Unreliable skiascopy data in children. Skiascopy is a modern method for diagnosing visual disorders. Procedure process

Introduction

This manual is intended for 1st year interns and residents. The manual contains the necessary theoretical knowledge and explanations for performing retinoscopy yourself. An online retinoscopy simulator is recommended for training ( http://www.eyedocs.co.uk/ophthalmology-learning/articles/optics-and-refraction/1508- retinoscopy-simulator), however, it does not replace practice in the field and is intended to prepare the researcher for the latter. Knowledge of the basics of physiological optics and the rules for recording refraction is required.

Information on this topic: Vorontsov A.A. ( https://vk.com/ophthalmica?w=wall-38116404_11914) .

If for any reason the simulator is unavailable, you can contact me by e-mail [email protected] or on the VKontakte page http://vk.com/rodionlxlnest. Any ideas for refining and improving the guide are also welcome.

Brief history

The observations that led to the creation of the retinoscopy technique were described back in 1859, when Sir William Bowman, using a flat mirror and lighting from an ordinary candle, observed the reflex from the fundus of the eye. The first to propose the method was the French physician Ferdinand Cuignet (1873). Cuignet offered a qualitative assessment of refraction (myopia, hyperopia, astigmatism). In 1875, discoveries in optics explained this phenomenon, and it was called the “shadow test,” which translated means “shadow test.” In 1880, H. Parent called this test “retinoscopy” and introduced a technique for quantitative assessment of ametropia (with lenses).

Definition and essence of the technique

Retinoscopy is a technique for objectively examining a patient’s clinical refraction. Synonyms: skiascopy, papilloscopy, scotoscopy, umbroscopy.

The technique involves the researcher observing the movement of light reflected from the patient’s fundus (reflex) and neutralizing this movement by attaching lenses of different refractive powers.

Retinoscopes

Retinoscopes are divided into mirror retinoscopes (with a separate light source, for example, a regular lamp) and retinoscopes with a built-in light source (streak and spot).

Rice. 1. A - Mirror retinoscope, B - retinoscope with built-in light source

When skiascopy with a mirror ophthalmoscope, a conventional flat mirror with a hole in the center is used (Fig. 1). The principles of using both mirror mirrors and radios with a built-in light source are absolutely identical, with the exception of some nuances, for example, the presence in some models of the latter of a regulator for changing the course of the rays, the so-called sleeve* (diverging rays - a flat mirror; converging rays - a concave one; and intermediate position - parallel rays). Accordingly, the position of the control knob must be set to the position of diverging rays, i.e. flat mirror**.

The advantages and disadvantages of each retinoscope are described in Table 1.

*the beam convergence-divergence regulator is necessary for an approximate and quick assessment of high ametropia **when the sleeve is positioned in flat mirror mode, the light from the retinoscope is more blurred than in the opposite position

Table 1. Advantages and disadvantages of individual types of retinoscopes.

*in essence they are all mirror images. Any retinoscope is nothing more or less than a light source and a mirror.

Methodology

For the study, you need a mirror R. with a light source (lamp) or a R. with a built-in light source and a set of skiascopic rulers, which consists of 2 frames with positive and negative lenses built into them. Skiascopic rulers can be replaced with ordinary lenses from a glasses selection kit (sometimes it is even preferable to use them (Fig. 2). The most convenient option is a phoropter, but it is not available to everyone.

Rice. 2. A – skiascopic rulers, B – trial set of lenses

Stage I Checking the movement of the reflex without a lens

1. The patient is at a distance from the researcher

0.67m or 1m.

The distance between the patient and the examiner can significantly affect the result of retinoscopy, so try to maintain the same distance from examination to examination. Measure the length of your outstretched arm with a meter and take this into account.

IN This manual uses the meaning

2. The patient fixes the retinoscope opening/bridge of the examiner's nose in case of cycloplegia or looks past the examiner's ear (from the side of the retinoscope) if cycloplegia has not been performed (with the exception of dynamic retinoscopy)

3. The researcher directs light into the patient's pupil, and he should see a reflex from the fundus in the form of a stripe.

A circular reflex will be visible during retinoscopy with a conventional mirror retinoscope without an overlay, a stripe will be visible during bar-skiascopy

Options for reflex movement at the first stage (without lens)

Reverse movement

Rule: if the movement is reversed, then myopia is more than 1.50D (and more than 1.00D at a distance of 1m)

2. Set the correction for the distance between the researcher and the patient to 1.50D (This value corresponds to a distance of 0.67m, the correction for a distance of 1m will be equal to 1.00D).

