Gaze-contingent flicker pupil perimetry detects scotomas in patients with cerebral visual impairments or glaucoma

The pupillary light reflex is weaker for stimuli presented inside as compared to outside absolute scotomas. Pupillograph perimetry could thus be an objective measure of impaired visual processing. However, the diagnostic accuracy in detecting scotomas has remained unclear. We quantitatively investigated the accuracy of a novel form of pupil perimetry. The new perimetry method, termed gaze-contingent flicker pupil perimetry, consists of the repetitive on, and off flickering of a bright disk (2 hz; 320 cd/m; 4° diameter) on a gray background (160 cd/m) for 4 seconds per stimulus location. The disk evokes continuous pupil oscillations at the same rate as its flicker frequency, and the oscillatory power of the pupil reflects visual sensitivity. We monocularly presented the disk at a total of 80 locations in the central visual field (max. 15°). The location of the flickering disk moved along with gaze to reduce confounds of eye movements (gaze-contingent paradigm). The test lasted ~5 min per eye and was performed on 7 patients with cerebral visual impairment (CVI), 8 patients with primary open angle glaucoma (age >45), and 14 healthy, age/gender-matched controls. For all patients, pupil oscillation power (FFT based response amplitude to flicker) was significantly weaker when the flickering disk was presented in the impaired as compared to the intact visual field (CVI: 12%, AUC = 0.73; glaucoma: 9%, AUC = 0.63). Differences in power values between impaired and intact visual fields of patients were larger than differences in power values at corresponding locations in the visual fields of the healthy control group (CVI: AUC = 0.95; glaucoma: AUC = 0.87). Pupil sensitivity maps highlighted large field scotomas and indicated the type of visual field defect (VFD) as initially diagnosed with standard automated perimetry (SAP) fairly accurately in CVI patients but less accurately in glaucoma patients. We provide the first quantitative and objective evidence of flicker pupil perimetry's potential in detecting CVI-and glaucoma-induced VFDs. Gaze-contingent flicker pupil perimetry is a useful form of objective perimetry and results suggest it can be used to assess large VFDs with young CVI patients whom are unable to perform SAP

Effects of age and eccentricity on visual target detection

The aim of this study was to examine the effects of aging and target eccentricity on a visual search task comprising 30 images of everyday life projected into a hemisphere, realizing a ±90° visual field. The task performed binocularly allowed participants to freely move their eyes to scan images for an appearing target or distractor stimulus (presented at 10°; 30°, and 50° eccentricity). The distractor stimulus required no response, while the target stimulus required acknowledgment by pressing the response button. One hundred and seventeen healthy subjects (mean age = 49.63 years, SD = 17.40 years, age range 20–78 years) were studied. The results show that target detection performance decreases with age as well as with increasing eccentricity, especially for older subjects. Reaction time also increases with age and eccentricity, but in contrast to target detection, there is no interaction between age and eccentricity. Eye movement analysis showed that younger subjects exhibited a passive search strategy while older subjects exhibited an active search strategy probably as a compensation for their reduced peripheral detection performance

Maintaining fixation by children in a virtual reality version of pupil perimetry

The assessment of visual field sensitivities in young children continues to be a challenge. Children often do not sit still, fail to fixate stimuli for longer durations, and have limited verbal capacity to report visibility. We investigated the use of a head-mounted VR display, gaze-contingent flicker pupil perimetry (gcFPP), and three fixation stimulus conditions to determine best practices for optimal fixation and pupil response quality. A total of twenty children (3-11y) passively fixated a dot, counted the repeated appearance of an animated character, and watched an animated movie in separate trials of 80s each. We presented large flickering patches at different eccentricities and angles in the periphery to evoke pupillary oscillations (20 locations, 4s per location). The results showed that gaze precision and accuracy did not differ significantly across the fixation conditions but pupil amplitudes were strongest for the dot and count task. We recommend the use of the fixation counting task for pupil perimetry because children enjoyed it the most and it achieved strongest pupil responses. The VR set-up appears to be an ideal apparatus for children to allow free range of movement, an engaging visual task, and reliable eye measurements

The worse eye revisited: Evaluating the impact of asymmetric peripheral vision loss on everyday function

