Phosphene Threshold Research Articles

Transcorneal Electrical Stimulation for Patients With Retinitis Pigmentosa: A Prospective, Randomized, Sham-Controlled Follow-up Study Over 1 Year.

After promising results of an exploratory study, this study was designed to assess the safety and efficacy of transcorneal electrical stimulation (TES) over 1 year in patients with retinitis pigmentosa (RP). We included 52 RP patients in this prospective, randomized, partially-masked study which was done in accordance with rules of good clinical practice. Transcorneal electrical stimulation by Okustim was applied monocularly for 30 minutes per week for 52 consecutive weeks. Patients were assigned randomly to the groups: sham, 150%, or 200% of individual electrical phosphene threshold (EPT). Visual acuity (retroilluminated Snellen charts), visual field (VF; Octopus 900), electroretinography (ERG), rod and cone full-field stimulus threshold, EPTs and IOP were assessed. Primary outcome measures were VF area; secondary outcome measures were development of ERG parameters. The application of TES was tolerated well. Dry eye symptoms (31 of 52 patients) were registered as the main adverse event. Throughout the study period, the VF area showed only a trend for prevention of VF loss in the 200% group (P = 0.24). A significant improvement of light-adapted single flash b-wave was noted for the 200% (P < 0.0001) and 150% (P = 0.006) groups compared to the sham group. Tendencies of improved function were observed for scotopic b-wave amplitude for the 200% group (P = 0.097). Other examination methods did not reach statistical significance. The safety and acceptable tolerability of weekly TES self-administered by patients at home was confirmed over the course of 1 year. Objectively measured improvements in retinal function with ERG provide support for the potential benefits of TES for RP patients.

No Modulation of Visual Cortex Excitability by Transcranial Direct Current Stimulation.

Measuring phosphene thresholds (PTs) is often used to investigate changes in the excitability of the human visual cortex through different brain stimulation methods like repetitive transcranial magnetic stimulation (rTMS) or transcranial direct current stimulation (tDCS). In several studies, PT increase or decrease has been shown after rTMS or tDCS application. Recently, using PT measurements we showed that the state of the neurons in the visual cortex after rTMS might have an influence on the modulatory effects of stimulation. In the present study we aimed to investigate whether visual cortex activity following stimulation influences the modulatory effects of tDCS as well. In a between-group design, anodal or cathodal tDCS was applied to the visual cortex twice per subject, with either high or low visual demand following stimulation. We observed no modulation of PT neither directly following both anodal and cathodal tDCS nor following the visual demand periods. We rather found high inter-individual variability in the response to tDCS, and intra-individual reliability in the direction of modulation was observed for cathodal tDCS only. Thus, our results do not confirm the modulatory effects of tDCS on visual cortex excitability published previously. Moreover, they support the confirmation that tDCS effects have little reliability on varied TMS outcome measurements.

Differential effect of visual motion adaption upon visual cortical excitability.

The objectives of this study were 1) to probe the effects of visual motion adaptation on early visual and V5/MT cortical excitability and 2) to investigate whether changes in cortical excitability following visual motion adaptation are related to the degree of visual dependency, i.e., an overreliance on visual cues compared with vestibular or proprioceptive cues. Participants were exposed to a roll motion visual stimulus before, during, and after visual motion adaptation. At these stages, 20 transcranial magnetic stimulation (TMS) pulses at phosphene threshold values were applied over early visual and V5/MT cortical areas from which the probability of eliciting a phosphene was calculated. Before and after adaptation, participants aligned the subjective visual vertical in front of the roll motion stimulus as a marker of visual dependency. During adaptation, early visual cortex excitability decreased whereas V5/MT excitability increased. After adaptation, both early visual and V5/MT excitability were increased. The roll motion-induced tilt of the subjective visual vertical (visual dependence) was not influenced by visual motion adaptation and did not correlate with phosphene threshold or visual cortex excitability. We conclude that early visual and V5/MT cortical excitability is differentially affected by visual motion adaptation. Furthermore, excitability in the early or late visual cortex is not associated with an increase in visual reliance during spatial orientation. Our findings complement earlier studies that have probed visual cortical excitability following motion adaptation and highlight the differential role of the early visual cortex and V5/MT in visual motion processing.NEW & NOTEWORTHY We examined the influence of visual motion adaptation on visual cortex excitability and found a differential effect in V1/V2 compared with V5/MT. Changes in visual excitability following motion adaptation were not related to the degree of an individual's visual dependency.

