Showing papers on "Foveal published in 2006"

Optical coherence tomography in group 2A idiopathic juxtafoveolar retinal telangiectasis

Abstract: Objective To describe the changes observed with optical coherence tomography in group 2A idiopathic juxtafoveolar retinal telangiectasis. Methods We retrospectively reviewed the medical records of 13 patients (25 eyes). All eyes underwent optical coherence tomography examination consisting of 6 radial scans, fundus color photography, and fluorescein angiography. We calculated retinal foveal and central foveal thicknesses from software mapping results. We compared the optical coherence tomography data with fundus photography and fluorescein angiography findings. Results Foveal cystoid spaces, very small or more prominent, were present in 20 of 25 eyes. Some degree of disruption of the inner segment/outer segment photoreceptor junction line was observed in 18 eyes as from stage 2 of idiopathic juxtafoveolar retinal telangiectasis, and intraretinal pigmentary proliferation was observed in 9. A foveal detachment without subretinal new vessels was also present in 2 eyes. Despite these abnormalities, central foveal thickness was below or within the range of reference values in all eyes; foveal thickness, in 23 of 25. In the more advanced cases, severe disruption of the inner segment/outer segment photoreceptor junction line and outer retinal atrophy were seen. Conclusions Early in the evolution of group 2A idiopathic juxtafoveolar retinal telangiectasis, the optical coherence tomography examination disclosed intraretinal cystoid spaces without foveal thickening and disruption of the inner segment/outer segment photoreceptor junction line. Foveal thinning was present in later stages.

Neuroplasticity as a Double-edged Sword: Deaf Enhancements and Dyslexic Deficits in Motion Processing

Abstract: We examined the hypothesis that aspects of processing that are most modifiable by experience (i.e., “plastic”) display the most vulnerability in developmental disorders and the most compensatory enhancement after sensory deprivation. A large literature reports that motion processing and magnocellular visual function is selectively deficient in dyslexia. A smaller literature reports enhancements in such functions in deaf individuals. However, studies with dyslexic and deaf individuals have used different experimental paradigms to assess visual function, and no research has yet examined both sides of modifiability (i.e., enhancements and deficits) using the same experimental paradigm. In the present research, visual function was compared in dyslexic (n = 15), deaf (n = 17), and control adults by using automated peripheral kinetic and foveal static perimetry. In the kinetic perimetry task, the dyslexic group showed deficits ( p < .003), whereas the deaf group showed enhancements ( p < .001) for detecting moving light points in the periphery. In the foveal static perimetry task, neither the dyslexic ( p = .866) nor the deaf ( p = .632) group differed significantly from controls in foveal contrast sensitivity thresholds, and no group or individual approached ceiling performance on this task. Taken together, the present data bridge previous literatures and suggest that motion processing tasks are selectively modifiable, either to decrement or enhancement, whereas foveal contrast sensitivity does not differ in dyslexic or deaf groups.

Use of dorzolamide for patients with X-linked retinoschisis.

Abstract: Purpose: To determine the value of a topical carbonic anhydrase inhibitor for the treatment of foveal lesions in patients with X-linked retinoschisis (XLRS). Methods: Eight patients with XLRS and foveal cystic-appearing spaces by fundus examination and by optical coherence tomography (OCT) were treated with a topical form of carbonic anhydrase inhibitor. Changes in “foveal thickness” and “foveal zone thickness” were measured by OCT, and changes of best-corrected visual acuity were measured by Early Treatment Diabetic Retinopathy Study (ETDRS) charts. Results: Seven of eight patients treated with 2% dorzolamide had a noticeable reduction in foveal thickness as well as cystic-appearing spaces by OCT. This reduction was found in both eyes in four of these patients and in one eye in one patient after 1 month of treatment. After an additional 1 month to 2 months of the same treatment regimen, two additional patients also had a noticeable reduction in foveal thickness as well as cystic-appearing spaces. Of these seven patients who had an improvement shown by OCT with treatment, five also had improvement of their visual acuity by ≥7 letters in at least one eye on ETDRS charts. Conclusion: The present study shows the efficacy of topical dorzolamide for treating foveal cystic-appearing lesions in patients with XLRS.

