Abnormalities of refraction in children

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

Emmetropia (Em) is a commensurate 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 the accommodation voltage - near (accommodation - the ability of the eye to change its optical power by changing the lens).

Myopia, or nearsightedness (M) is an incommensurable type of refraction. The main focus of the eye lies ahead of the retina. Obviously, with myopia or anterior-nondiscussion, the eye axis is too long (which happens more often with acquired short-sightedness), or the excessive optical power of the eye (which can be due to congenital myopia). Myopic eye does not see well in the distance, but it sees well near. Myopia is considered a strong type of refraction. To transfer the focus to the retina, dissipative concave minus lenses are used, therefore, myopia is denoted by the sign "-", and the degree of myopia corresponds to the value of the minus correcting lens, which transfers the main focus of the eye to the retina.

Hypermetropia, or farsightedness (Hm) is an incommensurable type of refraction, the main focus of the eye lies behind the retina. Obviously, with hypermetropia, either the anteroposterior axis of the eye is too short, or the optical strength of the eye is insufficient. The farsighted eye does not see well in the distance and sees it even worse near. Achievement of partial (rarely - complete) compensation of hypermetropia is possible due to the accommodation tension, in which there is good vision at different distances. Hypermetropia is considered a weak type of refraction. To transfer focus to the retina in farsightedness use collective convex positive lenses, therefore, hypermetropia is denoted by the "+" sign, and the degree of hypermetropia corresponds to the magnitude of the plus correcting lens, which transfers the main focus of the eye to the retina.

Astigmatism is not an independent type of clinical refraction, but represents a combination in one eye of its two species or one species of different magnitude.

Anisometropia is the difference in the refraction of the two eyes.

Development of refraction

When a person is born, the spread of the refraction of the eye is quite significant: from high myopia to hypermetropia of a high degree. The average refractive index of the newborn lies in the area of hypermetropia +2.5 ... +3.5 diopters. Most newborns have astigmatism, 1.5 dptr and more. During the first year of life in the process of active emmetropization, the spread of refractions sharply decreases - the refraction of far-sighted and myopic eyes shifts towards emmetropy, and astigmatism decreases. This process slows down a little during the 1-3 years, and at the end of the 3rd year of life, the majority of children develop refraction, close to emmetropia.

Refraction Study

The study of refraction in children has a number of characteristics. First, it is not always possible to give a subjective assessment of vision, and secondly, the influence of the habitual tonus of accommodation determines the determination of different refractions in natural conditions and with drug paresis of accommodation (cycloplegia). Until recently, only the reliable cycloplegic agent was considered atropine. In our country, till now, for standard cycloplegia, a 3-day (2 times a day) instillation of atropine into the conjunctival sac is taken. The concentration of the solution depends on the age: up to 1 year - 0.1%, up to 3 years - 0.3%, up to 7 years - 0.5%, over 7 years - 1%. Negative moments of atropinization are well known: the possibility of general intoxication, as well as a long accommodation cutoff. At present, for the induction of cycloplegia, short-term agents are increasingly used: 1% cyclopentolate (cyclomed) and 0.5-1% tropicamide (midriacil). Cyclopentolate in the depth of cycloplegic action is close to atropine, tropicamide is much weaker, for the study of refraction in children it is rarely used.

Correction of abnormalities of refraction in children

In children, correction of refraction abnormalities pursues two goals: tactical (to do everything to improve vision) and strategic (to create conditions for the proper development of the organ of vision). Points for children are prescribed for medical purposes. In this case, the difference of refraction from zero in itself is not an indication for correction of ametropia. Corrections are subject to ametropia, accompanied by signs of decompensation. When the correction is prescribed, the children take into account the magnitude of ametropia, age, functional state of the eyes, the presence of concomitant ocular pathology, the possibility of subjective research.

Hypermetropia. Indications for correction of hypermetropia - signs of its decompensation: convergent strabismus (even periodic), amblyopia (decreased corrected visual acuity), decreased uncorrected visual acuity, asthenopia (visual fatigue). If signs of decompensation are revealed, any degree of hyperopia should be corrected. Correction is also necessary for hyperopia 4.0 dptr and more, even if there are no obvious signs of decompensation.

With hypermetropia, a correction is usually prescribed, 1.0 dpts lower than the refraction detected objectively in cycloplegia.

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

[1], [2], [3]