Strabismus (general description) The medical term for crossed eyes is strabismus (strah-biz mus). This condition means that one or both eyes are misaligned. Strabismus may be caused by abnormalities with the eye muscles with the nerves controlling the eye muscles or with the brain where the vision signals are processed. The condition affects an estimated 5 per cent of the population. Strabismus is usually present in children before the age of three.
Crossed eyes can be a sign of a serious illness such as high blood pressure diabetes neurological disorders and thyroid disorders. Thus early diagnosis and treatment are extremely important.
Strabismus is classified according to the direction of misalignment. The three most common types of strabismus are esotropia when one eye is turned inward toward the nose exotropia when one eye is turned outward toward the ear and hypertropia when one eye is turned upward.
Esotropia is the most common form of strabismus. The two most prevalent causes of esotropia seen in children include:
Most infants look periodically crossed-eyed for the first three months as they are learning to focus. Infantile esotropia becomes obvious when the child s eyes remain misaligned or crossed after the age of six months. The cause is unknown but there is evidence that suggests a genetic basis. The in-turn of the eye is quite noticeable and there are often symptoms such as twitching eyes swinging eyes when gazing in certain directions and having one eye turned in all the time while the other eye looks in all directions. If the latter is the case the infant is in danger of developing a lazy eye or amblyopia. When the eyes are not aligned the brain receives two different images resulting in double vision. To avoid this a child s brain can suppress one image. Amblyopia results if vision from one eye is consistently suppressed and the other eye becomes dominant. Almost half of children with strabismus develop amblyopia.
This condition occurs in children who are very farsighted. Their eyes cross because of difficulty focusing on nearby objects. This is especially apparent when children are concentrating on close material. The problem usually presents itself when children are about 2.5 years old with a range of 6 months to 7 years. A genetic history of this condition is common.
Sometimes an infant looks crossed-eyed when no strabismus is present. Known as pseudo-esotropia the illusion of crossed eyes in an infant usually occurs when there is a noticeable skin fold that covers the inner whites of the eye. The flat broad nasal bridge of many infants adds to the crossed eyed appearance. As the infant grows the skin folds disappear and the illusion of crossed eyes passes.
In contrast to esotropia exotropia is an outward turning of an eye. It often occurs intermittently especially when a child is ill tired daydreaming or focusing on distant objects. The symptoms include misaligned eyes decreased vision and sensitivity to light.
The third common type of strabismus hypertropia occurs when the eyes are vertically out of alignment. One eye turns upward relative to the opposite eye. Partial paralysis of one of the eye muscles either elevates or depresses the eye. A person can be either born with hypertropia or acquire the condition.
Strabismus cannot be prevented. However complications of strabismus can be prevented with early detection accurate diagnosis and proper treatment. Children should be seen by an eyecare practitioner before their third birthday.
Treatments vary depending on the type of strabismus and the severity of the condition. Eyeglasses and vision therapy are used to improve vision in the weaker eye. In order to force children to use their suppressed eye eye patches can be placed over the stronger eye or eye drops can temporarily blur the vision in the stronger eye. Exercises can strengthen specific eye muscles.
Surgery can also be performed to loosen or tighten specific eye muscles. This allows the eyes to realign themselves. However sometimes the surgical effects are only temporary and surgical intervention must be repeated.