Analysis of retinal function using chromatic pupillography in retinitis pigmentosa and the relationship to electrically evoked phosphene thresholds.

To analyse pupil responses to specific chromatic stimuli in patients with advanced retinitis pigmentosa (RP) to ascertain whether chromatic pupillography can be used as an objective marker for residual retinal function. To examine correlations between parameters of the pupil response and the perception threshold of electrically evoked phosphenes. Chromatic pupillography was performed in 40 patients with advanced RP (visual acuity<0.02 or visual field ≤5°, non-recordable ERGs) and 40 age-matched healthy subjects. Pupil responses to full-field red (605nm) and blue (420nm) stimuli of 28 lx corneal illumination were recorded and analysed for two stimulus durations (1 and 4seconds). The perception threshold of phosphenes to transcorneal electrostimulation was ascertained and correlated to the pupil responses and visual acuity. Patients with RP showed significantly reduced pupil responses to red and blue stimuli compared with the controls. With red stimuli, pupillary escape could be observed; blue stimuli resulted in a well-preserved postillumination pupil response. Phosphene thresholds were significantly increased in patients with RP and correlated with the parameters of the pupil response if all subjects were considered. Within the RP group alone, this relationship was less pronounced and statistically not significant. Chromatic pupillography demonstrated a significant decrease in outer retinal photoreceptor responses but a persisting and disinhibited intrinsic photosensitive retinal ganglion cell function in advanced RP. These phenomena may be useful as an objective marker for the efficacy of any interventional treatment for hereditary retinal diseases as well as for the selection of suitable patients for an electronic retinal implant.

Repetitive Transcranial Direct Current Stimulation Induced Excitability Changes of Primary Visual Cortex and Visual Learning Effects-A Pilot Study.

Studies on noninvasive motor cortex stimulation and motor learning demonstrated cortical excitability as a marker for a learning effect. Transcranial direct current stimulation (tDCS) is a non-invasive tool to modulate cortical excitability. It is as yet unknown how tDCS-induced excitability changes and perceptual learning in visual cortex correlate. Our study aimed to examine the influence of tDCS on visual perceptual learning in healthy humans. Additionally, we measured excitability in primary visual cortex (V1). We hypothesized that anodal tDCS would improve and cathodal tDCS would have minor or no effects on visual learning. Anodal, cathodal or sham tDCS were applied over V1 in a randomized, double-blinded design over four consecutive days (n = 30). During 20 min of tDCS, subjects had to learn a visual orientation-discrimination task (ODT). Excitability parameters were measured by analyzing paired-stimulation behavior of visual-evoked potentials (ps-VEP) and by measuring phosphene thresholds (PTs) before and after the stimulation period of 4 days. Compared with sham-tDCS, anodal tDCS led to an improvement of visual discrimination learning (p < 0.003). We found reduced PTs and increased ps-VEP ratios indicating increased cortical excitability after anodal tDCS (PT: p = 0.002, ps-VEP: p = 0.003). Correlation analysis within the anodal tDCS group revealed no significant correlation between PTs and learning effect. For cathodal tDCS, no significant effects on learning or on excitability could be seen. Our results showed that anodal tDCS over V1 resulted in improved visual perceptual learning and increased cortical excitability. tDCS is a promising tool to alter V1 excitability and, hence, perceptual visual learning.

Visual cortical excitability in dementia with Lewy bodies.

