What is optical coherence tomography. What is retinal coherence tomography

Simple methods are not enough to fully diagnose most ophthalmological diseases. Optical coherence tomography allows you to visualize the structure of the visual organs and identify the smallest pathologies.

Benefits of OCT

Optical coherence tomography (OCT) is an innovative method of ophthalmological diagnostics, which consists of visualizing the structures of the eye in high resolution. You can evaluate the condition of the fundus and elements anterior chamber eyes at the microscopic level. Optical tomography allows you to study tissues without removing them, therefore it is considered a gentle analogue of a biopsy.

OCT can be compared with ultrasound and computed tomography. Resolution coherence tomography much higher than the capabilities of other high-precision diagnostic instruments. OCT allows you to detect the smallest damage down to 4 microns.

Optical tomography is the diagnostic method of choice in many cases because it is non-invasive and does not use contrast agents. The method does not require radiation exposure, and the images are more informative and clear.

Specifics of diagnostics using OCT method

Different body tissues reflect light waves differently. During tomography, the delay time and intensity of reflected light as it passes through tissue are measured. eyeball. The method is contactless, safe and highly informative.

Since the light wave travels at a very high speed, direct measurement is not possible. To decipher the results, a Michelson interferometer is used: the beam is divided into two beams, one of which is directed to the area being examined, and the second to a special mirror. A low-coherence beam of infrared light with a wavelength of 830 nm is used to examine the retina, and a wavelength of 1310 nm is used to examine the anterior segment of the eye.

Read also: – cancer arising from the immature retina.

When reflected, both beams enter the photodetector and an interference pattern is formed. The computer analyzes this picture and converts the information into a pseudo-image. In a pseudo-image, areas with high reflectance appear warmer, while areas with lower reflectance may appear almost black. Normally, nerve fibers and pigment epithelium appear “warm”. The average degree of reflection in the plexiform and nuclear layers of the retina, and vitreous appears black because it is optically transparent.

OCT capabilities:

• assessment of morphological changes in the retina and nerve fiber layers;
• determination of the thickness of eye structures;
• measurement of optic nerve head parameters;
• assessment of the state of the structures of the anterior chamber of the eye;
• determination of the spatial relationship of the elements of the eyeball in the anterior segment.

To obtain a three-dimensional image, the eyeballs are scanned longitudinally and transversely. Optical tomography may be difficult due to corneal edema, opacities, and hemorrhage in the optical media.

What can be examined in the process of optical tomography

Optical tomography makes it possible to study all parts of the eye, but the condition of the retina, cornea, optic nerve, and elements of the anterior chamber can be most accurately assessed. A separate tomography of the retina is often performed to identify structural abnormalities. More accurate methods for studying the macular zone do not currently exist.

For what symptoms is OCT prescribed:

• sudden decrease in visual acuity;
• blindness;
• blurred vision;
• spots before the eyes;
• increased intraocular pressure;
• acute pain;
• exophthalmos (bulging of the eyeball).

In the process of optical coherence tomography, it is possible to evaluate the angle of the anterior chamber and the degree of functioning of the drainage system of the eye in glaucoma. Similar studies are carried out before and after laser vision correction, keratoplasty, installation of intrastromal rings and phakic intraocular lenses.

Optical tomography is performed if the following diseases are suspected:

• (congenital and acquired);
• tumors of the organs of vision;
• increased intraocular pressure;
• proliferative vitreoretinopathy;
• atrophy, swelling and other abnormalities of the optic nerve head;
• epiretinal membrane;
• thrombosis of the central retinal vein and other vascular diseases;
• retinal disinsertion;
• macular holes;
• cystoid macular edema;
• deep keratitis;
• corneal ulcers;
• progressive myopia.

Coherence tomography is absolutely safe. OCT makes it possible to detect minor defects in the structure of the retina and start treatment on time.

For the purpose of prevention, OCT is performed for:

• diabetes mellitus;
• surgical intervention;
• hypertension;
• severe vascular pathologies.

Contraindications to optical coherence tomography

The presence of a pacemaker and other devices is not a contraindication. The procedure is not carried out in conditions where a person cannot fix his gaze, as well as in cases of mental disorders and confusion.

The contact environment in the organ of vision can also become an interference. By contact medium is meant the one that is used in other ophthalmic examinations. As a rule, several diagnostic procedures are not performed on the same day.

High-quality images can only be obtained in the presence of transparent optical media and a normal tear film. It can be difficult to perform OCT in patients with a high degree of myopia and optical opacities.

How is optical coherence tomography performed?

Optical coherence tomography is carried out in special medical institutions. Even in big cities it is not always possible to find an ophthalmology office with an OCT scanner. A retinal scan of one eye will cost approximately 800 rubles.

No special preparation for tomography is required; the study can be performed at any time. This procedure requires an OCT scanner, an optical scanner that sends beams of infrared light into the eye. The patient is seated and asked to fix his gaze on the mark. If it is not possible to do this with the examined eye, the gaze is fixed with the second one, which sees better. For a full scan, two minutes is enough in a stationary position.

In the process, several scans are made, and after that the operator selects the highest quality and most informative pictures. The result of the study are protocols, maps and tables, by which the doctor can determine the presence of changes in the visual system. The memory of the tomograph has a regulatory framework that contains information about how many healthy people there are similar indicators. The smaller the coincidence, the greater the likelihood of pathology in a particular patient.

Morphological changes in the fundus, visible on OCT images:

• high degree of myopia;
• benign formations;
• scleral staphyloma;
• diffuse and focal edema;
• swelling with subretinal neovascular membrane;
• retinal folds;
• vitreoretinal traction;
• lamellar and macular hole;
• through macular hole;
• macular pseudohole;
• detachment of the pigment epithelium;
• serous detachment of the neuroepithelium;
• Druze;
• ruptures of the pigment epithelium;
• diabetic macular edema;
• macular cystoid edema;
• myopic retinoschisis.

As can be seen, the diagnostic capabilities of OCT are extremely diverse. The results are displayed on the monitor as a layered image. The device independently converts signals that can be used to assess the functionality of the retina. It is possible to make a diagnosis based on OCT results within half an hour.

Interpretation of OCT images

To correctly interpret the results of optical coherence tomography, the ophthalmologist must have in-depth knowledge of retinal and choroidal histology. Even experienced specialists cannot always compare tomographic and histological structures, so it is advisable to have OCT images reviewed by several doctors.

fluid accumulation

Optical tomography makes it possible to identify and evaluate the accumulation of fluid in the eyeball, as well as determine its nature. Intraretinal fluid accumulation may indicate retinal edema. It is diffuse and cystic. Intraretinal fluid collections are called cysts, microcysts, and pseudocysts.

