The ChromaGen contact lens system: colour vision test results and subjective responses

Empirical tests of the effectiveness of EnChroma multi-notch filters for enhancing color vision in deuteranomaly

Manufacturers of notch filter-based aids for color vision claim that their products can enhance color perception for people with anomalous trichromacy, a form of color vision deficiency (CVD). Anecdotal reports imply that people with CVD can have radically enhanced color vision when using the filters. However, existing empirical research largely focussed on the effect of notch filters on performance on diagnostic tests for CVD has not found that they have any substantial effect. Informed by a model of anomalous trichromatic color vision, we selected stimuli predicted to reveal the effects of EnChroma filters. Using these stimuli, we tested the ability of EnChroma filters to enhance color vision for 10 deuteranomalous trichromats in three experiments: 1. asymmetric color matching between test and control filter conditions, 2. color discrimination measured using four alternative forced-choice, and 3. color appearance measured using dissimilarity ratings to reconstruct subjective color spaces using multidimensional scaling. To investigate potential effects of long-term adaptation or perceptual learning, participants completed all three experiments at two time points, on first exposure to the filters, and after a week of regular use. We found a significant effect of the filters on color matches in the direction predicted by the model at both time points, implying that the filters can enhance the anomalous trichromatic color gamut. However, we found minimal effect of the filters on color discrimination at threshold. We found a significant effect of the filters in enhancing the appearance of colors along the red-green axis at the first time point, and a trend in the same direction at the second time point. Our results provide the first quantitative experimental evidence that notch filters can enhance color perception for anomalous trichromats.

Discrimination of natural colors in anomalous trichromacy and the effects of EnChroma and Vino filters

It is still unclear how well anomalous trichromats discriminate natural colors and whether commercial spectral filters improve performance in these conditions. We show that anomalous trichromats have good color discrimination with colors drawn from natural environments. It is only about 14% poorer, on average, than normal trichromats in our sample of thirteen anomalous trichromats. No measurable effect of the filters on discrimination was found, even after 8 hours of continuous use. Computations of cone and post-receptoral signals show only a modest increase in medium-to-long-wavelength difference signals, which may explain the absent effect of the filters.

Masking Colour Blindness: A Case Report

Colour vision is an important aspect of visual function that might help individuals in doing daily activities. Some occupations require and test for good colour discrimination. We describe a case of a 20-year-old man who was referred to our centre to establish if he had colour vision deficiency (CVD). He had been tested for this twice as part of his assessment to enter the police force. At the first examination, he had normal colour vision, while the second examination revealed CVD, thus the patient was referred for confirmation. Colour vision tests using the Ishihara plates showed normal results with each eye, while a Roth test revealed an unspecified CVD in the right eye and deuteranopia in the left eye. During the evaluation, we noticed he was using a red-tinted contact lens in the right eye, and was wearing a red mask with transparent red plastic in the upper part. After removal of the contact lens and mask, he was asked to repeat the examinations and it revealed deuteranopia in both eyes. A tinted contact lens is a corrective device that can help to enhance colour discrimination in CVD subjects. However, in this case the tinted contact lens was used inappropriately to manipulate the colour vision examination. We highlight the case to raise awareness that the use of red contact lenses and red filters can mask CVD.

CVD-MET: an image difference metric designed for analysis of color vision deficiency aids

Color vision deficiency (CVD) has gained in relevance in the last decade, with a surge of proposals for aid systems that aim to improve the color discrimination capabilities of CVD subjects. This paper focuses on the proposal of a new metric called CVD-MET, that can evaluate the efficiency and naturalness of these systems through a set of images using a simulation of the subject's vision. In the simulation, the effect of chromatic adaptation is introduced via CIECAM02, which is relevant for the evaluation of passive aids (color filters). To demonstrate the potential of the CVD-MET, an evaluation of a representative set of passive and active aids is carried out both with conventional image quality metrics and with CVD-MET. The results suggest that the active aids (recoloration algorithms) are in general more efficient and produce more natural images, although the changes that are introduced do not shift the CVD's perception of the scene towards the normal observer's perception.

