Steady Fixation Research Articles

Orchestration of saccadic eye-movements by brain rhythms in macaque Frontal Eye Field

Visual perception has been suggested to operate on temporal ‘chunks’ of sensory input, rather than on a continuous stream of visual information. Saccadic eye movements impose a natural rhythm on the sensory input, as periods of steady fixation between these rapid eye movements provide distinct temporal segments of information. Ideally, the timing of saccades should be precisely locked to the brain’s rhythms of information processing. Here, we investigated such locking of saccades to rhythmic neural activity in rhesus monkeys performing a visual foraging task. We found that saccades are phase-locked to local field potential oscillations (especially, 9–22 Hz) in the Frontal Eye Field, with the phase of oscillations predictive of the saccade onset as early as 100 ms prior to these movements. Our data also indicate a functional role of this phase-locking in determining the direction of saccades. These findings show a tight—and likely important—link between oscillatory brain activity and rhythmic behavior that imposes a rhythmic temporal structure on sensory input, such as saccadic eye movements.

The effect of pedicle screw instrumentation at a young age on upper thoracic vertebra and canal development

BACKGROUND CONTEXTPedicle screws are widely used in spinal surgeries. Pedicle screw fixation has shown better clinical effects than other techniques by providing steady fixation from the posterior arch to the vertebral body. However, there are several concerns about the impact of pedicle screw instrumentation insertion on vertebral development in young children, including early closure of the neurocentral cartilage (NCC). The effect of pedicle screw insertion in an early age on further growth of the upper thoracic spine is still unclear. PURPOSEThis study aimed to evaluate the impact of pedicle screw insertion on further growth of the upper thoracic vertebra and spinal canal. STUDY DESIGNA retrospective case study. PATIENT SAMPLETwenty-eight patients. OUTCOME MEASUREMENTSX-ray and CT parameters including length, height and area of the vertebrae and spinal canal were manually measured. METHODSTwenty-eight patients who underwent pedicle screw fixation (T1-T6) before the age of 5 years from March 2005 to August 2019 at Peking Union Medical College Hospital were recruited, and records were retrospectively reviewed. Vertebral body and spinal canal parameters were measured at instrumented and adjacent noninstrumented levels and compared using statistical methods. RESULTSNinety-seven segments met the inclusion criteria (average age at instrumentation 44.57 months, range from 23–60 months). Thirty-nine segments had no screws, and 58 had at least one screw. There was no significant difference between the preoperative and final follow-up values of the measurement of vertebral body parameters. No significant difference was observed between the growth rates in levels with or without screws in pedicle length, vertebral body diameter, or spinal canal parameters. CONCLUSIONPedicle screw instrumentation in the upper thoracic spine does not cause a negative effect on the development of the vertebral body and spinal canal in children younger than 5 years old.

Spatial and Temporal Abnormalities of Spontaneous Fixational Saccades and Their Correlates With Positive and Cognitive Symptoms in Schizophrenia.

Visual fixation is a dynamic process, with the spontaneous occurrence of microsaccades and macrosaccades. These fixational saccades are sensitive to the structural and functional alterations of the cortical-subcortical-cerebellar circuit. Given that dysfunctional cortical-subcortical-cerebellar circuit contributes to cognitive and behavioral impairments in schizophrenia, we hypothesized that patients with schizophrenia would exhibit abnormal fixational saccades and these abnormalities would be associated with the clinical manifestations. Saccades were recorded from 140 drug-naïve patients with first-episode schizophrenia and 160 age-matched healthy controls during ten separate trials of 6-second steady fixations. Positive and negative symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS). Cognition was assessed using the Measurement and Treatment Research to Improve Cognition in Schizophrenia Consensus Cognitive Battery (MCCB). Patients with schizophrenia exhibited fixational saccades more vertically than controls, which was reflected in more vertical saccades with angles around 90° and a greater vertical shift of horizontal saccades with angles around 0° in patients. The fixational saccades, especially horizontal saccades, showed longer durations, faster peak velocities, and larger amplitudes in patients. Furthermore, the greater vertical shift of horizontal saccades was associated with higher PANSS total and positive symptom scores in patients, and the longer duration of horizontal saccades was associated with lower MCCB neurocognitive composite, attention/vigilance, and speed of processing scores. Finally, based solely on these fixational eye movements, a K-nearest neighbors model classified patients with an accuracy of 85%. Conclusions: Our results reveal spatial and temporal abnormalities of fixational saccades and suggest fixational saccades as a promising biomarker for cognitive and positive symptoms and for diagnosis of schizophrenia.

