Measuring the foveal avascular zone in diabetes: A study using optical coherence tomography angiography.

AIMS/INTRODUCTION: Diabetes is a global issue that currently affects 425 million people worldwide. One observable microvascular complication of this condition is a change in the foveal avascular zone (FAZ). In this study, we used optical coherence tomography angiography to investigate the effect of diabetes on the FAZ. MATERIALS AND METHODS: A total of 11 participants with diabetes and 11 participants without diabetes took part in this study. Participants in both groups were matched for age (P = 0.217) and sex (P = 0.338), and had no history of ocular disease. Macular optical coherence tomography angiography (OCT-A) scans of participants' right and left eyes were taken. Glycosylated hemoglobin (HbA1c ) and blood glucose levels were also measured. The FAZ area was manually segmented at the levels of the superficial capillary plexus (FAZSCP ) and deep capillary plexus (FAZDCP ). RESULTS: There was a strong relationship between the FAZ area of participants' right and left eyes (P ≤ 0.001) in both diabetes and non-diabetes groups. In the diabetes group, the FAZSCP (P = 0.047) and FAZDCP (P = 0.011) areas was significantly larger than in the non-diabetes group. Moreover, multiple linear regression analysis predicted a 0.07-mm2 increase in the FAZSCP and FAZDCP areas of individuals with diabetes for every 1% increase in their HbA1c level. CONCLUSIONS: Our findings show that there is enlargement of the FAZ in individuals with diabetes compared with individuals without diabetes. In the diabetes group, this enlargement appears to be correlated with HbA1c level. OCT-A imaging could, therefore, be a useful tool to monitor the FAZ and identify potential early microvasculopathy in diabetes.

Sub-clinical thickening of the fovea in diabetes and its relationship to glycaemic control: a study using swept-source optical coherence tomography.

BACKGROUND: Accumulation of multiple pockets of fluid at the fovea, as a complication of poor blood glucose control in diabetes, causes impairment of central vision. A new ability to demonstrate a pre-clinical phase of this maculopathy could be valuable, enabling diabetic individuals to be alerted to the need to improve their glycaemic control. This study aimed to use swept-source optical coherence tomography (SS-OCT) to measure foveal thickness and macular volume in diabetic individuals without cystoid macular oedema, and in non-diabetic individuals, and relate these measures to participants' glycaemic control. METHODS: Centre point thickness (CPT) and total macular volume (TMV) were measured using SS-OCT (DRI OCT Triton™, Topcon, Tokyo, Japan). Participants' glycosylated haemoglobin (HbA1c) level was also assessed (A1cNow®+ System, PTS Diagnostics, Indianapolis, IN, USA). The diabetic (n = 27) and non-diabetic (n = 27) groups were matched for age (p = 0.100) and sex (p = 0.414), and HbA1c level differed between diabetic and non-diabetic groups (p < 0.0005). The diabetic group comprised type 1 (n = 7) and type 2 (n = 20) diabetic individuals who were matched for duration of diabetes (p = 0.617) and whose glycaemic control was similar (p = 0.814). RESULTS: Diabetic individuals had significantly higher CPT (t(37) = 3.859, p < 0.0005) than non-diabetic individuals. In the diabetic group, multiple linear regression analysis revealed a conspicuous relationship between CPT and HbA1c level (ß = 0.501, t(21) = 3.139, p = 0.005): there was a 19-µm increase in CPT for each 1% increase in HbA1c level. This relationship was not present in the non-diabetic group (ß = - 0.068, t(23) = - 0.373, p = 0.712). CONCLUSIONS: SS-OCT is the only way to measure macular thickness in vivo. Diabetic individuals en bloc had higher CPT compared with non-diabetic individuals. Moreover, in the diabetic group, HbA1c level significantly predicted CPT. Our results suggest that, in diabetes, sub-clinical thickening may occur at the fovea before cystoid macular oedema becomes clinically evident. This could provide diabetic individuals with an early warning of disease progression and motivate them to improve control of their diabetes, with a view to avoiding the need of intra-vitreal injections with their attendant risks.

Environmental and behavioural interventions for reducing physical activity limitation and preventing falls in older people with visual impairment.

