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Skiascopy: methodology and results interpretation

Violation of visual acuity can be at any age. Modern ophthalmology is equipped with high-precision equipment that allows for the diagnosis and correction of vision in both adults and very young patients. However, on a par with the latest instruments, there are methods for studying the functional state of the visual organs, developed a long time ago and based on the experience and professionalism of the ophthalmologist. We are talking about skiascopy, or shadow sample.

Content

What is a shadow test and why

Skiascopy allows you to check the condition of the human eye, to determine the most distant point of clear vision. The essence of the method lies in the determination of the clinical refraction of the eye through the directional illumination of the pupil. Refraction is the ability to refract light rays by the optical structures of the organ of vision.

Syniasms of skiascopy - retinoscopy and keratoscopy.

The optical system includes the cornea, the anterior chamber filled with fluid, the lens and the gel-like contents of the vitreous body. Having passed all these areas, the light falls on the retina, which is able to transform light particles into impulses that enter the brain, where the image is formed. Units of visual acuity are diopters.

Clinical refraction is the location of the main focus, that is, the point at which the light rays intersect with respect to the retina. If this back focus is located on the retina, then the vision is one hundred percent, that is, absolutely normal - emmetropia. In case of a change in the focus position, visual acuity is disturbed. So, with far-sightedness, the location of the intersection point is behind the retina, and with myopia, in front of it.

The position of the focus in emmetropia and myopia

Skiascopy determines clinical refraction, which is the location of the point of intersection of the refracted light rays in relation to the retina

Skiascopy allows you to objectively assess the degree of refractive disorders in almost any person, including the youngest children. This is especially important if it is not possible to determine vision by means of visometry (using tables) or refractometry (assess visual acuity using special equipment).

Skiascopy can be performed under cycloplegia conditions (artificial shutdown of the muscle responsible for accommodation using medications) or active accommodation (adaptive ability of the eye to focus the view to see equally clearly objects that are far or near).

The study is shown in various disorders of visual acuity:

  • farsightedness, when a person sees poorly close objects;
  • myopia, in which the patient sees well near, but distant objects are blurred for him;
  • Astigmatism, a pathology in which several foci are present at once, while in one eye different types of refraction can be combined (+ or -).

The shadow test is a valuable diagnostic method for examining babies who still cannot perform refractometry with the aid of the apparatus and carry out diagnostics using ophthalmologic tables. The method is used for diagnosis, to assess the effectiveness of therapy and at the stage of follow-up.

Refractometry

Apparatus refractometry is performed using instruments that cannot be applied to very young children.

Contraindications to the procedure are:

  • intolerance to cycloplegics - drugs used for temporary paralysis of the ciliary (ciliary) muscle responsible for accommodation;
  • Glaucoma is a progressive disease that occurs with an increase in intraocular pressure and leads to blindness;
  • photophobia - fear of bright light, manifested by increased tearing;
  • mental disorders with inappropriate patient behavior;
  • state of intoxication (alcohol or drugs).

At present, the study of refraction is carried out not only by means of a shadow test, but also with the help of computer devices - refractometers. Both of these methods are objective, reliable and readily available for assessing the refractive power of the optical system of the eye.

The advantage of skiascopy is that it can be performed for the smallest patients who cannot be seated behind the device, and the advantage of automatic refractometry is in a more accurate determination of the degree of astigmatism in a person. The advantages of refractometry include its more rapid conduct compared to skiascopy, as well as the possibility of visometry directly after the procedure due to the lack of glare that the skiascope has on the eyes when performing retinoscopy.

Conducting a shadow test requires certain professional skills from the ophthalmologist, and the data that is obtained during this manipulation may have minimal errors, as in the examination by means of the apparatus.

How is retinoscopy performed

Preparation for the procedure consists in cycloplegia. In order to turn off the ciliary muscle for a while, a solution of atropine is instilled in both eyes at a certain age dosage twice within three days and in the morning of the fourth day. The shadow test can be started one hour after the last instillation. With controversial results, atropinization is extended to 7 or 10 days. A standard three-day cycloplegia is performed before the first skiascopy in children, as well as in adults in difficult cases. The use of atropine has a certain disadvantage - after instillation the patient has long difficulties in visual work at a short distance, for example, reading.

Eye burying

Cycloplegia is performed before skiascopy - preparations are instilled into the eyes that cause temporary paralysis of the ciliary muscle responsible for accommodation.

Recently, for relaxation of accommodation, ophthalmologists have used soft and short-acting drugs - solutions of scopolamine, homatropine, cycloborin, amisyl, or ready-made drugs - Tropics, Mydriacil, Cyclocloglium. They are instilled in 1 drop with an interval of 10 minutes and conduct a shadow test after 45 minutes. Such preparations are used by ophthalmologists in repeated retinoscopy procedures in children and, if necessary, accommodation in adults. For patients older than 40 years, cycloplegia drugs are used after the mandatory measurement of eye pressure and only in those situations when it is impossible to do without them. This is due to the fact that such drugs can provoke an attack in people prone to glaucoma.

Atropine Eye Drops

Classical cycloplegia consists of instillation of an atropine solution into the eyes.

Cycloplegia is necessary for a complete examination of the patient - the pupil expands, and the doctor has the opportunity to see not only the central region of the fundus, but also the peripheral areas.

