Strabismus is the inability of both eyes to look at the target at the same time. It is a disease of the extraocular muscles and can be divided into two categories: common strabismus and paralytic strabismus. Common strabismus is characterized by a temporal eye position, no eye movement disorder and no diplopia, while paralytic strabismus has limited eye movement, diplopia and systemic symptoms such as vertigo, nausea and unstable gait.
I. Etiology
1.Regulation theory.
The regulation of the eye and the collection of the eye are interrelated, and a certain regulation brings a corresponding collection. Often due to the strong reflex of regulation – collection, the role of the inner rectus muscle has a tendency to exceed the outer rectus muscle, and the formation of common internal strabismus. In myopic eyes, when looking at a near target with little or no accommodation, the pooling force is weakened at the same time, so the tension of the internal rectus muscle is reduced, which sometimes results in common exotropia. Zhang Key, Ophthalmology Department, Jinyang People’s Hospital
2. The theory of binocular reflex.
Binocular monocularity is a conditioned reflex, which relies on the fusion function to complete and is acquired later in life. If the two eyes have different visual acuity during the formation of this conditioned reflex, and one eye’s visual acuity is hindered by obvious sensory or motor disorders that prevent the function of binocular monocularity, a state of ocular separation will arise, i.e. strabismus.
3. Anatomical theory.
The overdevelopment or underdevelopment of the extraocular muscles of one eye, the abnormal attachment point of the extraocular muscles, the development of the orbit, and the abnormality of the intraorbital fascia structure can lead to the imbalance of the muscle force and produce strabismus.
4. Genetic theory.
Clinically, it is common that many people in the same family have common strabismus, and strabismus may be related to genetic factors.
Clinical manifestations
When a patient with strabismus pays attention to an object, the image of the object falls on the central retinal recess in the normal eye, but falls outside the central recess in the strabismic eye, so that double vision occurs.
1.Internal strabismus.
The eye position is skewed inward. It is called congenital internal strabismus when it occurs from birth. The angle of deviation is usually large. Acquired internal strabismus is divided into moderate and non-moderate. Moderate internal strabismus usually occurs in children aged 2-3 years old and is usually accompanied by moderate to high hyperopia or an abnormal moderate cohesion to moderate ratio.
2. Exotropia.
The eye position is skewed and can be divided into intermittent and constant exotropia. Intermittent emmetropia can be maintained in a normal position most of the time by the ability of the patient’s image blending, because the patient has a good image blending ability, and only occasionally in the sun or when fatigued and distracted, does the eye position show emmetropia. Some children also exhibit a tendency to close one eye in strong sunlight. Intermittent exotropia often develops into constant exotropia.
3. Upward and downward strabismus.
Upward or downward eye position is less common than internal and external strabismus, and upward and downward strabismus is often accompanied by head tilt, i.e. compensatory head position.
Examination
The following are the routine examinations of strabismus.
1. Examination of binocular visual function.
(1) Domestic common use of the same vision machine to check the three levels of binocular visual function.
(2) Quantitative determination of stereo visual function, using the same visual machine stereo quantitative drawing or Yan’s random dot stereogram to determine the stereo visual acuity.
2.Refractive examination.
Atropine paralysis ciliary muscle optometry: to understand the relationship between amblyopia and strabismus and refraction.
3. Determination of eye position and strabismus angle.
Determine which type of strabismus is present. The size of the strabismus angle must be checked for the purpose of surgical design.
4.Ocular movement examination.
To determine the function of the extraocular muscles and to see if the eye movement is in place normally.
5. Is there a compensatory head position.
To help diagnose which extraocular muscle is paralyzed.
6.Check to determine the paralyzed muscle.
Check the function of eye movement, separate gaze of both eyes, strabismus angle of each direction of gaze of one eye, using red lens test or
Hess screen method and other examinations can help to determine.
7. Retraction test.
(1) Estimation of postoperative diplopia and patient tolerance after pulling the eye to an orthotropic position before surgery.
(2) Passive retraction test can understand whether there is mechanical retraction of the extraocular muscles or muscle spasm.
(3) Active contraction test to understand the function of the muscle.
8. Examination of occlusion.
Quantitative determination is done with the occlusion meter. The test of collective proximal point: to help diagnose myopic fatigue.
9.Adjustment of the ratio of accommodation/adjustment (AC/A)
Help to determine the relationship between strabismus and regulation and assembly.
IV. Diagnosis
Diagnosis can be made by the following methods.
1.Inquiry about medical history.
Ask the patient’s age, the exact time of onset, the cause or trigger of onset, the development of strabismus, what kind of treatment has been done, and whether there is any family history, etc.
2.Ocular appearance examination.
Pay attention to the direction and degree of eye deviation, whether the lid fissure is equal in size, whether the face is symmetrical, and whether there is compensatory head position.
3. Visual acuity examination and refraction examination.
Check the patient’s distance and near vision and corrected visual acuity in detail. For highly myopic and astigmatic patients and adolescent patients, refractive examinations must be performed after pupil dilation.
4. Masking test.
The masking test can be a simple and precise qualitative examination of strabismus.
5.Check the movement of the eye.
Observe the six main movement directions to determine whether there are any abnormalities in the function of each eye muscle.
6.Strabismus examination.
The strabismus angle is divided into the first strabismus angle and the second strabismus angle. When the healthy eye gazes, the angle of oblique eye deflection is called the first oblique angle; when the oblique eye gazes, the angle of healthy eye deflection is called the second oblique angle. The measurement of the first and second oblique angle can assist in the diagnosis of paralyzed eyes. The methods commonly used in clinical practice to quantitatively measure the oblique angle are: corneal reflection method, simultaneous vision machine examination method, trigeminal lens with masking method, etc.
7.Other.
In addition, there are also strabismometer method of measuring oblique angle of view, malleolar plus trigonometric examination method, visual field meter measurement method, etc.
V. Treatment
1.Non-surgical treatment.
Treatment of strabismus is firstly for amblyopia to promote good vision development in both eyes, and secondly for correction of skewed eye position. The treatment methods of strabismus include: wearing glasses, eye patch covering, and orthoptic training. Eye shields are the main treatment for amblyopia caused by strabismus. Eye muscle surgery involves relaxing (weakening) or shortening (strengthening) one or more of the extraocular muscles in one or both eyes. Mild strabismus can be corrected by wearing prismatic lenses. Orthoptic training can be used as a supplement before and after surgery.
2. Surgical treatment.
The younger the age of strabismus treatment, the better the treatment effect. Strabismus surgery is not only to correct eye position and improve appearance, but more importantly to establish binocular vision function. The best time for surgery is before 6-7 years old. The long-term stability of the eye position and the establishment of stereopsis still require regular follow-up.