BACKGROUND: Impairment of vision is associated with a decrease in activities of daily living. Avoidance of physical activity in older adults with visual impairment can lead to functional decline and is an important risk factor for falls. The rate of falls and fractures is higher in older people with visual impairment than in age-matched visually normal older people. Possible interventions to reduce activity restriction and prevent falls include environmental and behavioral interventions. OBJECTIVES: We aimed to assess the effectiveness and safety of environmental and behavioral interventions in reducing physical activity limitation, preventing falls and improving quality of life amongst visually impaired older people. SEARCH METHODS: We searched CENTRAL (including the Cochrane Eyes and Vision Trials Register) (Issue 2, 2020), Ovid MEDLINE, Embase and eight other databases to 4 February 2020, with no language restrictions. SELECTION CRITERIA: Eligible studies were randomized controlled trials (RCTs) and quasi-randomized controlled trials (Q-RCTs) that compared environmental interventions, behavioral interventions or both, versus control (usual care or no intervention); or that compared different types of environmental or behavioral interventions. Eligible study populations were older people (aged 60 and over) with irreversible visual impairment, living in their own homes or in residential settings. To be eligible for inclusion, studies must have included a measure of physical activity or falls, the two primary outcomes of interest. Secondary outcomes included fear of falling, and quality of life. DATA COLLECTION AND ANALYSIS: We used standard Cochrane methods. We assessed the certainty of the evidence using the GRADE approach. MAIN RESULTS: We included six RCTs (686 participants) conducted in five countries (Australia, Hungary, New Zealand, UK, US) with follow-up periods ranging from two to 12 months. Participants in these trials included older adults (mean age 80 years) and were mostly female (69%), with visual impairments of varying severity and underlying causes. Participants mostly lived in their homes and were physically independent. We classified all trials as having high risk of bias for masking of participants, and three trials as having high or unclear risk of bias for all other domains. The included trials evaluated various intervention strategies (e.g. an exercise program versus home safety modifications). Heterogeneity of study characteristics, including interventions and outcomes, (e.g. different fall measures), precluded any meta-analysis. Two trials compared the home safety modification by occupational therapists versus social/home visits. One trial (28 participants) reported physical activity at six months and showed no evidence of a difference in mean estimates between groups (step counts: mean difference (MD) = 321, 95% confidence interval (CI) -1981 to 2623; average walking time (minutes): MD 1.70, 95% CI -24.03 to 27.43; telephone questionnaire for self-reported physical activity: MD -3.68 scores, 95% CI -20.6 to 13.24; low-certainty of evidence for each outcome). Two trials reported the proportion of participants who fell at six months (risk ratio (RR) 0.76, 95% CI 0.38 to 1.51; 28 participants) and 12 months (RR 0.59, 95% CI 0.43 to 0.80, 196 participants) with low-certainty of evidence for each outcome. One trial (28 participants) reported fear of falling at six months, using the Short Falls Efficacy Scale-International, and found no evidence of a difference in mean estimates between groups (MD 2.55 scores, 95% CI -0.51 to 5.61; low-certainty of evidence). This trial also reported quality of life at six months using 12-Item Short Form Health Survey, and showed no evidence of a difference in mean estimates between groups (MD -3.14 scores, 95% CI -10.86 to 4.58; low-certainty of evidence). Five trials compared a behavioral intervention (exercise) versus usual activity or social/home visits. One trial (59 participants) assessed self-reported physical activity at six months and showed no evidence of a difference between groups (MD 9.10 scores, 95% CI -13.85 to 32.5; low-certainty of evidence). Three trials investigated different fall measures at six or 12 months, and found no evidence of a difference in effect estimates (RRs for proportion of fallers ranged from 0.54 (95% CI 0.29 to 1.01; 41 participants); to 0.93 (95% CI 0.61 to 1.39; 120 participants); low-certainty of evidence for each outcome). Three trials assessed the fear of falling using Short Falls Efficacy Scale-International or the Illinois Fear of Falling Measure from two to 12 months, and found no evidence of a difference in mean estimates between groups (the estimates ranged from -0.88 score (95% CI -2.72 to 0.96, 114 participants) to 1.00 score (95% CI -0.13 to 2.13; 59 participants); low-certainty of evidence). One trial (59 participants) assessed the European Quality of Life scale at six months (MD -0.15 score, 95% CI -0.29 to -0.01), and found no evidence of a clinical difference between groups (low-certainty of evidence). AUTHORS' CONCLUSIONS: There is no evidence of effect for most of the environmental or behavioral interventions studied for reducing physical activity limitation and preventing falls in visually impaired older people. The certainty of evidence is generally low due to poor methodological quality and heterogeneous outcome measurements. Researchers should form a consensus to adopt standard ways of measuring physical activity and falls reliably in older people with visual impairments. Fall prevention trials should plan to use objectively measured or self-reported physical activity as outcome measures of reduced activity limitation. Future research should evaluate the acceptability and applicability of interventions, and use validated questionnaires to assess the adherence to rehabilitative strategies and performance during activities of daily living.

