Lens-Related Vision Disturbances
The presence of IOLs may cause numerous optical phenomena. Various light-related visual phenomena encountered by pseudophakic (and phakic) patients are termed dysphotopsias. These phenomena are divided into positive and negative dysphotopsias. Positive dysphotopsias are characterized by brightness, streaks, and rays emanating from a central point source of light, sometimes with a diffuse, hazy glare. Negative dysphotopsias are characterized by subjective darkness or shadowing. Such optical phenomena may be related to light reflection and refraction along the edges of the IOL. High-index acrylic lenses with square or truncated edges produce a more intense edge glare (Fig 6-11A). These phenomena may also be due to internal re-reflection within the IOL itself; such re-reflection is more likely to occur with materials that have a higher refractive index, such as acrylic (Fig 6-11B). With a less steeply curved anterior surface, the lens may be more likely to have internal reflections that are directed toward the fovea and are therefore more distracting (Fig 6-11C, D).
Figure 6-11 Lens-related vision disturbances. A, Light striking the edge of the intraocular lens (IOL) (not drawn to scale) may be reflected to another site on the retina, resulting in undesirable dysphotopsias. These problems arise less often with smoother-edged IOLs. B, Light may be internally re-reflected within an IOL, producing an undesirable second image or halo. Such re-reflection may be more likely to occur as the index of refraction of the IOL increases. C, Light may reflect back from the surface of the retina and reach the anterior surface of the IOL. The IOL acts as a concave mirror, reflecting back an undesirable dysphotopsic image. When the anterior surface of the IOL is more curved, the annoying image is displaced relatively far from the fovea. D, When the anterior IOL surface is less steeply curved, the annoying image appears closer to the true image and is likely to be more distracting.
(Redrawn by C. H. Wooley.)
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Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.