Convergent strabismus

Convergent strabismus (esotropia, a manifesting convergent strabismus) can be friendly or paralytic. With a friendly convergent strabism, differences in angle of deviation within 5 D are observed in different positions of the horizontal gaze. With paralytic convergent strabism, the angle of deflection in different positions of the gaze is different as a result of impaired innervation or restriction.

[1], [2], [3], [4], [5]

Types of convergent strabismus

Accomodative convergent strabismus

• Refractive convergent strabismus
  • fully accommodative
  • partially accommodative
• Non-refractional convergent strabismus
  • with the excess of convergence
  • with the weakness of accommodation
• Mixed convergent strabismus

Nonaccumodative convergent strabismus

• essential infantile
• microtropy
• basic
• excess of convergence
• spasm of convergence
• insufficiency of divergence
• paralysis of divergence
• sensory
• secondary
• with a sharp start
• cyclic

Accomodative convergent strabismus

In the visual act, at a short distance, both processes take place - accommodation and convergence. Accomodation is a process in which the eye focuses on a closely located object, which is accompanied by a change in the curvature of the lens. At the same time, the eyes are converged to achieve bifoveal fixation of the object. Both processes (accommodation and convergence) are quantitatively related to the distance to the object and are characterized by a relatively constant relationship between themselves. Changes in the AK / A index are the main cause of the appearance of some forms of convergent strabismus.

Refractive accommodative convergent strabismus

The AK / A index is not changed, convergent strabismus is a physiological response to excessive hypermetropia. Usually between +4.0 and +7.0 diopters. In this case, the accommodation voltage required to focus even a distant object is accompanied by an increase in convergence exceeding the negative fusions of the patient. Control is lost, there is a manifest form of convergent strabismus. The difference in the angle of strabismus with fixation of near and far objects is small (usually <10 D). Strabismus appears at the age of 2.5 years (from 6 months to 7 years).

1. Complete accommodative convergent strabismus is completely eliminated by optical correction of hypermetropia.
2. Partial accommodative convergent strabism decreases with optical correction of gynometropia, but not completely eliminated.

Non-inflexional accommodative convergent strabismus

Due to the high index of AK / L, in which the increase in accommodation is accompanied by a disproportionate increase in convergence in the absence of significant gynermetropia. There are 2 types:

The excess of convergence. It is characterized by:

High index AK / A due to the increase in AK (accommodation is normal, convergence is strengthened).

• Normal near point of accommodation.
• Correct position of the eyes when fixing a distant object, convergent strabismus when fixing a nearby object.

With disturbed accommodation (hypoacomodation). It is characterized by:

• A high A / A index due to a decrease in A (weak accommodation requires additional efforts, which are accompanied by increased convergence).
• Removal of the nearest accommodation point.
• When fixing a nearby object, an additional accommodation effort is required, leading to an excess of convergence.

Mixed accommodative convergent strabismus

Hypermetropia and a high index of AK / A can be combined, lead to a converging strabismus while fixing the far object and significantly increase the deflection angle (> 10 D) when fixing a nearby object. Deviation when fixing a distant object is usually corrected by glasses, convergent strabismus when fixing a nearby object will be preserved if it is not corrected by bifocal glasses.

Treatment of accommodative convergent strabismus

Refractive anomalies should be corrected, as described above. Children up to 6 years of age are recommended a full correction of refraction, revealed during retinoscopy in cycloplegia. With accommodative refractive convergent strabismus, this correction eliminates the angle when fixing the near and far objects. After 8 years, retinoscopy should be performed without cycloplegia (manifest hypermetropia) and assign the maximum tolerable plus correction.

Bifocal glasses are prescribed for accommodative convergent strabismus (high AK / A index). They facilitate accommodation (and, consequently, accommodative convergence), allowing the child to maintain a bifovel fixation and correct position of the eyes when fixing a nearby object. This is achieved by a minimal plus correction. The most convenient form of bifocals is when the dividing furrow passes along the lower edge of the pupil. The strength of the lower lenses should be gradually reduced with age: in early adolescence, it is advisable to switch to monofocal glasses. The final prognosis regarding the termination of spectacle correction is associated with the AK / A index, as well as with the degree of gynermetropia and astigmatism. Points may be necessary only when working with close objects.