Retinal image shifts, but not eye movements per se, cause alternations in awareness during binocular rivalry

Abstract: Particularly promising studies on visual awareness exploit a generally used perceptual bistability phenomenon, "binocular rivalry"--in which the two eyes' images alternately dominate--because it can dissociate the visual input from the perceptual output. To successfully study awareness, it is crucial to know the extent to which eye movements alter the input. Although there is convincing evidence that perceptual alternations can occur without eye movements, the literature on their exact role is mixed. Moreover, recent work has demonstrated that eye movements, first, correlate positively with perceptual alternations in binocular rivalry, and second, often accompany covert attention shifts (that were previously thought to be purely mental). Here, we asked whether eye movements cause perceptual alternations, and if so, whether it is either the execution of the eye movement or the resulting retinal image change that causes the alternation. Subjects viewed repetitive line patterns, enabling a distinction of saccades that did produce foveal image changes from those that did not. Subjects reported binocular rivalry alternations. We found that, although a saccade is not essential to initiate percept changes, the foveal image change resulting from a (micro)saccade is a deciding factor for percept dominance. We conclude that the foveal image must change to have a saccade cause a change in awareness. This sheds new light on the interaction between spatial attention shifts and perceptual alternations.

Foveal camera systems and methods

Abstract: Systems and methods are disclosed for providing foveal images. For example, high and low resolution images can be combined to provide foveal images. Parameters other than resolution can vary between the larger and smaller images of the foveal image. Real, artificial, 2D and 3D images can be used in any desired combination to form foveal images. The use of such foveal images can substantially enhance the ability of viewers to accurately and reliably interpret the content of images and provide reduce bandwidth for image transmission.

Foveated vision systems with two cameras per eye

Abstract: In this paper we discuss active humanoid vision systems that realize foveation using two rigidly connected cameras in each eye. We present an exhaustive analysis of the relationship between the positions of the observed point in the foveal and peripheral view with respect to the intrinsic and extrinsic parameters of both cameras and 3-D point position. Based on these results we propose a control scheme that can be used to maintain the view of the observed object in the foveal image using information from the peripheral view. Experimental results showing the effectiveness of the proposed foveation control are also provided

Chiasmal misrouting and foveal hypoplasia without albinism

Abstract: Background/aims: To present the ophthalmological and electrophysiological characteristics of three darkly pigmented, female patients with misrouting and foveal hypoplasia. One of the patients had primary ciliary dyskinesia and situs inversus totalis (Kartagener syndrome). Methods: Fundus photographs were taken and the angles at which the main temporal arterial branches leave the optic nerve head (ONH) were analysed. Optical coherence tomography (OCT) was performed through the presumed foveal region. Pattern onset visually evoked potentials (VEPs) (check sizes 60′, 40/400 ms) were recorded and the chiasmal coefficient was calculated to detect misrouting. Results: Fundus photography showed normally pigmented fundi with absence of the usual foveal hyperpigmentation, foveal avascular zone, and macular and foveal reflexes. On OCT no foveal pit was found. The VEP recordings showed the largest positive CI component over the right hemisphere for the left eye, and over the left hemisphere for the right eye, with the CI almost absent over the ipsilateral hemispheres. The differential derivations showed opposite polarity for the recordings of the two eyes. The chiasmal coefficients of all three patients were significantly indicative of misrouting (−0.99, −0.91, and −0.99, respectively). Conclusion: Based on the investigations in these patients the authors propose the hypothesis that foveal hypoplasia and misrouting exist as a distinct entity, and do not comprise the exclusive hallmark of albinism. The findings suggest that misrouting may exert a retrograde influence on foveal development.

Retinal locus for scanning text.

