Showing papers on "Foveal published in 2016"

Systems and methods using virtual reality or augmented reality environments for the measurement and/or improvement of human vestibulo-ocular performance

Abstract: A system and method for using a virtual reality or an augmented reality environment for the measurement and/or improvement of human vestibulo-ocular performance can be implemented by combining a video camera based eye orientation sensor, a head orientation sensor, a display, and an electronic circuit that connects the eye sensor, head sensor, and display. The system and method can be operated in the range of frequencies between 0.01 Hertz and 15 Hertz. The system and method can use a Fourier transform to compute a gain and a phase. The system and method can be used for measuring vestibulo-ocular reflex, dynamic visual acuity, dynamic visual stability, kinetic visual acuity, retinal image stability, or foveal fixation stability in a non-clinical setting. The system and method can be completely portable, head-worn, and self-contained.

Impairing the useful field of view in natural scenes: Tunnel vision versus general interference

Abstract: A fundamental issue in visual attention is the relationship between the useful field of view (UFOV), the region of visual space where information is encoded within a single fixation, and eccentricity. A common assumption is that impairing attentional resources reduces the size of the UFOV (i.e., tunnel vision). However, most research has not accounted for eccentricity-dependent changes in spatial resolution, potentially conflating fixed visual properties with flexible changes in visual attention. Williams (1988, 1989) argued that foveal loads are necessary to reduce the size of the UFOV, producing tunnel vision. Without a foveal load, it is argued that the attentional decrement is constant across the visual field (i.e., general interference). However, other research asserts that auditory working memory (WM) loads produce tunnel vision. To date, foveal versus auditory WM loads have not been compared to determine if they differentially change the size of the UFOV. In two experiments, we tested the effects of a foveal (rotated L vs. T discrimination) task and an auditory WM (N-back) task on an extrafoveal (Gabor) discrimination task. Gabor patches were scaled for size and processing time to produce equal performance across the visual field under single-task conditions, thus removing the confound of eccentricity-dependent differences in visual sensitivity. The results showed that although both foveal and auditory loads reduced Gabor orientation sensitivity, only the foveal load interacted with retinal eccentricity to produce tunnel vision, clearly demonstrating task-specific changes to the form of the UFOV. This has theoretical implications for understanding the UFOV.

Residual Foveal Cone Structure in CNGB3-Associated Achromatopsia.

Abstract: Purpose Congenital achromatopsia (ACHM) is an autosomal recessive disorder in which cone function is absent or severely reduced. Gene therapy in animal models of ACHM have shown restoration of cone function, though translation of these results to humans relies, in part, on the presence of viable cone photoreceptors at the time of treatment. Here, we characterized residual cone structure in subjects with CNGB3-associated ACHM. Methods High-resolution imaging (optical coherence tomography [OCT] and adaptive optics scanning light ophthalmoscopy [AOSLO]) was performed in 51 subjects with CNGB3-associated ACHM. Peak cone density and inter-cone spacing at the fovea was measured using split-detection AOSLO. Foveal outer nuclear layer thickness was measured in OCT images, and the integrity of the photoreceptor layer was assessed using a previously published OCT grading scheme. Results Analyzable images of the foveal cones were obtained in 26 of 51 subjects, with nystagmus representing the major obstacle to obtaining high-quality images. Peak foveal cone density ranged from 7,273 to 53,554 cones/mm2, significantly lower than normal (range, 84,733-234,391 cones/mm2), with the remnant cones being either contiguously or sparsely arranged. Peak cone density was correlated with OCT integrity grade; however, there was overlap of the density ranges between OCT grades. Conclusions The degree of residual foveal cone structure varies greatly among subjects with CNGB3-associated ACHM. Such measurements may be useful in estimating the therapeutic potential of a given retina, providing affected individuals and physicians with valuable information to more accurately assess the risk-benefit ratio as they consider enrolling in experimental gene therapy trials. (www.clinicaltrials.gov, NCT01846052.).

