Visibility of protective helmets worn by forestry workers

Background : High visibility helmets must be worn by Forestry workers in New Zealand for protection and as conspicuous ‘clothing’ to alert workers to the presence and location of other workers. The colours yellow-green (fluorescent yellow-green) and ‘water melon’ (fluorescent pink) are used and both appear to be conspicuous. To solve controversy, we investigated which helmet colour is more visible for use in a forest setting for workers having normal or defective colour vision. Method : We obtained threshold angular sizes for two-millimetre square samples met material presented against a textured background containing colours representative of those found in the foliage and bark of the most common forest type (Pinus Radiata). Observers with normal colour vision (n = 22) and with deutan (n = 8 and protan (n = 6) defects participated. Subjects with mild colour vision defects were excluded. Results : The yellow-green colour was significantly more visible than the pink for the normal (p < 0.001) and protan (p < 0.05) observers. For the deutan observers the pink helmet colour was significantly more visible (p < 0.01). The median equivalent out-door detection distances were for normal observers 400 m (pink) and 500 m yellow-green); for protan observers 185 m (pink) and 500 m (yellow-green); and for deutan observers 550 m (pink) and 450 m (yellow-green). Conclusions : The yellow-green helmet can be detected at large distances by all observers. The yellow-green helmet has greater reflectance and therefore greater luminance contrast. The pink helmet colour can be confused with green forest background colours by observers with protan defects. For some observers with a protan colour vision defect, detection distances for the pink helmet colour are less than half of normal detection distances.     

New investigations concerning the relationships between congenital colour vision defects and road traffic security

New extentive experiments demonstrated that: (a) protan observers are more deficient than deutan ones with regard to perception distances of some traffic panels, of vehicle red stop lights, of vehicle red rear-position lights and of white, yellow and red reflectors. Contrarily, deutan observers are more deficient than protan ones for the distinction of differently coloured traffic lights and vehicle rear lights; (b) protan and deutan drivers are nevertheless not responsible for more traffic accidents than drivers with normal colour vision; (c) this apparent contradiction is due to psychological compensation mechanisms. The practical conclusions are: (a) that persons with defective colour vision need not to be excluded from non professional road traffic; (b) that it is nevertheless useful that they should be aware of their handicap; (c) that the red traffic signal has to be larger than the other ones; and (d) that the stop and red position lights of vehicles must be sufficiently intense and that the filters transmitting only pure red should be avoided in them.     

The C-100:a new dichotomiser of colour vision defectives

This paper evaluates a new instrument (C-100) which employs flicker photometry or silent substitution to determine the type of colour vision defect (protan or deutan). Specifically, this study addresses the unit's capacity to: 1. detect colour vision defects; 2. differentiate protans from deutans; and 3. produce reliable measurements under different viewing conditions. We find that an average of five readings enables protans to be clearly separated from deutans in all cases (p < 0.0001), but that the distinction between these groups and normals is less clear. Dichromats are not distinguished from anomalous trichromats, so the instrument cannot be used as an index of severity. The results are shown to be robust to most of the test conditions likely to be encountered during normal clinical use. A clinical protocol is suggested that utilises the C-100 for classification of colour defective observers. It is concluded that normal, and some anomalous, trichromat settings are performed using flicker photometry, whereas dichromatic observers appear to utilise silent substitution.     

Repeatability of the C‐100 colour vision test

Background: The C‐100 colour vision test has been shown to have a high validity for diagnosing the type of red‐green colour vision defect, however, there is little information on the repeatability of the test. This study examines the repeatability of the C‐100 in classifying the colour vision defect as either protan or deutan. Methods: The C‐100 was administered on two occasions to 58 subjects with congenital red‐green colour vision defects: The sessions were separated by a minimum period of 10 days. Results: The repeatability of the C‐100 was high with a kappa coefficient of agreement for diagnosis of 0.96. The few discrepancies were misclassifying protans as deutans. Conclusion: The C‐100 is a highly repeatable test in terms of separating protans from deutans. However, if a discrepancy occurs, it is more likely to be a protan misclassified as a deutan rather than vice versa.     

