Lazy eye or amblyopia is the medical term used to describe reduced vision in one or both eyes due to the brain and eye not working together properly. There may not be any obvious problem with the eye, which may appear to be normal. Vision loss occurs because there is not proper stimulation of the nerve pathways between the brain and the eye. The brain then adapts to seeing only blurred images through the lazy eye, even if glasses are used. The brain therefore starts to favor the other eye that does not have poor vision. Amblyopia is the leading cause of vision loss in children.
Children with a lazy eye or amblyopia may or may not be aware that they are experiencing symptoms of the condition. While older children may notice that their vision is less clear in one eye, younger children may fail to bring the problem to their parents’ attention, either because they cannot tell their vision is being affected or because they cannot explain it.
In some cases, children may exhibit symptoms that occur as a result of an underlying pathology causing the amblyopia. These symptoms include:
- A squint - The child may develop a strabismic amblyopia (refer to “Amblyopia types”), characterized by a squint, where the weaker eye is orientated upwards, outwards, downwards or inwards while the normal or “good” eye is facing forwards.
- Cataract - The child may have developed a cataract in one eye, which will appear cloudy or patchy.
- Drooping eyelid - Also called ptosis, one eyelid may be drooping and partly covering the eye.
In younger children, one technique that can help to ascertain whether one eye is weaker, is to use a hand to cover each eye, one at a time. If the child pushes the hand away when it is over one eye but not while it is over the other, one eye may be working less well.
Other clues that a child may be experiencing vision problems due to amblyopia include:
- Poor ability to judge distance between themselves and an object.
- Poor depth of vision and inability to position themselves well to catch a ball, for example.
- The child may appear clumsy, running into furniture or falling over.
- Older children may find they have better vision in one eye and complain that reading, writing and drawing are challenging.
Amblyopia usually develops before a child is aged 6 years and the earlier the condition is diagnosed and treated, the better the chance of normal vision being restored. Therefore, guidelines suggest that children receive an eye exam at six months of age, followed by another exam at three years of age.
Several different forms of lazy eye exist, all of which cause reduced vision in one or both of the eyes. The different types of amblyopia are described below.
This is the most common form of amblyopia and it develops when the eyes are not straight. One eye may be turned outwards, upwards or downwards, which causes the brain to start ignoring information from that eye. Eventually, vision is lost in the eye that is not straight.
Here, cataracts or a similar problem cause the eye to become deprived of visual experience. Unless diagnosed and treated early, deprivation amblyopia can mean the child never learns to see properly and they may develop very poor vision. This form of amblyopia can sometimes affect both eyes.
In this form of amblyopia, a large or unequal amount of refractive error occurs between the eyes. The brain does not learn to see well using the eye that needs glasses more and instead learns to see well through the eye that needs glasses less. The problem may go unnoticed because the child does not mention that their vision is blurred because they see well with the stronger eye. Furthermore, the affected eye may not look any different to the healthy eye. This form of amblyopia may therefore not be detected until the child attends a visual examination. This condition can affect one or both of the eyes.
Successful prevention or correction of ambylopia is more likely the sooner the condition or risk factors for the condition are detected. If it is not treated by time the child reaches the age of 8, when the visual system has matured, the condition can become permanent and irreversible. In some cases, older children with amblyopia can find their vision improves with treatment.