Strabismus is the deviation of the eye from the common point of fixation, which leads to impaired binocular vision.
Concomitant convergent strabismus in children occurs quite often, since the development of the system of oculomotor muscles has not yet been completed, which easily lose stability under the influence of external factors.
The causes are brain diseases, refractive errors (myopia, hypermetropia, astigmatism), low visual acuity.
At the moment, the main theory of the development of concomitant descending strabismus (ICD-10 code has H 50.0) is the theory of the dependence of accommodation (the work of the eye to fix the image far and near) and convergence (reduction of the eyes when looking at a close object). These processes are interrelated, and at the moment of tracking an object that is at a close distance, the eyes converge, and when it is distant, some discrepancy occurs. With farsightedness, there is an excessive stimulus to accommodation,related to the very essence of this disease. Overaccommodation leads to overconvergence, resulting in an excessive alignment of the eye to the nose (convergent strabismus).
The opposite effect occurs with myopia, when the stimulus for accommodation is either very small or completely absent. As a result, insufficient convergence of the eyes occurs and one eye begins to deviate outward.
Classification of visual impairment
On the side to which the squinting eye deviates:
- Esotropia, in which the eye squints towards the nose.
- Exotropia, characterized by deviation of the eye to the temple.
- Hypertropia - the eye deviates upwards.
- Hypotropia - downward deviation of the eye.
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 it constantly mows.
- Alternating. Alternate mowing occurs with one eye and then with the other.
According to the degree of dependence on spectacle correction, concomitant convergent strabismus (ICD code 10 - H 50.0) happens as follows:
- Accommodative (strabismus disappears when wearing glasses).
- Partially accommodative (angle of strabismus decreases but does not disappear completely).
- Nonaccommodative (wearing glasses does not change the angle of strabismus).
How to check vision for strabismus?
Sivtsev's table for checking vision in special. institution or domestic environment includes12 lines of capital letters, the volume of which decreases in an established pattern from top to bottom. The size D is marked on the left side of each line. It means the distance in meters from which a person with excellent eyesight must clearly distinguish all the letters in the table. On the right side, the size V is indicated. This is the relative part, which means visual acuity. The norm is if an individual sees the tenth line V=1, 0 from a distance of 5 meters (according to this, D=5, 0).
It should be noted that in the Sivtsev table only 7 letters are used to test vision (M, K, H, W, Y, I, B). With standard refraction, the point of distinct vision is at infinity, which for the human eye actually starts at a distance of 5 meters. For this reason, visual acuity is diagnosed at such a distance from the table itself.
Optical correction of refractive errors
For the occurrence of strabismus, an uncorrectable refractive error plays an important role. It is necessary to choose the right glasses for the child, for this a cycloplegia procedure (relaxation of the ciliary muscle) is performed by instilling special drops.
When cycloplegia is reached, autorefractometry is performed and fitting of spectacle lenses begins.
For hypermetropia, glasses are assigned 0.5-1.0 diopters less than the detected value. Complete correction of myopia is justified only when it eliminates the angle of strabismus, and weaker lenses do not give the desired effect.
If, after correction with such glasses, the distance strabismus disappears, butappears again when looking at a close point, it makes sense to prescribe bifocal glasses that include two lenses in one glass for working at far and near distances.
Myopia in concomitant strabismus is less common, but it also needs to be corrected. If the value of myopia does not exceed 6.0 diopters, it is possible to assign a full correction. If the values are higher, the correction will be assigned according to the portability of these glasses.
Pleoptics
Pleoptics are methods aimed at correcting amblyopia (poor vision).
The main method of pleoptic therapy for children with amblyopia is occlusion - turning off the he althy eye from the act of seeing. It allows you to switch the entire visual load to the squinting, worse seeing eye, which leads to its activity. For occlusion, you can use plastic occluders, or make your own bandage or curtain, using a bandage and plaster for this. The amount of time a child spends with his eye closed varies, depending on the degree of low vision. For some it may be several hours a day, for others all day.
It is possible that the visual acuity of a he althy eye, which is under a bandage for a long time, decreases. To avoid this, it is necessary to change the glued eye with a schedule of 6/1 or 5/1. The main point of occlusion is to reduce the visual work of the he althy eye so that the amblyopic eye becomes the leading one.