Alterations in the visual system may underlie visual hallucinations in dementia with Lewy bodies (DLB). However, cortical excitability as measured by transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) activation of lower visual areas (V1–3) to visual stimuli appear normal in DLB. We explored the relationship between TMS-determined phosphene threshold and fMRI-related visual activation and found a positive relationship between the two in controls but a negative one in DLB. This double dissociation suggests a loss of inhibition in the visual system in DLB, which may predispose individuals to visual dysfunction and visual hallucinations.

23. Visuo-motor connectivity in photosensitive epilepsies

Objective Visual and motor cortex are involved in the origin/propagation of the photoparoxysmal response (PPR), a stronghold for the diagnosis of generalized photosensitive epilepsies. The study of the functional connection between these two distant areas with transcranial magnetic stimulation (TMS), could help clarify the pathophysiology of photosensitivity. Methods Eleven patients with idiopathic generalized epilepsy and photosensitivity were compared to 11 healthy subjects. We measured the resting motor threshold of the left hand motor area and the phosphene threshold. The paradigm consisted in a conditioning stimulus (CS) delivered over the phosphene hotspot of the visual cortex and followed at random interstimulus intervals (15–40 ms) by a test stimulus over the left motor cortex to evoke a motor evoked potential (MEP) of ∼1 mV from right FDI. The conditioned-MEP was expressed as a percentage of the unconditioned-MEP amplitude. Results In healthy subjects the CS over the visual cortex produced significant inhibitory changes on the corticospinal excitability with a time course between 18 and 40 ms. Patients with IGE and photosensitivity showed a failure of the physiological inhibition. Conclusions In photosensitive patients the alteration of the normal visuo-motor functional connectivity could be responsible for the origin/propagation of the PPR from the hyper-excitable visual cortex to the motor cortex.

High visual demand following theta burst stimulation modulates the effect on visual cortex excitability.

Modulatory effects of repetitive transcranial magnetic stimulation (TMS) depend on the activity of the stimulated cortical area before, during, and even after application. In the present study, we investigated the effects of theta burst stimulation (TBS) on visual cortex excitability using phosphene threshold (PTs). In a between-group design either continuous or intermittent TBS was applied with 100% of individual PT intensity. We varied visual demand following stimulation in form of high demand (acuity task) or low demand (looking at the wall). No change of PTs was observed directly after TBS. We found increased PTs only if subjects had high visual demand following continuous TBS. With low visual demand following stimulation no change of PT was observed. Intermittent TBS had no effect on visual cortex excitability at all. Since other studies showed increased PTs following continuous TBS using subthreshold intensities, our results highlight the importance of stimulation intensity applying TBS to the visual cortex. Furthermore, the state of the neurons in the stimulated cortex area not only before but also following TBS has an important influence on the effects of stimulation, making it necessary to scrupulously control for activity during the whole experimental session in a study.

Overactive visuomotor connections underlie the photoparoxysmal response. A TMS study.

The photoparoxysmal response (PPR) involves rapid spread of epileptic activity from visual to parietal and frontal areas. We used a transcranial magnetic stimulation (TMS) technique to assess the physiologic connections between primary visual (V1) and motor (M1) areas in patients with idiopathic generalized epilepsy (IGE). We hypothesized that in PPR-positive patients, M1 would respond excessively to inputs from V1. Eleven photosensitive patients with IGE who had a PPR at the time of the study were compared with 10 similar patients without a PPR, and with 11 healthy subjects of similar age and sex. The connection between V1 and M1 was assessed in resting participants by delivering a conditioning stimulus (CS) over the phosphene hotspot of the visual cortex (intensity 90% phosphene threshold, PT) followed at random interstimulus intervals (ISIs; 15, 18, 21, 24, 27, 30, 35 and 40 msec) by a test stimulus (TS) over the left motor cortex to elicit a motor evoked potential (MEP) of ~1 mV from the right first dorsal interosseous muscle. In healthy subjects, a CS over V1 suppressed M1 at ISIs between 18 and 40 msec. Similar effects occurred in IGE patients without a PPR. This was not true in PPR-positive IGE patients, in whom this type of physiologic inhibition was significantly (p < 0.05) reduced. IGE patients with a PPR have an overactive functional response of M1 to inputs traveling from V1. This may represent one core factor for the anterior spread of the PPR itself and for the origin of the abnormal epileptic motor phenomenon, such as myoclonus.