Neural correlates of word recognition: A systematic comparison of natural reading and rapid serial visual presentation

Abstract: Neural correlates of word recognition are commonly studied with rapid serial visual presentation RSVP, a condition that eliminates three fundamental properties of natural reading: parafoveal preprocessing, saccade execution, and the fast changes in attentional processing load occurring from fixation to fixation. We combined eye-tracking and EEG to systematically investigate the impact of all three factors on brain-electric activity during reading. Participants read lists of words either actively with eye movements eliciting fixation-related potentials or maintained fixation while the text moved passively through foveal vision at a matched pace RSVP-with-flankers paradigm, eliciting ERPs. The preview of the upcoming word was manipulated by changing the number of parafoveally visible letters. Processing load was varied by presenting words of varying lexical frequency. We found that all three factors have strong interactive effects on the brain's responses to words: Once a word was fixated, occipitotemporal N1 amplitude decreased monotonically with the amount of parafoveal information available during the preceding fixation; hence, the N1 component was markedly attenuated under reading conditions with preview. Importantly, this preview effect was substantially larger during active reading with saccades than during passive RSVP with flankers, suggesting that the execution of eye movements facilitates word recognition by increasing parafoveal preprocessing. Lastly, we found that the N1 component elicited by a word also reflects the lexical processing load imposed by the previously inspected word. Together, these results demonstrate that, under more natural conditions, words are recognized in a spatiotemporally distributed and interdependent manner across multiple eye fixations, a process that is mediated by active motor behavior.

Subclinical primary retinal pathology in neuromyelitis optica spectrum disorder

Abstract: Foveal thickness may be a more sensitive indicator of primary retinal pathology than retinal nerve fiber layer thickness since the fovea contains no or sparse retinal nerve fiber layer, which coalesces into axons of the optic nerve. To our knowledge, few quantitative in vivo studies have investigated foveal thickness. By using optical coherence tomography, we measured foveal thickness to evaluate intrinsic retinal pathology. Seventy-two neuromyelitis optica spectrum disorder patients (99 eyes with optic neuritis and 45 eyes without optic neuritis) and 34 age-matched controls were included. Foveal thinning was observed both in eyes with non-optic neuritis (185.1 µm, p < 0.001) and optic neuritis (185.0 µm, p < 0.001) relative to controls (205.0 µm). Compared to controls, eyes with non-optic neuritis did not have peripapillary retinal nerve fiber layer thinning, but showed foveal thinning (p < 0.001). In neuromyelitis optica spectrum disorder, foveal thickness correlated with 2.5 % low contrast visual acuity, while retinal nerve fiber layer thickness correlated with high or low contrast visual acuity, extended disability status scale, and disease duration. In this study, we observed foveal thinning irrespective of optic neuritis; thus, we believe that subclinical primary retinal pathology, prior to retinal nerve fiber layer thinning, may exist in neuromyelitis optica spectrum disorder.

Association Between Photoreceptor Regeneration and Visual Acuity Following Surgery for Rhegmatogenous Retinal Detachment.

Abstract: PURPOSE The purpose of this study was to evaluate foveal regeneration and the association between retinal restoration and visual acuity following reattachment surgery for rhegmatogenous retinal detachment (RRD). METHODS Twenty-nine eyes of 29 patients with successfully reattached macula-off RRD were retrospectively analyzed. We used spectral-domain optical coherence tomography to image macular regions and measure retinal thickness and Snellen chart visual acuity (VA) to evaluate best-corrected VA (BCVA) at 1, 2, 3, 6, 9, and 12 months after vitrectomy. Best-corrected visual acuity data were converted to the logarithm of the minimum angle of resolution scale. Opposite eyes were used as controls. RESULTS The thicknesses of the external limiting membrane (ELM)-ellipsoid zone (EZ) and EZ-retinal pigment epithelium (RPE) were significantly thinner in involved eyes than in corresponding unaffected eyes at 1 month after surgery (P < 0.001 for both), and the thickness increased over time (P < 0.001 for both). Best-corrected visual acuity significantly improved over time (P < 0.001), and the improvement correlated with EZ-RPE thickness (r = -0.45, P = 0.021). Multiple regression analysis demonstrated the presence of a foveal bulge as the independent predictor of final BCVA (P < 0.001). Eyes with a foveal bulge had significantly better BCVA and greater EZ-RPE thickness than those without throughout the follow-up period. Significant restoration of the integrity of EZ and cone interdigitation zone (CIZ) was observed over time (P < 0.001 for both) in eyes with a foveal bulge. CONCLUSIONS The thickness of EZ-RPE and cone density increased during foveal regeneration, as demonstrated by the continuous improvements in CIZ integrity over time, leading to the formation of foveal bulge and good vision following successful reattachment of macula-off RRD.

