12 research outputs found
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Sex-related differences in chromatic sensitivity
Generally women are believed to be more discriminating than men in the use of colour names and this is often taken to imply superior colour vision. However, if both X-chromosome linked colour deficient males (~8%) and females (<1%) as well as heterozygote female carriers (~15%) are excluded from comparisons, then differences between men and women in red-green colour discrimination have been reported as not being significant (e.g., Pickford, 1944; Hood et al., 2006). We re-examined this question by assessing the performance of 150 males and 150 females on the Colour Assessment and Diagnosis (CAD) test (Rodriguez-Carmona, 2005). This is a sensitive test that yields small colour detection thresholds. The test employs direction-specific, moving, chromatic stimuli embedded in a background of random, dynamic, luminance contrast noise. A four-alternative, forced-choice procedure is employed to measure the subject’s thresholds for detection of colour signals in 16 directions in colour space, while ensuring that the subject cannot make use of any residual luminance contrast signals. In addition, we measured the Rayleigh anomaloscope matches in a subgroup of 111 males and 114 females. All the age-matched males (30.8 ± 9.7) and females (26.7 ± 8.8) had normal colour vision as diagnosed by a battery of conventional colour vision tests. Females with known colour deficient relatives were excluded from the study. Comparisons between the male and female groups revealed no significant differences in anomaloscope midpoints (p=0.709), but a significant difference in matching ranges (p=0.040); females on average tended to have a larger mean range (4.11) than males (3.75). Females also had significantly higher CAD thresholds than males along the red-green (p=0.0004), but not along the yellow-blue discrimination axis. The differences between males and females in red-green discrimination may be related to the heterozygosity in X-linked cone photopigment expression common among females
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A study of unusual Rayleigh matches in deutan deficiency
Rayleigh match data were modeled with the aim of explaining the locations of match midpoints and matching ranges, both in normal trichromats and in subjects with congenital color deficiency. Model parameters included the wavelength of peak sensitivity of cone photopigments, the effective photopigment optical density, and the noise amplitude in the red-green color channel. In order to avoid the suprathreshold, perceptual effects of extreme L:M cone ratios on color vision, selective post-receptoral amplification of cone signals is needed. The associated noise is also amplified and this causes corresponding changes in red-green threshold sensitivity. We propose that the noise amplitude and hence the size of the matching range in normal trichromats relates to the known inter-subject variation in the relative numbers of L and M cones. If this hypothesis can be shown to account for the extremes of the red-green matching range measured in normal trichromats, it is of interest to establish the extent to which it also predicts the unexpected, small matching ranges that are observed in some subjects with red-green color deficiency. A subset of subjects with deutan deficiency that exhibited less common Nagel matches were selected for genetic analysis of their cone pigment genes in order to confirm the type of deficiency, and to predict the corresponding peak wavelength separation (δλmax) of their two, long-wavelength cone pigments. The Rayleigh match model predicted accurately the midpoint and the range for the spectral differences specified by the genes. The prediction also required plausible selection of effective optical density of the cone pigments and noise. The noise needed varied, but the estimates were confined to lie within the limits established from the matching ranges measured in normal trichromats. The model predicts correctly the small matching ranges measured in some deuteranomalous subjects, principally accounted for by a low estimate of noise level in the red-green channel. The model also predicts the “normal” matches made by some subjects that rely on two hybrid genes and therefore exhibit red-green thresholds outside the normal range, typical of mild deuteranomaly
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New test to assess pilot's vision following corneal refractive surgery.
NoAll forms of corneal refractive surgery can sometimes cause an increase in optical aberrations and scattered light, which can affect visual performance. The purpose of this study was to develop a suitable test that was sensitive to retinal image degradation in subjects who have undergone excimer laser refractive surgery and that was also relevant to visual demands in commercial aviation. Methods: Assessment of the visual environment and the tasks involved in piloting a commercial aircraft formed the basis for the selection of the test parameters. The new contrast acuity assessment (CAA) test covers a functional visual field of ±5° and is based on minimum spatial vision requirements for commercial pilots. Results: Data measured in 100 normal subjects were used to define the `standard normal observer' and the range of variation for the parameters of the test. This approach makes it possible to quickly establish whether a given subject's performance falls within the range of the standard normal observer. The test is also administered under low ambient illumination since flying at night involves mesopic levels of light adaptation when the pupil size is large and the effects of aberrations and scattered light are therefore more pronounced. Conclusion: The results of the test are simple to interpret and reveal visual performance that falls outside the normal range as a result of either significant degradation of retinal image quality (caused by increased aberrations and scattered light) or abnormal processing of visual information in the retina and/or the visual pathway
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Comparison of pupil responses to luminance and colour in severe optic neuritis
Objective: The pupil response to light flux increments is abnormal in severe optic neuritis, but little is known about the effects of this condition on the pupil colour response. The aim of this study was to examine how optic neuritis affects pupil responses to light flux and colour modulation and the extent to which such pupil responses mirror the loss and recovery of vision.
