Incomitant Strabismus: Clinical Guidelines

List of Abbreviations

DVD – Dissociated Vertical Deviation

D – diopter

IU – International Unit

PGFOM – Primary Hyperfunction of the Inferior Oblique Muscles

PD – prism diopter

CN – cranial nerves

EOM – extraocular muscle

EFPM – elastic Fresnel prism membrane

CD – chemodenervation

Terms and Definitions

Abduction is the movement of the eye outward from the primary gaze position

An agonist is an extraocular muscle whose action (duction) is being tested

Adduction is the movement of the eye inward from the primary gaze position

An antagonist is an extraocular muscle that moves the eye in the direction opposite to the action of the agonist (duction: ipsilateral antagonist; version: contralateral antagonist)

Vergence is the movement of the eyes in opposite directions (convergence, divergence)

Version is the movement of the eyes in the same gaze direction

Incycloduction is the rotation of the eye around the sagittal axis from outside inward

Duction is the monocular movement of the eye from the primary gaze position

A synergist is an extraocular muscle that moves the eye in the same gaze direction (duction: ipsilateral synergist; version: contralateral synergist)

Incomitant strabismus is strabismus in which the magnitude and direction of deviation vary in different directions of gaze

Orthotropic gaze position is the direction of gaze in which there are no ocular refixation movements during the cover test, accompanied by binocular vision (prototype of a record indicating normal retinal correspondence, where the objective angle of strabismus equals the subjective angle)

Diplopia-free orthotropic zone is the field of gaze in which double vision is absent (prototype of "fusion stability on smooth pursuit movements")

Chemodenervation is a dosed reduction in extraocular muscle function following the suppression of neuromuscular transmission of the efferent nerve impulse via intramuscular injection of botulinum toxin type A-based preparations

Excycloduction is the rotation of the eye around the sagittal axis from inside outward

1. Brief information on the disease or condition

1.1 Definition of the disease or condition

Incomitant strabismus is strabismus in which the magnitude and direction of deviation vary in different directions of gaze [1,2,3].

1.2 Etiology and pathogenesis of the disease or condition (group of diseases or conditions)

Primary inferior oblique overaction (PIOOA) is hyperelevation in adduction, which can be caused by a number of factors.

First, in adduction, there is a functional elevation imbalance of 5% between the superior and inferior oblique muscles favoring the latter; the superior oblique muscle spends 37% of its energy as a depressor, while the inferior oblique spends 42% as an elevator. Up to 77% of examined subjects without strabismus have a physiological hypertropia of more than 2 PD in any direction of gaze, of whom 85% exhibit a V-pattern of less than 15 PD.

Second, dystopia of horizontal muscles, specifically the inferior displacement of the anatomical insertion site of the lateral rectus, can induce inferior oblique overaction. Even an isolated downward dislocation of the lateral rectus muscle pulleys by less than 2 mm can lead to heterotropia with signs of inferior oblique overaction and/or a V-pattern, which should be kept in mind during the differential diagnosis of clinical signs of incomitant strabismus.

Third, prolonged eye occlusion can induce inferior oblique overaction in an individual without strabismus who has normal stereopsis, whereas early loss of binocular vision is perceived by the central vestibular system as a further step requiring an increase in tone in the extraocular muscles, manifesting as primary inferior oblique overaction [4,5,6,7,8,9,10,11].

Dissociated vertical deviation (DVD). There are two etiological hypotheses for DVD. One theory is that DVD is a vertical vergence movement aimed at suppressing latent nystagmus, with the oblique muscles playing a major role. An alternative theory suggests that insufficient fusion allows a primitive dorsal light reflex, observed in other species, to manifest [12,13].

Paralytic (paretic) strabismus is a multi-etiological disease [14], see Table 1.

Table 1. Comparative analysis of the etiology of cranial nerve palsies in children and adults.

1.3 Epidemiology of the Disease or Condition

At age 19 and older, newly diagnosed paralytic strabismus accounts for 23.91 cases per 100,000 population; the incidence increases with age and reaches a maximum after 80 years (incidence rate is 0.024%, although the total number of patients in the Russian Federation may reach 183,000), and small-angle vertical strabismus accounts for 7.19 cases (0.00719%; 5,485 people) [15].

Among all patients with strabismus, 4.75% of cases are paralytic, the mean age is 23.6 years (range, 3–63 years), and in 34.2% of cases, paralytic strabismus is congenital [16].

Infantile esotropia combined with primary inferior oblique overaction is observed in 78% of cases [17].

Primary inferior oblique overaction occurs in 72% of patients with congenital esotropia at a mean age of 3.6 years, in 34% of patients with accommodative esotropia at a mean age of 5.2 years, and in 32% of patients with intermittent exotropia also at a mean age of 5.2 years [18].

In cases of acquired esotropia, this probability decreases to 30% [19,20].

Primary inferior oblique overaction occurs in 17% of all hypertropia cases [18].

The prevalence of dissociated vertical deviation among diagnosed strabismus cases is 1.9%. Common strabismus subtypes associated with DVD were congenital esotropia (53%), esotropia in developmentally delayed patients (25%), and accommodative esotropia (3.4%) [21].

Among patients with sensory hypertropia, DVD occurs in 12.5% of cases [22].