3. By moving the mouse, determine that the reflex is moving in the opposite direction from the retinoscope (mouse).

Direct movement

Rule: if the movement is direct, then the patient has either emtropia, myopia up to 1.50D or hypermetropia.

1. Set hyperopia, for example, 1.00D.

2. Make sure the distance correction is 1.50D.

3. By moving the mouse, determine that the reflex is moving in the same direction as the retinoscope (mouse).

Movement neutralized

Rule: if the movement is neutralized (i.e. its direction is almost impossible to catch), then the patient’s refraction is equal to myopia equal to the distance correction, i.e. 1.50D (1.00D at 1m distance)

1. Set myopia to 1.50D in the simulator.

2. Make sure the correction is 1.50D.

3. By moving the mouse, determine that the reflex is neutralized.

Checking movement in the vertical meridian To check the movement of the reflex in the vertical meridian whenbar retinoscopy need to

rotate the stroke by 90 by rotating the stroke angle regulator on the retinoscope or by rotating the retinoscope itself (with mirror stroke-skiascopy).

Install a deliberately larger lens so that the movement is “straight”

Add “+” until “reverse” or “neutralized”

Add to previous

Meaning

value smaller lens

Stage III Subtraction. Distance correction

Rule: after determining the value of the neutralizing lens, you must subtract 1.50D from it (at a distance of 0.67m).

It is the final stage in determining refraction.

Subtraction must be made from both meridian values.

If the value is -1.50D, then after subtraction the result is -3.00D.

If the value is, for example, +2.50D, then after subtraction the result is +1.00D.

If the value is “0”, i.e. the movement is “neutralized”, then the refraction in the meridian is -1.50D.

1. Set myopia to 4.00D.

2. Make sure the distance correction is correct.

3. Determine the direction of the reflex in 2 meridians.

4. Achieve direct movement of the reflex by attaching a obviously larger lens.

5. By reducing the minus lens (adding “+”), find the neutralization value.

6. At these values, neutralization will be on the lens-2.50D.

7. Subtract-2.50-1.50D=-4.00D.

The yellow field shows the schematic location of the meridian foci

Astigmatism. Cylinder axis

1. Set the values sph-2.00cyl-2.50x25°.

2. Try to determine the direction of the reflex. You will notice that the reflex will move at an angle. To continue the study, you need to determine this angle.

3. Click on the button where the angle of the stroke is shown. Then change the angle so that it matches the reflex angle.

4. Determine the strength of the neutralizing lens using general rules.

5. Determine the power of the neutralizing lens for the perpendicular meridian.

6. Subtract using distance.

7. Spheres -4.50x25° and -2.00x115° were obtained. The cylinder is measured from one of the spheres (i.e. the difference between 1 and 2 spheres). For example, if the sphere is -2.00D, then the cylinder is -2.50D. If the sphere is taken -4.50. then the cylinder is +2.50D.

Found refraction: sph-2.00cyl-2.50Dx25° sph-4.00cyl+2.50Dx115° transposition

This data can also be seen in the FORMULA window.

In this case, the method of defining a cylinder using spherical lenses alone was used, but there are also methods using a sphere and a cylinder and only cylinders. These methods are not covered in this guide.

Cylindrical lenses

The human eyes are a complex system that perceives electromagnetic radiation and provides visual functions. If the level of vision decreases, the patient should visit a doctor and undergo diagnostics using a method such as skiascopy. It will determine the ability of the optic nerve to refract light.

Skiascopy or shadow test is a diagnostic method in which the doctor illuminates the pupil, where shadows are formed in the event of pathology development. It is by how shadows behave that we can draw conclusions about refractive errors.

Diagnostics are carried out using a skiascope - a mirror that has one flat and concave surface. In its very center there is a hole through which light is refracted so that its corner forms a bright spot at the bottom of the eyeball. By moving the mirror, the doctor achieves movement of the shadow in the examined area and thus determines possible violations.

Why is skiascopy performed?

The main task of skiascopy is to diagnose pathologies and visual impairment in the initial stages. It is the purpose of skiascopy that is stated in the indications for the procedure.

