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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Cerebral polyopia | 2/2 | https://en.wikipedia.org/wiki/Cerebral_polyopia | reference | science, encyclopedia | 2026-05-05T11:04:20.324237+00:00 | kb-cron |
== Theories of cerebral polyopia == The preliminary theory of cerebral polyopia proposed by Bender postulated that polyopia occurs as a result of instability of fixation due to occipital lobe disease. Under this explanation, small, involuntary eye movements that accompanied normal fixation were the cause of polyopic images. These involuntary eye movements lead to the development of new retinal and corresponding cortical regions that code for central vision called false maculae. Thus, polyopic images resulted from the stimulation of both the original and acquired maculae. However, Bender's theory does not account for recent studies in which fixation did not change and no eye movements were produced while polyopia was experienced, therefore polyopic images were not a result of involuntary eye movements. Instead, Cornblath offers a possible pathophysiological mechanism in which polyopia results from the recoding of visual receptive fields in primary visual cortex (Area V1). The report of polyopic images of complex objects at fixation suggests that the disorder is not limited to lower-order visual areas in occipital cortex (in which simple features such as borders and angles are encoded), but rather it involves the interaction between lower-order visual areas in the occipital lobe and higher-order visual areas in the temporal lobe that is postulated to code whole objects. Another possible pathophysiological mechanism for this disorder is the reorganization of receptive fields of neurons close to the damaged area of visual cortex. This theory is supported by findings that parafoveal retinal lesions deprive a region of striate cortex of visual input, and as a result, the receptive fields of neurons near the boundary of the deprived cortical region enlarge and expand into nearby regions of the visual field. Thus, polyopia results from altered coding of contour information by neurons near the lesioned area. This mechanism offers that after a focal lesion of neurons in striate cortex, or following a retinal lesion depriving these neurons of visual input, the receptive fields of nearby healthy neurons converge to code information about contours of objects normally coded by the damaged neurons while still coding the same information about retinal location prior to the injury. This mechanism may explain why polyopia extending into a patient's scotoma occurs following damage to primary visual cortex.
== Diagnosis ==
== Treatment == Since this condition is usually coupled with other neurological disorders or deficits, there is no known cure for cerebral polyopia. However, measures can be taken to reduce the effects of associated disorders, which have proven to reduce the effects of polyopia. In a case of occipital lobe epilepsy, the patient experienced polyopia. Following administration of valproate sodium to reduce headaches, the patient's polyopia was reduced to palinopsia. Further, after administering the anticonvulsant drug Gabapentin in addition to valproate sodium, the effects of palinopsia were decreased, as visual perseveration is suppressed by this anticonvulsant drug. Thus, in cases of epilepsy, anticonvulsant drugs may prove to reduce the effects of polyopia and palinopsia, a topic of which should be further studied. In other cases of polyopia, it is necessary to determine all other present visual disturbances before attempting treatment. Neurological imaging can be performed to determine if there are present occipital or temporal lobe infarctions that may be causing the polyopia. CT scans are relatively insensitive to the presence of cerebral lesions, so other neurological imaging such as PET and MRI may be performed. The presence of seizures and epilepsy may also be assessed through EEG. In addition, motor visual function should be assessed through examination of pupillary reactions, ocular motility, optokinetic nystagmus, slit-lamp examination, visual field examination, visual acuity, stereo vision, bimicroscopic examination, and funduscopic examination. Once the performance of such functions have been assessed, a plan for treatment can follow accordingly. Further research should be conducted to determine if the treatment of associated neurological disturbances can reduce the effects of polyopia.
== References ==