Ophthalmology is moving forward by leaps and bounds. Over the course of several decades, laser surgery has managed to advance almost from zero to incredible heights, and almost all manual methods studies of the organ of vision were replaced by hardware ones. There is no need to explain that they are much more accurate and reliable than studies that require calculations and measurements from humans. But the eye is not only a sensory organ, but also a highly complex optical system that requires filigree precision. Eat diagnostic methods, which are rarely used, only in special cases. But there are, on the contrary, routine ones, without which eye examination is no longer possible. These include refractometry - what is it, how and why is it carried out, how should its results be interpreted?
Refractometry is the measurement of the refraction of the eye. However, one cannot talk about refraction without paying attention to how the eye is structured, at least in general terms.
Table. What does the organ of vision consist of?
| Anatomical unit | Characteristic |
|---|---|
| Auxiliary device | Eyelids, eyelashes, eyebrows, eye socket, lacrimal glands and their system, muscle complex. |
| Eyeball | This is the perceptive apparatus of the organ. A light beam penetrates through its transparent elements and is fixed on the retina. In turn, it has several layers in its structure and plays a major role in the processes of refraction and accommodation. |
| Conducting system | Nerves connecting the retina and brain structures. |
| Subcortical elements and higher nerve centers | Areas in the brain responsible for processing visual signals. |
Separately, the structure of the eyeball should be considered. It consists of several structures:
Most people in their lives have come across or at least heard about such concepts as “myopia” and “farsightedness”. These words are not scientific terms and replace the more complex “” and “”, but they describe precisely violations of the refractory ability of the visual analyzer.
The process of refraction is the ability to bend light rays. The eye is a system of optical media, and the main refractive elements are the cornea and the lens. All other transparent media are light-conducting. In order for the refraction and conduction of light to be fully carried out, all media must be perfectly transparent.
In ophthalmology, there is a concept of physical and clinical refraction. This is due to the fact that the eye is not only a set of light-processing structures, but also an organ of the nervous system.
Physical refraction- this is directly the ability of the eye to refract light beams, the refractive power is described in diopters. Newborn children see practically nothing and the refractive power of their eyes does not exceed 50 diopters. But gradually the clarity of vision increases and eventually increases to 70 diopters.
And at this moment the game comes into play accommodation. This, in turn, is the process of changing the configuration of the lens, which is aimed at improving the clarity of the image - focusing. In ophthalmology, such concepts as the nearest and farthest point of clear vision are accepted. The further one is at infinity - at complete relaxation muscles responsible for accommodation. But as soon as a person needs to look at an object that is closer than this further point, tension in the muscles of the eye becomes necessary.
In this regard, two types of clinical refraction are distinguished.
So, based on the above information, the definition of refractometry as a process of measuring refraction becomes more understandable. A study of clinical refraction is being carried out, since it is the ability to focus the image on the retina that is important. Moreover, both the static and dynamic components are studied.
Some time ago, refraction could only be measured manually. For this purpose, special eye diagrams and manual refraction measurement techniques were used. In terms of accuracy, they were largely inferior modern devices Moreover, the possibility of error could not be ruled out.
Today, refractometry is a high-tech procedure that takes no more than five minutes. For this diagnostic method we use special devices- refractometers. The operating principle of this device is infrared radiation. The refractometer is located on the table, is about half a meter in height and has “outputs” on both sides - a screen with a control panel for the doctor and a special device where the patient looks. From a special lens, a beam of rays in the infrared spectrum is directed towards the pupils of the subject, which, penetrating through a hole in the iris, fall on the retina. There is a reflection from the bottom of the eye and return to the sensors of the device. The doctor only needs to direct the rays through the patient's pupil. The devices, in turn, record the received data, and the computer calculates the necessary indicators. The calculations are immediately displayed on the screen and can then be printed.