• a cost-effective diagnostic method that does not require the use of expensive equipment or complex diagnostic techniques;
• an accurate method that allows you to obtain objective and informative results and make the correct diagnosis;
• The method is painless, does not cause negative sensations or any discomfort, the optical system of the eye does not suffer.

The skiascopy method itself is easy to perform, but the results of deciphering the diagnosis depend on the doctor.

Indications and contraindications

• the ruler is placed vertically, at a distance of at least 12 mm from the upper, convex point of the eyeball - this is the only way to obtain accurate diagnostic results.
• if Cyclodol or is used, the patient looks at the hole in the mirror itself. If the eye adapts to changes in external conditions, the patient looks past the ophthalmologist.
• the interpretation of the results is directly determined by which mirror is used - flat or concave.

And ultimately, the shadow test itself is carried out in a darkened room - this is the only way to obtain accurate and reliable diagnostic results.

Skiascopy is the study of the condition of the eyes. This is an effective method used everywhere. It does not require the use of expensive and structurally complex devices. The procedure is carried out quickly and efficiently.

Skiascopy: what is the essence of the method?

Our eyes are a system that perceives electromagnetic radiation and provides visual function. It has a complex structure and processes a large amount of information in seconds. In the absence of diseases, the visual system fulfills its purpose, creating the correct sensation of the position of objects in space. In the presence of negative factors, ophthalmological diseases occur, which are manifested by decreased vision. People also develop myopia, acquired astigmatism, and hypermetropia.

Regular visits to doctors is an effective method by which you can avoid the above problems. To diagnose the functional functioning of the eyes, ophthalmologists use a proven method called skiascopy. It has been used for many years and is trustworthy. It is used to determine the ability of the visual organ to refract light rays.

Skiascopy is an objective method that is based on observation of a moving shadow. The first research was carried out in 1873. The technology was introduced by the famous French scientist Cunier. He developed an effective technique that is still used today. This suggests that during the procedure, specialists obtain the correct results.

Skiascopy: step-by-step process

The human eyes are an optical system that is capable of light refraction. Visual function is provided by the lens and cornea. Skiascopy is ideal for determining eye refraction. With its help, you can easily identify disorders that are difficult to determine through viziometry.

The word "skiascopy" consists of two parts. Translated from Greek, it means “shadow” and “I watch.” This is an instrumental diagnostic method carried out in several stages:

Skiascopy is a technique that opens up wide opportunities for ophthalmologists. With its help, you can identify disorders of the visual system and successfully correct them. After receiving the results, the doctor prescribes glasses or contacts. These are optical devices designed for vision correction. They are used to correct refractive errors.

Depending on the type of lenses used in the study, there are several methods for determining refraction. For example, to determine the degree of astigmatism, cylindroskiascopy is performed. A trial spectacle frame is placed over the eyes. The socket accommodates spherical and astigmatic lenses. They provide simultaneous neutralization of shadows. First, the ophthalmologist turns the mirror with the hole towards the astigmatic lens. If the shadow disappears, neutralization of ametropia is achieved. Ametropia means a change in the refractive power of the visual organ. After this, the specialist carries out other actions aimed at determining the level of refraction. At the end of the procedure, the doctor gives an opinion and provides qualified recommendations.

Bar-skiascopy is considered a separate type of research. This is a process carried out using special devices. Their key difference is the formation of a light source in the form of a strip. To assess refraction, the ophthalmologist determines the direction of movement of the shadow. Strip skiascopy is widely used to determine refraction in schoolchildren. It is characterized by high accuracy and reliability.

When performing skiascopy and making a diagnosis, the medical professional pays attention to the following important points:

• rulers with lenses should be held strictly vertically and placed at a distance of 12 mm from the top of the convex part of the eyeball. Then the results obtained will be as accurate as possible
• after using Cyclodol or Atropine, the patient looks at the hole in the mirror. If accommodation (adaptation of the eye to changes in external conditions) is preserved, the patient should look past the doctor's ear
• the absence of a shadow on the pupil of the eye when conducting a study from a distance of one meter indicates that the person has myopia - 1.0 diopters
• interpretation of the results depends on which mirror is used (flat or concave)
• the unstable nature of the movement of the shadow indicates insufficiency of cycloplegia, as well as the negative impact of accommodation on the final results
• The shadow test is carried out in a darkened room. An electric lamp is placed on the table. During the procedure it turns on

Indications for instrumental examination

The technique by which disorders of the visual system are identified is carried out in private and public ophthalmological centers. This is an informative diagnostic method applied to adults and children. It is based on objective data and ensures correct results.

