Visual acuity and ocular aberrations with different rigid gas permeable lens fittings in keratoconus.

OBJECTIVES

The aim of this case report is to investigate the effect of rigid gas permeable (RGP) lens fitting on visual acuity and ocular higher-order aberrations by systematically applying RGP lenses with different back optic zone radii (BOZR) to a keratoconic eye.

METHODS

Eight Menicon-EX RGP lenses (Menicon Co., Nagoya, Japan), which ranged from a BOZR of 7.40 to 8.10 mm in 0.10-mm steps, were fitted to a moderate keratoconic eye. All the trial lenses fitted had a total diameter of 9.60 mm, centre thickness of 0.15 mm, and a back vertex power of -3.00 diopter sphere. Measurements of the higher-order aberrations were made with the RGP lenses in place using a Shack-Hartmann aberrometer (IRX-3; Imagine Eyes, Paris, France). Visual acuities with the lenses were recorded using a high-contrast Early Treatment Diabetic Retinopathy Study letter chart at a distance of 4 m.

RESULTS

As the lens BOZR value changed from 7.40 to 8.10 mm, the vertical coma component was found to reduce from +0.34 to +0.21 microm; third-order root mean square error also reduced from +0.34 to +0.23 microm and total higher-order root mean square aberrations decreased from +0.35 to +0.23 microm. More over, changes in the lens BOZR from 7.40 to 8.10 mm led to a substantial change in best-corrected LogMAR acuity from +0.58 to -0.30 log units.

CONCLUSIONS

The results showed that a flatter RGP lens fit lead to a reduction in higher-order aberrations and improvement in visual acuity in this moderate keratoconic patient. Further investigations into the changes in aberrations with different RGP lens fittings and BOZR values in keratoconic eyes will help to improve our current understanding of how contact lens fitting impacts on optical performance.