1.4 Features of Coding the Disease or Condition

H49.9 – Unspecified paralytic strabismus

H50.2 – Vertical strabismus

Hypertropias

Hypotropias

1.5 Classification of the disease or condition

Paralytic strabismus [23].

1. By the time of onset of palsy:

– congenital form;

– acquired form.

2. By the affected cranial nerve:

– III pair (oculomotor nerve):

– complete;

– isolated:

– m. rectus medialis;

– m. rectus superior;

– m. rectus inferior;

– m. obliquus inferior.

– IV pair (trochlear nerve);

– VI pair (abducens nerve).

3. By etiology:

– congenital palsies:

– birth trauma;

– hypoplasia of cranial nerve nuclei;

– fiber anomalies;

– muscle aplasia or hypoplasia;

– fibrous anomalies.

– acquired paralyses:

– idiopathic;

– traumatic;

– oncological;

– vasculo-diabetic;

– aneurysmal;

4. By symmetry of cranial nerve involvement:

– unilateral palsy;

– bilateral palsy:

– symmetrical;

– asymmetrical;

– masked (hidden).

5. By restriction of mobility in the direction of action of the paretic muscle:

– grade 0: normal mobility;

– grade 1: mobility past the midline by 15–20 %;

– grade 2: mobility up to the midline;

– grade 3: lack of mobility to the midline.

6. By rate of development:

– acute: up to 3 months from onset;

– subacute: from 3 to 6 months;

– chronic: more than 6 months.

7. By localization level of the lesion:

– supranuclear;

– nuclear;

– fascicular (brainstem);

– orbital;

– neuromuscular.

Vertical:

1. True hyperphorias and hypertropias [3].

1. Vertical heterophorias:

– hyposupraphoria;

– hyperinfraphoria.

2. Vertical heterotropias:

– hyposupratropia;

– hyperinfratropia.

2. Dissociated vertical deviations (alternating sursumduction).

By symmetry:

– unilateral;

– bilateral:

– symmetrical;

– asymmetrical.

By manifestation:

– manifest;

– latent.

By degree:

– mild (from 0 to 9 prism diopters);

– moderate (from 10 to 19 prism diopters);

– severe (more than 20 prism diopters) [12,13].

By type:

– comitant;

– incomitant [24].

3. Paretic vertical deviations.

4. Hypertropia in adduction caused by primary overaction of the inferior oblique muscles.

Degree of overaction:

+1 – up to 7º;

+2 – 8-14º;

+3 – 15-21º;

+4 – more than 22º [25].

1.6 Clinical presentation of the disease or condition

Symptoms:

1. Cosmetically visible asymmetrical eye position horizontally, vertically, or combined. Strabismus may change its characteristics (magnitude and direction) in various gaze directions.

2. Restriction (absence) of mobility of the eye(s) towards the action of the paretic (paralyzed) or functionally weaker extraocular muscle is noted.

3. Diplopia: horizontal, vertical, torsional, combined. Diplopia may change in magnitude and type in various directions of gaze and upon fixation of objects at different distances. Diplopia may be absent (due to the mechanism of a functional suppression scotoma or abnormal retinal correspondence).

4. The patient may present with an abnormal head posture (head turn or tilt) that reduces or completely compensates for diplopia via fusional reserves.

Anamnesis. The condition may be congenital (manifesting within the first 6 months of life) or acquired. It may occur following trauma (physical or psycho-emotional), after infections, following prophylactic vaccinations, as a result of cardiovascular disorders, or in uncompensated endocrine diseases. In some patients, no clear cause for the onset of strabismus is identified. Symptom dynamics may be progressive, stable, or regressive.

If the condition develops in childhood and lacks proper treatment, a decreased best-corrected visual acuity may be detected (disbinocular amblyopia).

Examination of refraction under cycloplegia may reveal ametropia, which in some patients can serve as an etiopathogenetic factor for the onset or progression of strabismus.

Investigation of the character of binocular vision under haploscope conditions.

1. Congenital incomitant strabismus:

Primary gaze position – typically monocular.

Cardinal gaze positions – monocular or simultaneous (the type depends on the characteristics of heterotropia).

Gaze position with abnormal head posture – binocular.

2. Acquired incomitant strabismus.

Primary gaze position – typically simultaneous (the type depends on the characteristics of heterotropia).

Cardinal gaze positions – simultaneous (the type depends on the characteristics of heterotropia).

Gaze position with abnormal head posture – binocular.

Investigation of retinocortical retinal correspondence.

1. Congenital incomitant strabismus.

Normal retinal correspondence, abnormal retinal correspondence, type A or B functional suppression scotoma.

2. Incomitant strabismus acquired in early childhood (under 2 years of age).

Normal retinal correspondence, abnormal retinal correspondence, type A or B functional suppression scotoma.

3. Acquired incomitant strabismus.

Normal retinal correspondence.

In the majority of patients with incomitant strabismus, no anterior segment changes are detected. Media are clear. No specific fundus abnormalities are found.

Dissociated vertical deviation, cardinal signs:

– an oculomotor system condition in which each eye slowly drifts upward and outward with simultaneous extorsion during occlusion or visual inattention [12,13].

Primary inferior oblique overaction, cardinal signs:

– hypertropia in adduction [4,5,6,25].

2. Diagnostics, medical indications and contraindications for diagnostic methods

It is important to actively and purposefully screen patients for signs of incomitant strabismus, as the accuracy of the diagnosis determines the efficacy of subsequent treatment recommendations aimed at functional recovery or cosmetic improvement.

