2. Optic ataxia – impairment of visual control leading to misdirection of the arm to the visual object of interest associated with defective hand orientation and grip formation. [1]

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While no specific diagnostic criteria exist for Balint syndrome, certain tools can be used to elucidate symptoms. Asking patients to interpret complex scenes such as the “Boston Cookie Theft” and the “Telegraph Boy” can reveal symptoms of simultanagnosia.[31][32]Patients will identify individual items in the picture but cannot correctly interpret what is happening in the scene. Patients will also have difficulty interpreting Ishihara color plates, which require combining colored dots into a larger number.[33] However, this is not due to color vision abnormalities, as patients will be able to correctly identify the individual colors on the plate.[33] If the three cardinal features of Balint syndrome are identified together or in isolation, this may warrant further neurologic evaluation with neuroimaging, and the ophthalmologist should consider referral to neurology for a more complete workup. There are no defined diagnostic criteria for imaging studies in Balint syndrome, but findings will be consistent with the underlying etiology. Non-contrast computed tomography (CT) of the head is usually the best initial test to rule out intracranial hemorrhage. Magnetic resonance imaging (MRI) may reveal bilateral damage to the parietal and occipital lobes due to ischemia, hemorrhage, neoplasm, or cortical atrophy. Single-photon emission computed tomography (SPECT) may show decreased cerebral perfusion.

Simultanagnosia may be due to a visual attention deficit due to damage to the visuospatial attention system in the parietal lobe and is associated with lesions in Brodmann’s areas 7, 10, and 39.[6][22] It has also been postulated to be related to defects in visual processing speed.[23]

1. Simultanagnosia – the inability to identify multiple objects simultaneously and conceptualize the whole picture despite the ability to identify individual items in the same scene ( e.g. of a forest picture, they can only identity individual trees but cannot identify the forest)

Hemispatial neglect, a condition affecting awareness of one side of the body or environment, may present similarly to Balint syndrome and the two may be present simultaneously.[25] Patients with hemispatial neglect may have defects in visual search mimicking oculomotor apraxia and defects in hand movement with visual guidance similar to optic ataxia. Patients may also experience “extinction” of objects in the neglected hemifield when objects are present in both fields resembling simultanagnosia.[25] The lesions in Balint syndrome, however, are bilateral and affect the parieto-occipital junction, whereas the lesions in hemispatial neglect typically affect the temporo-parietal junction on the right side. An extensive lesion in the parietal lobes may lead to both Balint syndrome and hemispatial neglect.[2][25]

Group delayand phasedelay

Oculomotor apraxia is the inability to shift gaze voluntarily without any evidence of extraocular muscle paralysis. Patients with oculomotor apraxia are unable to produce voluntary saccades, but involuntary reflexive saccades are intact. Balint first described this finding as “psychic paralysis of gaze” and was later described as “spasm of fixation” by Holmes.[2][3] While optic ataxia and simultanagnosia can be reported independently, oculomotor apraxia is typically associated with either optic ataxia or simultanagnosia.[22] Patients with Balint syndrome may also have an absent blink to threat response and bilateral inferior altitudinal visual field defects.[3][30]

I have a question regarding the calculation of group delay dispersion (GDD) using a mode source and a mode expansion monitor.

Third orderdispersion

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Balint syndrome can be disabling and when severe, patients act as though they are blind due to limited visual and spatial awareness. Patients may describe frequently bumping into objects due to a combination of poor depth perception and distance perception ( of which the latter is sometimes added as the fourth element of Balint syndrome) as well as inability to synthesize their surroundings.[22] Patients may also have difficulty eating and drinking due to the inability to reach for and grasp objects from their optic ataxia. Reading may also be a challenge, as some patients perceive letters individually and have difficulties grouping them into words from their simultanagnosia.[28] A recent paper reported a case of Balint syndrome in association with hallucinatory palinopsia in the context of hypoglycemic coma.[29]

The word ataxia comes from the greek "lack of order". Optic ataxia refers to the lack of coordination between visual input and motor output. The term "Ataxia" in this case is not related to cerebellar disease. Optic ataxia is thought to be related to a lesion in the superior parietal lobule and around the intraparietal sulcus. [24] [21] Isolated optic ataxia is associated with lesions in Brodmann’s areas 5, 7 , 19, 39, 37.[25][26] Optic ataxia in Balint syndrome may be associated with disconnection of the occipital lobe from the frontal lobe where the anterior motor centers are located and upper extremity movements are initiated.[26][27] Other explanations include defects in integrating panoramic visual information with upper extremity proprioception and impairments in visuomotor control without impairment of perception.[6][26]

Chromaticdispersion

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Our simulation setup is as follows: we have a simple ridge (straight) waveguide surrounded by a lower refractive index material. The waveguide material is dispersive (user-defined). We inject a mode source (fundamental TM mode) and then use a mode expansion monitor at a different position in the waveguide, where we extract the acquired unwrapped phase (through the Angle() command) of the complex transmission coefficient. To get the GDD, we compute the second derivative of the phase (simply taking the difference of the phase between neighbor frequency points -> we use a frequency-dependent broadband mode source with more than 100 frequency points).

Group delay

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The prognosis of patients with Balint syndrome is variable and depends on the underlying etiology. Acute causes such as infectious or cerebrovascular etiologies may carry a good prognosis if managed appropriately. However, progressive neurodegenerative etiologies such as Alzheimer’s or posterior cortical atrophy typically have a poor prognosis. Rehabilitation, however, is possible in most patients with Balint syndrome and many regain some functional capabilities and an improved quality of life.[34]

Optic ataxia is the inability to accurately point to or reach for objects under visual guidance with intact ability when directed by sound or touch despite normal strength. Therefore, a patient who can see an object may be unable to reach for it accurately until they physically contact it.

