Fixational Saccades and Their Relation to Fixation Instability in Strabismic Monkeys

Upadhyaya, Suraj; Pullela, Mythri; Ramachandran, Santoshi; Adade, Samuel; Joshi, Anand C.; Das, Vallabh E.

doi:10.1167/iovs.17-22389

Cited by 16 publications

(15 citation statements)

References 34 publications

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“…They also show responses during quick-phases of nystagmus whose amplitudes overlap that of microsaccades. 50 We therefore suggest that misalignment-related cells are the same population of previously described fixation/microsaccade cells or perhaps constitute a subset that also carries information about strabismus angle.…”

Section: Are the Vergence And Misalignment-related Cells Distinct Frosupporting

confidence: 53%

Response Properties of Cells Within the Rostral Superior Colliculus of Strabismic Monkeys

Upadhyaya

Das

2019

Invest. Ophthalmol. Vis. Sci.

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PURPOSE. The superior colliculus (SC) is an important oculomotor structure which, in addition to saccades and smooth-pursuit, has been implicated in vergence. Previously we showed that electrical stimulation of the SC changes strabismus angle in monkey models. The purpose of this study was to record from neurons in the rostral SC (rSC) of two exotropic (XT; divergent strabismus) monkeys (M1, M2) and characterize their response properties, including possible correlation with strabismus angle.METHODS. Binocular eye movements and neural data were acquired as the monkeys performed fixation and saccade tasks with either eye viewing. RESULTS.Forty-two cells with responses likely related to eye misalignment were recorded from the rSC of the strabismic monkeys of which 29 increased firing for smaller angles of exotropia and 13 increased firing for larger exotropia. Twenty-six of thirty-five cells showed a pause (decrease in firing rate) during large amplitude saccades. Blanking the target briefly during fixation did not reduce firing responses indicating a lack of visual sensitivity. A bursting response for nystagmus quick phases was identified in cells whose topographic location matched the direction and amplitude of quick phases.CONCLUSIONS. Certain cells in the rSC show responses related to eye misalignment suggesting that the SC is part of a vergence circuit that plays a role in setting strabismus angle. An alternative interpretation is that these cells display ocular preference, also a novel finding, and could potentially act as a driver of downstream oculomotor structures that maintain the state of strabismus.A pproximately 5% of all infants in the world have some form of strabismus (ocular misalignment). 1,2 This developmental disorder is treated mostly at the level of muscles using surgical methods where the position of eye muscles are altered to correct for the eye misalignment. 3 Recent data from animal models of strabismus acquired using neurophysiological methods such as electrical stimulation, muscimol inactivation, and single cell recording within numerous brain areas including the motor nuclei, supraoculomotor area (SOA), fastigial and posterior interposed nuclei of the cerebellum, paramedian pontine reticular formation (PPRF), and the superior colliculus (SC), have shown that various structures within a vergence neural circuit contributes toward maintenance of the state of strabismus. [4][5][6][7][8][9][10][11] The SC has been extensively studied for its involvement in saccadic eye movements, 12-14 and this structure also appears to have a role in vergence. Van Horn et al.,15 in a study in normal monkeys, have shown that the rostral SC (rSC) contains vergence related neurons (convergence and divergence), which modulate with eye movements made to sinusoidal target motion in depth. 15 It has also been shown that stimulation of the rSC during an asymmetric vergence task affects vergence eye movement in normal monkeys. 16,17 Vergence related neurons have also been recorded in rSC of cat. 18 In humans, a case ...

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Section: Are the Vergence And Misalignment-related Cells Distinct Frosupporting

confidence: 53%

Response Properties of Cells Within the Rostral Superior Colliculus of Strabismic Monkeys

Upadhyaya

Das

2019

Invest. Ophthalmol. Vis. Sci.

