornea is curved too much or if the eyes too long.

Astigmatism?

This occurs due to changes in corneal curvatures.

Symptoms of Refractive Errors

• Children can have difficulty in reading small letters on the blackboard.
• Some children squeeze their eyes while trying to see distant objects like blackboard, television etc.
• Children hold books close to their face while reading.
• Children with myopia have defective vision for distance and clear vision for near.
• They can experience eye strain while trying to read for long hours.
• Some children with hyperopia can present with squint.
• Children can develop swelling on the lids due to constant rubbing of the eyes to see things clearly.
• Eye pain and headaches may occur. The child should be immediately brought to an Optometrist/Ophthalmologist, if anyone of the above symptoms is observed.Treatment for refractive errors
• Correction using spectacles is the best option available for refractive errors.
• The power of the glasses may change depending on the growth of the eye ball.
• An eye check up has to be done once in 6 month for children under 5 years of age and once a year thereafter and change of glasses when necessary.
• Children older than 15 years can use contact lenses if they don't want spectacles. Those over 18 years of age with stable power also have the option of Lasik, a laser refractive procedure apart from contact lenses.
• Glasses should be worn constantly according to the advice of your eye care professional.