ABC of Gaze and Ocular Oscillations.

The chief goal of all eye movements is to maintain the image of an object steady on the retina especially the macula to preserve visual acuity. Gaze palsy refers to lack of the conjugate movements due to a failure of supranuclear control mechanisms. Supranuclear control is maintained by not one, but multiple eye movement systems and gaze mechanisms. Supranuclear gaze palsies can be associated with a myriad of aetiologies- from trauma or metabolic abnormalities to stroke, demyelinating disorders and space occupying lesions like tumours. Culprit lesions may be in frontal motor centres, brainstem gaze centres gaze or interconnecting segments. While the brainstem network for horizontal gaze lies in pons, that for vertical gaze is situated in midbrain. Further, ocular oscillations and nystagmus are abnormal eye movements that disrupt a steady fixation of gaze. It is prudent to be aware of various gaze pathways and their anatomical corelates in order to establish a topographic relationship of clinical findings. A systematic clinical examination may provide deep insights on the patho-physiological mechanisms along with aiding in localizing the lesion accurately. This review deals with systematic clinical approach to various gaze control systems.

Seeing the future: Predictive control in neural models of ocular accommodation.

Ocular accommodation is the process of adjusting the eye's crystalline lens so as to bring the retinal image into sharp focus. The major stimulus to accommodation is therefore retinal defocus, and in essence, the job of accommodative control is to send a signal to the ciliary muscle which will minimize the magnitude of defocus. In this article, we first provide a tutorial introduction to control theory to aid vision scientists without this background. We then present a unified model of accommodative control that explains properties of the accommodative response for a wide range of accommodative stimuli. Following previous work, we conclude that most aspects of accommodation are well explained by dual integral control, with a “fast” or “phasic” integrator enabling response to rapid changes in demand, which hands over control to a “slow” or “tonic” integrator which maintains the response to steady demand. Control is complicated by the sensorimotor latencies within the system, which delay both information about defocus and the accommodation changes made in response, and by the sluggish response of the motor plant. These can be overcome by incorporating a Smith predictor, whereby the system predicts the delayed sensory consequences of its own motor actions. For the first time, we show that critically-damped dual integral control with a Smith predictor accounts for adaptation effects as well as for the gain and phase for sinusoidal oscillations in demand. In addition, we propose a novel proportional-control signal to account for the power spectrum of accommodative microfluctuations during steady fixation, which may be important in hunting for optimal focus, and for the nonlinear resonance observed for low-amplitude, high-frequency input. Complete Matlab/Simulink code implementing the model is provided at https://doi.org/10.25405/data.ncl.14945550.

Hierarchy-Assembled Dual Probiotics System Ameliorates Cholestatic Drug-Induced Liver Injury via Gut-Liver Axis Modulation.

Cholestatic drug‐induced liver injury (DILI) induced by drugs or other xenobiotics is a severe and even fatal clinical syndrome. Here, living materials of hierarchy‐assembled dual probiotics system are fabricated by sequentially encapsulating probiotic Lactobacillus delbrueckii subsp. bulgaricus (LDB) and Lactobacillus rhamnosus GG (LGG) into Ca2+‐complexed polymer microspheres for effective prevention of cholestatic DILI. Upon entering intestinal tract of the constructed living materials, LGG is released because of pH‐triggered dissolution of outer enteric polymer coating. The released LGG can inhibit hepatic bile acids (BAs) synthesis by activating intestinal farnesoid X receptor‐fibroblast growth factor 15（FGF‐15) signaling pathway. BAs excretion is also facilitated by LGG through increasing the abundance of bile salt hydrolase (BSH)‐active gut commensal bacteria. Furthermore, exposed positively‐charged chitosan shell can absorb the excessive BAs via electrostatic interaction, which leads to steady BAs fixation by the imprisoned LDB, decreasing the total BAs amounts in enterohepatic circulation. Together, the fabricated living materials, obtained here, can effectively prevent cholestatic DILI through dredging cholestasis via gut‐liver axis modulation. The therapeutic effect is demonstrated in α‐naphthylisothiocyanate and clinical antiepileptic drug valproate acid‐induced cholestatic DILI mouse models, which reveal the great potential for effective cholestatic DILI management.

