Advantages and disadvantages of corneal topography

As a new corneal analysis system, corneal topographic map has incomparable advantages compared with previous corneal anterior surface analysis methods, but it also has its shortcomings. (1) has a large measurement area and a large amount of information. Corneal curvature meter can only measure 8% of the total corneal area, while corneal topography can observe more than 95%. The density of data points can be as high as 34 rings, with 256 points in each ring, and the whole cornea can have 7000 ~ 8000 data points, some of which can reach tens of thousands of data points, such as AstraMax corneal topography instrument (Figure 5- 1), and the data points can reach 13000.

Fig. 5- 1 AstraMax corneal topographer

⑵ The measuring range of refractive power is wide. For the cornea that is too flat or steep, the refractive power can be measured accurately.

(3) High accuracy and small error. The accuracy of cornea is 0 ~ 0.07d in the range of 8.Omm. Due to the adoption of real-time digital video technology to display in 1/30s, the influence of blinking and heartbeat is avoided.

(4) It is easy to establish a mathematical model. Because of the grating photogrammetry technology, the changes of corneal surface are explained by the spherical reduction map and corneal meridian curvature map marked by relative height and absolute height, so it is easy to establish a mathematical model.

5] Less affected by keratopathy (compared with keratometer). The latest corneal topographers, such as PAR and CTS, can not only examine corneas with epithelial defects, ulcers and scars, but also their examination results are rarely affected by corneal lesions, so the examination results have high reference value.

[6] The result is intuitive. Due to the use of colors, different colors are used for different radii of curvature on the cornea. Warm color represents the part with strong refractive power, and cool color represents the part with weak refractive power, which makes the results of corneal topography display very intuitive and eye-catching.

Once a machine is used for multiple purposes. The corneal topography instrument also has the functions of automatic corneal curvature meter and corneal mirror. The new corneal topography instrument can also measure? Pupil diameter and corneal diameter under visual and dark vision. The function of the software has also been greatly improved, for example, the data of corneal aberration can be obtained through the conversion of setting function. (1) is more expensive;

⑵ Insensitive to peripheral cornea;

(3) When the aspheric component increases, the accuracy decreases;

⑷ It is easily influenced by orbital height and enophthalmos;

5] It takes time to check too many parameters.