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Carmen Canovas, Patricia Piers, Mengchan Sun, Aixa Alarcon, Henk A Weeber, George Waring; Impact of residual astigmatism on optical and visual performance for toric intraocular lenses. Invest. Ophthalmol. Vis. Sci. 2018;59(9):254. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The purpose of this study is to evaluate the effect of residual astigmatism on optical and visual performance using realistic eye models for toric intraocular lenses (TIOL).
Two computer eye models, one with average corneal spherical aberration (SA) and other with additional higher order aberrations (HOA), were used to evaluate the performance of two different TIOLs with two levels of SA and different amounts of dispersion (model ZCT, that fully compensates average corneal SA and has an Abbe-number of 55, and model SN60AT, that provides a partial correction of corneal SA and has an Abbe-number of 37). The radially averaged modulation transfer function (MTF) was calculated in white light by ray tracing in the presence of up to 1.6D of astigmatism (commensurate of 20° of TIOL rotation) for different toric powers (1.50, 2.25 and 3.00D) and for two different pupil sizes. Simulated visual acuity (sVA) was calculated using the area under the MTF from 0 to 50 cycles per mm (Alarcon et al. Biomed. Opt. Express 2016).
TIOL rotation resulted in residual astigmatism, that depended on the power of the TIOL and the rotation, not on the IOL model or the pupil size. For example, residual astigmatism for 10 degrees of rotation was between 0.4D and 0.8D for TIOL powers ranging between 1.5D and 3.0D. This residual astigmatism resulted in a loss of visual acuity between 0.10 and 0.14 logMAR per diopter of cylinder, in agreement with the literature (Waltz et al, Ophthalmology 2014).MTF was reduced by residual astigmatism for all IOL models and conditions. This reduction was lower for the eye model with HOA and larger for bigger pupils. Simulations in the eye with HOA for a 3mm pupil showed that, for residual astigmatism up to 0.8D, the model ZCT provided an improvement in contrast between 10% and 16% with respect to the SN60AT. For the same residual astigmatism range, contrast for 5mm pupil was between 16% and 25% better for ZCT than for SN60AT. For greater values of residual astigmatism, the contrast was comparable for the two TIOL models.
Simulations in computer eye models were able to predict the loss in VA due to residual astigmatism found in clinical data. Residual astigmatism caused by TIOL rotation degrades contrast and depends on pupil size and corneal aberrations. Up to a 10 degrees of rotation, ZCT provides contrast values approximately 10% and 25% better than SN60AT.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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