Abstract: --A method of mapping the retinal location of text during reading is described in which text position is plotted cumulatively on scanning laser ophthalmoscope retinal images. Retinal locations that contain text most often are the brightest in the cumulative plot, and locations that contain text least often are the darkest. In this way, the retinal area that most often contains text is determined. Text maps were plotted for eight control subjects without vision loss and eight subjects with central scotomas from macular degeneration. Control subjects' text maps showed that the fovea contained text most often. Text maps of five of the subjects with scotomas showed that they used the same peripheral retinal area to scan text and fixate. Text maps of the other three subjects with scotomas showed that they used separate areas to scan text and fixate. Retinal text maps may help evaluate rehabilitative strategies for training individuals with central scotomas to use a particular retinal area to scan text. Key words: eccentric viewing, fixation, fixation PRL, preferred retinal locus, reading, reading rehabilitation, retinal function mapping, scanning laser ophthalmoscope, text scanning, text-scanning PRL INTRODUCTION When individuals without vision loss read, their fast saccadic eye movements sequentially shift the characters in a line of text onto the fovea, the retinal area of highest acuity, where they are held in place and visually processed. This typical reading process is disrupted when foveal vision is lost because of macular disease. Normal reading rates usually exceeding 150 words a minute can drop to approximately 25 words a minute or less [1]. Individuals with foveal vision loss resulting in dense central scotomas use a peripheral retinal area (preferred retinal locus [PRL]) adjacent to the scotoma to fixate and inspect small visual objects, such as single letters. They may also use this fixation PRL (fPRL) to scan extended sentences and paragraph text. Over the past 25 years, various rehabilitative strategies have been proposed for enhancing use of eccentric (i.e., PRL) viewing and improving reading rates [2-4]. These rehabilitative measures have met with some success but may be less than optimal. One impediment to the development of effective reading rehabilitation strategies has been the lack of a means to adequately characterize the retinal area used for scanning text. Determining the fPRL for inspecting small visual objects such as fixation targets, letters, or short words is relatively straightforward because these visual stimuli are spatially discrete. Consequently, their positions on the retina are readily characterized with multiple scanning laser ophthalmoscope (SLO) images. Mapping the retinal locus for scanning multiple words in paragraphs is more problematic, however, since the text is spatially extensive and occupies a much larger retinal area. For example, Figure 1 shows an SLO image of paragraph text on a retina with a hypothetical scotomatous central lesion. The text extends beyond the scotoma on all sides. In this hypothetical example, the retinal area being used to inspect the text at the moment the SLO image was made is impossible to determine. As shown by the ovals with question marks, many possibilities exist (Figure 1). One cannot assume that the fPRL for inspecting small objects was also used for scanning the extended text. [FIGURE 1 OMITTED] Here we report a method for mapping the retinal area that subjects used to scan text during reading. This method is based on an earlier graphical method [5]. The present method cumulatively plots text position on an SLO retinal image. In the cumulative plot, retinal areas that contained text most often will be the brightest, and those that contained text least often will be the darkest. In this way, we can determine the retinal region that most often contains text. In essence, the method is like a time exposure of film in a camera. …

Stochastic re-calibration: contextual effects on perceived tilt

Abstract: The human visual system exaggerates the difference between the tilts of adjacent lines or grating patches. In addition to this tilt illusion, we found that oblique flanks reduced acuity for small changes of tilt in the centre of the visual field. However, no flanks—regardless of their tilts—decreased sensitivity to contrast. Thus, the foveal tilt illusion should not be attributed to orientation-selective lateral inhibition. Nor is it similar to conventional crowding, which typically does not impair letter recognition in the fovea. Our observers behaved as though the reference orientation (horizontal) had a small tilt in the direction of the flanks. We suggest that the extent of this re-calibration varies randomly over trials, and we demonstrate that this stochastic re-calibration can explain flank-induced acuity loss in the fovea.

Birefringence-based eye fixation monitor with no moving parts.

