What do color vision defectives say about everyday tasks?

Chromatic vision and structural assessment in primary congenital glaucoma

Primary congenital glaucoma is a rare disease that occurs in early birth and can lead to low vision. Evaluating affected children is challenging and there is a lack of studies regarding color vision in pediatric glaucoma patients. This cross-sectional study included 21 eyes of 13 children with primary congenital glaucoma who were assessed using the Farnsworth D-15 test to evaluate color vision discrimination and by spectral domain optical coherence tomography to measure retinal fiber layer thickness. Age, visual acuity, cup-to-disc ratio and spherical equivalent data were also collected. Global and sectional circumpapillary and macular retinal fiber layer thicknesses were measured and compared based on color vision test performance. Four eyes (19%) failed the color vision test with diffuse dyschromatopsia patterns. Only age showed statistical significance in color vision test performance. Global and sectional circumpapillary and macular retinal fiber layer thicknesses were similar between the color test outcomes dyschromatopsia and normal. While the color vision test could play a role in assessing children with primary congenital glaucoma, further studies are needed to correlate it with damage to retinal fiber layer thickness.

Comparison of Two Printed Pseudoisochromatic Tests for Color Vision Assessment

SIGNIFICANCE

The Waggoner PIP24 is a pseudoisochromatic test with a pattern similar to the Ishihara test. This study determined that the W-PIP24 can be used clinically to yield screening results (or sensitivity and specificity) comparable with the Ishihara.

PURPOSE

This study aimed to determine whether the W-PIP24 is equivalent to the Ishihara 38 edition pseudoisochromatic test in detecting red-green color vision defects. Also, the performance of each plate of the W-PIP24 in detecting the color vision defects relative to the Ishihara test was determined.

METHODS

Sixty-three individuals with congenital red-green color vision defects and 57 with normal trichromacy were recruited. Participants were tested with both the Ishihara and W-PIP24. The first-order agreement coefficients were calculated for the Ishihara and W-PIP24. The results were also analyzed using specificity, sensitivity, efficiency, and predictive pass and fail values.

RESULTS

The agreement between the W-PIP24 and Ishihara test using the recommended criterion of using all plates was perfect. The sensitivity, specificity, predictive pass, and predictive fail were 1.00 (95% confidence interval, 0.94 to 1.00).

CONCLUSIONS

This study showed that the W-PIP24 using a failure criterion of three or more errors on screening plates 1 to 15 is equivalent to the Ishihara test while screening for red-green color vision deficiency using a failure criterion of three or more errors on screening plates 1 to 17 of the Ishihara 38 edition.

Optical Properties and Interference Effects of the Lens Mitochondrion

The lens mitochondrion of the tree shrew, located along the optical pathway between the lens and photoreceptors, has been investigated. The results suggest that the lens mitochondrion acts as a quasi-bandgap or imperfect photonic crystal. Interference effects cause a shift in the focus and introduce wavelength-dependent behavior similar to dispersion. Optical channels within the mitochondrion form a mild waveguide, preferentially propagating light within certain compartments. The lens mitochondrion also functions as an imperfect UV-shielding interference filter. Overall, this study provides insights into the dual role of the lens mitochondrion and the complex behavior of light within biological systems.

The Impact of Color Vision Deficiency on the Capability of Ophthalmologists to Diagnose Benign and Malignant Choroidal Tumors

BACKGROUND

Color vision deficiency (CVD) is an under-reported problem among medical personnel, and its impact is still not well characterized. We aim to assess the impact of CVD among ophthalmologists on the accuracy of diagnosing different benign and malignant choroidal lesions.

METHODS

This is a cross-sectional study conducted on ophthalmologists. We used a web-based survey to collect responses through professional ophthalmology society social media. The survey included a set of five images for normal fundus, choroidal nevus, circumscribed choroidal hemangioma, choroidal metastasis, and choroidal melanoma, wherein each image simulated the three main types of CVD: protanopia, deuteranopia, and tritanopia, in addition to a non-simulated image.

RESULTS

Forty-one participants were included, with a mean age of 40 (±9.2) years. They were 28 (68%) men and 13 (32%) women. Participants showed significantly low accuracy for definite diagnosis for circumscribed choroidal hemangioma, nevus, melanoma, and metastasis when the images simulated protanopia and deuteranopia, but not tritanopia. Nevertheless, participants maintained the capability to recognize the nature of the lesions for both simulated and non-simulated images if they were benign or malignant, thereby ensuring immediate referral for specialized care. The exception was with simulated choroidal nevi images, wherein participants incorrectly assigned simulated protanopia and deuteranopia nevi images to malignant lesions.

CONCLUSION

Protanopia and deuteranopia affected the accuracy of diagnosing several choroidal lesions; however, ophthalmologists with those two simulated CVDs were still able to discriminate between benign and malignant tumors.

Color vision restrictions for medical school admission: a discussion on regulations in ASEAN countries compared to countries across the world

Color vision deficiency impairs one's ability to perceive and discriminate colors. Color-deficient individuals may face discrimination in various occupations, particularly in medical school admissions. This discussion seeks to compare the existing color vision requirements for entry to medical school in Southeast Asian countries as compared to countries across the world. Following this, we explore the published evidence in this field, to provide recommendations for future guidelines that will maximize the occupational opportunities for color-deficient individuals.

Daltonization or colour enhancement: potential uses and limitations [Invited]

The main perceptual-cognitive limitations of CDOs (Colour Deficient Observers) are analysed, along with the uses and limitations of tools that either transform images so that CNOs (Colour Normal Observers) see them as CDOs (simulation) or transform images so that CDOs can use them as CNOs (daltonization). The four main uses of colour (comparative, denotative, connotative, and aesthetic) are analysed, along with their relation to, alternatively, the ability to discriminate colour stimuli or to categorize colours. These uses of colour are applied to analyse the possible effects of daltonization tools.

Diagnosis of colour vision deficits using eye movements

We set out to develop a simple objective test of functional colour vision based on eye movements made in response to moving patterns. We exploit the finding that while the motion of a colour-defined stimulus can be cancelled by adding a low-contrast luminance-defined stimulus moving in the opposite direction, the "equivalent luminance contrast" required for such cancellation is reduced when colour vision is abnormal. We used a consumer-grade infrared eye-tracker to measure eye movements made in response to coloured patterns drifting at different speeds. An automated analysis of these movements estimated individuals' red-green equiluminant point and their equivalent luminance contrast. We tested 34 participants: 23 colour vision normal controls, 9 deuteranomalous and 2 protanomalous individuals. We obtained reliable estimates of strength of directed eye movements (i.e. combined optokinetic and voluntary tracking) for stimuli moving at 16 deg/s and could use these data to classify participants' colour vision status with a sensitivity rate of 90.9% and a specificity rate of 91.3%. We conclude that an objective test of functional colour vision combining a motion-nulling technique with an automated analysis of eye movements can diagnose and assess the severity of protanopia and deuteranopia. The test places minimal demands on patients (who simply view a series of moving patterns for less than 90 s), requires modest operator expertise, and can be run on affordable hardware.

