Effect of optical defocus on colour perception

Color vision research is not new for the Federal Aviation Administration (FAA); the Civil Aerospace Medical Institute has been conducting color vision research and publishing the results since 1967 ( 3 ). The FAA originally initiated color vision research because of the emerging use of color coding in the airport environment and the FAA has continued a line of color vision research because of the increasing use of color coding resulting from changing technology inside the cockpit, on air traffic control displays, and in the airport environment. Color can be used to convey meaning without supplemental signage such as the ubiquitous traffic signal that alerts drivers to proceed with caution via a yellow flashing light or to stop via a red flashing light. However, that meaning is only conveyed if the driver can distinguish between the yellow and the red colors. Approximately 8 to 10% of the male population ( 5 ) has a congenital color vision deficiency and, depending upon the type and severity of that deficiency, that task of interpreting the meaning of color coding may be difficult or impossible. Consequently, the FAA has long maintained a color vision standard for aero-medical screening to ensure that pilots and air traffic controllers can perform safety-related tasks without adverse consequences. Throughout the past few years, the FAA has explored a variety of color vision tests, searching for a valid screening test that has high sensitivity and specificity, meaning the ability to detect the presence or absence of the deficiency, respectively. Basically, color vision tests can be categorized as diagnostic, screening, or occupational tests. Diagnostic tests are designed to specifically diagnose the type and degree of deficiency, the screening tests focus on differentiating between normal or deficient color vision, and the occupational tests seek to separate those capable versus incapable of certain tasks such as identifying colors of wires or lights (e.g., the Farnsworth Lantern test that was developed to assess the ability of potential Navy signalmen for identifying red, green, and white lights). A few tests have been developed for the purpose of precisely diagnosing and classifying color vision; however, when color vision test scores are compared to performance on occupational tasks such as identifying or discriminating colors used in signal lights, precision approach path indicator (PAPI) lights, colored navigation lights, color coded map reading tasks, color coded air traffic control displays, and cockpit displays, a specific cut-point on those selection tests has not been found that can fully separate those who can from those who cannot accurately perform the color-coded pilot or air traffic control tasks. Some tests, including new computerized instruments, have been designed to differentiate defects involving the long wavelength sensitive cones (protan-type), middle wavelength sensitive cones (deutan-type), and short wavelength sensitive cones (tritan-type). Congenital protan and deutan deficiencies are, collectively, extremely common, affecting 1 in 12 men and 1 in 230 women; however, recent evidence indicates that tritan defects are virtually never present at birth (e.g., congenital) and the inherited forms involve S cone photoreceptor degeneration that develops later in life with the exact onset depending upon the specific mutation ( 1, 4 ). Thus, the exact frequency of inherited tritan defects is uncertain; however, it is probably less than 1 in 500. In part, because the underlying pathophysiology has not been well understood, few tests have been available that are capable of detecting tritan deficiencies. In the past, those tests included the single Farnsworth F2 pseudoisochromatic plate (PIP), the Moreland anomaloscope, the Hardy, Rand, Rittler PIP test, and, most recently, the Oculus anomaloscope. Consequently, the occupational color vision tests used by most agencies only screen for the most common (protan and deutan) types of defects. The newly developed computerized color vision tests, including the Colour Assessment and Diagnostic Test, the Cambridge Colour Test, the Cone Contrast Test, and the Computerized Color Vision Test, are all designed to detect tritan defects. However, tritan weaknesses have been noted in several of the FAA ‘ s recent studies in much higher than the traditionally expected numbers and diagnostic agreement is low among those tests when tritan deficiencies are involved. In the past, the FAA and other regulatory organizations have not, or have rarely, required tritan color vision screening in their occupational screening because of the following three factors: the rarity of the congenital defect, the unknown number of individuals affected by acquired deficiencies, and the lack of effective, reliable, valid, and affordable equipment with which to diagnose the deficiency.