Evaluation of the effect of eye movements on the Sweep VEP

AbstractPurposeTo evaluate the effect of fixation stability on the sweep visual evoked potential (sVEP) visual acuity estimate in normal subjects.MethodsTwenty eyes of 10 subjects with normal ophthalmic exam and best‐corrected Snellen chart visual acuity (BCVA) of 20/20 or better in the tested eye underwent sVEP visual acuity estimation using commercially available equipment and software (Diagnosys Espion E3 System Lowell, MA, USA). sVEP was sequentially recorded under two conditions: (i) steady fixation using a central stationary target; and (ii) simulated unsteady fixation with the subject allowed roving eye movements outside the central stationary target. Fixation was monitored using eye‐tracking technology (Tobii Eye Tracker 4C, Tobii Technology AB, Sweden). Fixation stability was classified based on the proportion of fixation points within 4° retinal diameter circle (stable fixation: >75% fixations within 4° circle; unstable fixation: <75% fixations within 4° circle). Within‐subject differences in the estimated sVEP visual acuities under the two tested conditions were assessed using Wilcoxon non‐parametric signed comparisons with significance level set at p < 0.05. Bland‐Altman plots were used to calculate 95% limits of agreement.ResultsSimulated unsteady fixation yielded significant differences in sVEP visual acuity estimation compared to steady fixation (p < 0.0001). The median difference between the two conditions was 0.19 logMAR (~2 Snellen VA lines), with 95% limits of agreement ranging from 0.05 to 0.49 logMAR. Steady fixation overestimated visual acuity compared to BCVA (p < 0.0001), contrary to simulated unsteady fixation, which yielded estimates not statistically different from the expected BCVA (p = 0.91).ConclusionsSimulated unsteady fixation affects sVEP acuity estimates in normal subjects. However, the estimated visual acuities are not significantly different from the expected normal visual acuity of 20/20. sVEP testing can therefore be used to document normal visual acuity without the requirement of steady and central fixation.

A prospective observational study for the safety of Nd-YAG Laster posterior capsulotomy procedure in patients of Posterior Capsular Opacification (PCO) at the ophthalmology outpatient department of a tertiary care teaching hospital in western India

: Nd YAG laser is preferred method to manage thickened posterior capsule because it is an easy, non-invasive and an OPD basis procedure considering the comfort of the patients.: The present study was carried out with objectives to evaluate the safety profile of Nd-YAG Laser Capsulotomy mainly in terms of rise in intraocular pressure (IOP) and other intra as well as post-operative complications.This prospective observational study was carried out with prior Institutional Ethics Committee (IEC) approval and written informed consent from the participants at Ophthalmology Outpatients Department (OPD) of a tertiary care teaching hospital of western India, for the duration of two years from Oct’2015 to Sept’2017. A detailed ocular, systemic, family history was taken of all the enrolled patients with pre- and post-procedure evaluation of IOP by Goldman’s Applanation Tonometry, Slit lamp examination and Fundus examination by direct and indirect ophthalmoscopy. Capsulotomy was done using VISULAS YAG III laser of Zeiss company.The data was entered and tabulated in Microsoft Excel 2007 and analyzed. Data was analyzed by frequency distribution. The ‘p’ value was determined to finally evaluate and P <0.05 was considered as statistically significant.Acute transient rise of IOP up to 5mmHg or more (P value <0.001) was found in Nine cases which is highly significant compared with pre-procedural stage. Intraocular lens pitting was observed in Four cases. Cystoid macular edema was found in one case. Two patients developed mild iritis. Nd-YAG laser capsulotomy is an easy, practical modality to treat posterior capsular opacities, but is not a completely innocuous procedure. Nd-YAG laser capsulotomy is an easy, practical modality to treat posterior capsular opacities, but is not a completely innocuous procedure. Due precautions should be taken in pre- and post-procedural stages including medications, thorough counselling, proper focusing and steady fixation of the patients to minimise the complication.

