Andy Franklin and Ngaire Franklin describe how to select the initial lens for a rigid gas-permeable (RGP) fitting and how to calculate the final order. Module
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The intended relationship between the cornea and the back optic zone of the lens will depend on the fitting philosophy adopted. The lens is held in place on the cornea both by the eyelids and by surface tension, which act at the lens edge where it is not covered by the lid. If the edge clearance is excessive no meniscus forms and no surface tension acts. Reduced edge clearance and edge thickness boosts surface tension. Broadly speaking, there are two extreme positions that can be adopted.
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