Loss Of Chromatic Sensitivity Research Articles

Cerebral achromatopsia

AbstractChromatic sensitivity was assessed in patients with pregeniculate and postgeniculate lesions. We examine changes in central vision along at foveal fixation and in each of the four paracentral quadrants of the visual field using the Colour Assessment and Diagnosis (CAD) test, a dynamic luminance contrast masking technique that isolates the use of Red / Green (RG) and Yellow / Blue (YB) colour signals. Because the extraction of colour signals in early visual processing involves opponent mechanisms, subjects with congenital RG loss of sensitivity exhibit symmetric increase in thresholds towards the long wavelength (“red”) and middle wavelength (“green”) regions of the spectrum locus. This is also frequently the case with acquired loss of chromatic sensitivity as a result of retinal or optic nerve disease. The findings from this study represent an exception to this rule. The patients investigated showed a marked asymmetry in colour thresholds. The study reveals how discrete, localized damage to visual pathways can cause selective loss of visual function and how the latter varies with retinal topography.The 36 pregeniculate patients investigated exhibited impairment in both RG and YB. Loss of colour vision was symmetrical for both RG and YB discrimination. Some pregeniculate patients exhibited substantial loss of colour vision in areas where perimetric loss was largely absent. All quadrants revealed similar symmetric loss of colour sensitivity.In 23 patients with postgeniculate lesions, patients with pre‐striate damage exhibited symmetric loss of chromatic sensitivity which affected either one or both chromatic mechanisms. Striate or extra‐striate lesions tended to exhibit general loss of colour vision within the area identified by visual field testing. More specific chromatic loss was associated with less impaired areas that were often normal on perimetric testing. Some patients with striate or extra‐striate lesions presented with asymmetric chromatic loss for one or more colour categories. When striate or extra‐striate lesions were also accompanied by underlying pre‐striate damage, chromatic sensitivity loss was always symmetric.The findings from this study show that the loss of chromatic sensitivity in cerebral achromatopsia depends strongly on the exact location and extent of the lesion with significant variation over the visual field. The same subject can exhibit loss of chromatic sensitivity that is either RG or YB specific, but also, spatially localized, non‐opponent loss of sensitivity for primary colours.

Detection of colour vision changes in patients with systemic diseases that can affect the eye

AbstractPurpose Changes in colour vision can provide the earliest signs of vision loss caused by either retinal or systemic disease (Expert Rev.Ophthalmol. 6(4):409‐420,2011). Both yellow‐blue (YB) and red‐green (RG) mechanisms are affected in acquired deficiency, but some diseases may cause different patterns of colour vision loss. Patients with different systemic diseases were examined to discover abnormal changes in colour vision using a newly developed, age‐corrected system for colour assessment.Methods 334 subjects (age range: 41 to 91years) were investigated. The subjects were classified as normal, hypertensive, diabetic, diabetic and hypertensive, idiopathic and other systemic conditions. RG and YB colour thresholds were measured monocularly in each eye using the Colour Assessment and Diagnosis (CAD) test.Results Subjects with early stage pathology were excluded using a number of criteria including the discovery of right / left eye asymmetric loss in colour sensitivity. Age‐corrected limits of normal colour vision were employed to detect significant changes in chromatic sensitivity. The results reveal significantly higher RG and YB thresholds in all groups (including the idiopathic and other systemic conditions group).Conclusion The use of age‐corrected normal limits of chromatic sensitivity makes it possible to detect reliably significant loss of colour vision in systemic disease. Loss of chromatic sensitivity that precedes retinopathy is present in every systemic condition examined. Further studies are needed to discover the extent to which the pattern of selective RG and YB losses can be attributed to specific diseases of the eye.

Severity of colour vision loss in diabetes

AbstractPurpose Vascular and structural changes in the retina are used to grade progression in diabetic retinopathy (DR) and this is often taken as an indicator of the severity of vision loss. Changes in visual function may, however, precede detectable structural damage. Red‐green (RG) and yellow‐blue (YB) thresholds were measured in patients with DR and related to their clinical grading classification.Methods 66 patients diagnosed with diabetes were examined. DR was graded according to ETDRS severity scale as no retinopathy, mild, moderate, severe DR and presence/absence of macular oedema. Colour thresholds were measured using the CAD test (Expert Rev.Ophthalmol. 6:409‐420, 2011) together with other patient‐specific information: VA, duration of diabetes, HbA1c and central subfield (CSF) thickness, and response of macular oedema to Ozurdex intravitreal implant injection.Results All diabetic patients showed loss of chromatic sensitivity (with mean RG and YB thresholds exceeding six times normal values). The clinical grading of disease progression showed negligible correlation with either RG (r2=‐0.0004) or YB thresholds (r2=0.052). Patients with no DR often exhibited normal visual acuity (~ 1 min arc), but showed significant loss of colour vision. Ozurdex treatment was associated with significant initial improvement in colour thresholds.Conclusion RG and YB colour thresholds provide a sensitive measure of functional change in diabetics that does not relate well to observed vascular and structural changes. These preliminary findings also suggest that measurement of colour thresholds can be used to monitor the efficacy of treatment in diabetic macular oedema.

