Strabismus (Strabismus)
The human eye has a tendency to strabismus, but under the control of normal fusion function, it can still maintain the right position, and external objects can still fall on the macular central sulcus of both eyes, but when the fusion is broken, it shows the deviation of eye position, and the objects can not be imaged in the corresponding parts of both eyes, for example, one eye is in the macular central sulcus, and the other eye is outside the central sulcus of the retina, and when the fusion control is restored, the right position is maintained again. This underlying strabismus is called heterophoria. The presence of heterophoria is very common in normal people, but under certain conditions it may also develop into a dominant strabismus, and there is no absolute boundary between the two. When the visual axis of the eye is significantly skewed and cannot be controlled by fusion, it is called heterotropia. Patients with strabismus cannot have perfect stereopsis (stereopsis). Amblyopia also often occurs if it occurs at birth or in the early postnatal period.
External objects imaged in the corresponding parts of the retina of both eyes are fused by the visual centers of the cerebral cortex into a stereoscopic image with a clear relationship to the surrounding environment and accurate localization in three-dimensional space, which is called binocularsinglevisison. Binocular monovision is divided into three levels, the first level is simultaneous perception (simrltaneousperception), where both eyes can see two different images at the same time, the second level is fusion, where both eyes see two mostly identical images with some differences in detail as one image, and the third level is stereopsis (stereopsis), where both eyes see two The third level is stereopsis, where the two images with parallax are seen as one stereoscopic image. Stereopsis is the highest level of binocular monovision and is relied upon by humans to perform a variety of advanced fine tasks. Binocular monovision is gradually developed and perfected in early infancy after birth, and understanding this makes it possible to recognize why strabismus is more dangerous in children.
The eye has six extraocular muscles, four rectus muscles and two oblique muscles, which control the movement of the eye. The movement of the eye in any direction must be accomplished by the combined action of several extraocular muscles. Each extraocular muscle may act as a synergist, a spouse, and a conjugate muscle in different situations. When a negative eye muscle exercises the main role to make the eye turn in a certain direction, there are other extraocular muscles of the same eye to help complete, these muscles are called synergistic muscles; two eyes to do the same direction of movement, both eyes must have muscles at the same time the same amount of contraction, this pair of muscles is called mate muscle; one eye of the extraocular muscles and the role of mutual antagonism, in the movement, the contraction of an extraocular muscle must be accompanied by the relaxation of the opposing muscles, this pair of muscles is called antagonistic muscles. This pair of muscles is called antagonist muscles.
Concomitant strabismus
I. Concept
The visual axes of both eyes are separated, and the strabismus angle is equal in different directions of gaze and when the eyes are exchanged. There is no organic lesion of the extraocular muscles and their innervated nerves.
Etiology
The etiology of common strabismus is still not clear, but the main theories are as follows.
1, anatomical factors due to the abnormal development of the extraocular muscles or the anatomical factors of the eye appendages lead to strabismus.
Patients with hyperopic refractive error need to be highly adjusted in order to see the target and cause excessive collection, which often leads to internal strabismus; on the contrary, patients with myopia need less adjustment and therefore often have insufficient collection, which leads to exotropia.
3, fusion function defects theory of binocular visual acuity, monocular visual deprivation and other factors to prevent the fusion of the two eyes, may cause strabismus.
4. Abnormal innervation theory says that both eyes rely on collective excitation to keep the visual axis of both eyes parallel, and when the collective nerve impulse is too strong or the central tension of the collective is insufficient, it may cause internal strabismus or external strabismus.
Third, common internal strabismus (concomitantesotropia)
The prevalence is highest in children with strabismus, and gradually decreases with age.
1. Congenital esotropia occurs at birth or within 6 months after birth (including 6 months), and is also called infantilecsotropia. The main clinical features are a large strabismus, usually above 40, and a stable strabismus with approximately the same distance and near vision; most patients have equal vision in both eyes and are able to alternate their gaze, while a few show monocular fixation; about 90% of patients have mild or moderate hyperopia, but the eye position cannot be corrected with glasses; increased function of the inferior oblique muscle is often seen on ocular motor examination, and a few have mild abduction deficit, but there is no Adduction nerve palsy is not present.
Congenital internal strabismus is often accompanied by nystagmus (nystagmus), and detached vertical deviation (DVD).
Because of its early onset, congenital internal strabismus has a more severe effect on the development of monocular function in both eyes than other strabismias, especially in some patients with monocular fixation, and amblyopia usually occurs.
The principle of treatment is to correct the eye position early so that the child can achieve parallelism of the binocular axis and establish some degree of binocular fusion during the developmental period. Although most of the congenital strabismus does not have adjustment factors, there are a few exceptions, so the pupil should be dilated first, and surgery should be performed when both eyes are able to alternate their gaze.
The relationship between regulation and accommodation must be coordinated, and a certain amount of regulation is accompanied by a corresponding amount of accommodation, which is expressed by accommodation/accommodation (AC/A). The relationship between the two is expressed by accommodative convergence/accommodation (AC/A), in which excessive accommodation causes excessive aggregation or certain accommodation causes excessive accommodative aggregation, which becomes the cause of internal strabismus.
