An assessment of the optimal lens fit rate in keratoconus subjects using three-point-touch and apical touch fitting approaches with the rose K2 lens

Abstract

Objectives: To compare the number of ordered lenses required to achieve an optimal lens fit between three-point-touch and apical touch fittings in keratoconus subjects with nipple and oval cones using the first definite apical clearance lens (FDACL) as a starting point.

Methods: First trial lens was selected following manufacturer's guidelines and the back optic zone radius (BOZR) was flattened or steepened in 0.10 mm steps until a FDACL was found. Subsequently, subjects were randomly allocated to three-point-touch (BOZR 0.10 mm flatter than FDACL) and apical touch fittings (BOZR 0.40 mm flatter than FDACL). Changes were made solely in total lens diameter, edge lift, and/or back vertex power until an optimal lens fit was achieved. Differences between fitting approaches were compared in terms of optimal lens fit rates defined as the percentage of subjects successfully fitted with the first lens ordered from the manufacturer.

Results: Sixty-one subjects (109 eyes) were randomly allocated to three-point-touch and apical touch fitting approaches. An average of 2.3 trial lenses were necessary to achieve the FDACL. An optimal lens fit rate was achieved with the first lens in 84 of 109 eyes (77%). No statistically significant differences in optimal lens fit rates were found between three-point-touch and apical touch fitting approaches (83% and 71%, respectively; P = 0.12) and between nipple and oval cones (81% and 68%, respectively; P = 0.12).

Conclusions: The use of the FDACL provides a systematic, reliable, and repeatable starting point for Rose K2 contact lens fitting in keratoconus. Eye care practitioners should anticipate higher optimal lens fit rates when using three-point-touch (83%) in comparison with apical touch contact lens fittings (71%).