Flicker Sensitivity Research Articles

IDF23-0387 The use of colour and rapid flicker sensitivity tests for early detection and monitoring of vision changes in diabetes

IDF23-0387 The use of colour and rapid flicker sensitivity tests for early detection and monitoring of vision changes in diabetes

New methods for detection of early loss of rapid flicker, spatial vision, and chromatic sensitivity in glaucoma

Purpose: To examine whether ocular hypertension and early glaucoma cause measurable changes in spatial vision, rapid flicker sensitivity and red/green and yellow/blue colour vision.Methods: We examined subjects aged 40 to 78 years with ocular hypertension (OHT), primary open angle glaucoma (POAG), normal tension glaucoma (NTG), and age matched controls. Monocular best corrected visual acuity (BCVA) was tested using EDTRS charts.VA and Functional Contrast Sensitivity (FCS) with Landolt ring stimuli of both positive and negative contrast were also measured monocularly with the Acuity‐Plus test. Red/green (RG) and yellow/blue (YB) colour thresholds were measured with the Colour Assessment and Diagnostics (CAD) test. Photopic (cone‐enhanced) and mesopic (rod‐enhanced) rapid flicker thresholds were measured at the fovea (0°) and at an eccentricity of 5° in each of the four quadrants using the Flicker‐Plus test. All subjects had their visual fields measured using the Humphrey visual field analyser (24–2 SITA standard protocol). Peripapillary retinal nerve fibre layer thickness (pRNFLT) and macular retinal layer thicknesses were measured using the Heidelberg Spectralis OCT.Results: The mean, logMAR BCVA for OHT patients was 0.00 and for POAG and NTG patients was −0.10 and 0.10, respectively. For control participants, mean logMAR BCVA was 0.00. Mean pRNFL thickness was significantly reduced for glaucoma patients (59.5 ± 7.7 μm) as compared to control subjects (94.6 ± 5.13 μm) and OHT patients (115.5 ± 3.5 μm). POAG and NTG patients showed significantly higher colour thresholds (mean red/green threshold 4.97, blue/yellow 5.28 CAD units) compared to control subjects (mean red/green threshold 2.07, blue/yellow 1.62 CAD units). One OHT patient showed acquired loss of blue/yellow colour vision (3.23 CAD units), with normal VA. The Acuity‐Plus test which employs briefly presented stimuli, also revealed significant loss of VA (3.78 and 3.64 min of arc) and FCS (141.32% and 100%) in an NTG patient, with results outside normal limits for both positive and negative contrast, respectively. Central FCS was higher and outside the normal age limits for POAG patients (73.41% and 89.27%) as compared to age matched controls (61.27% and 33.63%). OHT patients, on the other hand, produced FCS thresholds within normal limits. Flicker modulation thresholds were higher for both rod and cone enhanced stimulus conditions in glaucoma and OHT patients, when compared to control subjects.Conclusion: The results reveal non‐uniform, losses that can affect selectively each of the visual attributes examined in this study. These preliminary findings suggest that in addition to VA and FCS tests, colour vision and rapid flicker sensitivity should also be examined in patients with optic nerve pathologies like glaucoma.

The use of colour and rapid flicker sensitivity tests for early detection and monitoring of vision changes in diabetes

Aims/Purpose: There is increasing evidence of impaired visual function prior to the presence of diabetic retinopathy (DR), yet current diagnostic criteria and treatment onset rely mostly on retinal vascular changes. In this study we measured changes in chromatic and rapid flicker sensitivity in subjects with prediabetes and diabetes to establish the value of such tests as a potential biomarker in the detecting early diabetes.Methods: Three groups of subjects were recruited: 1) normal controls, 2) subjects with prediabetes (HbA1c between 42‐47 mmol/mol), and 3) diabetics (with or without DR). Monocular cone‐ and rod‐enhanced flicker modulation thresholds (FMTs) were measured at the point of regard and in four parafoveal (5°) locations using the Flicker‐Plus test. Monocular red/green (RG) and yellow/blue (YB) colour thresholds were also measured at the fovea using the Colour Assessment and Diagnosis (CAD) test.Results: Both the RG and YB thresholds, as well as rod‐ and cone‐mediated flicker thresholds were significantly higher in both diabetic and prediabetic groups (when compared with healthy controls). When examined individually, ~50% and ~ 63% of the prediabetics and ~ 58% and ~ 70% of the diabetics revealed abnormal RG and YB thresholds, respectively (when compared with the upper normal limits for the corresponding age). HBA1c levels also revealed a positive trend with increasing RG and YB thresholds in the prediabetic group.Conclusions: In agreement with previous findings, both colour and FMTs are affected in patients diagnosed with diabetes. Unexpectedly, those deemed prediabetic that do not meet the clinical criteria for diabetes exhibit considerable loss of both colour and flicker sensitivity. The results suggest that colour and rapid flicker tests can provide useful information when screening for diabetes.