Dissociating parafoveal preview benefit and parafovea‐on‐fovea effects during reading: A combined eye tracking and EEG study

Abstract: During reading, the parafoveal processing of an upcoming word n+1 can influence word recognition in two ways: It can affect fixation behavior during the preceding fixation on word n (parafovea-on-fovea effect, POF), and it can facilitate subsequent foveal processing once word n+1 is fixated (preview benefit). While preview benefits are established, evidence for POF effects is mixed. Recently, it has been suggested that POF effects exist, but have a delayed impact on saccade planning and thus coincide with preview benefits measured on word n+1. We combined eye movement and EEG recordings to investigate and separate neural correlates of POF and preview benefit effects. Participants read lists of nouns either in a boundary paradigm or the RSVP-with-flankers paradigm, while we recorded fixation- or event-related potentials (FRPs/ERPs), respectively. The validity and lexical frequency of the word shown as preview for the upcoming word n+1 were orthogonally manipulated. Analyses focused on the first fixation on word n+1. Preview validity (correct vs. incorrect preview) strongly modulated fixation times and electrophysiological N1 amplitudes, replicating previous findings. Importantly, gaze durations and FRPs measured on word n+1 were also affected by the frequency of the word shown as preview, with low-frequency previews eliciting a sustained, N400-like centroparietal negativity. Results support the idea that POF effects exist but affect word recognition with a delay. Lastly, once word n+1 was fixated, its frequency also modulated N1 amplitudes in ERPs and FRPs. Taken together, we separated immediate and delayed effects of parafoveal processing on brain correlates of word recognition.

Breaking object correspondence across saccades impairs object recognition: The role of color and luminance.

Abstract: Rapid saccadic eye movements bring the foveal region of the eye's retina onto objects for high-acuity vision. Saccades change the location and resolution of objects' retinal images. To perceive objects as visually stable across saccades, correspondence between the objects before and after the saccade must be established. We have previously shown that breaking object correspondence across the saccade causes a decrement in object recognition (Poth, Herwig, & Schneider, 2015). Color and luminance can establish object correspondence, but it is unknown how these surface features contribute to transsaccadic visual processing. Here, we investigated whether changing the surface features color-and-luminance and color alone across saccades impairs postsaccadic object recognition. Participants made saccades to peripheral objects, which either maintained or changed their surface features across the saccade. After the saccade, participants briefly viewed a letter within the saccade target object (terminated by a pattern mask). Postsaccadic object recognition was assessed as participants' accuracy in reporting the letter. Experiment A used the colors green and red with different luminances as surface features, Experiment B blue and yellow with approximately the same luminances. Changing the surface features across the saccade deteriorated postsaccadic object recognition in both experiments. These findings reveal a link between object recognition and object correspondence relying on the surface features colors and luminance, which is currently not addressed in theories of transsaccadic perception. We interpret the findings within a recent theory ascribing this link to visual attention (Schneider, 2013).

Classification of Eye Fixation Related Potentials for Variable Stimulus Saliency

Abstract: Objective. Electroencephalography (EEG) and eye tracking can possibly provide information about which items displayed on the screen are relevant for a person. Exploiting this implicit information promises to enhance various software applications. The specific problem addressed by the present study is that items shown in real applications are typically diverse. Accordingly, the saliency of information, which allows to discriminate between relevant and irrelevant items, varies. As a consequence, recognition can happen in foveal or in peripheral vision, i.e. either before or after the saccade to the item. Accordingly, neural processes related to recognition are expected to occur with a variable latency with respect to the eye movements. The aim was to investigate if relevance estimation based on EEG and eye tracking data is possible despite of the aforementioned variability. Approach. Sixteen subjects performed a free viewing search task where the target saliency was varied while the EEG was recorded and the unrestrained eye movements were tracked. Based on the acquired data, it was estimated which of the items displayed were targets and which were distractors in the search task. Results. Target prediction was possible also when the stimulus saliencies were mixed. Information contained in EEG and eye tracking data was found to be complementary and neural signals were captured despite of the unrestricted eye movements. The classification algorithm was able to cope with the experimentally induced variable timing of neural activity related to target recognition. Significance. It was demonstrated how EEG and eye tracking data can provide implicit information about the relevance of items on the screen for potential use in online applications.

Out of the corner of my eye: Foveal semantic load modulates parafoveal processing in reading.