Prevalence and population genetic data of colour vision deficiency among students from selected tertiary institutions in Lagos State, Nigeria

Background

Colour vision deficiency (CVD), also referred to as colour blindness, is the failure or decreased ability to distinguish between certain colours under normal lighting conditions. It is an X-linked genetic disorder with varying degrees of prevalence in different populations. There is presently no report on the prevalence of CVD among students of the selected tertiary institution. Hence, the present study was aimed at determining the occurrence and genetics of CVD among students from designated tertiary institutions in Lagos state. A cross-sectional survey was employed in recruiting 1191 study subjects from three tertiary institutions in Lagos, Nigeria.

Results

The overall occurrence of CVD among the study participants was 2.85%. There were 24 (4.29%) males and 10 (1.58%) females affected. Among the colour vision deficient individuals, 18 (1.51%) and 16 (1.34%) were deuteranomalous and protanomalous, respectively. Also, the prevalence of CVD varies across ethnic groups of the studied subjects with the highest occurrences (3.57%) observed in the Yoruba ethnic subpopulation and the least (1.45%) among the Hausas.

Conclusions

More males than females were found to be colour vision deficient, and there were more deutans than protans. Early screening for CVD should be encouraged among school children to guide the choice of future profession and help mitigate work hazards resulting from being colour deficient.

Inverse-Designed Aid Lenses for Precise Correction of Color Vision Deficiency

Color vision deficiency (CVD) is a common ocular disorder affecting more than 300 million people on the earth. Although no clinical cure for the disorder currently exists, some specialized color filtering glasses/lenses based on dyes, metasurfaces, or nanocomposites have been employed for CVD management. However, as CVD patients usually diversify in their classification and severity, none of the current lenses provides a customized correction for various CVD patients, resulting in undesirable correction effects. Here, we present an inverse-designed approach for the precise correction of CVD. The wavelength shift of a patient's abnormal cone photoreceptors was measured to inversely design the best blocking wavelength and blocking rate of the lens. Then the customized aid lenses were fabricated using silica-coated gold nanoparticles with appropriate sizes and concentrations, verified by the simulated color vision and human tests. This study demonstrates the potential of the inverse-designed aid lenses in precise color filtering and customized CVD management.

Implications of inherited color vision deficiency on occupations: A neglected entity!

Purpose:

To highlight the plight of individuals with congenital color vision deficiency (CVD).

Methods:

This is a retrospective study in which 191 electronic medical records of individuals with the diagnosis of inherited CVD, who visited the eye institute, between January 2010 and January 2021 were included. The inclusion criteria included diagnosis based on the failure in pseudoisochromatic plates (Ishihara / Hardy, Rand and Rittler (HRR) and age range between 18 and 35 years. The patient’s medical history, age, gender, type of defect, and preference for colored contact lenses was noted. Medical records were excluded if the participant had any other ocular pathology apart from congenital CVD.

Results:

At least 30% (57/191) of the individuals explicitly requested for color vision examination for a job-related purpose. Amongst them, the most common jobs aspired were army (~25%; [14/57]) followed by police (21%; [12/57]). There was only 2.6% (5/191) of individuals in which the type of CVD (protan/deutan) was classified. Only 5.2% of them (10/191) sought an X-Chrome contact lens trial.

Conclusion:

This study reported the occupational setbacks experienced by individuals with CVD. This study highlights the need to identify CVD at a younger age, thereby avoiding occupational-related setbacks later in life.

A mathematical approach to assess the ability of light filters to improve color discriminability of color vision deficient persons

Color vision deficiency (CVD) is a frequent condition that alters color perception to such an extent that many people encounter serious difficulties on their everyday lives. In this work, we present a strategy to analyze the effectiveness of light filters aimed to improve color discriminability of persons with CVD. The calculations are based on a simple model of color discrimination which has been successfully applied to several animal species. We first tested the calculations on three well-known commercial lenses designed for persons with CVD. In agreement with results of clinical studies, the calculations show that the highly colored lenses (VINO® and X-Chrom®) enhance chromaticity contrasts between problematic colors, whereas the more neutral Enchroma® do not provide any benefit. Also, we predict that two light filters proposed in recent works for novel lenses would not improve the performance of the commercial ones. Since the mathematical approach presented in this work enables predictive filter assessment, it opens the door to future research on the design of more effective lenses to improve color discriminability of persons with CVD. The calculations allow for large-scale screening of numerous light filters and different colored stimuli, CVD conditions, light sources, etc.

ColourSpot, a novel gamified tablet-based test for accurate diagnosis of color vision deficiency in young children

There is a need for a straightforward, accessible and accurate pediatric test for color vision deficiency (CVD). We present and evaluate ColourSpot, a self-administered, gamified and color calibrated tablet-based app, which diagnoses CVD from age 4. Children tap colored targets with saturations that are altered adaptively along the three dichromatic confusion lines. Two cohorts (Total, N = 772; Discovery, N = 236; Validation, N = 536) of 4–7-year-old boys were screened using the Ishihara test for Unlettered Persons and the Neitz Test of Color Vision. ColourSpot was evaluated by testing any child who made an error on the Ishihara Unlettered test alongside a randomly selected control group who made no errors. Psychometric functions were fit to the data and “threshold ratios” were calculated as the ratio of tritan to protan or deutan thresholds. Based on the threshold ratios derived using an optimal fitting procedure that best categorized children in the discovery cohort, ColourSpot showed a sensitivity of 1.00 and a specificity of 0.97 for classifying CVD against the Ishihara Unlettered in the independent validation cohort. ColourSpot was also able to categorize individuals with ambiguous results on the Ishihara Unlettered. Compared to the Ishihara Unlettered, the Neitz Test generated an unacceptably high level of false positives. ColourSpot is an accurate test for CVD, which could be used by anyone to diagnose CVD in children from the start of their education. ColourSpot could also have a wider impact: its interface could be adapted for measuring other aspects of children’s visual performance.

Prevalence of color vision deficiency among school-going boys in South India

Purpose:

Impact of color vision deficiency (CVD) on activities at school and productivity at work and consequential psychosocial difficulties has been reported. Although early detection and awareness help in overcoming these difficulties, screening for CVD is not a part of the school eye-screening initiatives in many countries. This study aimed at reporting the prevalence of CVD among school-going boys in Kanchipuram district, South India.

