Abstract
Abstract: :
Purpose: The purpose of this case study was to find a spectacle correction in keratoconus that can be used as an alternative when rigid contact lenses are too troublesome to wear. The subject has advanced keratoconus on both eyes, although the left eye has previously undergone penetrating keratoplasty. The uncorrected visual acuity of the best eye (OS) is 20/650 (0.03) and he is thus relying on rigid contact lenses for normal visual function. The aim was to find the best spectacle correction for the left eye from wavefront measurements. Methods: The wavefront aberrations of the left eye were measured with a specially designed Hartmann–Shack sensor. The reconstructed wavefront was then used to find the sphere and cylinder correction that optimizes the Strehl ratio of the retinal point spread function. Standard retinoscopy and subjective refraction were also tried in the examination the refractive errors. Results: The Strehl optimization rendered the spectacle correction –4.0 DS, –10.0 DC axis 10°. This refraction gives the subject a visual acuity of 20/40 (0.5), which is higher than what was found with subjective refraction. The importance of using image quality optimization to determine the refraction from the wavefront, compared to minimization of the RMS wavefront error, can be clearly seen in simulations of the retinal image quality. It was not possible to measure the refraction with retinoscopy, because the pupil reflex was too distorted. Conclusions: Since the aberrations of the current subject’s eye are large, it has previously not been clinically possible to give this subject a useful spectacle correction. The strength of the wavefront–based method, in cases with large irregular aberrations, is that it is truly objective. Thus, it can make a global optimization of the retinal image quality over a wide range of refractions without being confused by local maxima. It is thus an efficient tool to measure large and unusual refractive errors.
Keywords: keratoconus • low vision