[The flexure of on-eye rigid gas permeable contact lenses and its relationship with anterior corneal surface].

Objective: To investigate the effect of corneal irregularity on on-eye rigid gas permeable (RGP) contact lenses and the corneal shape changed by RGP contact lenses.

Methods: Corneal topography was taken for 42 bare eyes of 22 subjects before and 1 month after wearing of the RGP contact lens. Off-eye and on-eye wavefront aberrations of the anterior surface of the RGP contact lens were also measured by corneal topography for the same 42 eyes. Zernike aberrations of the RGP contact lens were examined and compared to those of baseline anterior corneal surface.

Results: For bare eyes, C4, C5, C7 and C8 were significantly different from the baseline 30 minutes after the RGP contact lens was removed. For the on-eye RGP contact lens, three mean Zernike aberrations were significantly different from those off-eye. These were defocus C4 [OD: (1.003 ± 0.131) µm off-eye and (1.065 ± 0.160) µm on-eye, P = 0.015; OS: (1.003 ± 0.130) µm off-eye and 1.069 (0.851, 1.594) µm on-eye, P = 0.017], main axis astigmatism C5 [OD: (0.072 ± 0.083) µm off-eye and (-0.312 ± 0.232) µm on-eye, P < 0.001; OS: (0.066 ± 0.056) µm off-eye and (-0.349 ± 0.242) µm on-eye, P < 0.001], and spherical aberration C12 [OD: (0.264 ± 0.039) µm off-eye and (0.295 ± 0.048) µm on-eye, P < 0.001; OS: (0.266 ± 0.035) µm off-eye and 0.290 (0.215, 0.471) µm on-eye, P < 0.001]. All these three Zernike aberrations of on-eye RGP contact lenses were significantly correlated to those of the baseline corneas (OD: rc4=0.557, rc5=0.596, rc12=0.581, P < 0.01; OS: rc4=0.684, rc5=0.497, rc12=0.543, P < 0.01).

Conclusions: The results suggest that the surface shape of on-eye RGP contact lenses is not rigid, and its change depends on irregularity of the anterior corneal surface, even if the cornea itself is changed by the RGP contact lens. It is better not to fit for RGP so flatter than the average curvature of the cornea.