Abstract: In 2 experiments, we examined the impact of foveal semantic expectancy and congruity on parafoveal word processing during reading. Experiment 1 utilized an eye-tracking gaze-contingent display change paradigm, and Experiment 2 measured event-related brain potentials (ERPs) in a modified flanker rapid serial visual presentation (RSVP) paradigm. Eye-tracking and ERP data converged to reveal graded effects of foveal load on parafoveal processing. In Experiment 1, when word n was highly expected, and thus foveal load was low, there was a large parafoveal preview benefit to word n + 1. When word n was unexpected but still plausible, preview benefits to n + 1 were reduced in magnitude, and when word n was semantically incongruent, the preview benefit to n + 1 was unreliable in early pass measures. In Experiment 2, ERPs indicated that when word n was expected, and thus foveal load was low, readers successfully discriminated between valid and orthographically invalid previews during parafoveal perception. However, when word n was unexpected, parafoveal processing of n + 1 was reduced, and it was eliminated when word n was semantically incongruent. Taken together, these findings suggest that sentential context modulates the allocation of attention in the parafovea, such that covert allocation of attention to parafoveal processing is disrupted when foveal words are inconsistent with expectations based on various contextual constraints. (PsycINFO Database Record

Emergence of foveal image sampling from learning to attend in visual scenes

Abstract: We describe a neural attention model with a learnable retinal sampling lattice. The model is trained on a visual search task requiring the classification of an object embedded in a visual scene amidst background distractors using the smallest number of fixations. We explore the tiling properties that emerge in the model's retinal sampling lattice after training. Specifically, we show that this lattice resembles the eccentricity dependent sampling lattice of the primate retina, with a high resolution region in the fovea surrounded by a low resolution periphery. Furthermore, we find conditions where these emergent properties are amplified or eliminated providing clues to their function.

AugKey: Increasing Foveal Throughput in Eye Typing with Augmented Keys

Abstract: Eye-typing is an important tool for people with physical disabilities and, for some, it is their main form of communication. By observing expert typists using physical keyboards, we notice that visual throughput is considerably reduced in current eye-typing solutions. We propose AugKey to improve throughput by augmenting keys with a prefix, to allow continuous text inspection, and suffixes to speed up typing with word prediction. AugKey limits the visual information to the foveal region to minimize eye movements (i.e., reduce eye work). We have applied AugKey to a dwell-time keyboard and compared its performance with two conditions with no augmented feedback: a keyboard with and one without word prediction. Results show that AugKey can be about 28% faster than no word prediction and 20% faster than traditional word prediction, with a smaller workload index.

Temporally flexible feedback signal to foveal cortex for peripheral object recognition

Abstract: Recent studies have shown that information from peripherally presented images is present in the human foveal retinotopic cortex, presumably because of feedback signals. We investigated this potential feedback signal by presenting noise in fovea at different object–noise stimulus onset asynchronies (SOAs), whereas subjects performed a discrimination task on peripheral objects. Results revealed a selective impairment of performance when foveal noise was presented at 250-ms SOA, but only for tasks that required comparing objects’ spatial details, suggesting a task- and stimulus-dependent foveal processing mechanism. Critically, the temporal window of foveal processing was shifted when mental rotation was required for the peripheral objects, indicating that the foveal retinotopic processing is not automatically engaged at a fixed time following peripheral stimulation; rather, it occurs at a stage when detailed information is required. Moreover, fMRI measurements using multivoxel pattern analysis showed that both image and object category-relevant information of peripheral objects was represented in the foveal cortex. Taken together, our results support the hypothesis of a temporally flexible feedback signal to the foveal retinotopic cortex when discriminating objects in the visual periphery.

A foveal target increases catch-up saccade frequency during smooth pursuit.

Abstract: Images that move rapidly across the retina of the human eye blur because the retina has sluggish temporal dynamics. Voluntary smooth pursuit eye movements are modeled as matching object velocity to minimize retinal motion and prevent retinal blurring. However, "catch-up" saccades that are ubiquitous during pursuit interrupt it and disrupt clear vision. But catch-up saccades may not be a common feature of ocular pursuit, because their existence has been documented with a small moving spot, the classic pursuit stimulus, which is a weak motion stimulus that may poorly emulate larger pursuit objects. We found that spot pursuit does not generalize to that of larger objects. Observers pursued a spot or a larger virtual object with or without a superimposed spot target. Single-spot targets produced lower pursuit acceleration than larger objects. Critically, more saccadic intrusions occurred when stimuli had a central dot, even when position and velocity errors were equated, suggesting that catch-up saccades result from pursuing a single, small object or a feature on a large one. To determine what differentiates a large object from a small one, we progressively shrank the featureless virtual object and found that catch-up saccade frequency was highest when it fit in the fovea. The results suggest that pursuit of a small target or an object feature recruits a saccade mechanism that does not compensate for a weak motion signal; rather, the target compels foveation. Furthermore, catch-up saccades are likely generated by neural circuitry typically used to foveate small objects or features.

