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H. Zhao, J. T. Holladay, C. R. Reisin; The Negative Dysphotopsia of IOLs. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3336.
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To identify and assess angular scotoma of the intraocular lens (IOL), including its appearance and relative intensity. This phenomenon potentially produces noticeable negative dysphotopsia in pseudophakic eyes.
The interactions of light rays from a wall in a typical clinic room (Lambersian Dispersion) and an eye model with a double-square-edge IOL were examined using the ZEMAX ray-tracing program (ZEMAX Development Corp.). The potential of the angular scotoma to produce negative visual sensations was analyzed from plots of the spatial location and the energy distribution of rays forming the retinal image from previous studies of positive dysphotopsias.
Angular scotoma is produced by the typical double square-edge IOLs. It is caused by the internal reflection from the IOL edge. The missing light appears as a dark line or arc on the periphery of the retina at about 68 -70 degrees from the center with a width of about 5 degrees depending on the specific design of the IOL design and particularly the design of the edge. Because the human visual field only exceeds 65 degrees in the temporal field, the patient only perceives the negative dysphotopsia temporally. The average intensity of the dark line was about 3-4 orders of magnitude weaker than the average intensity of the surrounding area filled with refracted light by the lens edge and the optical surface. We also found that the width and position of the dark line is dependent on the depth of the IOL in the eye relative to the pupil, corneal power, and pupil size.
We have simulated the pseudophakic angular scotoma produced by IOLs with double square edges. This scotoma potentially produces the negative dysphotopsia phenomenon. The scotoma is caused by the internal reflection from the square edge of the IOL. Our simulations have confirmed the existence of the persistent narrow dark arc or line shape on the peripheral retina on temporal orientations, which is much weaker in intensity than the primary images or the glare images on the surrounding area.
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