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Autorefractometry in ophthalmology
The human body of vision consists of a set of media, each of which has transparency for unobstructed penetration of light rays. Bunches of light are refracted, passing through the eye structures, and the retina of the eye catches images that are in the field of view. The absence of opacity of optical structures and uniform refraction of parallel rays ensures a clear perception, that is, good vision. In order to properly treat eye pathologies, it is necessary to understand what is the root of the problem. And this is impossible without knowledge of key indicators. Such a diagnosis exists. This refers to the hardware measurement of the refractive power of the optical structures of the eye - autorefractometry.
- Авторефрактометрия — в чём состоит суть метода 1 Autorefractometry - what is the essence of the method
- Методика проведения 2 Methods of conducting
- Расшифровка результатов 3 Interpretation of results
- Детская авторефрактометрия 4 Children's autorefractometry
- Видео: обзор и тестирование авторефрактометра 5 Video: review and testing of the autorefractometer
Autorefractometry - what is the essence of the method
Autorefractometry can literally be deciphered as an automatic measurement of refraction. This is a kind of computer diagnostics that detects errors of light refraction by the eye. On the basis of his results, glasses or contact lenses are prescribed. Autorefractometry is considered an objective method, since measurements are made without any patient action or subjective information from him. The computer determines the smallest violations of the refraction of light rays in the organ of vision - myopia, hyperopia, astigmatism. The method is suitable for people of any age, including children.
Recent publications in Western scientific literature, based on studies involving 39 children aged 4 to 6 years, state that the automatic refractometer is more accurate than retinoscopy (the "manual" method).
The examination is carried out with the help of a medical device - automatic refractor. During the procedure, a beam of infrared light emitted by the device passes through the pupil, reflected from the retina, is fixed by electronic sensors at the entrance and exit from the eye. Then the computer program analyzes the measurement results and gives the required values in figures on paper.
Indications and contraindications
Autorefractometry is carried out as:
- testing visual acuity;
- preparatory phase for ophthalmic surgery;
- preliminary program of laser vision correction;
- determination of the outcome of surgery or laser intervention;
- Control of rehabilitation after therapy against inflammation of the cornea of the eye.
And also with such problems:
- loss of visual clarity for no apparent reason;
- the need to determine the type of astigmatism (lens or corneal);
- posttraumatic visual defects.
The procedure is mandatory at the first, and sometimes with the re-selection of corrective lenses. Autorefractometry is used to prevent patients who are at risk for vision impairment: by age, with constantly high visual load, with a "blurred" focus.
Automatic refraction measurement is not desirable for children under the age of three due to the characteristics of their central nervous system. Mental illnesses are not a direct contraindication, but can indirectly affect the effectiveness of this type of ophthalmologic diagnosis.
With some eye defects, the transmission of light beam to the retina and its reflection are disrupted. Consequently, autorefractometry in such cases is not effective. Examples of such pathologies are:
- opaque optical environment of the eye;
- blurred vitreous body fibers;
- cataract ("clouded" lens);
- opacity of the cornea (spots, thorns);
- hemophthalmus - vitreous hemorrhage.
Advantages and disadvantages
Computer diagnosis of the eye is an advanced technology. It has a number of indisputable advantages:
- Testing is painless and does not cause any discomfort to the patient.
- The procedure does not take much time, as it only lasts a few minutes.
- The computer promptly analyzes the data and immediately outputs the results.
- Most ophthalmologists usually use an autorefractor as a starting point. The results obtained can then be compared with retinoscopy or a study of the foreopter for more accurate inferences.
Modern refractometers are able to measure separately the refraction of the cornea. Such data make it possible to distinguish a kind of lens astigmatism from corneal astigmatism. This is important for the correct selection of corrective lenses.
The disadvantages of the method include the increase in accommodation when the optics of the apparatus are located near the eye. For this reason, the diagnostic results may have an error with a bias toward myopia (myopic refraction). Sometimes, to obtain true data, it is necessary to drip into the eye a special drug that relaxes the accommodative muscle. This medication is called cycloplegia.
