Cerebral Polyopia (Cerebral Diplopia)
Visual perseveration is a positive visual phenomenon in which the visual image either recurs, persists, or is duplicated. There are three different types of visual perseveration which can occur in isolation or in combination; llusory visual spread in which the visual image is not contained within its spacial boundary, palinopsia in which there is perseveration of a visual image in time, and Cerebral Polyopia, also known as Cerebral Diplopia, in which there is perseveration of a visual image in space,1 resulting in the perception of multiple images from a single visual stimulus. In other words, there is persistence of two or more duplicated images even after the stimulus is removed.
Cerebral polyopia, which is an extremely rare phenomenon, occurs even with monocular viewing of each eye, distinguishing it from strabismic diplopia, but disappears when the stimulus is removed. Additionally, it does not improve with pinhole distinguishing it from ocular abnormalities such as cataract and refractive error.
The presentation of the duplicated image(s) varies between patients. When only two images are observed, the original and the duplicate, the phenomenon is labeled as cerebral diplopia, a subtype of cerebral polyopia. Additional differences between patients include but are not limited to the following;  the number of duplicated images which can reach up to hundreds of images, the distance between the target stimulus and the duplicated images, the size and color of the duplicated images compared to the original, and duration of time in which the duplicated images remains.
Cerebral polyopia was first reported in 1908 by Dr. Giovanni Mingazzini, who described the disease in relation to an occipital lobe injury . In 1945, Dr. Morris B. Bender’s work further described polyopia through the documentation of four individuals with the disease . Since then, reports of cerebral polyopia have remained limited. The extreme rarity of the disease, the similarities to other more common visual disturbances, and the variations in the presentation have hindered the ability to properly understand the etiology of the disease as well as find appropriate treatments .
The mechanisms underlying the disease are uncertain and continue to be investigated . However, most instances of polyopia are associated with a lesion in the occipital lobe, more specifically the visual association cortex, or following occipital lobe epilepsy . Cerebral polyopia may result from a variety of cerebral injuries including but not limited to trauma, ischemic stroke, migraine, encephalitis, seizures, tumors, and multiple sclerosis . Most of the cases of cerebral polyopia have been described to be associated with visual field deficits and are thought to localize to the occipital lobe. A more recent case reports cerebral polyopia in a patient with a left fronto-parietal infarction sparing the occipital lobe and with no visual field deficit 
Multiple theories have been postulated for the underlying mechanisms. The initial theory proposed by Bender explains the duplicated images as a result of the instability of fixation during small, involuntary eye movements. This leads to the creation of new retinal and cortical regions that code for a false macula which is the underlying cause of the duplicated images . However, evidence from more recent case studies did not support this theory as cases where the polyopic images were thought not to correspond with the degree of involuntary eye movement. Another possible pathophysiological mechanism proposed by Cornblath suggests that reorganization of the receptive fields of neurons near the damaged area of the visual cortex could lead to cerebral polyopia .
Kesserwani proposed an alternative theory suggesting the underlying mechanisms regarding cerebral polyopia resemble a hologram . The theory is modeled after a case study of a 70-year-old woman with a cerebral infarct of the striate cortex, V1, and visual association cortex V2 who displayed symptoms of cerebral polyopia. By providing a predictive mathematical and experimental foundation using Fourier transforms, Kesserwani provided a template for how the holographic or holonomic brain theory can explain the duplicated images seen in cerebral polyopia . Isherwood proposed that normal-appearing white matter that is microstructurally abnormal may be the cause of this phenomenon .
Visual Trailing Palinopsia is a condition that is often confused with polyopia. Visual trailing palinopsia occurs when an object that is seen in motion leaves copies behind in the visual field, thus creating a “visual echo” with multiple images appearing. Cerebral polyopia can be distinguished from visual trailing palinopsia by the effect of movement on the duplicated images. In visual trailing, the palinoptic images are left in the wake of a moving object, while in polyopia, the polyopic images move with the original object . In addition, the original object may be removed but the patient will continue to see the stationary image in cerebral polyopia. Kataoka proposes that the two diseases may be related pathophysiologically but acknowledges that they are two distinct phenomena .
Diplopia and polyopia can occur distinctively from cerebral polyopia when cerebral function is not involved. Diplopia is a relatively common occurrence and can be caused by the misalignment of the eyes, such as in strabismus . Monocular diplopia has a lower prevalence than binocular diplopia and occurs when two images are seen with one eye closed . This may occur when light is not reflected to the back of the retina appropriately, seen in refractive errors or cataracts . Cerebral polyopia specifically occurs following cerebral damage and is significantly rarer than the aforementioned phenomenon .
Determination of all visual disturbances is vital in the diagnosis of cerebral polyopia. Often, cerebral polyopia presents alongside other more common disturbances such as palinopsia . A thorough history, including medications and the onset of symptoms can help determine if the cause of the polyopia is cerebral. Following this analysis, neuroimaging should be done to detect possible infarctions or other lesions . CT scans are not the most effective at identifying lesions, so ideally PET and MRI may be performed to aid in the diagnosis of cerebral polyopia.
There is no known cure for cerebral polyopia, and treatments vary on a case-by-case basis. The underlying cerebral mechanism causing the visual disturbances may help guide treatment plans. A case study on a patient experiencing cerebral polyopia secondary to occipital lobe epilepsy reported positive effects following the administration of valproate sodium and Gabapentin, an anticonvulsant drug . Following treatment, the effects of polyopia were reduced to palinopsia and the severity of visual disturbances were reduced . Further testing and a larger sample size is required to analyze the effectiveness of these drugs on treating cerebral polyopia as well as the generalizability to future patients.
There is no known evidence or case-reports regarding appropriate medical follow-up.
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