Colour blindness does not preclude fame as an artist: celebrated Australian artist Clifton Pugh was a protanope

Purpose: The aim was to make a posthumous diagnosis of the abnormal colour vision of the acclaimed artist Clifton Pugh and to analyse his use of colours to discern the strategies he used to overcome his limited colour perception. Methods: A pedigree of Pugh's family was constructed by searching public records. Pugh had no daughters but he had two older brothers, one of whom was still living. We tested the colour vision of this brother and one of his daughters and one of his grandsons. Three children of the other brother were questioned about the colour vision of their father and one daughter was tested for heterozygosity with the Medmont C100. Four observers with normal colour vision categorised the colours used by Pugh in a sample of 59 of his paintings. Protanopic transformations of some of these paintings were made using the Vischeck algorithms to gain an appreciation of how Pugh saw his own paintings. The validity of the transformations was tested by asking a protanope to report if the transformations looked the same as the normal colour images of 10 of Pugh's paintings. Results: Pugh's brother was a severe protan. His daughter showed Schmidt's sign and was a carrier of the protan gene and her son was a protanope. The oldest brother was reported as having normal colour vision. Therefore, it is almost certain that Clifton Pugh was a protanope. Pugh used all colours in his paintings but preferred to structure them on brown, black and blue or, for high key paintings, on cream or flesh colours. He used greens and purples sparingly. The protanopic Vischeck transformations did not always look the same as the normal colour image for the protanope observer. Conclusion: A severe colour vision deficiency does not preclude success as a painter. It is a handicap but there are strategies artists can use to overcome it.     

Diagnosing protan heterozygosity using the Medmont C‐100 colour vision test

Background : A surprisingly high 15 per cent of women in Caucasian societies are carriers of the genes for abnormal colour vision but there is no clinical method to identify them. It has long been known that heterozygotes for the protan colour vision deficiencies can demonstrate a reduced luminous sensitivity to red light. This is known as Schmidt's sign, which is thought to arise from mosaicism (Lyonisation). The Medmont C‐100 colour vision test measures relative spectral sensitivity using flicker photometry to differentiate protans and deutans. It should be able to diagnose Schmidt's sign. Method : We tested six known protan heterozygotes (four whose sons have a protan colour vision deficiency and two whose fathers are protan) with the Medmont C‐100 test. Results : All six heterozygotes made average settings of ‐1.75 or more negative at the Medmont C‐100 test, settings which are at or beyond the boundary of the distribution of settings made by observers with normal colour vision. There have been two previous cases reported in the literature of protan heterozygotes, who made protan settings on the Medmont C‐100 or its predecessor test, the OSCAR. We also tested six daughters of the known heterozygotes, 50 per cent of whom are likely to be heterozygotes. Four of the six (66 per cent) made protan settings on the Medmont C‐100. The other two made normal 0.0 settings. Conclusion : We conclude that the Medmont C‐100 can be used clinically to diagnose carriers of protan colour vision deficiency.     

Protan colour vision deficiency and road accidents

Background : Protans are precluded from holding a commercial driver's licence in Australia because they have a substantially reduced ability to see red lights and have more road accidents involving signal lights. This exclusion has been in place since 1994 but is likely to be abandoned following a current review of medical standards for commercial drivers. This paper reviews the level of risk of road accidents due to protan colour vision deficiency. It also addresses the question of whether it is fair to regard all protans as having a higher risk of road accident because some protans might have a sensitivity to red light that is as good as that of some people with normal colour vision. Methods : Data of two studies by Verriest and co‐workers are re‐analysed to estimate the degree of overlap of the protan and colour normal distributions of sensitivity to red light. Results : Field trial data show that protans have a very reduced visual range for red signals compared to colour normal observers but there is considerable variability among both classes of observers and the distributions do overlap. However, some variability is due to differences in observers' choices of a detection criterion, their speed of response and the measurement method. A laboratory study of the spectral sensitivity of protan and colour normal subjects that largely removes these sources' variability shows that all protans have a sensitivity to red light that is less than that of the least sensitive colour normal. Conclusion : It is reasonable to conclude that all protans, regardless of the severity of their defect, have a lesser ability to see red signals than colour vision normal observers and for that reason will have a higher risk of road accident.     

Impairment of colour contrast sensitivity and neuroretinal dysfunction in patients with symptomatic HIV infection or AIDS.

