Disease Description
Concomitant exotropia is a condition in which the outward deviation of one eye is not overcome by the fusion of the two eyes. This eye position deviation is consistent in all directions of gaze. Because of the inability to parallelize the visual axes of both eyes, it affects the normal development of binocular vision in children and may lead to impairment or loss of binocular vision in adults. Normal binocular vision is an advanced visual function that humans should have and is indispensable for working life. Exotropia often requires surgery to correct. The timing of surgery is based on the patient’s degree of eye deviation, type of exotropia, age, visual acuity, binocular vision and general condition.
Classification of common strabismus
Common exotropia can be divided into primary exotropia and secondary exotropia.
Depending on the fusion status of the two eyes, primary exotropia can be classified as follows
(1) Exotropia: The eye axis has a tendency to be deviated, but the eye axis can be maintained parallel due to the good fusion ability of the two eyes, and the eye position is deviated outward only when one eye is blocked (the fusion mechanism cannot work).
(2) Intermittent exotropia: If the visual axis deviation cannot be overcome by the fusion ability of the two eyes, the visual axis of the two eyes cannot maintain parallelism, then the apparent obliquity appears. If the outward deviation of eye position sometimes appears and sometimes does not appear, it is intermittent exotropia.
(3) Constant exotropia: If the eye position deviation occurs continuously and the eye position cannot be orthogonal at any time, then it is called constant exotropia.
Depending on the degree of deviation when looking at distance and near, exotropia can be divided into four types.
(1) Under-assembled type: the angle of exotropia is large when looking at near and small when looking at far, with a difference of more than 15△.
(2) Basic exotropia: The angle of exotropia is approximately the same when looking at distance and when looking at near.
(3) Over-extension type: The angle of external obliquity is large when looking at the far side and small when looking at the near side, with a difference of more than 15△.
(4) Similar abduction type: When the trigeminal masking method was first performed, the external strabismus angle was larger in the distance and smaller in the near, but after the monocular masking, the distance and near strabismus angles were approximately the same or even larger in the near strabismus angle than in the far strabismus angle.
Secondary exotropia includes sensory exotropia and continuous exotropia. Perceptual exotropia is caused by a primary perceptual deficit that results in poor vision in one eye and impaired fusion in both eyes, for example, high myopia or cataracts in one eye that result in low vision. The eye with poor vision is often deviated outward. Continuous exotropia is the spontaneous conversion of an original internal strabismus to exotropia or the development of exotropia after correction of an internal strabismus (consecutive exotropia).
Causes of exotropia
The causes of exotropia are complex, and there is no consensus among scholars on the causes of exotropia, but the following causes are believed to exist.
(1) Innervation factors: It is believed that the dysregulation of innervation in the assembly and separation mechanism is the cause of exotropia.
(2) Anatomical factors: Abnormalities in the anatomical structure of the orbital and extraocular muscles are believed to be the cause of exotropia.
(3) Dualism theory: It is believed that emmetropia results from the action of both anatomical and innervation factors.
(4) Refractive influence: It is believed that refractive error can alter the innervation and thus affect the eye position.
Clinical manifestations
(1) Morbidity: It is believed that the incidence of exotropia is lower than that of internal strabismus, and the ratio is about 1:3. The incidence is higher in females than in males, accounting for about 70%. The proportion and type of refractive errors in patients with exotropia are similar to those in the non-strabismic population.
Most exotropia develops in the early postnatal period, within 2 years of age. It may begin as an intermittent exotropia and progresses to a constant exotropia. The progression of exotropia is often characterized by increasingly frequent episodic strabismus and a gradual increase in the angle of strabismus, during which visual function is gradually impaired or lost in both eyes. However, not all exotropia is progressive, and some intermittent exotropia can remain stable for a considerable period of time.
(2) Symptoms and signs: People with exotropia often complain of eye fatigue, blurred vision, headache, diplopia, and inability to read for long periods of time. Children with intermittent and constant exotropia rarely complain of symptoms, and adult patients can have the same discomfort as exotropia. It is worth noting, however, that people with intermittent exotropia often present with outdoor photophobia, which is squinting one eye in outdoor sunlight. Although this condition is not unique to intermittent exotropia, it is a common manifestation, and the mechanism for its occurrence is unclear. In addition, some patients with intermittent exotropia complain of small vision.