The Use of Chromagen Lenses in Different Ocular and Non-ocular Conditions: A Prospective Cohort Study

Background

In this study, we aimed to evaluate the efficacy of chromagen lenses and compare the pre- and post-intervention outcomes among individuals with non-ocular conditions such as dyslexia and Irlen syndrome and ocular conditions such as color vision deficiency (CVD) and cone-rod dystrophy (CRD).

Methodology

This prospective cohort study was conducted from 2016 to 2021 among cases (seven years or older) who were diagnosed with dyslexia, Irlen syndrome, CVD, or CRD. Participants were given a short questionnaire to read, followed by asking direct questions regarding medical health history, ocular history, eyeglasses prescription, and a full orthoptics evaluation. The main outcomes were the improvement in reading speed, reading accuracy, and visual stress.

Results

A total of 156 patients were included in this study; 110 patients with dyslexia, 19 with Irlen syndrome, 16 with CVD, and 11 with CRD. The findings showed that the reading speed and accuracy were improved in 96.34% of patients with dyslexia and 78.9% of patients with Irlen syndrome. The use of a chromagen lens was significantly associated with visual stress improvement in 89.8% of patients (p = 0.02). Photosensitivity was significantly improved after wearing the chromagen lenses in patients with CVD (87.5%) and CRD (63.6%).

Conclusions

The study findings showed a positive impact of chromagen lenses on reducing visual stress, including reading speed and accuracy, in patients with dyslexia and Irlen syndrome. Photosensitivity improved in patients with Irlen syndrome and CRD. Color vision was enhanced in patients with CVD. However, further studies are required to investigate the predictors of improvement and assess the long-term efficacy of chromagen lenses on daily activities and learning skills.

Color vision devices for color vision deficiency patients: A systematic review and meta‐analysis

Background and Aims

There is insufficient evidence to support that using electronic or optical color vision devices improve color perception with current advanced technology. The purpose of this study is to compare and analyze the different color vision devices available for patients with color vision deficiency (CVD) and evaluate whether these devices improved their color perception.

Methods

This review included randomized, experimental, comparative studies, as well as narrative reviews, prototype and innovation studies, and translational studies, followed by case‐control and clinical trials with nonsurgical interventions studies, that is, electronic color vision devices, optical devices, and contact lens‐based studies, with standardized inclusion and exclusion criteria.

Results

The primary outcome studied was the performance of color vision devices, both objective and subjective. Secondary outcomes included the ease of use and accessibility of color vision devices and technology. The grading of recommendation, assessment, development, and evaluation framework was used to develop a systematic approach for consideration and clinical practice recommendation for CVD devices for color‐deficient populations. We incorporated meta‐analysis reports from a total of n = 16 studies that met the criteria which consisted of case‐control studies, prototype and innovation studies, comparative studies, pre‐ and post‐clinical trial studies, case studies, and narrative reviews. Proportion and standard errors, as well as correlations, were calculated from the meta‐analysis for various available color vision devices.

Conclusion

This review concludes that commercially available color vision devices, such as EnChroma Glasses, Chromagen filters, and EnChroma Cx‐14 do not provide clinically significant evidence that subjective color perception has improved. As a result, recommending these color vision devices to the CVD population may not prove high beneficial/be counterproductive. However, only a few color shades can be perceived differently. This systematic review and analysis will aid future research and development in color vision devices.

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.

CLEAR - Medical use of contact lenses

The medical use of contact lenses is a solution for many complex ocular conditions, including high refractive error, irregular astigmatism, primary and secondary corneal ectasia, disfiguring disease, and ocular surface disease. The development of highly oxygen permeable soft and rigid materials has extended the suitability of contact lenses for such applications. There is consistent evidence that bandage soft contact lenses, particularly silicone hydrogel lenses, improve epithelial healing and reduce pain in persistent epithelial defects, after trauma or surgery, and in corneal dystrophies. Drug delivery applications of contact lens hold promise for improving topical therapy. Modern scleral lens practice has achieved great success for both visual rehabilitation and therapeutic applications, including those requiring retention of a tear reservoir or protection from an adverse environment. This report offers a practical and relevant summary of the current evidence for the medical use of contact lenses for all eye care professionals including optometrists, ophthalmologists, opticians, and orthoptists. Topics covered include indications for use in both acute and chronic conditions, lens selection, patient selection, wear and care regimens, and recommended aftercare schedules. Prevention, presentation, and management of complications of medical use are reviewed.

