Strabismus is the deviation of the eye from a common fixation point, which leads to a violation of binocular vision.
Friendly convergent strabismus in children occurs quite often, since the development of the oculomotor muscle system, which easily lose stability under the influence of external factors, has not yet been completed.
The causes are brain diseases, refractive errors (myopia, hyperopia, astigmatism), and low visual acuity.
At the moment, the main theory of the development of friendly convergent strabismus (the code according to ICD-10 has H 50.0) is the theory of the dependence of accommodation (the eye's work in capturing images far and near) and convergence (convergence of the eyes when looking at a close object). These processes are interconnected, and at the moment of tracking an object located at a close distance, the eyes converge, and when it is distant, there is a certain difference. With hyperopia, there is an excess incentive to accommodation associated with the very essence of this disease. Excessive accommodation leads to excessive convergence, resulting in excessive reduction of the eye to the nose (convergent strabismus).
The opposite effect occurs with myopia, when the incentive for accommodation is either very small or completely absent. As a result, there is insufficient convergence of the eyes and one eye begins to deviate outwards.
Classification of visual impairment
On the side to which the squinting eye deviates:
- Esotropia, in which the eye squints to the nose.
- Exotropy, characterized by a deviation of the eye to the temple.
- Hypertropia - the eye deviates upward.
- Hypotropy - deviation of the eye down.
According to the nature of the deviation, the classification of visual impairment is as follows:
- Monolateral. With this type of strabismus, one eye suffers, and only he constantly mows.
- Alternating. Alternating mowing occurs with one or the other eye.
According to the degree of dependence on spectacle correction, friendly convergent strabismus (ICD code 10 - H 50.0) is as follows:
- Accommodation (strabismus disappears when wearing glasses).
- Partially accommodative (the strabismus angle decreases, but does not disappear completely).
- Non-accommodating (wearing glasses does not change the angle of strabismus).
How to check eyesight for strabismus?
Sivtsev's table for eye examination in special. the institution or living conditions includes 12 lines of capital letters, the volume of which is reduced in the established pattern from top to bottom. The size D is marked in the left lobe of each line. It means the distance in meters from which a person with excellent vision must clearly distinguish all the letters in the table. The size V is indicated on the right side. This is a relative part, which means visual acuity. The norm is if the individual sees the tenth line V = 1.0 from a distance of 5 meters (in accordance with this, D = 5.0).
It should be noted that only 7 letters are used in the Sivtsev’s table for eye examination (M, K, H, W, S, I, B). With standard refraction, the point of clear vision is at infinity, which for the human eye starts from a distance of 5 meters. For this reason, the diagnosis of visual acuity is carried out at such a distance from the table itself.
Optical correction of refractive errors
For strabismus an important role is played by uncorrectable violation of refraction. It is necessary to choose the right glasses for the child, for this a cycloplegia procedure (relaxation of the ciliary muscle) is carried out by instillation of special drops.
Upon reaching cycloplegia, autorefractometry is performed and the selection of spectacle lenses begins.
For hyperopia, glasses are assigned 0.5-1.0 diopters less than the detected value. A full correction of myopia is justified only when it eliminates the angle of strabismus, and lenses weaker do not give the desired effect.
If after correcting with such glasses the strabismus disappears into the distance, but appears again when looking at a close point, it makes sense to assign bifocal glasses that include two lenses in the same glass for working at long and short distances.
Myopia with friendly strabismus is less common, but it is also necessary to correct it. If the magnitude of myopia does not exceed 6.0 diopters, it is possible to prescribe a full correction. At values above, the correction will be assigned by the portability of these points.
Pleoptics
Pleoptics refers to methods aimed at correcting amblyopia (low vision).
The main method of pleoptic therapy for children with amblyopia is occlusion - turning off the healthy eye from the act of vision. It allows you to switch the entire visual load on a squinting, worse seeing eye, which leads to its activity. For occlusion, you can use plastic occluders, or make a bandage or curtain yourself, using a bandage and a plaster for this. The time spent by a child with a closed eye is different, and depends on the degree of low vision. For some it can be a few hours a day, for others all day.
It is possible that a decrease in the visual acuity of a healthy eye that is under a blindfold for a long time. To avoid this, it is necessary to change the sealed eye with a schedule of 6/1 or 5/1. The main point of conducting occlusion is to reduce the visual work of the healthy eye so much that the amblyopic eye becomes the leading one.
Penalization
Penalization is a pleoptic method based on the creation of artificial irregular refraction. This leads to a deterioration in visual acuity of a better seeing eye. This is followed by the same process as with occlusion - the worse seeing eye takes on visual functions and comes first. Glasses are used for penalization, which significantly impair vision better than the seeing eye.
