Purpose: Rigid gas-permeable (RGP) contact lens fitting after penetrating keratoplasty (PK) is challenging due to significant irregular astigmatism. The aim of the study was to determine a guideline for selecting the initial base curve (BC) of the RGP contact lens fitting in post PK eyes.
Methods: The data of patients who had tricurve RGP contact lens fitting post PK were collected retrospectively. The following data were collected: best-corrected visual acuity with glasses and contact lenses; contact lens parameters which included the BC and diameter; corneal topography parameters which included steep keratometry value (K), flat-K, and mean-K; and anterior best fit sphere (BFS) measured using Scheimpflug imaging.
Results: The median age of the 40 subjects (46 eyes) who met the inclusion criteria was 37.5 years (IQR 26.7-45.5). The spherical equivalent was -3.00 diopter (D) (-8.31 to -1.56). The median steep-K, flat-K, and mean-K in them were 6.76 mm (6.28-7.07), 7.78 mm (7.37-8.14), and 7.26 mm (6.93-7.46), respectively. The median anterior BFS value of the transplanted cornea was 6.96 mm (6.6-7.37). The median BC of the final RGP lens was 7.0 mm (6.7-7.23) and the median diameter was 9.8 mm (9.4-10.4). Among all the Scheimpflug imaging parameters, the BFS correlated well with the final BC of the RGP contact lens dispensed (R 0.742, P < 0.0001).
Conclusion: The anterior corneal surface BFS value can be used as a reference in selecting the initial BC of tricurve RGP contact lens to achieve the best fitting and reducing the chair time of patients after PK.
Keywords: Best fit sphere; Scheimpflug imaging; keratoconus; penetrating keratoplasty; rigid gas-permeable contact lens.