Exotropia is an oculomotor disorder in which the eyeball is deflected outward. Clinical signs of pathology include permanent or periodic displacement of the eye, complaints of diplopia, violation of binocular vision. To make a diagnosis, visometry, autorefractometry, a closing-opening test, a study on a synoptophore, a Worth test are carried out. Conservative therapy is reduced to correction of refractive anomalies, pleoptic and orthoptic treatment. In the absence of the proper effect, surgical intervention is performed – recession of the external and resection of the internal rectus muscle.
H50.1 H50.3 Exotropia
Exotropia is a pathology characterized by a deviation of the optical axis of the eye from the fixation point in the lateral direction. This form of strabismus accounts for about 15-20% of cases. Secondary exotropia occurs 3.4 times more often than convergent strabismus. The disease is widespread everywhere. The first signs of the disease, with the exception of the sensory form, are usually found in childhood. Pathology is equally often diagnosed in men and women.
The etiology of strabismus has not been fully studied. There is a genetic predisposition, while patients inherit a number of factors (myopia, hypermetropia) that contribute to the development of the disease. The negative influence of teratogenic factors (intrauterine infections, ionizing radiation, occupational hazards) on the position of the eyeballs is confirmed. The main causes of exotropia are:
- Ametropia. Exotropia is observed in children with refractive errors, among which hypermetropia and high-grade myopia are more common. The most significant risk factor is unilateral axial hypermetropia of medium or high degree.
- Traumatic injuries. Limitation of the mobility of the eyeball is observed in injuries affecting extraocular muscles, bone walls of the eye socket or nerves. Posttraumatic strabismus requires early surgical treatment.
- Neurological diseases. The difficulty of convergent-divergent movements occurs in response to damage to the occipital lobes of the brain, lateral cranial bodies and the upper tubercles of the quadrilateral. The angle of strabismus is unstable. There is a correlation with the level of intracranial pressure.
- Opacity of the optical media of the eye. The cause of exotropia can be diseases such as corneal cataract, vitreous fibrosis. The worse-seeing eye deviates to the temple. The sensory form of strabismus occurs with a decrease in visual acuity below 0.1 dptr.
The mechanism of development of exotropia is based on a violation of the receipt of a nerve impulse in the visual cortex of the brain. The lesion can be localized at the level of the receptor apparatus, pathways, cortical and subcortical centers. The bifixation process becomes impossible. As a result, the patient is not able to simultaneously direct his gaze and focus it on the subject with both eyes. Both eyes or the one with lower vision are deflected outwards. With an intermittent type of disease, there is an alternate deviation of the left and right eyeballs.
There are congenital (infantile) and acquired forms of exotropia. Based on the deviation indicators, it is customary to classify primary exotropy into excess divergence (deviation in the distance is 7 degrees greater than near), basic exotropy (deviation indicators are stable), insufficient convergence (deviation in the distance is less than near by 7 degrees) and pseudoexcess divergence. The main clinical forms of exotropia:
- Constant exotropy. An early start is characteristic. The first signs of the disease are usually detected from birth. The deviation angle is stable. One eye is involved in the pathological process.
- Intermittent exotropy. The first symptoms appear at the age of 5 years. The development of pathology is preceded by exophoria, which, in the absence of timely treatment, is replaced by tropia.
- Secondary exotropy. It is detected in patients with monocular vision. As a rule, it becomes a consequence of clouding of the optical media of the eyeball. It can occur at any age. The eye with lower vision deviates outward.
- Sequential exotropy. It is formed spontaneously in the amblyopic eye. A prerequisite may be surgical treatment of esotropia in the past. The angle of the Girshberg strabismus does not exceed 5-7 degrees if the operation technique is followed.
Constant exotropy is characterized by a stable deviation of one eye outward. The angle of strabismus is large and constant, there are no refractive anomalies. Visual acuity on the affected side, as a rule, is sharply reduced. Dissociated vertical deviation is often observed. This form of exotropia is often combined with neurological abnormalities.
