1 - Colour vision: theories and principles

Ratios of excitations in each cone-photoreceptor class produced by light reflected from pairs of surfaces in a scene are almost invariant under natural illuminant changes. The stability of these spatially defined ratios may explain the remarkable ability of human observers to efficiently discriminate illuminant changes from changes in surface reflectances. Spatial cone-excitation ratios are not, however, exactly invariant. This study is concerned with observers' sensitivity to these invariance violations. Simulations of Mondrian paintings with either 49 or two natural surfaces under Planckian illuminants were presented as images on a computer-controlled display in a two-interval experimental design: in one interval, the surfaces underwent an illuminant change; in the other interval, the surfaces underwent the same change but the images were then corrected so that, for each cone class, ratios of excitations were preserved exactly. Although the intervals with corrected images corresponded individually to highly improbable natural events, observers systematically misidentified them as containing the illuminant changes, the probability of error increasing as the violation of invariance in the other interval increased. For the range of illuminants and surfaces tested, sensitivity to violations of invariance was found to depend on cone class: it was greatest for long-wavelength-sensitive cones and least for short-wavelength-sensitive cones. Spatial cone-excitation ratios, or some closely related quantities, seem to be the cues preferred by observers for making inferences about surface illuminant changes.

The antagonistic mechanism of human color vision is the physiological characteristics of the human visual system. The processing of spatial color information in visual color channels is opposite, which presents that the black-white opposition color channel, the red-green opponent color channel and the yellow-blue opposition color channel are all multi-scale. This paper aims to study the algorithm of the antagonistic mechanism of human color vision. Based on the theory of the visual receptive fields, seven filter operators associated with the human observation condition are designed; the mapping relation between these operators and human visual observation scale is established. The paper put forward to an algorithm for simulating the antagonistic mechanism of human color vision, which is carried out in visual opposite color space. The experiment results show that the algorithm has the ability of color constancy prediction, and the color reduction accuracy is not lower than the automatic white balance processing result of the professional digital SLR camera.

Nowadays, widespread usage of colours increases the need for accurate estimation of colour vision defects and their effect on performing daily activities and study/work tasks. To determine the prevalence and predictors of colour vision defects among Assiut university students and to identify their relationship with self-reported visual function and perceived difficulties in performing daily activities. A cross-sectional study was conducted among 1426 students at Assiut University, Egypt. Data were collected by self-administered questionnaire consisting of: personal characteristics, prior awareness of colour vision defects, difficulties in daily colour vision activities, and visual function. Colour vision was assessed using Ishihara's test of colour deficiency. The prevalence of colour vision defects among students was 6.9% (red-green colour vision was 4.3% and total colour blindness was 2.6%). Students with colour vision defects had significantly higher odds ratios for difficulties in daily activities and study/work tasks related to colour perception. Students with colour vision defects had significantly lower mean values of general health, role difficulties, and colour vision scores compared to students with normal colour insight. Male sex and family history of colour vision defects were risk factors. A non-negligible percentage of Egyptian university students had colour vision defects, which had a negative impact on performing daily activities, executing study/work tasks, and choice of study/work specialties. Colour vision defects affected quality of life with regard to general health, role difficulties and colour vision. Male sex and family history of colour vision defects are nonmodifiable risk factors. This emphasizes the need for genetic counselling, especially in consanguineous marriage.

To study colour vision in patients with tilted disc syndrome. Colour vision was examined using Boström-Kugelberg (B-K) plates, Farnsworth-Munsell 100-hue test (FM-100) and Farnsworth panel D-15 and Lanthony desaturated panel tests. A total of 35 eyes of 21 patients were examined. Seventeen eyes (49%) of 11 patients were found to have a colour vision defect in at least one eye. The severity of the colour vision defect differed between eyes for six of eight patients with bilateral tilted discs. In two of these patients, colour vision was normal in one eye. Seven patients had a unilateral tilted disc and three of these individuals had a colour vision defect in the affected eye. Of all eyes with a colour vision defect, a red-green defect was found in four eyes (24%), a blue defect in one eye (6%), and a mixed defect in 12 eyes (70%). Colour vision defects were not related to visual acuity or to severity of visual field defects. This is the first report of colour vision defects in tilted disc syndrome. In the differential diagnosis of tilted disc syndrome, chiasmal lesions and glaucoma, the examination of colour vision may add valuable information. Further, it is recommended that young people with tilted disc syndrome undergo an examination of colour vision so that they can be given appropriate career guidance.