Subretinal accumulation indicates serous detachment of the neuroepithelium. The images show elevation of the neuroepithelium, and the angle of detachment from the pigment epithelium is less than 30°. Serous detachment, in turn, indicates CSC or choroidal neovascularization. In rare cases, detachment is a sign of choroiditis, choroidal formations, angioid bands.

The presence of subpigmentary accumulation of fluid indicates detachment of the pigment epithelium. The photographs show elevation of the epithelium above Bruch's membrane.

Neoplasms in the eye

On optical tomography, epiretinal membranes (folds on the retina) can be seen, as well as their density and thickness can be assessed. In myopia and choroidal neovascularization, the membranes appear as spindle-shaped thickenings. They are often combined with fluid accumulation.

Hidden neovascular membranes appear on imaging as irregular thickening of the pigment epithelium. Neovascular membranes are diagnosed in age-related macular degeneration, chronic CSC, complicated myopia, uveitis, iridocyclitis, choroiditis, osteoma, nevus, pseudovitelliform degeneration.

The OCT method allows you to determine the presence of intraretinal formations (cotton wool-like foci, hemorrhages, hard exudate). The presence of cotton wool-like foci on the retina is associated with ischemic nerve damage in diabetic or hypertensive retinopathy, toxicosis, anemia, leukemia, and Hodgkin's disease.

Hard exudates may be star-shaped or isolated. They are usually localized at the border of retinal edema. Such formations are found in diabetic, radiation and hypertensive retinopathy, as well as in Coats disease and wet macular degeneration.

Deep formations are observed with macular degeneration. Fibrous scars appear, which deform the retina and destroy the neuroepithelium. On OCT, such scars give a shadow effect.

Pathological structures with high reflectivity on OCT:

• nevus;
• hypertrophy of the pigment epithelium;
• scarring;
• hemorrhages;
• hard exudate;
• cotton-wool tricks;
• neovascular membranes;
• inflammatory infiltrates;

Pathological structures with low reflectivity:

• cysts;
• edema;
• detachment of neuroepithelium and pigment epithelium;
• shading;
• hypopigmentation.

Shadow effect

Fabrics with high optical density may obscure other structures. Based on the shadow effect in OCT images, it is possible to determine the location and structure of pathological formations in the eye.

The shadow effect is given by:

• dense preretinal hemorrhages;
• cotton-wool tricks;
• hemorrhages;
• hard exudates;
• melanoma;
• hyperplasia, hypertrophy of the pigment epithelium;
• pigment formations;
• neovascular membranes;
• scarring.

Characteristics of the retina on OCT

Puffiness is the most common cause thickening of the retina. One of the advantages of optical tomography is the ability to evaluate and control the dynamics different types retinal edema. A decrease in thickness is observed with age-related macular degeneration with the formation of atrophy zones.

OCT allows you to estimate the thickness of a particular layer of the retina. The thickness of individual layers can change with glaucoma and a number of other ophthalmological pathologies. The retinal volume parameter is very important in identifying edema and serous detachment, as well as in determining the dynamics of treatment.

Optical tomography can reveal:

1. Age-related macular degeneration. One of the main causes of visual impairment in people over 60 years of age. Although in the diagnosis of dystrophy they use different methods, optical coherence tomography remains the leading one. OCT allows you to determine the thickness of the choroid in macular degeneration; it can be used to make a differential diagnosis with central serous chorioretinopathy.
2. Central serous chorioretinopathy. The disease is characterized by detachment of the neurosensory layer from the pigment epithelium. In most cases, chorioretinopathy disappears spontaneously within 3-6 months, although in some cases fluid accumulates, causing permanent visual impairment. Chronic CSH requires special treatment. As a rule, these are intravitreal injections and laser coagulation.
3. Diabetic retinopathy. The pathogenesis of the disease is due to vascular damage. Diagnostics allows you to identify retinal edema and check the condition of the vitreous body (including identifying posterior detachment).
4. Macular hole, epiretinal fibrosis. Using OCT, you can determine the degree of retinal damage and plan tactics surgical treatment and evaluate the results.
5. Glaucoma. With increased intraocular pressure, tomography is additional method examinations. The method is very useful in normotensive glaucoma, when damage to the optic nerve is noted with normal indicators intraocular pressure. OCT can confirm the disease and determine its stage.

Optical coherence tomography is the safest and most informative method for examining the visual system. OCT is allowed to be performed even in patients who have contraindications to other high-precision diagnostic methods.

Treatment of any eye pathology always begins with diagnostic measures. Often, optical coherence tomography is performed for this purpose. This study involves high-frequency scanning of the fundus. This technique provides very accurate data, due to which it is widely used in ophthalmology. Optical coherence tomography of the eye allows the ophthalmologist to determine pathological changes visual organ that cannot be detected using other diagnostic procedures.

OCT allows you to scan and diagnose the condition of the fundus

In this article you will learn:

What is OCT

The technique of coherent tomographic examination of the eye was first used back in the 90s. Now this diagnostic method has become quite popular, since its accuracy is comparable to examination under a microscope. The OCT device uses infrared rays on the retina of the eye, which does not have a negative effect on the tissue. The diagnostic method allows you to examine the organ of vision not only with high accuracy, but also in a fairly short time. Doctors can examine and evaluate the condition of the retina in just one or two minutes.

The OCT mechanism actually combines the principles of such studies as X-ray CT and ultrasound. However, diagnostics are performed using optical rays of the infrared spectrum, the wavelength of which is 820–1310 nm.

CT scan of the eye orbits shows any changes in the central parts of the organ. Tomography allows us to examine in detail both the shape and size, as well as the depth of pathological foci. In addition, doctors can see hidden manifestations: any form of edema, hemorrhage, scars, degenerative changes, inflammation and all kinds of pigment accumulations. Often, an examination is carried out to be able to monitor the progress of treatment. OCT is an indispensable method diagnostic study both the retina and the optic nerve.

Diagnostics is carried out due to the influence of infrared rays on the retina of the eye

What types of OCT are distinguished?

Currently, there are two types of OCT that are used to diagnose the orbit of the eye:

• Michelson's technique. This method, using an interferometer named after the inventor of the method, was previously the most common. The resolution of the technique is about 10 µm. The light source is a superluminescent diode, which produces a beam with low coherence. However, when carrying out such a diagnosis, the medical worker had to manually move a special mirror on his own. Both the quality of the images and the speed of scanning depended on the speed and accuracy of movement. The device is quite sensitive to any eye movements, so its data has some errors.