Methods: A new pupil examination technique that makes use of sinusoidal modulation of either luminance contrast or chromatic saturation was employed. This technique enables the automatic extraction of both pupil response amplitude and latency and achieves a high signal to noise ratio with fewer averages.
Results: The study reveals a greater loss of pupil response amplitude and significantly longer latencies to chromatic modulation (i.e. ∼80 ms). Stimulation of the unaffected eye in the optic neuritis group results in smaller response amplitudes when compared to the normal group for both light flux and colour modulation.
Conclusions: Pupil response components can be affected differently in optic neuritis. These findings suggest that the pupil colour response, in particular, may provide a useful, objective estimator to judge the extent of damage and recovery in diseases of the optic nerve
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Exploring eye movements in patients with glaucoma when viewing a driving scene
NoBACKGROUND: Glaucoma is a progressive eye disease and a leading cause of visual disability. Automated assessment of the visual field determines the different stages in the disease process: it would be desirable to link these measurements taken in the clinic with patient's actual function, or establish if patients compensate for their restricted field of view when performing everyday tasks. Hence, this study investigated eye movements in glaucomatous patients when viewing driving scenes in a hazard perception test (HPT). METHODOLOGY/PRINCIPAL FINDINGS: The HPT is a component of the UK driving licence test consisting of a series of short film clips of various traffic scenes viewed from the driver's perspective each containing hazardous situations that require the camera car to change direction or slow down. Data from nine glaucomatous patients with binocular visual field defects and ten age-matched control subjects were considered (all experienced drivers). Each subject viewed 26 different films with eye movements simultaneously monitored by an eye tracker. Computer software was purpose written to pre-process the data, co-register it to the film clips and to quantify eye movements and point-of-regard (using a dynamic bivariate contour ellipse analysis). On average, and across all HPT films, patients exhibited different eye movement characteristics to controls making, for example, significantly more saccades (P<0.001; 95% confidence interval for mean increase: 9.2 to 22.4%). Whilst the average region of 'point-of-regard' of the patients did not differ significantly from the controls, there were revealing cases where patients failed to see a hazard in relation to their binocular visual field defect. CONCLUSIONS/SIGNIFICANCE: Characteristics of eye movement patterns in patients with bilateral glaucoma can differ significantly from age-matched controls when viewing a traffic scene. Further studies of eye movements made by glaucomatous patients could provide useful information about the definition of the visual field component required for fitness to drive
Quantifying The Pattern Of Optic Tract Degeneration In Human Hemianopia
Background: The existence of transsynaptic retrograde degeneration (TRD) in the human visual system has been established, however the dependence of TRD on different factors such as lesion location, size and manner of lesion acquisition has yet to be quantified. Methods: We obtained T1-weighted structural and diffusion-weighted images for 26 patients with adultacquired or congenital hemianopia and 12 age-matched controls. The optic tract (OT) was defined and measured in the structural and diffusion-weighted images, and degeneration assessed by comparing the integrity of tracts in the lesioned and in the undamaged hemisphere. Results: OT degeneration was found in all patients with established lesions, regardless of lesion location. In patients with acquired lesions, the larger the initial lesion, the greater is the resulting TRD. However, this was not the case for congenital patients, who generally showed greater degeneration than would be predicted by lesion size. A better predictor of TRD was the size of the visual field deficit, which was correlated with degeneration across all patients. Interestingly, although diffusion-weighted imaging (DWI) is more frequently used to examine white matter tracts, in this study the T1- weighted scans gave a better indication of the extent of tract degeneration. Conclusions: We conclude that TRD of the OT occurs in acquired and congenital hemianopia, is correlated with visual field loss, and is most severe in congenital cases. Understanding the pattern of TRD may help to predict effects of any visual rehabilitation training.854379386NIHR; National Institute for Health ResearchZhang, X., Kedar, S., Lynn, M.J., Newman, N.J., Biousse, V., Homonymous hemianopia in stroke (2006) Journal of Neuro-Ophthalmology, 26 (3), pp. 180-183. , DOI 10.1097/01.wno.0000235587.41040.39, PII 0004132720060900000005Luu, S., Lee, A.W., Daly, A., Visual