Methods:

The study was carried out as part of a school eye-screening program (SES) conducted in Kanchipuram district, Tamil Nadu, India for children between 6 and 17 years. The SES followed a three-phased protocol, which also included screening for CVD for all the boys between 11 and 17 years. The boys underwent CVD screening with Dalton's pseudo isochromatic plates (PIPs) followed by confirmation with Ishihara's PIP. The data were analyzed and the proportion of CVD in boys among different class grades, type of schools, location of schools, blocks of the district, and other clinical characteristics are presented.

Results:

Totally 250,052 children were screened in 1047 schools of which 74986 (60.61%) were boys between 11 and 17 years (mean age: 13.75 ± 1.91). The overall prevalence of CVD was found to be 2.76% (n = 2073; 95% confidence interval [CI]: 2.65–2.88). CVD was associated with urban locations (3.17% odds ratio [OR]: 1.90 95%CI: 1.69–2.13 P < 0.05) and public schooling (2.87%) (OR: 1.29 95%CI: 1.17–1.43 P < 0.05). Boys with CVD were less likely to have vision impairment (P = 0.002) and myopia (P < 0.001) as compared with boys with normal color vision. There was no significant difference in the proportion of other ocular conditions between children with and without CVD (P > 0.05).

Conclusion:

The study shows a significant proportion of CVD among boys in Kanchipuram district, India and its association with various demographic and clinical characteristics. Identification of CVD and counseling the stakeholders earlier through school children screening is crucial.

The description of physical signs of illness in photographs by physicians with abnormal colour vision

BACKGROUND

Physicians with congenital colour vision deficiency (CCVD) have reported difficulties recognising certain physical signs of illness, for example, jaundice, red rashes and pallor, and interpreting coloured charts, diagrams and slide projections. However, there has been little study of the effects of CCVD on the performance of medical practitioners.

AIM

The aim of this study was to look for evidence of the effect of CCVD on the ability of physicians to recognise and describe physical signs of illness that have colour as either the main or an important feature.

METHOD

Twenty-three general practitioners with CCVD were shown 11 colour photographs depicting colour signs of illness and were asked to describe the signs they saw and rate their confidence in making their descriptions. Their responses were compared to those of 23 age-matched general practitioners with normal colour vision.

RESULT

General practitioners with CCVD compared to those with normal colour vision had less ability and confidence in detecting physical signs in the photographs and naming the colours.

CONCLUSIONS

The results of this study support other evidence that physicians with CCVD have difficulties detecting some colour signs of illness and naming the colours. Because of the use of photographs the extent of the problem in clinical practice is unknown but medical practitioners with CCVD should be aware of the possibility of failing to detect or correctly assess physical signs that are characterised by colour.

The handicap of abnormal colour vision

All people with abnormal colour vision, except for a few mildly affected deuteranomals, report that they experience problems with colour in everyday life and at work. Contemporary society presents them with increasing problems because colour is now so widely used in printed materials and in computer displays. Equal opportunity law gives them protection against unfair discrimination in employment, so a decision to exclude a person from employment on the grounds of abnormal colour vision must now be well supported by good evidence and sound argument. This paper reviews the investigations that have contributed to understanding the nature and consequences of the problems they have. All those with abnormal colour vision are at a disadvantage with comparative colour tasks that involve precise matching of colours or discrimination of fine colour differences either because of their loss of colour discrimination or anomalous perception of metamers. The majority have problems when colour is used to code information, in man-made colour codes and in naturally occurring colour codes that signal ripeness of fruit, freshness of meat or illness. They can be denied the benefit of colour to mark out objects and organise complex visual displays. They may be unreliable when a colour name is used as an identifier. They are slower and less successful in search when colour is an attribute of the target object or is used to organise the visual display. Because those with the more severe forms of abnormal colour vision perceive a very limited gamut of colours, they are at a disadvantage in the pursuit and appreciation of those forms of art that use colour.

Search for coloured objects in natural surroundings by people with abnormal colour vision

BACKGROUND

People with abnormal colour vision often report difficulty seeing coloured berries and flowers in foliage, which suggests they will have a diminished capacity for visual search when target objects are marked out by colour. There is very little experimental evidence of the effect of abnormal colour vision on visual search and none relating to search for objects in natural foliage.

METHOD

We showed 79 subjects with abnormal colour vision (seven protanopes, 10 deuteranopes, 16 protanomals and 46 deuteranomals) and 20 subjects with normal colour vision photographs of natural scenes and asked them to locate clumps of red berries, to trace the length of a red string on grass and to name the season depicted in a photograph taken in the Autumn and the same scene photographed in the Summer. Colour vision was assessed using the Ishihara, the Medmont C100, the Farnsworth D15, the Richmond HRR and the Nagel anomaloscope.

RESULTS

All the subjects with abnormal colour vision located fewer clumps of red berries than those with normal colour vision. The subjects who failed the Farnsworth D15 performed significantly worse than those who passed but the distribution of scores in the two groups overlaps. The majority of subjects with abnormal colour vision could not trace the full length of the string: only 38 per cent of anomalous trichromats who passed the Farnsworth D15 test and three per cent of those who failed it were able to trace the full length of the string. Fifty-five per cent of those classed as having a mild deficiency by the HRR test could trace the whole string. Most dichromats were unable to identify the Autumn season and those who did may have been assisted by guessing. Most (94 per cent) of those who passed the Farnsworth D15 test and all those classified as having a 'mild' deficiency by the HRR test could identify the season.

CONCLUSIONS

All people with abnormal colour vision, even those with a very mild deficiency, have some degree of impairment of their ability to see coloured objects in natural surroundings. A pass at the Farnsworth D15 test or a 'mild' classification with the Richmond HRR test identifies those likely to have the least problems with visual search and identification tasks. The results have practical implications for the selection of personnel in occupations that involve visual search in natural terrain.

Characterizing the Effects of Enchroma Glasses on Color Discrimination

SIGNIFICANCE

Enchroma glasses were designed to improve color vision among color-blind individuals. The putative aid of such optic filters in alleviating color blindness remains to be demonstrated. Our study shows that the beneficial impacts on color discrimination are quite small in comparison to the undesirable effects.

PURPOSE

Congenital color blindness is a common genetic anomaly, and there is still no effective aid for affected people. Enchroma glasses are selective filters designed to enhance color discrimination among red-green color-blind individuals. However, there is a lack of data supporting their efficiency. The present study aimed to characterize the effect of Enchroma filters on color discrimination.

METHODS

Colorimetric coordinates of figures from a pseudoisochromatic (American Optical Hardy-Rand-Rittler [AO H-R-R]) test were measured. Nine color-blind and five control adult participants performed the AO H-R-R test and a color-naming task using monochromatic stimuli. All data were collected with and without Enchroma filters.