Despite the simplicity, fast execution and lack of any negative consequences procedure, it is irrational to carry it out to everyone. Typically, refractometers are used in specialized ophthalmological centers, where vision is checked before any surgical interventions and other serious procedures, and the technique is also used to clarify the degree of refractive error after the primary diagnosis of visual impairment by a doctor. The use of refractometry as one of the routine dispensary examinations is possible, but not every hospital can afford it.
Clear indications for refractometry:
Contraindications to this technique are very conditional. Of the highly specific ones, only one is a violation of the transparency of the vitreous body, or a disease such as cataracts. From non-specific:
In order for the results to be as reliable as possible, short preliminary preparation is necessary. It consists of instilling a solution of atropine into the eyes in the morning and evening for three days before the intended examination.
The dose of instilled atropine is 1 drop in each eye. Depending on age, the concentration of the solution may vary:
When preparing, you should be careful, since such drops in the eyes can cause transient blurred vision, which is especially dangerous for drivers and people whose activities require maximum eye strain and attention to detail. In addition, atropine is a fairly strong allergen, so allergic conjunctivitis may develop - redness, tearing.
The actual process of performing refractometry is simple.
With hardware refractometry, several types of indicators can be detected on a printed sheet separately for the right (R) and left (L) eyes.
It is not at all necessary to be able to decipher these values on your own: the doctor will inform you about any deviations. But it is recommended to save the data after the study so that you can monitor the dynamics.
The main point of the conclusion voiced by the doctor is the type of refraction and the degree of visual impairment (important for obtaining lenses or glasses). Types of refraction:
Thus, refractometry is a modern informative method for diagnosing the state of vision, which takes a minimum of time, is absolutely safe for both adults and children, and is also very easy to perform.
In this work, an Abbe refractometer is used, the operation of which is based on measuring the limiting angle of refraction. The optical diagram of the refractometer is shown in Fig. 4. The test solution is placed between the planes of two prisms - the lighting 3 and measuring 4 made of glass with a high refractive index ( n = 1.9 ). The large refractive index of the measuring prism keeps the condition n p < n st for a wide range of densities of measured liquids. The instrument scale is calibrated to the value n p =1.7 .From source 1 a beam of light is directed by a condenser 2 to the entrance face of the lighting prism. Passing the lighting prism 3, light falls on the matte hypotenuse face AB given prism , bordering a thin layer of the test liquid. The matte surface has irregularities, the dimensions of which are several wavelengths. The light is scattered by these irregularities over the entire surface and, having passed through a thin layer of the solution, falls on the “solution-glass” interface at various angles of incidence, i.e. the angle of incidence varies from 0 0 before 90 0 .
On the mirror hypotenuse face CD measuring prism 4 light is refracted (the size of the irregularities on this face is less than the wavelength). Due to the fact that n p < n st , the angle of refraction varies from zero to γ etc . Angled γ > γ etc no radiation is observed. Thus, at a refraction angle equal to γ etc , a light-shadow boundary appears. Magnitude n p is determined from the relation sinγ etc = n p / n st , where is the value n st known.
The path of light rays as they exit the measuring prism is easily taken into account when calibrating the device, since light refraction occurs at the glass-air boundary. , Moreover, the refractive indices of both media are known. The angle of light refraction at this boundary does not affect the measurement accuracy n p .
Due to the illumination of the entire layer of solution, the boundary between light and shadow is observed quite sharply. Therefore, when setting up the device for operation, the light from the illuminator must be directed onto the prism so that it evenly illuminates the entire surface of the face. AB diverging prism. To determine the angle at which the rays emerge from the measuring prism, a telescope formed by the lens is used 6 and eyepiece 9, light enters through a system of direct vision prisms 5 . In this case, the property of the telescope is used that the rays coming to it parallel to its axis are collected at the rear focus, where a transparent plate is placed 7 with a grid cross mark on it. The crosshair is exactly in focus.
Rice. 4. The path of rays in a refractometer when measuring the refractive index using the grazing beam method.
