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Marrie Van der Mooren, Michelle Langeslag, George Beiko, Patricia Piers; visual impact of micro-vacuole defect in intraocular lenses. Invest. Ophthalmol. Vis. Sci. 2013;54(15):853.
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© ARVO (1962-2015); The Authors (2016-present)
The impact of micro vacuole defects in intraocular lenses (IOL) on quality of vision is subject to scientific debate. The purpose of this study is to estimate the visual effect of the micro vacuole defect in IOLs based on in-vitro straylight measurements.
The straylight induced by the micro vacuole defect was calculated by subtracting the straylight measurement results of an IOL with and without inclusions. The micro vacuole defects were induced by immersing IOLs in a saline solution and changing from room to eye temperature overnight. The visual effect is estimated by using the concept of equivalent veiling luminance introduced by Stiles-Holladay. The additional induced luminance could be calculated as function of visual angle and illuminance of the eye. Confocal microscopy, dark field imaging and straylight measurements were performed before and after the temperature change on the IOLs. Four different hydrophobic acrylic lenses made by respectively ALCON, B&L, AMO and HOYA were tested including IOLs recently manufactured with an improved process.
All lenses had straylight scatter less than a 20 yr old human crystalline lens before temperature change. After change of temperature in a water bath, micro vacuole formation was evident in dark field imaging in ALCON and HOYA hydrophobic acrylic lenses. The IOLs made with an improved process by the same manufacturer had similar levels of micro vacuole formation as previous IOLs. The straylight measurements results showed that IOLs susceptible to micro vacuole formation produced two optical fields arriving at different eccentric (retinal) locations. One field is diffracted by the surfaces of the micro vacuoles creating a white halo and the other field exists of colored fringes produced by the field propagating through the micro vacuole. An average micro vacuole size of 6 micrometer was obtained by confocal microscopy. For a typical micro vacuole density the scatter level increased 5 deg2/sr at 10 degrees of visual angle. In this condition and for 20 lux of ocular illuminance, a veiling retinal luminance of 1 cd/m2 is induced.
The angular straylight distribution induced by the micro vacuole defect consists of two optical fields: white halo and colored fringes. The visual effect was calculated in terms of veiling retinal luminance predicting a potentially debilitating contrast loss.
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