Disease mechanisms and neuroprotection by tauroursodeoxycholic acid in Rpgr knockout mice.

Mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene are the predominant cause of retinitis pigmentosa. RPGR plays a critical role as a scaffold protein in the regulation of protein trafficking from the basal body to the axoneme, where the cargoes are transported to the outer segments (OSs) of photoreceptors. This trafficking process is controlled directly by intraflagellar transport complexes and regulated by the RPGR protein complex, although the precise mechanisms have yet to be defined. We used an Rpgr conditional knockout (cko) mouse model to investigate the disease mechanisms during retinal degeneration and to evaluate the protective effects of tauroursodeoxycholic acid (TUDCA). Rhodopsin, cone opsins and transducin were mislocalized in Rpgr cko photoreceptors, while localization of NPHP4 to connecting cilia was absent, suggesting that RPGR is required for ciliary protein trafficking. Microglia were activated in advance of retinal degeneration in Rpgr cko mouse retinas. TUDCA treatment suppressed microglial activation and inflammation and prevented photoreceptor degeneration in Rpgr cko mice. Our data demonstrated that TUDCA has therapeutic potential for RPGR-associated RP patients.

Measuring visual cortical oxygenation in diabetes using functional near-infrared spectroscopy.

AIMS: Diabetes mellitus affects about 6% of the world's population, and the chronic complications of the disease may result in macro- and micro-vascular changes. The purpose of the current study was to shed light on visual cortical oxygenation in diabetic individuals. We then aimed to compare the haemodynamic response (HDR) to visual stimulation with glycaemic control, given the likelihood of diabetic individuals suffering from such macro- and micro-vascular insult. METHODOLOGY: Thirty participants took part in this explorative study, fifteen of whom had diabetes and fifteen of whom were non-diabetic controls. The HDR, measured as concentrations of oxyhaemoglobin [HbO] and deoxyhaemoglobin [HbR], to visual stimulation was recorded over the primary visual cortex (V1) using a dual-channel oximeter. The stimulus comprised a pattern-reversal checkerboard presented in a block design. Participants' mean glycated haemoglobin (HbA1c) level (± SD) was 7.2 ± 0.6% in the diabetic group and 5.5 ± 0.4% in the non-diabetic group. Raw haemodynamic data were normalised to baseline, and the last 15 s of data from each 'stimulus on' and 'stimulus off' condition were averaged over seven duty cycles for each participant. RESULTS: There were statistically significant differences in ∆[HbO] and ∆[HbR] to visual stimulation between diabetic and non-diabetic groups (p < 0.05). In the diabetic group, individuals with type 1 diabetes displayed an increased [HbO] (p < 0.01) and decreased [HbR] (p < 0.05) compared to their type 2 counterparts. There was also a linear relationship between both ∆[HbO] and ∆[HbR] as a function of HbA1c level (p < 0.0005). CONCLUSIONS: Our findings suggest that fNIRS can be used as a quantitative measure of cortical oxygenation in diabetes. Diabetic individuals have a larger HDR to visual stimulation compared to non-diabetic individuals. This increase in ∆[HbO] and decrease in ∆[HbR] appears to be correlated with HbA1c level.

Age-Related Changes in Global Motion Coherence: Conflicting Haemodynamic and Perceptual Responses.

