Amblyopia

One of the most frequently occurring sensory disturbances in monolateral strabismus is amblyopia, i.e., a functional decline in eye vision due to its inactivity, non-use.

Normally, fixation is foveal. Noncentral fixation can be paraphoretic, macular, paramacular, and disc (peripheral), with the image falling on the eccentric portion of the retina.

[1], [2], [3]

Causes of amblyopia

According to the mechanism of occurrence, amblyopia can be dysbinocular, that is, due to the violation of binocular vision, which is observed with strabismus, when the participation of the rejected eye in the visual act is significantly reduced, or refractive, which is the result of untimely appointment and unstable wearing glasses in ametropies creating fuzzy image on the fundus.

In the presence of uncorrected anisometropia, anisometropic amblyopia occurs. Refractive amblyopia can be successfully overcome by means of rational and constant optical correction (glasses, contact lenses).

Blurred vision (congenital cataract, throat) can cause obscure amblyopia difficult to treat, which requires prompt surgery (eg, extraction of congenital cataracts, transplantation of the cornea).

[4], [5], [6], [7]

Symptoms of amblyopia

Amblyopia can be one- and two-sided.

With amblyopia, color and contrast sensitivity also decrease.

When strabismus appears, inevitably there is double vision, since the image in the mowing eye falls on the disparate site of the retina, but thanks to adaptive mechanisms the optic-nervous system adapts to the asymmetric position of the eyes and there is functional suppression, inhibition, or "neutralization" [in the terminology of LI. Sergievsky (1951)], images in the mowing eye. Clinically, this is expressed in the emergence of a functional scotoma. Unlike true cattle, observed with organic lesions of the organ of vision, functional scotoma with strabismus exists only if both eyes are open, and disappears with monocular fixation (when the other eye is covered). Functional scotoma is a form of sensory adaptation, relieving of the dithering that is observed in most patients with a friendly strabismus.

With monolateral squint, the presence of a permanent scotoma in the mowing eye leads to a persistent decrease in vision. In the case of alternating strabismus, the scotoma appears alternately in the right or in the left eye, depending on which eye is currently mowing, so amblyopia does not develop.

One form of sensory adaptation with a friendly strabismus is the so-called abnormal correspondence of the retina, or asymmetric binocular vision. Diplopia disappears due to the appearance of the so-called false macula. There is a new functional connection between the central fossa of the fixing eye and the retinal segment of the mowing eye, on which the image falls due to deviation (eye deviation). This form of adaptation is extremely rare (in 5-7% of patients) and only at small angles of strabismus (microdeviation), when the retina of the deflected eye is organically and functionally little different from the central fossa. At large angulations of strabismus, when the image hits the insensitive peripheral part of the retina, the possibility of its interaction with the highly functional central fossa of the fixing eye is excluded.

Amblyopia degrees

In terms of the degree of visual acuity reduction, according to ES Avetisov's classification, amblyopia of low degree is distinguished - in the acuity of sight of the mowing eye 0,8-0,4, average - 0,3-0,2, high - 0,1-0, 05, very high - 0.04 and below. Amblyopia of high degree is usually accompanied by a violation of visual fixation of the mowing eye.

[8], [9], [10], [11], [12], [13], [14]

Classification of amblyopia

Amblyopia - one-sided or bilateral (more often) reduction of the most corrected visual acuity due to deprivation of uniform vision and / or pathological binocular connections in the absence of organic pathology of the eye and the visual pathway.

1. Disbinocular (strabismic) amblyopia develops in pathological binocular connections with prolonged monocular suppression of the rejected eye. A decrease in vision is characteristic even with violent fixation.
2. Anisometropic amblyopia occurs with a difference in refraction> 1 spherical dpt. Anomalous binocular connections occur when superimposed on each other are a differently focused and unfocused visual image (aniseikonium). The element of deprivation of uniform vision also takes place, since a constant projection of the fuzzy image occurs. It is often combined with micro-strabismus and can be combined with dysbinocular amblyopia.
3. Obscuration amblyopia occurs with visual deprivation and can be one-sided or two-sided. The reason may be the opacity of optical media (cataracts) or ptosis of the third degree.
4. Isometropic amblyopia occurs when deprived of uniform vision. Two-sided amblyopia is usually caused by symmetrical refractive anomalies, most often with hypermetropia.
5. Meridional amblyopia occurs with visual deprivation in one meridian and can be one-sided or two-sided. The cause is uncorrected astigmatism.

