RGP fitting philosophies for keratoconus.

Rigid gas permeable (RGP) lenses are the choice of vision correction for most keratoconic patients. Various fitting philosophies and different lens designs are available and the question of which technique is the most appropriate is a controversial issue in the field of contact lens practice. This article reviews the different philosophies with respect to their rationale, optical performance and physiological influence on the cornea. The 'three-point-touch' approach is now the most widely-accepted corneal lens fitting philosophy in clinical practice. It provides a well-distributed pressure between the cone apex and the relatively normal peripheral cornea but other philosophies such as apical bearing and apical clearance also have advantages. Having considered the advantages and disadvantages of each philosophy, a variant of the three-point-touch appears to be a practical solution. Practitioners can fit keratoconic patients with a three-point-touch tending towards apical clearance to allow for disease progression and unexpected lack of follow-up. Wearing time, visual acuity and comfort are also important issues to be considered as all of these are essential to constitute a successful contact lens fitting.