PURPOSE:To estimate the magnitude and determinants of color vision defects (CVD) among preparatory health science students.METHODS:A cross-sectional survey was conducted in 2017. Participants were assessed using 24-plate Ishihara's Test of Color Vision chart. If ≤9 plates were read correctly, the color vision was regarded as deficient. The CVD prevalence and its 95% confidence interval (CI) were calculated. CVD was associated with gender, family history of CVD, and other vision problems.RESULTS:We evaluated 1126 students (552, 49% males; mean age: 18.7 ± 0.7 years). The prevalence of CVD was 1.77% (95% CI: 1.0, 2.6). Among male students, it was 3.5% (95% CI: 1.9, 5.0). Only one female student had CVD. The Duran CVD was found in 18 (1.6%) students. However, only two students had Tritan CVD. Three among twenty CVD students knew that they suffer from CVD. CVD was positively associated to a family history of CVD (odds ratio [OR] = 3.8; 95% CI: 1.4, 10.1;P = 0.02) and male gender (OR = 20.4 [95% CI: 2.7, 153]). CVD was not significantly associated to other vision problems (OR = 0.8 [95% CI: 0.3, 2.0]).CONCLUSION:Eighteen in thousand health sciences students suffered from CVD. Ten percent of them had Tritan CVD. Duran CVD seems to be a male sex-related and/or a familial condition. Most of the CVD students seem to have adopted to this defect and were not aware of suffering from it. Screening for CVD is therefore debatable.

The red-green axis of colour vision evolved recently in primate evolutionary history. Signals serving red-green colour vision travel together with signals serving spatial vision, in the parvocellular (PC) division of the subcortical visual pathway. However, the question of whether receptive fields of PC pathway cells are specialized to transmit red-green colour signals remains unresolved. We addressed this question in single-cell recordings from the lateral geniculate nucleus of anaesthetized marmosets. Marmosets show a high proportion of dichromatic (red-green colour-blind) individuals, allowing spatial and colour tuning properties of PC cells to be directly compared in dichromatic and trichromatic visual systems. We measured spatial frequency tuning for sine gratings that provided selective stimulation of individual photoreceptor types. We found that in trichromatic marmosets, the foveal visual field representation is dominated by red-green colour-selective PC cells. Colour selectivity of PC cells is reduced at greater eccentricities, but cone inputs to centre and surround are biased to create more selectivity than predicted by a purely 'random wiring' model. Thus, one-to-one connections in the fovea are sufficient, but not necessary, to create colour-selective responses. The distribution of spatial tuning properties for achromatic stimuli shows almost complete overlap between PC cells recorded in dichromatic and trichromatic marmosets. These data indicate that transmission of red-green colour signals has been enabled by centre-surround receptive fields of PC cells, and has not altered the capacity of PC cells to serve high-acuity vision at high stimulus contrast.

In this study, involving students between 14 and 16 years old, the psychological dimensions of cognition and personality affected by red-green colour vision deficiencies were investigated. From the results of a factorial analysis it appears that the influence of colour vision abnormality on the psychological factors that we tested is always minor. Colour vision defect is correlated with such cognitive variables as spatial aptitude and visual difference perception, and with such personality variables as praxemia and submission. The weighting of the cognition and personality factors linked to colour vision abnormality, however, varies considerably and does not in any case contribute more than 20% to the total variance.