RESULTS

Colorimetric coordinates of AO H-R-R figures were shifted out of their respective pseudoisochromatic line. The AO H-R-R error scores of participants with color blindness were not clearly improved by the filters except for the protanopic subgroup. However, the filters promoted a change in the classification of the defect, specifically by increasing protan errors in deutan participants. In the color-naming task, Enchroma filters impaired perception in all participants, specifically for cyan stimuli.

CONCLUSIONS

Enchroma filters may affect the nature of a color vision deficiency without necessarily alleviating its severity. Although the performance of protan participants increased in the pseudoisochromatic task with Enchroma filters, this was the only improvement observed across tasks and subgroups. In summary, this study does not support the efficacy of Enchroma filters in correcting color discrimination in color-blind individuals.

Evidence-Based Clinical Practice Guideline: Comprehensive Pediatric Eye and Vision Examination

Republished with written permission granted from the American Optometric Association, October 2, 2020.

On Random and Systematic Variation in the Prevalence of Defective Color Vision

Defective color vision comes in various forms and its frequency varies from population to population. This article is concerned with only the sex-linked form of essential hereditary color blindness. A model of a 'small' population is constructed to explore the dynamics of occurrence of color blindness. Different mutation rates are introduced for eggs and sperm. Birth and death rates of affected individuals are assumed to be the same as those in the unaffected. Simulation demonstrates that large changes in frequency occur randomly from the combined effects of mutation, transmission of genes from generation to generation and births and deaths. A reference is made to the hypothesis that observed differences in rates are due to selection in the transition from hunter-gatherer to farmer.

Prevalence of colour vision deficiency in the Republic of Ireland schoolchildren and associated socio-demographic factors

CLINICAL RELEVANCE

Early screening is essential to counsel schoolchildren with congenital colour vision deficiency (CVD) in determining their future career path and to advise teachers of the impact of CVD on classroom difficulties.

BACKGROUND

Congenital CVD is an X-linked genetic abnormality relatively commonplace in humans. This study aimed to determine the prevalence of congenital CVD in the Republic of Ireland schoolchildren and associated socio-demographic factors.

METHODS

A total of 1,626 schoolchildren (882 boys and 744 girls), in two age groups (728 aged 6-7-years and 898 aged 12-13-years) were examined from randomly selected schools. Colour vision testing was carried out using the Richmond Hardy-Rand-Rittler pseudoisochromatic test for colour vision (fourth edition); diagnostic plates were used to determine CVD type and extent if participants failed to identify symbols on the screening plates.

RESULTS

CVD was detected in 73 boys (8.3 per cent, 95% confidence interval (CI) 6.6-10.3) and in 13 girls (1.8 per cent, 95% CI 1.0-3.1, p < 0.001). As expected, deutan (boys 4.8 per cent, girls 0.8 per cent) was the most common type of CVD, followed by protan (boys 1.7 per cent, girls 0.1 per cent), unclassified red/green CVD (boys 1.2 per cent, girls 0.8 per cent) and then tritan (boys 0.5 per cent). One case of achromatopsia was detected based on failure on all diagnostic plates. Traveller participants (boys 21.0 per cent, girls 8.6 per cent) had a higher CVD prevalence than their White non-Traveller (boys 7.2 per cent, girls 1.0 per cent) and non-White (boys 5.4 per cent, girls 1.1 per cent) counterparts (odds ratio 3.00, 95% CI 1.1-8.1, p = 0.006). In boys, CVD was also associated with twin birth (odds ratio 2.7, 95% CI 1.1-6.7, p = 0.03) and low birthweight (p = 0.04).

CONCLUSION

This investigation of CVD in the Republic of Ireland schoolchildren should alert clinicians to the association between CVD and Traveller ethnicity, twin birth and lower birthweight. The prevalence of CVD found was similar to previous studies involving predominantly White populations and higher among Traveller participants; hence, counselling regarding inherited anomalies in the Traveller community is recommended. Early screening is essential to counsel schoolchildren with CVD in determining their future career path and to advise teachers of the impact of CVD on classroom difficulties.

Dalton's pseudo-isochromatic plates and congenital colour vision deficiency

BACKGROUND

Diagnosing colour vision deficiency is vital, owing to its impact on the choice of career and activities of daily living. Conventional screening methods require frequent replacement due to soiling of the materials, and hence are expensive and not feasible for large-scale community screening. This study aims to construct and validate a new screening tool, Dalton's pseudo-isochromatic plates (PIP), addressing the disadvantages of the conventional methods.

METHODS

The two phases of the study included the construction and validation of the Dalton's PIP. Construction involved utilising specific wavelengths based on spectral tuning, selection of numerals as targets for the chart and identification of a material with durability and resistance to wear and tear. Validation of the chart was done against the 38-plate edition of Ishihara's PIP by two masked examiners for 1,019 school children aged between 11-17 years (mean ± SD: 14 ± 2 years) as part of a school eye-health program.

RESULTS

The sensitivity and the specificity of the Dalton's PIP was found to be 94.12 per cent (95% CI 71.31-99.85) and 99.60 per cent (95% CI 98.98-99.89) respectively and the positive and negative predictive values were 80 per cent and 99.90 per cent respectively. Dalton's PIP when used with a failure criterion of less than three plates correct in two screening sets had the maximum sensitivity and specificity and the area under the curve was 0.96 (95% CI 0.90-0.99, p < 0.05).

CONCLUSION

The newly constructed Dalton's PIP is found to be a valid screening tool to detect congenital colour vision deficiency and is comparable to the Ishihara PIP. This screening tool with its shorter screening time, cost and longer durability would effectively serve in large-scale vision screening programs.

The effect of the ChromaGen contact lens system on visual performance

BACKGROUND

To evaluate the effects of the ChromaGen contact lens (CCL) on best-corrected visual acuity, contrast sensitivity and pseudoisochromatic test plate performance in patients with congenital colour vision deficiency (CVD).

METHODS

CCLs were inserted into 50 eyes of 25 patients with congenital red-green CVD. The patients were tested with the Ishihara and Hardy-Rand-Rittler test plates before and after the insertion of Magenta 2, Magenta 3, and Violet 3 CCLs. The patients' mean numbers of recognised symbols were calculated and the most appropriate CCL was determined for each eye. The best-corrected visual acuity for both far and near vision and contrast sensitivity were evaluated before and after the insertion of the appropriate CCLs, and the results were compared.