P69. Does theta burst stimulation on visual cortex only modulate phosphene threshold after high visual demand?

Transcranial magnetic theta burst stimulation (TBS) modulates excitability of motor cortex in dependence of prior activity of the motor system. Little is known about TBS effects in other cortical areas. We investigated the effect of TBS with 100% phosphene threshold (PT) intensity on the excitability of the visual cortex, using PT as dependent variable. Additionally, as hypothesized in previous work (Bruckner and Kammer, 2014), we examined whether enhanced activity in the visual cortex might influence TBS modulation. In a within-design, 32 healthy subjects (12 men) so far underwent 2 TBS sessions with either enhanced demand on visual cortex following TBS or no demand. Visual cortex demand consisted in measuring visual acuity using a Landolt C optotype. At the beginning of a session, PT was measured 4 times, 2 times to get familiar with the procedure and 2 times for mean baseline value. Then, TBS was applied with 100% of the individual baseline PT. 14 subjects (4 men, mean age 24.2 ± 3.6 years) received continuous TBS (cTBS) and in another 18 subjects (8 men, mean age 23.1 ± 2.4 years) intermittent TBS (iTBS) was applied (between group design). Two minutes after the end of TBS, PT was again estimated. Then, for the next 10 min, subjects in one session kept their eyes open looking at a white wall doing nothing else, or performed the visual acuity task (about 5–6 runs of the task) in the other session. After these 10 min, PT was measured again. The acuity task was performed to enhance activity in the visual cortex only, acuity thresholds were not analysed further. Mean baseline PT value was 38.5 ± 8.8 of maximum stimulator output. Baseline PT did not differ between sessions (F1,30 = 0.51, p > 0.4). Pre and post TBS PTs were subjected to an rmAnova (separately for iTBS and cTBS) with the within factor SESSION (with or without visual acuity task) and TIME (pre, post1, post2). For the cTBS group, no main effect was found but the interaction of SESSION × TIME was significant (F2,26 = 5.3, p = 0.012). Post hoc analysis revealed that cTBS had no direct effect on PT but an increased PT was found after the visual acuity task. For the iTBS group, there was no main effect for SESSION nor for TIME, and no interaction. We aim to complete measurements up to 20 subjects per TBS group. Our preliminary data suggest that neither cTBS nor iTBS applied with 100% of individual PT had an effect on PT 2 min after the end of stimulation. PT increased after cTBS (but not after iTBS) followed by enhanced activity in the visual cortex. Our findings are in contrast to the observation by Franca et al., (2006) showing an increase of PT after cTBS at 80% of PT. It is conceivable that cTBS directly modulates PT only at subthreshold intensity levels. Applied with PT intensity, cTBS might only have an influence on visual cortex excitability if visual demand is high after stimulation, whereas iTBS seems not able to modulate visual cortex excitability at all.

P68. Theta burst stimulation effects on visual cortex: Dependency of coil geometry