field defects after stroke: A practical guide for GPs (2010) Aust Fam Physician, 39, pp. 499-503Pambakian, A.L.M., Kennard, C., Can visual function be restored in patients with homonymous hemianopia? (1997) British Journal of Ophthalmology, 81 (4), pp. 324-328Zhang, X., Kedar, S., Lynn, M.J., Newman, N.J., Biousse, V., Natural history of homonymous hemianopia (2006) Neurology, 66 (6), pp. 901-905. , DOI 10.1212/01.wnl.0000203338.54323.22, PII 0000611420060328000023Schofield, T.M., Leff, A.P., Rehabilitation of hemianopia (2009) Curr Opin Neurol, 22, pp. 36-40Ajina, S., Kennard, C., Rehabilitation of damage to the visual brain (2012) Rev Neurol, 168, pp. 754-761Mueller, I., Mast, H., Sabel, B.A., Recovery of visual field defects: A large clinical observational study using vision restoration therapy (2007) Restorative Neurology and Neuroscience, 25 (5-6), pp. 563-572Sahraie, A., Macleod, M.J., Trevethan, C.T., Improved detection following Neuro-Eye Therapy in patients with post-geniculate brain damage (2010) Exp Brain Res, 206, pp. 25-34Vanburen, J.M., Trans-synaptic retrograde degeneration in the visual system of primates (1963) J Neurol Neurosurg Psychiatry, 26, pp. 402-409Weller, R.E., Kaas, J.H., Parameters affecting the loss of ganglion cells of the retina following ablations of striate cortex in primates (1989) Vis Neurosci, 3, pp. 327-349Cowey, A., Stoerig, P., Williams, C., Variance in transneuronal retrograde ganglion cell degeneration in monkeys after removal of striate cortex: Effects of size of the cortical lesion (1999) Vision Research, 39 (21), pp. 3642-3652. , DOI 10.1016/S0042-6989(99)00097-8, PII S0042698999000978Cowey, A., Alexander, I., Stoerig, P., Transneuronal retrograde degeneration of retinal ganglion cells and optic tract in hemianopic monkeys and humans (2011) Brain, 134, pp. 2149-2157Cowey, A., Stoerig, P., Perry, V.H., Transneuronal retrograde degeneration of retinal ganglion cells after damage to striate cortex in macaque monkeys: Selective loss of Pβ cells (1989) Neuroscience, 29 (1), pp. 65-80. , DOI 10.1016/0306-4522(89)90333-3Bridge, H., Plant, G., Conclusive Evidence for Human Transneuronal Retrograde Degeneration in the Visual System (2012) J Clin Exp Ophthalmol, 3 S, p. 003Jindahra, P., Petrie, A., Plant, G.T., Retrograde trans-synaptic retinal ganglion cell loss identi fied by optical coherence tomography (2009) Brain, 132, pp. 628-634Jindahra, P., Petrie, A., Plant, G.T., The time course of retrograde trans-synaptic degeneration following occipital lobe damage in humans (2012) Brain, 135, pp. 534-541Jindahra, P., Petrie, A., Plant, G.T., Thinning of the retinal nerve fibre layer in homonymous quadrantanopia: Further evidence for retrograde trans-synaptic degeneration in the human visual system (2012) J Neuroophthalmol, 36, pp. 79-84Bridge, H., Jindahra, P., Barbur, J., Imaging reveals optic tract degeneration in Hemianopia (2011) Invest Ophthalmol Vis Sci, 52, pp. 382-388Behrens, T.E.J., Berg, H.J., Jbabdi, S., Rushworth, M.F.S., Woolrich, M.W., Probabilistic diffusion tractography with multiple fibre orientations: What can we gain? (2007) NeuroImage, 34 (1), pp. 144-155. , DOI 10.1016/j.neuroimage.2006.09.018, PII S1053811906009360Behrens, T.E.J., Woolrich, M.W., Jenkinson, M., Johansen-Berg, H., Nunes, R.G., Clare, S., Matthews, P.M., Smith, S.M., Characterization and Propagation of Uncertainty in Diffusion-Weighted MR Imaging (2003) Magnetic Resonance in Medicine, 50 (5), pp. 1077-1088. , DOI 10.1002/mrm.10609Burgel, U., Amunts, K., Hoemke, L., Mohlberg, H., Gilsbach, J.M., Zilles, K., White matter fiber tracts of the human brain: Three-dimensional mapping at microscopic resolution, topography and intersubject variability (2006) NeuroImage, 29 (4), pp. 1092-1105. , DOI 10.1016/j.neuroimage.2005.08.040, PII S105381190500649XSmith, S.M., Jenkinson, M., Johansen-Berg, H., Tract-based spatial statistics: Voxelwise analysis of multi-subject diffusion data (2006) NeuroImage, 31, pp. 1487-1505Hoyt, C.S., Visual function in the brain-damaged child (2003) Eye, 17 (3), pp. 369-384. , DOI 10.1038/sj.eye.6700364Cowey, A., Stoerig, P., The neurobiology of blindsight (1991) Trends Neurosci, 14, pp. 140-145Warner, C.E., Kwan, W.C., Bourne, J.A., The early maturation of visual cortical area MT is dependent on input from the retinorecipient medial portion of the inferior pulvinar (2012) J Neurosci, 32, pp. 17073-17085Schmid, M.C., Mrowka, S.W., Turchi, J., Blindsight depends on the lateral geniculate nucleus (2010) Nature, 466, pp. 373-377Bridge, H., Thomas, O., Jbabdi, S., Cowey, A., Changes in connectivity after visual cortical brain damage underlie altered visual function (2008) Brain, 131 (6), pp. 1433-1444. , DOI 10.1093/brain/awn063Sincich, L.C., Park, K.F., Wohlgemuth, M.J., Horton, J.C., Bypassing V1: A direct geniculate input to area MT (2004) Nature Neuroscience, 7 (10), pp. 1123-1128. , DOI 10.1038/nn1318Bridge, H., Hicks, S.L., Xie, J., Visual activation of extra-striate cortex in the absence of V1 activation (2010) Neuropsychologia, 48, pp. 4148-415