Retinal OCT is prescribed for patients with macular degeneration

• Spectral OCT. Unlike the first type, spectral research does not require constant manual movement of part of the device. This type of diagnosis is carried out using a broadband diode. The device is equipped with a spectrometer and a special camera, thanks to which almost all ranges of the reflected wave are simultaneously recorded. A spectral tomograph examines the eye much faster. During the time period required to form an image using a high-speed camera, the eye does not have time to make any movements. Therefore, this type of diagnosis allows you to get the most accurate information.

Common types of procedures include:

• Optical coherence tomographic study of the condition of the optic nerve head. It is performed during the diagnosis or treatment of diseases such as glaucoma (caused by increased intraocular pressure), ischemic neuropathy(occurs due to impaired arterial circulation), neuritis (disease of peripheral nerve endings), hypoplasia (underdevelopment of an organ or tissue).

Spectral OCT allows for a short time conduct an accurate diagnosis of the eye orbits

• Optical CT of the retina. During the study, the central part of the retina and its neighboring sections are assessed. This diagnostic method is used for hemorrhages, retinopathy, chorioretinitis, macular degeneration, tumors and edema. Often, in addition to OCT of the retina, fluorescein angiography is also used.
• OCT of the cornea. The study is carried out for dystrophies, as well as before and after operations on the cornea.

Data diagnostic methods are completely painless and provide the doctor with a complete picture of the structure of the eye.

In what cases is the procedure indicated

A retinal CT scan is performed in case of suspicion or in case of the presence of diseases such as:

• retinal dystrophy;
• macular degeneration;
• glaucoma;
• retinitis pigmentosa;
• diseases of the optic nerve, cornea;
• macular edema;
• thrombosis;
• diabetes;
• tumor;
• aneurysm rupture.

If there are complaints of decreased vision and pain in the eyes, it is recommended that the patient undergo OCT of the eyes

In addition, patients undergo such a study for ruptures, retinal detachment, before or after surgical intervention and in case of corneal clouding of unknown origin.

The procedure is also performed if the patient complains of certain symptoms. This may be the appearance of floaters before the eyes, painful sensations in the organ, decreased visual acuity or its sudden disappearance.

How should a patient prepare?

No special preparation is required for computed tomography of the eyes. However, in order to obtain a better image, doctors recommend dilating the pupil. To do this, a special medication is instilled into the patient's eyes.

After diagnosis with contrast, redness and itching in the eyes may appear.

In some cases, MSCT of the eye orbit with contrast is required. For this procedure, an iodine-containing substance is used. Before such a study, the patient should not eat for four hours. If you have an allergy (even to anything), you should definitely inform your doctor about this, since sometimes performing a procedure with contrast causes negative reaction in the form of redness and itching.

How is OCT performed?

The study is performed in a diagnostic room in which an OCT tomograph is located. The patient needs to look at a certain point. The device is equipped with an optical scanner. The infrared rays produced by the device are directed to the organ of vision. In this case, the patient needs to focus his gaze on these rays and try not to move his eyes.

At this time, the doctor moves the camera closer and closer to the patient’s face until an image appears on the computer monitor. The clearest pictures are formed when there is a distance of about 9 mm between the camera and the eye. After receiving the necessary images, the doctor compares the indicators and determines the presence or absence of diseases.

During diagnosis, the patient must look at the selected point and not move his eyes

What results does the doctor get?

An ophthalmologist interprets the results of the study. CT scan of the eye shows the data indicated in the table.

The doctor must study the location of the damage, its size, and the thickness of the cornea.

You can learn more about the OCT eye procedure by watching the video:

When to avoid the procedure

There are some contraindications to performing optical CT of the eye. These include:

• Pregnancy, especially the first trimester. During the procedure, the human body is exposed to a small dose of radiation, and the fetus’s reaction to it has not been fully studied. Therefore, doctors do not advise pregnant women to take risks.
• Children's age (up to age 14).
• Renal failure and an allergy to the contrast agent (when performing a procedure with contrast). The drug is excreted through the kidneys, which can negatively affect the patient's health.
• Mental disorders.

For people with claustrophobia this procedure will not cause any harm, since only the patient’s head is in the scanned area. The presence of a pacemaker or any implants in the person being studied is not a contraindication for diagnosing the visual organ.

Almost all eye diseases, depending on the severity, can have a negative impact on the quality of vision. In connection with this very important factor that determines the success of treatment is timely diagnosis. The main cause of partial or complete loss of vision in ophthalmological diseases such as glaucoma or various lesions retina, is the absence or mild manifestation of symptoms.

Thanks to the possibilities modern medicine, detection of such pathology at an early stage allows one to avoid possible complications and stop the progression of the disease. However, the need for early diagnosis implies examination of relatively healthy people who are not ready to undergo grueling or traumatic procedures.

The advent of optical coherence tomography (OCT) not only helped resolve the issue of choosing a universal diagnostic technique, but also changed the opinion of ophthalmologists about some eye diseases. What is the principle of OCT operation based on, what is it and what are its diagnostic capabilities? The answer to these and other questions can be found in the article.

Operating principle

Optical coherence tomography is a diagnostic beam method used mainly in ophthalmology, which allows to obtain a structural image of the tissues of the eye on cellular level, cross-sectional and high resolution. The mechanism for obtaining information in OCT combines the principles of two main diagnostic techniques - ultrasound and X-ray CT.

If data processing is carried out according to principles similar to computed tomography, which records the difference in the intensity of X-ray radiation passing through the body, then when performing OCT, the amount of infrared radiation reflected from tissues is recorded. This approach has some similarities with ultrasound, where the travel time of an ultrasonic wave from the source to the object being examined and back to the recording device is measured.

A beam of infrared radiation used in diagnostics, having a wavelength from 820 to 1310 nm, is focused on the object of study, and then the magnitude and intensity of the reflected light is measured. light signal. Depending on the optical characteristics of various tissues, part of the beam is scattered and part is reflected, allowing one to get an idea of ​​the structure of the examined area at different depths.

The resulting interference pattern, with the help of computer processing, takes the form of an image in which, in accordance with the provided scale, areas characterized by high reflectivity are painted in the colors of the red spectrum (warm), and low ones - in the range from blue to black (cold) . The layer of pigment epithelium of the iris and nerve fibers has the highest reflectivity, the plexiform layer of the retina has an average reflectivity, and the vitreous body is absolutely transparent to infrared rays, so it is colored black on the tomogram.

