Visual Illusions

    • Visual transformations of viewed objects
    • Common causes
      • Optical disorder
      • Retinocortical disorder
      • Encephalopathy
      • Psychotropic medication
      • Recreational drug use
    • Faint, slightly displaced, reduplication of a viewed image that persists when one eye is covered (“ghosting”) = refractive error, corneal or lens imperfection
    • One or more haloes around an image = corneal edema
    • Minified image (“micropsia”) = maculopathy if monocular; vision-related cortex lesion if binocular and appearing identical to both eyes
    • Magnified image (“macropsias”) = maculopathy if monocular; vision-related cortex lesion if binocular and appearing identical to both eyes
    • Mildly distorted image (“retinal metamorphopsia”) = maculopathy; may be monocular or binocular, but if binocular, the distortion never appears identical to both eyes
    • Grossly (and sometimes grotesquely) distorted image (“cerebral metamorphopsia”, “Alice-in-Wonderland illusion”) = occipital stroke, tumor, psychotropic medications, recreational drugs, and rarely and temporarily in migraine; the distortion is always binocular and appears identical to both eyes
    • Smeared image that trails behind moving object (“comet illusion”) = psychotropic medications or recreational drugs, anxiety, psychosis
    • Moving object perceived as made up of multiple stationary copies of that object (“akinetopsia,” “stroboscopic vision,” “motion picture reel vision”) = occipital stroke, tumor, psychotropic medications, recreational drugs, anxiety
    • Two copies of a viewed image, one less clear than the other, one of which disappears as either eye is covered (“binocular diplopia”) = ocular misalignment of any cause
    • Multiple copies of a single image tailing off into homonymous hemianopia (“cerebral polyopia”) = occipital stroke, tumor
    • Reduced brightness or faded color of an image = optic neuropathy
    • Yellow tinge on borders of images (“xanthopsia”) = digitalis intoxication, trazodone
    • Golden brown image discoloration (“brunescence”) = cataract
    • Pink image discoloration (“erythropsia”) = pseudophakia
    • Blue image (“cyanopsia”) = use of phosphodiesterase inhibitors to improve erectile function
    • Visual hallucinations, which are not distortions of viewed objects, but “visual figments” unrelated to what is being viewed (See Visual Hallucinations )
    • Use the description of the altered image as a guide to diagnosis; confirm by examination
    • Ophthalmic, systemic, and neurologic examinations usually yield a diagnosis, but…
    • Trap: medications, recreational substances, and psychosis are often overlooked as causes!

    Visual Illusions

    Visual Illusions