Changes in color vision with decreasing light level: separating the effects of normal aging from disease

The purpose of this study was to obtain additional information about the health of the retina (HR) by measuring the rate of loss of chromatic sensitivity with decreasing light level. The HR(index) is introduced to separate the effects of normal aging from early stage disease. For normal subjects the HR(index is largely independent of age (r(2)~0.1), but ~11% of clinically normal, asymptomatic, older subjects exhibit values below the 2σ limit. The HR(index provides a single number that captures how light level affects chromatic sensitivity irrespective of age and can be used to screen for preclinical signs of retinal disease.

Evidence for Non-Opponent Coding of Colour Information in Human Visual Cortex: Selective Loss of “Green” Sensitivity in a Subject with Damaged Ventral Occipito-Temporal Cortex

Damage to ventral occipito-temporal extrastriate visual cortex leads to the syndrome of prosopagnosia often with coexisting cerebral achromatopsia. A patient with this syndrome resulting in a left upper homonymous quadrantanopia, prosopagnosia, and incomplete achromatopsia is described. Chromatic sensitivity was assessed at a number of locations in the intact visual field using a dynamic luminance contrast masking technique that isolates the use of colour signals. In normal subjects chromatic detection thresholds form an elliptical contour when plotted in the Commission Internationale d’Eclairage, (x-y), chromaticity diagram. Because the extraction of colour signals in early visual processing involves opponent mechanisms, subjects with Daltonism (congenital red/green loss of sensitivity) show symmetric increase in thresholds towards the long wavelength (“red”) and middle wavelength (“green”) regions of the spectrum locus. This is also the case with acquired loss of chromatic sensitivity as a result of retinal or optic nerve disease. Our patient’s results were an exception to this rule. Whilst his chromatic sensitivity in the central region of the visual field was reduced symmetrically for both “red/green” and “yellow/blue” directions in colour space, the subject’s lower left quadrant showed a marked asymmetry in “red/green” thresholds with the greatest loss of sensitivity towards the “green” region of the spectrum locus. This spatially localized asymmetric loss of “green” but not “red” sensitivity has not been reported previously in human vision. Such loss is consistent with selective damage of neural substrates in the visual cortex that process colour information, but are spectrally non-opponent.

Loss of chromatic sensitivity in AMD and diabetes: a comparative study

Abnormalities in rod and cone photoreceptor morphology have been reported in normal aging retinas in the absence of known pathology and have been taken as an indicator of susceptibility to retinal disease. Some loss of visual performance may therefore precede retinal structural changes that can be detected reliably using conventional fundus imaging techniques. Red/green (RG) and yellow/blue (YB) colour discrimination thresholds are sensitive measures of normal retinal function and poor YB discrimination is often taken as an indicator of retinal disease, though it is generally acknowledged that RG loss is also present in most cases of acquired deficiency. Although structural changes in age-related macular degeneration (AMD) and diabetes share some similarities, significant differences remain and this may result in different patterns of RG and YB loss. The aim of this study was to quantify and compare the severity of RG and YB loss of chromatic sensitivity in patients with AMD and diabetes. Patients with varying severity of AMD and diabetes and normal subjects of similar age were recruited for the study. RG and YB colour detection thresholds were measured in the two groups of patients and the control group, using the Colour Assessment and Diagnosis (CAD) test. Each AMD subject investigated showed significant, but unequal loss of YB and RG chromatic sensitivity, with YB discrimination showing the greatest loss. Diabetic subjects also exhibited reduced chromatic sensitivity, but with almost equal and highly correlated RG and YB thresholds (R(2) = 0.99). The severity of colour vision loss measured with the CAD test also correlates well with a clinical classification index of disease progression in AMD, and with the level of hyperglycaemic control in diabetes. These findings suggest that accurate measurements of RG and YB colour thresholds can provide a sensitive measure of functional change in diseases of the retina with patterns of loss that differ significantly in AMD and diabetes.

Acquired loss of chromatic sensitivity

Abstract Purpose A range of ophthalmic and neurological conditions cause diminished visual performance, even when the subject is often unaware of any problems and the loss of vision remains undetected in conventional perimetry and visual acuity tests. The extent to which detection of acquired colour vision loss can revealed in subclinical cases and distinguished from congenital loss has been investigated. Methods Over 400 subjects with congenital and acquired colour vision loss have been examined using conventional colour screening methods. In addition, the loss of yellow / blue and red / green chromatic sensitivity has been quantified using the CAD test (http://www.caa.co.uk/docs/33/200904.pdf). Those investigated included subjects with diseases of the retina and / or the optic nerve as well as patients with selective damage to central visual pathways. Patients with various stages of glaucoma, photoreceptor dystrophies, diabetes, optic neuritis, age‐related macular degeneration as well as tobacco and alcohol toxicity have been examined. Results Algorithms developed for analysis of colour vision loss and automatic classification of congenital and / or acquired colour deficiency will be described. In acquired deficiency, the loss of chromatic sensitivity tends to affect both the rg and the yb channels. Significant differential effects have, however, been observed in relation to stimulus size, retinal location and state of light adaptation. Conclusion The findings from these studies show that in the majority of these conditions, the loss of chromatic sensitivity is the most sensitive measure of early changes in diseases of the eye.

