What Is strabismus?
Strabismus is a type of ocular problem in which the eyes have a heterogeneous position in proportion to each other and their looks are in different directions. This heterogeneity may be clear or only present occasionally. While one eye is looking directly at the front, the other eye is turned inward, outward, upward or downward. The turned eye sometimes returns to its original and direct position and, on the contrary, the straight eye gets out of its position.
Strabismus is a common problem in the pediatric age group and is observed in about 4% of children; however, the time of its incidence may in higher ages, too. Its prevalence in males and females is identical and sometimes it has a family origin. However, some of the affected individuals do not mention a history of such a problem in their family.
With a normal two-eye view, both eyes look at same point. The visual part of the brain combines the two received images as a 3D image.
When one of the eyes gets out of its position due to strabismus, two different images will be sent to the brain. In a young child, the brain learns to ignore the image of the distorted eye and only accept the image of the direct eye or the same eye with a better look. This will remove the depth perception and two-eye vision. Adults experiencing strabismus often will be involved in double vision since their brain is able to accept or receive the image of both eyes. In this case, the brain will not be able to eliminate the image of the distorted eye. Unfortunately, this rapidly happens in children, i.e. the removal of the image of the distorted eye, and this leads to lazy eye or amblyopia.
The normal position of the eyes over the childhood period provides the possibility of the development of a suitable vision for these ages. Abnormal position, as seen in strabismus, reduces the vision and leads to amblyopia. The brain detects the better image and removes the image received from the obscure or amblyopic eye. This occurs in about half of the children with strabismus.
Amblyopia may be treated by closing the better eye and improving the visual acuity of the weaker eye. If detected in the early years of life, the treatment of amblyopia will be often successful; however, if treatment is delayed, amblyopia or reduced vision becomes permanent. Certainly, the earlier the amblyopia is treated, the better the vision will be provided.
Causes and Symptoms of Strabismus
Six muscles are attached to the outer wall of each eye; they are responsible for controlling eye movements. In each eye, two muscles move the eye to the right or left. Other four muscles are responsible for moving the eyes upward and downward or controlling the diagonal movements of the eye. To concentrate both eyes on a specific sign, all eye muscles require coordinating with each other and with the cooperator muscles of the other eye. Any agent disrupting this coordination can lead to strabismus.
The control role of brain on eye muscles is also of great importance. Thus, children with brain disorders like cerebral palsy, mental retardation, hydrocephalus and brain tumors often experience strabismus. Anything leading to vision loss, such as refractive error, cataract, ocular injury, etc. can be the factor for strabismus.
The fundamental symptom of strabismus is indeed the eye that is not in its original place. Sometimes the child closes one of his eyes in sunshine; sometimes he tries to move his head toward a particular position to use both of his eyes; and sometimes it is observed as severe tiredness of eyes and headache during ocular activity and sometimes the signs of lack of an appropriate deep vision are seen. Adults experiencing strabismus often complain of double vision.
It is necessary for any child to be examined by a family doctor, pediatrician or ophthalmologist during infancy or at pre-school ages to detect his probable problems. This is more important in particular in cases where another member of the family is with strabismus or amblyopia. In infants, it is often difficult to realize the difference between the apparent deviation of the eyes and the real strabismus. In young children, the wide nose and the skin wrinkle of the inner part of the eyelid lead the eyes to be hidden in the left and right looks of the eyes and thus they appear to be distorted. This apparently strabismus will gradually improve with the growth of the child, while real strabismus is not related to the child growth, and the ophthalmologist is well capable of distinguishing between real and false strabismus.
The goals of treating strabismus include vision preservation, direct vision and returning the two-eye vision. Depending on the cause of strabismus, treatment may be in the form of prescription of glasses, removal of cataracts, or modification of other filed causes of deviation or alteration of the position of the unbalanced muscles of the eye. After performing a complete ophthalmologic examination including a detailed examination of the internal parts, the ophthalmologist will select the appropriate optical, medical or surgical treatment. Closing the better eye will be often necessary to strengthen the vision of the amblyopic eye.
Esotropia (Inward Turning of One or Both Eyes)
Esotropia is actually the deviation of the eyes inward that is the most common type of infant strabismus. Young children with esotropia never use both of their eyes at the same time.
Early surgery will be necessary in most cases for aligning the eyes, two-eye vision, and avoidance of permanent vision loss.
Esotropia is the deviation of the eyes inward and in fact, it is the most common type of strabismus.
During surgery, the amount of muscles strength is adjusted in one or both eyes. For instance, in esotropia surgery, the tighter internal muscle may require to be loosened from the eye and attached to the eye in some backward place. This will weaken the tensile effect of the muscle and allow the eye to move outwards. Sometimes the outer muscle can be shortened in order to ease the movement of the eye to the outside, thereby increasing its tensile force.
Accommodative esotropia is a common form of esotropia occurring most often in hyperopic children at the ages of 2 years or older. At an early age, the child is capable of increasing his accommodative effort to compensate for his hyperopia; nevertheless, this obviously results in the deviation of his eyes to the inside.
To compensate for the accommodative esotropia, glasses are prescribed for the child. To compensate for the accommodative esotropia, bifocal glasses are prescribed for the child.
The glasses will reduce the mentioned accommodative effort and it can center the eyes. In some cases, using a special type of bifocal glasses is necessary (as shown in the figure below); and sometimes eye drops and special lenses called prisms can be used. Eye exercises sometimes help correct this situation in older children, too.
Exotropia (Outward Turning of the Eyes)
Exotropia or extraocular deviation is another common type of strabismus. It occurs more often when the child focuses on a distant object. Exotropia is often intermittent and especially occurs when the child is tired or stressed. Parents say that the child compresses an eyelid against sunlight. Although eyeglasses, eye exercise, or prism help control extraocular rotation of the eyes, in most cases it is necessary to perform a surgical procedure.
The sphere of the eye leaves its place never and during no surgery. Strabismus surgery is indeed a small shear in the tissue covering the eye that it allows the ophthalmologist to access the muscles under this tissue. Which muscles will undergo surgery depends on the orientation of the eye turn. Sometimes both eyes are required to undergo surgery.
Anesthesia is essential for strabismus surgery in children; however, adult surgeries are also possible with local numbness.
Recovery is rapid. The individual often returns to his normal activities within a few days. Sometimes it is necessary to use glasses with prism after surgery. Sometimes, the modification may be more or less than the required amount, where another surgery will be necessary.
It is recommended that strabismus correction surgery be performed as soon as possible, since as soon as the eyes of the infant are straight, he will be able to have two-eye and normal vision. On the other hand, strabismus eyes may have a negative impact on the child's self-confidence.
Like any other surgery, surgery on the eye muscles is also associated with some side effects. The complications include infection, bleeding and other rare side effects that may lead to a vision loss. Although strabismus surgery is often safe and effective, it never replaces the glasses or amblyopia treatment.
• The growth of the child does not treat strabismus by itself.
• The most effective time for treatment of strabismus is when the child is at an early age.
• Straitening the eyes is possible at any age.
• Strabismus may be treated without eye surgeries, and through eye drops, eye exercises or glasses.
• If surgical treatment is required, the lower the age of the surgery is, the greater the chance of supplying two-eye vision will be.