Orthoptic assessment of vision in patients with complex disability: the importance of understanding the patient’s communication methods

ABSTRACT Care for children with acquired brain injury requires a multi-disciplinary team (MDT) to maximize rehabilitation. These children frequently present to the orthoptic clinic with complex difficulties impacting visual functions and eye movements. We report on one case which led to a reevaluation of our current assessment methods, clinical care pathways and the contents of clinic correspondence. We present a case report of a 14-year-old girl who suffered a cardiac arrest due to underlying Wolff–Parkinson–White syndrome; MRI revealed hypoxic brain injury with extensive white matter and basal ganglia volume loss. On presentation, it was evident there was a significant impact on visual function. Conventional optotype acuity testing was not possible. Her inability to maintain fixation made observational responses unreliable. Observations revealed no steady fixation, exotropia and roving eye movements. Although she was reported to be unable to speak, progress with communication was reported and she was able to give repeatable, reliable responses to indicate “yes” or “no.” These cues were used and a response of 1.70 cycles per degree was obtained under binocular conditions. This communication method was also utilized to assess visual fields by confrontation. However, the clinic letter written by the ophthalmologist based on the orthoptic assessment simply provided the acuity score with no interpretation of the information or how it was obtained. This case highlighted the importance of understanding a child’s communication methods so that assessment can be appropriately adapted. The referral letter was lacking in detail regarding the patient’s abilities but equally the ophthalmology letter provided limited detail impacting on the MDT practitioner’s ability to understand and apply the information. This case has highlighted the importance of good communication: professionals need to acknowledge and work with an individual’s communication methods so that assessment can be completed. Professionals also need to improve communication of relevant findings to others involved in the patient’s care.

Neuro-Ophthalmological Findings in Early Fatal Familial Insomnia.

Fatal familial insomnia (FFI) is a rare inherited prion disease characterized by sleep, autonomic, and motor disturbances. Neuro-ophthalmological abnormalities have been reported at the onset of disease, although not further characterized. We analyzed video recordings of eye movements of 6 patients with FFI from 3 unrelated kindreds, seen within 6 months from the onset of illness. Excessive saccadic intrusions were the most prominent findings. In patients with severe insomnia, striking saccadic intrusions are an early diagnostic clue for FFI. The fact that the thalamus is the first structure affected in FFI also suggests its role in the control of steady fixation. ANN NEUROL 2021;89:823-827.

The Rotating Snakes Illusion Is a Straightforward Consequence of Nonlinearity in Arrays of Standard Motion Detectors.

The Rotating Snakes illusion is a motion illusion based on repeating, asymmetric luminance patterns. Recently, we found certain gray-value conditions where a weak illusory motion occurs in the opposite direction. Of the four models for explaining the illusion, one also explains the unexpected perceived opposite direction.We here present a simple new model, without free parameters, based on an array of standard correlation-type motion detectors with a subsequent nonlinearity (e.g., saturation) before summing the detector outputs. The model predicts (a) the pattern-appearance motion illusion for steady fixation, (b) an illusion under the real-world situation of saccades across or near the pattern (pattern shift), (c) a relative maximum of illusory motion for the same gray values where it is found psychophysically, and (d) the opposite illusion for certain luminance values. We submit that the new model’s sparseness of assumptions justifies adding a fifth model to explain this illusion.

Understanding the underlying mechanisms of Quiet Eye: The role of microsaccades, small saccades and pupil-size before final movement initiation in a soccer penalty kick

Experts keep a steady final fixation at a specific location just before final movement initiation, the so-called “quiet eye” (QE). However, the eyes are rarely “quiet”, and small eye movements occur during visual fixation. The current research investigated the subtle eye movements and underlying mechanisms immediately prior to and during QE. The gaze behaviour of 8 intermediate-level goalkeepers was recorded as they moved (either left or right) in an attempt to predict the future direction of the ball during a soccer penalty kick. Goalkeepers were more likely to predict the direction of the penalty, which was coupled with delaying movement initiation. The temporal sequence of microsaccade rates dropped ∼1000 ms before goalkeepers’ final movement initiation. Saccade rates increased, reaching a peak ∼500 ms before final movement initiation, concomitant with microsaccades reduction. Microsaccades predicted the goalkeepers’ direction, oriented to the right when goalkeepers moved to the right, and conversely to the left when they moved to the left. Microsaccades may be modulated by attention and appear functionally related to saccadic intrusions. Pupil-size increased proportionally with the lead up to the instance of the penalty being kicked, reaching a plateau at final movement initiation. In conclusion, microsaccades and small saccades could improve the perception of the soccer penalty kick, helping athletes during the period that precedes the critical movement initiation, shifting from covert to overt attention for identifying the useful cues necessary to guide the action.