Our aim was to use both behavioural and neuroimaging data to identify indicators of perceptual decline in motion processing. We employed a global motion coherence task and functional Near Infrared Spectroscopy (fNIRS). Healthy adults (n = 72, 18-85) were recruited into the following groups: young (n = 28, mean age = 28), middle-aged (n = 22, mean age = 50), and older adults (n = 23, mean age = 70). Participants were assessed on their motion coherence thresholds at 3 different speeds using a psychophysical design. As expected, we report age group differences in motion processing as demonstrated by higher motion coherence thresholds in older adults. Crucially, we add correlational data showing that global motion perception declines linearly as a function of age. The associated fNIRS recordings provide a clear physiological correlate of global motion perception. The crux of this study lies in the robust linear correlation between age and haemodynamic response for both measures of oxygenation. We hypothesise that there is an increase in neural recruitment, necessitating an increase in metabolic need and blood flow, which presents as a higher oxygenated haemoglobin response. We report age-related changes in motion perception with poorer behavioural performance (high motion coherence thresholds) associated with an increased haemodynamic response.

Using Functional Near Infrared Spectroscopy (fNIRS) to Study Dynamic Stereoscopic Depth Perception.

The parietal cortex has been widely implicated in the processing of depth perception by many neuroimaging studies, yet functional near infrared spectroscopy (fNIRS) has been an under-utilised tool to examine the relationship of oxy- ([HbO]) and de-oxyhaemoglobin ([HbR]) in perception. Here we examine the haemodynamic response (HDR) to the processing of induced depth stimulation using dynamic random-dot-stereograms (RDS). We used fNIRS to measure the HDR associated with depth perception in healthy young adults (n = 13, mean age 24). Using a blocked design, absolute values of [HbO] and [HbR] were recorded across parieto-occipital and occipital cortices, in response to dynamic RDS. Control and test images were identical except for the horizontal shift in pixels in the RDS that resulted in binocular disparity and induced the percept of a 3D sine wave that 'popped out' of the test stimulus. The control stimulus had zero disparity and induced a 'flat' percept. All participants had stereoacuity within normal clinical limits and successfully perceived the depth in the dynamic RDS. Results showed a significant effect of this complex visual stimulation in the right parieto-occipital cortex (p < 0.01, η(2) = 0.54). The test stimulus elicited a significant increase in [HbO] during depth perception compared to the control image (p < 0.001, 99.99 % CI [0.008-0.294]). The similarity between the two stimuli may have resulted in the HDR of the occipital cortex showing no significant increase or decrease of cerebral oxygenation levels during depth stimulation. Cerebral oxygenation measures of [HbO] confirmed the strong association of the right parieto-occipital cortex with processing depth perception. Our study demonstrates the validity of fNIRS to investigate [HbO] and [HbR] during high-level visual processing of complex stimuli.

Reduced Haemodynamic Response in the Ageing Visual Cortex Measured by Absolute fNIRS.

The effect of healthy ageing on visual cortical activation is still to be fully explored. This study aimed to elucidate whether the haemodynamic response (HDR) of the visual cortex altered as a result of ageing. Visually normal (healthy) participants were presented with a simple visual stimulus (reversing checkerboard). Full optometric screening was implemented to identify two age groups: younger adults (n = 12, mean age 21) and older adults (n = 13, mean age 71). Frequency-domain Multi-distance (FD-MD) functional Near-Infrared Spectroscopy (fNIRS) was used to measure absolute changes in oxygenated [HbO] and deoxygenated [HbR] haemoglobin concentrations in the occipital cortices. Utilising a slow event-related design, subjects viewed a full field reversing checkerboard with contrast and check size manipulations (15 and 30 minutes of arc, 50% and 100% contrast). Both groups showed the characteristic response of increased [HbO] and decreased [HbR] during stimulus presentation. However, older adults produced a more varied HDR and often had comparable levels of [HbO] and [HbR] during both stimulus presentation and baseline resting state. Younger adults had significantly greater concentrations of both [HbO] and [HbR] in every investigation regardless of the type of stimulus displayed (p<0.05). The average variance associated with this age-related effect for [HbO] was 88% and [HbR] 91%. Passive viewing of a visual stimulus, without any cognitive input, showed a marked age-related decline in the cortical HDR. Moreover, regardless of stimulus parameters such as check size, the HDR was characterised by age. In concurrence with present neuroimaging literature, we conclude that the visual HDR decreases as healthy ageing proceeds.

Neural and vascular responses to fused binocular stimuli: a VEP and fNIRS study.