Colour‐related, binocular interactions in patients with dyschromatopsia

AbstractWe report findings of monocular and binocular assessments of colour vision and thresholds for rod‐ and cone‐mediated sensitivity in two young patients (P1 and P2) diagnosed with monocular dyschromatopsia. Altered, monocular, colour perception with no clear diagnosis was reported in each patient based on results from a number of clinical visual assessment tests carried out over several years. Electrodiagnostic tests also revealed reduced Yellow / Blue (YB) chromatic sensitivity in P1. Both patients exhibited unexpected binocular interactions of colour signals. This abstract focuses mostly on the results obtained in P1, but similar results using the same visual assessment tests will also be presented for P2.P1 experienced visual discomfort, often manifested as differences between monocular and binocular viewing, noise‐like appearance of uniform fields and colours over the field, when viewed monocularly with either eye. As a result of these reports, we re‐examined P1's visual deficits using the Colour Assessment and Diagnosis (CAD) and the Flicker‐Plus (FP) tests (http://www.city-occupational.co.uk/). The FP test measures rod‐ and cone‐mediated rapid flicker sensitivity centrally (along the direction of gaze) and at 6 deg eccentricity in each of the four quadrants.Colour Vision. P1 shows significant loss of YB colour vision when tested monocularly in the right eye, but normal red‐green (RG) and YB colour vision in the left eye. When tested binocularly, P1 continues to show the same loss of YB colour vision observed when using only the right eye. These results were unexpected since P1 shows ‘normal’ binocular summation for both colour and flicker sensitivity, even when the thresholds are above the normal range.Rod‐ / Cone‐sensitivity. The patient's cone‐mediated, flicker sensitivity at all five locations investigated (under binocular viewing) was normal (with flicker detection thresholds, often under 2%), but only for the cone‐enhanced condition. When tested with rod‐enhanced stimuli, P1 shows much reduced sensitivity with larger thresholds in the periphery, but only in binocular viewing. Such responses have not been observed previously.In conclusion, P1 shows loss of YB colour vision in the right eye and also significant loss of rod‐mediated sensitivity at each of the five locations investigated. The patient's cone mediated thresholds, at every location tested, were consistently below the mean expected for normal trichromats, both binocularly and with each eye. The YB colour vision measured binocularly remained severely abnormal with thresholds similar to the right eye, in spite of normal colour vision in the left eye. Preliminary observations also suggest that the patient's colour and rapid flicker sensitivity can be affected by fatigue and other factors.Although patient, P2, varied significantly to P1 in monocular thresholds, a similar binocular, inhibitory interaction between the two eyes was observed when processing colour signals. These observations and the unusual interactions between signals derived from the two eyes point towards abnormal central processing of colour signals.