It should nevertheless be noted that manufacturers of automatic refractors are trying to reduce the effect of instrumental accommodation in models of new generation devices.
Method of conducting
The process is fully automated, and the essence of the procedure is extremely simple. It is conducted by a nurse or a nurse, since the performance of actions does not require specialized knowledge.
The patient sits down opposite the refractometer and fixes a look at the image located arbitrarily far away. It can be any picture, causing a certain interest in the review. This innovation, instead of the usual dotted label, was invented so that the patient could look more closely into the distance, being in a state of relaxed accommodation of the eyes. It is not forbidden to blink. This idea is especially useful in examining children's eyes, since it is difficult for children to focus on one point for several minutes in a row.
It's amazing that our retina initially perceives the image upside down. But after the transformation of electromagnetic radiation into nerve impulses, it is recreated by the human brain correctly. Otherwise people would see the world around inverted.
After the patient has taken a comfortable position, the nurse or nurse using the control knob guides a beam of infrared light into the middle of the pupil. Further it makes measurements manually or automatically. Each eye is examined separately.
After the end of the procedure, the patient receives a printout of the study data, which then must be provided to the treating doctor for interpretation. The doctor, as a rule, additionally checks the reliability of the results with the help of instrumental methods.
Autorefractometry with a narrow pupil
Evaluation of refraction with a narrow pupil (with normal accommodation) is considered to be incorrect. The data of such a study may contain a significant error. After all, the tonus of accommodative muscle is influenced by many factors, for example:
- fatigue and overexertion;
- Times of Day;
- nedosyp, etc.
With age, the maximum tension of accommodation - the contraction and relaxation of the ciliary muscle - decreases, and the error in the examination will not be so noticeable. However, any ophthalmologist will advise to determine refraction with complete paralysis of accommodation, in other words - to wide pupils.
Autorefractometry using cycloplegia
Diagnosis can be performed without the use of cyclopelegic (paralyzing the eye muscle) funds or with them. Preferably the second option is to avoid the influence of instrumental myopia.
For a reliable definition of refraction, it is important to smooth accommodation so that the tension of the intraocular muscles does not affect the purity of the clinical study. Therefore, most often it is carried out in conditions of temporary "disconnection" of accommodation with medicinal preparations - drops dilating the pupils. After all, the results of autorefractometry, in which cycloplegic drugs were not used, can not be considered by modern specialists as an unconditional basis for assigning any kinds of optical correction. Most often use cycloplegia Atropine.
Explanation of results
So, what will the patient see in the printout received? Abbreviations in English and incomprehensible numbers with a plus or minus sign.
The decoding of the notation is as follows:
- Ref - results of the study.
- R / OD is the right eye.
- L / OS is the left eye.
- Sph - the optical power of a spherical lens, equal to the refraction in one of the two main eye meridians, the unit of measurement is diopter.
- PD is the intercentre (interpupillary) distance.
- mm is the value specified in millimeters.
- R1 and R2 are the measurements of the largest and smallest corneal meridians in millimeters (mm) or diopters (D).
- VD - vertex distance, measured from the cornea to the back of the lens (norm - 12-15 mm).
- # - designation of insufficiently reliable data.
- Cyl is the optical power of a cylindrical lens equal to refraction in one of the two major eye meridians. The unit of measure is diopter. Its addition to the value of Sph shows refraction in another main meridian. The magnitude of the cylinder always indicates the difference in refraction of the two main meridians.
- Ax is the axis of the cylindrical lens.
- AVE is the average refractive index.
- Ker - the results of keratometry (assessing the curvature of the anterior surface of the cornea).
- AVE / Cyl is the average of the results of the basic curvature or the radius of curvature of the cornea (in mm) and the refractive force in its smallest and largest meridians (in diopters).
- D - the values indicated in the diopters (D).
The designation Cyl is the magnitude of astigmatism. In a number of models, the device also calculates the spherical equivalent (SE), which can be determined by summing the optical strength of a spherical and cylindrical lens, previously dividing the latter by 2.