Balint syndrome is a rare condition with only a number of cases reported in the literature. It is most often secondary to a bilateral parieto-occipital lesion of which infarction is the most common. It is a disorder of visual and spacial coordination causing a discrepancy between visual input and motor output and constitutes the following triad:

Dispersion

We have a reference COMSOL 2D eigenmode simulation, and when calculating the GDD in "transmission", so placing the mode expansion monitor a certain distance in front of the mode source, we can nicely reproduce the reference result. Here, the waveguide length extends beyond the boundaries ("infinite" waveguide).

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We are also interested in "reflection", where the waveguide is now terminated a certain distance in front of the mode source (waveguide facet), and a part of the light is reflected back into the waveguide. When we compute the GDD using the phase in the mode expansion monitor (now in the backwards direction), the resulting GDD follows the general trend of the reference result, but is very noisy (oscillations).

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Balint syndrome most often occurs from bilateral symmetric lesions in the parietal and occipital areas however has been described with unilateral disease.[6] These lesions are typically due to watershed infarction from cerebral hypoperfusion at the location of the middle cerebral and posterior cerebral arteries which are particularly susceptible to hypoperfusion and cardiac arrest.[6][7][8] Other reported causes include neurodegenerative disease (such as Alzheimer's disease, posterior cortical atrophy /the visual variant of Alzheimer's disease, and cortical basilar degeneration), infectious diseases ( such as Creutzfeldt-Jakob disease (CJD), subacute HIV encephalitis, and cerebral toxoplasmosis), posterior reversible encephalopathy syndrome (PRES), progressive multifocal leukoencephalopathy (PML), primary central nervous system angiitis, cerebral adrenoleukodystrophy, brain metastasis, and reversible cerebral vasoconstriction syndrome). There is also a reported case of NMDA receptor encephalitis, and interestingly, during the COVID-19 pandemic, a couple of reported cases were related to bilateral occipital parietal strokes in patients with SARS-Cov-2[9][10][11][12][13][14][15][16][17][18][19]. Balint syndrome can also present in a specturm such as a recent case report of a patient who presented with optic ataxia, oculomotor apraxia and a left homonymous hemianopsia without simultanagnosia post resecetion of a right occipito-parietal glioblastoma. [20]

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Opticaldispersion

Groupvelocitydispersion

More recent research in non human primates suggests that a number of aspects of this condition is related to damage to specific functional modules related to attention, reaching, and saccades as well as state estimation.[21]

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Balint syndrome was first described in 1909 by Reszo Balint.[2] The original findings he described included an inability to perceive different items in a visual scene at the same time, an inability to voluntarily shift gaze to a fixation target, and the inability to reach for an object with the right hand but maintained ability to do so with the left hand.[2] Balint originally postulated that the constellation of findings was due to discordance between sensory and motor output.[2] Holmes and Horrax[3] described similar findings in a patient in 1919 but suggested that these deficits were due to visuospatial disturbances alone because the patient had no motor or sensory disturbances. The term “Balint’s syndrome” was not coined until 1954.[4] Today, many studies focus on the neural mechanisms of the individual components that comprise Balint syndrome rather than the syndrome itself.[5]

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See the attached plot for a comparison. We suspect that in reflection, there is some numerical noise/artifacts in the phase, giving rise to the large oscillations. Our question is how we should modify the simulation settings (for example monitor size/position, auto shutoff level, boundary conditions, ? , ...) to improve the phase in reflection? Could it be there is some numerical artifacts coming from the interaction between the injected mode source, the transmitted/reflected light or something close to the boundaries?

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The diagnosis of Balint syndrome is made clinically and is defined by the presence of three key features: (1) simultanagnosia (2) optic ataxia, and (3) oculomotor apraxia. Certain tools can assist in the evaluation of a patient’s symptoms and neuroimaging can identify the underlying etiology.

Group delay dispersioncalculator

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Simultanagnosia is the inability to visually recognize more than one object at a time. A classic example is a patient’s inability to recognize a picture of a forest despite recognizing the trees within it (literally missing the forest for the trees). Two types of simultanagnosia have been described.The dorsal type and the ventral type. The dorsal type (usually seen in bilateral parietal lesions) is when the patient cannot see more than one object at a time in the same scene. This would cause the patient to bump into objects when navigating the surroundings. The ventral type ( usually seen in left inferior occipital temporal lesions) , on the other hand, refers to patients who can see multiple items at the same time within the same scene however cannot conceptualize the whole scene when put together. These patients do not have problems bumping into objects. [25]

3. Oculomotor apraxia – the inability to voluntarily shift gaze to the object of interest despite intact extra-ocular muscle function

The management of Balint syndrome begins with addressing the underlying etiology and employing secondary preventive measures. Beyond this, treatment is centered on rehabilitation and adaptive strategies to reduce disability. Neuropsychological rehabilitation strategies include restoration which works by training the impaired function and therefore the damaged part of the brain, and compensation, which refers to improving an intact function to compensate for the loss of another.[34] Most rehabilitation regimens in Balint syndrome are multifaceted, but compensatory strategies have appeared to be the most beneficial.[34] Some studies, however, have employed the restorative approach by using eye movement or convergence exercises which is sometimes successful.[34]