OPTICAL COHERENCE TOMOGRAPHY IN DIAGNOSTICS OF OPTIC NERVE PATHOLOGY

Аннотация

Optical coherence tomography (OCT) is a modern non-invasive, non-contact method for intravital visualization and analysis of the morphological properties of the structures of the optically transparent tissues of the eye, based on the principle of light interferometry. The first OCT devices used a sequential (time) imaging method (time-domain optical coherence tomography, TD-OCT). Keywords: optic nerve, OCT, OCT, OST. Introduction: The principle of operation of the interferometer is based on Michelson. The low-coherence light beam of a superluminescent light-emitting diode is split into two beams, one of which is reflected by the object under study, and the other passes along the reference path inside the device and is reflected by a mirror whose position is adjusted by the researcher. When the length of the beam reflected from the tissue under study and the beam on the mirror are equal, an interference phenomenon occurs, which is recorded by the LED, which in turn is analyzed by the software. The scanning results are presented as a gray or pseudo-color image. Each measurement point corresponds to one A-scan. The resulting single A-scans are combined to form a two- dimensional image. The axial resolution of the first generation devices is 8-10 μm, the scanning speed is 400 A-scans per second. The appearance of artifacts and the decrease in scan quality are due to eye movements that occur during the examination. Research methods and materials: With the advent of high-speed cameras, spectral tomographs have replaced time-lapse cameras [7, 10]. The light source in spectral tomographs is a broadband superluminescent diode, which allows obtaining low-coherence light containing several wavelengths. As in time-domain OCT, in spectral OCT, the light beam is split into two beams, one of which is reflected from the object under examination (the eye) and the other from a fixed mirror. At the output of the interferometer, the light is spatially decomposed into a spectrum, and the entire spectrum is recorded by a high-speed camera. Then, using the mathematical Fourier transform, the interference spectrum is processed and a linear A-scan is formed. 609 Mart, 2025-Yil Unlike time-domain OCT, where a linear A-scan is obtained by sequentially measuring the reflectance properties of each individual point, spectral OCT produces a linear A-scan by simultaneously measuring the reflected rays from each individual point [4, 7]. Modern spectral OCT scanners have an axial resolution of 3–7 μm and scan rates exceeding 26,000 A-scans per second. High scan rates can significantly improve the quality of the acquired images by reducing artifacts that occur during eye movement during the examination [4]. High-resolution spectral tomographs (collective source OCT, SS-OCT) use laser sources whose emission frequency is tuned at high speed in a specific spectral range (frequency sweep). During the frequency tuning cycle, the amplitude of the reflected signal is not recorded, but rather the frequency [15]. By using two parallel photodetectors, the scanning speed increases to 70-100 thousand A-scans. SS-OCT technology (due to the increase in wavelength and scanning speed) allows imaging of deep structures such as the choroid and lamina cribrosa of the optic disc. The development of the method, the creation and implementation of new generation devices have helped to expand our knowledge of the structures of the eye and improve the interpretation of the obtained data. Modern optical coherence tomographs allow obtaining images comparable to microscopic examination. Given the current body of knowledge, in 2014 an international panel of experts (the International Nomenclature for Optical Coherence Tomography Panel) presented an improved version of the interpretation of normal OCT anatomy of the retina. Most of the layers retained their previous names, but some underwent fundamental changes. The rate of evolution of tomographs began to exceed the capabilities of specialists in analyzing and interpreting data. The amount of data that needs to be described, classified and evaluated has increased. In ophthalmological practice, the capabilities of modern OCT scanners are widely used in the diagnosis and monitoring of pathologies of the retina and the anterior segment of the optic nerve and the macular region. Modern optical coherence tomographs allow you to build three-dimensional models of the studied area and maps of the thickness of individual layers of the retina, which allows you to objectively assess the dynamics of the pathological process and the effectiveness of treatment. The latest generation of tomographs, thanks to the use of innovative technologies, allow you to visualize the blood flow of the retina and optic nerve head, which opens up fundamentally new opportunities for the diagnosis and treatment of retinal diseases. In the diagnosis of anterior segment diseases, OCT is used to assess: the precorneal tear film and tear meniscus profile;