Transcranial magnetic theta burst stimulation (TBS) is an efficient method to modulate excitability of the motor cortex. There have been some demonstrations of TBS effects in non-motor cortical regions, but it is still not clear whether the scheme from motor cortex, i.e. inhibitory effects by continuous TBS (cTBS) and excitatory effects by intermittent TBS (iTBS) can be transferred to other cortical regions. Applying TBS with 100% of individual phosphene threshold (PT) intensity on visual cortex with a figure-of-eight coil we observed a modulation of PT neither with cTBS nor with iTBS (Bruckner & Kammer 2015, this conference). As our findings were in contrast to Franca et al. (2006), who described an increase in PT following cTBS (80% of individual PT) we aimed to directly replicate their results. To that end we compare cTBS effects elicited with a focal figure-of-eight-coil with those elicited by a simple, less focal round coil, since Franca et al. (2006) were using a round coil. In a between-group-design continuous TBS (cTBS, 600 pulses) with 80% of individual PT intensity was applied using either a figure-of-eight-coil or a round coil. PT was measured before and 2 min after cTBS application. So far (October 2014), 14 subjects (7 men, mean age 24.6 ± 3.7 years) participated in the figure-of-eight-coil-group and 4 subjects in the round coil-group. Mean baseline PT value of the figure-of-eight-coil group was 39.3 ± 7.3% of maximum stimulator output. After cTBS PT values slightly decreased (trend to significance in paired two-tailed t -test, t = 2.07, p = 0.059). First visual inspection of the round coil group data indicate that cTBS applied with 80% of individual PT might increase PT, comparable to Franca et al. (2006). We will complete the data set up to 16 subjects in each group. CTBS effects in the visual system seem to depend on the focality of the applied electromagnetic field varied by the different coil geometries used.

P151. The effects of occipital tDCS on phosphene thresholds in dependence of visual demand

Effects of transcranial direct current stimulation (tDCS) were reported in motor and cognitive domains. From the motor system we know that anodal tDCS causes facilitation whereas cathodal stimulation has a slight inhibitory effect. Same effects have been reported in visual cortex using phosphene thresholds (Antal et al., 2003), whereas contrast detection thresholds were only changed by cathodal tDCS (Antal et al., 2001). The aim of this study is to investigate the effect of either anodal or cathodal tDCS on the phosphene threshold in the absence and presence of a controlled activity in visual cortex. Phosphene thresholds were measured with transcranial magnetic stimulation (TMS) pulses using the method of constant stimuli. We applied 7 TMS pulses per intensity using 7 different ones in steps of 3% stimulator output. After each pulse participants had to respond by key press whether they saw a phosphene or not. Thresholds were calculated by fitting a sigmoid psychometric function to the data. After establishing a stable phosphene threshold within 4 measurements, TDCS was applied for 15 min (1 mA, 15 s ramp in/out) with electrodes placed over occipital cortex at the site of optimum phosphene stimulation and over Cz. Following tDCS two phosphene thresholds were measured beginning at minute 2 and at minute 22 after the end of tDCS. In a within-subjects design after the first threshold measurement a visual acuity task using a Landolt-C optotype lasting 10 min was applied in one session, whereas in a second session subjects just waited until minute 22 without visual task. Polarity of tDCS is varied between subjects. So far we have measured 6 participants with anodal stimulation at the occipital site. Preliminary analysis demonstrates a decrease of phosphene threshold with anodal tDCS, confirming previous observations. It is planned to measure up to 32 participants (16 anodal, 16 cathodal). The experimental design is similar to another study presented on the conference, where theta burst stimulation (TMS) instead of tDCS was applied as modulatory intervention. Thus, a direct comparison of effects in visual cortex with two different modulatory brain stimulation techniques is provided.

P78. Feasibility and safety aspects of retinofugal alternating current stimulation

