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R. C. Bakaraju, K. Ehrmann, D. Falk, E. Papas, A. Ho; Prediction of the Optical Performance of Multifocal Contact Lenses Using a Physical Model Eye. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5753.
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To evaluate the in vitro optical performance of multifocal contact lenses (MFCL) using a physical model eye (ME) and also investigate the effects of lens decentration.
A physical ME with the facility to change refractive, accommodative states, and pupil sizes, permitting the ‘fitting’ and optical testing of contact lenses was constructed. The ME was configured to simulate the presbyopic state with an axial refractive error and then corrected with MFCLs (AirOptixTM, AcuvueTM, Focus ProgressivesTM, ProclearTM, and PureVisionTM) with high add (+2.50D). The performance of MFCL in conjunction with ME was tested using an optical bench set-up consisting of HeNe laser (632.8 nm), pinhole, microscope objective and a collimator. Single-pass points spread function (PSF) measures were obtained at 3, 4mm pupils and 3 accommodative states [0, 1.50 and 2.50D], using a photo-sensor (2.2µm pixel pitch) situated at the retinal plane. PSF’s were post-processed to yield radial modulation transfer function (rMTF). Through-focus Strehl ratio was evaluated in the image plane by moving the sensor back and forth by 0.75mm, in steps of 0.1mm. Full-width on-axis interval occurring at half-maximum of Strehl’s was considered as depth-of-focus (DoF). Centration of MFCL was monitored by an integrated tracking camera.
In comparison with the best achievable single vision correction, all MFCLs drew smaller areas under the rMTF, particularly for distant and intermediate target vergences and 4mm pupil. For near, AirOptixTM and PureVisionTM designs achieved better performance than others at low (5c/d) and mid (15c/d) spatial frequencies. Through-focus Strehl’s predicted DoF in the range of 0.4 to 0.8 mm (1.25 to 2.50D). The DoF measures were higher for center-near designs. Decentration of MFCLs reduced both overall performance and the cut-off spatial frequency, as expected.
The physical ME could discriminate between the performances of different MFCLs. When validated against clinical results, these predictions may facilitate better understanding of the performance and pitfalls of certain designs and assist practitioners in proper lens selection.
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