Important! The short infrared wavelength used in OCT does not allow the study of deep-lying organs, as well as tissues of significant thickness. In the latter case, information can be obtained only about the surface layer of the object under study, for example, the mucosa.

Pain syndrome is an indication for optical coherence tomography

Kinds

All types of optical coherence tomography are based on the registration of an interference pattern created by two beams emitted from a single source. Due to the fact that the speed of a light wave is so high that it cannot be fixed and measured, the property of coherent light waves is used to create an interference effect.

To do this, the beam emitted by the superluminescent diode is split into 2 parts, with the first directed to the area of ​​study, and the second to the mirror. A prerequisite for achieving the interference effect is an equal distance from the photodetector to the object and from the photodetector to the mirror. Changes in the radiation intensity make it possible to characterize the structure of each specific point.

There are 2 types of OCT used to study the orbit of the eye, the quality of the results of which differ significantly:

• Time-domain OST (Mikhelson’s technique);
• Spestral OST (spectral OCT).

Time-domain OCT is the most common, until recently, scanning method, the resolution of which is about 9 microns. To obtain 1 two-dimensional scan of a certain point, the doctor had to manually move the movable mirror located on the reference arm until an equal distance between all objects was reached. From the accuracy and speed of movement, the scanning time and the quality of the results depended.

Spectral OCT. In contrast to Time-domain OCT, spectral OCT used a broadband diode as an emitter, which makes it possible to obtain several light waves of different wavelengths at once. In addition, it was equipped with a high-speed CCD camera and spectrometer, which simultaneously recorded all the components of the reflected wave. Thus, to obtain several scans, it was not necessary to manually move the mechanical parts of the device.

The main problem of obtaining the highest quality information is the high sensitivity of the equipment to minor movements of the eyeball, causing certain errors. Since one study on the Time-domain OCT takes 1.28 seconds, during this time, the eye manages to make 10-15 micro movements (movements called "microsaccades"), which makes it difficult to read the results.

Spectral tomographs allow you to get twice the amount of information in 0.04 seconds. During this time, the eye does not have time to move, accordingly, final result does not contain distorting artifacts. The main advantage of OCT can be considered the possibility of obtaining a three-dimensional image of the object under study (cornea, optic nerve head, retinal fragment).

Image acquisition principle widely used in ophthalmology

Indications

Indications for optical coherence tomography of the posterior segment of the eye are the diagnosis and monitoring of the results of treatment of the following pathologies:

• degenerative changes in the retina;
• glaucoma;
• macular holes;
• macular edema;
• atrophy and pathology of the optic nerve head;
• retinal disinsertion;
• diabetic retinopathy.

Pathologies of the anterior segment of the eye requiring OCT:

• keratitis and ulcerative lesions of the cornea;
• assessment of the functional state of drainage devices in glaucoma;
• assessment of corneal thickness before laser vision correction using the LASIK method, lens replacement and installation of intraocular lenses (IOLs), keratoplasty.

Preparation and execution

Optical coherence tomography of the eye does not require any preparation. However, in most cases, when examining the structures of the posterior segment, drugs are used to dilate the pupil. At the beginning of the examination, the patient is asked to look through the lens of the fundus camera at an object blinking there and fix his gaze on it. If the patient does not see the object due to low visual acuity, then he should look straight ahead without blinking.

The camera is then moved toward the eye until a clear image of the retina appears on the computer monitor. The distance between the eye and the camera to obtain optimal image quality should be 9 mm. At the moment of achieving optimal visibility, the camera is fixed with a button and the image is adjusted, achieving maximum clarity. The scanning process is controlled using the knobs and buttons located on the control panel of the tomograph.

The next step in the procedure is to align the image and remove artifacts and noise from the scan. After receiving the final results, all quantitative indicators are compared with the indicators of healthy people of the same age group, as well as with the patient's indicators obtained as a result of previous examinations.

Important! OCT is not performed after ophthalmoscopy or gonioscopy, as the use of the lubricating fluid required for the implementation of the above procedures will not provide a high-quality image.

Scanning takes no more than a quarter of an hour

Interpretation of results

Interpretation of results computed tomography eyes is based on the analysis of the obtained images. First of all, pay attention to the following factors:

• the presence of changes in the external contour of tissues;
• the relative position of their various layers;
• the degree of light reflection (the presence of foreign inclusions that enhance reflection, the appearance of foci or surfaces with reduced or increased transparency).

Using quantitative analysis, it is possible to identify the degree of decrease or increase in the thickness of the structure or its layers being studied, and to evaluate the dimensions and changes of the entire examined surface.

Corneal examination

When examining the cornea, the most important thing is to accurately determine the area of ​​existing structural changes and record their quantitative characteristics. Subsequently, it will be possible to objectively assess the presence of positive dynamics from the therapy used. OCT of the cornea is the most accurate method that allows you to determine its thickness without direct contact with the surface, which is especially important when it is damaged.

Iris examination

Due to the fact that the iris consists of three layers with different reflectivity, it is almost impossible to visualize all layers with equal clarity. The most intense signals come from the pigment epithelium - the posterior layer of the iris, and the weakest - from the anterior border layer. Using OCT, you can accurately diagnose a number of pathological conditions that do not have any symptoms at the time of examination. clinical manifestations:

• Frank-Kamenetsky syndrome;
• pigment dispersion syndrome;
• essential mesodermal dystrophy;
• pseudoexfoliation syndrome.

Retinal examination

Optical coherence tomography of the retina allows you to differentiate its layers, depending on the light reflecting ability of each. The layer of nerve fibers has the highest reflectivity, the layer of the plexiform and nuclear layers has an average reflectivity, and the layer of photoreceptors is absolutely transparent to radiation. On the tomogram, the outer edge of the retina is limited by a red-colored layer of choriocapillaris and RPE (retinal pigment epithelium).

The photoreceptors appear as a darkened band just anterior to the choriocapillaris and RPE layers. The nerve fibers located on the inner surface of the retina are bright red. The strong contrast between colors allows precise measurements of the thickness of each layer of the retina.

Retinal tomography allows you to identify macular holes at all stages of development - from pre-tear, which is characterized by detachment of nerve fibers while maintaining the integrity of the remaining layers, to a complete (lamellar) break, determined by the appearance of defects in the internal layers while maintaining the integrity of the photoreceptor layer.

Important! The degree of preservation of the RPE layer, the degree of tissue degeneration around the tear, are factors that determine the degree of preservation of visual functions.

Retinal tomography will even show a macular hole

Optic nerve examination. Nerve fibers, which are the main building material of the optic nerve, have a high reflectivity and are clearly defined among all the structural elements of the fundus. Particularly informative is a three-dimensional image of the optic disc, which can be obtained by performing a series of tomograms in various projections.