Ophthalmic and neurological complications are frequent findings in patients with AIDS. Little is known about neuroretinal dysfunction in patients with HIV infection. The purpose of this study was to measure and evaluate colour vision in patients with HIV infection or AIDS. Colour contrast sensitivity tests were performed on 75 patients (150 eyes) in different stages of HIV infection. A highly sensitive computer graphics system was used to measure tritan, deutan, and protan colour contrast thresholds. Patients were classified into three clinical groups: (a) asymptomatic HIV infection, (b) lymphadenopathy syndrome or AIDS-related complex, and (c) AIDS. Overall, tritan (p < 0.0001), deutan (p = 0.003), and protan (p = 0.009) colour contrast sensitivities were significantly impaired in patients with HIV infection compared with normal controls. Colour thresholds in patients with asymptomatic HIV infection (mean tritan threshold: 4.33; deutan: 4.41; protan: 3.97) were not impaired compared with normal controls. Colour vision was slightly impaired in patients with lymphadenopathy syndrome or AIDS-related complex (tritan: 6.25 (p < 0.0001); deutan: 4.99 (p = 0.02); protan: 4.45 (p = 0.05)). In patients with AIDS the impairment was even more marked (tritan: 7.66 (p < 0.0001); deutan: 5.15 (p < 0.0009); protan: 4.63 (p = 0.004)). Analysis of covariance controlling for age demonstrated a close association between impairment of tritan colour contrast sensitivity and progression of HIV disease (p < 0.0001). Following Köllner''s rule, our study suggests that neuroretinal dysfunction occurs in patients with symptomatic HIV infection or AIDS. This is emphasised by the finding that the relative impairment in tritan vision compared with deutan/protan vision might reflect the difference in the number of cones or receptive fields. Measurement of tritan colour contrast sensitivity appears to be an appropriate and easily applicable method to detect early neuroretinal dysfunction in patients with HIV disease.     

Normality of colour vision in a compound heterozygous female carrying protan and deutan defects

Background: Inherited red‐green colour vision defects are quite common, affecting one in 12 males, but are less common in women, affecting about one in 250. Because red‐green defects are X‐linked, nearly 15 per cent of females are heterozygous carriers of red‐green colour deficiency. In addition, about one in 150 females are ‘double carriers’, where both of their X chromosomes have L/M gene arrays encoding a red‐green defect. If a woman carries the same type of colour vision defect on each X‐chromosome, she will be red‐green colour deficient, whereas if she carries opposing defects (protan versus deutan) on each X chromosome, she will have normal colour vision, owing to the process of X‐inactivation. These women are referred to as compound heterozygotes, though very few have been reported. Questions remain about whether the colour vision capacity of these women is comparable to that of ‘normal’ trichromats. Methods: We examined a compound heterozygote carrier of both protanopia and deuteranomaly. We also examined male members of her family representing both forms of red‐green defect carried by the female proband. Complete colour vision testing was done, including Rayleigh matches, pseudoisochromatic plates, unique hue measurements and 100‐Hue tests. Flicker‐photometric ERG estimates of L : M cone ratio were obtained, as were Medmont C100 settings. Results: Genetic analyses provided direct confirmation of compound heterozygosity. The compound heterozygote showed Schmidt's sign, consistent with an extreme skew in her L : M cone ratio and usually associated with protan carrier status. Conclusion: Apart from Schmidt's sign, we found the colour vision of the compound heterozygote to be indistinguishable from that of a normal trichromat.     

Color vision in relation to age: a study of normal values]

BACKGROUND: It is difficult to quantify thresholds in most colour vision tests, and this is especially the case for tritan hues, where a strong age-related increase of threshold has been reported. With the development of computer-graphic methods it is possible to remove brightness clues caused by lens absorption. This study attempts to give normative values for colour contrast thresholds and assess the age related changes therein. PATIENTS AND METHODS: 115 patients aged between 6 & 71 years were tested for central and peripheral colour contrast sensitivity. No patient had any systemic or eye disease. As a preliminary, heterochromatic flicker balance between the luminosities of the R and G and B and G phosphors was established, so that all colours subsequently generated were isoluminant for the person tested. Then, using a modified binary search technique, colour contrast thresholds were established using both 2 degree optotypes, for central vision, and a ring, 12.5 degrees in radius for peripheral vision. In the latter case, the observer had to name the position of the missing quadrant in the ring. Stimuli were presented for 200 msec at 1 Hz. Colours were modulated on protan, deutan or tritan colour axis. RESULTS: No correlation between age and central colour vision thresholds was observed. By contrast a significant but only minor increase of peripheral colour vision threshold was observed for the peripheral protan and tritan axis. DISCUSSION: The present system removes luminance clues from colour vision tests and permits both central and peripheral retina to be tested. The results are simple in that the influence of age can be neglected. The variability of threshold results is small, and it is easy to detect the relatively large changes associated with disease. Since high-quality monitors are standardised and calibrated, providing the stimulus parameters described are adhered to, the results given here for upper limits of normal may be used for other similar systems.     