We have studied about some effects on the normal color vision under various environmental conditions, and relationships between the abnormal color vision and road signals.1) Visual acuity standard and color visionThree classifications of visual acuity are distinguished in the license of car driving in Japan. These are as follows:(1) 1st. group ordinary license)visual acuity-1) above 0.7 with both eyes and above 0.3 with each eye.2) below 0.3 with one eye, the other eye required to be above O. 7, and visual field more than 150°2) 2 nd. group (professional license)visual acuity...above 0.8 with both eyes and above 0.5 with each eyeHere, these steps are named 0.8 for (2), 0.7 for (1)-1 and 0.3 for (1)-2, to the normol vision 1.2 provisionaly.The visual acuity was measured by the color contrast test types, Landolt's ring, which were combinations of six colors using traffic signs. They were illuminated by fluorescent lamp, mercury lamp and sodium lamp. The relative legibility was compared with normal vision 1.2. On an average the rate was 0.8, 70%, 0.7, 60% and 0.3, 55% of the normal viewing distance. Decreasing rates were always almost constant for different color combinations and different light sources. Between the signs of white and color combinations, white on color sign was better recognized than color on white. Under the mercury lamp, red on blue was hard to see.On the highway experiment, the legibility of same color combination signs varied depending on the conditions of environs and the pattern of signs.2) DazzlingQuantitative static perimetry was used to measure the changes of visual threshold by dazzling. At fi rst, the threshold was obtained at eath 5 degrees point from center to 30 degrees tempolo-horizontal axis, then one dazzling light was put on the side of fixation point. The changing ratio of the threshold with or wothout dazzling, at 5 degrees fom fixation point, was about 1/30 and from 15 degrees to 30 degrees it was about 1/20.After dazzling to whole retina, the retardation time of perception was obtained for nine color test objects from 401 nm to 658 nm. “The time was not the same for each color, after 3, 000 asb, 5” dazzling. At the fixation point, the maximum retarding was found at 401nm (violet), 502nm (bluegreen) and 603nm (red), At 25 degrees periphery from center, the same result was obtained, but at 502nm, the delay was more marked than that of the center.3) Abnormal color visionAmong 47 drivers of dyschromatopsy, we found considerable numbers with strong daltonism. The classification by anomoloscope was 12 protan, 5 protanope, 21 deutan, 8 deutetanope and 1 protan or deutan. These dyschromats have not experienced any traffic accident caused by an error of the signal colors.A color name call test, using a frame by with 145 spots of signal colors on one plate, was done with the dyschromats. The rate of errors was as follows: colorblindness 62.0%, colorweakness 32.2%. It is evident that there is some difference in color perception of dyschromatopsy between the experimental results and discrimination of signals on the traffic.These results suggest that the red signal of the road traffic should be made larger and brighter than the other colors.

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.

Purpose:To investigate the quality of life (QoL) in a sample of color vision deficit (CVD) patients in India and how color vision deficiency affects them psychologically, economically, and in productivity related to their work and occupation.Methods:A descriptive and case–control study design using a questionnaire was conducted on N = 120 participants, of whom 60 were patients of CVD (52 male and eight female) who visited two eye facilities in Hyderabad between 2020 and 2021 and 60 were age-matched normal color vision participants who served as controls. We validated English–Telugu adapted version of CVD-QoL, developed by Barry et al. in 2017 (CB-QoL). The CVD-QoL consists of 27 Likert-scale items with factors (lifestyle, emotions, and work). Color vision was assessed using the Ishihara and Cambridge Mollen color vision tests. A six-point Likert scale was used, with lower scores indicating poor QoL (from 1 = severe issue to 6 = no problem).Results:The CVD-QoL questionnaire’s reliability and internal consistency were measured, including Cronbach’s α (α =0.70–0.90). There was no significance between the group in age (t = −1.2, P = 0.67) whereas the Ishihara colour vision test, scores showed a significant difference (t = 4.50, P < 0.001). The QoL scores showed a significant difference towards lifestyle, emotions and work (P = 0.001). The CVD group had a poorer QoL score than the normal color vision group odds ratio [OR] =0.31, 95% confidence interval [CI], (P = 0.002, CI = 0.14–0.65, Z = 3.0) . In this analysis, a low CI indicated that the OR was more precise.Conclusion:Color vision deficiency affects Indians’ QoL, according to this study. The mean scores of lifestyle, emotions, and work were lower than the UK sample.Since CVD is underreported and possibly affects developing countries more, advocacy for a new health care plan on CVD is essential. Increasing public understanding and awareness could also help diagnosing the CVD population.

Optic neuritis is an inflammatory condition affecting the optic nerve. It presents with sudden diminution of vision, also affecting colour vision, contrast sensitivity and stereoacuity. Steroids are given in optic neuritis to reduce inflammation of optic nerve. The aim of this study was to compare the visual functions in patients with optic neuritis before and after treatment with steroid therapy. This prospective study was conducted from November 2021 to October 2022 in the Department of Ophthalmology of a tertiary-level hospital. Thirty-seven eyes affected by optic neuritis of were included in the study. All the patients were given IV methylprednisolone for 3 consecutive days followed by oral prednisolone for 11 days in tapering doses. Visual functions such as visual acuity, colour vision, contrast sensitivity and stereoacuity at presentation and after treatment were compared. Among 37 eyes, 24 (64.86%) had best corrected visual acuity <1/60-perception of light at presentation, improving after six weeks with 21 (56.76%) achieving visual acuity 6/6-6/18. At presentation, only 1 (2.71%) had normal colour vision while at six weeks, 9 (24.32%) had normal colour vision. Contrast sensitivity could not be assessed in 29 (78.37%) cases at presentation due to poor vision, which reduced to 12 (32.43%) at six weeks. None had good stereoacuity at presentation; however, 6 (16.22%) had good stereoacuity after six weeks. The study showed that steroid therapy improved visual functions in patients with optic neuritis.

