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M. J. Simpson, D. R. Carson, F. Zhou, X. Hong, X. Zhang, M. Karakelle; Laboratory Evaluation of Nighttime Halos for Multifocal IOLs. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5281. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the nighttime halos of multifocal intraocular lenses (IOLs) in the laboratory.
Nighttime halos are caused by defocused light that is directed to the second image of a multifocal IOL. The characteristics of the defocused light energy were evaluated in the laboratory using a model eye for several multifocal IOL designs. A 5 mm illuminated lens diameter was used to simulate typical conditions of nighttime vision in a pseudophakic eye. Direct measurement of the line spread function (LSF), which is the intensity across the image of a bright slit object, was found to provide an objective method for evaluating the defocused light energy. Quantitative measurements of the defocused halo intensity and size were made from LSF plots recorded using monochromatic light for several different lens designs. The LSF is the integral across the point spread function (PSF), which is the image of a point source. The LSF has the property of amplifying the intensity of the defocused halo of the PSF, which makes the measurement robust when evaluating the extremely faint halo of the ReSTOR Aspheric IOL. Images of the PSF were also recorded, using a pinhole to simulate a distant light source at night, with the same system settings for the different lenses so that a direct visual comparison can be made of the nighttime optical properties.
LSF measurements and pinhole images demonstrated that the ReSTOR Aspheric apodized diffractive multifocal intraocular lens, which directs most of the incident light to the distance focus under large pupil conditions at night, has a minimal defocused image component. These results were compared to those from a full-aperture equal-energy constant step height diffractive IOL (AMO Tecnis), and a 5-zone refractive IOL (AMO ReZoom). The laboratory results agree with clinical data, where the incidence of nighttime visual disturbances is low for ReSTOR IOLs.
Measurement of the LSF in a laboratory model eye can be used to quantitatively measure the nighttime halos for multifocal IOLs, and laboratory images of a pinhole source can be used for comparative evaluations of different IOL designs.
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