Strabismus
Strabismus is misaligment of the eyes. In this condition, only one eye can focus on an object and the other eye looks beside it. If this condition occurs suddenly in adults, double pictures can appear and give extreme discomfort occur.
However, the brain of a child can inhibit the perception of the eye which deviates so as not to see double. This condition may lead to serious outcomes in terms of visual acuity, because amblyopia (lazy eye) can develop if the eye of a child is not involved in the process of vision for a long time. If this is not treated early, it may persist throughout their lifetime, and thus, this child can never achieve a full visual acuity. Approximately 4% of the population has strabismic amblyopia. This condition prevents 3-dimensional vision. Strabismus in children is divided into two groups: unilateral strabismus (the deviating eye is always the same) and alternating strabismus (either of the eye can be seen deviated). The deviating eye may shift internally, laterally, upwards or downwards. It may also rotate around its own axis. Most of the time, a combination of these deviations is observed. The degree of strabismus (the size of the strabismic angle) is usually different in different gaze directions and may change from day to day. Development of strabismus is independent of the degree of strabismus. In microstrabismus of 0,5 and 5 degrees which is not noticed cosmetically, a severe amblyopia may develop in the deviating eye.
Paralytic strabismus is completely different from typical pediatric strabismus. Paralyic strabismus may arise from affection of one or more muscles of the eye, which happens due to a defect in stimulus transfer between nerves and eye muscles or nerve damage. Strabismus arises mostly from cranium-brain injuries and infectious diseases in young patients and from cranial blood circulation disorders, hypertension and diabetes mellitus in the elderly. The degree of paralysis ranges from limitation in a certain movement to loss of muscle function. The important point is the fact that paralytic strabismus can be observed not only in adults, but also in children. Mostly, paralysis occurs in the upper oblique muscle of the eye (Musculus obliquus superior) (Trochlear nerve palsy). The second most common paralysis is observed in the lateral rectus muscle (Musculus rectus lateralis) (Abducens palsy). Paralysis occurs less commonly in the other extraocular muscles supplied by a common nerve (Nervus oculomotorius) (Oculomotor nerve palsy).
Strabismus in children may not always be noticed cosmetically. The other symptoms of strabismus include photosensitivity, lacrimation or blinking of one eye. Chronic blepharitis or bent posture of the head may be possible symptoms. Strabismus does not show early symptoms. Paralysis of one extraocular muscle disturbs the balance of the other six extraocular muscles. The eye can not be moved freely in every direction and deviation occurs. Therefore, double pictures are seen. These cause orientation disorders, dizziness and nausea. Double pictures appear differently in various gaze directions according to the degree of muscle paralysis. The head is turned to the direction which the paralysed muscle should normally turn the eye to in order to prevent double pictures. Even this forced position of the head may not be able to prevent double pictures and frequently causes to muscle stiffness.
The visual acuity and refraction power of both eyes should be determined before strabismus in children is investigated in detail. Correction of a probable refraction disorder with eyeglasses is very important and may decrease or completely eliminate strabismus in children. One of the most important parts of examination of strabismus is the cover test. While the patient is focusing on a small lamp, the opthalmologist closes the patient’s eyes firstly unilaterally and then alternately with a small disc and observes the small movements of the eyes. These movements give an idea about the type of strabismus. If a prism is additionally held in front of the eyes during this examination, the angle of strabismus can be measured accurately. Especially in paralytic strabismus, evaluation of the eye movements is very important. The patient looks in different directions and the physician observes the position and movements of the eye. More detailed results are obtained with measurement tables and special optic devices.
Children with strabismus have the risk of amblyopia. After they are provided with glasses, if necessary, amblyopia treatment should be aimed for. Depending on the age of the child and the degree of strabismus, the eyes are closed with a special band for hours or days with a certain rythm. This is called occlusion treatment.
When the eye that can see better is closed, the lazy eye is forced to see and usually achieves a much better visual acuity in time. The lazy eye should also be closed frequently for short times so that the eye that can see better does not lose its visual acuity. For a successful occlusion treatment this procedure should be applied without interruption. In most cases, this treatment lasts for years. The position of the eyes can be corrected by operating the extraocular muscle. In paralytic strabismus, the disease that has caused strabismus should be treated if possible. In paralytic strabismus, one should wait for one year to operate extraocular muslces, because spontaneous improvement may occur during this time. Sometimes prism-integrated eyeglasses may be helpful in preventing or decreasing diplopia.