Treatment with miotics can be short-lived in children with accommodative convergent strabismus due to a high AK / A index, who do not want to wear glasses. The initial dose of eco-thiopate iodide 0.125% or pilocarpine 4% - 4 times daily for 6 weeks. With the effectiveness of treatment, strength and frequency are gradually reduced to a minimally effective dose. The formation of cysts on the iris caused by the ecothiopath can be prevented by the simultaneous administration of phenylepinephrine 2.5% 2 times in laziness. The mechanism of treatment of miotics is to stimulate the "peripheral" accommodation (ie stimulation of the ciliary muscle to a greater extent than the action of the third pair of cranial nerves). A lower accommodation voltage is required, and accommodative convergence is less induced. Possible side effects - blurred vision when fixing a distant object.

Treatment of amblyopia is extremely important and must precede surgical correction.

Surgical correction is indicated after the treatment of amblyopia, if the glasses do not completely eliminate the deviation. The principle of surgical intervention is the weakening of the internal rectus muscles; muscles responsible for convergence.

• Two-sided recession of internal muscles is performed in patients with symmetrical visual acuity in both eyes, when the deflection when fixing a nearby object is greater than the distance.
• If there is no significant difference between the magnitude of the angle when fixing a near and distant object and vision is the same in both eyes, then some surgeons perform a combined intervention with resection of the medial and lateral rectus muscles, while others prefer a bilateral recession of medial rectus muscles.
• Recession-resection on the amblyopic eye is performed in patients with residual amblyopia.

[6], [7], [8], [9]

Essential infantile convergent strabismus

Essential infantile convergent strabismus is idiopathic, developing during the first 6 months of life in healthy infants in the absence of an abnormality of refraction and limitations of eye mobility.

Symptoms

• The angle is usually large (> 30 D) and constant.
• In the majority of patients, alternating fixation is in the primary position and cross-fixation of the right eye - with a gaze to the left (Figure 16.636), the left eye - with a gaze to the right (Figure 16.63a). This can give a false impression of bilateral abnormalities of abduction, as in the bilateral paralysis of the VI pair of cranial nerves. But abduction can usually be demonstrated with the help of the "head of the doll" maneuver or the child's rotation. If this is difficult, then a one-sided occlusion for a few hours will unmask the ability of the other eye to abduction.
• Nystagmus manifest is usually horizontal, in case of manifestation it can be latent or manifest-latent.
• An abnormality of refraction corresponds to the age of the child (about +1.5 diopters).
• Asymmetry of the optokinetic nystagmus.
• The hyperfunction of the lower oblique muscle can be initially or develop later.
• Dissociated vertical deviation occurs in 80% of patients by 3 years.
• Low potential for the development of binocular vision.

Differential diagnostics

• Congenital bilateral paralysis of the sixth pair of cranial nerves, which can be excluded on the basis of the previously mentioned methods.
• Sensory convergent strabismus due to organic pathology of the organ of vision.
• Syndrome of nystagmus blockade, in which horizontal nystagmus is inhibited by convergence.
• Syndrome Duane I and III types.
• Mobius syndrome.
• Fixed strabismus.

The first stages of treatment

Ideally, the correct position of the eyeballs should be achieved by surgical intervention at 12 months of age or a little later - by 2 years only after the removal of amblyopia or significant refractive anomalies. Firstly, a bilateral recession of the internal rectus muscles is performed. At large angles, the recession may be 6.5 mm or more. It is necessary to take into account the combined hyperfunction of the lower oblique muscle. The acceptable result is a residual convergent strabismus within 10 D "associated with peripheral fusion (combats diplopia) and central suppression (combats confusion). Such a residual small angle is sufficiently stable, even when the child does not have a bifoveal fusion.

