What is Amblyopia?
The term ‘amblyopia’ – or the more commonly used ‘lazy eye’ – implies poor vision in one eye (rarely both) which is not correctable with spectacle lenses. Amblyopia occurs when the area responsible for vision in the brain fails to develop during early childhood.
The eyes effectively compete for representation in the brain from birth, and the visual cortex at the back of the brain continues to develop up until we are about 8 years old. If, during this time, the vision from one eye is impaired for any reason the brain favours the better eye – effectively ignoring the information from the weaker eye.
It is important that treatment to overcome amblyopia occurs within this 8 year period. As a child’s age increases it becomes more difficult to improve vision, so the earlier treatment is instituted the more likely a good visual outcome will be obtained.
Common causes of amblyopia are:
- Refractive error (focusing problem)
- one eye being more longsighted (hypermetropic),
- or more short sighted (myopic),
- or having more astigmatism than the other.
Strabismus or ‘squint’
If one eye is constantly turned in or out the brain favours the straight eye and ignores the information from the turning eye which results in amblyopia.
Anything that prevents light entering the eye may impair normal visual development a droopy eyelid or cataract.
How do we treat amblyopia?
The treatment recommended for the management of amblyopia will depend on its cause and is always a long process. Glasses may be needed to help the eyes focus properly and may alone be sufficient to improve the vision. Sometimes glasses are not necessary, but other treatment such as patching, or surgery are required to encourage visual development.
Treating amblyopia by patching is often difficult because the child is being forced to use an eye with poor vision and young people do not understand why they have to wear a patch. Patching will only work if a child wears the patch as instructed. If started at an early age, patching is usually successful but it will only help the vision of the lazy eye and will not improve a squint. Your Orthoptist will advise you how long your child needs to wear the patch each day and when your child needs to return for a follow up check.
In some cases, atropine eye drops can be instilled on a regular basis into the good eye as an alternative to patching. Atropine dilates the pupil and impairs the focusing mechanism which blurs the vision in the better eye, particularly at shorter distances. This encourages the use of the amblyopic eye and improves the vision of that eye. Atropine drops can be used on their own or in conjunction with glasses and/or patching.
Surgery to properly align an eye to correct a squint does not in itself overcome amblyopia, nor can an amblyopic eye be treated with laser or in adulthood.