Optical design of the device: 1-light source, 2-condenser, 3-illuminating prism, 4-measurement prism, 5-direct vision prism, 6-spotting scope lens, 7-reticle with crosshair, 8-scale, 9-spotting scope eyepiece , 10-field of view of the eyepiece.
Direct vision prisms and the telescope are rigidly connected to each other and can be rotated relative to the measuring prism. The rotation angle is measured using a fixed scale 8, located in the common focal plane of the lens and eyepiece. The scale is graduated in the values of the refractive index of the solution under study based on formula (6). By rotating the telescope, you can set its axis parallel to the rays refracted at the edge CD at extreme angle γ etc. In this case, light and dark areas will be observed in the field of view of the eyepiece, the boundary between which will coincide with the crosshair. The light area is formed by rays refracted at the edge CD at angles less than the limit, and the dark area arises due to the absence of rays traveling at angles greater than the limit. The position of the boundary of light and shadow formed by rays refracted at the maximum angle will indicate on the scale 8 the desired value of the refractive index of the solution.
Light source 1 is not monochromatic. Therefore, due to the dispersion of both the substance under study and the material of the measuring prism (the dependence of their refractive indices on the wavelength of light), the boundary of light and shadow observed through the telescope turns out to be blurred and colored. To eliminate this effect, direct vision prisms are used 5 , forming dispersion compensator. The prisms are designed so that rays with a wavelength λ D= 589.3 nm (average sodium wavelength) did not deviate when passing through them. When one prism is rotated relative to another, their total dispersion changes, which makes it possible to compensate for the difference in the exit angles of rays with different wavelengths from the measuring prism and direct them into the telescope parallel to rays with wavelengths λ D. The boundary between light and shadow is sharp, uncolored and gives the value of the refractive index of the solution under study n D at wavelength λ D .
Refraction is a measurement using the refraction method. This term was coined in the 18th century by Newton. A refractometer gets its name from its operating principle. The principle of a refractometer is to measure the concentration of solutions and oils through the refractive index of light.
The refractometer device is based on a prism. Today there are several types of such devices:
Industrial and laboratory devices are used in factories and research centers. They are not portable because they are large. Heavy devices are usually not moved; they are used on site. The advantage of such equipment is the high accuracy of the indicators.
Digital and manual mechanical refractometers are highly mobile. They are small and light, such devices can be easily transported. The refractometer scale is displayed on a hand-held mechanical instrument. A digital refractometer displays the refractive index in numbers without a scale.
Industrial and laboratory refractometers have one important advantage - they are characterized by high accuracy of indicators. Such devices are used in laboratories of large enterprises. For example, a cutting fluid company tests oils using laboratory instruments. An automobile manufacturer can select oils and other fluids for vehicles using an industrial refractometer.
Manual mechanical and digital instruments are used where great importance has equipment mobility. For example, in a car service it is better to use one of the compact and simple devices. The TechLube RB-18 ATC handheld refractometer is ideal for such purposes. The refractometer scale will quite accurately display the concentration of coolant and other liquids (including antifreeze).
The TechLube RB-18 ATC refractometer does not have batteries, it is ideal even for field conditions. If you need to quickly measure the concentration of a substance, a refractometer will display the refractive index instantly. It is enough to apply a little substance to the lens. Even a beginner who has no experience in carrying out such measurements can cope with this task. You can master the measurement procedure in a few minutes.
An electronic refractometer has expanded functionality - this is the main advantage of a portable device. It can display the refractive index and density of the composition simultaneously on the LCD screen, converting the results into the desired units of measurement. The device is convenient, but requires more experience and requires batteries.
The design of a refractometer can be illustrated using the example of a simple and practical TechLube RB-18 ATC device. The main element of the device is a prism with a high refractive index. It is on this that the test substance is applied, the concentration of which must be determined.
A ray falls on the lens and is refracted at a certain angle. The angle of refraction of light in a lens on which a substance (for example, coolant) has already been applied depends on the density of the substance under study. The light, refracted, hits the lens system and is displayed on the scale. The refractive index is the relationship between the angle of entry of the beam and the angle of refraction in the medium.