Abstract: For the purpose of vision screening, we develop an eye fixation monitor that detects the fovea by its unique radial orientation of birefringent Henle fibers. Polarized near-infrared light is reflected from the foveal area in a bow-tie pattern of polarization states, similar to the Haidinger brush phenomenon. In contrast to previous devices that used scanning systems, this instrument uses no moving parts. It rather utilizes four spots of linearly polarized light-two aligned with the "bright" arms and two aligned with the "dark" arms-of the bow-tie pattern surrounding the fovea. The light reflected from the fundus is imaged onto a quadrant photodetector, whereby the circular polarization component of the polarization state of each reflected patch of light is measured. The signals from the four photodetectors are amplified, digitized, and analyzed. A normalized differential signal is computed to detect central fixation. The algorithm is tested on a computer model, and the apparatus is tested on human subjects. This work demonstrates the feasibility of a fixation monitor with no moving parts.

Constant contour integration in peripheral vision for stimuli with good Gestalt properties

Abstract: The visual system integrates discrete but aligned local stimuli to form percept of global contours. Previous experiments using "snake'' contours showed that contour integration was mainly present in foveal vision but absent or greatly weakened in peripheral vision. In this study, we demonstrated that, for contour stimuli such as circles and ellipses, which bore good Gestalt properties, contour integration for shape detection and discrimination was nearly constant from the fovea to up to 35 degrees visual periphery! Contour integration was impaired by local orientation and position jitters of contour elements, indicating that the same local contour linking mechanisms revealed with snake contour stimuli also played critical roles in integration of our good Gestalt stimuli. Contour integration was also unaffected by global position jittering up to 20% of the contour size and by dramatic shape jittering, which excluded non-contour integration processes such as detection of various local cues and template matching as alternative mechanisms for uncompromised peripheral perception of good Gestalt stimuli. Peripheral contour integration also presented an interesting upper-lower visual field symmetry after asymmetries of contrast sensitivity and shape discrimination were discounted. The constant peripheral performance might benefit from easy detection of good Gestalt stimuli, which popped out from background noise, from a boost of local contour linking by top down influences and/or from multielement contour linking by long-range interactions.

Fundus foveal localization based on vessel model.

Abstract: The problem of automatically locating the fovea, a spot located in the center of the macula and responsible for sharp central vision, on the retinal surface image is considered. The uniqueness of the strategy presented here is the relatively small amount of computational expense of a quick and robust method conducive to real-time applications. The algorithm first identifies the main blood vessels using the modified active shape model (ASM) and then expeditiously attempts to fit the parabolic shape to the overall result to locate the fovea. A reliable tracking strategy is also proposed here to estimate the required vertex when the prior information of the optic disk is not available. When a patient's retinal vessel data have been modeled a priori and used as template, the technique brought up here should find its advantage in real-time image-guided applications like a computer-assisted photocoagulation treatment. Index term: retinal image, ASM, foveal localization, vessel tracking

Visual Development and Amblyopia

Abstract: At birth, visual acuity is poor, in the range of hand motions to count fingers. For the most part, this is due to immaturity of visual centers in the brain responsible for vision processing. Visual acuity rapidly improves during the first few months of life as clear in-focus retinal images stimulate neurodevelopment of visual centers, including the lateral geniculate nucleus and striate cortex.52 Dropout and growth of neuronal connections give rise to the organizational refinement and establish high-resolution receptive fields corresponding to the central foveal area.18,23 Normal visual development requires appropriate visual stimulation, including clear retinal images, with equal image clarity in both eyes (Table 10-1).

A foveal inset for large display environments

Abstract: We introduce a system that adds a foveal inset to large-scale projection displays. The effective resolution of the foveal inset projection is higher than the original display resolution, allowing the user to see more details and finer features in large data sets. The foveal inset is generated by projecting a high-resolution image onto a mirror mounted on a pan--tilt unit that is controlled by the user with a laser pointer. Our implementation is based on Chromium and supports many OpenGL applications without modifications. We present experimental results using high-resolution image data from medical imaging and areal photography.