CLEAR - Contact lens technologies of the future

Contact lenses in the future will likely have functions other than correction of refractive error. Lenses designed to control the development of myopia are already commercially available. Contact lenses as drug delivery devices and powered through advancements in nanotechnology will open up further opportunities for unique uses of contact lenses. This review examines the use, or potential use, of contact lenses aside from their role to correct refractive error. Contact lenses can be used to detect systemic and ocular surface diseases, treat and manage various ocular conditions and as devices that can correct presbyopia, control the development of myopia or be used for augmented vision. There is also discussion of new developments in contact lens packaging and storage cases. The use of contact lenses as devices to detect systemic disease has mostly focussed on detecting changes to glucose levels in tears for monitoring diabetic control. Glucose can be detected using changes in colour, fluorescence or generation of electric signals by embedded sensors such as boronic acid, concanavalin A or glucose oxidase. Contact lenses that have gained regulatory approval can measure changes in intraocular pressure to monitor glaucoma by measuring small changes in corneal shape. Challenges include integrating sensors into contact lenses and detecting the signals generated. Various techniques are used to optimise uptake and release of the drugs to the ocular surface to treat diseases such as dry eye, glaucoma, infection and allergy. Contact lenses that either mechanically or electronically change their shape are being investigated for the management of presbyopia. Contact lenses that slow the development of myopia are based upon incorporating concentric rings of plus power, peripheral optical zone(s) with add power or non-monotonic variations in power. Various forms of these lenses have shown a reduction in myopia in clinical trials and are available in various markets.

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.

Metasurface-based contact lenses for color vision deficiency: reply

The filtering of overlapping spectral regions may be used to increase the observer's gamut in some cases. Therefore, metasurface-based contact lenses (M-CL) may improve the color coding for specific stimuli and deuteranomaly conditions. Here, we address the concerns made by Huertas et al. [Opt. Lett.45, 5117 (2020)OPLEDP0146-959210.1364/OL.394717], regarding the color perception improvement obtained by color filters, in general, and specifically by our M-CL, in case of deuteranomaly.

Effect of EnChroma glasses on color vision screening using Ishihara and Farnsworth D-15 color vision tests

BACKGROUND

The prevalence of color vision deficiency (CVD) is about 0.5% in females and 8% in males. Although there is no cure for CVD, specially filtered glasses are purported to improve color contrast. One recent development is the EnChroma filter. The purpose of this study was to assess the effect of the EnChroma filter on color vision screening (CVS) using Ishihara and Farnsworth D-15 color vision tests.

METHODS

The medical records of patients with CVD were reviewed retrospectively. Responses to color vision testing with and without the EnChroma filter were evaluated using Ishihara and Farnsworth D-15 tests, and the overall scores were analyzed.

RESULTS

A total of 38 eyes of 19 patients were included. Mean error scores of no filter compared to EnChroma were significantly reduced in 17 eyes using the Ishihara test (0.88 ± 0.03 vs 0.85 ± 0.03, P = 0.017). The error score significantly reduced only in deutans (P = 0.022), not in protans (P = 0.44). The confusion index of no filter to the EnChroma filter was significantly reduced in 20 eyes using the Farnsworth test (3.30 ± 0.15 vs 2.98 ± 0.17; P = 0.01). The confusion index significantly reduced only in protans (P = 0.01), not in deutans (P = 0.19).

CONCLUSIONS

In this study cohort, the EnChroma filter significantly reduced overall error scores using the Ishihara and Farnsworth tests; error scores on Ishihara testing reduced only in deutans. Conversely, the confusion index using Farnsworth reduced only in protans. The majority of patients reported subjective increase in color perception.

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.