Examination and diagnosis methods of exotropia
(1) Visual acuity examination: the visual acuity of patients with exotropia is closely related to the cause, classification and diagnosis, the choice of further examination methods, the timing of surgery and the choice of operation style, and is the first-hand information that doctors should obtain.
(2) Eye position examination: including corneal reflection method, trigeminal masking method, trigeminal illumination method, synoptic machine method measurement, etc. To measure the strabismus of looking near (33CM) and looking far (6M) at the same time and the oblique perspective of looking at both eyes separately. The visual marker can be a flashlight, a light or a letter or a figure. The eye position examination is very important for the surgeon to observe and determine the type of strabismus, the size of the strabismus angle, the strabismus in each direction of gaze, the AC/A ratio, and the monocular masking test to identify emmetropia like abduction. Sometimes it is necessary to choose different time periods and different states of the patient to perform the examination.
(3) Oculomotor function examination: Using the gaze target to move at a distance of one foot in front of the patient’s eyes, observe whether the patient’s bilateral and monocular eye movements in following the nine gaze directions are smooth and symmetrical, whether they can reach each functional position smoothly, and whether there is over- or under-functioning. It is an important test to diagnose common exotropia and exclude abnormalities of extraocular muscles.
(4) Binocular visual function examination: including various distance and near stereopsis examinations, tertiary function examination of the same visual machine, and other perceptual adaptation status examinations, such as linear mirror, Worth four-point test, etc. The impaired visual function of both eyes is an important reference indicator for understanding the degree of exotropia and choosing the timing of surgery.
(5) Refractive state examination: mainly dilated pupil examination. The dilated pupil examination to understand the corrected visual acuity and the nature and degree of refractive error is also essential in the diagnosis and treatment of exotropia. Patients who need glasses to correct their vision should have their visual acuity, eye position and visual function checked after wearing appropriate glasses. In the surgical design, the type and degree of refractive error has a certain reference value for the surgeon to select the operated eye, the design of the surgical volume and the expected surgical results.
(6) Examination of the anterior segment of the eye and fundus: These are routine ophthalmic examinations, except for organic eye pathology.
(7) Other ophthalmic examinations: including all examinations of the ophthalmic specialty. After the basic examination as above, if it is necessary to further understand the more functional condition of the eye, or unless the patient has other eye problems, other ophthalmic examinations can be selected for further detailed investigation.
(8) General examination and imaging
Diagnosis and differential diagnosis
The diagnosis of exotropia can be made only after careful examination of the patient by a professional doctor. In layman’s terms, if the reflection point of the spotlight bulb falls on the side of the nasal edge of the patient’s pupil instead of the center of the pupil during the examination, and if the black eye moves from the outside to the middle when further masking is done to cover the examination, it is a sign of exotropia. However, a professional doctor needs to make a clear and detailed diagnosis based on the state and degree of the deviation and other examinations.
Common exotropia needs to be diagnosed differently from other strabismus and paralytic strabismus. The degree of strabismus in each direction of gaze, the degree of strabismus in each eye, and the eye movements are important factors in the diagnosis and differential diagnosis. Treatment of external strabismus
(a) Non-surgical treatment: The purpose is to enhance and improve the fusion function, improve the patient’s ability to control the eye position and postpone the surgery. It is used for patients who do not need surgery temporarily or are not convenient for surgery.
1. Correction of refractive error and negative spherical lens treatment: Patients with exotropia who have myopic refractive error and astigmatism, especially refractive aberration, should be given correction to make the retinal imaging clear and enhance the stimulation of fusion. Children with hyperopia of +2.00D or less can be corrected without glasses; in case of high hyperopia, undercorrected glasses should be worn to take into account the visual acuity. Adding 3-5D negative spherical lenses to patients with emmetropia to increase the patient’s regulatory stimulation, thus improving fusion and enhancing the ability to control eye position is also used by some experts.
2, trigeminal treatment: Some scholars attach trigeminal degrees to the lenses to partially or completely correct the patient’s strabismus to improve the fusion function and eye position control ability, and some reported improvement of exotropia. Some scholars also believe that wearing trigeminal lenses for postoperative residual small-angle exotropia can stimulate fusion and facilitate orthotropia.
(3) Masking treatment: Masking the dominant eye (eye with good visual acuity) to prevent monocular suppression and amblyopia, especially for intermittent exotropia with suppression and abnormal retinal counterparts.
(ii) Surgical treatment.
