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Professional papers

The second report of CRT orthokeratology --Matching practice

Published people:Internet Society Published time:2020.11.10 Download the number:0

After theoretical study, exciting practice begins.

Several colleagues and friends of the children to do a try on model, complete the basic inspection. According to the process, select the appropriate test piece by using the "draw card", and then similar to the VST process - wearing glasses and evaluation.

In order to observe the evaluation changes after adjusting different parameters on the "suitable" fitting, we specially made some contrast film changes and photos.

1、 The change of BC and lza was not obvious

A in Figure 1 is the trial piece selected according to the "draw card": 8755033. We have evaluated and compared the trial piece with parameters nearby, and we think that this is the ideal fit condition. B is a comparison of changing lza from - 33 to - 34 (tightening) with the remaining parameters unchanged (87 550 34) - there is no obvious change from the figure. C is to flatten BC from 8.7mm to 8.8mm, while the other parameters remain unchanged (8855033), it seems that there is no obvious change.

What thickness of tear film can be observed in fluorescence assessment? ——According to the classic keratoplasty study, the value is 20 μ M. In CRT, the lza adjustment of each gear brings about 15 μ m change, so the parameter adjustment here is not obvious in the evaluation and observation.

 The lza adjustment of the first gear brings about a change of 15 μ m, so the parameter adjustment here is not obvious in the evaluation and observation.


 Fig. 1 Comparison of fluorescence evaluation of lza change of 1 ° and base arc change of 0.1 mm


2、 By changing the first gear of RZD, the adaptation change is more obvious than that of VST

In Figure 2, a is 8050033 lens, B is 8052533 lens, C is 8055033 lens, three different RZD lenses on the same eye fluorescence evaluation performance. It can be seen from the figure that the difference of fitness assessment map is more obvious than that of VST with only changing RZD and other parameters unchanged.

Each shift of RZD corresponds to 25 μ m sagittal height change, which can be observed by fluorescence evaluation. In the process of adjusting CRT sagittal height, the change of RZD (25 μ m) is larger than that of lza (15 μ m). Therefore, lza is considered as a way of fine adjustment.

However, we can't confirm whether the fit is suitable or not based on the fluorescence assessment without corneal topography after overnight trial.


Figure 2 CRT evaluation chart of different RZD on the same eye


3、 The performance of topographic map after wearing for 2 hours and overnight

The next morning after getting up, do not wash face, do not rub eyes, wear glasses to check, lens activity, cornea intact.

Figure 3 shows the axial topographic map after we have selected the appropriate fit, and the axial topographic map after wearing glasses for 2 hours and overnight; Figure 4 shows the differential map of tangenic after overnight trial, and the position of lens is acceptable in the middle.


图3  A原始地形图  B试戴2小时过一夜后的地形图

图片4.pngFig. 4 difference of tangenic after overnight trial


4、 Experience of fitting practice:

  1. The effect of RZD (return zone depth) adjustment on adaptation (25 μ m for first gear) is more obvious than that of VST system. ——This means that the change of fluorescence evaluation is more obvious than that of VST system, and the adjustment direction is more sure.

  2. A small amount of adjustment of lza and BC (15 μ m in first gear) did not observe significant evaluation changes.

  3. The adjustment of RZD can be observed by evaluation, while that of lza is difficult to be observed.

  4. The evaluation can only be used as a reference index for film fixation, which can be used to judge the relationship between lens diameter and corneal diameter, tear exchange level, edge warping degree, lens mobility, etc. the final film fixation confirmation still depends on the topographic map, which is the same as VST plastic lens.

  5. The new lens has a layer of protective film. It must be cleaned carefully and repeatedly when using, otherwise it will affect the comfort of wearing glasses and evaluation and observation.

  6. The treatment area is larger, and lza is thinner than VST. However, lens positioning is not unstable because lza is thin. In some eyes, the width of lza is very thin, but there is no deviation when wearing glasses overnight. This may be caused by the difference between the tangent design of lza and the arc matching principle of VST. This feature will be summarized after more samples are made.

  7. Because of the small sample size, the selection relationship between E value and lza and diameter has not been explored. We expect to do more sample summary in the future.

  8. The lens is very thin, the wearer complains that it is comfortable to wear the lens. We repeatedly operate and use it normally, and there is no rupture of the lens. Further understanding of the situation in the U.S. market, manufacturers reflect that the CRT fragmentation rate in the United States is 0.01%, that is, one in ten thousand. ——It seems that thin does not necessarily mean that it is easy to break. After all, it has the largest share in the U.S. market. If it was really fragile, it would have been reported.

  9. We thought that thin lenses could reduce the grip force of the eyelid on the lens and reduce the lens deviation caused by eyelid pressure. I found a child who repeatedly tried to wear the VST orthosis lens because of the tight eyelid deviation (signed the informed consent of the trial wearing experiment), but the result was not ideal. No matter how the adjustment was made, the deviation was also difficult to deal with. It seems that the reduction of lens thickness does not reduce the effect of eyelid pressure too much.