Ocular Higher-Order Aberrations and Visual Acuity with Different RGP Lens Fittings in Keratoconus: A Case Report

BACKGROUND: Higher-order aberrations (HOA) become significantly elevated in keratoconic (KC) eyes. Changes in HOA with contact lens wear can be measured using a Shack-Hartmann aberrometer. This case report investigates the effect of rigid gas permeable (RGP) contact lens fitting on ocular HOA and visual acuity by systematically applying RGP lenses of different back optic zone radii (BOZR) to a KC eye. CASE REPORT(S): A 25-year old Asian male presented for contact lens fitting after being diagnosed with bilateral, moderate keratoconus. The patient had no previous history of contact lens wear and habitually wore spectacles with a refraction of +2.50/-2.25 x 80 in the right eye with logMAR acuity of +0.04 log units at 4 m. The patient’s right eye was systematically fitted with spherical Menicon-EX RGP lenses (Menicon Co., Nagoya, Japan), which ranged from a BOZR of 7.40 mm to 8.10 mm in 0.10 mm steps. The lenses were approximately 0.15 mm steeper to 0.55 mm flatter than the subjects average keratometric readings. All lenses fitted had a total diameter of 9.60 mm, centre thickness of 0.15 mm and back vertex power of –3.00 DS. Measurements of HOA were made with the lenses in place using a Shack-Hartmann aberrometer (IRX-3, Imagine Eyes, Paris, France). Best-corrected visual acuities with the lenses were recorded using a high-contrast logMAR chart at 4 m. As the lens BOZR value changed from 7.40 mm to 8.10 mm, vertical coma reduced from +0.34 µm to +0.21 µm; 3rd-order root mean square (RMS) error also reduced from +0.34 µm to +0.23 µm; total higher-order RMS aberrations decreased from +0.35 µm to +0.23 µm and the best-corrected acuity changed from +0.58 to -0.30 log units. CONCLUSIONS: The results showed that a flatter RGP lens fit led to a reduction in HOA and improvement in visual acuity in this moderately KC patient. Further investigations into the changes in ocular HOA with different RGP contact lens fittings and BOZR values in KC eyes will help to improve our understanding of how contact lens fitting impacts on optical performance.