Overview
Amblyopia is a condition whereby there is a reduction in visual acuity due to a problem with focussing in early childhood. This results in reduced acuity as the brain is not stimulated to develop correctly.
There is not necessarily an inherent problem with the eye itself.
It affects about 1-5% of the population.
The most common cause is strabismus (‘lazy eye’). In this condition the two eyes do not align correctly, and the brain suppresses the image received from one of the eyes to avoid a perception of diplopia. The results is that vision in the suppressed eye does not develop properly.
Other causes including refractive defects (often due to different shape eyes) and congenital cataracts.
It can be treated if detected early enough. If it is only detected late, then the neurological pathways required for the correct development of vision cannot be formed and there is lifelong reduction of visual acuity.
Diagnosis
- Is easy when made with a Snellen chart and formal acuity testing – but often children can’t perform this testing until they at least 4-5 years old.
- Can be diagnosed earlier if there is obvious strabismus. Eye movement assessment in children is important for this reason. This, obviously, can only detect the strabismus form of the condition (which is the most common).
Treatment
- Strabismus
- Treated with patches or eye drops. Both of these methods obscure the vision of the ‘good’ eye and force the brain to process the image from the affected eye.
- Drops used are dilating drops (usually atropine). The dilation of the pupil causes the vision to become very blurry and as such the input from that eye is ignored by the brain.
- Drops reduce the incidence of bullying at school, but can be difficult to administer to reluctant children!
- Treatment should only be used for 4-6 hours a day so as not to impact the development of the good eye. Over-patching can cause “reverse amblyopia”
- It can be untreatable if not detected until school age
- All new instances of strabismus need specialist referral to rule out a significant cause (e.g. retinoblastoma, congenital cataract)
- Refractive error – is treated with glasses
- Congenital cataracts are treated surgically. These cases account for less than 3% of the total number of cases of amblyopia
- Cataracts are diagnosed simply by checking the red reflex. Also look out for retinoblastoma (rare, and can be bilateral in 30% of cases)
- Commonly caused by intrauterine infection, such as rubella
References
Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt