Cerebral polyopia is one of three types of visual perseveration. It is a phenomenon in which multiple images are spatially replicated from a single visual stimulus, and is also called “cerebral diplopia.” When only two replicated images are perceived, it is classified as “cerebral diplopia.”
The three types of visual perseveration are as follows:
Illusory visual spread
Palinopsia (a phenomenon in which an image perceived in the past reappears)
Cerebral polyopia: a phenomenon in which multiple images are perceived simultaneously from a single stimulus
It occurs even with monocular vision in each eye, so it is distinguished from strabismic diplopia due to eye movement disorders. It can also be distinguished from monocular diplopia caused by cataracts or refractive errors because it does not improve with a pinhole.
Historical background: In 1908, Dr. Giovanni Mingazzini first reported it as a condition associated with occipital lobe damage. In 1945, Dr. Morris B. Bender described four cases.
Epidemiology: It is extremely rare, with limited reports. Its rarity, similarity to other visual disorders, and wide variation in symptoms pose barriers to understanding its etiology and discovering treatments.
QHow is cerebral polyopia different from ordinary double vision?
A
Strabismic diplopia is binocular and disappears when one eye is closed. In contrast, cerebral polyopia produces duplicate images even with monocular vision and does not disappear when one eye is closed. Furthermore, it does not improve with a pinhole, distinguishing it from monocular diplopia due to refractive errors or cataracts.
Perception of multiple images: A single object appears as two or more images. The number of images can range from two (cerebral diplopia) to several hundred.
Monocular occurrence: The multiple images do not disappear when one eye is closed.
Disappearance after stimulus removal: The multiple images often disappear when the stimulus is removed. In some patients, they persist as static images.
Movement with the original object: The multiple images move together with the original object. This helps differentiate from palinopsia.
Induced by gaze: Can be triggered by watching TV or near gaze 1).
Painless and intermittent: In cases of PPC infarction, painless and intermittent horizontal diplopia was reported. There was no directional preference 1).
Variation among patients: The number of duplicate images, distance from the original image, size, color, and duration vary greatly among patients.
Clinical Findings (Findings Confirmed by Physician Examination)
Eye movements: Often normal in all directions. The absence of obvious eye movement disorder is characteristic 1).
Pupils and eyelids: Often no abnormalities are observed 1).
Visual field: Many occipital lobe lesions involve visual field defects (e.g., homonymous hemianopia). However, in PPC infarction cases, the visual field may be normal 1). Occipital lobe disorders may lack neurological symptoms other than homonymous hemianopia.
Visual neglect: Not observed in the above PPC infarction cases 1).
Cognitive function: In patients with cerebral disorders, cognitive decline or attention deficits may cause the patient to be unaware of visual symptoms.
MRI-DWI: In acute infarction, the responsible lesion (e.g., occipital lobe or posterior parietal cortex infarction) can be visualized 1).
QHow to differentiate cerebral polyopia from palinopsia?
A
In palinopsia (visual afterimage type), duplicate images remain in the wake of a moving object after it passes. In cerebral polyopia, the key distinguishing point is that duplicate images move together with the original object.
The main causes of cerebral polyopia are lesions of the occipital lobe (especially the visual association cortex) and occipital lobe epilepsy. Most previous reports are associated with occipital lobe disease, and the case of PPC infarction by Kesserwani (2021) was the first report 1).
List of causative diseases is as follows.
Ischemic stroke: Often caused by infarction of the posterior cerebral artery supplying the occipital lobe.
Head trauma: Onset due to traumatic occipital lobe injury.
Migraine: May appear transiently in association with migraine attacks.
Tumor: Space-occupying lesion in the occipital or parieto-occipital lobe.
Encephalitis: Inflammatory lesion affecting the occipital lobe.
Multiple sclerosis: When demyelinating lesions involve the occipital lobe.
Many cases involve visual field defects, with lesions localized to the occipital lobe. There are also reports of cases with left frontoparietal infarction sparing the occipital lobe and lacking visual field defects (Isherwood).
Right parieto-occipital damage may cause visual perseveration. Bilateral parieto-occipital lesions lead to Balint syndrome.
When cerebral infarction is the cause, it is important to search for embolic sources including the heart and aorta. In cases of PPC infarction, paroxysmal atrial fibrillation (heart rate 132/min) was detected by a cardiac event monitor one week after onset, and it was determined to be an embolic infarction 1).
The most common causes are ischemic infarction of the occipital lobe, trauma, epilepsy, and migraine. Tumors, encephalitis, and multiple sclerosis can also be causes. Cerebral diplopia associated with posterior parietal cortex (PPC) infarction has also been reported, and the lesion site is not limited to the occipital lobe.
For the diagnosis of cerebral polyopia, it is essential to identify all visual disturbances. Since it often coexists with other visual disturbances such as palinopsia, a detailed medical history is important. Based on an interview including medications and timing of symptom onset, it is determined whether the condition is of cerebral origin.
MRI (including DWI): Useful for detecting acute infarction. PET is also effective for identifying lesions. CT is not the most effective for lesion identification.
MRI-DWI: In cases of PPC infarction, acute infarction of the left posterior parietal cortex was confirmed1).
Cardiac event monitor: Useful for detecting arrhythmias such as atrial fibrillation in embolic infarction1).
Carotid ultrasound and transcranial Doppler: Used to rule out vascular lesions (stenosis/occlusion)1).
Visual field test: Used to assess the presence of visual field defects and estimate the location of the lesion. Correlation with neuroimaging is useful for precise lesion estimation.