Introduction Non-invasive Brain Stimulation is now widely used, yet little is known about its mechanisms of action and its safety. The more critical aspect of the two is safety. An assessment of stimulation parameters and measures such as charge density, impedances, amplitudes and thresholds as well as a sufficient investigation of side effects deem necessary. Here we compare the novel retinofugal transorbital alternating current stimulation (rtACS) and the well-known Photic Stimulation (PS, “Photic Driving”) regarding their safety aspects and conclude on the feasibility of rtACS. Methods We stimulated 21 healthy subjects with rtACS as well as PS at a frequency of 10 Hz. Prior to stimulation, we assessed phosphene thresholds (rtACS) or light thresholds (PS). The stimulation intensity was set to 120% threshold in both cases. Post-stimulation, pain and other side effects were reported via questionnaire. We also recorded electrode impedances and calculated the resulting charge density. Results We noted an average phosphene threshold at 290.24 μV (±44.16), impedances at 12.57 kΩ (±1.8). The charge density amounted to a mean 47.90 C/cm2 (±12.37). The mean light threshold for PS was 1.24 (±0.44). The most common side effect for rtACS was a tingling sensation (67%), followed by fatigue (33%). PS evoked mostly fatigue (19%) and headache (14%). Pain was reported in 30% of the subjects during rtACS (mean intensity 2.5 ± 1.85 on a numeric rating scale) and in 25% during PS (2.75 ± 0.96). In direct comparison, rtACS showed no significant difference in pain, a significantly (p Conclusions Firstly, the theoretical stimulation parameters calculated from amplitude and impedance are well below the damage limits found in the animal model. Secondly, the subjective measures showed no strong feelings of discomfort. The intensity of pain experienced by stimulation did not differ significantly between rtACS and the well-established, safe PS. This reassures the safety and feasibility of rtACS. To complete these findings, we will to perform neuron specific enolase (NSE) and MRI measurements pre- and post-stimulation.

Prophylactic treatment in menstrual migraine: A proof-of-concept study

The present study aimed to investigate the efficacy of repetitive cathodal direct current stimulation (rctDCS) over the visual cortex as a prophylactic treatment in patients with menstrual migraine. 20 female patients were recruited in this double-blind, placebo-controlled study and were assigned to receive either cathodal or sham stimulation. Over 3 menstrual cycles, tDCS with 2mA intensity and 20min duration was applied to the visual cortex of the patients, in 5 consecutive sessions 1–5days prior to the first day of their menstruation. The primary endpoint of the study was the frequency of the migraine attacks at the end of the treatment period, however, additional parameters, such as the number of migraine related days and the intensity of pain were also recorded 3months before, during and 3months post-treatment. Visual cortex excitability was determined by measuring the phosphene thresholds (PTs) using single pulse transcranial magnetic stimulation (TMS) over the visual cortex.Sixteen patients completed the study. A significant decrease in the number of migraine attacks (p=0.04) was found in the cathodal group compared to baseline but not compared to sham (p=0.053). In parallel the PTs increased significantly in this group, compared to the sham group (p<0.05).Our results indicate that prophylactic treatment with rctDCS over the visual cortex might be able to decrease the number of attacks in patients with menstrual migraine, probably by modifying cortical excitability.

Phosphene Perception Relates to Visual Cortex Glutamate Levels and Covaries with Atypical Visuospatial Awareness.

Phosphenes are illusory visual percepts produced by the application of transcranial magnetic stimulation to occipital cortex. Phosphene thresholds, the minimum stimulation intensity required to reliably produce phosphenes, are widely used as an index of cortical excitability. However, the neural basis of phosphene thresholds and their relationship to individual differences in visual cognition are poorly understood. Here, we investigated the neurochemical basis of phosphene perception by measuring basal GABA and glutamate levels in primary visual cortex using magnetic resonance spectroscopy. We further examined whether phosphene thresholds would relate to the visuospatial phenomenology of grapheme-color synesthesia, a condition characterized by atypical binding and involuntary color photisms. Phosphene thresholds negatively correlated with glutamate concentrations in visual cortex, with lower thresholds associated with elevated glutamate. This relationship was robust, present in both controls and synesthetes, and exhibited neurochemical, topographic, and threshold specificity. Projector synesthetes, who experience color photisms as spatially colocalized with inducing graphemes, displayed lower phosphene thresholds than associator synesthetes, who experience photisms as internal images, with both exhibiting lower thresholds than controls. These results suggest that phosphene perception is driven by interindividual variation in glutamatergic activity in primary visual cortex and relates to cortical processes underlying individual differences in visuospatial awareness.

Ophthalmological assessment of cannabis-induced persisting perception disorder: is there a direct retinal effect?