[15], [16], [17], [18], [19], [20], [21],

Diagnosis of amblyopia

Visual acuity. In the absence of organic changes, the difference in corrected visual acuity in two lines or more indicates amblyopia. Visual acuity with amblyopia and the process of visual acuity study by individual optotypes is higher than in line. This phenomenon of "crowding" can occur and is normal, but more pronounced with amblyopia.

Neutral dense filter allows you to indirectly differentiate reduced vision in organic pathology from amblyopia. The filter reduces the visual acuity in the norm by two lines. It is used in the following cases:

• when determining visual acuity with correction;
• when determining visual acuity with a filter
  installed in front of the eye;
• if the visual acuity when using the filter does not decrease, this indicates amblyopia;
• if the visual acuity when using the filter is reduced, then an organic pathology is assumed.

The visual acuity, determined from the sinusoidal gratings (ie the ability to distinguish gratings of different spatial frequencies), is often higher than the visual acuity determined by Snellen optotypes.

[22], [23], [24], [25], [26], [27], [28]

Amblyopia: treatment with occlusion, pleoptics and penalization

The sensitive period, during which the treatment for amblyopia is effective, is 7-8 years for disbinocular amblyopia and 11-12 years for anisometropic amblyopia.

Pleoptics is a section of ophthalmology that develops methods for the treatment of amblyopia, which affects about 70% of children with strabismus. The main task of treating amblyopia is to obtain visual acuity allowing the possibility of binocular vision. This should be considered visual acuity, equal to 0.4 Dpt and higher. To treat amblyopia proceeds after wearing glasses.

The main methods of treatment of amblyopia include direct occlusion, treatment with the use of a negative sequential image, local "blinding" stimulation by light of the central fossa of the retina.

Occlusion - switching off from the act of seeing one eye. The goal of permanently turning off the leading eye is to achieve the same visual acuity of both eyes and to translate monolateral squint to alternating. Such treatment is carried out for at least four months.

Occlusion of the healthy eye to enhance the visual load of the amblyopic eye is the most effective method of treatment. The mode of wearing an occluder (all day or periodically) depends on the age of the patient and the degree of amblyopia. The younger the patient, the faster the improvement, but at the same time the risk of amblyopia on the healthy eye increases. In this connection, in the treatment process, control over the visual acuity of both eyes is necessary. The higher the visual acuity with the appointment of an occlusion, the shorter the time of wearing the occluder. If visual acuity does not increase within 6 months. Then it is unlikely that the treatment will be effective.

The use of a negative sequential image is that, while lighting the retina of the posterior pole of the eye, simultaneously cover the uveal zone with a ball. As a result, a sequential visual image appears, which, according to the covering object, has a central field.

Local "blinding" stimulation with light from the central fovea of the retina consists in stimulation of the central fovea with the light of an impulse lamp or helium-neon laser introduced into the system of a large nonreflex ophthalmoscope.

Orthoptics - the development of binocular vision. As soon as orthophoria is established under the influence of treatment or surgery, if the visual acuity of the amblyopic eye is 0.4 and higher, it is necessary to attach to the pleoptics exercises for the development of binocular vision. This treatment is performed on haploscopic devices - synoptophores.

Synoptophor is an improved stereoscope. It consists of two tubes with eyepieces, through which each eye is presented with a drawing. If the patient has the ability to drain foveal images of objects, exercises on synoptophor for the development of fusional reserves are carried out.

If after a complex of pleopto-orthoptic exercises the strabismus is not eliminated, then they resort to surgical treatment. In some cases (usually at large angulations of strabismus), surgical intervention may precede pleopto-orthotopic treatment.

Penalization is an alternative method, in which vision is better than seeing eye blurred by the installation of atropine. The method can be effective in treating amblyopia of low degree (6/24 and above) when combined with hypermetropia. Penalization does not lead to an effect as quickly as occlusion, and is effective only if the vision of the normal eye under conditions of penisation is below the visual acuity of the amblyopic, at least when fixing a nearby object.

[29], [30], [31], [32], [33]