The ultimate goal in fitting rigid gas permeable contacts is to maintain a healthy corneal-lens relationship while satisfying the patient. The fitter may chose between an interpalpebral lens, an under the lid lens, and an upper lid attachment lens modality. The interpalpebral modality is fit at least 0.50D steeper than the flattest keratometer reading and has a diameter between 7.8 and 8.3mm. The base curve chosen for an under the lid fit depends on the size of lens used. Large or small lenses can be fit with this modality depending on the palpebral fissure width. In contrast the upper lid attachment fit uses a diameter larger than 8.8mm and rests under the upper lid. The fitter must understand the relationships between lens diameter, base curves, lens edge and center thickness, and peripheral curves when designing the rigid gas permeable (RGP) lens. The use of fluorescein is an invaluable tool in assessing the fit of a RGP lens and the patient's corneal health. This paper /video will discuss and illustrate these various effects.
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