The principle of a refractometer has been used for a very long time; the device is used in many fields. It has proven its effectiveness. The refractometer device has been improved over time, and digital instruments have appeared, but the system operates according to the old scheme.
The refractive index can change due to temperature. In some devices, the temperature of the substance is kept stable thanks to a special bimetallic plate. If the temperature of a substance rises or falls, the plate reacts to this. It adjusts the scale readings taking into account changes in the temperature of the substance. However, such a function is needed in some cases.
In order for the refractometer scale to show accurate results, it is necessary to prepare the instrument for use and carry out the calibration procedure. For such purposes, the most common distilled water is used. It is needed in order to set the value to zero. It is known that distilled water does not affect the refraction of light in the lens in any way - it gives a zero coefficient.
To prepare the device, apply a little distilled water to the main lens using a pipette. Then the device is closed and set to zero using the calibration screw. When the value 0.0 is set, you need to clean the lens with a special cloth. After such a little preparation, you can conduct research - the refractometer will display the refractive index very accurately.
In the manner described above, you can configure manual refractometer TechLube RB-18 ATC. It is very easy to use. After calibration the device gives exact values. Using the device is not difficult - just repeat the same steps as during calibration, without touching only the calibration screw.
To carry out measurements, you need to apply a substance to the lens with a pipette, then you need to close the glass and wait about 30 seconds. When 30 seconds have passed, you can point the device at any available light source. It could be the sun or a light bulb - the power source will not affect the value. The refractometer will display the refractive index even in dim lighting.
The main thing is not to touch the calibration screw during the measurement process, otherwise you will have to carry out the entire procedure from scratch. When you have to carry out many measurements using different liquids, it is worth calibrating the device and cleaning it more often. Otherwise, errors in the indicators are possible.
An example of a simple but effective device is the TechLube RB-18 ATC. An optical refractometer is ideal for measuring the concentration of water-miscible cutting fluids. It has an automatic temperature compensation system, which sets it apart from many similar devices. If the temperature of the test composition changes, this will not affect the refractometer readings.
The device guarantees high accuracy measurements in any conditions. You can take the device with you on the road, use it in a laboratory, at an enterprise, in a car service center or in a garage. The refractometer will not take up much space.
The device is resistant to mechanical damage. To calibrate it, it is enough to have some distilled water. TECHLUBE offers discounts when purchasing refractometers in this series in bulk. The service life of such devices is long, they are reliable and practical. The durability of the device is ensured by its relatively simple design and high quality assemblies.
TechLube RB-18 ATC has a comfortable rubberized handle that does not slip in your hands. Even if your hands are covered in oil, the device will not slip out. The manufacturer has thought through the design of the refractometer down to the smallest detail, taking into account the specifics of its application.
The refractometer (Fig. 2a) is designed to measure the refractive index of solutions various substances. The principle of operation of a refractometer when measuring the refractive index of transparent solutions is to measure the limiting angle of refraction at the interface of the liquid under study and a glass prism with a known refractive index. The refractometer consists of two prisms: an auxiliary folding prism (1) with a matte surface; edge (2) and measuring prism (3). Between them there is a thin gap 0.1 mm thick, into which a few drops of the test liquid are placed (4). The limiting angle of refraction at the interface between the liquid and the measuring prism is measured. The compensator built into the device allows you to make the light-shadow boundary black and white when illuminated with white light. Readings are made by the eye (7).
The refractometer works as follows. The light beam passes through the auxiliary folding prism (1) and is scattered on the lower edge (2). In this case, the scattered rays propagate in all directions, including parallel to the surface of the measuring prism (3) (Fig. 26).
Next, these rays are refracted at the boundary between the liquid (4) and the measuring prism (3), and, having passed through this prism (3), enter the device (5). If the light-shadow boundary turns out to be colored and blurred, you need to use the compensator (6) to achieve a sharp black-and-white white boundary. The design of the reading device allows, when turning a special lever, to combine the light-shadow boundary with the marker of the reading device. At the same time, the marker shows the refractive index values directly on the built-in scale .