MANAGEMENT AND OUTCOME ANALYSIS OF PROXIMAL HUMERUS FRACTURES BY PHILOS - A PROSPECTIVE STUDY

Introduction: Proximal humerus fracture is considered as one of the commonest fractures in clinical practice. Most of these fractures occur as a result of osteoporosis. Proximal humerus fractures are often nondisplaced or minimally displaced fractures with two parts, which can be managed conservatively. Surgical interventions include closed reduction and percutaneous pinning (CRPP). It also involves trans-osseous suture fixation, Open Reduction Internal Fixation (ORIF) with either conventional or Proximal Humerus Interlocking Osteosynthesis System (PHILOS) or hemiarthroplasty. Good clinical outcomes have been achieved by the PHILOS as they stabilize the proximal humeral fractures with steady fixation in osteoporotic bone and assisted aged patients in early functional exercises which resulted in early recovery. 
 Aim: To analyse the functional results and complications associated with management of proximal humerus fractures treated with PHILOS.
 Materials and Methods: This is a prospective study conducted at Department of Orthopaedics, Prathima Institute Of Medical Sciences, Nagunur, Karimnagar, from July 2017 to January 2019. 58 patients were taken into study with two-part, three-part, four-part fracture of the proximal humerus in adults >18 years of age. In all patients PHILOS plating was done and surgical events and surgical difficulties faced, post-surgery local or systemic complications, time needed for fracture union and time taken to return to pre-fracture activity were documented. They were followed up till there were signs of union on radiographs or for at least a period of 1 year.
 Results: The results were assessed with Constant Murley Score at 6 months post-surgery and Visual Analogue Scale at 6 weekly intervals. The mean Constant score for two-part fractures was 88.1, for Three-part 82.5, for Four-part 72.7. The patients with two-part and three-part fractures had a significantly better VAS than patients with four-part fractures till 18 months of surgery. After 18 months the VAS was similar for all 3 groups. 6.9% developed shoulder stiffness, 2 patients from four-part fracture group developed Varus angulation.
 Conclusion: we conclude that the PHILOS is safe, effective and provides stable fixation for proximal humerus fractures and in patients with indigent bone quality. 
 Keywords: PHILOS, Proximal Humerus Fracture

Eye contact in active and passive viewing: Event-related brain potential evidence from a combined eye tracking and EEG study

Eye contact is a salient social cue, which is assumed to influence already early neural correlates of face perception. Specifically, the N170 component of the event-related potential (ERP) has often been found to be larger for faces with an averted gaze as compared to faces that directly look at the observer. In most existing ERP studies, effects of eye contact were investigated under comparatively artificial conditions where participants were instructed to maintain a steady fixation while they passively observed gaze changes in the stimulus face. It is therefore unclear to what extent neural correlates of eye contact generalize to more naturalistic situations that involve a continuous interplay between directed and averted gaze between the communication partners. To start bridging this gap, the present study compared the passive viewing of gaze changes to an active condition in which the participant's own gaze (measured online with an eye tracker) interacted with the gaze position of a continuously presented stimulus face. We also investigated whether eye contact effects were modulated by the face's emotional expression. In both the passive and the active viewing condition, N170 amplitudes were larger when the gaze of the stimulus faces was averted rather than directed towards the participant. Furthermore, eye contact decreased P300 amplitudes in both conditions. The emotional expression of the face also modulated the N170, but this effect did not interact with that of gaze direction. We conclude that the neural correlates of gaze perception during active gaze interactions are comparable to those found during passive viewing, encouraging the further study of eye contact effects in more naturalistic settings.

Measurement of the useful field of view for single slices of different imaging modalities and targets.