Cannabis is a psychotomimetic agent that induces impairment of sensory perception. We present detailed clinical and electrophysiological data of patients with hallucinogen persisting perception disorder (HPPD) after marijuana consumption. A HPPD patient and four heavy cannabis smokers with no visual disturbances (controls) underwent complete ophthalmological examination including psychophysical tests (visual acuity, color vision, visual field, and dark adaptation) and detailed electrophysiological examinations, including extended Ganzfeld ERG, multifocal ERG, and electrooculography (EOG). Furthermore, electrically evoked phosphene thresholds (EPTs) were measured to further evaluate retinal function. Ophthalmological and most electrophysiological examinations were within normal limits for the HPPD patient and for all control subjects. Interestingly, EOG results of the HPPD patient showed a slightly reduced fast oscillation ratio, diminished standing potentials of the slow oscillations, and a light peak within normal range resulting in higher Arden ratios. The EPTs of the patient were reduced, in particular for pulses with long durations (50ms) causing visual sensations even at lowest possible currents of the neurostimulator. The control subjects did not reveal such alterations. Our findings suggest a direct effect of cannabinoids on the retina and retinal pigment epithelium function, which may be involved in disturbances of the visual function experienced after drug consumption. The observations presented here may contribute to the elucidation of the detailed mechanism. Furthermore, EOG and EPT measurements may be useful tools to demonstrate long-term retinal alterations in cannabis-induced HPPD in patients.

Surgical treatment for optic neuropathy in high myopia

To improve the effectiveness of surgical treatment for optic neuropathy in high-degree myopia. A total of 54 patients (96 eyes) aged 18-30 with high myopia and signs of optic neuropathy were observed. The main group consisted of 20 patients (28 eyes) who underwent meridional scleral reinforcement with type I collagen-based implant placed over the posterior segment. The control group included 34 patients (68 eyes) who were given a 10-day vitamin and vascular therapy course. In most of the controls (21 patient, 21 eyes) indirect revascularization with ligation of the superficial temporal artery was performed. Ophthalmological examination was done before the beginning of the treatment and then at 1, 6, and 12 months. Results. At the end of the follow-up period best corrected visual acuity in the main group was 19.2% higher, on average, than baseline values, but remained unchanged in the controls. Light sensitivity of the retina in both group increased by 7% and 2% respectively. Electrically evoked phosphene thresholds decreased by 22.5% and 10.4% respectively. The main group also demonstrated a near-constant mean peripapillary nerve fiber layer (RNFL) thickness and a 16.4% higher than baseline blood flow velocity in the ophthalmic artery. In the control group the latter parameter showed no change. Scleral reinforcement surgery in patients with high myopia complicated by optic neuropathy enables improvement of visual functions and regional blood flow as well as stabilization of RNFL thickness and volume, thus, preventing subsequent development of optic nerve atrophy.

