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Impact Of Astigmatism And Decentrations On Presbyopic Contact Lenses


Purpose: : The performance of presbyopic contact lenses usually depends on different wearer dependent factors. An approach to improve their success rate is to design lenses more tolerant to the most common factors. In particular, we studied the impact of residual astigmatism and decentration on the through-focus visual acuity (TFVA) with a multifocal contact lens by using an adaptive optics visual analyzer.

Methods: : A laboratory version of an adaptive optics (AO) visual analyzer was used. The instrument consists of a wavefront sensor to measure the eye’s aberrations and a liquid-crystal spatial light modulator to induce controlled optical phase maps into the subject’s eye while he or she is performing visual testing. The phase profile corresponding to the Air Optix Aqua Multifocal contact lens (CIBA VISION Corporation, Duluth, GA, USA) was induced on two normal early presbyopic subjects. TFVA was measured with SLOAN letters for a variety of conditions in white light for a 4 mm pupil diameter. The replicated contact lens profile was first well centered to the subject’s pupil, and subsequently decentered up to 1 mm in steps of 0.25 mm. In addition, -0.75 D and -1.25 D of astigmatism were also induced for the centered case. The complete measurement procedure was performed for one subject wearing the actual contact lens with the AO system in a passive mode and compared with the results obtained when the lens profile was replicated with the AO system.

Results: : TFVA curves were very similar between the actual contact lens case and the AO-generated phase profile case. This result supports the idea that this experimental approach can be followed to optimize the design of new contact lenses in real time. When the profile was decentered, the shape of the TFVA curves remained similar as in the centered case, but VA values were found to gradually decrease with decentration, to around 1/2 the original value (3-line loss) for 1 mm. The effect of residual astigmatism appears to be axis-dependent: while the addition of horizontal astigmatism had a small impact on the through-focus VA curves, vertical astigmatism produced a noticeable decrease in the VA values.

Conclusions: : We used an AO instrument to evaluate the tolerance of a presbyopic contact lens for decentration and residual uncorrected astigmatism. The particular tested phase profile appears to have different sensitivities to decentration and astigmatism. Future design modifications could lead to improved contact lenses more tolerant to common factors deteriorating image quality and reducing depth of focus.

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