Higher visual function tests: Perform tests specific to symptoms predicted from the lesion location.
In the differential diagnosis of diplopia, monocular diplopia is often caused by problems in the anterior segment or transparent media (e.g., refractive errors, cataracts). Binocular diplopia includes differential diagnoses such as ocular motility disorders, cranial nerve palsy, myasthenia gravis, and thyroid eye disease. Cerebral polyopia differs from these as eye movements are normal.
There is no established curative treatment. Treatment varies by case, and the brain mechanisms causing visual disturbances guide the treatment plan. There are no known evidence or case reports regarding appropriate follow-up.
Embolic cerebral infarction: Anticoagulation therapy is indicated. For cases of PPC infarction (embolic infarction + atrial fibrillation + elderly), apixaban 2.5 mg twice daily was initiated1).
Prevention of recurrence of cerebral infarction: Antithrombotic therapy (antiplatelet drugs: aspirin, etc.; anticoagulants: warfarin, etc.) is performed.
Cerebral infarction in the very early stage after onset: Consider thrombolytic therapy with t-PA or endovascular treatment.
Cases secondary to occipital lobe epilepsy: A case (Kataoka) has been reported in which cerebral polyopia reduced to oscillopsia after administration of sodium valproate plus gabapentin.
Several theories have been proposed regarding the mechanism of cerebral polyopia.
Fixational Instability Theory
Proponent: Bender
Overview: Fixational instability during involuntary microsaccades leads to the formation of a pseudofovea, resulting in duplicate images.
Current status: Recent case studies have reported instances where the degree of polyopia does not correlate with eye movements, and this theory is no longer supported.
Receptive Field Reorganization Theory
Proponent: Cornblath
Overview: It was proposed that duplicate images occur due to reorganization of receptive fields of neurons near the damaged area of the visual cortex.
Holonomic Brain Theory
Proponent: Kesserwani (2020)
Overview: Based on a case of a 70-year-old woman with V1/V2 infarction. Proposed as a holographic/holonomic brain theory with mathematical and experimental foundations using Fourier transforms.
Convergence Insufficiency Theory
Proponent: Kesserwani (2021)
Overview: Convergence insufficiency due to a network disorder of the posterior parietal cortex (PPC) → frontal eye field (FEF) → midbrain reticular formation/PPRF causes horizontal diplopia1).
Convergence pathway: Occipital lobe + PPC → FEF → thalamus (pulvinar) + basal ganglia → midbrain reticular formation (near-response cells: tonic cells, burst cells, tonic-burst cells; firing rate proportional to convergence angle and velocity) → Edinger-Westphal nucleus (EWN, final common pathway; controls pupillary constriction and convergence). PPRF, NRTP, and the interposed and fastigial nuclei of the cerebellum are also involved.
MLF and convergence: The medial longitudinal fasciculus (MLF) is not involved in convergence. MLF lesions alone do not cause convergence insufficiency.
Diaschisis (functional deafferentation): PPC infarction causes electrical silence in the FEF, and this cascade spreads to the midbrain reticular formation and PPRF, resulting in convergence insufficiency and horizontal diplopia.
QWhy does posterior parietal cortex infarction cause diplopia?
A
Kesserwani (2021) proposed that convergence insufficiency due to network disruption of the posterior parietal cortex (PPC) → frontal eye field (FEF) → midbrain reticular formation/PPRF causes horizontal diplopia1). The mechanism is thought to be functional deafferentation (diaschisis) of the FEF due to PPC infarction, impairing convergence control.
7. Latest Research and Future Perspectives (Research-Stage Reports)
Kesserwani (2021) reported the first case of cerebral diplopia associated with left posterior parietal cortical ischemic infarction in a 90-year-old right-handed man 1). It was sudden-onset painless intermittent horizontal diplopia with normal eye movements in all directions, no visual neglect, and normal confrontation visual fields. Paroxysmal atrial fibrillation (heart rate 132/min) was detected on a cardiac event monitor, and embolic infarction was diagnosed. Based on this case, the convergence insufficiency theory was proposed, but direct confirmation of convergence insufficiency was not possible because the patient refused an ophthalmological examination.
fMRI studies on the neural basis of convergence control
In an fMRI study by Alvarez (2014), patients with convergence insufficiency showed decreased blood flow in the PPC, FEF, and cerebellar vermis, and blood flow in these regions significantly correlated with peak convergence velocity 1). It was also reported that vergence training improved blood flow patterns.
Future fMRI studies are needed to verify the mechanism of cerebral diplopia due to PPC infarction 1).
The efficacy of antiepileptic drugs (valproic acid + gabapentin) for cerebral polyopia secondary to occipital lobe epilepsy requires further clinical trials and validation with larger sample sizes.
Verification of the microstructural abnormality white matter hypothesis (Isherwood) also remains as a future challenge.
Kesserwani H. A Novel Case of Cerebral Diplopia Secondary to a Posterior Parietal Cortex Ischemic Infarct: Proposal of a Mechanism of Generation of Polyopia Due to Convergence Insufficiency. Cureus. 2021;13(1):e12962.
References (without citation numbers)
Bender MD. Polyopia and monocular diplopia of cerebral origin. Arch Neurol Psychiatry. 1945;54:323-38.
Cornblath WT, et al. Spatial characteristics of cerebral polyopia: a case study. Vision Res. 1998;38(24):3965-78.
Jones MR, et al. Cerebral polyopia with extrastriate quadrantanopia. J Neuroophthalmol. 1999;19(1):1-6.