All parameters that determine the thickness of the nerve fiber layer are automatically calculated by the computer and presented as quantitative values ​​for each projection (temporal, upper, lower, nasal). Such measurements make it possible to determine both the presence of local lesions and diffuse changes optic nerve. Evaluation of the reflectivity of the optic nerve head (OND) and comparison of the obtained results with the previous ones makes it possible to assess the dynamics of improvements or the progression of the disease with hydration and degeneration of the OD.

Spectral optical coherence tomography provides the doctor with extremely extensive diagnostic options. However, each new diagnostic method requires the development of various criteria for assessing the main groups of diseases. The multidirectionality of the results obtained during OCT in the elderly and children significantly increases the requirements for the qualification of an ophthalmologist, which becomes a determining factor when choosing a clinic where to do the examination.

Today, many specialized clinics have new models of OK tomographs, which are staffed by specialists who have completed courses additional education, and received accreditation. The international center “Clear Eyes” has made a significant contribution to improving the qualifications of doctors, providing an opportunity for ophthalmologists and optometrists to improve their level of knowledge on-the-job, as well as to obtain accreditation.

OCT is a modern non-invasive non-contact method that allows you to visualize various structures of the eye with higher resolution (from 1 to 15 microns) than ultrasonography. OCT is a type of optical biopsy that does not require removal of a piece of tissue and its microscopic examination.

OCT is a reliable, informative, sensitive test (resolution is 3 µm) in the diagnosis of many fundus diseases. This non-invasive examination method, which does not require the use of a contrast agent, is preferred in many clinical cases. The resulting images can be analyzed, quantified, stored in a patient database, and compared with subsequent images, providing objective, documented information for disease diagnosis and monitoring.

For high-quality images, transparency of the optical media and normal tear film (or artificial tears) are required. The study is difficult with high myopia and clouding of the optical media at any level. Currently, scanning is performed within the posterior pole, but rapid advances in technology promise the possibility of scanning the entire retina in the near future.

The American ophthalmologist Carmen Puliafito first proposed the use of the concept of optical coherence tomography in ophthalmology in 1995. Later, in 1996-1997, the first device was introduced into clinical practice by Carl Zeiss Meditec. Currently, using these devices, it is possible to diagnose diseases of the fundus and anterior segment of the eye at the microscopic level.

Physical basis of the method

The examination is based on the fact that body tissues, depending on their structure, can reflect light waves differently. When it is carried out, the delay time of reflected light and its intensity after passing through the tissue of the eye are measured. Given the very high speed of the light wave, direct measurement of these indicators is impossible. For this purpose, tomographs use a Michelson interferometer.

A low-coherence beam of infrared light with a wavelength of 830 nm (for visualizing the retina) or 1310 nm (for diagnosing the anterior segment of the eye) is divided into two beams, one of which is directed to the tissues under study, and the other (control) to a special mirror. When reflected, both are perceived by the photodetector, forming an interference pattern. This, in turn, is analyzed by software, and the results are presented in the form of a pseudo-image, where, in accordance with a preset scale, areas with a high degree of light reflection are painted in “warm” (red) colors, with low ones - in “cold” up to black.

The layer of nerve fibers and pigment epithelium has a higher reflective ability, while the plexiform and nuclear layers of the retina have a medium reflective ability. The vitreous body is optically transparent and normally appears black on a tomogram. To obtain a three-dimensional image, scanning is carried out in the longitudinal and transverse directions. OCT can be complicated by the presence of corneal edema, clouding of optical media, and hemorrhages.

The optical coherence tomography method allows:

• visualize morphological changes in the retina and nerve fiber layer, as well as assess their thickness;
• assess the condition of the optic nerve head;
• examine the structures of the anterior segment of the eye and their relative spatial arrangement.

Indications for OCT

OCT is a completely painless and short-term procedure, but it gives excellent results. To conduct an examination, the patient needs to fixate his gaze on a special mark with the eye being examined, and if this is impossible, with the other eye that has better vision. The operator performs several scans and then selects the image with the best quality and information content.

When examining pathologies of the posterior part of the eye:

• degenerative changes in the retina (congenital and acquired, AMD)
• cystoid macular edema and macular hole
• retinal disinsertion
• epiretinal membrane
• changes in the optic nerve head (abnormalities, swelling, atrophy)
• diabetic retinopathy
• thrombosis of the central retinal vein
• proliferative vitreoretinopathy.

When examining pathologies of the anterior part of the eye:

• to assess the angle of the anterior chamber of the eye and the functioning of drainage systems in patients with glaucoma
• in case of deep keratitis and ulcers of the cornea
• during examination of the cornea during preparation and after laser vision correction and keratoplasty
• for control in patients with phakic IOLs or intrastromal rings.

When diagnosing diseases of the anterior part of the eye, OCT is used in the presence of ulcers and deep keratitis of the cornea, as well as in the case of diagnosing patients with glaucoma. OCT is also used to monitor the condition of the eyes after laser vision correction and immediately before it.

In addition, the optical coherence tomography method is widely used to study the posterior part of the eye for the presence of various pathologies, including retinal detachment or degenerative changes, diabetic retinopathy, as well as a number of other diseases

OCT analysis and interpretation

The application of the classical Cartesian method to OCT image analysis is not uncontroversial. Indeed, the resulting images are so complex and varied that they cannot be considered simply as a problem solved by the sorting method. When analyzing a tomographic image, consideration should be given to

• cut shape,
• thickness and volume of tissue (morphological features),
• internal architectonics (structural features),
• the relationship of zones of high, medium and low reflectivity with both the internal structure and tissue morphology features,
• the presence of abnormal formations (fluid accumulation, exudate, hemorrhage, neoplasms, etc.).

Pathological elements may have different reflectivity and form shadows, which further changes appearance Images. In addition, disturbances in the internal structure and morphology of the retina during various diseases create certain difficulties in recognizing nature pathological process. All this complicates any attempt at automatic image sorting. At the same time, manual sorting is also not always reliable and carries a risk of errors.

OCT image analysis consists of three basic steps:

• morphology analysis,
• analysis of the structure of the retina and choroid,
• reflectivity analysis.

It is better to study scans in detail in black and white rather than in color. The shades of color OCT images are specified by the system software, each shade is associated with a certain degree of reflectivity. Therefore, in a color image we see a wide variety of color shades, while in reality there is a consistent change in the reflectivity of the tissue. A black-and-white image allows you to identify minimal variations in tissue optical density and see details that may go unnoticed in a color image. Some structures may be better visible on negative images.

