Corneal topography is one of the most frequently used examinations in the process of wearing orthokeratology lens. It can conduct precise morphological analysis of the cornea as a whole. It can directly show the shape of the cornea in the form of two-dimensional or even three-dimensional, and reflect the refractive power of each part of the cornea through different colors; for corneal astigmatism, regional irregularity, keratoconus and even the posterior surface morphology of cornea and Corneal thickness has good resolution, which is very important for the preliminary screening before the fitting of orthokeratology lens or laser surgery. In addition, reviewing the topographic map after wearing can judge the position of wearing glasses and corneal flattening at night, reflect the wearing position and degree of pressure of orthokeratology lens, and effectively evaluate the effect of orthokeratology.

Advantages of corneal topography:

Large amount of information: the data points are determined by the number of projection rings, which can include up to 14000 data points, and the measurement area covered by the corneal modeling device (CMS) can reach 95%.

High accuracy: the accuracy of corneal topography in the range of 8 mm is 0 ~ 0.07 D (100% ~ 99.03%), and the error of CMS system in human eyes is within ± 0.25 D.

Strong intuition: for the cornea with different refractive power and different colors, the warm color represents the part with strong refractive power, and the cold color represents the part with weak refractive power, which is the non intuitive and eye-catching corneal morphology.

Small error: try the image capture of digital video monitoring system within 1 / 30 seconds to avoid the influence caused by blink and heartbeat.

Significance of corneal topography before and during orthokeratology

1. Selection and exclusion of unsuitable groups: those with abnormal topographic map diseases, including keratoconus and marginal corneal degeneration, should not be worn if the cornea is too flat (less than 39.00d) or too steep (more than 46.00d);

2. Selection of base arc of standard lens: 70% ~ 80% of standard lens can be used as the final lens according to K value test results of corneal topography map. 20% - 30% of the lenses need to be re selected according to their neutral, mobility and fluorescent staining status.

3. Prediction of wearing effect: the expected effect of orthokeratology lens can be preliminarily judged by e value data provided on corneal topography map. The effect of corneal e value (eccentricity, eccentricity) on the effect of orthokeratology.

The significance of corneal topography in orthokeratology

1. Evaluation of the correction effect: in the later review, the corneal topography can directly feed back the shaping strength of the cornea, the size of the shaping area and the position of the lens through the two-dimensional and three-dimensional graphics, which can help the fitting doctor to draw a conclusion intuitively and quickly;

2. To observe the corneal data after stopping wearing orthokeratology lens: after wearing orthokeratology lens for 1 ~ 2 years, it is possible to stop wearing orthokeratology lens and re optometry to judge the control effect and re fitting. After stopping wearing, the corneal morphology will gradually return to its original shape, but it usually takes 2 to 8 weeks to get the original corneal shape. The higher the degree of myopia, the longer it takes. Through the topography map of orthokeratology mirror, we can directly observe the changes of corneal morphology and whether it is completely restored.

Precautions for corneal topography examination:

During the examination of corneal topography, the patients should be allowed to open their eyes as much as possible to fully expose the cornea, and the head position and eye position of the examinee should not be tilted; if the corneal surface is moist and the tear film is unstable, the artificial tears can be dripped before the examination, so as not to affect the examination results due to dryness; if the patient's orbit or facial shadow is affected, the patient can be instructed to face slightly in the opposite direction of the examined eye, Make the examined eye fully exposed; if the upper eyelid is covered too much, ask someone else to help lift the upper eyelid, but avoid pressing the eyeball to affect the results.