Amblyopia

Amblyopia

Vision develops from birth. If the visual brain receives an abnormal, blurred or shifted image from one eye, it will neutralise the visual messages from that eye and develop only the vision of the healthy eye. Gradually, the visual brain will no longer be able to use the amblyopic eye, even after correction of the responsible disorder.

Amblyopia can be treated during the period of vision development, i.e. during the first 6 years of life, after which it gradually becomes permanent. It is one of the main causes of poor vision in one eye, although its detection and treatment are fairly simple, if done in time.

Amblyopia: this is the lack of vision development in one eye. The other eye usually sees normally and the child does not complain about anything. Amblyopia can only be detected and treated (before the age of 6) if screening is carried out in good time. The cause is most often related to a refraction problem (glasses) or a strabismus in one eye. Other more rare causes exist. The treatment consists in penalising the good eye in a dosed way with “blinders” (bandages) until visual recovery. Glasses are most often necessary.

1/ What is amblyopia?

Amblyopia is the discovery of poor vision in one eye (more rarely in both), which persists even though any refraction (glasses), transparency (cataract, etc.) or fixation (strabismus) problem has been treated. It is not related to the eye since it persists even though a possible defect has been treated. Amblyopia is due to a defect in the function of the visual brain: it has not “learned” to use the eye in question during the period of vision development, i.e. from 0 to 8-10 years of age. Several situations can lead to this, all of which have in common the transmission of a poorer quality image of an eye, occurring during this period of visual acquisition (see next question).

If amblyopia is discovered during the first years of life, in any case before the age of 6, it can be treated. To do this, it must of course be treated quickly, as soon as it is diagnosed. In fact, the visual skills are progressively fixed, so the earlier the treatment, the easier and more effective it is. Conversely, what is lost after 6 to 8 years will be lost for good. No treatment, no matter how modern it may be, will allow this eye to be seen again.

The most important challenge concerning amblyopia is to discover it in time to treat it. Indeed, amblyopia cannot be “seen”… and the child does not complain about it. It is therefore the role of visual screening to find it. It is currently well organised, carried out by doctors, paediatricians and also at nursery and primary schools. This has allowed the frequency of amblyopia to fall considerably over the last fifteen years.

The treatment starts of course with the treatment of the cause of the amblyopia (glasses, strabismus, opacity…). But the most important part of the treatment consists in forcing the brain to use the amblyopic eye by hiding the good eye, until visual recovery. Once the vision is balanced between the two eyes, a prolonged consolidation treatment is necessary. This treatment is sometimes continued until the end of the maturation period, which is around 10 years.

2/How does amblyopia develop?

It occurs when a favourable situation is not treated during the period of visual maturation (0 to 6-8 years). Most often the cause can be treated, but sometimes it is beyond any possibility because of excessive abnormalities of one eye or its motor skills.

For a harmonious visual development, each eye must send a good quality image, identical to the other eye and both eyes must look at the same place. The most frequent causes of amblyopia are deduced from these findings.

Unilateral amblyopia (of one eye only) is linked to asymmetrical stimulation of the two eyes for various reasons:

– Refractive disorders: if one eye has a different refraction from the other, more hyperopic, myopic or astigmatic, it transmits a blurred image and the brain will neutralize it for a long time and then “forget” the images transmitted by this eye. When adapted glasses are put on, the vision will not improve. If the disorder was discovered before the age of 6, it will be necessary to penalize (hide) the good eye to force the use of the amblyopic eye. If the discovery is late, the amblyopia is usually permanent.

– Strabismus: a “good” strabismus must be alternating, i.e. each eye must fixate alternately. In this way, vision develops symmetrically. If the strabismus is not alternating, this often reassures the parents who think that it is better to have only one eye that squints than both!… alas, in this case, vision only develops in the fixing eye and the child develops amblyopia in the strabismus eye. The treatment consists of alternating fixation in a forced manner, by performing an occlusion, first of the good eye, then alternating.

– Anything that interferes with the transmission of images from one eye to the brain can cause amblyopia: occlusion of one eye by a significant ptosis, opacity of the transparent media of the eye (scar on the cornea, congenital or traumatic cataract, etc.), more rarely acquired or congenital unilateral retinal diseases, damage to an optic nerve, etc. The resulting amblyopias are complex and must be treated by a specialised ophthalmic and paediatric team. Once again, the earlier the treatment, the better the results.

– All of these causes can accumulate, and each amblyopia is ultimately a unique case. Treatment is always individualised for each child.

Bilateral amblyopia is more rare. Vision remains poor bilaterally, despite treatment of the cause:

– High ametropia (myopia, hyperopia, astigmatism) bilaterally

– Congenital nystagmus. In this case, the instability of the gaze, of the fixation, prevents the development of a good quality image, and therefore of a correct visual acuity.