Abstract
Purpose: :
To measure visual acuity (VA) and contrast sensitivity (CS) through-focus functions (TFF) of eyes wearing multifocal contact lenses and to test the ability of image quality metrics based on wave aberration measurements to predict VA and CS TFF.
Methods: :
We measured the high-contrast VA (computer-generated Landolt-C optotypes) and the 12-c/deg CS (computer-generated randomly oriented sine-wave gratings) of 4 subjects aged between 20 and 37 years at various proximities in three conditions: (i) naked eye, (ii) with a center-distance Proclear multifocal addition 2D contact lens and (iii) with a center-near Proclear multifocal addition 2D contact lens. The accommodation of the subjects was paralysed using 0.5% cyclopentolate hydrochloride. The defocus term was subjectively adjusted by the observer to optimize the image quality of a 0.1 logMAR E-letter and the astigmatism term was corrected using the Imagine Eyes CRX1 Adaptive Optics System. The residual astigmatism was always lower than 0.1-D (0.08-µm on a 5-mm pupil diameter). Subjects viewed the stimulus, generated on a calibrated LCD micro-display subtending a visual angle of 114x86 arcmin, through a 5-mm artificial pupil conjugated to the pupil plane. The subject’s head was stabilized using a bite bar.
Results: :
Calculated CS TFF were comparable to measured CS TFF for all the test conditions. The CS TFF was defined as the product of the calculated MTF 12-c/deg and the neural contrast sensitivity measured by Williams. Moreover, a good correlation was obtained between predictions and measurements (r²=0.75). To predict VA TFF, MTF and OTF based metrics were calculated. The better correlation was obtained with the area under the MTF and CSF calculated between 5 and 15-c/deg (r²=0.67). However, the quality of the correlation was better when considering only the naked eye (r²=0.91).
Conclusions: :
Image quality metrics based on the MTF are able to predict the through-focus functions and consequently the depth-of-focus of an eye wearing or not a multifocal contact lens. The optical designers could predict the enhanced DOF occurring with new multifocal designs without the need to manufacture and test them in clinical studies, hence saving time and money.
Keywords: aberrations • presbyopia • contrast sensitivity