Keratotopography

Keratotopography is a remote method of examining the cornea of ​​the eye without interfering with the eye structure. The cornea is a transparent convex plate in the anterior part of the eyeball, in which the luminous flux is focused to the lens. It plays the role of a lens, and any changes in its curvature, damage or pathological changes lead to serious visual impairment.

The principle of keratotopography and the field of application

The name of this method consists of the Greek word kerato, which means horny fabric and topography - the definition of the geometry of any surface.Keratotopography is the acquisition of a detailed map of the cornea of ​​the eye. This method is used only in ophthalmology.The use of keratotopography can reveal the following pathologies:

• Keratoconus;
• Dystrophic epithelial lesions;
• Various forms of corneal degeneration;
• Astigmatism.

In addition, keratotopography can assess the condition of the cornea before and after surgery.

In ophthalmology, devices operating on different physical principles are used to carry out this procedure:

• Rings of Placido;
• Optical slot scanner;
• High resolution camera;
• Pentacam system;
• Raster camera;
• Laser interferometry.

Pentacam System

The keratotopograph, working with the Placido rings, removes the reflection of the ring structures from the cornea by a special camera. This method is considered very accurate, since the camera records at least 8000 points of the entire surface. The disadvantage of this method is the dependence of image quality on the condition of the tear coating.

In an optical scanner, two light sources are used, in which a light beam passes through a narrow slit.The lights are at an angle to each other. For each light line, up to 20 images are taken.You can scan a section with a diameter of up to 10 millimeters. As a disadvantage, low accuracy is considered when scanning the posterior surface of the cornea.

The camera with high resolution makes up to 40 reflected images. The computer program processes at least 240 points of each image, which allows you to accurately calculate the thickness of the cornea and the geometry of its rear surface. This method is most widely used in ophthalmic practice.

The rotating Pentacam camera, per, seconds, performs up to 50 pictures of the corneal surface.The image is divided into 500 points, that is, 25 000 points are determined. The Pentacam system allows to obtain an exact geometry of both surfaces of the cornea.The system is distinguished by the high resolution of all zones, and the ability to conduct corneal examinations with serious pathologies.

In raster photography, a calibrated grid is projected onto the front surface of the cornea, and the camera removes its reflection from different angles. This method is highly accurate.In order to make the image clear, the tear film is stained with a contrasting reagent.

Laser interferometry is a method based on the interference of two intersecting light waves. The beam from the helium-neon laser focuses on the front surface of the cornea.

Part of the light flux falls on the back surface and is reflected from it. As a result, two reflected beams interfere with each other and the resulting image is projected onto the monitor screen via a video camera. To obtain the results, the image is processed by a computer using a special algorithm.

Simple methods for determining visual acuity

Modern ophthalmological equipment based on high technologies, using computers and laser technology is not always available, especially in remote rural areas.Therefore, ophthalmologists continue to use affordable and inexpensive means to test visual acuity. The most common of these are tables.

A table is a poster on which ordinary letters or circles with cuts are marked. The top line contains the largest characters.They gradually decrease from top to bottom. The number of lines is 12. If the patient confidently calls all the signs in line 10, then his vision is considered ideal.Rarely, who can correctly identify the letters located in 11 and 12 lines. This vision is commonly called "eagle eye".

There are no letters in the children's tables, because the kids do not know them yet.Instead, on the poster there are animals, birds, fish and other items that the child is familiar with.The tables usually indicate the distance from which the patient should recognize the signs in a particular line. This method allows you to assess only visual acuity, so for more accurate diagnosis, other methods are used.

How to test for color perception

Procedure and results of the survey

This procedure is completely painless, since the keratotopogram is obtained remotely and no damage is done to the eye. The patient sits in front of the device in a free position, and the cornea of ​​the eye is scanned by an optical device.

After processing the data with a special program, the computer displays a keratotopogram on the display.It can also be printed on the printer. On this topographic map, different parts of the cornea are depicted in different colors.There is an international scale, where colors indicate the following properties of the cornea:

• Red and orange- convex surfaces;
• Green and Yellow- the absolute norm;
• Purple and blue- flat areas.

Example of results of keratotopography

On the keratotopogram there is also the following information:

• Curvature of the cornea indicated in diopters;
• The upper point of keratoconus;
• Indicators of symmetry of astigmatism.

The topographic map of the cornea shows the meridians of the most convex and flatest section. The difference between them is indicated in the diopters.

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conclusions

Keratotopography can reveal many eye pathologies in the early stages, so it is recommended to everyone without exception. After eye surgery, the procedure should be performed every three months. This procedure does not have any contraindications.

Also, read about this method of diagnosis, such as visometry and why conduct a test for color perception of drivers.