Orthoptics
Orthoptics is another way to get rid of strabismus. This is a system of methods for training and developing fusion (bringing two images together in the brain) and binocular vision (the ability to see with both eyes at the same time).
Orthoptic exercises are possible only after reaching visual acuity in both eyes above 0.3. They are carried out on an apparatus capable of separating visual fields (synoptophore).
The purpose of the procedures is to reduce or completely eliminate functional scotomas. As well as improved fusion ability. To achieve the effect, several light stimulation techniques are used:
- A variable in which test objects are shown to each eye in turn.
- Simultaneous, during which there is a simultaneous effect on both eyes.
Test objects are fixed at the desired strabismus angle and their blinking begins with a variable frequency.
Also, exercises are carried out to develop fusional reserves, for which purpose test objects are installed on the apparatus at the required angle, and after fixing them by the patient, they gradually increase and decrease the deflection angle.
Surgery
The purpose of the operation to correct strabismus is to restore symmetry in the position of the eyes. This effect is achieved by changing the balance of the effects of the oculomotor muscles on the eyeball.
At the moment, strobismologist surgeons adhere to the tactics of multi-stage intervention with strong deflection angles. This means that in cases where intervention is required on several muscles at once, it is divided in time into several operations. Such a scheme allows you to avoid the hyper-effect of the first operation and to track in detail the dynamics of normalization of muscle balance.
In surgery, two main methods are used to get rid of strabismus:
- Strengthening weak muscles.
- Weakening of the strong.
Strengthening weak muscles
The first type of operations include:
- Muscle resection. The technique of the operation is as follows: part of the muscle is cut off, depending on the angle of strabismus, and then the remaining ends are sutured again.
- Tenorrafia. With this operation, muscle gain is achieved by creating folds on the muscle or tendon.
- Anteposition. To enhance the effect of the muscle, it can be transplanted in front of the original attachment point, this will strengthen the lever.
Weakening strong muscles
The operation to correct strabismus includes:
- Recession. The essence of the operation is to transplant the muscle to a new location that is located behind the original attachment site. This leads to weakening traction.
- Tenotomy. A complete cutting of the tendon of the muscle is made without further attachment to the eye. The muscle, in addition to the main place of attachment, also has a connection with the tenon capsule, due to which, even with such an operation, a certain effect is preserved during muscle work.
- Partial myotomy. With this operation, the muscle is incised from both edges. This leads to its partial lengthening and weakening of excessive contraction.
- Muscle lengthening. For such an operation, various plastic materials are used that are sutured to the ends of the cut muscle, which increases its length.
For surgery of convergent strabismus, the following algorithm is used:
- Loosen the internal rectus muscle.
- Strengthen the outer line.
Treatment of friendly convergent strabismus
Treatment of monolateral strabismus begins with surgery on the squinting eye, since movement disorders are more pronounced on it. The logic of such an operation is much easier to explain to the patient so that he understands why he is at risk. Psychologically, it is easier for a person to decide on an operation on a sore eye than on a healthy one.
In the treatment of alternating strabismus , the question arises of which eye to start with, because both mow. It will be right to start with the eye, in which the deviations are more pronounced. Such deviations will include impaired mobility, or reduced visual acuity.
When performing surgery for strabismus, do not forget about their effect on the palpebral fissure. It is known that surgery for muscle gain leads to a partial narrowing of the palpebral fissure. In contrast, debilitating operations widen the palpebral fissure.
The recommendation for the treatment of strabismus even with large deviation angles is not to perform manipulations on many muscles at once. In the postoperative period, this can give a hyper-effect. The tactics of gradual operations with an interval of 6 months will be correct, which will reliably assess the effect of the treatment.
If the eye deviates not only horizontally, but also a vertical component is present, treatment should begin with surgery on horizontal muscles. This recommendation is due to the fact that the vertical element of strabismus may well be a consequence of the vertical phoria, which will disappear when the eye is centered after the first operation.
In cases where the vertical component of strabismus prevails over the horizontal, it is necessary to start with it.
In the postoperative period, secondary exotropia (deviation of the eye outside) may occur, associated with a weakening of the internal rectus muscle during weakening operations.
Risk factors
Risk factors for secondary exotropia:
- Increased refraction in childhood and adolescence.
- Anisometropia (difference in the amount of refraction) of more than two diopters.
- Incorrect spectacle correction of refractive errors.
- The impossibility of binocular image fusion.
In order to avoid the appearance of a secondary deviation of the eye, it is necessary after the operation to observe a child under 5 years old. You should also conduct correct eyeglass correction or correction with soft contact lenses. Provide treatment for binocular vision impairment.
With a weak degree, exercises with strabismus are used. Their effectiveness has been proven over many years. But the trouble is that they are more suitable for prevention.