Changes in visual function associated with hydroxychloroquine retinal toxicity

AbstractIntroduction: Non‐infectious inflammatory diseases, such as systemic lupus erythematosus, rheumatoid arthritis, dermatomyositis, antiphospholipid antibody syndrome and others cause significant morbidity and are treated with immunosuppression. Hydroxychloroquine (HCQ) sulfate is used as a second line immunosuppressant and has many advantages over other agents. These include increased life expectancy, reduced risk of neoplasia, reduced risk of diabetes and hypercholesterolaemia. HCQ is safe in pregnancy. After more than 5 years of treatment, HCQ can cause a degenerative maculopathy characterized by loss of parafoveal photoreceptors and RPE cells, leading to a ring‐like visual field defect. Current detection of early retinal toxicity relies on central visual field testing, optical coherence tomography (OCT) scan and fundus autofluorescence. The reason for the parafoveal predilection for retinopathy is not understood. HCQ is concentrated in melanin‐containing cells, and there is increased melanin concentration in the macular RPE cells. A hypothesis is that HCQ concentrated in the macular RPE cells leads to toxicity, with macular pigment protecting the fovea but leaving a ring of potentially vulnerable tissue in the parafoveal region. We were interested to investigate parafoveal function in patients with mild HCQ maculopathy and report the results of detailed macular function assessment of red/green (RG) and yellow / blue (YB) colour vision and rod‐ and cone‐mediated rapid flicker sensitivity.Methods: Two patients with confirmed early hydroxychloroquine maculopathy participated in the study. RG and YB colour thresholds were measured with the Colour Assessment and Diagnosis (CAD) test. Cone and rod‐mediated rapid flicker sensitivity was also measured in both central and paracentral vision using the Flicker‐Plus test. Both patients had taken HCQ for more than 15 years and had paracentral scotomas on 10–2 field test and loss of the parafoveal outer nuclear layer and ellipsoid layer, confirming the presence of maculopathy. To test the hypothesis of parafoveal toxicity risk, 20 short wavelength (BAF) and infrared wavelength (IRAF) autofluorescence images were reviewed. The BAF images are surrogate markers of the macular pigment and the IRAF the melanin concentration. Normalized maps of the difference between BAF and IRAF were calculated to investigate the possibility of a ring of vulnerable tissue.Results: Both patients had normal RG, but abnormal YB colour thresholds. One subject had normal cone flicker thresholds, but the rod flicker thresholds were raised in all quadrants in both eyes. The second subject had significantly elevated rod thresholds and elevated cone flicker thresholds in both eyes. Of note is that the degree of retinopathy in the second patient was greater than in the first. The areas of greatest threshold elevation correlated with the areas of greatest field loss and anatomical disruption on OCT.Conclusion: These new findings show that hydroxychloroquine retinopathy affects preferentially both YB colour vision and rod‐mediated flicker sensitivity. The cone‐mediated flicker sensitivity is also affected in more advanced disease. A model for the anatomical location of the toxicity will be presented, based on the hypothesis outlined above.

Loss of colour vision in patients at risk of developing diabetes

AbstractRecent studies carried out in diabetic patients with no more than moderate maculopathy revealed that over 70% had significant losses of both Yellow/Blue (YB) and Red/Green (RG) colour vision (https://doi.org/10.1111/j.1755-3768.2012.F073.x). The purpose of this study was to investigate whether clinically ‘normal’ subjects, identified as being at ‘risk’ of developing diabetes show significant changes in rod‐ and cone‐mediated rapid flicker sensitivity as well as RG and YB colour vision.Three groups of subjects were recruited; a normal subject group (n = 40), a ‘high‐risk’ group (n = 150) and subjects diagnosed with diabetes (n = 23). The inclusion criteria for ‘high‐risk’ group required 3 or more recognized risk factors for diabetes (e.g., age > 45, HbA1C >5.7, high blood pressure, smoking history, high BMI, family history of diabetes, FPG levels >100 mg/dL). All subjects had full ophthalmic assessment and their RG and YB colour vision, Functional Contrast Sensitivity (FCS), Visual Acuity (VA) and Rod‐ and Cone‐mediated flicker sensitivity were measured using AVOT tests (https://researchcentres.city.ac.uk/applied-vision/avot).Consistent with previous findings, the diabetic group show significant loss of both RG and YB colour vision. Our findings show that these subjects also exhibit higher thresholds for rod and cone mediated vision. In addition, the ‘high‐risk’ group who are clinically classified as ‘normal’, also show significant loss of colour vision and rod and cone sensitivity. The latter group, do not, however, show significant differences in either VA or FCS. These findings suggest that accurate assessment of colour vision and rod‐ and cone‐ mediated rapid flicker sensitivity qualify as important risk factors in prediabetic screening.