Rice. 2.a, b - block diagram of the refractometer: 1 - auxiliary folding prism with a matte bottom edge (2); 3 - measuring prism; 4 - investigated liquid; 5 - reading device; 6 - compensator; 7 - eye; b - diagram of light scattering by the matte lower edge (2) of the folding prism
Design and purpose of an endoscope
Endoscopy-- a medical method of examining the cavity organs of the body (for example, the bladder, esophagus, stomach) by directly examining them by introducing them into them special tools- so-called endoscopes. An endoscope is actually a microscope with low magnification, adapted for insertion into a cavity, that is, having a small diameter at long length tube.
Rice. 3. Beam propagation in a light guide
Currently, flexible endoscopes are widely used, in which not a lens system is used to transmit images, but light guides - glass threads with a diameter of 10-50 microns.
Flexible light guide devices are based on the phenomenon of total internal reflection of light. The glass filament in the light guide is surrounded by a shell of another substance with a lower refractive index (Fig. 3a). As a result, rays incident on the interface between two media at an angle a > a and propagate along the core of the fiber without going beyond it (Fig. 36). Thus, the light guide allows light to be transmitted to significant distances, both along a straight and curved path.
Using a separate light guide with a diameter of 5-20 microns is convenient to illuminate cavities, but it is inconvenient to image objects. Therefore, as a rule, the image of objects is transferred using a fiberglass bundle made up of individual fibers.
Having chosen beekeeping as a hobby or as the main activity, you need to understand all the instruments and technical devices that help you obtain high-quality, tasty honey. You definitely need to know about a honey refractometer: what is it and how to use it?
At least the requirements modern market the quality of products is not high, many beekeepers still rely on the proven GOST. According to it, the mass fraction of moisture content in honey should not exceed 19-21%.
To obtain such results, it is believed that it is advisable to pump out honey only from those combs that have been covered with wax to three-quarters of the total height. But when pumping out honey, this requirement is not always met, as a result of which the water content in the collected product significantly exceeds the norm.
Honey high humidity is a favorable environment for fermentation processes, which quickly make it unfit for consumption. To avoid such situations, during the collection process you need to strictly control the water content; for this you will need a honey refractometer. It accurately measures the mass fraction of water in the total mass of the product. This device has long been used not only by beekeepers, but also by wholesale honey buyers.
In general, refractometers are designed to test sugar-containing liquids such as fruit juices and drinks, wines and honey. When choosing a device specifically for honey, you need to pay attention to some parameters:
Portable devices are very compact and do not require connection to a power supply. More technologically advanced models are equipped with a built-in temperature corrector, which is a bimetallic plate connected to the optics system of the refractometer itself.
Under the influence of temperature fluctuations, this plate is compressed or, conversely, stretched, thereby smoothly adjusting the operation of the entire measuring system in accordance with temperature conditions. Thanks to automatic calculations of these shifts, maximum accuracy is achieved when measuring humidity in the range from 12% to 27%.
Before purchasing the device, you should carefully read the instructions. Before the first use, it is necessary to calibrate the refractometer. It must be carried out according to the readings of a reference device, using identical honey samples. To make adjustments, you need to clean the calibration screw with a screwdriver and enter the border, which is most often painted blue and white, to read the same as the standard.
Video: refractometer for honey.
Having understood what a refractometer is and how it works, it becomes clear that for maximum accuracy measurement results, the instrument must be carefully calibrated. It is also possible to draw conclusions about the influence on the temperature measurements taken not only of the product, but also environment. Moreover, the measuring prism itself must also be at room temperature.
There are no special storage requirements for the refractometer. It should be cleaned with a soft damp cloth after the last measurements and placed in dry room so that the measuring eyepiece does not fade. You should not try to disassemble the device and clean it yourself; it is better to contact a specialized service center.