RESULTS

The mean age of the patients was 26.56 ± 10.30 years. While all CCLs increased the mean numbers of recognised symbols on the Ishihara (p < 0.001 for all), Magenta 3 was observed to be the most useful CCL. On the other hand, while all CCLs increased the mean numbers of recognised symbols on Hardy-Rand-Rittler (p < 0.001 for all), Magenta 2 and Magenta 3 were detected as the most useful CCLs. After insertion of the most appropriate CCL for each eye, the mean best-corrected visual acuity for both far and near vision were decreased (p < 0.001 for both). Statistically significant alterations were also detected at some spatial frequencies of contrast sensitivity measurements.

CONCLUSION

CCLs decrease the far and near best-corrected visual acuity, and static and dynamic contrast sensitivity at some spatial frequencies, and invalidate the pass criteria of pseudoisochromatic test plates by increasing the number of recognised symbols.

Prevalence of Color Vision Deficiency in an Adult Population in South Korea

SIGNIFICANCE

Large differences in failure rates for color vision screening have been reported among different regional groups. However, color vision deficiency prevalence in Korea has only been investigated within a small area of the country.

PURPOSE

This study examines the prevalence of failing a color vision screening and its sex-related differences using a sample that is representative of the whole Korean population.

METHODS

This population-based cross-sectional study evaluated 2686 subjects (age, 19 to 49 years) who participated in the sixth Korea National Health and Nutrition Examination Survey (2013). Color vision deficiency was assessed using the Hardy-Rand-Rittler (HRR) test by an ophthalmologist. According to standard criteria for the HRR, it classified each subject as color normal, protan, deutan, tritan, or unclassified color vision loss. All participants had comprehensive medical evaluations and ocular history taken.

RESULTS

The weighted overall prevalence of color vision deficiency in the Korean population was 3.9% (95% confidence interval, 3.0 to 5.4%). The prevalence of color vision deficiency was higher in male participants (6.5%) than in female participants (1.1%). Among all participants, deutan deficiency (2.5%) had a higher prevalence than did protan deficiency (0.4%). For male participants who failed the HRR screening, deutan-type deficiency was detected most often (64.2%), whereas an unclassified color vision deficiency type was the most common (52.9%) among female participants who failed the HRR screening. As expected, male participants were more likely to fail the HRR screening compared with female participants (prevalence ratio, 6.08; 95% confidence interval, 3.61 to 10.26).

CONCLUSIONS

This large population-based study of color vision deficiency among Koreans gives the most accurate estimate of failing a color vision screening test to date and provides useful information for planning adaptive strategies.

Impact of congenital color vision defect on color-related tasks among schoolchildren in Durban, South Africa

BACKGROUND

People with congenital color vision deficiency can experience some difficulties with seeing colors in everyday life, and these problems vary according to the nature and severity of the defect, the individual's circumstances and their ability to develop coping or adaptive strategies.

PURPOSE

To determine the impact of congenital color vision deficiency on color-related tasks among Black South African schoolchildren.

METHODS

A cross-sectional descriptive study was conducted among 1305 public schoolchildren in Durban, South Africa. Structured questionnaires were administered to determine the difficulties they encountered in aspects of color matching and recognition.

RESULTS

Of the 1305 schoolchildren who participated, 601 (46.1%) were boys and 704 (53.9%) were girls, with 29 (2.2%) having congenital color vision defects. The prevalence of congenital color vision deficiency was higher in boys (n=25; 4.2%) than in girls (n=4; 0.6%). A statistically significant proportion (P<0.0001) reported difficulties with color-related schoolwork and activities of daily living.

CONCLUSION

Congenital color vision deficiency affects many aspects of life and extends across play, sports, education, health and safety issues. Early detection of children with congenital color vision defect through regular school screenings is needed to offer affected children appropriate vocation and career guidance.

Colour vision deficiency among students in Lagos State, Nigeria

Background

Congenital colour vision defects are x-linked inherited, non-progressive and untreatable disorders that describe poor colour discrimination.

Objective

To determine the prevalence of congenital colour vision deficiency among students in Lagos, Nigeria.

Methods

A school-based cross-sectional, cluster sample study was conducted to test the colour vision of 2326 primary and high school students. Inclusion criteria were Snellen VA 20/20 or better and absence of known ocular pathologies. Colour vision deficiency (CVD) was evaluated with the Richmond-HRR colour vision test plates.

Results

There were 1014 (43.6%) males and 1312 (56.4%) females with a mean age of 13.40 ± 2.40 years (range = 7–22 years). The prevalence of CVD was 58 (2.5%), which was higher in males 49 (4.8%) than females 9 (0.7%). The prevalence of congenital CVD was significantly associated with males (p = 0.00), but not with females (p = 0.22). Of the 58 cases of CVD, 17 (0.7%) had protan deficiency, 38 (1.6%) had deutan deficiency and three (0.1%) were unclassified.

Conclusion

The prevalence of congenital CVD among students in Lagos is comparable to findings in other parts of Nigeria but differs from other parts of the country. These results strengthen the need to establish school vision screening.

Discrimination of colors by red-green color vision-deficient observers through digitally generated red filter

Previous studies have shown that with the use of tinted lenses (or colored filters), individuals with red-green color vision deficiency (CVD) report an improvement in their performance on certain color vision tests. In this context, this study examines the effects of a digitally generated red-colored filter and identifies the mechanism mainly responsible for the changes in red-green CVD observers' performance on a D-15 arrangement test performed using the filter. We simulate the red filter digitally with the spectral transmittance similar to that of the X-Chrom, which is a red-tinted lens. Fourteen red-green CVD subjects are subjected to the D-15 test on a computer monitor under four filter conditions, consisting of one condition without the filter and three conditions with the filter, corresponding to the opacity of the red filter. The results show that while the simulated red filter improves the performance of deutans to arrange the caps in the D-15 test, this is not the case for protans. In addition, considerations based on the human cone-contrast model enable us to identify that the improvement in deutan observers largely results from the increase in the luminance contrast between stimuli and a background. To summarize, the red filter simulated in this study induces different changes in the red-green CVD observer luminance contrast between the protan and deutan types, with the result that the performance of deuteranopes improves while that of protanopes deteriorates.

Spatial visual function in anomalous trichromats: Is less more?

Color deficiency is a common inherited disorder affecting 8% of Caucasian males with anomalous trichromacy (AT); it is the most common type of inherited color vision deficiency. Anomalous trichromacy is caused by alteration of one of the three cone-opsins’ spectral sensitivity; it is usually considered to impose marked limitations for daily life as well as for choice of occupation. Nevertheless, we show here that anomalous trichromat subjects have superior basic visual functions such as visual acuity (VA), contrast sensitivity (CS), and stereo acuity, compared with participants with normal color vision. Both contrast sensitivity and stereo acuity performance were correlated with the severity of color deficiency. We further show that subjects with anomalous trichromacy exhibit a better ability to detect objects camouflaged in natural gray scale figures. The advantages of color-deficient subjects in spatial vision performance could explain the relatively high prevalence of color-vision polymorphism in humans.