The value of colour assessment in diagnostic dilemmas

AbstractBackground: When the goal of clinical assessment is to segment, divide, and classify cases into neat discrete boxes it can often be frustrating to encounter cases which do not fit standard diagnosis algorithms. However, such diagnostic dilemmas often provide a valuable insight into the boundaries of current clinical procedures and the potential value psychophysical assessment can provide when used in conjunction with standard diagnosis algorithms. We present such a case involving localized retinal dysfunction that is not fully consistent with signs of either autoimmune retinopathy or occult maculopathy.Methods: Specific visual function loss was investigated in a health 32‐year‐old male with suspected localized retinal dysfunction, affecting the central retina. Blood tests and electro‐diagnostics were carried out after the patient presented with acute onset ‘foggy’ central vision. The working diagnosis from this initial visit was autoimmune retinopathy and oral steroids were prescribed. Following no change in symptoms a year after initially presenting, the patient was referred to City, University of London for bespoke assessments of specific visual functions. These included assessments of central and peripheral red / green (RG) and yellow / blue (YB) colour vision, mesopic visual acuity (VA), functional contrast sensitivity (FCS), rod‐ and cone‐mediated flicker sensitivity, and pupil responses measured using both rod‐ and cone‐enhanced stimuli.Results: The loss of vision affected primarily the central 20° with a mean VA of 6/36 in each eye. Fundus images, fluorescein angiography, and full field electroretinograms (ERGs) were normal, but pattern and focal ERGs were undetectable indicating localized dysfunction in central vision with OCT images showing a disrupted ellipsoid zone in each eye. The patient's mean corpuscular volume was 69 femtoliters, with red cell indices suggestive of thalassemia. Testing at City, University of London confirmed a loss of VA and FCS in the central 10° field, although both VA and FCS depended strongly on light level and were less affected with negative contrast stimuli. A loss of RG and YB colour vision was also measured centrally. Outside the central 10° field EA had almost normal colour and spatial vision. Rod‐ and cone‐mediated, flicker thresholds were elevated, with cone thresholds 10‐fold higher than normal. Pre‐stimulus pupil size, constriction amplitudes and latencies were normal with both centrally presented and peripheral stimuli.Conclusions: Psychophysical measurements in a patient with presumed autoimmune maculopathy showed atypical macular dysfunction that appears to preferentially affect negative contrast stimuli. Despite damage to the retinal mechanisms involved in spatial vision and light adaptation pupil responses remained unaffected. This unusual case highlights the importance of detailed phenotyping in understanding unknown aetiology.

Colour vision changes in patients with pressure differences across the lamina cribrosa

AbstractThe retinal nerve fibre layer (RNFL) thickness parameters describe the integrity of retinal ganglion cells (RGC) and their axons and can be affected in pathological processes involving the optic nerve. Glaucoma and papilledema are two conditions where RGCs and hence RNFL, are damaged due to the pressure differences across the lamina cribrosa. The latter separates the intraocular and intracranial pressure compartments. In glaucoma, the intraocular pressure (IOP) is elevated and in papilledema, the intracranial pressure is elevated. When intracranial pressure is managed, papilledema patients can recover without significant loss of RGC. Conversely irreversible RGC loss can occur in severe cases.Subtle, functional changes that are often not detected clinically can remain following recovery. The detection of such changes require sensitive functional tests and a knowledge of normal age limits for the stimulus attribute investigated.Results of preliminary studies designed to assess how colour vision and rod and cone mediated flicker sensitivity recover in papilledema will be reported for a number of patients. Following recovery, the results often reveal binocular summation effects, even when the differences between the two eyes remain significant. Patients classed clinically as fully recovered continue to show small differences between the two eyes, even when the measured binocular thresholds are within the expected age limits.In summary, the preliminary findings from this investigation show how various attributes of vision are affected during the early stages of the disease and after treatment and recovery from late stage of severe papilledema with loss of RGCs.

ERG and Behavioral CFF in Light-Damaged Albino Rats.

The full-field ERG is useful for index rod- or cone-mediated retinal function in rodent models of retinal degeneration. However, the relationship between the ERG response amplitudes and visually guided behavior, such as flicker detection, is not well understood. A comparison of ERG to behavioral responses in a light-damage model of retinal degeneration allows us to better understand the functional implications of electrophysiological changes. Flicker-ERG and behavioral responses to flicker were used to determine critical flicker frequency (CFF) under scotopic and photopic conditions before and up to 90 d after a 10-day period of low-intensity light damage. Dark- and light-adapted ERG flash responses were significantly reduced after light damage. The a-wave was permanently reduced, while the b-wave amplitude recovered over three weeks after light damage. There was a small, but significant dip in scotopic ERG CFF. Photopic behavioral CFF was slightly lower following light damage. The recovery of the b-wave amplitude and flicker sensitivity demonstrates the plasticity of retinal circuits following photopic injury.

Relationship Between Flicker Modulation Sensitivity and Retinal Ganglion Cell Related Layer Thicknesses.