Skiascopy is performed on patients who have previously been diagnosed with the following ophthalmological diseases:

1. myopia– a visual defect characterized by an error in the refraction of the eye. In the medical literature, the disease is called myopia. It occurs due to a number of reasons: genetic predisposition, lens displacement due to injury, excessive stress. The main symptoms of myopia are decreased vision at dusk, rapid eye fatigue and difficulty in distinguishing objects that are at a long distance. Myopia is a progressive disease. It often occurs in school-age children and students. Therefore, if you have myopia, you need to constantly visit an ophthalmologist and follow his instructions.
2. farsightedness– a pathological condition in which a person has difficulty distinguishing between nearby objects. This is a common vision problem. It occurs in people of different ages. Farsightedness occurs for various reasons. These include reduced size of the eyeball, disruption of the lens, and congenitality. As this disease develops, eye fatigue increases, vision deteriorates, and a burning sensation appears. Farsighted people also suffer from headaches. Successful treatment of the disease depends on the correct diagnosis and the measures taken. Glasses or contact lenses are used to correct the problem.
3. astigmatism- a defect due to which people lose the ability to clearly see the world around them. This disease cannot be left untreated. As it progresses, it leads to decreased vision and strabismus. Astigmatism is a common problem that appears in childhood and adulthood. The causes of the development of ophthalmological disease have not been sufficiently studied. It manifests itself with numerous symptoms: blurred vision, tension, headache, distorted lines. Astigmatism can be complex myopic and farsighted, as well as mixed. It can be corrected using glasses with special lenses

Skiascopy is performed not only to determine the refraction of the eyes and monitor the rate of progression of the disease. It is used to identify visual impairments that have not previously been diagnosed. If astigmatism is suspected, the information obtained during the study is not informative enough. Therefore, further examination is recommended.

The technique turns out to be useful if a person feigns visual impairment. After carrying out diagnostic measures, doctors receive accurate results. Therefore, further simulation of the disease becomes pointless.

The instrumental research method is applied to children. Young patients cannot talk about their complaints and clearly explain the essence of the problem. Skiascopy is also indicated for patients who have intellectual impairments. After the procedure is completed, the ophthalmologist makes a diagnosis and informs relatives about it.

Skiascopy is impossible if a person is under the influence of drugs or alcohol. Mentally unbalanced people who may harm themselves and others during the procedure are also not allowed to participate in the study. As for other contraindications, it may be photophobia or glaucoma.

Skiascopy is a common technique with many advantages:

• economic benefit for patients - the use of complex and expensive equipment is not required. Therefore, ophthalmologists working in private clinics provide inexpensive services
• Accuracy is an important indicator on which the correct diagnosis depends. Doctors get the best results after using cycloplegic drugs that cause paralysis of the ciliary muscle
• painlessness – a person does not experience any discomfort. This is a significant point if the optical system of children is being studied.
• simplicity - the results depend on the professionalism of the doctor. The specialist observes the patient’s reactions, which cannot be controlled. You need to sit still in a chair and follow the doctor's instructions

Skiascopy devices

Instrumental examination is carried out using skiascopic rulers. Sets of devices made from high-quality materials are on sale. They are intended to carry out a procedure aimed at determining the refraction of the eyes. The kits consist of frames with negative and positive lenses of various diopters.

Rulers are devices that have a simple design. These are metal products made in the form of a frame with optical glasses. Plus lenses are installed on one ruler, and minus lenses on the other. It is also envisaged to use an engine with additional lenses, the optical power of which is 0.5 and 10 diopters.

Skiascopic rulers are rectangular frames with a handle. The engine moves along their outer contour. Optical glasses are installed in the holes. The engine moves along the outer grooves of the ruler and is fixed opposite each lens. This procedure is carried out without applying excessive force.

The skiascopic ruler set should be stored in a closed case. This is an important requirement because metal is susceptible to corrosion. The surfaces of the devices are periodically wiped with a clean cloth or cotton wool moistened with rectified alcohol. After the examination, the handle of the instruments is disinfected with a three percent solution of hydrogen peroxide. Once a week, the rulers are completely disinfected.

Skiascopy is a procedure performed in all medical institutions where ophthalmologists work. Its main advantages are accessibility and painlessness. Specialists receive reliable information about the presence of an eye disease and the degree of its development. Therefore, a simple technique based on shadow observation is widely used to determine the quality of vision.