System and method for image mapping and visual attention

Abstract: A method is described for mapping dense sensory data to a Sensory Ego Sphere (SES) (220) Methods are also described for finding and ranking areas of interest in the images that form a complete visual scene on an SES (220) Further, attentional processing of image data is best done by performing attentional processing on individual full-size images from the image sequence, mapping each attention location to the nearest node, and then summing all attentional locations at each node More information is available through this method since attentional processing is repeatedly done on each image in the sequence An attentional point that has persisted in several adjacent images will have a higher activation value and, therefore, will be deemed more salient than an attentional point found in only one image Therefore, the confidence that a location deemed salient by this method is an actual salient feature is greater than with the alternative processing methods in which attentional processing is performed only once on the image reconstructed from the foveal windows posted on the SES (220)

Foveal detachment after successful retinal reattachment for macula on rhegmatogeneous retinal detachment: an ocular coherence tomography evaluation.

Abstract: Foveal detachment after apparently successful retinal reattachment surgery for macula-on retinal detachments (RDs) has been previously documented. This pilot study aimed to utilize ocular coherence tomography (OCT) imaging to investigate foveal architecture after routine retinal detachment surgery and correlate this to visual acuity. Prospective recruitment of patients attending one unit with macula-on RDs. Patients underwent full clinical examination including OCT preoperatively and RD surgery undertaken by scleral buckling, external drainage and air injection. Postoperatively patients had clinical examinations and OCT at 1 week, 1, 3, 6, and 12 months. A total of 12 consecutive patients were recruited into the study. All had macula-on RDs and normal OCTs at onset. There were no operative or postoperative complications. Retinal reattachment was achieved in all cases within 24 h postoperatively. At 1 month six of 12 patients (50%) showed foveal detachment on OCT, which was invisible on clinical examination. At 3 months, the foveal detachment persisted in four (33%) of these patients. In these cases the foveal detachment persisted at 6 months follow-up, however, a reduction in subfoveal fluid was noted. All cases had foveal reattachment by 12 months postoperatively. Visual acuity was closely correlated to the presence of foveal attachment. A high proportion of patients with successful retinal reattachment surgery had foveal detachments postoperatively. This phenomenon was associated with reduced visual acuity. The aetiology of this occurrence is unknown and warrants further investigation as there is the potential of a long-term effect on vision.

Perception of very small visual stimuli in the fovea: normative data for the Rarebit Foveal Test

Abstract: Background: Conventional visual tests are not sensitive enough to detect low degree neural damage, as 6/6 (1.0) visual acuity can be upheld with less than two-thirds of the normal number of optic nerve axons. The aim of the current study was to evaluate the physiologic properties of a new computerised test, the Rarebit Fovea Test (RFT), using very small stimuli, by quantifying the effect of age and binocular summation in relation to stimulus luminance. Methods: The RFT relies on the perception of very small (less than 0.5 minutes of arc) bright stimuli. Two different experiments were performed. 1 Thirty-five subjects (age 19 to 63 years) were tested with five different stimulus luminances, 158, 64, 53, 41 and 33 cd/m2. 2 Nineteen subjects (age 19 to 63 years) were tested using binocular stimulation to define the binocular summation. Results: Significantly reduced median hit rates were observed at luminances of 53 cd/m2 or below. Age and mean hit rate correlated negatively at all luminance levels below 158 cd/m2. The mean hit rate from binocular stimulation, compared to the highest value from monocular stimulation in the same subject, was increased by a factor of 1.54 ± 0.45 (SD). No age effect was found regarding binocular summation. Conclusions: The results in the current study indicate that RFT can identify some of the well-known features of the visual system, that is, the effects of age and binocular summation, provided that the stimulus luminance is adequately selected.