It is worth noting that during the passage of commissions, for example, military medical or disability, the plus sign or minus before the figure in the printout of the results of autorefractometry, indicating the magnitude of astigmatism, does not matter. Since there is indicated not the refraction itself, but only - the necessary degree of its correction.
An example of what an ophthalmological conclusion looks like:
OD sph = 4.25 D; cyl - 0.25 D, ax 45;
OS sph - 5.75 D; cyl - 0, **, ax 0.
Spherical lens (sph) is used to correct hypermetropia (hyperopia) and myopia (myopia). The figure (in the existing example 4.25 and 5.75) is the indicator of the optical force presented in the diopters. If we are talking about a hypermetropic lens, then before its magnitude it is necessary to put plus, in the case of myopic - minus. In the example above, "-" is indicated, which means that it is necessary to correct myopia.
Cylindrical lenses (cyl) are used to correct astigmatism. It is also myopic, that is, with the sign "-", and hypermetropic, when the value is "+" before the value.
In the given sample: medium degree myopia is combined with a low degree of astigmatism. Since there are zeros on the left eye, there is no astigmatism. The right eye of the conditioned patient requires correction of myopia and astigmatism simultaneously. It is necessary to use a spherical lens with an optical power of 4.25 D. and cylindrical - 0,25 Dpt. respectively, taking into account the cylinder axis at 45 degrees. The left eye needs correction of myopia at 5.75 Dpt.
Detailed interpretation of the results of autorefractometry is handled by an ophthalmologist, since for proper interpretation of the data it is necessary to have appropriate knowledge.
In the examination of children, a pediatric non-contact autorefractometer is used, which operates within a certain distance. This makes it possible to measure refraction at a distance of up to 1 meter simultaneously on two eyes, even with a narrow pupil. Thus, the oculist is able to examine a child without direct contact. Approaching the right distance to the pupil of a small patient, the device beeps, attracting the attention of the child. The procedure itself lasts only a few seconds.
Pediatric devices allow measuring refraction:
- in infants;
- in children with involuntary eye movements;
- in complex patients.
Diagnosis of toddlers is always hampered by their age characteristics and inability to concentrate the eye for any length of time. Small patients can not always understand and fulfill all the requests of the doctor and sit quietly, without unnecessary movements of their head, in one place. Autorefractometers for children take into account these nuances: funny pictures that appear on the screen are designed for the game form of the procedure.
Despite the possibilities of innovative instruments to measure refraction without pupil dilatation, most experienced ophthalmologists still insist on preliminary atropinization, after which the data is considered more reliable. Parents should pay attention to the main rules of the procedure for children:
- it is advisable to dig for the eye for at least two weeks - the longer, the more reliable the result of the study will be;
- during atropine cycloplegia, the child is allowed to write, read, use a computer, television, etc.;
- It is necessary to avoid brightly lit places or wear dark glasses during the period when the medicine drips, as the dilated pupil reacts to solar and other intensive illumination;
- Because of the temporary paralysis of accommodation in different children, vision may be near, far away or at a specific distance from the organ of vision. If a child needs to do anything near, it is recommended that you use appropriate glasses for reading. It is desirable to choose narrow lens rims, on top of which the child can look into the distance if necessary. For other temporary inconveniences, you just need to get used to and wait.
Approximately 8 out of 10 newborns are hypermetropic (long-sighted). Gradually, with the growth of the eyeball in some children, hyperopia becomes normal or nearsighted. Hypermetrophic refraction in infants is 4.0-5.0 diopters, in children of 3 years of age it is about 2.0-3.0 diopters, and from 6 to 8 years this figure is about 1.5 diopters. Such average data are accepted by ophthalmologists for the conditional norm when it is a question of setting corrective glasses for the child.
Video: review and testing of autorefractometer
Autorefractometry is a fast, convenient and reliable way of diagnosing visual impairment. Like most eye studies, she needs a preliminary cycloplegia. Despite the fact that the average medical staff performs the procedure, only a graduate doctor can interpret the final results of automatic refractometry.