Morphological analysis includes examination of the slice shape, vitreoretinal and retinochoroidal profiles, as well as the chorioscleral profile. The volume of the studied area of ​​the retina and choroid is also assessed. The retina and choroid lining the sclera have a concave parabolic shape. The fovea is a depression surrounded by an area thickened due to the displacement of the nuclei of ganglion cells and cells of the inner nuclear layer here. The posterior hyaloid membrane has the densest adhesion along the edge of the optic disc and in the fovea (in young people). The density of this contact decreases with age.

The retina and choroid have a special organization and consist of several parallel layers. In addition to parallel layers, the retina has transversal structures that connect different layers.

Normally, the retinal capillaries, with their specific organization of cells and capillary fibers, represent true barriers to fluid diffusion. Vertical (cell chains) and horizontal structures of the retina explain the location, size and shape of pathological accumulations (exudate, hemorrhages and cystic cavities) in the retinal tissue, which are detected on OCT.

Anatomical barriers vertically and horizontally prevent the spread of pathological processes.

• Vertical elements- Müller cells connect the inner limiting membrane to the outer limiting membrane, extending across the layers of the retina. In addition, the vertical structures of the retina include cell chains that consist of photoreceptors associated with bipolar cells, which, in turn, contact ganglion cells.
• Horizontal elements: retinal layers- The inner and outer limiting membranes are formed by Müller cell fibers and are easily recognized on a histological section of the retina. The inner and outer plexiform layers contain horizontal, amacrine cells and a synaptic network between photoreceptors and bipolar cells on the one hand and bipolar and ganglion cells on the other.
  From a histological point of view, the plexiform layers are not membranes, but to some extent function as a barrier, although much less durable than the inner and outer limiting membranes. Plexiform layers include a complex network of fibers that form horizontal barriers to fluid diffusion across the retina. The inner plexiform layer is more resistant and less permeable than the outer one. In the foveal region, Henle's fibers form a sun-like structure that can be clearly seen on the frontal section of the retina. The cones are located in the center and are surrounded by the nuclei of photoreceptor cells. Henle's fibers connect the cone nuclei to the bipolar cell nuclei at the periphery of the fovea. In the fovea region, Müller cells are oriented diagonally, connecting the inner and outer limiting membranes. Due to the special architecture of Henle fibers, the accumulation of fluid in cystoid macular edema has the shape of a flower.

Image segmentation

The retina and choroid are formed by layered structures with varying reflectivity. The segmentation technique makes it possible to identify individual layers of homogeneous reflectivity, both high and low. Image segmentation also makes it possible to recognize groups of layers. In cases of pathology, the layered structure of the retina may be disrupted.

The retina is divided into outer and inner layers (outer and inner retina).

• Inner retina includes a layer of nerve fibers, ganglion cells and an inner plexiform layer, which serves as the boundary between the inner and outer retina.
• Outer retina- inner nuclear layer, outer plexiform layer, outer nuclear layer, outer limiting membrane, line of articulation of the outer and inner segments of photoreceptors.

Many modern tomographs allow segmentation of individual retinal layers and identification of the most interesting structures. The automatic nerve fiber layer segmentation function was the first of its kind to be introduced into the software of all tomographs, and remains central to the diagnosis and monitoring of glaucoma.

Fabric reflectivity

The intensity of the signal reflected from the tissue depends on the optical density and the ability of the tissue to absorb light. Reflectivity depends on:

• the amount of light reaching a given layer after absorption in the tissues through which it passes;
• the amount of light reflected by a given fabric;
• the amount of reflected light that reaches the detector after further absorption by the tissues through which it passes.

Normal structure (reflectivity of normal tissues)

• High
  • layer of nerve fibers
  • Line of articulation of the outer and inner segments of photoreceptors
  • External limiting membrane
  • Pigment epithelium-choriocapillaris complex
• Medium
  • Plexiform layers
• Low
  • Nuclear layers
  • Photoreceptors

Vertical structures, such as photoreceptors, are less reflective than horizontal structures (eg, nerve fibers and plexiform layers). Low reflectivity can be caused by a decrease in the reflectivity of the tissue due to atrophic changes, the predominance of vertical structures (photoreceptors) and cavities with liquid contents. Structures with low reflectivity can be observed especially clearly on tomograms in cases of pathology.

Choroidal vessels are hyporeflective. Reflectivity connective tissue choroid is regarded as average, sometimes it can be high. The dark plate of the sclera (lamina fusca) looks like a thin line on tomograms; the suprachoroidal space is not normally visualized. Typically the choroid is about 300 microns thick. With age, starting from the age of 30, there is a gradual decrease in its thickness. In addition, the choroid is thinner in patients with myopia.

Low reflexivity (fluid accumulation):

• intraretinal accumulation of fluid: retinal edema. Diffuse edema (diameter of intraretinal cavities less than 50 µm) and cystic edema (diameter of intraretinal cavities more than 50 µm) are distinguished. To describe intraretinal fluid accumulation, the terms “cysts,” “microcysts,” and “pseudocysts” are used.
• subretinal accumulation of fluid: serous detachment of the neuroepithelium. The tomogram reveals elevation of the neuroepithelium at the level of the tips of rods and cones with an optically empty space under the elevation zone. The angle of the detached neuroepithelium with the pigment epithelium is less than 30 degrees. Serous detachment can be idiopathic, associated with acute or chronic CSC, and also accompany the development of choroidal neovascularization. Less commonly found in angioid streaks, choroiditis, choroidal neoplasms, etc.
• Subpigmented accumulation of fluid: detachment of the pigment epithelium. Elevation of the pigment epithelium layer above Bruch's membrane is detected. The source of fluid is the choriocapillaris. Often the detachment of the pigment epithelium forms an angle of 70-90 degrees with Bruch's membrane, but always exceeds 45 degrees.

Optical coherence tomography (OCT) of the anterior segment of the eye is a non-contact technique that creates high-resolution images of the anterior segment of the eye, superior to the capabilities of ultrasound devices.

OCT can accurately measure the thickness of the cornea (pachymetry) along its entire length, the depth of the anterior chamber of the eye at any segment of interest, measure the internal diameter of the anterior chamber, and also accurately determine the profile of the anterior chamber angle and measure its width.

The method is informative when analyzing the state of the anterior chamber angle in patients with a short anteroposterior axis of the eye and large lens sizes, in order to determine indications for surgical treatment, as well as to determine the effectiveness of cataract extraction in patients with a narrow APC.