Common strabismus (comitantexotropia)
In comitantexotropia, the incidence of exotropia is lower than that of internal strabismus, but gradually increases with the age of the population. Comitant exotropia is not closely related to refractive error and has a slow onset, with many patients going through a definite interval before moving to a constant exotropia. For this reason, patients with common exotropia may maintain a certain degree of fusion and have better monocular function than patients with internal strabismus.
1. Congenital exotropia occurs before the age of 1 year, with a large and constant strabismus, usually manifested as alternating gaze. Due to the early onset, alternate gaze of both eyes, it is difficult to obtain better binocular monocular function after correction of eye position.
2.Intermittent exotropia (intermittentexotropia) Most intermittent exotropia occurs in early childhood and may pass through an occluded phase before onset. Intermittent exotropia alternates with internal strabismus, and is easily manifested when fatigue, poor physical condition, or lack of concentration are present, and strabismus can be induced by covering one eye. Strabismus is highly variable, and most patients have monocular function in both eyes at the same level. Adults may have symptoms of visual fatigue, children have almost no symptoms, but often have a very specific manifestation of squinting in the sunlight in one eye, a photophobic manifestation that may not be exclusive to intermittent exotropia, but is most common in children with intermittent exotropia.
The examination of intermittent exotropia is much more difficult than the examination of general exotropia. In addition to repeated examinations, it is necessary to examine at different times of the day and to cover one eye for at least one hour to fully expose the exotropia in order to accurately determine the oblique angle of intermittent exotropia.
There are different opinions on the treatment of intermittent exotropia. One opinion is that the patient maintains good binocular monovision during the interval, and surgical correction of the eye position is easy to achieve more satisfactory results, while another opinion is that children should try to take conservative treatment, because if the surgery is overcorrected, resulting in postoperative internal strabismus, the harm to binocular monovision will far exceed that of intermittent exotropia, so negative spherical lenses can be worn to If the strabismus does not improve during the observation of eye position and the monocular function of both eyes is gradually lost, surgery can be considered again to correct the eye position.
3.Constant external strabismus (constantexotropia) Some patients may first go through an interval period, so they have different degrees of binocular monocular function, and the prognosis is better after surgery to correct the eye position. Most patients with juvenile onset have alternating gaze, although they may not have amblyopia, and generally do not have binocular monovision, and some have monocular fixation exotropia, and most of these patients have amblyopia.
4. Secondary exotropia (secondaryexotropia)
(1) The internal strabismus surgery is not properly designed and the surgery volume is too large, resulting in exotropia after surgery.
(2) Perceptual strabismus (sensoryexotropia) is a visual impairment of one eye, such as an aphakic eye, trauma, etc., so that the fusion function of both eyes is damaged and exotropia occurs. Surgical treatment only improves the appearance.
There are many ways to classify exotropia, and for the purpose of surgical design, common exotropia is classified according to the difference between abnormalities in abduction and collective visual meridian innervation resulting in oblique viewing angles when looking at distance and near
(1) The abduction-overpowered type has a greater strabismus in distance viewing than in near viewing, at least 15, with a high AC/value.
(2) Under-assembled type with a greater oblique angle of view at near than at far, at least 15, and a low AC/A value.
(3) The basic type of oblique angle of view is basically equal when looking at the distance and looking at the near, the difference is not more than 10, and the AC/A value is normal.
(4) Similar to the abduction hyperacuity type, the oblique angle of vision at first examination is greater than that at near, and after covering one eye for one hour, the oblique angle of vision at distance is equal to that at near, or may even be less than that at near.
V. Treatment
The goal of treatment for children is first to eliminate amblyopia and to obtain binocular monocularity. For adults, the main purpose is to improve the appearance, and for some patients, to eliminate diplopia and reduce visual fatigue.
1, correction of refractive error for strabismus patients should first be dilated pupil examination shadow, when wearing if the internal strabismus with hyperopia should be fully corrected, exotropia with myopia should also be fully corrected; if exotropia with hyperopia, should be appropriate to reduce the degree of hyperopia, if the patient also has amblyopia, should pay attention to reduce the degree under the premise of ensuring visual acuity, astigmatism should be fully corrected.
2, treatment of amblyopia for children generally first amblyopia treatment, after the amblyopia cure and then strabismus correction surgery.
3, non-surgical treatment of adjustable internal strabismus should first wear farsighted corrective glasses, a certain patient with intermittent exotropia can wear negative spherical lenses to stimulate the collection function and improve eye position. After surgery, the smaller degree residual strabismus can be corrected with trigeminal lenses.
4, surgery to correct the eye position of most exotropia eventually need surgery, part of the regulatory internal strabismus and non-regulatory internal strabismus must also be surgically corrected, surgery for congenital internal strabismus should be carried out as early as possible, 6 months after birth can be implemented, as far as possible to obtain the opportunity to obtain the function of binocular monovision. Children should consider early surgery to correct eye position when amblyopia is cured or visual acuity is improved and binocular vision is balanced in order to obtain binocular monovision. In adults, whose primary goal is cosmetic, surgery should be performed to avoid diplopia.