Introduction: Colour vision deficiency is a common but unnoticed condition. Medical students must be aware of their congenital colour vision deficiency and its effects on their work, so that color vision deficient student may not choose the discipline such as pathology and radiology, where colour vision is very important. Methods: This is a cross-sectional study conducted in the Department of Clinical Physiology, Maharajgunj Medical Campus, Institute of Medicine, Kathmandu from February 2013 to January 2016. Total of 556 medical and nursing students selected by convenient sampling, underwent color vision evaluation by using Ishihara chart. Results: Out of 302 male students, 20 (6.6%) were color vision deficient. Similarly, out of 254 female students, two (0.8%) were colour vision deficient. Among the male students, two (10%) were total colour blind, eight (40%) were suffering from deuteranomaly and 10 (50%) were suffering from deuteranopia. Colour vision deficiencies were observed more in Chhetri (9.5%), followed by Brahmin (7.1%) and Madhesi ethnicity (6.9%). Conclusion: The prevalence of colour vision deficiency in Nepalese medical students is significant. Therefore, they should be screened for colour vision deficiency, so that the students with colour vision defect can choose appropriate discipline as their future carrier where colour vision defect may not affect their work.

Numerical Confusion Errors in Ishihara Testing: Findings From a Population-based Study

Impact of visual function on computer task accuracy and reaction time in a cohort of patients with age-related macular degeneration

Objectives: We have treated people who have color vision defects with oriental medicine; here we demonstrate several representative cases to illustrate the effectiveness of our treatment. Material and methods: We recruited study patients who visited one oriental hospital for color vision defects. We show several representative cases to illustrate the effectiveness of our treatment. The study initially consisted of 178 subjects who took part during a 3-year period. Subjects, all of whom consented to this treatment and trial, were classified by those who have a color vision defect and those who dont by the Ishihara test and another by the Hahn color vision test. We tried color vision correction treatment with acupuncture. Acupuncture therapy where the retina and optic nerves were activated was conducted in parallel with vision correction. Assessment of therapy was conducted at 30 times, 60 times, 90 times, or 120 times of therapy. Results: Assessment of therapy was performed by conducting treatment 30 times, 60 times, 90 times, or 120 times. Surprisingly, all subjects could correctly recognize color after the treatment; although there were case by case differences according to the number of therapy treatments each individual received. Conclusions: Color vision defects can be treated. To enable those with color vision defects to enjoy better quality of life and increased opportunity in color vision-dependent job fields, therapy to correct the problem is a viable option.

One of the most common inherited vision disorders is congenital color vision deficiency (CVD). Its prevalence in men can be as high as 8% and 0.5% in women.[1] Men are predominately affected by the X-linked inheritance pattern, while women become carriers of the abnormal gene.[2] There are also different causes for acquired color vision defects, such as ocular or neurological disease, some metabolic disorders, drug toxicity and exposure to certain solvents.[3] Congenital CVD results from genetic mutations that affect the expression of the full complement of normal cone photoreceptors. They’re divided into three categories based on their intensity (anomalous trichromacy, dichromacy, and monochromacy). CVD places the sufferer at a distinct disadvantage when performing certain visual tasks—in particular those tasks in which a colored target is embedded in a variegated background of a different color. CVD affects many areas of life, and its adverse impact is experienced at all stages, i.e., from childhood to adolescence and adulthood.[45] Population is one of the biggest problems in India and the reason for so many compromises starting from lack of resources at every level. Healthcare is just one example. When providing even simple vision assessment in school children becomes a big task few tests like color vision examination is rarely being performed. Population diagnosis is usually late at the time of medical examination at the time of higher education or specific job. They are rarely diagnosed early in life. Late diagnosis leads to rejection for a particular job most of the time which has a psychological impact on individuals. In India where an education system doesn’t give a student to choose multiple streams, it turns out, several professional choices can be negatively impacted by a color blindness diagnosis. CVD is a hidden disability because, though present from birth, its role comes to play only when children begin to attend regular schools to learn some tasks.[6] From here onwards process of considerable difficulties in learning starts. Children with CVD are frequently marked as lethargic students, which could mentally affect them, or could evoke negative responses from instructors and guardian. This can lead to not only problems in learning but also in playing and in their social bonding. Various studies have been carried out all over the world to see the prevalence of CVD among school children.[789] Xie JZ, et al.[10] suggested that successful CVD testing can be done starting at age four. Cole stressed that school children should know if they have CVD so they can be helped more quickly to find adaptive strategies and be able to take it into account when planning their career.[11] Largest study on CVD in children is conducted to see the burden of this disability in India.[12] Authors have used Dalton’s psuedoisochromatic plates for color vision screening. It is based on Ishihara color vision chart principle. The Dalton screener consists of 6 sets with 4 plates in each that includes one demo plate and three screening plates. Those, who failed to read three or more plates in two or more random sets of the Dalton’s pseudoisochromatic plate were considered to have CVD after confirming with Ishihara’s PIP color vision testing (38 plate edition). The result shows CVD among boys was found to be 2.76%. Children from urban region (3.17%) were more likely to be color vision deficient than children from rural region (1.79%). These results are similar to the other parts of the country and few other countries from Asia. Screening of CVD is relatively easy does not require any formal training and can be performed by any assigned staff. Various plate tests are available, such as Ishihara, Tokyo, HRR plate test, which are highly sensitive and specific to detect CVD. Because of rapidly evolving technologies with more and more use of color coded tasks in each sector including education sector and specific job requiring color differentiation, the efforts should be made at a fundamental level in screening of color vision defects during comprehensive school eye health programs. Since CVD is congenital and there is no permanent cure for it. However, advice at an early age could help to find adaptive strategies, which enable them to avoid disappointments in the choice of their future career. Parental education, awareness, genetic counseling strategies in the regions with high CVD incidence could help a lot in minimizing the occurrence of the disorder among their offspring.