Also, anterior segment OCT can be extremely useful for anatomical assessment of the results of glaucoma surgery and visualization of drainage devices implanted during surgery.

Scan Modes

• allowing to obtain 1 panoramic image of the anterior segment of the eye in the selected meridian
• allowing to obtain 2 or 4 panoramic images of the anterior segment of the eye in 2 or 4 selected meridians
• allowing to obtain one panoramic image of the anterior segment of the eye with a higher resolution compared to the previous one

When analyzing images, you can

• a qualitative assessment of the condition of the anterior segment of the eye as a whole,
• identify pathological foci in the cornea, iris, anterior chamber angle,
• analysis of the area of ​​surgical intervention in keratoplasty in the early postoperative period,
• assess the position of the lens and intraocular implants (IOL, drains),
• measure corneal thickness, anterior chamber depth, anterior chamber angle
• to measure the size of pathological foci - both relative to the limbus and relative to the anatomical formations of the cornea itself (epithelium, stroma, Descimet's membrane).

In case of superficial corneal pathological foci, light biomicroscopy is undoubtedly highly effective, but if the corneal transparency is impaired, OCT will provide additional information.

For example, in chronic recurrent keratitis, the cornea becomes unevenly thickened, the structure is heterogeneous with foci of seals, it acquires an irregular multilayer structure with a slit-like space between the layers. In the lumen of the anterior chamber, reticular inclusions (fibrin threads) are visualized.

Of particular importance is the possibility of non-contact visualization of the structures of the anterior segment of the eye in patients with destructive-inflammatory diseases of the cornea. With long-term keratitis, destruction of the stroma often occurs from the endothelium. Thus, a lesion in the anterior parts of the corneal stroma, clearly visible during biomicroscopy, can mask the destruction occurring in the deep layers.

OCT retina

OCT and histology

Using the high resolution of OCT, it is possible to assess the state of the retinal periphery in vivo: to record the size of the pathological lesion, its location and structure, the depth of the lesion, and the presence of vitreoretinal traction. This allows you to more accurately determine the indications for treatment, and also helps document the results of laser and surgical operations and monitor long-term results. To correctly interpret OCT images, it is necessary to have a good understanding of the histology of the retina and choroid, although tomographic and histological structures cannot always be accurately compared.

In fact, due to the increased optical density of some retinal structures, the line of articulation of the outer and inner segments of the photoreceptors, the line of connection of the tips of the outer segments of the photoreceptors and the villi of the pigment epithelium are clearly visible on the tomogram, while they are not differentiated on the histological section.

On the tomogram you can see the vitreous body, the posterior hyaloid membrane, normal and pathological vitreal structures (membranes, including those that have a traction effect on the retina).

• Inner retina
  The inner plexiform layer, the ganglion cell layer, or multipolar cell layer, and the nerve fiber layer form the ganglion cell complex or inner retina. The internal limiting membrane is a thin membrane that is formed by the processes of Müller cells and is adjacent to the layer of nerve fibers.
  The layer of nerve fibers is formed by processes of ganglion cells that extend to the optic nerve. Since this layer is formed by horizontal structures, it has increased reflectivity. The layer of ganglion, or multipolar, cells consists of very voluminous cells.
  The inner plexiform layer is formed by the processes of nerve cells; synapses of bipolar and ganglion cells are located here. Thanks to the many horizontally running fibers, this layer has increased reflectivity on tomograms and distinguishes the inner and outer retina./
• Outer retina
  The inner nuclear layer contains the nuclei of bipolar and horizontal cells and the nuclei of Müller cells. On tomograms he is hyporeflective. The outer plexiform layer contains synapses of photoreceptor and bipolar cells, as well as horizontally located axons of horizontal cells. On OCT scans it has increased reflectivity.

Photoreceptors, cones and rods

The layer of photoreceptor cell nuclei forms the outer nuclear layer, which forms the hyporeflective stripe. In the fovea area, this layer thickens significantly. The photoreceptor cell bodies are somewhat elongated. The nucleus almost completely fills the cell body. The protoplasm forms a conical protrusion at the apex, which contacts the bipolar cells.

The outer part of the photoreceptor cell is divided into inner and outer segments. The latter is short, conical in shape and includes discs stacked in successive rows. The inner segment is also divided into two parts: the inner myodal and outer filament.

The line of articulation between the outer and inner segments of the photoreceptors on the tomogram looks like a hyperreflective horizontal stripe located at a short distance from the pigment epithelium-choriocapillaris complex, parallel to the latter. Due to the spatial increase in cones in the foveal zone, this line is somewhat removed at the level of the fovea from the hyperreflective stripe corresponding to the pigment epithelium.

The external limiting membrane is formed by a network of fibers coming mainly from Müller cells that surround the bases of photoreceptor cells. The external limiting membrane on the tomogram appears as a thin line located parallel to the line of articulation of the outer and inner segments of the photoreceptors.

Supporting structures of the retina

Müller cell fibers form long, vertically arranged structures that connect the inner and outer limiting membranes and perform a supportive function. The nuclei of Müller cells are located in the layer of bipolar cells. At the level of the outer and inner limiting membranes, the Müller cell fibers diverge in the form of a fan. The horizontal branches of these cells are part of the structure of the plexiform layers.

Other important vertical elements of the retina include chains of cells consisting of photoreceptors connected to bipolar cells and through them to ganglion cells, whose axons form a layer of nerve fibers.

pigment epithelium is represented by a layer of polygonal cells, the inner surface of which is cup-shaped and forms villi in contact with the tips of cones and rods. The nucleus is located in the outer part of the cell. Externally, the pigment cell is in close contact with Bruch's membrane. On high-resolution OCT scans, the line of the pigment epithelium-choriocapillaris complex consists of three parallel stripes: two relatively wide hyperreflective stripes, separated by a thin hyporeflective stripe.

Some authors believe that the internal hyperreflective stripe is the line of contact between the villi of the pigment epithelium and the outer segments of the photoreceptors, and the other, the outer stripe, represents the cell bodies of the pigment epithelium with their nuclei, Bruch's membrane and choriocapillaries. According to other authors, the inner stripe corresponds to the tips of the outer segments of the photoreceptors.

The pigment epithelium, Bruch's membrane and choriocapillaris are closely interconnected. Typically, Bruch's membrane is not differentiated on OCT, but in cases of drusen and small detachment of the pigment epithelium, it is defined as a thin horizontal line.