Follow-up treatment

1. Hypocorrection may require a repeated recession of the internal rectus muscle or a resection of one or both of the outer rectus muscles.
2. Hyperfunction of the lower oblique muscle can develop later, most often - to 2 years of age. In this regard, parents should be warned that subsequent surgical treatment may be required, despite the initially good result. Initially, surgical treatment is unilateral, but often within 6 months, there is a need for surgical intervention and the second eye. Procedures aimed at weakening the lower oblique muscle include myotomy, myoectomy and resection.
3. Dissociated vertical deviation may occur several years after primary surgical correction, especially in children with nystagmus. It is characterized by the following:
   • Drifting upward eye with an excloddeaviation under the damper or in case of attention disturbance.
   • When the flap is removed, the affected eye will move downward without the accompanying movement down the opposite eye.

Thus, the DVD is not subject to Hering's law. The deviation is usually two-sided and may be asymmetric. Surgical treatment is indicated for cosmetic reasons. The recession of the upper straight line with Faden operation or without it and / or lower scythe movement is a frequently used intervention in DVD, although full correction is rarely achieved.

Amblyopia develops over time in 50% of cases.

The accommodation component may be suspected if, after surgery, the eye position is correct or nearly correct, and then a reconversion occurs. In this regard, to correct the emerging accommodation component, it is necessary to reexamine the refraction in all children.

[10], [11], [12], [13], [14]

Basic convergent strabismus

Symptoms

• There are no significant violations of refraction.
• The same angle when fixing near and far objects.

Treatment is surgical.

[15], [16], [17],

The excess of convergence

Symptoms

• There are no significant violations of refraction.
• Orthophoria or small esophoria when fixing a distant object.
• Ezoforiya at fixation of a close object at normal or low index AK / A.
• The normal closest accommodation point.

Treatment: bilateral recession of internal rectus muscles.

Cyclic oculomotor spasm

Represents a periodic phenomenon usually hysterical, but can be an organic genesis (trauma or swelling of the posterior cranial fossa).

Symptoms during the attack:

• Ezotropka due to the supported convergence.
• False myopia due to spasm of accommodation.
• Two-sided miosis.

Treatment with cycloplegic drugs and bifocals.

[18], [19], [20], [21], [22]

Insufficient divergence

Strikes healthy young people.

Symptoms

• Periodic or permanent esotropia when fixing a distant object.
• Minimum deviation when fixing a nearby object or its absence.
• Full two-sided abduction.
• Reduction of negative fusiotic reserves.
• Absence of neurological disease.

Treatment: prismatic correction to spontaneous recovery, and in case of failure - bilateral resection of external rectus muscles.

Divergence paralysis

Can manifest at any age. Differential diagnostics with one-sided or bilateral paralysis of the VI pair of cranial nerves is necessary. Paralysis of divergence is characterized by:

• A convergent strabismus that does not change or may diminish when viewed from the outside, unlike paralysis VI of a pair of cranial nerves.
• Negative fusional reserves are significantly reduced or absent.
• It can be accompanied by neurological diseases, for example as a result of head trauma, intracranial voluminous formations and cerebrovascular disorders.

[23], [24], [25], [26], [27], [28], [29]

Sensory convergent strabismus

The cause of sensory convergent strabismus is a one-sided reduction in visual acuity that interferes with or eliminates fusions, such as in cataracts, atrophy of the optic nerve or hypoplasia, toxoplasmosis retinchoroiditis, or retinoblastoma.

It is necessary to study the fundus under mydriasis in children with strabismus.

Secondary convergent strabismus

Secondary convergent strabism follows after excessive correction of exodeviation. If the deviation is not very large, surgical correction should be postponed for several months, as spontaneous improvement can occur.

Acutely arose convergent strabismus

A sharply arisen convergent strabism arises when the decompensation of a convergent strabismus or microtropy occurs suddenly. The patient complains of double vision. It is important to exclude paralysis of the VI pair of cranial nerves or paralysis of divergence.

[30], [31], [32], [33], [34]

Cyclic convergent strabismus

Cyclic convergent strabismus is a very rare condition, characterized by alternating manifesting convergent strabismus and orthophores, lasting for 24 hours. The condition can last for months and years and, ultimately, lead to a constant convergent strabismus requiring surgical treatment.

[35], [36], [37], [38]