Optical coherence tomography eyes OCT
Optical coherence tomography (OCT) is a method for layered visualization of tissue based on their ability in different ways to reflect the light beam. The method of obtaining an image reminiscent of an ultrasound, but instead of ultrasound uses a beam of infrared colors. The light pulse is focused on the investigated tissue and, reaching her, a little scattered and partially reflected at a certain angle.
The sensor device records the feedback and compares it to the intensity and depth of the signal with the original. As a result of complicated computer processing of this information transformirovalsya in layer-by-layer image of the investigated structures with high resolution. These data are sufficient for obtaining three-dimensional images of the structures of anterior and posterior segments of the eye.
Most often, optical CT is used in ophthalmology. Using this method at the microscopic level to examine the retina, the cornea, the iris and the structures of the anterior segment of the eye without disrupting their integrity. With high precision can be performed early diagnosis in the preclinical stage, i.e. in the absence of symptoms such eye diseases as:
- detachment and degenerative changes of the retina;
- macular breaks and macular dystrophy;
- diabetic retinopathy;
- nevus and choroidal melanoma;
- thrombosis of Central retinal vein;
- neurodegenerative diseases of the brain.
Informative studies can be reduced in diseases that are accompanied by cloudiness of transparent media: hemophthalmus, Mature cataract, fibrosis, or inflammation of the vitreous body, in this case, choose alternative diagnostic methods: ultrasonography, fluorescein angiography of the retina biomicroscopy. To get the image you want the focus and fixation of the eyeball in a certain position, and in patients with nystagmus, his conduct can be difficult.
Preparation for optical imaging of the eye and the procedure
Special training optical coherence tomography of the eye does not require, however, the results will be more credible if conducted medicamental mydriasis (not performed in cases of suspected glaucoma). Before scanning the patient is asked to put the chin on a special support and focus your eyes on the mark. If the visual acuity of the eye subject to examination greatly reduced and it is impossible to see the label, to focus, need to use healthy eyes.
The results can be presented in a table with quantitative indicators, a two-dimensional or three-dimensional images. All data is written to disk, which is handed to the patient, and stored in a database computer program. If optical coherence tomography of the eye is performed again to assess changes in the condition of eye tissues in dynamics. Most often this is used to assess the result of surgical treatment of glaucoma, macular detachment, and retinal pathology.
Definition of pathological changes using the OCT
- Coherence tomography of the retina gives information about the integrity and thickness of its layers, as well as the condition of the macula (Central area of the retina located some distance from the optic disc). Normally, the layers have uniform thickness, and the macula is visualised as a hollow in the centre. With this research is early diagnosis of rheumatoid ruptures and degenerative changes in the retina, macular degeneration and diabetic retinopathy. If you need detailed visualizzatori retina, prescribe fluorescein angiography of the retina as optical tomography of the eye does not give such information.
- The optic disc presents a cavity, which lacks the retina and choroid. Using optical imaging to assess the thickness of nerve fiber layer around the periphery of the optic disc, and the angle of tilt relative to it and the retina, the shape and diameter of the Cup and of the optic nerve head. This method is ideal for early detection of pits and stagnant optic disc, and various forms of optic neuropathy. The deepening and the increase in diameter of exacavation, along with narrowing of the disc rim band of the optic nerve head may indicate a chronic increase in intraocular pressure, which is characteristic of glaucoma. For a more accurate diagnosis in identifying such changes is carried out the imaging of the structures of the anterior segment of the eye;
- Examination of the structures of the anterior eye segment are primarily conducted for the diagnosis of glaucoma and assessment of the quality of surgical treatment. By means of optical tomography are exploring the value of the opening angle, the view of the iridocorneal ratio and the depth of the anterior chamber of the eye. Noncontact coherence tomography of the anterior eye segment allows to use it in the early postoperative period after surgical interventions for glaucoma.
How else apply OCT?
Optical imaging, in addition to ophthalmology, is used in dentistry, dermatology, vascular surgery and interventional cardiology. With the help of optical tomography to investigate the structure of the surface layer of the skin, mucous membranes and hard tissues of the tooth. The structure of the inner wall of the vessel, including the coronary arteries, it is also possible to study using the OCT – the possibilities of this method exceed considerably the diagnostic value of coronary angiography or intravascular ultrasound.
This is interesting: optical coherence tomography is used not only to study the eyeball. It is also used in dentistry, dermatology, vascular and cardiac surgery.
A light beam from a broadband superluminescent of the led passes through the fiber optic cable, which is delivered to the area of study with cardiac surgery or endovascular conduit. Thus, it is possible to diagnose changes in the walls of the coronary arteries at the microscopic level. Coronary angiography allows to ascertain the presence of cholesterol plaques and to determine their localization zones of narrowing of the lumen of the vessel. OCT gives an idea about the microstructure, level of maturity and activity of platelet, which is of great prognostic value. After stent or balloon angioplasty optical tomography allows not only to assess the patency of the vessel or stent, but also to identify structural changes in the place of surgery.