PURPOSE: The aim of our study was to investigate the correlation between neural and hemodynamic responses to stereoscopic stimuli recorded over visual cortex. METHODS: Test stimuli consisted of a static checkerboard (checks) and dichoptic static random dot (RD) presentations with no binocular disparity (ZD) or with horizontal disparity (HD). Hemodynamic responses were recorded from right and left occipital sites using functional near-infrared spectroscopy (fNIRS). Visual evoked potentials (VEPs) were recorded over three occipital sites to the onset of the same stimuli. RESULTS: Early components, N1 and P2, were sensitive to HD, suggesting that an enhanced N1-reduced P2 complex could be an indicator of binocular disparity and stereopsis. VEPs to checks and ZD stimulation were similar. fNIRS recordings showed changes in hemodynamic activation from baseline levels in response to all stimuli. In general, HD elicited a larger vascular response than ZD. Oxyhemoglobin concentration (HbO) was correlated with the VEP amplitude during the checks and HD presentations. CONCLUSIONS: We report an association between neural and hemodynamic activation in response to checks and HD. In addition, the results suggested that N1-P2 complex in the VEP could be a neural marker for stereopsis and fNIRS demonstrated differences in HbO. Specifically, checks and HD elicited larger hemodynamic responses than random dot patterns without binocular disparity.

Interventions for age-related visual problems in patients with stroke.

BACKGROUND: The prevalence of eye problems increases with age and, consequently, so does the level of visual impairment. As the incidence of stroke also increases with age, a significant proportion of stroke patients will have age-related visual problems. It is possible that the effect of interventions for age-related visual problems may differ in the population of stroke patients compared to the wider population of older people. The interaction between the problems arising directly from stroke and those arising directly from age-related visual problems will be complex. Interventions for age-related visual problems may also be affected by the presence of other stroke-related co-morbidities. Consequently, the nature and outcome of interventions for age-related visual problems may be different in patients with stroke. OBJECTIVES: The aim of this review is to determine if interventions for age-related visual problems improve functional ability following stroke. SEARCH METHODS: We searched the Cochrane Stroke Group Trials Register (March 2011), the Cochrane Eyes and Vision Group Trials Register (December 2009) and nine electronic bibliographic databases including: the Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 1), MEDLINE (1950 to February 2011), EMBASE (1980 to February 2011), CINAHL (1982 to February 2011), AMED (1985 to February 2011) and PsycINFO (1967 to February 2011). We also searched reference lists and trials registers, handsearched journals and conference proceedings, and contacted experts. SELECTION CRITERIA: Randomised trials in adults after stroke, where the intervention is specifically targeted at assessing, treating or correcting age-related visual problems, or improving the ability of the patient to cope with visual impairment. Primary outcome was functional ability in activities of daily living and secondary outcomes included functional ability in extended activities of daily living, visual acuity, visual field, visual function, balance, falls, depression and anxiety, discharge destination/residence after stroke, quality of life and social isolation, adverse events and death. DATA COLLECTION AND ANALYSIS: Two review authors independently screened abstracts and planned to extract data and appraise trials. We planned that assessment of methodological quality would be undertaken for allocation concealment, blinding of outcome assessor, method of dealing with missing data and other potential sources of bias. MAIN RESULTS: We considered 7357 titles, 460 abstracts and 85 full papers. We identified no studies for inclusion in this review. AUTHORS' CONCLUSIONS: There are no implications for practice arising from this review. Evidence relating to the management of patients (from the general population) with age-related visual problems is available from other Cochrane reviews and is likely to be the best evidence available for making treatment decisions about individual patients. Subgroup analyses within these reviews to explore the effect of interventions for age-related visual problems in patients with stroke are recommended. We recommend that the objectives and selection criteria for this Cochrane review are amended and clarified prior to any future updates.

Localization of hemodynamic responses to simple visual stimulation: an fNIRS study.