Skiascopy was invented at the end of the 19th century. This is a simple technique for determining the pupil's ability to refract light. This method is characterized by its simplicity, accessibility, and the receipt of reliable information. Skiascopy is widely used to diagnose various ophthalmological diseases caused by improper functioning of the pupil. An experienced ophthalmologist will tell you about the specifics of the procedure.

About the features

Diagnosis of the pupils is carried out using a simple device called a skiascope. This is a kind of mirror that has two parts - concave and flat. There is a hole in the center of the product through which the doctor examines the patient's eyes. To study the visual organ, a light beam is directed into the pupil. At the moment, the diagnostician is assessing the reaction of the pupil. The spot is located at the bottom of the eye. When the device is rotated, the shadow moves, which indicates disturbances in the structure of the pupil.

Skiascopy in children and adults makes it possible to identify the exact degree of disturbances in the functioning of the pupil. This technique is applicable in the following situations:

• To diagnose the condition of the pupil in children who cannot describe their sensations.
• To identify truthful information when the patient is trying to pretend.
• To determine refraction in patients who have mental disorders.

About examination technology

The skiascopy technique involves placing the patient and the doctor in a darkened room. To carry out the procedure, the doctor uses:

• Line with mirrors.
• A set of additional lenses for the skiascope.
• Light source.

Before the diagnosis begins, drops are instilled into the examinee's eyes, which help to enlarge the pupils. This is necessary so that the information received is as accurate as possible.

The ophthalmologist then sits opposite the patient and begins the examination.

• A switched-on lamp is placed on the left side of the patient at eye level.
• Using a skiascope, the doctor directs a beam of light into the patient's eyes.
• After the light beam reaches the bottom of the eye, the diagnostician rotates the lenses from different angles.

At the moment the light beam moves, the physician draws conclusions about the refractometry of the eye. To achieve accurate results, drops may be used to dilate the pupils before starting the procedure, but they may not be used. In the second case, the doctor asks the patient to look forward behind the doctor's head. If the patient is concerned about the issue of dermatology, he should consult a doctor of the appropriate specialization.

To whom is it assigned?

The diagnostic method of skiascopy is used in relation to patients who complain of problematic vision.

Refractometry is mandatory when:

• Astigmatism.
• Myopia.
• Farsightedness.

Due to the simplicity and information content of the technique, skiascopy is used to determine the positive dynamics after the prescribed treatment. Also, this type of examination allows you to determine how quickly a particular ophthalmological disease develops.

About contraindications

It would seem that the skiascopy method cannot have contraindications, but refractometry is not prescribed for such patients:

• Having increased sensitivity to light.
• Children under seven years of age.
• Drunk and under the influence of drugs.
• If a history of glaucoma is detected or this disease is suspected.
• In the presence of psychological illnesses in which a person may behave inappropriately.

About the results

If, when diagnosing astigmatism, farsightedness or myopia, the shadow from the mirror moves in the same direction as the mirrored object, deciphering the results of skiascopy should indicate the minimum degree of development of these diseases.

If the patient has severe myopia, especially if there are values ​​greater than 1.5 diopters, the shadow from the mirror will be located on the opposite side of the skiascope. This result makes it possible to quickly and absolutely painlessly diagnose eye refractometry for adult patients and children.

It is important to remember that the results of skiascopy depend on the distance at which the doctor is from the patient. At a distance of 67 cm, the direction of the spot in the opposite direction indicates that the patient has myopia of one and a half diopters. If you maintain a distance of one meter, obtaining similar results means that myopia is one diopter. When using a mirror with the concave side, the results obtained will be the opposite of those shown above.

Ophthalmologists know that the norm of skiascopy is an immovable spot resulting from the direction of the mirror. In this case, decoding is not required, since the doctor immediately determines the normal state of the pupil.

An experienced ophthalmologist talks about the details of the skiascopy technique in the video.

Thus

Every patient in an ophthalmology office is familiar with the skiascopy procedure. Doctors often resort to this type of examination because it is always accessible, informative and has a limited list of contraindications. No special preparation is required to undergo the procedure. The technique is simple and takes a short period of time.