In instances of asymmetric peripheral vision loss (e.g., glaucoma), binocular performance on simple psychophysical tasks (e.g., static threshold perimetry) is well-predicted by the better seeing eye alone. This suggests that peripheral vision is largely ‘better-eye limited’. In the present study, we examine whether this also holds true for real-world tasks, or whether even a degraded fellow eye contributes important information for tasks of daily living. Twelve normally-sighted adults performed an everyday visually-guided action (finding a mobile phone) in a virtual-reality domestic environment, while levels of peripheral vision loss were independently manipulated in each eye (gaze-contingent blur). The results showed that even when vision in the better eye was held constant, participants were significantly slower to locate the target, and made significantly more head- and eye-movements, as peripheral vision loss in the worse eye increased. A purely unilateral peripheral impairment increased response times by up to 25%, although the effect of bilateral vision loss was much greater (>200%). These findings indicate that even a degraded visual field still contributes important information for performing everyday visually-guided actions. This may have clinical implications for how patients with visual field loss are managed or prioritized, and for our understanding of how binocular information in the periphery is integrated

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Psychophysical Studies Of Motion Perception In Autism Spectrum Disorders

Introduction Studies have shown considerable evidence of visual dysfunction in Autism Spectrum Disorders (ASD). Motion perception research in ASD reports a superior performance in processing motion information of fine details and neglects global information. However, there are many variabilities in these experimental results, particularly in adults with autism. Several theories have been put forward as the underlying cause(s) of motion deficits in autism. These include: enhanced local domain information processing at early visual area V1; abnormal processing at the higher visual cortical area MST including V5/MT; and/or abnormal functional and structural connectivity between and within cortical networks that are recruited during different motion processing tasks. In this study, we used multiple motion perception tasks in order to activate different visual neural networks that may contribute to perception of specific motion domains in order to understand visual perception abnormalities in autism. The specific aims of each experiment included in this thesis are as follow: • Chapter 3: To investigate the theory of enhanced local details and neglected global picture, using- for the first time- local/global motion coherence stimuli in autism. • Chapter 4: To investigate the neural response biased found in autism in response to radial optic flow. We used optic flow stimuli in self-heading direction discrimination tasks. • Chapter 5: To investigate whether speed parameter is normal in autism-based on the previous outcome- using drifting grating stimuli in a speed discrimination task. Participants and Methods This study recruited two groups of subjects –one with ASD (n = 14), and another with Typical Development (TD) (n= 14), age range (16- 40 years). • Chapter 3 : We used Random Dot Kinatogram (RDK) as global coherence stimuli and employed it in two tasks : (1) Coherent Motion (CM) task, where coherence levels were varied and the subjects had to detect the global direction of the coherent dots, (2) CM with Form From Motion (FfM) stimulus where the FfM consisted of one of four different shapes embedded in the global RDK task. • Chapter 4: We used RDK with optic flow stimuli, which investigated self-direction discrimination in two tasks: angle of eccentricity, and contrast sensitivity. In both tasks we randomized the dot density (15, 80 dots) and speed (4, 10 deg/sec) of the moving stimulus dots. • Chapter 5: We used a pair of drifting gratings with a spatial frequency 2 cycle/ degree, oriented vertically and drifting perpendicular to the direction of orientation, and varied the speed (2, 6 deg/ sec) and the stimuli presentation (250 – 500ms) Results • Chapter 3: Although adults with autism showed comparable performance in reporting global direction similar to the control group, their ability to process global properties, when FfM shape was embedded, declined ( Mean threshold ASD: MC= 13.58, CM-FfM= 30.65) In addition, ASD required more time to respond to global coherence even when their performance was comparable to that of the control group. • Chapter 4: No significant group differences were found for low dot density (15 dots), while high dot (80 dots) density showed low sensitivity to OF motion in the ASD group compared to the TD. Contrast sensitivity task, however, showed lower sensitivity in the ASD group for detecting OF motion when dot density was low (15 dots) and no differences at higher dot density (80 dots) was found. Both tasks showed no group differences in the dot speed changing and no significant differences in response time were observed. • Chapter 5: No group differences (p = 0.226) in sensitivity to speed-discrimination task were found between the ASD and control group in all parameters used in this experiment. The response times were also comparable between both groups (p = 0.855). Conclusions • Chapter 3: Motion perception in ASD found enhanced to local details particularly when motion stimuli involve both local/global information segregation at the same time. We suggest increased internal neural noise and worse external noise filtering as cause of poor global performance in this type of task. • Chapter 4: There were selective impairments in OF processing that may related to altered neural connectivity between the activated visual areas in ASD. Another suggestion might be related to long neural trajectory within higher visual areas, ex. MST. • Chapter 5: Normal motion processing may be found in ASD, however, it this might triggered by task complexity and the visual neural areas that are involved in processing motion information. The overall results suggest selective impairments in visual motion perception in ASD. These impairments would depend upon the task requirements and therefore on the activated visual networks that contribute to different aspects of motion information processing. The present studies provide novel findings in defining deficits in motion perception in autism, which thereby may contribute in understanding disturbed visual function in ASD