PURPOSE: The purpose of the study was to use functional near-infrared spectroscopy (fNIRS) to explore the extent of activation in occipito-parietal cortices to high-contrast checkerboard stimuli. The distributions of oxyhemoglobin (HbO), deoxyhemoglobin (Hb), and total hemoglobin (THb) concentrations were used as measures of cortical activation. METHODS: Data were collected sequentially using the Frequency Domain Multi-Distance oximeter to record absolute chromophore concentration. Responses to three presentation modes (static, pattern reversal, and ON/OFF stimulation) were compared over 15 locations in two participants. The most effective stimulus was used in 10 participants at the most responsive occipito-parietal sites. RESULTS: Pattern-reversal stimulation evoked the largest increase in HbO, and this increase was greatest at O1 and O2 (5% to the right and left of the midline occipital location Oz) and diminished at recording locations over the posterior parietal regions in the vertical direction. Hb changes were smaller than those observed for HbO. Significantly smaller responses were recorded over the midline (Oz) compared with those at O1 and O2. Changes in hemoglobin concentration reflected the location of activated brain tissue. CONCLUSIONS: The authors have demonstrated the distribution of the hemodynamic response using absolute values of hemoglobin chromophores in response to simple but strong stimulation using checkerboard presentations.

Interventions for visual field defects in patients with stroke.

BACKGROUND: Visual field defects are estimated to affect 20% to 57% of people who have had a stroke. Visual field defects can affect functional ability in activities of daily living (commonly affecting mobility, reading and driving), quality of life, ability to participate in rehabilitation, and depression, anxiety and social isolation following stroke. There are many interventions for visual field defects, which are proposed to work by restoring the visual field (restitution); compensating for the visual field defect by changing behaviour or activity (compensation); substituting for the visual field defect by using a device or extraneous modification (substitution); or ensuring appropriate diagnosis, referral and treatment prescription through standardised assessment or screening, or both. OBJECTIVES: To determine the effects of interventions for people with visual field defects after stroke. SEARCH STRATEGY: We searched the Cochrane Stroke Group Trials Register (February 2011), the Cochrane Eyes and Vision Group Trials Register (December 2009) and nine electronic bibliographic databases including CENTRAL (The Cochrane Library 2009, Issue 4), MEDLINE (1950 to December 2009), EMBASE (1980 to December 2009), CINAHL (1982 to December 2009), AMED (1985 to December 2009), and PsycINFO (1967 to December 2009). We also searched reference lists and trials registers, handsearched journals and conference proceedings and contacted experts. SELECTION CRITERIA: Randomised trials in adults after stroke, where the intervention was specifically targeted at improving the visual field defect or improving the ability of the participant to cope with the visual field loss. The primary outcome was functional ability in activities of daily living and secondary outcomes included functional ability in extended activities of daily living, reading ability, visual field measures, balance, falls, depression and anxiety, discharge destination or residence after stroke, quality of life and social isolation, visual scanning, adverse events and death. DATA COLLECTION AND ANALYSIS: Two review authors independently screened abstracts, extracted data and appraised trials. We undertook an assessment of methodological quality for allocation concealment, blinding of outcome assessors, method of dealing with missing data, and other potential sources of bias. MAIN RESULTS: Thirteen studies (344 randomised participants, 285 of whom were participants with stroke) met the inclusion criteria for this review. However, only six of these studies compared the effect of an intervention with a placebo, control or no treatment group and were included in comparisons within this review. Four studies compared the effect of scanning (compensatory) training with a control or placebo intervention. Meta-analysis demonstrated that scanning training is more effective than control or placebo at improving reading ability (three studies, 129 participants; mean difference (MD) 3.24, 95% confidence interval (CI) 0.84 to 5.59) and visual scanning (three studies, 129 participants; MD 18.84, 95% CI 12.01 to 25.66) but that scanning may not improve visual field outcomes (two studies, 110 participants; MD -0.70, 95% CI -2.28 to 0.88). There were insufficient data to enable generalised conclusions to be made about the effectiveness of scanning training relative to control or placebo for the primary outcome of activities of daily living (one study, 33 participants). Only one study (19 participants) compared the effect of a restitutive intervention with a control or placebo intervention and only one study (39 participants) compared the effect of a substitutive intervention with a control or placebo intervention. AUTHORS' CONCLUSIONS: There is limited evidence which supports the use of compensatory scanning training for patients with visual field defects (and possibly co-existing visual neglect) to improve scanning and reading outcomes. There is insufficient evidence to reach a conclusion about the impact of compensatory scanning training on functional activities of daily living. There is insufficient evidence to reach generalised conclusions about the benefits of visual restitution training (VRT) (restitutive intervention) or prisms (substitutive intervention) for patients with visual field defects after stroke.

Interventions for disorders of eye movement in patients with stroke.

