Refractive anomalies in children

Clinical refraction characterizes the proportionality of the optical power of the eye and its anteroposterior axis (the distance from the apex of the cornea to the central fovea of the retina). Clinical refraction is understood as the position of the main focus of the eye relative to the retina. The magnitude of refraction reflects the distance from the main focus of the eye to the retina, expressed in diopters (D). There are three types of clinical refraction of the eye.

Emmetropia (Em) is a proportionate type of refraction, the main focus of the eye lies in the plane of the retina. The emmetropic eye sees well into the distance, and with accommodation tension - close (accommodation is the ability of the eye to change its optical power by changing the lens).

Myopia, or nearsightedness (M) is a disproportionate type of refraction, the main focus of the eye is in front of the retina. Obviously, with myopia, either the anterior-posterior axis of the eye is too long (which often happens with acquired myopia), or the optical power of the eye is excessive (which can happen with congenital myopia). The nearsighted eye sees poorly into the distance, but sees well up close. Myopia is considered a strong type of refraction. To transfer the focus to the retina, diverging concave minus lenses are used, therefore myopia is designated by the sign "-", and the degree of myopia corresponds to the size of the minus correcting lens, which transfers the main focus of the eye to the plane of the retina.

Hyperopia, or farsightedness (Ht) is a disproportionate type of refraction, the main focus of the eye is behind the retina. Obviously, with hyperopia, either the anterior-posterior axis of the eye is too short, or the optical power of the eye is insufficient. The farsighted eye sees poorly into the distance and sees even worse up close. Partial (less often, complete) compensation of hyperopia is possible due to the tension of accommodation, in which there is good vision at different distances. Hyperopia is considered a weak type of refraction. To transfer the focus to the retina in farsightedness, convex converging plus lenses are used, therefore hyperopia is designated by the sign "+", and the degree of hyperopia corresponds to the size of the plus correcting lens, which transfers the main focus of the eye to the plane of the retina.

Astigmatism is not an independent type of clinical refraction, but is a combination of two types in one eye or one type of different sizes.

Anisometropia is a difference in refraction between the two eyes.

Development of refraction

At birth, the spread of refraction of the eye can be quite significant: from high myopia to high hyperopia. The average value of refraction of a newborn is in the hyperopia range of +2.5... +3.5 diopters. Most newborns have astigmatism, 1.5 diopters or more. During the first year of life, in the process of active emmetropization, the spread of refractions decreases sharply - the refraction of farsighted and nearsighted eyes shifts towards emmetropia, and astigmatism decreases. This process slows down somewhat in the period from 1 to 3 years, and by the end of the 3rd year of life, most children have a refraction close to emmetropia.

Refraction study

The study of refraction in children has a number of features. Firstly, it is not always possible to give a subjective assessment of vision, secondly, the influence of the habitual tone of accommodation determines the determination of different refraction in natural conditions and with drug-induced paresis of accommodation (cycloplegia). Until recently, atropine was considered the only reliable cycloplegic agent. In our country, a 3-day (2 times a day) instillation of atropine into the conjunctival sac is still considered standard cycloplegia. In this case, the concentration of the solution depends on age: up to 1 year - 0.1%, up to 3 years - 0.3%, up to 7 years - 0.5%, over 7 years - 1%. The negative aspects of atropinization are well known: the possibility of general intoxication, as well as prolonged paresis of accommodation. Currently, short-acting agents are increasingly used to induce cycloplegia: 1% cyclopentolate (cyclomed) and 0.5-1% tropicamide (mydriacil). Cyclopentolate is close to atropine in terms of the depth of its cycloplegic action, tropicamide is significantly weaker, and is rarely used to study refraction in children.

Correction of refractive errors in children

In children, correction of refractive anomalies has two goals: tactical (to do everything to improve vision) and strategic (to create conditions for the correct development of the visual organ). Glasses are prescribed to children for therapeutic purposes. At the same time, the difference in refraction from zero in itself is not an indication for correction of ametropia. Ametropia accompanied by signs of decompensation is subject to correction. When prescribing correction to children, the magnitude of ametropia, age, functional state of the eyes, the presence of concomitant eye pathology, and the possibility of subjective examination are taken into account.

Hyperopia. Indications for correction of hyperopia are signs of its decompensation: convergent strabismus (even periodic), amblyopia (decrease in corrected visual acuity), decrease in uncorrected visual acuity, asthenopia (visual fatigue). If signs of decompensation are detected, hyperopia of any degree is subject to correction. Correction is also necessary for hyperopia of 4.0 D or more, even if there are no obvious signs of decompensation.

In case of hyperopia, correction is usually prescribed at 1.0 D weaker than the refraction determined objectively under cycloplegia conditions.

Astigmatism. Indications for astigmatism correction are signs of its decompensation: amblyopia, development and progression of myopia in at least one eye, cases when cylinder correction increases visual acuity compared to a sphere, asthenopia. As a rule, astigmatism of 1.0 D or more is subject to correction. Astigmatism of less than 1.0 D is corrected in special cases. The general principle for astigmatism is correction close to the full value of astigmatism detected objectively. Reduction of correction is possible with astigmatism of more than 3.0 D, as well as in cases when full correction causes signs of disadaptation (distortion of space, dizziness, nausea, etc.).

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