Criteria for diagnosing incomitant strabismus based on a set of pathognomonic findings: the appearance of horizontal and/or vertical deviation or a change in their parameters by more than 5° in various directions of gaze, limitation of ocular motility by more than 10° from the age-adjusted mean norm, with or without accompanying diplopia.

2.1 Complaints and Anamnesis

Comments: evaluate complaints regarding decreased distance and near visual acuity, double vision, cosmetically visible strabismus, limited eye mobility, and the presence of a head posture that compensates for double vision in adult patients with incomitant strabismus and in children starting from the age when the child is able to formulate complaints, in order to identify and assess incomitant strabismus and its dynamics.

Special attention should be paid to the age at which incomitant strabismus was first detected, the potential cause of strabismus development, and symptom dynamics in adult patients and children with incomitant strabismus to evaluate the potential efficacy of previously administered or planned treatment.

Complaints and medical history are described in the section "Clinical Presentation".

2.2 Physical Examination

Physical examination is not performed for incomitant strabismus.

2.3 Laboratory Diagnostics

Laboratory diagnostic tests are not performed for incomitant strabismus.

2.4 Instrumental Diagnostics

Comments: visometry in preverbal children (under three years of age) is performed approximately. In infants under one year of age, it is determined whether the child has object vision (visual fixation of objects, recording of optokinetic nystagmus, and visual evoked potentials).

In children older than one year, visual acuity can be determined in a game format: the examiner shows optotypes on the Orlova chart, and the child points to the corresponding optotypes on a flyer with optotypes used in that chart, or indicates the direction of the gap in optotypes (Landolt rings) on the Golovin chart.

Uncorrected visual acuity, visometry with spectacles and optimal correction providing maximal distance visual acuity in verbal children (approximately three years of age and older) are performed using Orlova charts (picture optotypes), Sivtsev charts (letter optotypes), Golovin charts (Landolt ring optotypes), or Snellen optotype charts (E in four orientations).

In adult patients, visual acuity is examined using the Sivtsev or Golovin chart, or a visual acuity projector.

Visual acuity is defined as the chart row in which optotypes are correctly recognized, allowing 1 error in rows 6–8 and 2 errors in row 9 and below.

Achieving the minimum age-appropriate visual acuity for pediatric patients and a visual acuity of 1.0 for adult patients is not a criterion for terminating the examination.

Comments: automatic refractometry and keratorefractometry are reliable methods for diagnosing ametropia when the testing protocol is strictly observed. These methods allow for rapid and accurate refraction testing in adults and children over the age of three under natural conditions of the accommodation mechanism and following optimal cycloplegia. If it is technically impossible to perform refraction tests using stationary equipment, mobile keratorefractometers, distant autorefractometers, or autorefractors are used.

Comments: measurement of the angle of strabismus is performed using the Hirschberg method [33], with the cover test or cover-uncover test. The fact that extraocular muscles with cyclovertical action anatomically perform primary, secondary, and tertiary actions is taken into account.

It is necessary to describe the angle of strabismus (horizontal and vertical components) for each eye separately, during alternate visual fixation, in at least five diagnostic gaze positions.

The angle of the horizontal component of strabismus in vertical diagnostic gaze positions is evaluated by shifting the gaze along the beam of the ophthalmoscope at its maximum displacement relative to the horizontal line upwards and downwards to exclude the influence of convergence on the hypo- or overdiagnosis of alphabetical patterns.

If the horizontal component of strabismus changes divergently in the upward gaze relative to the downward gaze (appearance/increase of exodeviation, decrease/elimination of esodeviation by more than 15 prism diopters (8º)), a V-pattern is diagnosed.

If the horizontal component of strabismus changes divergently in the downward gaze relative to the upward gaze (appearance/increase of exodeviation, decrease/elimination of esodeviation by more than 10 prism diopters (5º)), an A-pattern is diagnosed.

Y-pattern is a clinical variant of the V-pattern manifestation (however, the aforementioned difference in horizontal deviation is detected between the upward and primary diagnostic gaze positions).

Lambda (λ) pattern is a clinical manifestation of the A-pattern (however, the aforementioned difference in horizontal deviation is detected between the downward and primary diagnostic gaze positions).

X-pattern is a combination of the V-pattern in the upward gaze and the A-pattern in the downward gaze.

O-pattern is a combination of the A-pattern in the upward gaze and the V-pattern in the downward gaze [3,5,6,7,34].

The test for changes in vertical deviation during head tilting, known as the Bielschowsky head tilt test, is of great diagnostic value in palsies of the vertical rectus and oblique extraocular muscles (EOMs). This phenomenon allows for compensating or reducing the magnitude of deviation and diplopia. In this case, the head tilt will always be toward the side of action of the affected EOM [28].

Unfortunately, this test may yield false results in long-standing paresis and in cases of restrictive EOM conditions [34,54].

Comments: eye motility testing is performed monocularly. The patient's head must remain strictly in a straight horizontal and vertical position throughout the entire examination. The ophthalmologist should be positioned directly opposite the patient during the examination. The fixation test object must be located at a distance from the patient's eye sufficient to exclude a convergence effect on the examination results (more than 1 m, even during monocular testing). The test object is moved slowly. It is optimal to start the eye motility examination (duction) in the direction of gaze that, based on complaints, should not be limited. Moving the test object in the direction of action of the extraocular agonist muscle (the muscle whose function is being tested) must be repeated at least three times. The result of the examination is the displacement of the ophthalmoscope light reflex according to the Hirschberg method. The highest result obtained during the examination is entered into the examination protocol.

