Abstract
PURPOSE
To evaluate visual benefit of correcting higher order aberrations in abnormal eyes when typical amounts of contact lens movement exist and to compare the tolerance of the movement to the visual benefit between normal and abnormal eyes.
METHODS
The large dynamic range Shack-Hartmann wavefront sensor1 was used to measure the wave aberration (up to 10th order) of four abnormal eyes, two with keratoconus and two with penetrating keratoplasty. From these data, the modulation transfer function (MTF) was calculated under the white light viewing condition and the volume MTF up to a 60 cycles/degree spatial frequency was used as a metric of retinal image quality. Visual benefit was also computed as the ratio of the MTF with the residual aberrations due to the different amounts of the lens movements to that with the conventional spectacle correction. The lens movement is statistically simulated based on Gaussian distribution.
RESULTS
When the lens is perfectly centered, averaged visual benefit for normal and abnormal eyes with a 6 mm pupil was a factor of approximately 3 and 9, respectively. The visual benefit was decreased as the lens movement increased. With a decentration of 0.2 mm (one standard deviation in Gaussian distribution), the visual benefit was reduced to a factor of 3 for the abnormal eyes and 2 for the normal eyes.
CONCLUSIONS
The movement of the contact lenses reduces visual benefit of correcting higher order aberrations in both normal and abnormal eyes. Based on four abnormal eyes, the tolerance of the movement to obtain visual benefit is larger in abnormal eyes than in normal eyes. When typical amounts of decentration and rotation of the contact lenses are considered, customized contact lenses can still improve retinal image quality of normal and abnormal eyes.
1.
PantanelliS.YoonG.JeongT.M.MacRaeS.(2003). “Large dynamic range Shack-Hartmann wavefront sensor for highly aberrated eyes,” Invest Ophthalmol Vis Sci, 2003; 44: ARVO E-Abstract 2536.