PurposeEarly detection of structural changes in retinal ganglion cells (RGCs) and corresponding changes in visual function is important in early degenerative diseases of the retina, but the sensitivity of both measurements is limited by the inherent variability in healthy subjects. This study investigates the relationships between RGC-related layer thicknesses and foveal and parafoveal flicker modulation sensitivity (FMS) across photopic and mesopic light levels in healthy subjects.MethodsPhotopic and mesopic FMS was measured in 56 young adults, at the point of fixation and at an eccentricity of 5 degrees, in each of the four quadrants. Spectral-domain optical coherence tomography (SD-OCT) was used to measure retinal thicknesses. Relationships between foveal and parafoveal FMS and the retinal thickness in the corresponding region were examined after adjusting for confounding variables.ResultsTotal macular and inner retinal layer (IRL) thicknesses in the parafoveal ring were significant predictors of photopic (P = 0.034) and mesopic (P = 0.034) parafoveal FMS, respectively. The superior peripapillary retinal nerve fiber layer (pRNFL) thickness was a contributing factor to the inferior parafoveal FMS (photopic: P = 0.006 and mesopic: P = 0.021) and the inferior pRNFL thickness was also a contributing factor to the superior parafoveal FMS (photopic: P < 0.001 and mesopic: P = 0.015).ConclusionsThe pRNFL thicknesses predict parafoveal FMS for both mesopic and photopic conditions in healthy eyes.Translational RelevanceThe measurement of rapid flicker sensitivity in the parafoveal retina together with the pRNFL thickness profiles measured before the onset of disease, may provide a more sensitive biomarker for detecting loss of sensitivity caused by the earliest neurodegenerative changes in the eyes.

Melanopic stimulation does not alter psychophysical threshold sensitivity for luminance flicker

In addition to the rod and cone photoreceptors the retina contains intrinsically photosensitive retinal ganglion cells (ipRGCs). These cells express the photopigment melanopsin and are known to be involved in reflexive visual functions such as pupil response and photo-entrainment of the circadian rhythm. It is possible that the ipRGCs contribute to conscious visual perception, either by providing an independent signal to the geniculo-striate pathway, or by interacting with and thus modifying signals arising from “classical” retinal ganglion cells that combine and contrast cone input. Here, we tested for the existence of an interaction by asking if a 350% change in melanopsin stimulation alters psychophysical sensitivity for the detection of luminance flicker. In Experiment 1, we tested for a change in the threshold for detecting luminance flicker in three participants after they adapted to backgrounds with different degrees of tonic melanopsin stimulation. In Experiments 2 and 3, this test was repeated, but now for luminance flicker presented on a transient pedestal of melanopsin stimulation. Across the three experiments, no effect of melanopsin stimulation upon threshold flicker sensitivity was found. Our results suggest that even large changes in melanopsin stimulation do not affect near-threshold, cone-mediated visual perception.

Chromatic and flicker threshold changes in age-related macular degeneration following anti-VEGF treatment

ABSTRACT Clinical relevance Red-green chromatic sensitivity and photopic (cone-mediated) flicker sensitivity showed marked improvement after anti-VEGF treatment. The use of flicker and chromatic sensitivities as potential functional tests to monitor treatment outcomes in age-related macular degeneration highlights the clinical importance. Background High-contrast visual acuity (VA) is not a sensitive clinical marker in the management of age-related macular degeneration (AMD). Therefore, flicker and chromatic sensitivity changes were assessed following anti-VEGF treatment in subjects with neovascular AMD. Methods Subjects diagnosed with neovascular AMD were recruited. VA was measured using a COMPlog chart. Flicker (in central 5°) and chromatic thresholds (red-green and yellow-blue) were measured using Flicker-plus test and Colour Assessment and Diagnosis (CAD) tests, respectively. Baseline thresholds and foveal thickness were measured on the same day, just before anti-VEGF injection delivery and 5 weeks ± 5 days later. Results Thirteen subjects (8 males, 5 females) with a mean age of 67.5 ± 8.2 years completed the study. Median VA was not significantly different post-treatment (0.57 logMAR [~6/22: Snellen equivalent], IQR: 0.33) compared to baseline (0.56 logMAR, IQR: 0.33), Wilcoxon matched-pair test, p = 0.55). Median Red-Green thresholds improved significantly post-treatment (22.15 CAD units, IQR: 26.06, n = 9), compared to baseline (24.24 CAD units, IQR: 26.21, p = 0.02). Median photopic and mesopic FMT did not show significant change post treatment compared to baseline (p > 0.01, statistical significance of p-value corrected for multiple comparisons was set to 0.01). Similarly, the foveal thickness was not significantly different at post-treatment visit than baseline (p = 0.53). Conclusion Red/green sensitivity recovered better than yellow/blue sensitivity, thus, providing insight into recovery mechanisms in AMD and usefulness of these tests as clinical markers in the management of AMD.

