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H. S. Ginis, D. Kaltsa, D. Siedlecki, I. Pallikaris; Longitudinal Chromatic Aberration in Eyes Implanted With Acrylic Itraocular Lenses. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2423.
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© ARVO (1962-2015); The Authors (2016-present)
It has been reported that acrylic Intraocular lenses (IOLs) are characterized by increased longitudinal chromatic aberration (LCA) in respect to the natural crystalline lens. It was the purpose of this study to employ a method based on subjective refraction to measure LCA in a series of cataract patients implanted with monofocal acrylic IOLs.
A Badal optometer with interchangeable narrow-band (5nm FWHM) optical filters and broadband (incandescent lamp) target illumination was developed. A rail system enabled the axial displacement of the target and the measurement of its position. The target consisted of a vertical orientation grating involving various spatial frequencies ranging from 3 to 30 cycles/degree. Fourteen patients (sixteen eyes) implanted with acrylic IOLs (Lenstec Inc, St. Petersburg, FL) with dioptric powers ranging from 17 to 23.5 D and ten normal subjects (ten eyes) were enrolled in the study. All subjects had best spectacle corrected visual acuity higher or equal to 0.8. The subjects (corrected with trial lenses for sphere and cylinder) were instructed to focus the target by maximizing the number of visible grating lines. This ensured that in a simple criterion of subjective best focus was employed throughout the measurements. The task was repeated ten times for each wavelength and the corresponding positions of the target were recorded. The additional refraction of each patient was evaluated -using the above mentioned method- for seven different wavelengths ranging from 490 to 630 nm. Ten normal subjects under cycloplegia underwent the same measurements in order to validate the method. The study was conducted under Institutional board approval. An informed consent was obtained from each subject prior to the measurement.
The chromatic focal shift for the normal subjects as determined with the present method was 0.905 D (SD=0.24) between 490 and 630 nm, similar to the corresponding mean value reported in the literature (0.85D). The pseudophakic eyes exhibited a markedly higher chromatic focal shift (1.58 ± 0.52 D). Various polychromatic image quality metrics were calculated and retinal image quality was simulated.
Our results demonstrate that pseudophakic eyes implanted with acrylic IOLs have increased LCA in respect to intact eyes. Alternative IOL materials and designs with reduced LCA may provide better polychromatic retinal image quality. The corresponding visual benefit for cataract patients needs to be further investigated.
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