Amblyopia

Amblyopia (sometimes called a 'lazy' eye) is a developmental loss of vision in one eye. Amblyopia occurs as a child and is most commonly caused when one eye points in the wrong direction or is badly defocused compared to the fellow eye. As only a sub-standard image is capable of being detected by the brain from that eye, the visual processing pathways cannot fully form.

If amblyopia is detected by your optometrist at a young enough age then treatment can be started to improve the vision in the amblyopic eye to a better level. Without treatment the eye will continue to see poorly for the remainder of the patient's life, even when accurately corrected with glasses or contact lenses.

Amblyopia can be due to several different reasons, the common factor being that one eye does not receive the same clear image focussed at the correct part of the retina as the other eye. As a result during visual development the connections made from the eye to the visual cortex in the brain are unable to form fully. If untreated this developmental barrier becomes permanent and will affect vision in that eye for the rest of life despite optical correction.

There are three main types of amblyopia:

  • Refractive amblyopia - This is where a high presciption in the eye such as astigmatism or hyperopia results in a blurry image being formed on the retina of the worse eye.
  • Strabismic amblyopia - This is where one eye is misaligned compared to the normal eye (called a strabismus, or commonly a 'squint', or 'turned' eye) and as a result the clear image is focussed in the wrong part of the retina.
  • Form-deprivation amblyopia - This is apparent in much younger patients that are born with a congenital cataract or a droopy lid (ptosis) that stops the eye from seeing clearly through the obstruction.

There is a 'critical period' that occurs before the age of 8-9 years where the visual cortex is still 'plastic' and can be modified. During this time treatment can be initiated to try and improve the vision. The earlier this treatment starts the better the chance of improvement. Treatment for amblyopia initially consisted of removing the causative factor, for example prescribing glasses or contact lenses or surgically straightening the eye. If amblyopia persists with these modifications then amblyopia therapy can be instigated including:

  • Occlusion therapy: This involves the child using an occlusive patch over the _good _eye to force the bad eye to carry out visual tasks and make the correct connections with the brain. Typically patching is only required for a few hours a day and is best combined with visually stimulating tasks such as video games, reading or television programmes. Visit our Patching page for more information about this therapy.
  • Atropine therapy: 1% Atropine eyedrops cause blurry vision and pupil dilation. These are instilled in the good eye to make the bad eye do most of the visual work. These drops are only using in low-moderate levels of amblyopia.

Patches worn for amblyopia therapy are often fun and brightly coloured to encourage wear.

In some eyes even with amblyopia treatment the amblyopic eye may not recover the same vision as the good eye. Enabling the amblyopic eye to see at a level that can meet a driving standard is often deemed a success, This is so that the patient can still function in society should something happen to affect the good eye. In these instances care should be taken to protect the good eye with safety glasses in the future during sports etc.

Exciting new research is showing that older children and adults may be able to improve their amblyopia to some extent with the use of computer assisted therapy.