Maintaining fixation by children in a virtual reality version of pupil perimetry

The assessment of the visual field in young children continues to be a challenge. Children often do not sit still, fail to fixate stimuli for longer durations, and have limited verbal ca-pacity to report visibility. Therefore, we introduced a head-mounted VR display with gaze-contingent flicker pupil perimetry (VRgcFPP). We presented large flickering patches at different eccentricities and angles in the periphery to evoke pupillary oscillations, and three fixation stimulus conditions to determine best practices for optimal fixation and pupil response quality. A total of twenty children (3-11y) passively fixated a dot, counted the re-peated appearance of an animated character(counting task), and watched an animated movie in separate trials of 80s each (20 patch locations, 4s per location).The results showed that gaze precision and accuracy did not differ significantly across the fixation conditions but pupil amplitudes were strongest for the dot and count task. The VR set-up appears to be an ideal apparatus for children to allow free range of movement, an engaging visual task, and reliable eye measurements. We recommend the use of the fixation count-ing task for pupil perimetry because children enjoyed it the most and it achieved strongest pupil responses

Perceptual modelling for 2D and 3D

Livrable D1.1 du projet ANR PERSEECe rapport a été réalisé dans le cadre du projet ANR PERSEE (n° ANR-09-BLAN-0170). Exactement il correspond au livrable D1.1 du projet

Ocular aberrations and visual quality in aspherical and multifocal contact lenses

Good visual quality and precise accommodation are required to be able to focus objects at distance and near, and are essential in order to be able to perform most tasks in life. Most eyes are not ideal eyes, i.e., they have different refractive errors which distort the produced image. The well-known refractive errors (lower order aberrations), myopia, hyperopia and astigmatism, have long been correctable. In addition to these common errors, irregularities in the refractive media create higher order aberrations, which are described by the Zernike polynomials. To achieve a higher level of visual quality, it is important to correct aberrations. Spherical aberration and chromatic aberration, present in polychromatic light, serve as cues for accurate accommodation in order to provide a clear image of the object. It is of interest to know how a reduction or increase of certain aberrations might affect visual quality and accommodation. The aim of this project was to develop techniques to measure the changes in optical aberrations and accommodation in subjects while wearing standard contact lenses, and lenses with aberration control and to find new strategies to enhance the fitting of these lenses in order to achieve a higher level of visual quality. Using an aberrometer, residual spherical aberration was evaluated with a standard contact lens and with a lens with spherical aberration control. Visual quality (i.e. visual acuity and contrast sensitivity) was also evaluated with the different contact lenses. Aberration and accommodation were measured with and without accommodative cues present. Accommodation was evaluated with a multifocal contact lens with a near reading addition. The results show that it is possible to evaluate residual spherical aberration with contact lenses on the eye, but the change in aberration gave no difference in visual acuity or contrast sensitivity at distance or near with the methods used. Spherical aberration and chromatic aberration were shown not to be strong directional cues for accommodation, indicating that there are other cues more important for directional information. Since the multifocal contact lens, a centre distance design with reading addition +1.00, was not able to relax the accommodation for the subjects, it is therefore unlikely that subjects with reduced accommodative ability can effectively be treated with such a lens. In conclusion, a wavefront measurement should be performed both with and without contact lenses, in order to know the amount of aberration in the eye and to note any change from a contact lens. The relatively small change in spherical aberration that non-customised lenses induce does not affect visual acuity, contrast sensitivity or accommodation. These lenses may then be fitted without worrying about affecting accommodation and they do not seem suitable to be fitted on young subjects with the ability to accommodate with the purpose of reducing their accommodative load. There is still reason to believe that there are subgroups of patients who can achieve better visual quality, but more sensitive clinical methods have to be developed