Purpose: With three-dimensional (3-D) images displayed as stacks of 2-D images, radiologists rely more heavily on vision away from their fixation point to visually process information, guide eye movements, and detect abnormalities. Thus the ability to detect targets away from the fixation point, commonly characterized as the useful field of view (UFOV), becomes critical for these 3-D imaging modalities. We investigate how the UFOV, defined as the eccentricity, in which detection performance degrades to a given probability, varies across imaging modalities and targets. Approach: We measure the detectability of different targets at various distances from gaze locations for single slices of liver computed tomography (CT), 2-D digital mammograms (DM), and single slices of digital breast tomosynthesis (DBT) cases. Observers with varying expertise were instructed to maintain their gaze at a point while a short display of the image was flashed and an eye tracker verified observer's steady fixation. Display times were 200 and 1000ms for CT images and 500ms for DM and DBT images. Results: We find variations in the UFOV from 9 to 12deg for liver CT to as small as 2.5 to 5deg for calcification clusters in breast images (DM and DBT). We compare our results to those reported in the literature for lung nodules and discuss the differences across methods used to measure the UFOV, their dependence on case selection/task difficulty, viewing conditions, and observer expertise. We propose a complementary measure defined in terms of performance degradation relative to the peak foveal performance (relative-UFOV) to circumvent UFOV's variations with case selection/task difficulty. Conclusion: Our results highlight the variations in the UFOV across imaging modalities, target types, observer expertise, and measurement methods and suggest an additional relative-UFOV measure to more thoroughly characterize the detection performance away from point of fixation.

SITA standard testing with Humphrey visual field analyzer versus full threshold testing with frequency doubling perimetry: a comparison of patient preference and perception

Purpose: To compare patient preference for Swedish Interactive Threshold Algorithm (SITA) standard 24-2 protocol in Humphrey visual field analyzer (HVF) and full threshold N-30 protocol in frequency doubling perimetry (FDP) by primarily evaluating their perception about the test procedure and test targets along with surveying the factors that influence the patient concentration during perimetry and elements that determine the level of perimetry task difficulty.
 Methods: This study enrolled a subset of subjects from the Chennai Glaucoma Study. Each subject underwent a comprehensive ophthalmic examination after which they were randomly allocated to perform HVF and FDP with a 30-minute interval between the two procedures. SITA standard 24-2 protocol in HVF and full threshold N-30 protocol in FDP were used. This was followed by the administration of a questionnaire that mainly assessed the components such as (a) the patient preference for test procedure and test targets, (b) the factors influencing the patient concentration during perimetry performance, and (c) the impression about the level of perimetry task difficulty. The patient responses from the survey for each of the subcategories were obtained and analyzed using Chi-square test.
 Results: A total of 42 subjects with a mean age of 59.7 (SD 9.7) years were included, among which 18 (42.86%) were male and 24 (57.14%) were female. Thirty-two (76.19%) subjects felt both FDP and HVF were easy to perform, eight subjects (19.05%) felt that both perimetry techniques were difficult to perform, and two subjects (4.76%) found FDP procedure was easier than HVF, whereas the distribution was not statistically significant (Chi-square, p = 0.7). Pressing the button as a response to peripheral stimulus perception and inability to maintain steady central fixation for prolonged duration were the most commonly reported factors that influenced the level of difficulty of the perimetry tasks. A dark room ambience set for performing HVF was preferred by 32 (76.20%) subjects.
 Conclusion: There was no significant difference in the patient preference for test procedure and peripheral test targets. A black central fixation as in FDP and dark room ambience set for HVF were preferred.

Amblyopia with Eccentric Fixation: Is Inverse Occlusion Still an Option?

ABSTRACTPurpose: To present a treatment protocol for patients with amblyopia and eccentric fixation who do not respond to conventional occlusion therapy.Material and methods: In this consecutive case series, 11 patients were included (age 3.5 to 5.0), all with mixed amblyopia and eccentric fixation, who had only minor improvement of their visual acuity (VA) despite good compliance with 6 hours/day to full time occlusion of the sound eye for at least 6 months. Visual acuity of amblyopic eyes ranged from 20/50 to 20/400 at the time of initiation of inverse occlusion. Total inverse occlusion of the amblyopic eye was prescribed for 4 to 8 weeks to convert the steady eccentric fixation to wandering fixation. No binocular viewing was allowed. Once the fixation became wandering, the sound eye was occluded day and night and in most patients, a red filter was placed before the amblyopic eye to stimulate foveal fixation. In nine patients, the fixation became central and occlusion of the sound eye was continued without red filter. All children continued full time occlusion until VA failed to improve after two consecutive visits despite good compliance.Results: In nine children, the VA improved to at least 20/32 in the amblyopic eye. The VA of the sound eye did not change.Conclusion: Inverse occlusion is still a valuable option if conventional occlusion appears to be insufficient to improve VA in amblyopic eyes with eccentric fixation. Full time inverse occlusion should be performed until the eccentric point is no longer used for fixation and should be followed with full time occlusion of the sound eye. Placing a red filter before the amblyopic eye may be helpful to stimulate foveal fixation.

