Strabology studies all types and effects of strabismus, a misalignment of both eyes relative to each other resulting from disturbances in the balance of the eye muscles. It is a special discipline of ophthalmology and includes prevention, diagnosis as well as therapy of strabismus. It is practiced in eye clinics and most ophthalmologists’ offices.
What is strabology?
In strabismus, the lines of sight of the eyes do not coincide temporarily or permanently during fixation of a particular object. These misalignments can be very diverse in their severity and form, but can be accurately determined using a variety of optical methods. The so-called squint angle provides detailed information about the extent of such a disorder. In severe cases, it is accompanied by massive functional visual impairment and is then considerably more than just an aesthetic or cosmetic problem. An estimated five to six percent of people in Germany are affected by strabismus. In many cases strabismus is inherited, but it can also be acquired through health causes as well as accidents. Some forms are not pathological, but merely deviate from a normal condition. In esophoria the eye squints inwards, in exophoria outwards. Hyperphoria means an upward squinting eye. The earlier strabismus is treated in children, the better the visual impairment can be compensated. Strabismus is often underestimated, especially in young children. Often, the chances of success of a treatment that only begins at school age are already considerably limited. Strabismus usually results in unilateral visual impairment. Considerable disorders of three-dimensional vision are also usually encountered. In order to effectively eliminate strabismus, surgery is necessary in many cases. This involves correcting the lines of vision of the affected eyes. In most cases, this position correction takes place on the eye muscles. The squinting eye is straightened again. This is done either by shortening or lengthening the cords on the eyeball. It is also possible to shift the point of attachment of these cords. In children, the procedure is performed under general anesthesia, but is usually associated with low risks. In them, the external eye muscles are often corrected. Postoperatively, further treatment of the visual defect, also in the spatial area, is necessary. In most cases, the operation does not eliminate the need to wear glasses. Under normal conditions, the procedure requires a hospital stay of two to three days in children.
Treatments and therapies
Even in infancy, thanks to simple examinations, reliable statements can be made as to whether and how strabismus develops in the child. A small flashlight is used to assess corneal reflexes and movements that follow them. The ocular fundus reflexes also provide information about possibly developing strabismus. Apart from the apparative methods in the ophthalmologic practice, so-called free-space examinations are an important basis for the diagnosis of strabismus. In the natural environment, the patient’s ability to perceive objects and light sources correctly can often be best assessed. In addition, the position of the eyes must always be examined in the distance and near categories. One of the most common examination procedures, the cover test, also takes place outdoors. Here, a prism bar and various color filters are used to determine any strabismus deviations at near and distance. This is also done using the so-called Maddox cross, which is equipped with a fixation light and allows examination over a distance of five meters. The numerous devices used in free space have in common the requirement of being able to measure horizontal, vertical and rotational deviations of the angle of vision of the eyes. A comprehensive diagnosis of the squint angle requires about 180 measurements in a wide variety of gaze directions.
Diagnosis and examination methods
The most common is so-called latent strabismus (heterophoria), which predominantly results from eye strain and is usually left untreated. In these cases, the brain is often able to compensate for impaired vision by self-correcting deviating eye positions.However, concomitant strabismus (strabismus concomitans), which can occur as early as infancy, and paralytic strabismus (strabismus paralyticus) require medical intervention. Paralytic strabismus is often the result of inflammation or injury leading to paralysis of the eye muscles. In very severe strabismus, double vision occurs in many cases. Then the parallel position of the eyes is disturbed to such an extent that the two visual impressions no longer merge into one image. Children try to compensate for this by using one eye less and the other more, which leads to a pronounced visual impairment later on. This is why early treatment of strabismus in childhood is so important. As a result, surgery can usually be avoided. For example, the doctor prescribes suitable glasses and individual eye training. In addition, the conservative method of occlusion therapy, in which both eyes are alternately covered with a patch, is still widely used. In this way, the weaker eye is effectively trained to slowly align with the stronger eye. If this is successful, children often overcome their visual impairment by the age of twelve and do not need to undergo eye surgery. If surgery is nevertheless necessary to treat early childhood internal strabismus in the damaged eye muscles, the child’s eyes are often able to look approximately in the same direction again, but it is not uncommon for longer-term deficiencies in three-dimensional vision to remain.