Optical Coherence Tomography Angiography in Fovea Plana.

Abstract: Fovea plana is characterized by the anatomical absence of the foveal pit in eyes with normal visual function. The authors have analyzed three cases of idiopathic fovea plana with optical coherence tomography angiography (OCTA). As previously reported, the authors found the absence of a foveal avascular zone in all cases with OCTA; however, a preserved fusion of both the superficial and the deep capillary plexuses was found around the foveal center. This novel observation cannot be detected with conventional dye-based angiography, in which the deep capillary plexus is not visualized. [Ophthalmic Surg Lasers Imaging Retina. 2016;47:670-673.].

Oculomotor Remapping of Visual Information to Foveal Retinotopic Cortex.

Abstract: Our eyes continually jump around the visual scene to bring the high-resolution, central part of our vision onto objects of interest. We are oblivious to these abrupt shifts, perceiving the visual world to appear reassuringly stable. A process called remapping has been proposed to mediate this perceptual stability for attended objects by shifting their retinotopic representation to compensate for the effects of the upcoming eye movement. In everyday vision, observers make goal-directed eye movements towards items of interest bringing them to the fovea and, for these items, the remapped activity should impinge on foveal regions of the retinotopic maps in visual cortex. Previous research has focused instead on remapping for targets that were not saccade goals, where activity is remapped to a new peripheral location rather than to the foveal representation. We used functional MRI and a phase-encoding design to investigate remapping of spatial patterns of activity towards the fovea/parafovea for saccade targets that were removed prior to completion of the eye movement. We found strong evidence of foveal remapping in retinotopic visual areas, which failed to occur when observers merely attended to the same peripheral target without making eye movements toward it. Significantly, the spatial profile of the remapped response matched the orientation and size of the saccade target, and was appropriately scaled to reflect the retinal extent of the stimulus had it been foveated. We conclude that this remapping of spatially structured information to the fovea may serve as an important mechanism to support our world-centered sense of location across goal-directed eye movements under natural viewing conditions.

A clinical test for visual crowding

Abstract: Crowding is a major limitation of visual perception. Because of crowding, a simple object, like a letter, can only be recognized if clutter is a certain critical spacing away. Crowding is only weakly associated with acuity. The critical spacing of crowding is lowest in the normal fovea, and grows with increasing eccentricity in peripheral vision. Foveal crowding is more prominent in certain patient groups, including those with strabismic amblyopia and apperceptive agnosia. Crowding may lessen with age during childhood as reading speed increases. The range of crowding predicts much of the slowness of reading in children with developmental dyslexia. There is tantalizing evidence suggesting that the critical spacing of crowding indicates neural density (participating neurons per square deg) in the visual cortex. Thus, for basic and applied reasons, it would be very interesting to measure foveal crowding clinically in children and adults with normal and impaired vision, and to track the development of crowding during childhood. While many labs routinely measure peripheral crowding as part of their basic research in visual perception, current tests are not well suited to routine clinical testing because they take too much time, require good fixation, and are mostly not applicable to foveal vision. Here we report a new test for clinical measurement of crowding in the fovea. It is quick and accurate, works well with children and adults, and we expect it to work well with dementia patients as well. The task is to identify a numerical digit, 1-9, using a new “Pelli” font that is identifiable at tiny width (0.02 deg, about 1 minarc, in normal adult fovea). This allows quick measurement of the very small (0.05 deg) critical spacing in the normal adult fovea, as well as with other groups that have higher critical spacing. Preliminary results from healthy adults and children are presented.