From the primary gaze position, the range of adduction is determined by moving the test object inward (function of the medial rectus muscle), abduction outward (lateral rectus muscle), elevation upward (superior rectus and inferior oblique muscles), and depression downward (inferior rectus and superior oblique muscles). Although the superior rectus muscle is the primary elevator and the inferior rectus muscle is the primary depressor from the primary gaze position, it is advisable to test elevation and depression from gaze positions when the eye is abducted (functions of the inferior and superior rectus muscles only), and then in adduction (the cardinal gaze position for testing the function of the superior and inferior oblique muscles) [3,28].

Comments: based on patient questioning, it is necessary to determine the type of diplopia: horizontal (images of visual fixation are perceived as two objects located side by side at the same horizontal level), vertical (one object above the other), torsional (one object straight, the second tilted clockwise or counterclockwise). Combined double vision in various manifestations is possible.

Is the double vision constant? Do its characteristics change in various gaze directions? Is there a gaze direction where the double vision of objects is compensated? Does the patient have an abnormal head turn or tilt to eliminate diplopia [28]?

2.5 Other Procedures

Comments: being simple to perform and highly informative, the forced duction test has become popular nowadays for determining the presence of mechanical restriction of eye mobility.

After local anesthesia, the eye is fixed with two toothed forceps at the conjunctiva near the limbus and rotated in the direction opposite to the suspected mechanical restriction. The forced duction test is necessary for the differential diagnosis of the cause of strabismus: paralysis (paresis) of the extraocular muscle or a mechanical restrictive condition of its antagonist (myositis, extraocular muscle contracture, conjunctival or Tenon's capsule contracture). However, restriction of passive eye mobility during the forced duction test may also occur when extraocular muscle action is weakened due to retroequatorial adhesion of the muscle to the sclera. When performing the test, it is important not to exert pressure on the globe [38].

When examining oblique extraocular muscles, a modified forced duction test is performed. To check the state of the superior oblique muscle, the eye is fixed with two toothed forceps at the 6 and 9 o'clock positions. The eye is elevated, adducted, rotated backward and outward, and then moved within the orbit by performing intorsional and extorsional rocking movements across the tendon. Tendon tension becomes apparent when the eye seems to jump over the tendon during these manipulations. The state of the inferior oblique muscle is tested similarly by moving the eye downward and nasally [39,40].

When succinylcholine chloride is used as an anesthetic, generalized tension of the extraocular muscles occurs, which can simulate eye restriction [38].

3. Treatment, including drug and non-drug therapies, diet therapy, and pain management

Comments: the frequency of follow-up examinations depends on the type of incomitant strabismus, the patient's age, and the treatment method.

Acquired paralytic strabismus in children and adults.

It is optimal to evaluate the dynamics of the symptom complex (deviation magnitude, duction volume, diplopia magnitude, presence of an abnormal head position in which diplopia decreases or is compensated) to select the optimal method of treatment and rehabilitation:

– acute period (first three months from disease onset) – every 2–4 weeks;

– subacute period (from the third to the sixth month) – monthly;

– chronic period (later than the sixth month) – every 3–6 months.

Congenital paralytic strabismus in children:

– under 1 year of age – monthly;

– from 1 year to 3 years of age – every 6 months;

– over 3 years of age – annually.

In cases of diagnosing other types of incomitant strabismus in children under 7 years of age – once every 6 months, in older children and adults – once a year.

When selecting or prescribing prismatic correction, during the first month every two weeks, during the subsequent three months – monthly, then once every 3–6 months.

After chemodenervation – at 14 days, then at 1, 3, and 6 months.

After surgical treatment – the next day, at 1, 3, 6, and 12 months.

3.1 Optical correction

The presence of ametropia is one of the causes of refractive or anisometropic amblyopia in pediatric patients. Functional inequality of the eyes is an obstacle to initiating effective orthoptic treatment. The establishment of normal binocular vision is the basis for successful multimodal treatment of incomitant strabismus.

Comments: the presence of ametropia requiring spectacle correction combined with an abnormal head posture compensating for diplopia, or caused by restricted ocular motility, is an indication for surgical treatment. The aim is to ensure that the patient's visual axis/axes pass through the optically most effective zone of the spectacle lenses.

Optimal correction of ametropia is the basis for successful pleoptic treatment of refractive amblyopia in pediatric patients with incomitant strabismus.

3.2 Prismatic Correction

Double vision (diplopia) is one of the fundamentally important subjective symptoms of strabismus in general and incomitant strabismus in particular. Diplopia entails a number of suppression mechanisms, which inevitably leads to further aggravation of binocular vision and oculomotor system disorders. Patients may develop a functional suppression scotoma and abnormal retinal correspondence. The patient may subjectively eliminate diplopia by excluding the eye from binocular activity (squinting, patching the affected eye) or by adopting an abnormal head posture (turning, tilting) that eliminates the oculomotor imbalance and compensates for diplopia.

In pediatric patients with congenital incomitant strabismus, prismatic alignment of the visual axes creates the conditions for the development of binocular vision as part of comprehensive treatment.