Skiascopy is an objective method for determining the refraction of the eye, based on observation of the movement of shadows in the area of ​​the pupil when the eye is illuminated by a beam of light reflected from a mirror: when the mirror is turned, a moving shadow appears against the background of the illuminated pupil, the position of which in the pupil depends, in particular, on the refraction of the subject being examined eyes. The method is used in ophthalmology to determine the type of refraction of the eye, the degree of myopia, farsightedness, astigmatism - sometimes the name “shadow test” is used.

Research technique:

The main position of this technique can be formulated as follows: the movement of the shadow is not observed if the further point of clear vision coincides with the source of illumination of the pupil, that is, in fact, from the position of the researcher.

The doctor sits opposite the patient, usually at a distance of 1 meter, and illuminates the pupil of the eye being examined with a flat mirror (skiascope) or a concave mirror and, turning it around a horizontal or vertical axis in one direction or the other, observes the nature of the movement of the shadow in the area of ​​the pupil. The examination can also be carried out from a distance of 67 or 50 centimeters.

Sequence of research

Determine the type of refraction (presence of anomaly).

When using a flat mirror:

• in the case of emmetropia, hypermetropia and myopia less than −1.0D (diopter), the shadow on the pupil moves in the same direction as the ophthalmoscope mirror;
• for myopia greater than −1.0D - in the opposite direction.

When using a concave mirror, the relationships are reversed.

Establishing the degree - the shadow neutralization method is usually used. The absence of a shadow on the pupil (with skiascopy with both a flat and a concave mirror from a distance of 1 meter) means that the subject has myopia of −1.0D. To neutralize the shadow, the following can be used: special skiascopic rulers (when using, try to hold it vertically and at a distance of approximately 12 millimeters from the top of the cornea); lenses from the kit, which are inserted into the trial frame.

When examining an eye in conditions of cycloplegia, the examinee should look at the opening of the mirror, and in the case of intact accommodation, past the doctor’s ear, on the side of the eye being examined. For myopia greater than −1.0D, negative lenses, first weak and then stronger, are applied to the eye being examined until the shadow on the pupil disappears. The degree of myopia is determined by adding 1.0D (distance correction) to the power of the glass at which the shadow disappeared. For myopia greater than −1.0D, its degree can be determined in another way - gradually approaching the eye being examined during skiascopy until the shadow disappears. In this position, measure the distance between the eye of the examiner and the person being examined and divide 100 centimeters by the resulting distance. (For example, if the shadow disappeared from a distance of 50 cm, then the subject has myopia −2.0D = 100 / 50). For hypermetropia, emmetropia and myopia less than −1.0D, a similar procedure is performed with positive lenses and the degree of refraction is determined by subtracting 1.0D from the power of the glass at which the shadow on the pupil disappeared. For astigmatism, the same is done separately in two main perpendicularly located meridians.

Clarification of eye refraction with astigmatism. To clarify the refraction of the eye with astigmatism, a shadow test with astigmatic (cylindrical) lenses is recommended - the so-called cylindroskiascopy or strip skiascopy ("stripe skiascopy"), which is carried out with special skiascopes that cast a strip of light onto the eye being examined; this strip can rotate and change its direction.

A conventional skiascopy is performed with spherical lenses (rulers): the position of the main meridians of the astigmatic eye and the strength of the lenses that neutralize the shadow in each of them are approximately determined. A trial spectacle frame is put on the patient and a spherical and astigmatic lens is installed in the socket opposite the eye being examined, which should provide simultaneous neutralization of shadows in both main meridians. Skiascopy is performed by turning the mirror first in the direction of the axis of the astigmatic lens, and then in the direction of its active section. If the shadow disappears in both cases, neutralization of ametropia has been achieved. If the shadow disappears in the direction of the axis of the astigmatic lens and does not disappear in the direction of its active section, the cylinder is weakened or strengthened until the shadow disappears. If the shadow does not disappear in both directions, first achieve its neutralization in the direction of the axis of the astigmatic lens by selecting a sphere, and then in the perpendicular direction by selecting a cylinder.

If the shadow does not move in the direction of the axis of the astigmatic lens or its active section, but between them, at approximately an angle of 45°, the axes of the cylinder are incorrect. At the same time, the cylinder in the frame is rotated until the direction of movement of the shadow coincides with the direction of the axis. Achieve neutralization of the shadow in both sections. Then the spherical lens is weakened, that is, the positive lens is reduced or the negative lens is strengthened in accordance with the distance from which skiascopy was performed: at a distance of 1 meter - by 1.0 D, 67 cm - by 1.5 D, 50 cm - by 2.0 D.