Do myopes have deficits in peripheral flicker sensitivity?

PurposeSignals from the peripheral retina are important for myopia development. Unlike temporal vision, deficits in peripheral spatial visual functions of myopes have been investigated previously. This study investigated temporal contrast thresholds in emmetropes and myopes at different retinal eccentricities. MethodsForty-four young adults (mean age 23 ± 3 years) including 21 emmetropes (Spherical Equivalent (SE): +0.01 ± 0.30D) and 23 myopes (SE: -3.98 ± 2.41D) participated in this prospective study. Flicker modulation thresholds (FMT) were determined monocularly (right eye) for 15 Hz flicker stimulus at 0°, nasal (23°, 10°) and temporal (-23°, -10°) retinal eccentricities along the horizontal meridian. FMTs were measured psychophysically using 5-adaptive interleaved staircases and threshold was taken as the average of the last 6 reversals. ResultsIn both the groups (emmetropes and myopes), there was a naso-temporal asymmetry in FMTs with higher thresholds in the far temporal retina (Median; Interquartile range: 40.97%; 17.06) than the nasal retina (28.07%; 9.36) (p < 0.001). Flicker modulation thresholds were significantly higher in myopes (30.58%; 12.15) compared to emmetropes (26.77%; 7.74; p = 0.04) at far nasal retina (23°), while at other eccentricities there was no effect (p > 0.05). Further sub-analysis revealed only high myopes (34.48 %, 21.9) showed significantly higher FMT compared to emmetropes (26.77%; 7.74; p = 0.04). ConclusionGreater FMTs were seen in high myopes than that of emmetropes in the nasal retina. Further studies exploring the structural aspects of the myopic eye with FMT would provide a better understanding of role of flicker sensitivity in myopiogenesis.

Visual function deficits in eyes with resolved endophthalmitis

To evaluate the changes in functional vision in patients with resolved endophthalmitis. This was a cross-sectional study. The study included 20 patients with resolved endophthalmitis and best-corrected visual acuity of 20/100 or better. Visual acuity (VA), contrast threshold (CT), red/green (RG) and yellow/blue (YB) colour vision and 15 Hz flicker modulation threshold (FMT) were assessed using standard psychophysical techniques. The median age was 54 years. The median visual acuity was 0.27 (~ 20/40—Snellen Equivalent) ((interquartile range [IQR]), 0.30) logMAR). The median log contrast threshold (CT) was − 1.13 (IQR, 0.36) log units (normative value for age-matched CT: − 1.61 log units). The median red/green (RG) and yellow/blue (YB) thresholds were 11.52 (IQR, 26.19) and 9.45 (IQR, 16.20) CAD units respectively, which were at least 5 times higher than age-matched normative RG and YB thresholds. The median central cone- mediated FMT was 17.64% (IQR, 23.40%), which was much higher compared to age-matched FMT (5.48% [IQR, 3.47]). Linear regression revealed significant relationship between contrast thresholds and foveal thickness (y = 0.001x−1.47, R2 = 0.20, p = 0.048). Though endophthalmitis may resolve with a good visual acuity, deficits in visual functions like chromatic discrimination, cone-mediated flicker and contrast sensitivity persist.

Clinical vision and molecular loss: Integrating visual psychophysics with molecular genetics reveals key details of normal and abnormal visual processing.

Over the past two decades we have developed techniques and models to investigate the ways in which known molecular defects affect visual performance. Because molecular defects in retinal signalling invariably alter the speed of visual processing, our strategy has been to measure the resulting changes in flicker sensitivity. Flicker measurements provide not only straightforward clinical assessments of visual performance but also reveal fundamental details about the functioning of both abnormal and normal visual systems. Here, we bring together our past measurements of patients with pathogenic variants in the GNAT2, RGS9, GUCA1A, RPE65, OPA1, KCNV2 and NR2E3 genes and analyse the results using a standard model of visual processing. The model treats flicker sensitivity as the result of the actions of a sequence of simple processing steps, one or more of which is altered by the genetic defect. Our analyses show that most defects slow down the visual response directly, but some speed it up. Crucially, however, other steps in the processing sequence can make compensatory adjustments to offset the abnormality. For example, if the abnormal step slows down the visual response, another step is likely to speed up or attenuate the response to rebalance system performance. Such compensatory adjustments are probably made by steps in the sequence that usually adapt to changing light levels. Our techniques and modelling also allow us to tease apart stationary and progressive effects, and the localised molecular losses help us to unravel and characterise individual steps in the normal and abnormal processing sequences.