Saccadic Suppression of Displacement Does Not Reflect a Saccade-Specific Bias to Assume Stability.

Across saccades, small displacements of a visual target are harder to detect and their directions more difficult to discriminate than during steady fixation. Prominent theories of this effect, known as saccadic suppression of displacement, propose that it is due to a bias to assume object stability across saccades. Recent studies comparing the saccadic effect to masking effects suggest that suppression of displacement is not saccade-specific. Further evidence for this account is presented from two experiments where participants judged the size of displacements on a continuous scale in saccade and mask conditions, with and without blanking. Saccades and masks both reduced the proportion of correctly perceived displacements and increased the proportion of missed displacements. Blanking improved performance in both conditions by reducing the proportion of missed displacements. Thus, if suppression of displacement reflects a bias for stability, it is not a saccade-specific bias, but a more general stability assumption revealed under conditions of impoverished vision. Specifically, I discuss the potentially decisive role of motion or other transient signals for displacement perception. Without transients or motion, the quality of relative position signals is poor, and saccadic and mask-induced suppression of displacement reflects performance when the decision has to be made on these signals alone. Blanking may improve those position signals by providing a transient onset or a longer time to encode the pre-saccadic target position.

Estimation of Contrast Sensitivity From Fixational Eye Movements

Even during steady fixation, people make small eye movements such as microsaccades, whose rate is altered by presentation of salient stimuli. Our goal was to develop a practical method for objectively and robustly estimating contrast sensitivity from microsaccade rates in a diverse population. Participants, recruited to cover a range of contrast sensitivities, were visually normal (n = 19), amblyopic (n = 10), or had cataract (n = 9). Monocular contrast sensitivity was estimated behaviorally while binocular eye movements were recorded during interleaved passive trials. A probabilistic inference approach was used to establish the likelihood of observed microsaccade rates given the presence or absence of a salient stimulus. Contrast sensitivity was estimated from a function fitted to the scaled log-likelihood ratio of the observed microsaccades in the presence or absence of a salient stimulus across a range of contrasts. Microsaccade rate signature shapes were heterogeneous; nevertheless, estimates of contrast sensitivity could be obtained in all participants. Microsaccade-estimated contrast sensitivity was unbiased compared to behavioral estimates (1.2% mean), with which they were strongly correlated (Spearman's ρ 0.74, P < 0.001, median absolute difference 7.6%). Measurement precision of microsaccade-based contrast sensitivity estimates was worse than that of behavioral estimates, requiring more than 20 times as many presentations to equate precision. Microsaccade rate signatures are heterogeneous in shape when measured across populations with a broad range of contrast sensitivities. Contrast sensitivity can be robustly estimated from rate signatures by probabilistic inference, but more stimulus presentations are currently required to achieve similarly precise estimates to behavioral techniques.

The eardrums move when the eyes move: A multisensory effect on the mechanics of hearing

Interactions between sensory pathways such as the visual and auditory systems are known to occur in the brain, but where they first occur is uncertain. Here, we show a novel multimodal interaction evident at the eardrum. Ear canal microphone measurements in humans (n = 19 ears in 16 subjects) and monkeys (n = 5 ears in 3 subjects) performing a saccadic eye movement task to visual targets indicated that the eardrum moves in conjunction with the eye movement. The eardrum motion was oscillatory and began as early as 10 ms before saccade onset in humans or with saccade onset in monkeys. These eardrum movements, which we dub Eye Movement Related Eardrum Oscillations (EMREOs), occurred in the absence of a sound stimulus. The EMREOs’ amplitude and phase depended on the direction and horizontal amplitude of the saccade. They lasted throughout the saccade and well into subsequent periods of steady fixation. We discuss the possibility that the mechanisms underlying EMREOs create eye movement-related binaural cues that may aid the brain in evaluating the relationship between visual and auditory stimulus locations as the eyes move.