MYOPIA CONTROL EXPERT
Five training modules are available to enable you to train yourself with regard to ortho K and DRL:
The success of an orthokeratology lens adaptation essentially depends on the quality of the initial topographies:
The topographic map displays corneal powers or radii of curvature using a colour scale: cold colours (blue) represent flat areas and warm colours (red) represent convex areas.
Topography by specular reflection, which measures the radii of curvature, is made possible by the reflection of Placido discs on the anterior surface of the cornea.
After having correctly installed the patient in the chin and forehead support, the quality of the topography can be easily checked using various tips and tricks:
1. When taking measurements, checking the regularity of the test pattern is a decisive factor. Since the disks reflect on the tears, and the quality of the tears determines the regularity of the rings, it is recommended that you check the quality of the tears by instilling artificial tears beforehand, making the patient blink 3 times and asking them to open their eyes wide.
Before instilling artificial tears
After instilling artificial tears
2. The measurement of corneal eccentricity in both meridians is essential for the calculations for corneal remodelling lenses. The average eccentricity is about 0.48. In a healthy cornea, if the eccentricities are negative or close to 0, a repeat measurement is necessary. They are generally similar across both eyes.
3. Colour-coding can also guide the examiner with regard to the quality of the measurements. On the topographies shown above (before artificial tears are instilled), certain measurements appear in yellow and red, indicating a suspected or confirmed anomaly. If all values are in green, they are within the normal parameters.
4. The use of different indices also makes it possible to check corneal regularity. They are used in the detection of corneal ectasia or corneal warpage. It is necessary to forgo wearing the old lenses for about two weeks before taking the measurements. These indices also use the principle of colours, with green indicating normal. The SAI (Surface Asymmetry Index) is one of the most widely used.
5. To determine the parameters of an ortho K lens, it is necessary to check the reproducibility of the measurements by performing several topographies, usually 4 per eye.
A well-adapted ortho K lens will allow optimal corneal remodelling. The internal parameters of the lens are determined exclusively based on topographic elements. Topography is therefore the essential tool for successful adaptation in orthokeratology.