A Distal Model of Congenital Nystagmus as Nonlinear Adaptive Oscillations

Abstract: Congenital nystagmus (CN) is an incurable pathological spontaneous oscillation of the eyes with an onset in the first few months of life The pathophysiology of CN is mysterious There is no consistent neurological abnormality, but the majority of patients have a wide range of unrelated congenital visual abnormalities affecting either the cornea, lens, retina or optic nerve In this theoretical study, we show that these eye oscillations could develop as an adaptive response to maximize visual contrast with poor foveal function in the infant visuomotor system, at a time of peak neural plasticity We argue that in a visual system with abnormally poor high spatial frequency sensitivity, image contrast is not only maintained by keeping the image on the fovea (or its remnant) but also by some degree of image motion Using the calculus of variations, we show that the optimal trade-off between these conflicting goals is to generate oscillatory eye movements with increasing velocity waveforms, as seen in real CN When we include a stochastic component to the start of each epoch (quick-phase inaccuracy) various observed waveforms (including pseudo-cycloid) emerge as optimal strategies Using the delay embedding technique, we find a low fractional dimension as reported in real data We further show that, if a velocity command-based pre-motor circuitry (neural integrator) is harnessed to generate these waveforms, the emergence of a null region is inevitable We conclude that CN could emerge paradoxically as an ‘optimal’ adaptive response in the infant visual system during an early critical period This can explain why CN does not emerge later in life and why CN is so refractory to treatment It also implies that any therapeutic intervention would need to be very early in life

Strategies for Object Manipulation using Foveal and Peripheral Vision

Abstract: Visual feedback is used extensively in robotics and application areas range from human-robot interaction to object grasping and manipulation. There have been a number of examples of how to develop different components required by the above applications and very few general vision systems capable of performing a variety of tasks. In this paper, we concentrate on vision strategies for robotic manipulation tasks in a domestic environment. In particular, given fetch-and-carry type of tasks, the issues related to the whole detect-approach-grasp loop are considered. We deal with the problem of flexibility and robustness by using monocular and binocular visual cues and their integration. We demonstrate real-time disparity estimation, object recognition and pose estimation. We also show how a combination of foveal and peripheral vision system can be combined in order to provide a wide, low resolution and narrow, high resolution field of view.

Integrity of foveal cones in multiple evanescent white dot syndrome assessed with OCT and foveal reflection analyser.

Abstract: In this report, foveal photoreceptor involvement in a case of multiple evanescent white dot syndrome (MEWDS) is described by using two optical techniques: optical coherence tomography (OCT) and foveal reflection analysis (FRA). OCT showed a transient disruption of the foveal photoreceptor outer segments. FRA, a recently developed quantitative technique, showed disarray of the foveal cones. A 20 year old myopic Sudanese female presented at our hospital with a central visual field defect of her right eye, associated with photopsia. Visual acuity was 0.3; intraocular pressure was 16 mm Hg. Funduscopic examination of the affected eye showed some pigment epithelial alterations in the macular area, with an irregular macular reflex. Upon visual field examination, the affected eye showed a 12 dB decrease in central sensitivity, and a small blind spot enlargement was seen. No such changes were found in the left eye. OCT showed degeneration or disarray of foveal photoreceptor outer segments in the …

A reinforcement learning approach to active camera foveation

Abstract: In this paper we report on techniques for automatically learning foveal sensing strategies for an active pan-tilt-zoom camera. The approach uses reinforcement learning to discover foveal actions maximizing the performance of visual detectors, that are in turn assumed to be highly correlated with the task at hand. In our case,the main goal is to recognize people, hence a frontal face detection module is employed. The system uses reinforcement learning to learn if when and how to foveate on a subject, basedonits previous experience in terms or successful actions in similar situations. An action is successful if it leads to a correct face detection in the high resolution images obtained when the subject is zoomed in. In contrast with existing methods,the proposed approach obviates the need for camera calibration and camera performance modeling. Also, the method does not rely on active tracking of targets. Experimental results show how the system can be deployed in unconstrained surveillance environments, and is capable of learning foveation strategies without requiring extensive a priori information or environmental models. Results also illustrate how the system effectively learns a strategy that allows the camera to foveate only in situations where successful detection is highly likely.