Comments: to create an effective treatment regimen for patients with paralytic strabismus, a technique for prescribing and fitting prismatic correction at various stages of treatment has been developed and implemented into clinical practice to reduce or eliminate primary and/or secondary deviation, diplopia, expand the field of single binocular vision, and increase the effectiveness of restoring the function of extraocular muscles involved in paralysis (paresis).

An elastic Fresnel prism (EFP) with a power of 6 to 30 prism diopters is applied to the inner surface of the corrective spectacle lens in front of the healthy eye.

The power and direction of the prismatic correction, as well as the width and configuration of the prism, are calculated individually for each patient depending on the magnitude of the primary and secondary strabismus, and the degree of preserved oculomotor function of the muscle or muscles involved in paresis (paralysis), depending on the type of paralysis.

3.3 Pleoptic Treatment

Functional equality of the eyes (a difference in maximum corrected visual acuity of no more than 2 lines) is the foundation necessary for the normal functioning of binocular vision. The presence of dysbinocular, refractive, or mixed amblyopia in a pediatric patient is an indication for optimal pleoptic measures.

Comments: the choice of tactics and methods of pleoptic treatment depends on the type of fixation.

Central fixation.

Comprehensive pleoptic treatment using the entire arsenal of methods is possible (afterimages, computer programs, laser stimulation, electrical stimulation, magnetic stimulation, accommodation training).

In non-central types of fixation, it is important to first reorient them to central fixation. Otherwise, the use of the above treatment methods will lead to the consolidation of non-central fixation.

Non-central intramacular types of fixation.

The primary treatment is reorientation using a maculotester.

Non-central extramacular types of fixation.

Monocular spatial reorientation is performed after exposure to a glare source using a reflection-free ophthalmoscope.

After fixation correction, pleoptic measures are performed according to the standard protocol.

Following successful treatment of amblyopia, patients must be under dispensary observation by an ophthalmologist [50,51].

3.4 Exercises for Restoring and Strengthening Binocular Vision

At any stage of treating patients with paralytic strabismus (pre-surgical, post-chemodenervation, post-surgical, and inter-stage), it is fundamentally important to constantly expand the binocular field of gaze toward the action of the affected muscle.

Comments: a number of new terms have been proposed and introduced into clinical practice for performing orthoptic treatment in patients with paretic strabismus:

1. Orthotropic gaze position – the direction of gaze in which there are no fixing movements of the eyes during the cover test, accompanied by binocular vision (a prototype of a record indicating normal retinal correspondence, where the objective angle of strabismus equals the subjective angle);

2. Orthotropic zone free of diplopia – the field of gaze in which double vision is absent (prototype of "fusion stability on tracking movements").

A feature of the orthoptic examination and treatment of patients with paretic strabismus is that the orthotropic gaze position is taken as the reference point when improving fusional reserves.

The goal of orthoptic treatment in patients with paretic strabismus is to shift the orthotropic gaze position to the primary gaze position, or to expand fusional reserves to the point of compensating for diplopia (relieving the patient of abnormal head posture) and expanding the orthotropic zone free of diplopia in the horizontal (primarily) and vertical directions.

Prior to orthoptic treatment, the interpupillary distance is measured using a measuring ruler (GOST 427-75) or an electronic interpupillary distance meter PD-82 in the primary gaze position during the cover test, taking into account the angle $\gamma$, or in an abnormal head posture if it is impossible to bring the paretic eye(s) into the primary gaze position.

Comments: positional training is performed under natural conditions without visual field separation, allowing patients to perform it multiple times a day and anywhere.

Treatment is carried out under optical correction of ametropia if the patient is diagnosed with a refractive error.

The methodology for performing positional training is as follows.

1. Exercises are performed statically – the patient is sitting or standing.

2. Gaze is fixed on a distant object.

3. If the object appears double, the patient turns the head in the direction opposite to the field of gaze where diplopia occurs and increases, until it is completely eliminated.

4. The patient very slowly turns the head in the direction opposite to the compensatory position until persistent diplopia insurmountable by fusion appears.

5. Next, a slow reverse head movement is made until double vision is reliably eliminated.

6. The cycle is repeated at the boundary of "compensation-non-compensation".

7. The maximum possible regimen of training in terms of location and time is recommended.

3.5 Chemodenervation of Extraocular Muscles

Any type of strabismus as early as 1 month after onset may be accompanied by secondary structural changes in the agonist muscle, which lengthens due to the addition of sarcomeres, while in its ipsilateral antagonist the number of structural units decreases, the muscle shortens, and a contracture state develops. Chemodenervation of the antagonist muscle creates conditions for eliminating these secondary morphological changes in the pair of antagonistically functioning muscles [28].

Table 2. Criteria for calculating the optimal dosage of #botulinum toxin (M03AX01) type A in the treatment of paralytic strabismus (Units)

GDR CLE 5Grade of recommendation C (level of evidence – 5)

Comments: as part of improving the organization of medical care for citizens in medical organizations and authorizing the use of preparations based on #botulinum toxin (M03AX01) type A in the treatment of non-comitant strabismus in children and adults, a positive decision by the medical commission is required in some cases. The functions of the medical commission are listed in paragraph 4 of the Order of the Ministry of Health and Social Development of the Russian Federation No. 502n dated May 5, 2012. Specific functions of the medical commission are established by the medical organization depending on the types of services specified in the medical activity license.