Flicker Propagation Pricing in Power Systems Using a New Short-Circuit-Based Method for Determining the Flicker Transfer Coefficient

Increasing power quality disturbances is one of the significant concerns of power systems that have attracted attention in recent years. One of the most important power quality disturbances is flicker. Flicker not only leads to flickering lighting systems but also damages network equipments, especially those with a high degree of sensitivity. As power systems are restructured, it is possible to take some measures against polluting subscribers. In this article, a new short-circuit-based method is proposed for determining the flicker transfer coefficient. Moreover, four new indices are introduced to assess the effect of flicker sources on target buses' voltage. In the proposed indices, the flicker sensitivity coefficient and the amount of load supplied by each target bus are considered. Using these indices, one can take an accurate impression of the effect of one or more flicker sources on the target buses' voltage. Finally, using the proposed indices, a new flicker propagation pricing method is presented, which can be used to penalize the flicker sources based on their flicker contribution in the target buses. To demonstrate the effectiveness of the proposed method in determining the contribution of flicker sources, the simulations are conducted on IEEE 14-bus test system. The simulation results show that by doing so, while taking into account the introduced indices, it is possible to identify and evaluate the contribution of different flicker sources. Moreover, experimental measurements are conducted on Isfahan region power system as a part of Iran transmission network. Finally, as a result, by applying proper penalty fees to subscribers, it is possible to reduce the flicker level of the network.

Early Ophthalmic Changes in Macula Does Not Correlate with Visual Function.

PurposeEarly detection and treatment of age-related macular degeneration require a clear understanding of the early progress of the disease. The purpose of this study was to investigate whether minimal macular ophthalmoscopic changes corresponded to changes in visual function.MethodsColor macular photos from a group of older subjects who were classified as grade 0 on AREDS simplified grading were further evaluated by a retinal specialist using 5x magnification for possible minimal macular anomalies. Group 0-A (N = 15) were defined as subjects with no visible macular anomalies while Group 0-B (N = 19) comprised subjects for whom minimal macular mottling, pigment changes or very small drusen (< 63 µm) were observed in the study eye. All subjects had best VA of 20/25 or better and had no evidence of other retinal diseases in the study eye. All subjects underwent a series of visual function tests such as standard ETDRS VA, low luminance ETDRS VA, Pelli-Robson contrast sensitivity, variable contrast flicker (VCF) sensitivity, and reading speed (words per minute, wpm) using both MNRead and low luminance reading on a tablet.ResultsThere was no significant difference between the mean age between the two groups (74.8 ± 5.2 years for 0-A vs 74.5 ± 4.4 for 0-B, p = 0.82). None of the visual function tests identified any significant difference between the two groups. Mean ETDRS VA was 0.0 ± 0.11 for 0-A subjects and 0.08 ± 0.12 for 0-B (p = 0.063). Mean Pelli-Robson log contrast sensitivity was 1.75 ± 0.29 for 0-A and 1.78 ± 0.17 for the 0-B group (p = 0.73). VCF threshold was 0.47 ± 0.25 for 0-A and 0.43 ± 0.22 for 0-B (p = 0.64). Reading speed using MNRead was 214 ± 47.4 wpm for 0-A and 210 ± 64.7 for 0-B (p = 0.85). Low luminance tablet reading speed was 137 ± 71.8 wpm for 0-A and 151 ± 39.4 (0-B) (p = 0.49).ConclusionA panel of psychophysical tests did not demonstrate significant differences between subjects with and without minimal macular changes.

Predicting visible flicker in temporally changing images

Novel display algorithms such as low-persistence displays, black frame insertion, and temporal resolution multiplexing introduce temporal change into images at 40-180 Hz, on the boundary of the temporal integration of the visual system. This can lead to flicker, a highly-objectionable artifact known to induce viewer discomfort. The critical flicker frequency (CFF) alone does not model this phenomenon well, as flicker sensitivity varies with contrast, and spatial frequency; a content-aware model is required. In this paper, we introduce a visual model for predicting flicker visibility in temporally changing images. The model performs a multi-scale analysis on the difference between consecutive frames, normalizing values with the spatio-temporal contrast sensitivity function as approximated by the pyramid of visibility. The output of the model is a 2D detection probability map. We ran a subjective flicker marking experiment to fit the model parameters, then analyze the difference between two display algorithms, black frame insertion and temporal resolution multiplexing, to demonstrate the application of our model.

