Illusions

Illusions are false perceptions of visual stimuli that disappear with eye closure. An illusion does not generally exist physically. These illusions can be monocular or binocular. Many illusions, whether those that are found in nature or those that are artificially created, are not associated with any disease state. There are, however, some illusions that occur in a diseased state. Multiple images seen out of one eye can be the result of ocular media aberrations such as corneal edema, irregular astigmatism or cataract. The pinhole technique can be used to differentiate between refractive or pathological etiology. Altered size and shape of images can be the result of anisometropia, aniseikonia, or anisophoria. Macular disease can also cause image differences such as retinal metamorphopsia, retinal micropsia, and retinal macropsia. Patients can see altered color imagery illusions, including cyanopsia, brunescence, or erythropsia. Decreased brightness is either a result of optic neuropathy, a dense hyphema, or vitreous hemorrhage. Clinical testing for optic neuropathy includes testing for relative afferent pupillary defect, photo-stress recovery test, neutral density filter, and testing for altered motion illusions with the Pulfrich stereo-illusion. Motion illusions can also occur with oscillopsia when there is a defective vestibulo-ocular reflex.