In complex and combined treatment of patients with paralytic strabismus at the pre-surgical stage, it is necessary to perform chemodenervation of extraocular muscles that are the ipsilateral antagonist and contralateral synergist of the affected muscle.

The dosage of administered #botulinum toxin (M03AX01) type A depends on a combination of determining factors: the duration of cranial nerve palsy or paresis, the degree of functional competence of the affected extraocular muscle at the time of treatment, and the patient's age (see Table 2).

The decisive criterion for choosing the dosage of #botulinum toxin (M03AX01) type A is the combination of all signs of cranial nerve palsy or paresis.

A smaller amount of the drug should be injected into the ipsilateral antagonist muscle than into the contralateral synergist muscle.

3.6 Surgical Treatment

Surgical treatment must be pathogenetically grounded, and the technique physiologically sparing (not disrupting the duction and vergence mechanisms of ocular motility), leaving opportunities for re-intervention without worsening the non-comitance of the oculomotor system functioning.

Comments: personalized tactics and methods should be applied for each type of surgical treatment of non-comitant strabismus.

Tactics and methods of surgical treatment for paralytic (paretic) strabismus.

The scope of surgical treatment depends on the magnitude of primary and secondary deviation, eye mobility towards the action of the affected muscle, and the degree of contracture of the ipsilateral antagonist muscle

The objectives of surgical treatment are to maximally achieve the combination of the following results.

1. Cosmetic results:

– elimination of strabismus in the primary gaze position;

– elimination of abnormal compensatory head posture.

2. Functional results:

– elimination of diplopia, primarily when looking straight ahead;

– restoration of the functional capacity of the affected lateral rectus muscle to at least 50% of the age norm;

– maximum expansion of the zone of the horizontal binocular field of vision free from diplopia (under normal conditions, the eye moves no more than 15–20º from the primary position of gaze, after which a head turn occurs);

– maintenance of convergence sufficient for comfortable near-vision work [28].

Primary inferior oblique overaction.

In primary inferior oblique overaction, it is recommended to follow the treatment algorithm below [25]:

1. The first diagnostic step is to assess the 1st-level criterion (magnitude of esotropia) in order to choose the optimal surgical management strategy for primary inferior oblique overaction in patients with congenital or early-acquired esotropia;

2. Next, the strabologist must reliably assess the 2nd-level diagnostic criterion, which is the range of abduction;

3. The final 3rd-level criterion is the evaluation of the intraoperative forced duction test.

Dissociated vertical deviation.

Indications for surgical correction of dissociated vertical deviation (DVD) are:

– moderate and severe presentation;

– frequent manifestation of pronounced DVD;

– abnormal head posture;

– pronounced cosmetic defect [55].

To eliminate or reduce DVD, the following procedures are performed:

– recession of the inferior oblique muscle [56];

– anteriorization of the inferior oblique muscle [57];

– combined anteriorization and resection of the inferior oblique muscle [58];

– large recession of the superior oblique muscle [59,60];

– Faden operation combined with recession of the superior rectus muscle [61];

– resection of the inferior rectus muscle [62];

– anteronasal transposition of the inferior oblique muscle [63];

– inferior oblique muscle duplication [64];

– four-oblique-muscle surgery [65];

– recession with anteriorization of the inferior oblique and recession of the superior rectus [66].

3.7 Other Treatment

Not performed.

Medical nutrition therapy is not prescribed.

4. Medical Rehabilitation and Sanatorium-Resort Treatment

Sanatorium-resort treatment and the use of medical rehabilitation methods based on natural therapeutic factors are not required (data on their efficacy, indications, and contraindications are lacking).

5. Prevention and Dispensary Observation

6. Organization of Medical Care

Medical care for non-comitant strabismus is provided on a scheduled basis.

Primary health-nursing care for non-comitant strabismus is provided by medical personnel with secondary medical education; primary physician-led health care for non-comitant strabismus is provided by district pediatricians and general practitioners (family physicians). When symptoms or signs of decreased vision, diplopia, including signs of non-comitant strabismus, are suspected or identified, medical personnel with secondary medical education, district pediatricians, and general practitioners (family physicians) refer patients for consultation with an ophthalmologist. For non-comitant strabismus, primary specialized health care is provided by an ophthalmologist.

In accordance with Order No. 514n of the Russian Ministry of Health dated August 10, 2017, "On the Procedure for Conducting Preventive Medical Examinations of Minors" (as amended by Orders of the Russian Ministry of Health No. 410n dated July 3, 2018, No. 396n dated June 13, 2019, No. 1235n dated November 19, 2020), during medical examinations of minors, including upon admission to and during their studies in educational institutions, an ophthalmologist examines children at the age of 1 month, 12 months, 3 years, 6 years, 7 years, 10 years, 13 years, 15 years, 16 years, and 17 years.

