What is Amblyopia?
Amblyopia or lazy eye is poor eyesight in an eye. It arises because this eye was unable to develop normally in early childhood.
When one eye develops good vision, while the other eye does not, the eye with the worse sharpness of sight is called the “lazy eye.” The deviation is fairly common: in four in every 100 adults. Usually only one of the two eyes is lazy, but in rare cases a ‘lazy eye’ can occur double-sided.
Amblyopia can only be successfully treated in early childhood and therefore it is very important that it is detected early. All children under the age of three must therefore have their eyes examined at least once.
If there are strabismus, strong spectacle lenses, ‘lazy eyes’ or other ophthalmic abnormalities in the family, it is advisable to carry out an ophthalmic examination at a younger age than three years.
In the Netherlands, eye examination forms part of the PBL (periodic medical examination) at the consultation center. In the case of abnormal findings, the ophthalmological examination is repeated and in cases of doubt or in the case of abnormalities, the child is referred to an ophthalmologist or orthoptist.
The development of normal seeing
In the first months after birth, a baby’s eyesight develops rapidly under the influence of all the images he receives from his environment. Even in early childhood, eyesight is still capable of change.
The vision continues to develop when the eyes can function well. But if there is a disturbance in the eyes, vision does not develop normally, it may stand still or even deteriorate.
It is believed that vision development is complete around the tenth year of life; after that no improvements can occur.
The development of good eyesight in both eyes is very important. For example, good eyesight is demanded in both eyes for different professions. Now that people are getting older, it is of great importance to maintain self-reliance that one has two good eyesight in case of loss of vision in one eye at an older age as a result of an accident or an eye defect.
The diagnosis Amblyopia
Diagnosing a ‘lazy eye’ can be very difficult. A child is often not aware that he has a good eye and a bad eye, and if there is no clear strabismus, the parents often do not notice that there is a ‘lazy eye’.
The diagnosis of amblyopia is made by showing a clear difference in visual acuity between the two eyes. Since it is difficult to determine the exact visual acuity at a young age, the ophthalmologist / orthoptist often estimates the visual acuity by assessing the following movements, ie how well a child follows a light or an object with one eye while the other is covered.
If one eye clearly sees less than the other eye, due to amblyopia, this is often quickly apparent during the examination due to poor following, protesting or even crying of the baby. In this case, further investigation is certainly necessary. In this study, after dripping pupil-widening drops, the refractive state of the eyes is determined.
The eye doctor also assesses the brightness of the cornea and the lens and the condition of the retina. Due to these drops, temporary light shyness can occur and the sight is sometimes less. From the age of infancy, the visual acuity is determined with the ‘picture card’, and with slightly older children, symbols (E-hooks or C-rings) or letters can be used to measure visual acuity.
The causes and symptoms Amblyopia
Amblyopia (‘lazy eye’) can be caused by any situation that adversely affects normal eye use. In general, there are three main reasons for the development of amblyopia:
- strabismus, where the eyes are not on the same point
- uneven breaking power in both eyes (difference in spectacle strength)
- the normally clear parts of the eye are blurred.
Amblyopia usually occurs in combination with strabismus. The image of the abnormal eye is turned off in the brain to prevent double vision, and eventually the eye forgets to look and thereby becomes lazy or amblyope. The child always looks with good eye.
Amblyopia can also occur when the image formed in one eye is out of focus due to a deviation of the eye’s strength. This blurred image receives less attention in the brain and is more or less displaced. In the long run this can also lead to a ‘lazy eye’. Sometimes there is nothing to be seen externally on such an eye and this is therefore the most difficult form of amblyopia to detect. This form of ‘lazy eye’ is only reflected in a careful visual acuity assessment.
An eye disease in which media turbidity occurs, such as cataracts, can also lead to amblyopia. In this case the cloudiness does not form a sharp image, which can also lead to a ‘lazy eye’.
A certain genetic predisposition also plays a role in the creation of a ‘lazy eye’. Children from families with a lot of strabismus, ‘lazy eyes’ or severe abnormalities, should be examined at a young age for the existence of a predisposition in this direction.
The treatment of Amblyopia
To practice a ‘lazy eye’ a child must be forced to use this ‘lazy eye’. In general this is achieved by covering the good eye (occluding) for a number of hours per day and for a certain period that can be weeks to months. In general, the older the child is and the lower the visual acuity, the longer the occlusion and the greater part of the day is necessary to achieve a good effect.
In younger children, the same effect can often be triggered by shorter-term occlusion. This is the main argument to treat a ‘lazy eye’ from an early age. It is very important to realize that the treatment of amblyopia can actually only begin when the causes underlying the development of amblyopia have been eliminated. So first glasses must be given to correct strength deviation or cataract must be removed so that an eye with a good correction can learn to look.
In certain cases it is not possible to treat a lazy eye through a patch on the right eye; in such a case pupil-widening drops are sometimes given in the right eye, so that this eye cannot be used for close-up viewing. In this way, the child is forced to use his lazy eye for close-up. For the same reason, special glasses or contact lenses are sometimes prescribed.
Parents are the most important for successful amblyopia treatment. They must ensure that a child wears the plaster and that the occlusion is sustained long enough. The ophthalmologist and the orthoptist will assist the parents as well as possible.
In certain cases, a child is too old to start amblyopia treatment. It is generally assumed that after the age of about 10 years, treatment of amblyopia will no longer be successful.