Automated Fovea Detection in Spectral Domain Optical Coherence Tomography Scans of Exudative Macular Disease

Abstract: In macular spectral domain optical coherence tomography (SD-OCT) volumes, detection of the foveal center is required for accurate and reproducible follow-up studies, structure function correlation, and measurement grid positioning. However, disease can cause severe obscuring or deformation of the fovea, thus presenting a major challenge in automated detection. We propose a fully automated fovea detection algorithm to extract the fovea position in SD-OCT volumes of eyes with exudative maculopathy. The fovea is classified into 3 main appearances to both specify the detection algorithm used and reduce computational complexity. Based on foveal type classification, the fovea position is computed based on retinal nerve fiber layer thickness. Mean absolute distance between system and clinical expert annotated fovea positions from a dataset comprised of 240 SD-OCT volumes was 162.3 µm in cystoid macular edema and 262 µm in nAMD. The presented method has cross-vendor functionality, while demonstrating accurate and reliable performance close to typical expert interobserver agreement. The automatically detected fovea positions may be used as landmarks for intra- and cross-patient registration and to create a joint reference frame for extraction of spatiotemporal features in ?big data.? Furthermore, reliable analyses of retinal thickness, as well as retinal structure function correlation, may be facilitated.

Modulating foveal representation can influence visual discrimination in the periphery.

Abstract: A previous study by Williams et al. (2008) provided evidence for a novel form of feedback in the visual system, whereby peripheral information is contained in foveal retinotopic cortex. Beyond its possible implication for peripheral object recognition, few studies have examined the effect of a direct behavioral manipulation of the foveal feedback representation. To address this question, we measured participants' peripheral visual discrimination performance while modulating their foveal representation in a series of psychophysical experiments. On each trial, participants discriminated the identities of briefly presented novel, three-dimensional objects or the orientations of gratings in a peripheral location while fixating at the center. Besides the peripheral target, another stimulus (foil) was also presented and masked at the fovea. Our results showed that for objects, when the foveal foil that was identical to the peripheral target was presented 150 ms after the onset of the peripheral target, visual discrimination of the peripheral target was improved. This congruency effect occurred even though participants did not consciously perceive the foveal stimulus. No such effect was observed when the foveal foil was presented simultaneously with the peripheral target, or when the foil was presented in a parafoveal location. The foil effect in gratings was different from that in objects in terms of its effective timing and foveal specificity, suggesting that foveal feedback may be specific to high-level objects. These results indicate that modulating foveal information can affect individuals' ability to discriminate peripheral objects, suggesting a functional role of foveal representations in peripheral visual perception.

Ocular Fixation Abnormality in Patients with Autism Spectrum Disorder.

Abstract: We examined the factors that influence ocular fixation control in adults with autism spectrum disorder (ASD) including sensory information, individuals' motor characteristics, and inhibitory control. The ASD group showed difficulty in maintaining fixation especially when there was no fixation target. The fixational eye movement characteristics of individuals were consistent regardless of the presence or absence of a fixation target in the controls, but not in the ASD group. Additionally, fixation stability did not correlate with an ability to suppress reflexive saccades measured by an antisaccade task. These findings suggest that ASD adults have deficits in converting alternative sensory information, such as retinal signals in the peripheral visual field or extraretinal signals, to motor commands when the foveal information is unavailable.

FOVEA: a new program to standardize the measurement of foveal pit morphology.

Abstract: The fovea is one of the most studied retinal specializations in vertebrates, which consists of an invagination of the retinal tissue with high packing of cone photoreceptors, leading to high visual resolution. Between species, foveae differ morphologically in the depth and width of the foveal pit and the steepness of the foveal walls, which could influence visual perception. However, there is no standardized methodology to measure the contour of the foveal pit across species. We present here FOVEA, a program for the quantification of foveal parameters (width, depth, slope of foveal pit) using images from histological cross-sections or optical coherence tomography (OCT). FOVEA is based on a new algorithm to detect the inner retina contour based on the color variation of the image. We evaluated FOVEA by comparing the fovea morphology of two Passerine birds based on histological cross-sections and its performance with data from previously published OCT images. FOVEA detected differences between species and its output was not significantly different from previous estimates using OCT software. FOVEA can be used for comparative studies to better understand the evolution of the fovea morphology in vertebrates as well as for diagnostic purposes in veterinary pathology. FOVEA is freely available for academic use and can be downloaded at: http://estebanfj.bio.purdue.edu/fovea.

Approaches to a cortical vision prosthesis: implications of electrode size and placement.

