What is Amblyopia?

Amblyopia is often called a ‘lazy eye’.

Amblyopia is a condition where the vision in an eye is poor even after correcting for long or short-sightedness with glasses or contact lenses. In most cases, only one eye is affected, but it sometimes affects both eyes. 

Understanding the development of vision

Newborn babies can see. However, as they grow, the visual pathways continue to develop from the eye to the brain, and within the brain which learns how to interpret the vision signals that come from an eye. This visual development continues until about age 7-8 years. After this time, the visual pathways and the parts of the brain involved with vision are fully formed and cannot change.

If, for any reason, a young child cannot use one or both eyes normally, then vision is not learnt properly. This results in poor sight (poor visual acuity) called amblyopia. The amblyopia develops in addition to whatever else is affecting the eye. In effect, amblyopia is a developmental problem of the brain rather than a problem within the eye itself. Even if the other eye problem is treated, the visual impairment from amblyopia usually remains permanent unless it is treated before the age of about seven years.

What can cause Amblyopia?

Amblyopia can be caused by a squint (misalignment of the eyes), a large difference in visual weakness between the eyes (anisometropia), an abnormality of the eye itself (such as a childhood cataract) or by obstruction of the vision (for instance, by a droopy upper eyelid – ptosis).

Squint (strabismus)

A squint is a condition where the eyes do not look together in the same direction. As the eyes are not straight (aligned), they focus on different things. The result is that the brain ignores the signals from one of the eyes to avoid seeing double. Most cases of squint occur in early childhood – the critical time when the brain is learning to see. The ‘turning eye’ becomes the nondominant eye which then fails to develop the normal visual pathways in childhood and as a result amblyopia develops.

Other disorders that prevent clear vision

Any disorder in a young child that prevents good vision can lead to amblyopia as the brain fails to develop the visual pathways. For example, a cataract in a lens of an eye or a scarred cornea stops light getting to the back of the eye. Even a droopy eyelid can cause amblyopia if it covers enough of the eye to prevent it seeing properly.

Refractive errors

‘visual weakness in the eyes’

Refractive errors are eyesight problems due to poor focusing of light through the lens in the eye. Refractive errors include:

  • Short sight (myopia)
  • Long sight (hypermetropia)
  • Astigmatism

If there is a refractive error in one eye, often the other eye will be the same or similar. Where there is a difference of refraction between the two eyes a situation called anisometropia can occur. If this difference is large, the brain cannot understand the images coming from both eyes, and will choose to ignore the signals coming from one eye. Usually the brain selects the eye with the better refractive error in preference. The other (weaker) eye then becomes amblyopic.

Refractive errors can usually be corrected with glasses but unless vision is tested, a parent may not realise their child has any refractive error. This is particularly true if the child has anisometropia since one eye might have good enough vision to get by with and, without anyone realising, amblyopia may develop in the eye not being used.

What are the treatments for amblyopia?

Treatments include:

  • Correcting any underlying eye disorder, such as strabismus (squint), or correcting refractive errors (for example, long or short sight).
  • Training the amblyopic eye to work properly, so that vision can develop correctly.
  • Correcting the underlying eye disorders

Refractive errors such as short or long sight can be corrected with glasses. Cataracts can be treated with an operation. Improvement in eyesight after being fitted with glasses for a refractive error can take 4 -6 months.

FAQ’s

How common is amblyopia?

About 1 in 25 children develop some degree of amblyopia.

How is amblyopia diagnosed and assessed?

Amblyopia can be diagnosed by examining the eyes and testing vision. Different techniques are used to test vision, depending on the age of the child.

Why is amblyopia important?

If you have permanent amblyopia, you do not see properly out of one eye. Although the severity of visual impairment can vary it is always best to have two fully functioning eyes.

Even with mild amblyopia you may not have a good sense of depth when looking at objects. If you only have good vision in one eye, you risk severe sight problems if you have an injury or disease of the good eye later in life. So, treatment is usually always advised if it is likely to restore vision.

What is the outlook (prognosis)?

As a rule, the younger the child is treated, the quicker the improvement in vision is likely to be, and the better the chance of restoring full normal vision. If treatment is started before the age of about 6-7 years then it is often possible to restore normal vision. If treatment is started in older children then some improvement in vision may still occur, but full normal vision is unlikely to be achieved.

Making the affected eye work

The main treatment for amblyopia is patching (occlusion) of the better-seeing eye for a number of hours each day. The earlier in a child’s life this can be started, the more effective it will be. By the age of 8 most cases of amblyopia will not respond to patching treatment.

The length of treatment with an eye patch is dependent on the age of the child and the severity of the amblyopia. Treatment is continued until either the vision is normal, or until no further improvement is found. Usually you would be followed up every 6-12 weeks and if the vision becomes normal or stable for six months, the use of the eye patch may be tapered down. It may take from several weeks to several months for eye patching to be successful.

On average, patches may be worn for between 2 and 4 hours per day, although in severe cases they may have to be worn for most of the day. it is always better to use the eyepatch when the child is doing an enjoyable ‘visually demanding’ task. this might be colouring in for younger children or using a computer for older kids.

Modern patches come in many colours and patterns and can be quite appealing to children, especially when used with reward charts.