1. Surgical indications: Not all experts hold the same opinion on the choice of timing and indications for exotropia surgery; some hold a more positive attitude toward surgery, while others want to observe it for a longer period of time. In general, the indication for surgery depends on several aspects such as fusion status, age and degree of strabismus, in addition to the patient’s or parents’ opinion. There should be good communication with the patient or parents before surgery.
(1) Degree of strabismus: Generally, surgery should be considered when the strabismus angle is >15-20△.
(2) Fusion status: For children with constant exotropia occurring after birth or early after birth, >20△, who can alternate gaze and accurately measure the strabismus, surgery can be considered, and the recovery of postoperative visual function varies depending on the early and late onset, birth condition, accompanying diseases, etc. The recovery of postoperative visual function varies depending on the onset of the disease, birth conditions, and concomitant diseases. Adult hyperopic strabismus is also a clear indication for surgery. Surgery is required for those with visual fatigue and those for whom non-surgical treatment is ineffective. The timing of surgery for intermittent exotropia may vary, with some experts advocating early surgery to facilitate the development of binocular vision. Other experts believe that surgery should be observed for a longer period of time and considered when the degree of exotropia has progressed, fusion control has gradually been lost, and the frequency of apparent strabismus has increased to more than 50% of the waking time.
(3) Patient’s age: There is no rigid age requirement for strabismus surgery, and the decision is generally based on the nature and degree of strabismus, fusion function, and the degree of cooperation in examination. At present, a more diverse choice is for intermittent exotropia. Some experts advocate early surgery to facilitate the development of binocular vision. On the one hand, intermittent exotropia is likely to remain stable and non-progressive for a long period of time, and the visual function is slowly impaired; on the other hand, early surgery for young children with immature visual system development is likely to be overcorrected, and after surgery, internal strabismus and amblyopia will occur, and the visual function of both eyes will not be well developed or even impaired.
2. Purpose of surgery
In recent years, the importance of strabismus correction for improving visual function and normal binocular vision has been gradually recognized and emphasized by ophthalmologists and the general public.
The purpose of strabismus correction varies depending on the patient’s condition. For children who are at the stage of visual development, strabismus surgery is firstly to improve binocular vision or to provide suitable conditions for normal binocular vision development, and secondly whether the improvement in appearance will play a positive role in the child’s psychological growth is also a subject worthy of study. For adults with long-term permanent exotropia, the visual function of both eyes is often impaired and difficult to recover, so surgery is more about improving the appearance. However, for adults with intermittent exotropia, even if the strabismus has occurred for many years and the visual function of both eyes has been impaired, there is a possibility of restoring binocular vision after surgical correction.
3.Selecting the surgical method
The choice of surgical method for exotropia is mainly based on the type of strabismus, the degree of strabismus, as well as the visual acuity and refractive status. In the case of the hypertropia type, a symmetrical double external rectus posterior migration is used; in the case of the deficient collection type, a monocular external rectus posterior migration with internal rectus shortening is preferred; in the case of the basic exotropia type, a double external rectus posterior migration or a monocular truncation can be performed. In large-angle strabismus, three extra-ocular muscles are required in both eyes. Children should be overcorrected by a small amount for a short period of time after surgery, while adults should not be overcorrected for surgery.
Prognosis of exotropia
Most strabismus requires surgery, but non-surgical treatment is rarely effective in controlling the eye position and avoiding surgery. Exotropia is a recurring condition, and there is a risk of recurrence within months or years after surgical correction. Some patients delay surgery for fear of recurrence, so that the strabismus becomes intermittent to constant. The idea of not having surgery for fear of recurrence is undesirable because, the orthotropic phase after surgery can provide an opportunity for the development or improvement of binocular vision, and not all exotropia recurs after surgery, and some recurrent cases can be treated conservatively to avoid reoperation; for the few who require reoperation for correction, reoperation still provides an opportunity for recovery of binocular vision.
Post-operative care
1.Spot antibiotics or eye drops containing hormones on time after surgery.
2.Avoid rubbing the eyes, rapid eye rotation and impact for 2 weeks after surgery.
3, pay attention to eye hygiene, do not overuse the eyes, avoid eye overwork, and ensure sufficient sleep.
4.Eat a light and balanced diet, avoid smoking, alcohol and spicy stimulating food.
5.Patients with refractive error need to be treated with lenses in time after surgery.