Choriocapillaris layer It is represented by polygonal vascular lobules that receive blood from the posterior short ciliary arteries and conduct it through venules into the vorticose veins. On the tomogram, this layer is part of a wide line of the pigment epithelium complex - choriocapillaris. The main choroidal vessels on the tomogram are hyporeflective and can be distinguished in the form of two layers: the layer of medium vessels of Sattler and the layer of large vessels of Haller. From the outside, you can visualize the dark plate of the sclera (lamina fusca). The suprachoroidal space separates the choroid from the sclera.

Morphological analysis

Morphological analysis includes determining the shape and quantitative parameters of the retina and choroid, as well as their individual parts.

General retinal deformation

• Concav deformation(concave deformation): in case of high myopia, posterior staphyloma, including in cases of scleritis, a pronounced concave deformation of the resulting slice can be detected on OCT.
• Convex deformation(convex deformity): occurs in cases of dome-shaped pigment epithelial detachment, and can also be caused by a subretinal cyst or tumor. In the latter case, the convex deformation is flatter and involves the subretinal layers (pigment epithelium and choriocapillaris).

In most cases, the tumor itself cannot be localized on OCT. Edema and other changes in the adjacent neurosensory retina are important in the differential diagnosis.

Retinal profile and surface deformation

• The disappearance of the fovea indicates the presence of retinal edema.
• Retinal folds, which form as a result of tension from the epiretinal membrane, are visualized on tomograms as irregularities in its surface, resembling “waves” or “ripples”.
• The epiretinal membrane itself can differentiate as a separate line on the surface of the retina, or merge with the layer of nerve fibers.
• Tractional deformation of the retina (sometimes star-shaped) is clearly visible on C-scans.
• Horizontal or vertical traction from the epiretinal membrane deforms the surface of the retina, leading in some cases to the formation of a central tear.
  • Macular pseudohole: the fovea is widened, the retinal tissue is preserved, although deformed.
  • Lamellar tear: the fovea is enlarged due to the loss of part of the inner retinal layers. Above the pigment epithelium, the retinal tissue is partially preserved.
  • Macular hole: OCT allows you to diagnose, classify macular hole and measure its diameter.

According to the Gass classification, there are 4 stages of macular hole:

• Stage I: detachment of the neuroepithelium of traction origin in the fovea;
• Stage II: through defect of retinal tissue in the center with a diameter of less than 400 microns;
• Stage III: a through defect of all layers of the retina in the center with a diameter of more than 400 microns;
• Stage IV: complete detachment of the posterior hyaloid membrane, regardless of the size of the through defect in the retinal tissue.

Tomograms often reveal swelling and slight detachment of the neuroepithelium at the edges of the tear. Correct interpretation of the rupture stage is possible only when the scanning beam passes through the center of the rupture. When scanning the edge of a rupture, erroneous diagnosis of a pseudofracture or an earlier stage of rupture is possible.

Pigment epithelium layer may be thinned, thickened, in some cases it may have an irregular structure throughout the scan. The bands corresponding to the pigment cell layer may appear abnormally saturated or disorganized. In addition, the three stripes can merge together.

Retinal drusen cause the appearance of irregularity and wave-like deformation of the pigment epithelium line, and Bruch's membrane in such cases is visualized as a separate thin line.

Serous detachment of the pigment epithelium deforms the neuroepithelium and forms an angle of more than 45 degrees with the choriocapillaris layer. In contrast, serous detachment of the neuroepithelium is usually flatter and forms an angle equal to or less than 30 degrees with the pigment epithelium. Bruch's membrane is differentiated in such cases.

If there are vision problems in one or both eyes, a comprehensive diagnosis is prescribed. Optical coherence tomography - modern, highly accurate diagnostic procedure, which allows you to obtain clear images in a cross-section of the structures of the eyeball - the cornea and retina. The study is carried out according to indications so that the results are as accurate as possible. It is important to prepare properly for the procedure.

When is optical coherence tomography prescribed?

Modern ophthalmology has at its disposal a variety of diagnostic technologies and techniques that make it possible to accurately examine complex intraocular structures, making treatment and rehabilitation much more successful. Optical coherence tomography of the eye - informative, non-contact and painless method, with the help of which it is possible to study in detail transparent ocular structures, invisible during traditional studies, in a cross section.

The procedure is carried out according to indications. OCT makes it possible to diagnose the following ophthalmological diseases:

• macular edema and rupture;
• optic disc deformation (OND);
• glaucoma;
• retinal vitreous dystrophy;
• retinal dissection;
• macular degeneration;
• subretinal neovascular and epiretinal membrane;
• senile macular degeneration.

There are 2 types of optical coherence tomograph - for scanning the anterior and posterior segment. Modern devices have both functions, so diagnostic results can be obtained more advanced. Ocular OCT is often performed on patients following glaucoma surgery. The method shows in detail the effectiveness of therapy in postoperative period, while electrical tomography, ophthalmoscopy, biomicroscopy, MRI or CT of the eye are not able to provide data of such accuracy.

Pros of the procedure

OCT of the retina can be prescribed to patients at any age.

The procedure is non-contact, painless and at the same time as informative as possible. During scanning, the patient is not exposed to radiation, since the examination process uses the properties of infrared rays, which are absolutely harmless to the eyes. Tomography makes it possible to diagnose pathological changes in the retina even at initial stages development, which significantly increases the chances of successful treatment and rapid recovery.

How is the preparation going?

There are no restrictions on eating and drinking before the procedure. On the eve of the study, you should not drink alcohol or other prohibited substances; the doctor may also ask you to stop using medications some groups. A few minutes before the examination, drops are instilled into the eyes to dilate the pupil. It is important for the patient to concentrate his gaze on the flashing dot located in the focus camera lens. Blinking, talking and moving your head is prohibited.

How is OCT done?

Optical coherence tomography of the retina lasts on average up to 10 minutes. The patient is placed in a sitting position, the tomograph with an optical camera is installed at a distance of 9 mm from the eye. When optimal visibility is achieved, the camera is fixed, then the doctor adjusts the image to get the most accurate image possible. Once the picture is accurate, a series of pictures are taken.

The finished survey result may look like a map.

• the presence or absence of changes in the external ocular structures;
• the relative position of the layers of the eyeball;
• the presence of pathological formations and inclusions;
• decreased or increased transparency of tissues;
• thickness of the structures being studied;
• dimensions and presence of deformations on the surface under study.

The interpretation of the tomogram is presented in the form of a table, map or protocol, which can most accurately show the state of the studied areas of the visual system and establish an accurate diagnosis even in the early stages. If necessary, the doctor can prescribe a repeat OCT study; this will allow tracking the dynamics of the progression of the pathology, as well as the effectiveness of the treatment process.