The medical term for a “lazy eye” is amblyopia. Amblyopia is a childhood eye condition where the vision in one eye fails to develop adequately. This usually affects the child’s ability to see using the less developed eye meaning they come to rely more on the “good” eye. Around one in 50 children aged about four years are diagnosed with lazy eye or amblyopia.

Signs of lazy eye

While older children may notice their sight is poor in one eye, younger children are usually either unaware or unable to explain that there vision is less clear using the affected eye. Parents may suspect their child has a lazy eye if the following physical eye problems develop, as these can cause a lazy eye:

• A squint may develop, where the weaker eye is orientated upwards, outwards, downards or inwards while the normal eye is facing forwards.
• One eye may be cloudy due to the development of cataracts.
• One eyelid may be drooping and partly covering the eye. This is called ptosis.

These conditions will need to be treated before the issue of the lazy eye can be addressed.

A lazy eye can also affect a child’s ability to judge depth and parents may notice their child has trouble judging the distance between an object and themselves, or positioning themselves well to catch a ball, for example.

Causes of lazy eye

Light is directed through the lens of each eye towards the light-sensitive layer at the back of eyes called the retina. This generates an image that is translated into nerve signals by the retina and sent to the brain, which combines the signals sent from both eyes to create a three-dimensional image. When the brain fails to correctly interpret the signals, a lazy eye may develop. This can happen if the amount of light entering the eye is reduced, if there is a lack of focus in the eye or if the two images from each eye are different (as in the case of squint). The brain then ignores the signals from the weaker eye and relies only on the “good” eye. If the condition is left untreated, central vision in the weak eye may never full develop.

Diagnosis of lazy eye

Cases of amblyopia are often picked up during routine eye tests before parents are aware their child has a problem. All children should have an eye check up before they start school and then repeat eye examinations at least every two years. A diagnosis of amblyopia is confirmed by an eye specialist or ophthalmologist.

Treatment of lazy eye

The treatment of this condition is usually divided into two stages. In the first stage, glasses are prescribed to correct the squint. Then, the child is encouraged to start using the weaker eye again. This can be achieved by placing an eye patche over the good eye or using eye drops to temporarily reduce the visual acuity of the good eye. The recovery of normal vision in the weak eye is usually gradual, with the lazy eye taking weeks or months to “catch up” with the good eye.