Varifocal contact lenses for the correction of presbyopia.
A Nissel +1.75 D PS45 lens' label power seems to be made up of about +0.75 D distance and +0.75 D near addition. There are individual variations which will depend on pupil size, corneal shape, lens position and ocular aberrations. When a +0.75 Bausch & Lomb U3 lens was used as a control, there was also a significant increase in 'accommodation' measured (+0.75 D), but this could not be explained. When two other lenses with an aspheric surface were studied, they also showed a near addition effect. In this supplementary study the changes were explained by changes in spectacle accommodation. A lens with two spherical surfaces did not show the expected increase in spectacle accommodation. Astigmatism, as a general rule, was not corrected by the PS45 lens, although the very occasional case did show some reduction. Visual acuity and contrast sensitivity at 8 cpd and 3 cpd were not significantly affected when compared to the control lens.
Port
M
M
Department of Optometry and Visual Science, City University, London, UK.
Refson
K
K
Minards
J
J
D000065:Accommodation, Ocular / Q000502:physiology; D000293:Adolescent; D000328:Adult; D001251:Astigmatism / Q000628:therapy; D003263:Contact Lenses, Hydrophilic; D015350:Contrast Sensitivity; D005139:Eyeglasses; D005260:Female; D006801:Humans; D008297:Male; D011305:Presbyopia / Q000534:rehabilitation*; D014792:Visual Acuity