The clinical symptoms of intermittent exotropia are more pronounced against the background of visual overstrain, general weakness or stress. Often parents notice signs of strabismus in the afternoon. The symptoms of exodeviation are more noticeable when the patient looks into the distance. It should be noted that the intermittent form of exotropia is often replaced by a permanent one.
Patients with exotropia present asthenopic complaints. They are concerned about increased fatigue against the background of visual loads, burning in the eyes, pain, pain, the appearance of a veil in front of the eyes. Attempts to merge images received from the right and left eyes lead to double vision. Friendly movements become difficult, keeping the eyes in the correct position requires considerable effort.
The consequence of strabismus is binocularity disorder. The most common complication of exotropia is high-grade amblyopia with incorrect fixation and abnormal correspondence of the retina. Parents note that exotropia is accompanied by an incorrect head position. With a constant form of the disease, there is a high risk of torticollis (spastic torticollis).
Examination of a patient with strabismus begins with a detailed history collection. During an objective examination, the ophthalmologist pays attention to the mobility of the eyeballs. The position of the eyes is evaluated when fixing the gaze at the near and far distance, using corrective lenses from the set and without them. The complex of necessary studies includes the following procedures:
- Visometry. With constant exotropia, vision on the affected side is reduced. With an intermittent form, visual functions can be maintained at a high level for a long time. The examination is performed without correction and with glasses.
- Autorefractometry. Exotropia is often combined with refractive anomalies. According to statistics, hypermetropia prevails in patients, high-grade myopia is less common. The study is carried out in conditions of cycloplegia.
- The overlap test (cover test). With alternate overlapping, eye movements are visualized from the outside to the inside. The test results may vary depending on the distance at which the patient’s gaze is fixed. With the correct correction, the amplitude of movements in glasses is usually lower.
- Four-point Worth test. The study allows us to determine the nature of vision. With a small angle of strabismus, binocular or simultaneous vision. A constant and large angle is associated with the monocular nature of vision.
- Examination on the synoptophore. Allows you to determine the deviation angle with high accuracy with and without the use of eyeglass correction. In the case of permanent exotropy, the ability to bifoveal fusion is lost.
Conservative treatment of strabismus is aimed at achieving a symmetrical eye position and the highest possible visual acuity, correcting the forced position of the head. The course of hardware treatment includes exercises for the formation of binocular and stereoscopic vision. The approach to therapy is complex. The following non – drug methods are used:
- Correction of refractive anomalies. Correction of myopia can positively affect the position of the eyes. With a mild degree of hypermetropia, the appointment of glasses is not shown. With medium and high degree of farsightedness, optical correction helps to increase visual acuity, allows better control of the position of the eyes. These measures are temporary.
- Occlusion. With exotropia, the closing of the eye, which does not deviate to the side, is shown with the help of a special occluder. In case of alternating strabismus, alternate occlusion is recommended in order to prevent amblyopia.
- Orthoptic treatment. It is aimed at the development and training of reserves of bifoveal fusion on the synoptophore. Special computer programs make it possible to increase the volume of fusion and develop stereoscopic vision in natural conditions.
Surgical treatment is carried out in cases of exotropia, when it is not possible to achieve orthophoria in a conservative way. Indications for surgery are a constant angle of deviation, diplopia and forced head position. With stable exotropia with an early onset, the main treatment is reduced to a recession of the external rectus and resection of the internal rectus muscles. In the intermittent variant, a recession of the external rectus muscles of both eyes is first performed. If necessary, resection of the internal rectus muscles is subsequently performed.
Prognosis and prevention
With timely diagnosis and treatment of exotropia, the prognosis is favorable. The criterion for the effectiveness of therapy is the reduction of the angle of strabismus to 5 degrees according to Hirschberg and the presence of binocular vision. Prevention is reduced to adequate correction of refractive errors according to age norms. A child with strabismus should undergo routine examinations by an ophthalmologist every 6 months, adults – 1 time a year.