Strabismus

Strabismus

Strabismus is a visual impairment in which one or both eyes deviate from the visual axis towards the object.
Normally, the image is received by the retina of both eyes, and then along the optic nerve it goes to the occipital part of the cerebral cortex. There, the visual analyser combines the images obtained by the right and left eyes separately into one image, adding it depth and the concept of distance. Binocular vision is formed in this way. However, in case of strabismus, there is no complete overlapping of images, and the brain sees a double image. Therefore, to avoid confusion, it simply excludes one eye from work, ignoring the information received.

Prevalence rate

In paediatric practice strabismus is a common vision pathology and, on average, occurs in 2% of cases, and an average of 1 in 400 children are born with congenital strabismus. Subsequently, this number increases, and among all paediatric ophthalmological pathology in preschool children, it rises to 10%.

Although the disease is easily diagnosed, it is possible to get rid of it only with the qualified ophthalmic help.

Causes and risk factors

The immediate cause of strabismus is a disfunction of the oculomotor muscles, which can be caused by:

• congenital malformations of the vision organ,
• paralysis, paresis,
• severe psychological trauma,
• birth injury,
• traumatic damage to the eye and its muscles at an older age,
• diseases of the central nervous system,
• an apparent decrease in visual acuity in one eye (for example, leucoma, cataract, etc.),
• infectious diseases which can cause complicating disorder of the nervous system and paralysis of the oculomotor muscles,
• stress,
• some somatic diseases.

Strabismus in babies up to 6 months of age is considered physiological, and in order to avoid further more serious problems, it is necessary to create appropriate conditions for the baby’s eyes, namely:

• you should hang the same type of balls or rings with a diameter of 6-10 cm, fixed at a distance of at least 50 cm from the baby’s eyes,
• you should evenly distribute the visual load in the baby’s field of vision,
• you should remove large objects from the newborn’s crib – mirrors, bright lamps, large colourful toys.

The crib should be placed in such a way as to approach it from different sides.

Strabismus in adults

In adults, strabismus can be triggered by diseases which lead to visual impairment or disorders of the oculomotor muscles. For example, diabetes mellitus, myasthenia gravis, cerebral injury, brain tumours, strokes. Also, strabismus may appear after any operations in the orbit area, if the muscles of the eye were damaged.

Classification

Strabismus can be congenital and acquired. By the nature of the movement of the pupils, such types of strabismus are distinguished:

• Horizontal – the visual axis deviates horizontally. This is a convergent and divergent strabismus.
• Vertical – the visual axis deviates upward (hypertropia) or downward (hypotropia).

Depending on whether one or both eyes are involved, one can distinguish monocular strabismus (one eye squints) and alternative (alternately, one or the other eye squints).

In the case of monocular strabismus, the brain adapts to read information from one eye, and simply excludes the other from work. Due to this, amblyopia occurs, when, even after getting rid of the pathology, the lazy eye does not restore its functions.

In the alternative type of disease, the brain involves both eyes, so even if amblyopia does occur, it is more benignant.

Also, experts distinguish concomitant and paralytic strabismus. In the first case, the eyeballs move in full, and in the second one – there is the movement of the eyeball is restricted in the direction of the paralyzed muscle.

Symptoms

A clear symptom of strabismus is laterodeviation, deviation upward or downward when trying to focus the gaze on an object.
Other symptoms which can be observed in case of strabismus:

• headache,
• diplopia,
• eyesight strain when working with small details.

If one eye is not involved, binocular vision disappears, and a person is not able to orient properly in space. Visual symptoms are clumsiness and stumbling over various objects.

Diagnostics

Strabismus is diagnosed with a primary ophthalmologic examination. To clarify the nature of the disorder and identify the causes of the disease, an in-depth examination can be prescribed, including some of the following tests:

• eye examination according to the Golovin-Sivtsev Table,
• measurement of eyesight, intraocular pressure, cornea thickness,
• electrophysiological tests,
• Ultrasound of the eye,
• fundus examination, etc.

All examinations are performed using modern equipment in a non-contact and patient-friendly way. The final stage is a repeated consultation with an ophthalmologist and elaboration of an individual treatment plan.

Treatment

To prevent irreversible visual impairments, such as amblyopia, strabismus treatment should be started as early as possible.

Surgery

Surgical treatment in case of strabismus applies to adults, as well as children, if conservative methods have proved ineffective. The essence of the operation is correcting position of the oculomotor muscles.

The most common types of such operations are:

• shortening of the muscle due to exsection of its fragment,
• muscle lengthening,
• changing the place of fixation of the oculomotor muscle in order to strengthen or, on the contrary, weaken its action.

An innovative technique is adjustable suturation, when the doctor inserts sutures, leaving some extra suture material. And after the operation, the doctor manually adjusts the sight angle which is comfortable for the patient.
To recover eyesight after surgery, instrumental treatment is prescribed for 1-2 weeks.

Conservative therapy

The main objectives of conservative treatment for strabismus are to eliminate the lazy eye syndrome and recover binocular (stereoscopic) vision.
To involve the lazy eye in the work, the doctor prescribes special digital glasses, occlusive patches, exercises using special computer programs and simulators.