Strabismus is a defect in parallelism of the visual axes. This defect can appear from birth, during the first months or years of life or, suddenly, in an adult. It may occur intermittently or permanently.
There are several strabismus classified depending on the direction in which the visual axes deviate. When one eye looks straight forwards and the other eye turns inwards, this is known as estropia or convergent strabismus. This is the most frequent form of strabismus. The eye can also turn outwards. This is known as exotropia or divergent strabismus. More rarely the eye turns downwards (hypotropia) or upwards (hypertropia).
We should however point out that in strabismus normally both eyes have a parallelism defect and not just one, even if one eye may appear to be the “culprit”.
In children suffering from strabismus, a third, even half develop amblyopia. This phenomenon appears when both eyes cannot manage to establish the same image. To avoid double vision, the brain adjusts by ignoring the images transmitted by one of the eyes. So one eye becomes dominant and the other is “forgotten”. Amblyopia is dangerous because the forgotten eye may become lazy or less functional over time: over 6 years of age this situation is irreversible.
Amblyopia does not appear in adults suddenly suffering from strabismus. This is because the brain is already developed for vision and the affected person will normally suffer from double vision.
Symptoms of strabismus are the following:
Strabismus appears at a very young age in about 3% of children. Girls and boys are equally affected. There is often a family history.
Adults can also be affected by the sudden appearance of strabismus.
Most frequent in families with a history of this problem, the exact cause of strabismus in children is not well established.
Strabismus in adulthood may be caused by injuries to the eye socket or nerves controlling the eye muscles or problems in the base of the brain, where visual signals are processed, including intra-cranial injuries and circulation problems.
Strabismus may accompany certain illnesses such as diabetes, high blood pressure, multiple sclerosis or thyroid problems. In these cases an overall approach should be made.
In children strabismus may be intermittent initially then become permanent.
In adults, certain strabismus of circulation origin may disappear over time.
An ophthalmologist assesses the alignment of the child’s eyes by looking for a sign of uncoordinated eye movements.
In babies or children with limited possibility of cooperating, the doctor tests the alignment by comparing the position of a light reflection projected onto each eye. However, this test may not detect intermittent strabismus, except if strabismus occurs during the test.
In children capable of cooperating, intermittent and constant strabismus can be detected by using the alternated occlusion technique. During these tests, the child stares at an object and the examiner observes the behaviour of each of the child’s eyes when the other eye is covered or uncovered.
Some ophthalmologists detect vision problems using a special camera taking snapshots of the child’s eyes.
The patient may also be asked to look through a series of prisms to determine the size of the eyes’ convergence or divergence.
A complete eye examination, including checking the retina, is necessary to eliminate all organic causes. Measurements are also taken to obtain the best vision correction possible with a pair of glasses. Other tests may be necessary depending on the cause of the strabismus.
To prevent the negative consequences of strabismus to a maximum, children should be closely monitored for any eye problems, especially if a family member suffers from strabismus.
The sooner the diagnosis is established and treatment is in place, the better the results will be from a vision point of view.