The grading of risk factors for diabetes based on early loss of colour and flicker sensitivity

AbstractPurposeThe purpose of this study was to identify and grade risk factors (in clinically normal subjects) that can lead to diabetes based on early changes in chromatic sensitivity and rod‐ and cone‐mediated vision.MethodsA group of ‘high‐risk’ subjects (n = 82) were recruited for this study. All attended a healthcare centre for detailed vision assessment, in addition to other diagnostic and screening tests. The inclusion criteria required subjects to have at least three or more recognised risk factors for diabetes. The factors examined included HbA1C (&gt;5.7), high blood pressure, smoking history, high BMI, family history of diabetes, FPG levels (&gt;100 mg/dl), age (&gt;45 years), unhealthy diet and lack of exercise. In addition, Visual Acuity, Functional Contrast Sensitivity, rod and cone sensitivities and red‐green (RG) and yellow‐blue (YB) colour thresholds were measured in each subject using the Advanced Vision and Optometric Tests (www.avot/city.ac.uk).ResultsEach of the risk factors for diabetes listed above was examined to establish its effects on RG and YB colour thresholds and the loss of rod and cone sensitivity. Subjects with hypertension had higher RG (p = 0.009) and YB (p = 0.003) colour thresholds and increased contrast thresholds for rod‐ (p = 0.04) and cone‐mediated (p = 0.006) vision. In addition, age (&gt;45) (p = 0.02) and the lack of exercise (p = 0.04) caused worsening of YB colour vision. Lack of exercise is also linked to a statistically significant difference (p = 0.02) in cone mediated vision. Neither family history, nor BMI or unhealthy diet had significant effects on colour or rod‐ and cone‐mediated flicker sensitivity.ConclusionsSubjects at risk of developing diabetes can have significant loss of RG and/or YB colour vision and rod and cone‐mediated flicker sensitivity. The most significant risk factors according to this study are high blood pressure, lack of exercise and age. Although these findings are of immediate clinical interest, it remains to be established how these factors are correlated and the neural changes that can be linked directly to the worsening of colour vision and rod and cone‐mediated flicker sensitivity.

Colour assessment in patients at risk of developing diabetes

AbstractDiabetes has frequently been linked to loss of colour vision. A recent study has shown that over 70% of diabetics have significant loss of both Yellow/Blue (YB) and Red/Green (RG) colour vision (https://doi.org/10.1111/j.1755-3768.2012.f073.x), in the absence of clinical signs of retinopathy. This study also showed poor correlation between the severity of RG or YB loss and parameters such as duration of diabetes, age, HbA1c, body mass index, visual acuity or central retinal thickness. The aim of this study was to investigate whether clinically ‘normal’ subjects, who have been identified as being at ‘risk’ of developing diabetes, show significant changes in colour vision and rod and cone sensitivities.A ‘high‐risk’ group (n = 62) and subjects diagnosed with diabetes (n = 23) were recruited from a healthcare centre that offers diagnostic and screening services, including vision assessment. The inclusion criteria for ‘high‐risk’ group required 3 or more recognised risk factors for diabetes (e.g., age &gt;45, HbA1C &gt;5.7, high blood pressure, smoking history, high BMI, family history of diabetes, FPG levels &gt;100 mg/dl). All subjects had full ophthalmic assessment and their RG and YB colour vision, Functional Contrast Sensitivity, Visual Acuity and Rod‐ and Cone‐mediated flicker sensitivity were measured using the Advanced Vision and Optometric Tests (AVOT) developed at City University (www.avot/city.ac.uk).Consistent with previous findings, the diabetic group show significant loss of both RG and YB colour vision. They also have higher thresholds for rod‐ and cone‐mediated vision. Surprisingly, the ‘high‐risk’ subject group who do not meet the clinical criteria for early diabetes also show significant loss of colour and rod and cone sensitivity. These findings suggest that accurate assessment of colour vision and rod and cone mediated thresholds can be used as early biomarkers in in prediabetic screening.