- Diplopia & repulsion,
- The connection between
Strabismus & Vision,
- Strabismus & binocular vision,
- Tilting the head
to compensate strabismus
Diplopia and repulsion
If strabismus is developed in adulthood, the result is the perception of two images of the same object, a condition called diplopia.
One image may appear sharper than the other, but anyway diplopia is very annoying and is likely to make the person unable to perform the simplest daily activities.
In a young child though, whose visual system is not fully developed, the brain tends to actively reject the second image in an attempt to stop the nuisance that diplopia causes.
This repulsion leads to irreversible reduction of vision in the eye that is not used, although the eye can otherwise be healthy. This condition is called amblyopia or "lazy eye" and is discussed in detail in another chapter.
The connection between Strabismus and Vision
Strabismus and visual function are interdependent, meaning that strabismus leads to impaired vision or that poor vision can correspondingly lead to strabismus. The brain of a young child with strabismus involuntary repels an image of the eye that squints in an attempt to stop the diplopia.
Even if both eyes had an equally good vision prior to initiation of strabismus, in a short time (weeks or months) the underactive eye loses the maximum of its visual acuity. This can be avoided by giving the eye that squints the opportunity to also operate and receive useful visual stimuli, which is achieved by covering the other eye. The whole process of covering the "good" eye needs special attention and a specific implementation plan, so we won’t reach the opposite end and the "good" eye becomes underactive.
Still, in other cases, the poor eyesight in one eye, may lead to strabismus. This is because the "bad" eye does not produce enough and useful visual information, in order for it to harmonize with the 'good' eye, and this condition is called sensory strabismus. In young children the eye that squints due to failing eyesight turns inwards (sensory esotropia). In older children and adults the turn is usually outwards (sensory exotropia). Regardless the age, the "bad" eye is usually higher than the "good" one.
Strabismus, due to poor vision in one eye can be resolved, or even eliminated by correcting the underlying problem. But if the eye deviates significantly or the period that has passed is long, you may need to resort to other methods of alignment.
The glasses for example can help a child with sensory esotropia, who has hyperopia in the "good" eye. Surgery is another option, but unfortunately it does not correct vision while sometimes the deterioration recurs.
Strabismus and binocular vision
A key question for children with strabismus is how this condition affects their daily activities. Can the child read properly? Can it ride a bike or participate regularly in sports or other activities?
Normal vision is binocular, resulting from the merger of slightly different images that both our eyes produce, forming rich information of a colored stereoscopic image with a characteristic sense of depth. The human eye is in other words much more than a simple "picture" of the room.
If strabismus is present from birth or the early months of life, it is practically impossible for the child to acquire binocular vision. It may be able to use each eye separately and have excellent visual acuity, but it cannot have real stereoscopic vision unless it is subjected to corrective surgery in its first year of life.
Even then the binocular vision is not fully developed and lags other children who did not develop strabismus. Strabismus usually appears before the age of 4. In the first year of life the child has already learned to use both eyes collaboratively and therefore understands that it sees in double.
Unless there is a compensatory mechanism by the child or a treatment, the image of the eye that squints will be suppressed by the brain in an attempt to eliminate diplopia. When this happens, the child feels and functions very well. He can only use one eye to focus, or sometimes one and sometimes the other, but in any case he can see well. He has, though, lost his stereoscopic vision, but gradually learns to appreciate in an indirect way distances, and actually will not differ from other children with true binocular vision.
A child's peripheral vision is not affected by strabismus. The repulsion mechanism is only related to central vision with peripheral vision remaining unaffected. In fact, children with exotropia (with an eye permanently pointing outwards), may have an even greater range of visual field than the ordinary.
Tilting the head to compensate strabismus
In certain types of strabismus, the eyes have a limited range of motion in one or more directions. As a result, the eyes cannot be aligned in a straight eye position line (primary).
Children face this state by leaning their head in such a manner that both the eyes can cooperate properly. Children who cannot, for example, raise an eye to the straight ahead position, lift instead their chin to look ahead, as the lower eye position is the only one in which the eyes can be placed on the same level and be synchronized.
This abnormal head tilt is the first thing that is perceived by the child's family and should not be discouraged, because thanks to this tilt these children often develop both good visual acuity and binocular vision.
Coping strategies of strabismus
The first step, before any treatment of strabismus, is to ensure that both eyes have a good vision. If one eye sees better than the other, our first action is to improve vision in the eye that lags. This is usually accomplished by covering the "good" eye for some hours of the day in order to give both eyes the opportunity to be equally used.
In most cases only one eye squints. But when its vision improves, then the other eye, the "good" one, can begin to degenerate. If both eyes have the same ‘’good’’ vision, the child has no reason to prefer one or the other, concluding in sometimes one eye squinting and sometimes the other.
In general, children with low grade asymptomatic exceptions just need observation. In some cases again, strabismus can be corrected by using glasses. Surgical correction is only recommended in high angles of strabismus or where there is diplopia or abnormal positions of the head.