BACKGROUND: Eye movement disorders may affect over 70% of stroke patients. These eye movement disorders can result in difficulty maintaining the normal ocular position and difficulty moving the eyes appropriately. The resulting functional disabilities include a loss of depth perception, reduced hand-to-eye co-ordination, marked difficulties with near tasks and reading and reduced ability to scan the visual environment. They can also impact on the effectiveness of rehabilitation therapy. There are a wide variety of different treatment interventions proposed for eye movement disorders after stroke. However, in the past, there has been a lack of evidence specific to the impact of interventions on the functional outcome of patients with stroke. OBJECTIVES: To determine the effects of interventions for eye movement disorders on functional ability following stroke. SEARCH STRATEGY: We searched the Cochrane Stroke Group Trials Register (February 2011), the Cochrane Eyes and Vision Group Trials Register (December 2009) and nine electronic bibliographic databases including CENTRAL (The Cochrane Library 2009, Issue 4), MEDLINE (1950 to December 2009), EMBASE (1980 to December 2009), CINAHL (1982 to December 2009), AMED (1985 to December 2009), and PsycINFO (1967 to December 2009). We also searched reference lists and trials registers, handsearched journals and conference proceedings, and contacted experts. SELECTION CRITERIA: Randomised trials in adults after stroke where the intervention was specifically targeted at improving the eye movement disorder or improving the ability of the participant to cope with the eye movement disorder. The primary outcome was functional ability in activities of daily living. Secondary outcomes included functional ability in extended activities of daily living, eye movement measures, balance, falls, depression or anxiety, discharge destination or residence after stroke, quality of life and social isolation, adverse events, and death. DATA COLLECTION AND ANALYSIS: Two authors independently screened abstracts, extracted data and appraised trials. We undertook assessment of methodological quality for allocation concealment, blinding of outcome assessor, method of dealing with missing data, and other potential sources of bias. MAIN RESULTS: Two studies (28 participants but only five were people with stroke) met the inclusion criteria and were included in this review. Both studies investigated pharmacological interventions for disorders of eye movement in patients with stroke. It was not appropriate to pool data and we were not able to draw conclusions from these studies. We found no other randomised studies which investigated interventions for disorders of eye movement in patients with stroke. AUTHORS' CONCLUSIONS: There is insufficient evidence to reach conclusions about the effectiveness of interventions for patients with eye movement disorders after stroke. High quality research in the form of well-designed randomised trials are urgently required.

Monocular and binocular steady-state flicker VEPs: frequency-response functions to sinusoidal and square-wave luminance modulation.

Steady-state VEPs to full-field flicker (FFF) using sinusoidally modulated light were compared with those elicited by square-wave modulated light across a wide range of stimulus frequencies with monocular and binocular FFF stimulation. Binocular and monocular VEPs were elicited in 12 adult volunteers to FFF with two modes of temporal modulation: sinusoidal or square-wave (abrupt onset and offset, 50% duty cycle) at ten temporal frequencies ranging from 2.83 to 58.8 Hz. All stimuli had a mean luminance of 100 cd/m(2) with an 80% modulation depth (20-180 cd/m(2)). Response magnitudes at the stimulus frequency (F1) and at the double and triple harmonics (F2 and F3) were compared. For both sinusoidal and square-wave flicker, the FFF-VEP magnitudes at F1 were maximal for 7.52 Hz flicker. F2 was maximal for 5.29 Hz flicker, and F3 magnitudes are largest for flicker stimulation from 3.75 to 7.52 Hz. Square-wave flicker produced significantly larger F1 and F2 magnitudes for slow flicker rates (up to 5.29 Hz for F1; at 2.83 and 3.75 Hz for F2). The F3 magnitudes were larger overall for square-wave flicker. Binocular FFF-VEP magnitudes are larger than those of monocular FFF-VEPs, and the amount of this binocular enhancement is not dependant on the mode of flicker stimulation (mean binocular: monocular ratio 1.41, 95% CI: 1.2-1.6). Binocular enhancement of F1 for 21.3 Hz flicker was increased to a factor of 2.5 (95% CI: 1.8-3.5). In the healthy adult visual system, FFF-VEP magnitudes can be characterized by the frequency-response functions of F1, F2 and F3. Low-frequency roll-off in the FFF-VEP magnitudes is greater for sinusoidal flicker than for square-wave flicker for rates ≤ 5.29 Hz; magnitudes for higher-frequency flicker are similar for the two types of flicker. Binocular FFF-VEPs are larger overall than those recorded monocularly, and this binocular summation is enhanced at 21.3 Hz in the mid-frequency range.