Shadow test is carried out in a darkened room. The subject is seated on a chair, to the side of which the light source is placed - at the level of the patient's ear. Most often it is an ordinary incandescent lamp. The light should not fall on the face of the person who holds skiascopy. The ophthalmologist sits opposite, keeping a distance of 67 cm or 1 meter. For the procedure, a skiaskop is needed - a device that is a concave mirror on one side and a round mirror that is smooth on the other, with a hole in the middle and a handle. The doctor takes the device in his hand and directs the light beam reflected from the lamp into the eye of the patient so that he reaches the eye fundus through the pupil.

Skiascope with different nozzles

Skiascopy is performed using a skiascope - a mirror with a hole in the middle

If cycloplegia was previously performed, the patient is instructed to look into the center of the skiascope, with the accommodation being kept, past the ear of the ophthalmologist on the side of the eye being examined.

Then the doctor begins to slowly move the device around the vertical and horizontal axis of the handle, while the fundus illumination area moves, a shadow (dark spot) is formed. Usually, the flat mirror-like side of the skiascope is used for the survey, since in this case the spot is clearer and more pronounced, its movement is easier to assess. Based on the direction in which the darkening area is moving, the ophthalmologist concludes about the nature of the patient's refraction.

Carrying out skiascopy

When conducting a skiascopy, the doctor may be at a distance of 1 meter or 67 cm from the patient

After determining the type of visual impairment, the doctor conducts more accurate measurements of the refractive power of the optical structure of the eyes, for which the device uses skiascopic rulers. They are frames, between which lenses of different optical power are fixed, on each instrument there are only negative or only positive glasses.

The method of neutralizing the movement of a dark spot is applied. A ruler with the right lenses is given in the hand to the patient, while it should be placed vertically no closer than 12 mm from the cornea of ​​the eye. The doctor directs the beam to the pupil through the lenses, starting with the lowest diopter (0.5) and gradually moving towards the strongest glasses, determines the one at which the dark spot disappears. Neutralization of the shadow occurs when the eye is located in the very center of the focus of the rays reflected from the fundus of the eye.

Skiascopic rulers

After determining the type of refraction, the ophthalmologist measures the degree of myopia or hyperopia using skiascopic rulers

Instead of skiascopic rulers sometimes use lenses with different optical power, which are inserted into a special frame. This technique requires time-consuming, however, it has the advantages of greater accuracy in comparison with rulers and the possibility of diagnosing with astigmatism by means of cylindrical lenses (cylindroskiascopy). Before this study, the doctor may apply a banded, or bar-skiascopy. It uses special nozzles on skiascope, having not a hole, but a slot in the form of a strip.

Video: procedure

Interpretation of survey results

If during the examination with the use of a flat skiascope, a dark spot moves in the same direction that the doctor turns the mirror, then this indicates that a person has emmetropia (vision is normal), long-sightedness or weak myopia ( from the patient - 1.0 d, at a distance of 0.67 m - 1.5 d).

If the shadow slides in the direction opposite to the skiascope rotation, this indicates myopia above 1.0 diopters (or above 1.5 diopters in case of a distance of 67 cm).

If there is no movement of the dark spot during skiascopy, the doctor concludes: the patient has myopia 1.0 d, that is, the point of the clearest vision coincides with the skiascope located at a distance of 1 meter (1.5 d at a distance of 0.67 meters).

The movement of the light spot with skiascopy

In the direction of movement of the shadow during movement skiaskopa doctor makes a conclusion about the nature of refraction

Blackout can move in different directions with complex astigmatism. This phenomenon is called the symptom scissors and requires additional examinations.

At the second stage of retinoscopy, using a skiascopic ruler, the doctor determines the amount of myopia or hyperopia with an accuracy of 0.25 to 0.5 diopters. To calculate the refraction to the power of the lens on which the examination stopped (the shadow was neutralized), add 1.0 d for myopia and take 1.0 d for far-sightedness. The most correct test results can be obtained only after accommodation is turned off.

Features of skiascopy in children

The first examination by an ophthalmologist should be carried out at 1 month (no later than three months old). In addition to the standard examination, the doctor can determine the refraction of the organs of vision of the child using a shadow test. In six months and a year, repeated examinations are carried out with control of the dynamics of refraction of the eye. At this age, normal babies have refraction from +1 to +3 diopters (farsightedness). Repeated skiascopy is used in view of the fact that it is difficult for newborns to induce complete relaxation of accommodation even with potent means.

Conducting skiascopy in a small child

Skiascopy - an objective method for studying refraction in young children

Modern devices allow you to explore refraction and inspect the fundus with a narrow pupil. However, in young children, skiascopy is often used, and always with an enlarged pupil, since many pathological changes on the periphery of the fundus can remain outside the doctor’s view. As a rule, short-acting preparations, Midriacyl (Tropicamide) or atropine solution, are instilled into the eyes of children.

Midriacil

For cycloplegia in young children use short-acting drugs such as Midriacil

Another feature of the skiascopy in babies up to a year is the placement of a doctor from the patient at a distance of 67 cm, while the skiascopic ruler the oculist holds and moves himself. From four to five years, children can already determine refraction using apparatus and ophthalmic tables.

Despite the fact that the method of studying eye refraction with skiascope was developed almost 150 years ago, it is still successfully used by ophthalmologists. The high accuracy and objectivity of the shadow test allows timely detection of visual impairment in adults and children and timely optical correction.

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