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

Sickle cell disease (SCD) is a prevalent genetic disease worldwide and particularly in Nigeria. Retinopathy is a known complication of SCD, underscoring the need to assess visual parameters in children. This study aimed to evaluate the visual acuity (VA), color vision (CV), packed cell volume (PCV), and erythrocyte sedimentation rate (ESR) of Sickle cell anemic (SCA) patients attending the Sickle cell counseling unit of Murtala Muhammad Specialist Hospital (MMSH) in Kano. It was a descriptive cross-sectional study consisting of 60 participants, including 30 SCA patients and 30 healthy controls without systemic or ocular diseases, aged between 8 and 14 years. Visual acuity, CV, PCV, and ESR were assessed using Snellen Chart, Ishihara chart, Hematocrit test, and Westergren Method respectively. Data were analyzed using SPSS version 22.0. Statistical significance was set at P &lt; 0.05. Both SCA patients and controls demonstrated limited knowledge about VA, CV, and ESR tests, and a significant percentage had never undergone these tests. SCA patients exhibited mild to moderate visual impairment (VI) in both eyes, while controls had no VI. Abnormally low PCV and ESR values were observed in all SCA patients, whereas controls had normal values. Gender differences were observed in ESR levels, with females showing higher levels. Significant differences were found between controls and SCA patients in terms of VA, ESR, and PCV values. There was a general lack of awareness regarding the importance of VA and CV tests in the community. Visual impairment and abnormal PCV and ESR values were exclusive to the SCA patients, indicating their association with the disease.

Background: Colour vision assessment correlates with damage of the visual pathway and might be informative of overall brain damage in multiple sclerosis (MS). Objective: The objective of this paper is to investigate the association between impaired colour vision and disease severity. Methods: We performed neurological and ophthalmic examinations, as well as magnetic resonance imaging (MRI) and optical coherence tomography (OCT) analyses, on 108 MS patients, both at baseline and after a follow-up of one year. Colour vision was evaluated by Hardy, Rand and Rittler plates. Dyschromatopsia was defined if colour vision was impaired in either eye, except for participants with optic neuritis (ON), for whom only the unaffected eye was considered. We used general linear models adjusted for sex, age, disease duration and MS treatment for comparing presence of dyschromatopsia and disease severity. Results: Impaired colour vision in non-ON eyes was detected in 21 out of 108 patients at baseline. At baseline, patients with dyschromatopsia had lower Multiple Sclerosis Functional Composite (MSFC) scores and Brief Repeatable Battery-Neuropsychology executive function scores than those participants with normal colour vision. In addition, these patients had thinner retinal nerve fiber layer (RNFL), and smaller macular volume, normalized brain volume and normalized gray matter volume (NGMV) at baseline. Moreover, participants with incident dyschromatopsia after one-year follow-up had a greater disability measured by the Expanded Disability Status Scale and MSFC-20 and a greater decrease in NGMV than participants with normal colour vision. Conclusions: Colour vision impairment is associated with greater MS severity.

Normal human color vision is usually thought to be based on only three spectrally different cone types. However, two facts suggest the possibility that some color-normal males could have more than three cone pigment types: (1) Most people with normal color vision have more than two photopigment genes on each X-chromosome and (2) there appear to be genetically specified variations in spectral positions of the normal middle-wavelength-sensitive (MWS) and long-wavelength-sensitive (LWS) pigments. For example, a male might have one gene encoding an LWS pigment and two genes encoding slightly different MWS pigments. If all three different X-encoded genes were expressed in different cones, then this person would have four spectrally different cone types. How firm is the assumption that more than two of the X-encoded pigment genes can be expressed? Both analysis of the statistics of photopigment gene number among different color vision phenotypes and analysis of the arrangement of pigment genes on the X-chromosome yield insight into this aspect of photopigment gene expression. These analyses suggest that individuals with multiple pigment genes on the X-chromosome may express more than two of those genes.