Behavioural and emotional issues among primary school pupils with congenital colour vision deficiency in the Federal Territory of Kuala Lumpur, Malaysia: A case-control study

Background: Congenital colour vision deficiency (CCVD) is an untreatable disorder which has lifelong consequences. Increasing use of colours in schools has raised concern for pupils with CCVD. This case-control study was conducted to compare behavioural and emotional issues among age, gender and class-matched pupils with CCVD and normal colour vision (NCV). Methods: A total of 1732 pupils from 10 primary schools in the Federal Territory of Kuala Lumpur were screened, of which 46 pupils (45 males and 1 female) had CCVD. Mothers of male pupils with CCVD (n=44) and NCV (n=44) who gave consent were recruited to complete a self-administered parent report form, Child Behaviour Checklist for Ages 4-18 (CBCL/ 4-18) used to access behavioural and emotional problems. The CBCL/ 4-18 has three broad groupings: Internalising, Externalising and Total Behaviour Problems. Internalising Problems combines the Withdrawn, Somatic Complaints and Anxiety/ Depression sub constructs, while Externalising Problems combines the Delinquent and Aggressive Behaviour sub constructs. Results: Results from CBCL/ 4-18 showed that all pupils from both groups had scores within the normal range for all constructs. However, results from the statistical analysis for comparison, Mann-Whitney U test, showed that pupils with CCVD scored significantly higher for Externalising Problems (U=697.50, p=0.02) and Total Behaviour Problems (U=647.00, p= 0.01). Significantly higher scores were observed in Withdrawn (U=714.00, p=0.02), Thought Problems (U=438.50, p<0.001) and Aggressive Behaviour (U=738.00, p=0.04). Odds ratios, 95% CI, showed significant relative risk for high Total Behaviour Problem (OR:2.39 ,CI:1.0-5.7), Externalising Problems (OR:2.32, CI:1.0-5.5), Withdrawn (OR:2.67, CI:1.1-6.5), Thought Problems (OR:9.64, CI:3.6-26.1) and Aggressive Behaviour (OR:10.26, CI:3.4-31.0) scores among pupils with CCVD. Conclusion: Higher scores among CCVD pupils indicates that they present more behavioural and emotional problems compared to NCV pupils. Therefore, school vision screenings in Malaysia should also include colour vision to assist in the early clinical management of CCVD children.

The impacts of abnormal color vision on people's life: an integrative review

BACKGROUND

This article shows an integrative review on the impact that abnormal color vision may have on the daily routine of individuals.

PURPOSE

We followed the PRISMA guidelines for reviews and carried out researches in four databases (Pubmed, Lilacs, Scopus, and Web of Science) using keywords related to the impact of abnormal color vision.

METHOD

Initially, 805 articles were retrieved and after a first filtering stage, we selected 74 articles for a detailed analysis of the abstracts in which it was found that a total of 20 studies were in fact related to the topic of this review. We then read the selected studies in full and those included in the final selection were analyzed and categorized into specific topic groups of findings. Seven categories were created in total: "impact on daily routine activities", "occupational impact", "impact on product choice motivation", "emotional impact", "impact on school or professional qualification", "impact on self-care and health", and "advantages".

RESULTS

From the definition of these categories we could understand that people with some degree of color vision loss face challenges in different aspects of their daily life, especially in their work activities. Still, the amount of research and hence technical support which could be offered to this population is restricted. Additionally, the scarce availability of publications on the topic and the fact that they include very specific groups of people, such as drivers and medical students, allow us to draw only partial conclusions about the all possible impacts yield by such perceptual difference since they observe the impact of the color-vision deficiency in their daily routine from a specific and precise point of view.

CONCLUSIONS

A broader view of the impact of this problem on the daily life of its carriers is fundamental for implementing strategies that allow such people to be included in all sorts of activities or for the impact of this sensory change to be decreased or treated in a way that would reduce the detrimental impacts.

Case Report: Invalidation of the Farnsworth D15 Test in Dichromacy Secondary to Practice

SIGNIFICANCE

The Farnsworth D15 test can be subverted by patients even with severe red-green color deficiency.

PURPOSE

To describe a case showing that perfect performance on the Farnsworth D15 is possible after practicing the test.

CASE REPORT

A 23-year-old man presented for a comprehensive color vision evaluation. He had only minor complaints with regard to color vision and otherwise normal vision and ocular health. Based on anomaloscope findings, he was diagnosed with protanopia, a form of dichromacy in which the patient does not have any functional L cones, only S and M cones. The patient practiced the Farnsworth D15 test and returned for a follow-up visit in which he performed the test perfectly four times (i.e., twice in the regular order and twice using cap 15 as the pilot cap). In addition, the patient returned a year later and again performed the test perfectly, indicating long-term learning.

CONCLUSIONS

All studies to date have shown that patients with dichromacy fail the Farnsworth D15 test. This case report shows that it is indeed possible for highly motivated patients to subvert the test through practice, and knowledge of this possibility is very important, especially in occupational testing.

Occupational styrene exposure and acquired dyschromatopsia: A systematic review and meta-analysis

BACKGROUND

Styrene is a chemical used in the manufacture of plastic-based products worldwide. We systematically reviewed eligible studies of occupational styrene-induced dyschromatopsia, qualitatively synthesizing their findings and estimating the exposure effect through meta-analysis.

METHODS

PubMed, EMBASE, and Web of Science databases were queried for eligible studies. Using a random effects model, we compared measures of dyschromatopsia between exposed and non-exposed workers to calculate the standardized mean difference (Hedges'g). We also assessed between-study heterogeneity and publication bias.

RESULTS

Styrene-exposed subjects demonstrated poorer color vision than did the non-exposed (Hedges' g = 0.56; 95%CI: 0.37, 0.76; P < 0.0001). A non-significant Cochran's Q test result (Q = 23.2; P = 0.171) and an I² of 32.2% (0.0%, 69.9%) indicated low-to-moderate between-study heterogeneity. Funnel plot and trim-and-fill analyses suggested publication bias.

CONCLUSIONS

This review confirms the hypothesis of occupational styrene-induced dyschromatopsia, suggesting a modest effect size with mild heterogeneity between studies.

Applications of Color in Design for Color-Deficient Users

Color vision deficiency is common, affecting one in every 12 men. Despite its prevalence, displays are seldom designed to accommodate color-vision-deficient (CVD) users, who confront daily challenges interpreting color in a broad range of applications, whether weather displays, informational graphics, road signs, or computer interfaces. In this article we discuss the prevalence of color deficiency, its effects, and the availability of tools that enable design teams to evaluate candidate solutions that meet the needs of CVD users, thereby ensuring universal accessibility.

