Amblyopia (Lazy Eye)

Amblyopia is poor vision in an eye that did not develop normal sight during early childhood. It is commonly called ‘lazy eye’. Usually, only one eye is affected by amblyopia, but it is possible for both eyes to be ‘lazy’.

This condition is quite common, affecting approximately two or three out of every 100 people. The best time to correct amblyopia is during infancy or early childhood. If a child cannot use his or her eyes normally, vision does not develop properly and may even decrease. After the first nine years of life, the visual system is normally fully developed and usually cannot be changed. For these reasons, amblyopia must be detected and treated as early as possible.

Amblyopia is caused by any condition that affects normal use of the eyes and visual development.

The three major causes:

Strabismus (squint or misaligned eyes)

Amblyopia occurs most commonly with misaligned or crossed eyes. The crossed eye ‘turns off’ to avoid double vision and the child uses only the better eye. The misaligned eye then fails to develop normal vision.

Unequal focus and refractive errors

Refractive errors are eye conditions that are corrected by wearing glasses. Amblyopia occurs when one eye is out of focus because it is more nearsighted, farsighted or astigmatic than the other.

The unfocused (blurred) eye ‘turns off’ and becomes amblyopic. The eyes can look normal, but one eye has poor vision. This is the most difficult type of amblyopia to detect since the child appears to have normal vision when both eyes are open.

Amblyopia can also occur in both eyes if both eyes have very blurred vision. This can happen when there is a high amount of nearsightedness, farsightedness or astigmatism (irregularity of the focus).

Cloudiness of normally clear inner eye structures

An eye disease such as a cataract (a clouding of the eye’s naturally clear lens) may lead to amblyopia. Any factor that prevents a clear image from being focused inside the eye can lead to the development of amblyopia in a child. This is often the most severe form of amblyopia.

It is not easy to recognise amblyopia. A child may not be aware of having one strong eye and one weak eye. Unless the child has a misaligned eye or other obvious abnormality, there is often no way for parents to tell that something is wrong. In general to qualify the diagnosis of amblyopia there must a difference in visual acuity of two or more lines between the two eyes, or corrected acuity in both eyes were 6/9 or worse.

Amblyopia is detected by finding a difference in vision between the two eyes or poor vision in both eyes.  Using a variety of tests, the eye specialist observes the reactions of the baby/child when one eye is covered. If one eye is amblyopic and the good eye is covered, the baby/child may attempt to look around the patch, try to pull it off or cry.

Poor vision in one eye does not always mean that a child has amblyopia as other eye diseases may be causing decreased vision. These diseases can include cataracts, inflammations, tumours and other disorders of the inner eye such as retinal dystrophy.

To correct amblyopia, a child must be made to use the weak eye. This is usually done by covering or blurring the strong eye for weeks or months.

Glasses may be prescribed to correct errors in focusing. If glasses alone do not improve vision, then patching is necessary.

Amblyopia may also be treated by blurring the vision in the good eye with special eyedrops or glasses to force the child to use the amblyopic eye.

If there is a cataract or other abnormality, surgery may be required to correct the problem. An intraocular lens may be implanted. After surgery, glasses or contact lenses can be used to restore focus while patching improves vision.

If the amblyopia is detected and treated early, most children will gain improved vision. Amblyopia caused by squints or unequal refractive errors may be treated successfully during the first nine years of age. After this time, amblyopia does not normally recur. If amblyopia is not detected until after early childhood, treatment may not be successful. Amblyopia caused by cloudiness of the eye tissue needs to be detected and treated extremely early (within the first few months of life) in order to be treated successfully.