Chromatic sensitivity in subjects with diabetes

Abstract Purpose Diabetic retinopathy is a major cause of blindness in the Western World and remains one of the most serious complications of diabetes mellitus. The gold standard to measure functional change in diabetic (DB) patients is LogMAR or Snellen VA. The aim of this study was to measure and characterise the severity of visual function loss in subjects with DB using sensitive psychophysical tests and to quantify accurately how changes in management of the disease correlate with changes in visual function. Methods Three groups of patients (n=50) were included in this study:DB patients with and without retinopathy and patients with no DB. Each patient had a full ophthalmic examination prior to psychophysical assessment. Colour vision assessment was carried out using the CAD test (Colour Assessment & Diagnosis) that provides a measure of both yellow‐blue and red‐green loss of chromatic sensitivity (CS). Rapid flicker (RF) was also measured by assessing sensitivity to a 20Hz flicker stimulus at five locations in the central visual field (fovea and 1.5 degrees from fixation in each quadrant). All tests were carried out at photopic and high mesopic light. Results The results show significant loss of CS (p <.001) and some loss in RF sensitivity (p <.01). The most sensitive measure of visual loss was CS.There was also a positive correlation between CAD thresholds as a measure of CS and improved DB control. Conclusion The results suggest that loss of visual function precedes structural changes in the retina and could be used as a means of detecting early structural changes in the retina that precede clinical diagnosis of retinopathy. Preliminary results also suggest that changes in CAD thresholds provide an objective way of monitoring the progress of DB and/or treatment outcome.

Acquired colour vision deficiency in subjects with ARMD and Diabetes

Abstract Purpose Age Related Macular Degeneration (ARMD) is the leading cause of blindness in the developed world in people over the age of 50. Its prevalence increases with age as does diabetes. Such conditions affect the metabolic stability of the retina, resulting in non‐inflammatory damage to retinal structures, and finally retinopathy. These changes to the visual pathway result in colour vision loss and in general, diminished visual performance. The aim of this study was to quantify accurately using sensitive visual tests the severity of visual loss in subjects with ARMD and diabetes. Methods We investigated a large number of ARMD and Diabetic subjects with varying degrees of retinopathy and assessed their colour vision, achromatic high contrast acuity and flicker sensitivity under photopic and mesopic viewing conditions. Results Results show a loss of chromatic sensitivity in both the red‐green and yellow‐blue channels, more pronounced under mesopic viewing condition. It was observed that chromatic loss was not localised to the site of retinopathy but affected peripheral retina also. Flicker sensitivity and contrast acuity loss were also observed in all subjects diagnosed with the above conditions. Preliminary findings show that significant loss of chromatic and flicker sensitivity precedes structural changes in the retina as revealed in conventional fundus imaging. Conclusion The results so far suggest that loss of chromatic sensitivity is the most sensitive measure for detection of early damage in subjects with eye disease and can be used to detect and to monitor the progress of disease or the outcome of treatment.

The relative merits of anomaloscope matches and colour discrimination tests in assessing loss of chromatic sensitivity

The relative merits of anomaloscope matches and colour discrimination tests in assessing loss of chromatic sensitivity

Functional evidence for cone‐specific connectivity in the human retina

Physiological studies of colour vision have not yet resolved the controversial issue of how chromatic opponency is constructed at a neuronal level. Two competing theories, the cone-selective hypothesis and the random-wiring hypothesis, are currently equivocal to the architecture of the primate retina. In central vision, both schemes are capable of producing colour opponency due to the fact that receptive field centres receive input from a single bipolar cell - the so called 'private line arrangement'. However, in peripheral vision this single-cone input to the receptive field centre is lost, so that any random cone connectivity would result in a predictable reduction in the quality of colour vision. Behavioural studies thus far have indeed suggested a selective loss of chromatic sensitivity in peripheral vision. We investigated chromatic sensitivity as a function of eccentricity for the cardinal chromatic (L/M and S/(L + M)) and achromatic (L + M) pathways, adopting stimulus size as the critical variable. Results show that performance can be equated across the visual field simply by a change of scale (size). In other words, there exists no qualitative loss of chromatic sensitivity across the visual field. Critically, however, the quantitative nature of size dependency for each of the cardinal chromatic and achromatic mechanisms is very specific, reinforcing their independence in terms of anatomy and genetics. Our data provide clear evidence for a physiological model of primate colour vision that retains chromatic quality in peripheral vision, thus supporting the cone-selective hypothesis.