Color vision tests use estimative of threshold color discrimination or number of correct responses to evaluate performance in chromatic discrimination tasks. Both approaches have advantages and disadvantages. In the present investigation, we compared the number of errors during color discrimination task in normal trichromats and participants with color vision deficiency (CVD) using pseudoisochromatic stimuli at fixed saturation levels. We recruited 28 normal trichromats and eight participants with CVD. Cambridge Color Test was used to categorize their color vision phenotype, and those with a phenotype suggestive of color vision deficiency had their L- and M-opsin genes genotyped. Pseudoisochromatic stimuli were shown with target chromaticity in 20 vectors radiating from the background chromaticity and saturation of 0.06, 0.04, 0.03, 0.02, 0.01, and 0.005 u’v' units. Each stimulus condition appeared in four trials. The number of errors for each stimulus condition was considered an indicator of the participant's performance. At high chromatic saturation, there were fewer errors from both phenotypes. The errors of the normal trichromats had no systematic variation for high saturated stimuli, but below 0.02 u’v' units, there was a discrete prevalence of tritan errors. For participants with CVD, the errors happened mainly in red-green chromatic vectors. A three-way ANOVA showed that all factors (color vision phenotype, stimulus saturation, and chromatic vector) had statistically significant effects on the number of errors and that stimulus saturation was the most important main effect. ROC analysis indicated that the performance of the fixed saturation levels to identify CVD was better between 0.02 and 0.06 u’v’ units reaching 100%, while saturation of 0.01 and 0.005 u’v’ units decreased the accuracy of the screening of the test. We concluded that the color discrimination task using high saturated stimuli separated normal trichromats and participants with red-green color vision deficiencies with high performance, which can be considered a promising method for new color vision tests based in frequency of errors.

Aims: To investigate whether there is an association between congenital colour vision defects (CVD) and occupational choice and employment history, in order to inform the debate about the value of...

Clinical relevance Accurate colour vision assessment is important in clinical settings to minimise false-positive errors and enhance the reliability of diagnoses outcomes. Background Colour vision testing is valuable in assessing the visual system, particularly given the high proportion of individuals with poor vision. This study aimed to determine the minimum visual acuity level required to perform a colour-vision test without errors. Methods After fogging the right eyes of 52 healthy participants using plus lenses to 1.60 logMAR, vision was evaluated using Ishihara, Hardy – Rand – Rittler Standard Isochromatic, Waggoner Pseudo-isochromatic, City University, Waggoner Computerised, and Farnsworth D-15 tests. Participants then completed these tests at lower fogging degrees (in 0.1-logMAR intervals). The acuity at which 5% of the tested population was considered abnormal was determined. Results Significant differences were found in the average visual acuity required to perform colour vision tests without errors (p < 0.05). The Waggoner Computerized test required the highest average visual acuity among the tests utilised. The Farnsworth D-15 test yielded the highest logMAR values. No significant differences were observed between the Waggoner Pseudo-isochromatic test and Hardy – Rand – Rittler Standard Isochromatic, Ishihara, and Farnsworth D-15 tests (p > 0.05). Additionally, no significant differences were found between the Ishihara and Hardy – Rand – Rittler tests (p > 0.1) or between the Waggoner Computerized and City University tests (p = 0.11). Colour vision testing maintained an accuracy ≤ 1.0 logMAR with the Ishihara and Hardy – Rand – Rittler tests, 1.1 logMAR with the Waggoner Pseudo-isochromatic and Farnsworth D-15 tests, and 0.9 logMAR with the Waggoner Computerized and City University tests. Conclusions Insights are provided into the visual acuity thresholds required for accurate colour vision testing, which can serve as a basis for future research and provide a reference for clinical practice in this field.

Clinical Color Vision Testing and Correlation With Visual Function

The X-linked red- and green-pigment genes are arranged in a head-to-tail tandem array. The colour-vision defect of deuteranomaly (in 5% of males of European descent) is associated with a 5'-green-red-3' visual-pigment hybrid gene, which may also exist in males with normal colour vision. To explain why males with a normal red, a normal green and a green-red hybrid gene may have either normal or deutan colour vision, we hypothesized that only the first two genes are expressed and deuteranomaly results only if the green-red hybrid gene occupies the second position and is expressed preferentially over normal green-pigment genes occupying more distal positions. We used long-range PCR amplification and studied 10 deutan males (8 deuteranomalous and 2 deuteranopic) with 3 visual pigment genes (red, green and green-red hybrid) to investigate whether position of the hybrid gene in the array determined gene expression. The green-red hybrid gene was always at the second position (and the first position was always occupied by the red gene). Conversely, in two men with red, green and green-red hybrid genes and normal colour vision, the hybrid gene occupied the third position. When pigment gene mRNA expression was assessed in post-mortem retinae of three men with the red, green and green-red genotype, the green-red hybrid gene was expressed only when located in the second position. We conclude that the green-red hybrid gene will only cause deutan defects when it occupies the second position of the pigment gene array.

In living color