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This is a simple idea but works very well especially in advanced or unusually shaped cones. In short a soft carrier lens of minimal prescription, usually a silicone hydrogel for increased oxygen permeability, is inserted to provide a more even surface for an RGP lens which corrects the bulk of the refractive error.
It is usual to use a silicone hydrogel daily disposable, for ease of use only one cleaning regimen is then needed. As you can see from the topographic images opposite the soft lens can have a dramatic affect on the corneal curvature. This base lens can even out the surface just enough to provide a more stable surface to then fit a bespoke RGP lens. This system has a similar affect to the hybrid type design, however, the lenses are much more versatile with toric, asymmetric and larger diameters all customisable. Due to this versatility these lenses are indicated in the more advanced stages of the ectasias and in personal experience it is particularly suitable for those with PMD. It's only disadvantage with regard to the patient being that a total of four lenses are needed on a daily basis. |
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