Investigating the mechanisms that may underlie the reduction in contrast sensitivity during dynamic accommodation.

Head and eye movements, together with ocular accommodation enable us to explore our visual environment. The stability of this environment is maintained during saccadic and vergence eye movements due to reduced contrast sensitivity to low spatial frequency information. Our recent work has revealed a new type of selective reduction of contrast sensitivity to high spatial frequency patterns during the fast phase of dynamic accommodation responses compared with steady-state accommodation. Here were report data which show a strong correlation between the effects of reduced contrast sensitivity during dynamic accommodation and velocity of accommodation responses, elicited by ramp changes in accommodative demand. The results were accounted for by a contrast gain control model of a cortical mechanism for contrast detection during dynamic ocular accommodation. Sensitivity, however, was not altered during attempted accommodation responses in the absence of crystalline-lens changes due to cycloplegia. These findings suggest that contrast sensitivity reduction during dynamic accommodation may be a consequence of cortical inhibition driven by proprioceptive-like signals originating within the ciliary muscle, rather than by corollary discharge signals elicited simultaneously with the motor command to the ciliary muscle.

Absolute quantification of oxygenated hemoglobin within the visual cortex with functional near infrared spectroscopy (fNIRS).

PURPOSE: To examine absolute changes in oxygenated (HbO) and deoxygenated (Hb) hemoglobin concentrations over the visual cortex in response to visual stimulation. Before this study, only relative changes have been reported at the visual cortex. METHODS: Near infrared spectroscopy (NIRS) can be used to assess changes in hemoglobin concentration in tissue. A frequency domain oximeter with a specially designed probe was placed over the visual cortex while the participant viewed a checkerboard stimulus. The stimulus was alternated at 7.5 Hz for 30 seconds before being replaced by a control gray screen. RESULTS: The mean HbO concentration when the stimulus was presented was 26.8+/-3.9 microM, as opposed to 25.9+/-3.9 microM for the control condition, and the mean Hb concentration was 18.8+/-2.3 microM during stimulation and 19.1+/-2.3 microM during the control condition. The greatest change in HbO concentration occurred within the first 10 seconds. It did not increase significantly (P>0.01) after that time. CONCLUSIONS: This study is the first to demonstrate absolute quantification of HbO and Hb concentrations in the visual cortex with functional changes in hemoglobin concentrations in response to a visual stimulus. NIRS has the potential to be a valuable clinical tool in assessing the hemodynamics of the visual system in a quantitative and localized manner.

Two eyes: square root 2 better than one?

Classical data on the detection of simple patterns show that two eyes are more sensitive than one eye. The degree of binocular summation is important for inferences about the underlying combination mechanism. In a signal detection theory framework, sensitivity is limited by internal noise. If noise is added centrally after binocular combination, binocular sensitivity is expected to be twice as good as monocular. If the noise is added peripherally at each eye prior to combination, binocular sensitivity will be sqrt[2] higher than monocular. In a large sample of observers (51), we measured contrast sensitivity for detection of gratings at several spatial frequencies using left, right, or both eyes. Estimates of binocular summation using both binocular summation ratios and Minkowski coefficients show a summation ratio with means in the range of 1.5-1.6. The 95% confidence interval overlaps with the value of sqrt[2] predicted by the peripheral noise model and does not overlap with the value of 2 predicted by the central noise model.

Illusory percepts of moving patterns due to discrete temporal sampling.

Continuously, moving objects under continuous illumination can be seen to move in a direction opposite to their actual motion. This illusory reversed motion can be explained as due to discrete temporal sampling of the moving stimulus by the visual system. If temporal sampling lies behind the illusory motion, then the probability of illusory motion should depend on the temporal frequency of the motion stimulus. By presenting contracting bull's-eye gratings of various spatial frequencies we were able to tease apart the drift speed and temporal frequency. The prevalence of illusory percepts depended on the temporal frequency, not the speed. The data suggest that the human visual system samples the incoming stimulation at a rate near 16 Hz.