Strabismus is a condition in which the eyes are misaligned or are not looking at the same target at the same time. The word "strabismus" is derived from the Greek word "strabismos", which means, "to squint". Many patients with strabismus will squint on occasion, especially in bright light outdoors. It is sometimes referred to as "lazy eye" because the wandering eye appears to be lazy. Many people think that strabismus is the result of an eye muscle problem but this is usually not the case. In most instances, the eye muscles are quite healthy. The problem lies in the part of the brain that controls fusion, or keeping both eyes simultaneously directed toward the object of interest.
Types of Strabismus
Congenital strabismus is present at birth or develops within the first six months of life. If strabismus develops after six months of life, it is considered to be acquired strabismus. Some forms of strabismus are the result of abnormally functioning eye muscles, or nerves that stimulate an eye muscle; this is known as paralytic strabismus because a muscle is believed to be paralyzed. There are also medical conditions that can cause an eye muscle to be too tight or restricted, causing restrictive strabismus. Some people are born with a special form of strabismus that results from unique eye muscle, or eye muscle nerve abnormalities. If an eye is crossed inward toward the nose, esotropia exists. If an eye is turned away from the nose (toward the ear), exotropia exists. If an eye is turned upward or downward, a hypertropia or hypotropia, respectively, exists.
Who Gets Strabismus?
In the preschool age group, three to five percent of children have some form of strabismus. The genetics or inheritance pattern of strabismus is very complex and in most instances, it is not completely understood. I usually tell my patients that overall, about 30 percent of patients with strabismus will have a first-degree relative who has some form of strabismus, too. It may be a sibling, parent, or a child. In most cases, however, there is no known relative with strabismus. There are certain groups of patients who have a higher incidence of strabismus. These include those children born prematurely, children who had retinopathy of prematurity (a potentially blinding condition of premature infants that affects the retina in the back of the eyes), children who are developmentally delayed, children with a family history of strabismus, and children with craniofacial (skull shape) abnormalities, just to name a few. Adults can develop strabismus, also. It may be the result of a medical or neurological problem that has developed in adulthood or it can be a recurrence of childhood strabismus. Strabismus can also develop following certain forms of head trauma in both children and adults.
Why is Treatment Necessary?
There are several reasons why strabismus needs to be treated. For one, it does not improve by itself. It is a myth that children usually outgrow strabismus. Second, young children with strabismus have a significant chance of permanently losing vision in one eye-a vision loss that is not recoverable with eyeglasses. If a child does not develop the ability to use both eyes together as a young child, this ability will not develop later in life. For children whose vision develops in only one eye, as older children and later as adults, they may also experience limitations or restrictions in both their vocations and avocations. Some people whose eyes are visibly misaligned have difficulty communicating with others, and some may have difficulty with self-esteem. Finally, and certainly not least important, strabismus can be an early sign of a serious, ocular or neurologic problem.
In children, strabismus may be detected by the child's primary care practitioner during routine exams. Sometimes it is first noticed by family members, childcare providers, or friends. Older patients may notice it themselves or may develop double vision.
An adult who suspects he or she may have strabismus should get a referral to an eye doctor who is experienced in treating this condition. A complete examination should then be performed. The exam includes taking a thorough history and reviewing the patient's medical history, measuring the patient's vision, examining the health of the eyes, measuring the eye alignment with the patient looking in different directions, measuring how well the eyes move in various directions, and measuring the patient's refractive error, i.e., whether the patient is nearsighted, farsighted, has an astigmatism, or some combination of these. Sometimes additional testing may be necessary.
Medical or Nonsurgical Treatment
There are many different ways to treat strabismus, depending on the clinical situation and the patient's age. Some patients with strabismus will be treated with eyeglasses if it is thought that eyeglasses will improve the sight in one or both of the eyes. Sometimes, by improving the clarity of the vision, the strabismus disappears. If one eye does not see as well as the other, and the patient is a child, the doctor may decide to patch the eye that is functioning better to help recover vision in the poorer seeing eye. This is known as amblyopia therapy.
Esotropia, or crossing of the eyes, is sometimes caused by excess farsightedness in a child. This type of strabismus may be treated with eyeglasses to help the child focus and to eliminate the inward crossing of the eyes. Some of these children may even be given bifocal eyeglasses to give extra help with focusing on near objects if it is felt that the near focusing is contributing to the strabismus.
Prescription eyedrops are sometimes used in one or both eyes for weeks or months at a time. There are also some forms of strabismus that may be treated with eye exercises.
Eye muscle surgery is sometimes necessary for patients with strabismus. Eye muscle surgery is almost always performed on an outpatient basis, which means that the patient does not stay overnight at the hospital. For children and some adults, general anesthesia is used and the patient is "asleep" during the entire operation. Sometimes local anesthesia is used and the patient is awake during the operation, although they may be sleepy from systemic or intravenous medications that are also used.
In most operations, one or more of the eye muscles are repositioned. In some cases, a muscle may be weakened, or recessed, by separating it from the eye and reattaching it in a slightly weaker position. Alternatively, a muscle may be strengthened, or resected, by splicing out a small piece of the muscle and then reattaching the muscle so it has a stronger effect on the eye's position.
For some cases of strabismus, the doctor will inject a powerful paralyzing agent, botulinum toxin, into the muscle to weaken the muscle's action. Some surgeons will use adjustable sutures for older children and adults, especially if the patient has had eye muscle surgery previously. An adjustable suture is a stitch that is used during surgery that can be manipulated within 24 hours after the surgery when the patient is no longer under anesthesia in order to increase the success of the surgery. This procedure is performed on the patient after anesthetic eyedrops are instilled. Using special instruments, one or more eye muscles can be repositioned and then secured. This "fine tuning" may increase the success of the surgery.
There are many different kinds of strabismus that can affect both children and adults. It is important that patients with strabismus be evaluated, as early diagnosis and treatment result in the best outcome. In most instances, strabismus can be treated effectively, and the patient can enjoy many years of good vision as well as a more normal ocular appearance.