Adults with non-comitant strabismus are examined by an ophthalmologist during preliminary and periodic medical examinations upon employment and during employment in accordance with departmental regulatory acts and/or in accordance with Order No. 988n of the Ministry of Labor and No. 1420n of the Russian Ministry of Health dated December 31, 2020, "On Approval of the List of Harmful and (or) Hazardous Production Factors and Jobs, in the Performance of Which Mandatory Preliminary Medical Examinations upon Admission to Employment and Periodic Medical Examinations Are Carried Out" and Order No. 29n of the Russian Ministry of Health dated January 28, 2021, "On Approval of the Procedure for Conducting Mandatory Preliminary and Periodic Medical Examinations of Workers Provided for by Part Four of Article 213 of the Labor Code of the Russian Federation, the List of Medical Contraindications to the Performance of Work with Harmful and (or) Hazardous Production Factors, as well as Jobs in the Performance of Which Mandatory Preliminary and Periodic Medical Examinations Are Carried Out."

Non-comitant strabismus is also identified during active presentation of children and adults to the ophthalmology office in the served area with complaints of diplopia or cosmetically visible strabismus.

The ophthalmologist of the ophthalmology office provides: consultative, diagnostic, and therapeutic care; in the presence of medical indications, refers children to the pediatric vision conservation office or pediatric ophthalmology department, and adult patients to the ophthalmology department.

Indications for hospital admission to provide planned inpatient medical care (children and adults) or day-care inpatient care (adults):

1) Chemodenervation of extraocular muscles;

2) Surgical treatment of extraocular muscles.

Indications for discharging a patient from a medical organization after receiving planned inpatient medical care (children and adults) or day-care inpatient care (adults):

1) Absence of intraoperative complications following patient examination on the day after chemodenervation;

2) Absence of intraoperative complications following patient examination on the day after surgical treatment.

7. Additional Information

In non-comitant strabismus, two main tasks are addressed: first, the elimination or clinically significant reduction of the oculomotor system imbalance (reduction or elimination of strabismus, restoration or increase in the range of ocular motility); second, the elimination of functional disorders (diplopia, dysbinocular or mixed amblyopia, impairment of binocular vision functions, ocular torticollis).

Treatment of patients with non-comitant strabismus should be comprehensive: optimal correction of identified ametropia, a set of pleoptic measures, improvement of binocular vision functions, elimination of diplopia by prescribing prismatic correction, and staged elimination of oculomotor imbalance through extraocular muscle chemodenervation and surgical treatment.

Dynamic monitoring and identified changes in the symptom complex require modifications to the treatment plan.

Delayed initial presentation of the patient to an ophthalmologist, failure to prescribe the optimal scope of treatment, and lack of proper dynamic monitoring can contribute to the exacerbation of non-comitant strabismus symptoms [28].

Criteria for Evaluating the Quality of Medical Care

References

Appendix A1. Working Group Composition

1. Aklaeva, Naila Anvarovna, Cand. of Sci. (Med.), National Medical Research Center of Eye Diseases named after Helmholtz of the Russian Ministry of Health, Association of Ophthalmologists LLC;

2. Antsiferova, Natalya Gennadyevna, Cand. of Sci. (Med.), Novosibirsk Branch of the S.N. Fyodorov Eye Microsurgery Federal State Institution of the Russian Ministry of Health, Russian Ophthalmologists Society LLC, Association of Strabologist Ophthalmologists;

3. Markova, Elena Yuryevna, Dr. of Sci. (Med.), Russian University of Medicine of the Russian Ministry of Health; Russian Ophthalmologists Society LLC;

4. Plisov, Igor Leonidovich, Group Head, Dr. of Sci. (Med.), Novosibirsk Branch of the S.N. Fyodorov Eye Microsurgery Federal State Institution of the Russian Ministry of Health, Russian Ophthalmologists Society LLC, Association of Strabologist Ophthalmologists;

5. Proskurina, Olga V., D.Sc. (Medicine), Helmholtz National Medical Research Center of Eye Diseases, Russian Ministry of Health; Association of Ophthalmologist Doctors;

6. Pushchina, Varvara B., Ph.D. (Medicine), Novosibirsk Branch of the S.N. Fyodorov Eye Microsurgery Federal State Institution, Russian Ministry of Health; Society of Ophthalmologists of Russia, Association of Strabologopedic Ophthalmologists.

Conflict of interest: none declared.

Appendix A2. Methodology for Developing Clinical Guidelines

Methods used for evidence collection/selection: electronic database search; analysis of current scientific developments on non-comitant strabismus in Russia and abroad; synthesis of practical experience of Russian and foreign colleagues.

When selecting publications as potential sources of evidence, the methodology used in each study is examined to ensure its reliability. The result of this examination affects the level of evidence assigned to the publication, which in turn influences the strength of the resulting recommendations.

A preliminary version of these guidelines was reviewed by independent experts who were asked to comment primarily on whether the interpretation of the evidence underlying the recommendations is reliable and accessible to practicing physicians and patients.

Comments were received from ophthalmologists dealing with oculomotor system pathology and binocular vision, and from primary care physicians regarding the clarity of presentation and the importance of recommendations as a working tool for daily medical practice.

Comments received from experts were thoroughly systematized and discussed by the working group chairs and members. Each item was discussed. Changes and additions recommended as a result of the discussion were incorporated into the text of the recommendations.