Visual Search in the Real World: Color Vision Deficiency Affects Peripheral Guidance, but Leaves Foveal Verification Largely Unaffected

BACKGROUND

People with color vision deficiencies report numerous limitations in daily life, restricting, for example, their access to some professions. However, they use basic color terms systematically and in a similar manner as people with normal color vision. We hypothesize that a possible explanation for this discrepancy between color perception and behavioral consequences might be found in the gaze behavior of people with color vision deficiency.

METHODS

A group of participants with color vision deficiencies and a control group performed several search tasks in a naturalistic setting on a lawn. All participants wore a mobile eye-tracking-driven camera with a high foveal image resolution (EyeSeeCam). Search performance as well as fixations of objects of different colors were examined.

RESULTS

Search performance was similar in both groups in a color-unrelated search task as well as in a search for yellow targets. While searching for red targets, participants with color vision deficiencies exhibited a strongly degraded performance. This was closely matched by the number of fixations on red objects shown by the two groups. Importantly, once they fixated a target, participants with color vision deficiencies exhibited only few identification errors.

CONCLUSIONS

In contrast to controls, participants with color vision deficiencies are not able to enhance their search for red targets on a (green) lawn by an efficient guiding mechanism. The data indicate that the impaired guiding is the main influence on search performance, while foveal identification (verification) is largely unaffected by the color vision deficiency.

Ability of Bottle Cap Color to Facilitate Accurate Patient-Physician Communication Regarding Medication Identity in Patients with Glaucoma

PURPOSE

To determine the accuracy of patient-physician communication regarding topical ophthalmic medication use based on bottle cap color, particularly among individuals who may have acquired color vision deficiency from glaucoma.

DESIGN

Cross-sectional, clinical study.

PARTICIPANTS

Patients aged ≥18 years with primary open-angle, primary angle-closure, pseudoexfoliation, or pigment dispersion glaucoma, bilateral visual acuity of ≥20/400, and no concurrent conditions that may affect color vision.

METHODS

A total of 100 patients provided color descriptions of 11 distinct medication bottle caps. Color descriptors were then presented to 3 physicians. Physicians matched each color descriptor to the medication they thought the descriptor was describing.

MAIN OUTCOME MEASURES

Frequency of patient-physician agreement, occurring when all 3 physicians accurately matched the color descriptor to the correct medication. Multivariate regression models evaluated whether patient-physician agreement decreased with degree of better-eye visual field (VF) damage, color descriptor heterogeneity, or color vision deficiency, as determined by the Hardy-Rand-Rittler (HRR) score and Lanthony D15 color confusion index (D15 CCI).

RESULTS

Subjects had a mean age of 69 (±11) years, with VF mean deviation of -4.7 (±6.0) and -10.9 (±8.4) decibels (dB) in the better- and worse-seeing eyes, respectively. Patients produced 102 unique color descriptors to describe the colors of the 11 bottle caps. Among individual patients, the mean number of medications demonstrating agreement was 6.1/11 (55.5%). Agreement was less than 15% for 4 medications (prednisolone acetate [generic], betaxolol HCl [Betoptic; Alcon Laboratories Inc., Fort Worth, TX], brinzolamide/brimonidine [Simbrinza; Alcon Laboratories Inc.], and latanoprost [Xalatan; Pfizer, Inc., New York, NY]). Lower HRR scores and higher D15 CCI (both indicating worse color vision) were associated with greater VF damage (P < 0.001). Extent of color vision deficiency and color descriptor heterogeneity significantly predicted agreement in multivariate models (odds of agreement = 0.90 per 1 point decrement in HRR score, P < 0.001; odds of agreement = 0.30 for medications exhibiting high heterogeneity [≥11 descriptors], P = 0.007).

CONCLUSIONS

Physician understanding of patient medication use based solely on bottle cap color is frequently incorrect, particularly in patients with glaucoma who may have color vision deficiency. Errors based on communication using bottle cap color alone may be common and could lead to confusion and harm.

Prevalence and gene frequency of color vision impairments among children of six populations from North Indian region

X-linked red-green color blindness is the most widespread form of vision impairment. The study aimed to determine the prevalence and gene frequencies of red-green color vision impairments among children of six different human populations of Jammu province. A total of 1028 healthy subjects (6-15 years of age) were selected from five Muslim populations and the color vision impairments were determined using the Ishihara's test of color deficiency. The gene frequency was calculated using Hardy-Weinberg equilibrium method. The prevalence of color vision deficiency (CVD) ranged from 5.26% to 11.36% among males and 0.00%-3.03% among females of six different populations. The gender based differences in the frequency of CVD was found to be statistically significant (p < 0.0001), with a higher prevalence among male (7.52%) as compared to female (0.83%) children. We observed high frequency of deutan as compared to protan defects. The incidences of deuteranomaly (5.68%) and deuteranopia (2.27%) were higher among male children of Syed population while the frequencies of protanomaly (1.94%), protanopia (1.28%) and achromacy (2.27%) were the highest among male subjects of Khan, Malik and Syed populations, respectively. The allele and genotype frequencies showed cogent differences among six populations. The population based assessment of CVDs help patients to follow adaptive strategies that could minimize the risks of the disease.

Is screening for congenital colour vision deficiency in school students worthwhile? A review

This review analyses the literature on screening for congenital colour vision deficiency in school students, which predominantly uses the Ishihara test. The review was framed with respect to the established Wilson and Jungner criteria for screening programs. These criteria relate to the characteristics of the condition concerned, the performance of the screening test, the existence of treatment options and the performance of screening programs. The literature reviewed suggests that congenital colour vision deficiency has not been shown to increase risk of road traffic crashes and is not a preclusion to driver licensing in most developed countries. The occurrence of congenital colour vision deficiency has been used to limit entry into certain occupations; however, the value of screening school students with regard to occupational preclusion is questionable. Stronger evidence exists indicating no association between congenital colour vision deficiency and level of educational achievement. Studies showing any association between congenital colour vision deficiency and other health and lifestyle impacts were rare. The most commonly used screening test (using Ishihara pseudoisochromatic plates) performs well with respect to detecting red-green colour vision deficiencies. Finally, the only interventions we identified for congenital colour vision deficiency were management ones around the availability of specific tinted lenses and computer programs to aid colour perception in certain tasks. Given this picture, the weight of evidence appears to be in favour of not adopting (or discontinuing) routine colour vision screening programs for school students; however, it may be worthwhile for a career advisor to refer school students to an optometrist or ophthalmologist for colour vision screening, upon expression of interest in an occupation where normal colour vision is either particularly desirable or is a regulatory requirement.