Novel color filters for the correction of red-green color vision deficiency based on the localized surface plasmon resonance effect of Au nanoparticles

Color filters are promising tools for the correction of color vision deficiency because a medical cure of this physiological deficiency is unattainable. After the introduction of organic-dye based color filters, however, no appreciable progress has been made. In this study, gold nanoparticle-based plasmonic color filter devices, that is, EyEye-lens and EyEye-film, were developed for the correction of color vision deficiency. The EyEye-lens was prepared by a simple immobilizing technique, and the EyEye-film was readily synthesized through a one-pot method. These color filter devices are based on tunable localized surface plasmon resonance in the visible and near-infrared spectral range. Plasmonic nanoparticles embedded in the color filter provide a specific spectral color range for the correction of color vision deficiency. Careful color vision tests using an Ishihara plate were performed on subjects with red-green color deficiency. Statistical analysis of the color vision tests revealed that the EyEye-lens and EyEye-film have similar or better performance in the correction of red-green color deficiency than a commercial ChromaGen lens. The newly developed color filter devices should be considered as alternative personalized color filter devices for practical applications.

Assessment of VINO filters for correcting red-green Color Vision Deficiency

In our ongoing research on the effectiveness of different passive tools for aiding Color Vision Deficiency (CVD) subjects, we have analyzed the VINO 02 Amp Oxy-Iso glasses using two strategies: 1) 52 observers were studied using four color tests (recognition, arrangement, discrimination, and color-naming); 2) the spectral transmittance of the lenses were used to model the color appearance of natural scenes for different simulated CVD subjects. We have also compared VINO and EnChroma glasses. The spectral transmission of the VINO glasses significantly changed color appearance. This change would allow some CVD subjects, above all the deutan ones, to be able to pass recognition tests but not the arrangement tests. To sum up, our results support the hypothesis that glasses with filters are unable to effectively resolve the problems related to color vision deficiency.

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.

Efficacy of red contact lens in improving color vision test performance based on Ishihara, Farnsworth D15, and Martin Lantern Test

Background

The aim of this study was to evaluate the efficacy of red contact lens in improving color vision test performance based on Ishihara, Farnsworth D15, and Martin Lantern Test (MLT).

Methods

Thirty subjects with a known color vision defect were enrolled after consent. The color vision was assessed using Ishihara test, D15 test, and MLT. The error scores were recorded. The test was repeated after using a red contact lens.

Results

The mean error scores were 7.87 (±1.00), 3.33 (±3.15), and 5.67 (±2.52) on Ishihara, MLT, and D15 test, respectively. The error scores reduced to 3.93 (±3.78), 1.33 (±1.34), and 2.77 (±2.12) Ishihara, MLT, and D15 test, respectively (P value < 0.05, Wilcoxon rank test). None of the subjects were in color perception (CP) II at presentation but 47.5% became CP II with the lens on Ishihara test. Ninety percent could pass the MLT CP III standard.

Conclusion

This study shows that red lens reduced error scores and subjects could pass the color vision tests. Notwithstanding the improvement in performance on color vision tests, lens is not recommended for personnel on active combat duty. The recruiting medical officer needs to be aware of the fact that a subject with defective color vision can pass various tests with a red contact lens.

Illuminations that improve color discrimination ability of people with red-green color vision deficiency

In this research, three illuminants that improve color discrimination ability of people with red-green color vision deficiency were developed. The illuminants are close to daylight-colored and were produced by using spectral optimization. Deutans were the focus of this research, but a few protans were also tested for reference. The illuminants were produced by combining different types of LEDs, and their effects were tested with several test subjects with and without color vision deficiency using the Ishihara color vision test and the Farnsworth Panel D-15 test. The illuminant with the most powerful effect provided near perfect results with the Ishihara test for deutans, while the other two illuminants produced smaller improvements. The Farnsworth Panel D-15 test produced results that were similar to the Ishihara test though generally the color discrimination of blue hues was weaker under the most powerful illuminant.

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.