This paper describes a novel test of colour vision using a standard personal computer, which is simple and reliable to perform. Twenty healthy individuals with normal colour vision and 10 healthy individuals with a red/green colour defect were tested binocularly at 13 selected points in the CIE (Commission International d'Eclairage, 1931) chromaticity triangle, representing the gamut of a computer monitor, where the x, y coordinates of the primary colour phosphors were known. The mean results from individuals with normal colour vision were compared to those with defective colour vision. Of the 13 points tested, five demonstrated consistently high sensitivity in detecting colour defects. The test may provide a convenient method for classifying colour vision abnormalities.

Aim: To assess the changes in color vision in diabetic patients in different stages of diabetic retinopathy compared to healthy individuals. MATERIALS AND METHODS: This cross-sectional comparative study included sixty-eight eyes of 40 diabetic patients, divided into four subgroups (10 patients / group) at different stages of diabetic retinopathy (Eighteen of them had maculopathy) as well as 20 eyes of 10 healthy individuals as controls. Diabetic retinopathy and maculopathy were assessed clinically by direct and indirect fundus examination along with fluorescein fundus angiography, optical coherence tomography. Color vision was assessed quantitatively by Ishihara pseudo iso-chromatic plates test and qualitatively by Farnsworth D-15 test. Results: Only two control eyes (10%) failed the Ishihara pseudo iso-chromatic plates test, compared to 19 diabetic eyes (27.9%), 14 eyes (20.58%) were suspects. Also just two control eyes (10%) failed the Farnsworth d-15 test while 34 (50%) diabetic eyes failed the test showing; with Tritanopia was the most encountered color vision defect. We find that color vision defects also increases with increasing disease duration, severity of diabetic retinopathy, increased macular thickness and presence of maculopathy, while type of diabetes shows no significant effect. Conclusion: Diabetes mellitus has a clear negative effect upon the color vision in both qualitative and quantitative manner leading to loss of color vision perception with a varying degree in relation to the type of diabetes, degree of retinopathy, the duration of illness, presence of maculopathy and the increased macular thickness when compared to normal healthy individuals.

IN an earlier report on the Ishihara test for color blindness 1 we presented a brief history of the test from the original edition, issued in 1917, to the last Japanese edition of which we have a record in this country, the ninth edition, issued in 1940. Mention was also made of the British reprint of the ninth edition, issued in London in 1943. That report is the first of a series designed to evaluate in turn various color tests as means of analyzing and detecting defective color vision. The data reported were collected during the course of a study of some 106 persons having defective color vision of varying types and amounts, including 74 who had definite defects in color vision and 32 who had low, but normal, color vision. To study these persons a comprehensive battery of color tests was used ; some of these are well known in