Abstract: Objective In order to move forward with the development of a cortical vision prosthesis, the critical issues in the field must be identified. Approach To begin this process, we performed a brief review of several different cortical and retinal stimulation techniques that can be used to restore vision. Main results Intracortical microelectrodes and epicortical macroelectrodes have been evaluated as the basis of a vision prosthesis. We concluded that an important knowledge gap necessitates an experimental in vivo performance evaluation of microelectrodes placed on the surface of the visual cortex. A comparison of the level of vision restored by intracortical versus epicortical microstimulation is necessary. Because foveal representation in the primary visual cortex involves more cortical columns per degree of visual field than does peripheral vision, restoration of foveal vision may require a large number of closely spaced microelectrodes. Based on previous studies of epicortical macrostimulation, it is possible that stimulation via surface microelectrodes could produce a lower spatial resolution, making them better suited for restoring peripheral vision. Significance The validation of epicortical microstimulation in addition to the comparison of epicortical and intracortical approaches for vision restoration will fill an important knowledge gap and may have important implications for surgical strategies and device longevity. It is possible that the best approach to vision restoration will utilize both epicortical and intracortical microstimulation approaches, applying them appropriately to different visual representations in the primary visual cortex.

On the Differentiation of Foveal and Peripheral Early Visual Evoked Potentials

Abstract: The C1 is one of the earliest visual evoked potentials observed following the onset of a patterned stimulus. The polarity of its peak is dependent on whether stimuli are presented in the upper or lower regions of the peripheral visual field, but has been argued to be negative for stimuli presented to the fovea. However, there has yet to be a systematic investigation into the extent to which the peripheral C1 (pC1) and foveal C1 (fC1) can be differentiated on the basis of response characteristics to different stimuli. The current study employed checkerboard patterns (Exp 1) and sinusoidal gratings of different spatial frequency (Exp 2) presented to the fovea or within one of the four quadrants of the peripheral visual field. The checkerboard stimuli yielded a sizable difference in peak component latency, with the fC1 peaking ~32 ms after the pC1. Further, the pC1 showed a band-pass response magnitude profile that peaked at 4 cycles per degree (cpd), whereas the fC1 was high-pass for spatial frequency, with a cut-off around 4 cpd. Finally, the scalp topographies of the pC1 and fC1 in both experiments differed greatly, with the fC1 being more posterior than the pC1. The results reported here call into question recent attempts to characterize general C1 processes without regard to whether stimuli are placed in the fovea or in the periphery.

Monocular microsaccades are visual-task related.

Abstract: During visual fixation, we constantly move our eyes. These microscopic eye movements are composed of tremor, drift, and microsaccades. Early studies concluded that microsaccades, like larger saccades, are binocular and conjugate, as expected from Hering's law of equal innervation. Here, we document the existence of monocular microsaccades during both fixation and a discrimination task, reporting the location of the gap in a foveal, low-contrast letter C. Monocular microsaccades differ in frequency, amplitude, and peak velocity from binocular microsaccades. Our analyses show that these differences are robust to different velocity and duration criteria that have been used previously to identify microsaccades. Also, the frequency of monocular microsaccades differs systematically according to the task: monocular microsaccades occur more frequently during fixation than discrimination, the opposite of their binocular equivalents. However, during discrimination, monocular microsaccades occur more often around the discrimination threshold, particularly for each subject's dominant eye and in case of successful discrimination. We suggest that monocular microsaccades play a functional role in the production of fine corrections of eye position and vergence during demanding visual tasks.

Optical Coherence Tomography Angiography in Foveal Hypoplasia.

Abstract: BACKGROUND AND OBJECTIVE A retrospective case series reporting optical coherence tomography angiography (OCTA) findings in foveal hypoplasia. PATIENTS AND METHODS Patients with foveal hypoplasia who presented to the authors' tertiary eye center. Cases of foveal hypoplasia that underwent OCTA were reviewed, and the clinical histories as well as imaging findings were summarized. RESULTS Three patients presented to the authors' eye center for evaluation of foveal hypoplasia and underwent OCTA: a 5-year-old girl, a 40-year-old woman, and a 22-year-old man. OCTA images were taken for both eyes of all patients. Four of five eyes with foveal hypoplasia had a small but present foveal avascular zone in the deep capillary plexus, whereas all eyes had an absent or severely reduced superficial capillary plexus. CONCLUSION OCTA can be helpful in the diagnosis of foveal hypoplasia and can aid in the anatomical characterization of disease. [Ophthalmic Surg Lasers Imaging Retina. 2016;47:1127-1131.].