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H. A. Weeber, P. A. Piers; Analysis of the Bull’s Eye Intraocular Lens Concept in the Presence of Defocus. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1627.
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© ARVO (1962-2015); The Authors (2016-present)
To analyze the effect of a central optical refractive structure imposed on a monofocal refractive intraocular lens (IOL) on the pseudophakic retinal image quality, in the presence of defocus.
The bull's eye concept consists of an aspherical monofocal IOL, correcting for the population averaged corneal spherical aberration, with a central circular zone having an additional power. The optical quality was expressed in terms of volume within the polychromatic modulation transfer function (pMTFV). A multivariate analysis was performed considering the following parameters: central zone diameter (1.0, 1.5, and 2.0 mm), add power (0.5, 1.0 and 1.5 diopters), and the pupil diameter (2.0, 3.0 and 4.0 mm). The pMTFV was calculated in the presence of defocus up to 2.5 diopters. As a reference, standard spherical and aspherical IOLs, having different amounts of negative spherical aberration, were evaluated.
For 2.0 mm and 3.0 mm pupil, the best pMTFV for the bull’s eye concept was equal or lower than that of the standard spherical or aspherical IOL. For a 4.0 mm pupil, the best pMTFV for all bulls eye concept was comparable or better than that of the standard spherical, but lower than that of a standard aspherical IOL.Loss of pMTFV was generally accompanied by an increased tolerance to defocus. The combinations of central zone diameter/add power of 2.0mm/1.0D and 2.0mm/1.5D showed a distinct bifocal behavior (see figure). This may indicate that the concept is prone to dysphotopsia (halos) under certain conditions.
The bull’s eye concept reduces the best focus retinal image quality, while increasing the tolerance to defocus. For large pupils, the best focus retinal image quality is comparable to that obtained with a regular IOL. Under certain conditions, the concept can exhibit a bifocal behavior, suggesting that dysphotopsia may occur.
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