Penalization
Penalization is a pleoptic method based on the creation of an artificial wrong refraction. This leads to a deterioration in visual acuity of the better seeing eye. This is followed by the same process as with occlusion - the worse seeing eye takes over the visual functions and comes out on top. For penalization, spectacle glasses are used, which significantly impair the vision of the better 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 achieving visual acuity in both eyes above 0.3. They are carried out on a device capable of dividing the fields of view (synoptophore).
The aim of the procedures is to reduce or completely eliminate functional scotoma. As well as improving the ability to fuse. To achieve the effect, several light stimulation techniques are used:
- 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 angle of strabismus and start blinking at variable frequency.
Exercises for the development of fusion reserves are also carried out, for which test objects are installed on the apparatus at the required angle, and after fixing them by the patientslowly increase and decrease the deflection angle.
Surgical treatment
The goal of strabismus surgery is to restore symmetry in the position of the eyes. This effect is achieved by changing the balance of the impact of the oculomotor muscles on the eyeball.
At the moment, strobismologist surgeons adhere to the tactics of multi-stage intervention with strong deviation angles. This means that in cases where intervention is needed on several muscles at once, it is divided in time into several operations. Such a scheme makes it possible to avoid the hypereffect of the first operation and to trace in detail the dynamics of the 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:
- Resection of the muscle. The operation procedure is as follows: a part of the muscle is cut off, depending on the angle of strabismus, and then the remaining ends are sutured again.
- Tenorrhaphy. In this operation, muscle strengthening is achieved by creating a fold in the muscle or tendon.
- Anteposition. To enhance the effect of the muscle, it can be transplanted in front of the original attachment site, this will increase the leverage.
Weaken strong muscles
The strabismus surgery includes:
- Recession. The essence of the operation is the transplantation of a muscle ona new location that is behind the original attachment location. This causes traction to weaken.
- Tenotomy. A complete cutting of the tendon of the muscle is performed without further attaching it to the eye. The muscle, in addition to the main site of attachment, also has a connection with the Tenon's capsule, so that even with such an operation, some effect on the work of the muscle is preserved.
- Partial myotomy. With this operation, the muscle is incised from both edges. This leads to its partial lengthening and weakening of the excessive contraction.
- Lengthening of the muscle. For such an operation, various plastic materials are used, which are sutured to the ends of the cut muscle, which increases its length.
For convergent strabismus surgery, the following algorithm is used:
- Relax the internal rectus.
- Strengthen the outer straight line.
Treatment of concomitant descending strabismus
Treatment of monolateral strabismus begins with an operation 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 taking risks. Psychologically, it is easier for a person to decide on an operation on a diseased eye than on a he althy one.
When treating alternating strabismus, the question arises which eye to start with, because both mow. It would be correct to start with the eye, in which the deviations are more pronounced. Such deviations will include impaired mobility, or reduced visual acuity.
When performing an operation onstrabismus should not forget about their effect on the palpebral fissure. It is known that operations for muscle strengthening lead to a partial narrowing of the palpebral fissure. In contrast, loosening operations widen the palpebral fissure.
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 hypereffect. The tactic of gradual operations with an interval of 6 months will be correct, which will allow you to reliably assess the effect of the treatment.
If the eye deviates not only horizontally, but also has a vertical component, treatment should begin with surgery on the horizontal muscles. This recommendation is due to the fact that the vertical element of strabismus may well be the result of vertical phoria, which will disappear when the eye is centered after the first operation.
In cases where the vertical component of the strabismus predominates over the horizontal, it is necessary to start with it.
Secondary exotropia (outward deviation of the eye) may occur in the postoperative period, associated with weakening of the internal rectus muscle during laxative operations.
Risk factors
Risk factors for secondary exotropia:
- Intensification of refraction in childhood and adolescence.
- Anisometropia (difference in refraction) more than two diopters.
- Incorrect spectacle correction of refractive errors.
- Unable to binocular image fusion.
To avoidthe appearance of a secondary deviation of the eye, it is necessary to observe the child up to 5 years after the operation. You should also carry out the correct spectacle correction or correction with soft contact lenses. Treat binocular vision disorder.
With a weak degree, exercises for strabismus are used. Their effectiveness has been proven over many years of use. But the trouble is that they are more suitable for prevention.
