By Bjarne Lühr Hansen PhD, MD and Philipp Skafte-Holm MD, Mentor Institute
Normally, both eyes point in the same direction and look at the same target. In the case of squinting, only one eye looks at the target. The other eye looks in another direction. Our two eyes are moved by a total of 12 muscles that is attached to the eyeball.
There are several different causes of squinting and there is a difference between squinting children and adults. 5% of all children squint and the most common cause is that the child is long-sighted (hypermetropia). Newly arisen squinting with adults is rare and is seen in connection with rare illnesses.
In the case of ordinary squinting the muscles surrounding the eyes are healthy and normal but the coordination of the muscles is not perfect. The defect is in the part of the brain that controls the many muscles. Only rarely is squinting sign of an actual illness in the brain, instead, squinting may be perceived as our difference as human beings where some have better motor skills than others.
In the case of some rare forms of squinting, the cause lies with a poorly functioning muscle of the eye. This is for example seen following a cerebral thrombosis, serious blows to the head or in the case of metabolic disorders.
Children: When children squints, they see double. Therefore, the child instinctively starts to suppress the visual impression of one eye to make the double vision disappear. A child who squints therefore rarely complains. If the child always ‘switches off’ the same eye, the child’s eyesight on this eye does not develop normally and the eye become ‘lazy’. If the child instinctively switches between the two eyes, the child’s eyesight develops normally on each eye individually but its 3D vision does not fully develop.
When you read and perform other tasks that require close study, the eyes must cooperate. This happens by the eyes turning towards the nose (convergence) and both eyes focuses (accommodation). It requires strength to accommodate and in cases where the child is long-sighted the ability to accommodate is used to focus. The child’s dominating eye takes over and this causes the non-dominating eye to start squinting. Squinting with children should be treated with an eyepatch and glasses to secure a healthy development of eyesight on both eyes.
Youngsters and Adults: When you pass the age of 8-10 years, your eyesight is fully developed. If a person starts squinting after the age of 8-10, and his/her eyesight is fully developed, there is no risk of losing it because of squinting. In other words, you cannot develop a ‘lazy’ eye after you have passed the age of 10. If you start squinting as a youngster or adult, you, however, often experience double vision. At this point in time, the brain cannot learn to supress the visual impression of one of the eyes. If you start squinting as a youngster or adult, you can also experience headache, fatigue of the eyes and trouble with reading because you consciously or instinctively work the muscles of the eyes hard to keep the eyes straight and avoid double vision. Newly arisen squinting with adults is usually caused by an illness like for example diabetes, a metabolic disorder, cerebral thrombosis and in very rare cases, the cause of it may be cancer.
Therapy for squinting for children: The treatment of children who squints has to separate phases: Primarily, the strength of the vision is trained to secure a normal development of the eyesight. If the child has a lazy eye, you put an eyepatch over the good eye to force the child into using the lazy eye and train its eyesight. Treatment with an eyepatch continues until the eyesight is normal on both eyes and can last many months. Training the strength of the eyesight is usually not enough to remove squinting. The development of the eyesight should be monitored until the child is 10 years old. This is also the case even if the child has had surgery and has been cured for its squinting. After a child turns 10 years old, it is not possible to train the lazy eye, and therefor laser surgery is not possible. Secondarily, the misalignment of the eyes is treated. Surgery is often necessary to change the misalignment of the eyes. Surgery is performed to make sure the child has a healthy social development without bullying. Therefore, surgery is often performed as the child becomes old enough to attend school. However, there are a few exceptions and they are clarified by an examination by an ophthalmologist. Surgery cannot cure a lazy eye. Therefore, it is also important to monitor the development of the eyesight following surgery.