Colour Vision Deficiency: Is it a Handicap? A Narrative Review of its Impact on Medical & Dental Education and Practice

Colour vision is required in medical and dental practices. This article seeks to present the impact of colour vision deficiency (CVD) on medical, dental education and practices using narrative review of literature. Relevant English publications, comprising of experimental and observational studies, topic and systemic reviews, meta-analyses and randomised controlled trials, were searched and identified from PubMed, National University of Singapore (NUS) database, Cochrane electronic databases and Proceedings of the thirteenth Symposium of the International Research Group on CVD. “Google” and “Google Scholar” were used to search for paramedical literature. Seventy articles were retrieved, of which 38 were included in this review. It shows that CVD affects broad spectrum of medical, dental education and practices, and varies in its impact. Detecting colour cues in clinical practice constitutes one of the many complex processes in establishing the clinical diagnoses, thus the deficiency alone may not handicap the clinicians. Nonetheless, early colour vision screening for medical and dental students, and practitioners would result in early recognition of their limitations and allow time for devising coping strategies.

Spotting fruit versus picking fruit as the selective advantage of human colour vision

The spatiochromatic properties of the red-green dimension of human colour vision appear to be optimized for picking fruit in leaves at about arms' reach. However, other evidence suggests that the task of spotting fruit from a distance might be more important. This discrepancy may arise because the task a system (e.g. human trichromacy) is best at is not necessarily the same task where the largest advantage occurs over the evolutionary alternatives (dichromacy or anomalous trichromacy). We tested human dichromats, anomalous trichromats and "normal" trichromats in a naturalistic visual search task in which they had to find fruit pieces in a bush at 1, 4, 8 or 12 m viewing distance. We found that the largest advantage (in terms of either performance ratio or performance difference) of normal trichromacy over both types of colour deficiency was for the largest viewing distance. We infer that in the evolution of human colour vision, spotting fruit from a distance was a more important selective advantage than picking fruit at arms' reach.

A look through 'lens' cubic mitochondria

Cell membranes may fold up into three-dimensional nanoperiodic cubic structures in biological systems. Similar geometries are well studied in other disciplines such as mathematics, physics and polymer chemistry. The fundamental function of cubic membranes in biological systems has not been uncovered yet; however, their appearance in specialized cell types indicates a role as structural templates or perhaps direct physical entities with specialized biophysical properties. The mitochondria located at the inner segment of the retinal cones of tree shrew (Tupaia glis and Tupaia belangeri) contain unique patterns of concentric cristae with a highly ordered membrane arrangement in three dimensions similar to the photonic nanostructures observed in butterfly wing scales. Using a direct template matching method, we show that the inner mitochondrial membrane folds into multi-layered (8 to 12 layers) gyroid cubic membrane arrangements in the photoreceptor cells. Three-dimensional simulation data demonstrate that such multi-layer gyroid membrane arrangements in the retinal cones of a tree shrew's eye can potentially function as: (i) multi-focal lens; (ii) angle-independent interference filters to block UV light; and (iii) a waveguide photonic crystal. These theoretical results highlight for the first time the significance of multi-layer cubic membrane arrangements to achieve near-quasi-photonic crystal properties through the simple and reversible biological process of continuous membrane folding.

Worldwide prevalence of red-green color deficiency

Literature that describes the prevalence of inherited red-green color deficiency in different populations is reviewed. Large random population surveys show that the prevalence of deficiency in European Caucasians is about 8% in men and about 0.4% in women and between 4% and 6.5% in men of Chinese and Japanese ethnicity. However, the male: female prevalence ratio is markedly different in Europeans and Asians. Recent surveys suggest that the prevalence is rising in men of African ethnicity and in geographic areas that have been settled by incoming migrants. It is proposed that founder events and genetic drift, rather than natural selection, are the cause of these differences.

Structural and functional correlates in color vision deficiency

PURPOSE

The aim of this study is to assess the photoreceptor integrity, using spectral domain optical coherence tomography (SD-OCT), and to measure the retinal sensitivity of patients with congenital red-green color vision deficiency (CVD).

METHODS

In all, 14 eyes from 7 patients with congenital red-green CVD (diagnosed by Farnsworth Munsell 100 hue test), and 14 eyes from 7 control subjects were examined by SD-OCT and microperimetry. Radial scans (7-mm) were taken of the macula. The center of the fovea was defined. The thickness of different retinal layers, at the foveal center, and at multiple defined points along all six radial scans, was measured. The median readings were compared between the two groups using Mann-Whitney U-test.

RESULTS

SD-OCT demonstrated normal total retinal thickness, normal thickness of the photoreceptor layer, normal thickness of the outer nuclear layer, normal vertical thickness of the outer segments (OSs), and normal vertical thickness of the inner segments. OS horizontal diameter was less in left eye in cases with CVD when compared with controls. The mean retinal and foveal sensitivity was similar between cases and controls.

CONCLUSIONS

In subjects with congenital red-green CVD, there are no discernible anatomical abnormalities seen on SD-OCT in various retinal layers, except for a narrower foveal pit. However, further studies with larger sample size are required.

Discriminating colors through a red filter by protanopes and colour normals

Individuals with color vision deficiency have difficulties in differentiating colour in their daily activities. Through certain coloured filters, dichromats may report an improvement of their capacity to differentiate colors, but it is not known if this is achieved by means of a chromatic mechanism. The present study attempts to explain the mechanism by which a coloured filter can produce a beneficial effect in dichromatic visual perception and what is the nature of this improvement. Four male protanopes and four normal trichromats (two males and two females) participated in the present study. We evaluated the effect of the red filter (with a spectral transmittance similar to that of the X-Chrom filter) on the detection thresholds for monochromatic light stimuli from 420 to 660 nm in 20 nm steps. The increment spectral sensitivity functions were measured for 1.2 degrees diameter test flashes presented for 300 ms on a 60-cd m(-2) illuminant C background using an optical bench with a monochromator, for both filter and no filter conditions. The capacity to correctly name green, yellow and red for the monochromatic lights of 550, 575 and 625 nm presented for 300 ms on a 60 cd m(-2) illuminant C background screen was also evaluated with and without the red filter. The spectral sensitivity data suggest that, the use of a red filter improves the protanope's capacity to detect long wavelength light stimuli. The results on the colors naming procedure demonstrate that the red filter modifies colour perception in normal and protanope subjects. In normals, only the red color perception is preserved, and typical colour perception for the green and the yellow is lost. Without the filter, all the protanopes demonstrated a residual colour perception for red and green colours. Through the red filter only red colour perception remains. A red filter does not improve the protanopic red-green perception, but it does improve the ability of the protanope to detect long-wavelength light. This improvement seems to arise by means of the luminance mechanism.