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Ashley Valdez, Jim Schwiegerling; Novel Imaging Method for Multifocal and Monofocal Soft Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4638.
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© ARVO (1962-2015); The Authors (2016-present)
To develop an imaging method to assess depth of field across various ADD powers of soft multifocal contact lenses compared with monofocal soft contact lenses.
A system for measuring the imaging properties of soft contact lenses was developed using an achromatic doublet as a model cornea. The doublet was chosen so that one of its outer surfaces matched the base curve of the soft contact lens. An infrared imaging system was used after the contact lens was centered, hydrated and free of bubbles under its surface. Through the back of the doublet-contact lens system, a digital camera photographed images of external targets. The external targets consisted of a series of letter E’s placed at distances corresponding to object vergences of 0.75D to 4.00D in 0.25D steps. The sizes of the letters were scaled so that each letter subtended 20 arc min for their respective distances corresponding to a spatial frequency of 7.5 cyc/deg. In addition to these targets, a large distant target (20 feet) was used to facilitate focusing the system to infinity. Our focusing procedure was to place a -3.00D monofocal soft contact lens onto the eye model and focus the system on the distant target simulating corrected distance vision. While keeping the focus fixed, the monofocal lens was replaced with multifocal lenses of different add powers. Images were captured for each of the lenses and the contrast of the bars in the letter E was measured to determine the imaging properties of the lenses.
The contrast of the monofocal lens was negligible for the near targets across the 0.75D to 4.00D range. Peak contrasts and depths of field were identified for the multifocal lenses and were dependent upon add power.
A system for evaluating the add power and depth of field of soft monofocal and multifocal contact lenses was developed. This system is capable of differentiating optical properties across soft lenses.
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