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Amblyopia (Lazy Eye) – Causes, Symptoms, Diagnosis, Treatment & Prevention

What is Amblyopia?

Amblyopia, sometimes known as “lazy eye”, is when there is reduced vision (usually in one eye) due to abnormal visual development in early childhood. When the weaker eye transmits less signal, the brain focuses its efforts more on the better seeing eye. This results in the vision of the one eye much weaker (“lazy”), while the other eye works better. Amblyopia begins in young children (from birth up to age ten years), and if it is untreated, can last a lifetime. Amblyopia is relatively common, affecting 2 – 3% of the population.

Causes of Amblyopia

Visual development occurs during from birth and progresses in first few years of life. At birth, neonates have poor vision. As vision centres in the brain develop, the vision improves rapidly in the first few weeks and months of life. Anything affecting normal vision leads to the brain pathways not developing properly. Causes includes:

Refractive errors

These are common issues, where the eye(s) cannot focus on the properly, leading to Refractive Amblyopia. There are different types of refractive errors. Myopia (Nearsightedness) – close objects are clear while far objects are blurry, Hypermetropia (Farsightedness) – far objects are clear while near objects are blurry, and Astigmatism – blurred vision at all distances due to asymmetric curvature of the cornea. A focusing issue can be treated easily with glasses or contact lenses, but if ignored, they can cause the brain to permanently depend on one eye only.

Strabismus (crossed eyes)

Strabismus is when the two eyes are not aligned with each other (one eye position is different to the other). This can lead to amblyopia, as the brain can only use one eye at a time and may start to ignore the eye that is turned more often.

Deprivation

Deprivation amblyopia occurs when there is an obstruction to light entering the eye, such as clouding of the lens (cataract) or droopy eyelid (ptosis). Deprivation amblyopia is one of the serious types of amblyopia which requires urgent attention even in early infancy. These, if not treated at the right time, can lead to permanent blindness. In some cases, deprivation amblyopia can affect both eyes.

Amblyopia Risk Factors

Factors that pose a high risk for Amblyopia in children include:

  1. Premature birth
  2. History of Amblyopia or similar condition in the family
  3. Developmental disabilities

Symptoms and Signs of Amblyopia

Amblyopia is quite difficult to notice without a detailed eye examination. Some symptoms and signs include:

  1. Bumping into objects more frequently
  2. The eye wanders inward or outward
  3. Trouble with depth perception
  4. Blurred vision in one eye

If untreated, the person will have poor vision in the weaker eye for the rest of their life. This can affect the ability to get a driving license, and choice of occupations.

Diagnosis

Diagnosis of Amblyopia usually involves an eye professional testing visual function in detail. It is important to cover one eye and then the other, to test vision in each eye separately. In Australia, most children have a “screening” vision check in the community before they start school. In NSW, it is known as the StEPS program (Statewide Eyesight Preschooler Screening Program). This is so that any child with amblyopia can be picked up and treatment given while the visual pathways are still developing. A complete eye examination by an ophthalmologist will help find out if there are any other problems.

Treatment

It is important to start amblyopia treatment as early as possible. Early intervention leads to better visual outcomes. The treatment prescribed depends on the cause and severity of amblyopia. Treatments include:

Glasses/contact lenses

This is the most common method for treating Refractive Amblyopia. Children are to wear the required glasses / contact lenses for the prescribed period with regular eye check-ups. This helps to determine the improvements in vision and to make necessary adjustments. Moreover, glasses can sometimes also help in correcting eye turn (accommodative esotropia). For mild cases of Amblyopia, glasses wear can cure the problem.

Eye patch (occlusion treatment)

Eye patches are used to cover the stronger eye for a certain number of hours every day. This forces the brain to communicate with the weaker eye, and improve its function. It should be used according to the directions of the doctor. The patch can be work directly on the skin, or placed over glasses (less effective). Patching treatment is usually weaned after months to years, when the vision has equalized, or the maximum benefit has been reached. 

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Bangerter filter

These are translucent filtersthat are worn over the glasses to create a blur of the image seen from the stronger eye.

Eye drops

Atropine is a medication used to temporarily blur vision in the stronger eye. It dilates the pupil and paralyses the focusing ability, creating a blur effect when looking at objects. These are recommended to be used on weekends or weekdays according to the requirement. This is an alternative to eye patches, but is not as strong as the vision from the stronger eye is not completely blocked.

Surgery

It is rare to perform surgery for Amblyopia, but if conditions like cataracts or droopy eyelids block the light from entering the eye, then surgery is necessary. In certain cases of Strabismus, eye muscle surgery may help to re-align the eyes and help with amblyopia management.

Prevention

There are no preventive measures for Amblyopia. Early detection and treatment is helpful. Parents are encouraged to seek a detailed eye examination with an ophthalmologist if they feel that their child is not seeing well out of one or both eyes.

Conclusion

Amblyopia is a vision disorder starting in childhood but lasting for a person’s whole life. It may be curable if diagnosed early enough.

Dr Parth Shah is a Sydney based ophthalmologist who is committed to providing excellent eye care to all of his patients. He implements modern research and technology in order to achieve better visual outcomes.