Quantitative assessment of commercial filter 'aids' for red-green colour defectives

The claims made for 43 commercial filter 'aids', that they improve the colour discrimination of red-green colour defectives, are assessed for protanomaly and deuteranomaly by changes in the colour spacing of traffic signals (European Standard EN 1836:2005) and of the Farnsworth D15 test. Spectral transmittances of the 'aids' are measured and tristimulus values with and without 'aids' are computed using cone fundamentals and the spectral power distributions of either the D15 chips illuminated by CIE Illuminant C or of traffic signals. Chromaticities (l,s) are presented in cone excitation diagrams for protanomaly and deuteranomaly in terms of the relative excitation of their long (L), medium (M) and short (S) wavelength-sensitive cones. After correcting for non-uniform colour spacing in these diagrams, standard deviations parallel to the l and s axes are computed and enhancement factors E(l) and E(s) are derived as the ratio of 'aided' to 'unaided' standard deviations. Values of E(l) for traffic signals with most 'aids' are <1 and many do not meet the European signal detection standard. A few 'aids' have expansive E(l) factors but with inadequate utility: the largest being 1.2 for traffic signals and 1.3 for the D15 colours. Analyses, replicated for 19 'aids' from one manufacturer using 658 Munsell colours inside the D15 locus, yield E(l) factors within 1% of those found for the 16 D15 colours.

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.

A placebo-controlled trial of tinted lenses in adolescents with good and poor academic performance: reading accuracy and speed

Purpose

A placebo-controlled, double-masked study was designed in order to evaluate the effect of tinted lenses in adolescents with good and poor academic performance.

Methods

Teenagers from two different age groups were enrolled in this study, after ascertaining that no uncorrected visual anomalies were present. A rate of reading test was developed for Catalan as a first language and students were asked to read it aloud, in two different sessions. Students first read the test without lenses and, later, they read it again without lenses, with their lenses of choice and with a placebo set of clear lenses. Reading speed and accuracy were monitored.

Results

No significant difference was encountered between the baseline reading speed and accuracy from the first and second sessions, thus ruling out any effect due to experience or training. When comparing reading speed and accuracy without lenses, in placebo conditions, and with tinted lenses, reading accuracy was discovered to be more sensitive than reading speed in order to differentiate between these conditions. These differences were more noticeable when the group with poor academic performance was evaluated, in contrast to the group with good academic performance or the whole group.

Conclusion

It was concluded that reading accuracy should be evaluated as well as reading speed and that lenses were more beneficial if only adolescents with poor academic performance were targeted.

Colour vision deficiency

Colour vision deficiency is one of the commonest disorders of vision and can be divided into congenital and acquired forms. Congenital colour vision deficiency affects as many as 8% of males and 0.5% of females--the difference in prevalence reflects the fact that the commonest forms of congenital colour vision deficiency are inherited in an X-linked recessive manner. Until relatively recently, our understanding of the pathophysiological basis of colour vision deficiency largely rested on behavioural data; however, modern molecular genetic techniques have helped to elucidate its mechanisms. The current management of congenital colour vision deficiency lies chiefly in appropriate counselling (including career counselling). Although visual aids may be of benefit to those with colour vision deficiency when performing certain tasks, the evidence suggests that they do not enable wearers to obtain normal colour discrimination. In the future, gene therapy remains a possibility, with animal models demonstrating amelioration following treatment.

Orienteers with poor colour vision require more than cunning running

BACKGROUND

Highly detailed colour coded maps are used in the sport of orienteering to enable competitors to navigate from one check point to another and to provide guidance on the nature of the terrain to be traversed. The colours are defined by the International Orienteering Foundation (IOF) and are said to have been chosen so they will not be confused by competitors who have abnormal colour vision. However, there are anecdotal reports that individuals with colour vision defects do have problems with the colour coding.

METHOD

A Minolta Spectrophotometer CM-503i was used to measure the CIE x,y chromaticity co-ordinates and the reflectances of the standard colours recommended by the IOF for the colour coding of orienteering maps, as well as the colours on two maps used in orienteering events.

RESULTS

Four pairs of IOF standard colours are likely to be confused by protan observers and four pairs by deutan observers. There were three pairs of colours likely to be confused by both deutan and protan observers on one of the competition maps and one pair likely to be confused by protan observers on the other map. Some of the colours on the actual competition maps differed noticeably from the standard IOF colours.

DISCUSSION

Orienteers with more severe forms of abnormal colour vision are likely to be disadvantaged by their inability to differentiate some colours used on orienteering maps. The IOF should choose different colours that are less likely to be confused or should employ a redundant code (such as a pattern or texture). There is need for better quality control of the colours of competition maps to ensure they do conform to the IOF standard colours.