Target audience for these clinical guidelines:

1. Ophthalmologists;

2. General practitioners (family physicians);

3. Pediatricians;

4. Urban (district) pediatricians;

5. District pediatricians;

6. General practitioners;

7. Adolescent general practitioners;

8. District general practitioners;

9. Neurologists;

10. Neurosurgeons;

11. Plastic surgeons;

12. Trauma and orthopedic surgeons;

13. Maxillofacial surgeons;

14. Endocrinologists;

15. Medical and social expert evaluation physicians;

16. Preventive medicine physicians;

17. Medical rehabilitation physicians;

18. Resident physicians;

19. Medical optics optometrists.

Methods used for evidence collection/selection: electronic database search, analysis of modern scientific developments on the problem of non-comitant strabismus in Russia and abroad; synthesis of practical experience of Russian and foreign specialists; library resources. Description of methods used for evidence collection/selection: the evidence base for the recommendations includes publications included in the Cochrane Library, EMBASE and MEDLINE databases, as well as monographs and articles in leading specialized peer-reviewed domestic medical journals on this topic. The search depth was 10 years. Methods used to assess the quality and strength of evidence: expert consensus, significance assessment according to a rating scheme.

Table 1. Levels of Evidence (LoE) grading scale for diagnostic methods (diagnostic interventions)

Table 2. Scale for grading levels of evidence (LE) for prevention, treatment, and medical rehabilitation methods, including those based on natural therapeutic factors (preventive, therapeutic, rehabilitation interventions)

Table 3. Scale for grading grades of recommendation (GR) for prevention, diagnostics, treatment, and medical rehabilitation methods, including those based on natural therapeutic factors (preventive, therapeutic, rehabilitation interventions)

Procedure for updating clinical guidelines.

The mechanism for updating clinical guidelines provides for their systematic revision at least once every three years, as well as upon the emergence of new evidence-based medicine data on the diagnosis, treatment, prevention, and rehabilitation of specific diseases, or in the presence of justified additions/comments to previously approved clinical guidelines, but no more frequently than once every 6 months.

Appendix A3. Reference Materials

These clinical guidelines were developed taking into account the following regulatory legal documents:

1. Order of the Ministry of Health of the Russian Federation dated October 9, 2025, No. 614n "On approval of the procedure for providing medical care to children in the profile 'ophthalmology'."

2. Order of the Russian Ministry of Health dated October 24, 2025, No. 633n "On approval of the Procedure for providing medical care to the adult population in the profile 'ophthalmology'."

3. Order of the Russian Ministry of Health dated April 14, 2025, No. 203n "On approval of criteria for assessing the quality of medical care."

4. Order of the Ministry of Health of the Russian Federation dated April 14, 2025, No. 211n "On approval of the procedure for minors undergoing preventive medical examinations, accounting form No. 030-PO/u 'Minor's Preventive Medical Examination Card', the procedure for its maintenance, as well as the industry statistical observation form No. 030-PO/o 'Information on preventive medical examinations of minors', the procedure for its completion."

5. Order of the Ministry of Labor No. 988n, Ministry of Health of the Russian Federation No. 1420n dated December 31, 2020 "On approval of the list of harmful and (or) hazardous production factors and jobs, upon performance of which mandatory preliminary medical examinations upon admission to work and periodic medical examinations are carried out."

6. Order of the Ministry of Health of the Russian Federation dated January 28, 2021, No. 29n "On approval of the procedure for conducting mandatory preliminary and periodic medical examinations of workers provided for by part four of article 213 of the Labor Code of the Russian Federation, the list of medical contraindications to carrying out work with harmful and (or) hazardous production factors, as well as jobs upon performance of which mandatory preliminary and periodic medical examinations are carried out."

7. State Register of Medicines.

8. Order of the Russian Ministry of Health dated April 10, 2025, No. 180n "On approval of the procedure for the creation and activities of the medical commission of a medical organization."

9. Decree of the Government of the Russian Federation No. 3867-r dated December 18, 2025 "On Approval of the List of Vital and Essential Medicines, as well as Lists of Medicines for Medical Use and the Minimum Assortment of Medicines Required for Medical Care".

Appendix A3.1 Drugs used for the diagnostics of non-comitant strabismus

Appendix B. Physician Action Algorithms

Appendix C. Patient Information

Non-comitant strabismus is a complex disorder of the oculomotor system and binocular vision. The magnitude of the deviation angle varies in different directions of gaze. Non-comitant strabismus is not only a cosmetic feature, but can also be combined with various functional disorders. Diplopia occurs, which may be accompanied by a compensatory head tilt (ocular torticollis), binocular vision is impaired (the patient looks with only one eye), and if one eye turns inward or outward more frequently, a decrease in visual acuity (dysbinocular amblyopia) develops.

Non-comitant strabismus can be caused by various reasons, far from always directly related to the visual organ, but if it occurs, you must immediately make an appointment with an ophthalmologist so that they can make primary therapeutic prescriptions and coordinate non-ophthalmological additional examinations aimed at finding and eliminating the cause of strabismus.

Acute-onset non-comitant strabismus in the vast majority of cases does not resolve spontaneously and tends to worsen symptoms.

You should strictly follow the ophthalmologist's recommendations and carry out all prescribed stages of treatment: wearing glasses, performing occlusion (patching) in a specific regimen, pleoptic treatment (increasing monocular visual acuity), orthoptic treatment (improving binocular vision), phased minimally invasive (chemodenervation of extraocular muscles) and surgical treatment.

In each specific case, there is a specific schedule of follow-up examinations. However, if the dynamics of the disease are negative, it is necessary to urgently consult your attending ophthalmologist.

Appendix G. Assessment Scales, Questionnaires, and Other Evaluation Tools

Not used.