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L. Zheleznyak, M.-J. Kim, S. MacRae, G. Yoon; Effects of Chromatic Aberration, Decentration and Corneal Astigmatism on Through Focus Performance of Premium IOLs. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5725.
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Accommodating and multifocal premium IOLs (PIOLs) are intended to extend pseudophakic depth-of-field (DoF). Our aim is to measure the effects of chromatic aberration and corneal astigmatism on retinal image quality (RIQ) and DoF of PIOLs in vitro.
An optical bench system was developed to measure through focus image quality of a poly- and monochromatically illuminated USAF resolution target through a model eye. The model eye consisted of a wet cell with a Gullstrand-model artificial cornea (0.085µm spherical aberration for 4mm pupil) and an IOL mounted with decenter capability. Ophthalmic trial lenses were placed before the artificial cornea to simulate corneal astigmatism (up to 1.0D) and varying object distance (up to 5.0D). PIOLs examined were the aspheric accommodating Bausch and Lomb Crystalens HD (CHD), and the aspheric diffractive multifocals Alcon ReSTOR 3D (RST) and Tecnis ZM900 (TCN). The AcrySof SN60AT spherical monofocal (ASF) served as a control. All IOLs had 20D power and were tested with a 4mm pupil. RIQ was determined by measuring the contrast of images of the USAF target at spatial frequencies of 30 and 15 cycles per degree (cpd), corresponding to 20/20 and 20/40 Snellen letter sizes, respectively. DoF was defined as the dioptric range with RIQ at 15cpd greater than 50% of peak RIQ for ASF.
ASF had the best RIQ but was limited to distant vision (0 to 1.0D). CHD extended its DoF by 30% compared to ASF. Multifocal IOLs sacrificed distant RIQ (60% of ASF) for extended DoF with the addition of near vision, however they lacked intermediate vision. Chromatic aberration had a detrimental effect on RIQ for all lenses. RST and TCN were impacted less than ASF and CHD due to their inherently lower RIQ at distant vision. For up to 700µm decentration, changes in RIQ of white-light images for all IOLs were insignificant. Corneal astigmatism also reduced RIQ for all IOLs. DoF was not decreased with astigmatism up to 0.25D for TCN, although RIQ at 15cpd decreased by 5%. DoF was not decreased with astigmatism up to 0.5D for ASF (35% RIQ decrease), CHD (28% RIQ decrease) and RST (4.% RIQ decrease). With corneal astigmatism larger than 0.5D, DoF for PIOLs did not significantly differ from that with ASF.
The benefit of extended DoF with PIOLs is absent in the presence of corneal astigmatism larger than 0.5D. The uncorrected corneal astigmatism in pseudophakic patients can affect through focus performance of PIOLs and needs to be compensated to maximize their efficacy.
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