Cortical excitability modulates the sensory strength of visual mental imagery

Event Abstract Back to Event Cortical excitability modulates the sensory strength of visual mental imagery Rebecca Keogh1* and Joel Pearson1* 1 University of New South Wales, Australia Visual mental imagery occurs when people generate a mental representation of an image that is not physically present. One of the hallmarks of mental imagery is the large variance in reported vividness and strength of imagery between individuals. Numerous studies to date using neuroimaging and behavioural techniques have suggested that the early visual areas play an important role in imagery generation, however the exact cause of individual variance in mental imagery strength remains unknown. Here we used transcranial magnetic stimulation (TMS) to measure the cortical excitability of the visual cortex (using an automated phosphene threshold procedure). To measure imagery strength participants imagined one of two patterns followed by the presentation of a brief binocular rivalry display. Imagery strength was measured as the percent imagery primed rivalry. We found a negative correlation between cortical excitability and imagery strength. We then investigated whether we could manipulate imagery strength through increasing or decreasing cortical excitability of the early visual areas by using transcranial direct current stimulation (tDCS). tDCS uses a weak electrical current to increase (anodal) or decrease (cathodal) cortical excitability in the area under the active electrode. All participants completed both the cathodal and anodal conditions of this study on two separate days. tDCS was applied during the imagery task and performance was measured before, during and immediately after (post) tDCS. Cathodal stimulation increased imagery strength during stimulation, however no increases were found post-stimulation. Anodal stimulation had no effect on imagery strength during or after stimulation. Taken together these results suggest that visual cortex excitability plays a key role in governing the strength of mental imagery. Keywords: imagery, tDCS, Binocular Rivalry, TMS, cortical excitability Conference: XII International Conference on Cognitive Neuroscience (ICON-XII), Brisbane, Queensland, Australia, 27 Jul - 31 Jul, 2014. Presentation Type: Poster Topic: Cognition and Executive Processes Citation: Keogh R and Pearson J (2015). Cortical excitability modulates the sensory strength of visual mental imagery. Conference Abstract: XII International Conference on Cognitive Neuroscience (ICON-XII). doi: 10.3389/conf.fnhum.2015.217.00301 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 19 Feb 2015; Published Online: 24 Apr 2015. * Correspondence: Miss. Rebecca Keogh, University of New South Wales, Sydney, Australia, r.keogh@unsw.edu.au Dr. Joel Pearson, University of New South Wales, Sydney, Australia, jpearson@unsw.edu.au Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Rebecca Keogh Joel Pearson Google Rebecca Keogh Joel Pearson Google Scholar Rebecca Keogh Joel Pearson PubMed Rebecca Keogh Joel Pearson Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Results of complex treatment of diabetic retinopathy

Aim. To investigate the results of complex treatment of diabetic retinopathy. Methods and results. Diabetic retinopathy (DR) is a late complication of diabetes mellitus (DM), which leads to severe disability and significantly reduces the quality of life of patients. In the DR peroxidation of proteins with decreased antioxidant activity is enhanced in the blood of patients. These findings point to the desirability of placing products containing short carotenoids into the complex therapy of diabetic patients with DR in order to maintain visual function.Conclusion. In the DR under the influence of short carotenoids in complex treatment decreased severity of microvascular complications, increased total retinal lability by 8-16 Hz on the average are noted, the level of electrical retinal sensitivity phosphene threshold decreased to 87 uA (p &lt;0.05), photosensitivity of the retina increased by 16 dB on the average, the amount of relative scotomas reduced.

Transcranial direct current stimulation in the prophylactic treatment of migraine based on interictal visual cortex excitability abnormalities: A pilot randomized controlled trial

PurposeThe aims of this paper are (i) to compare the excitability of visual cortex in migraine patients with healthy volunteers; and (ii) if an abnormal excitability has been found, to modulate cortical excitability in migraine patients with transcranial direct current stimulation (tDCS) and observe their clinical and neurophysiological effects. MethodsThe study was divided into two steps. A cross-sectional study (step 1) was conducted to compare the cortical excitability of 23 migraineurs (11 with and 12 without aura) on 11 healthy individuals. On step 2, a randomized, double blinded, controlled pilot trial was carried on with 19 migraineurs, randomly divided into: experimental and control group. During 12 sessions, experimental and group received active tDCS to visual cortex and control group received sham tDCS. The headache diary was applied for a total of 90days (before, during and after tDCS sessions). Phosphene threshold (PT) induced by transcranial magnetic stimulation was recorded to measure the excitability of the visual cortex before and after each session. ResultsStep 1 showed higher level of cortical excitability between migraineurs when compared to healthy volunteers; therefore, cathodal tDCS was applied over visual cortex in step 2. After tDCS application, a significant decrease was observed in a number of migraine attacks, painkiller intake and duration of each attack just in experimental group. The analysis of PT indicated no difference in cortical excitability after tDCS. ConclusionsFindings of the study suggested that inhibitory tDCS on visual cortex might be an alternative and non-pharmacological treatment for migraine prophylaxis. However the clinical improvements of patients after tDCS treatment are not correlated with changes in cortical excitability.