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“…BCEA as a measure has several limitations including assumption of normality of the underlying position distributions; thus, the values can be affected by the presence of outliers (Castet & Crossland, 2012). Because BCEA is a measure of dispersion of eye position, it takes into account both the fast and slow eye movements and does not identify the presence of FMN (Upadhyaya et al, 2017). FMN is a characteristic oculomotor deficit suggestive of disruption of binocularity in the first six months of life.…”

Section: Introductionmentioning

confidence: 99%

Fixational eye movement waveforms in amblyopia: Characteristics of fast and slow eye movements

Kang

Beylergil

Otero‐Millan

et al. 2019

JEMR

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Fixational eye movements comprise of fast microsaccades alternating with slow inter-saccadic drifts. These physiologic eye movements play an important role in visual perception. Amblyopic patients are known to have fixation instability, particularly of the amblyopic eye. We examined eye movement abnormalities that contribute to this instability. We found that fixation stability is affected by the presence of fusion maldevelopment nystagmus (FMN). However, some amblyopes can have nystagmus without nasally directed slow phases and reversal in direction of the quick phase on ocular occlusion, features seen in FMN. In patients without nystagmus, we found increased amplitude of fixational saccades and inter-saccadic drifts. We categorized amblyopia patients by type (anisometropic, strabismic, or mixed) and eye movement waveform (no nystagmus, nystagmus without FMN, and FMN). We found specific fast and slow eye movement abnormalities of the fellow and amblyopic eye during fellow, amblyopic and both eyes viewing conditions across eye movement waveforms and types of amblyopia. These eye movement abnormalities can serve as biomarkers that can predict the impact of amblyopia as measured by visual acuity and stereopsis. Evaluation of fixational eye movements in amblyopia could be important to diagnose these common eye diseases and predict treatment effectiveness.

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“…Animal model studies have shown that disruption of binocularity during infancy is invariably associated with gaze instabilities, most often FMNS 6 , 58 . Tychsen and colleagues have shown in experiments that the prevalence and severity of FMNS increases with the longer duration of binocular decorrelation with 100% prevalence of FMNS in primates who are exposed to periods of binocular decorrelation that is equivalent to 3 months in humans.…”

Section: Discussionmentioning

confidence: 99%

Fixational eye movements abnormalities and rate of visual acuity and stereoacuity improvement with part time patching

Scaramuzzi

Murray

Nucci

et al. 2021

Sci Rep

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Residual amblyopia is seen in 40% of amblyopic patients treated with part-time patching. Amblyopic patients with infantile onset strabismus or anisometropia can develop fusion maldevelopment nystagmus syndrome (FMNS). The purpose of this study was to understand the effects of presence of FMNS and clinical subtype of amblyopia on visual acuity and stereo-acuity improvement in children treated with part-time patching. Forty amblyopic children who had fixation eye movement recordings and at least 12 months of follow-up after initiating part-time patching were included. We classified amblyopic subjects per the fixational eye movements characteristics into those without any nystagmus, those with FMNS and patients with nystagmus without any structural anomalies that do not meet the criteria of FMNS or idiopathic infantile nystagmus. We also classified the patients per the clinical type of amblyopia. Patching was continued until amblyopia was resolved or no visual acuity improvement was noted at two consecutive visits. Children with anisometropic amblyopia and without FMNS have a faster improvement and plateaued sooner. Regression was only seen in patients with strabismic/mixed amblyopia particularly those with FMNS. Patients with FMNS had improvement in visual acuity but poor stereopsis with part-time patching and required longer duration of treatment.

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Fixational Saccades and Their Relation to Fixation Instability in Strabismic Monkeys

Cited by 16 publications

References 34 publications

Response Properties of Cells Within the Rostral Superior Colliculus of Strabismic Monkeys

Response Properties of Cells Within the Rostral Superior Colliculus of Strabismic Monkeys

Fixational eye movement waveforms in amblyopia: Characteristics of fast and slow eye movements

Fixational eye movements abnormalities and rate of visual acuity and stereoacuity improvement with part time patching

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