Anomaloscope examination: scotopization (the luminance fall).

PURPOSE: The evaluation of a criterion for the detection of pathologic scotopization in routine anomaloscope examination. METHODS: Fifty congenital protan subjects, 50 congenital deutan subjects, 30 autosomal recessive congenital achromats, and 25 (44 eyes) acquired type I red-green defective subjects were selected. The anomaloscope examination was according to the Linksz procedure. The luminance fall was calculated as the slope quotient SQ: Y units luminance fall per X units width of the matching range. RESULTS: The mean SQ was -0.01 for congenital deutan subjects, -0.40 for congenital protan subjects and -1.30 for congenital achromats. There was no overlap between the three groups. Pathologic scotopization was found in 98% of the eyes presenting with an acquired type I colour vision defect. CONCLUSION: Calculation of the slope quotient SQ is helpful for the detection of pathologic scotopization in acquired colour vision deficiency.     

Abnormal colour vision is a handicap to playing cricket but not an insurmountable one

Background: Two studies have reported that abnormal colour vision is under‐represented among cricketers, presumably because cricketers with abnormal colour vision have difficulty seeing the red ball against the green grass of the cricket field and the green foliage around it. We have previously reported on the difficulties of five cricketers with abnormal colour vision but we have also reported that one of Australia’s finest cricketers was a protanope. This survey was undertaken to confirm the under‐representation of abnormal colour vision among cricketers and to ascertain whether those playing tend to be (1) those with a mild colour vision deficiency, (2) bowlers rather than batsman and (3) prefer to field close to the batsman rather than in the outfield. Methods: The colour vision of 293 members of seven Melbourne Premier cricket clubs was tested using the Ishihara test. Those who failed were examined further to confirm their abnormal colour vision, to assess its severity with the Farnsworth D15 test and to classify it as either protan or deutan using the Medmont C100 test. A questionnaire about cricketing ability and problems playing cricket was administered. Results: Twenty‐six (8.9 per cent) of the cricketers had abnormal colour vision, of whom six played in the First Grade (6.7 per cent of First Grade players). The proportion of cricketers with a severe deficiency was significantly less than expected for the First Grade players. There were only two protans. Bowlers were not over‐represented among the colour vision defective cricketers but those preferring to field close to the batsman were significantly over‐represented. Conclusion: Abnormal colour vision is a modest handicap to playing cricket, especially at the higher levels of the game. It may impede batting and the ability to field in the outfield.     

Does the Farnsworth D15 test predict the ability to name colours?

Background: The Farnsworth D15 test is designed to categorise colour vision deficiency as severe or moderate. The level of difficulty of the test was set so that those who passed it should be able to recognise surface colour codes, such as those used for electrical wiring. The test is widely used to provide advice to patients with abnormal colour vision and is often used for occupational selection when reliable recognition of surface colour codes is required. However, there has been only one previous study of the correlation between performance at the D15 test and the naming of surface colour codes and there has been no study of whether a person who passes the D15 can reliably name surface colours. Methods: One hundred and two people aged 11 to 65 years with abnormal colour vision were recruited from consecutively presenting optometric patients and were asked to name the colours of fabric, paint and cotton thread samples. There were 10 colours in each class of material and the samples were presented in a large (five to 10 degree angular subtense) and small size (2.5 deg and a single thread). The errors made were compared to those made by an age‐matched control group of equal size with normal colour vision. Results: The correlations between the Farnsworth D15 colour confusion index and colour naming errors were 0.62 for the large stimuli and 0.73 for the small stimuli. Its sensitivity and specificity identifymg those who made more errors than the worst performing colour normal person were 0.80 and 0.69 (large stimuli) and 0.75 and 0.71 (small stimuli). A Nagel anomaloscope range of less than 35 scale units provides essentially the same sensitivity and specificity. Conclusions: About 40 per cent of those with abnormal colour vision can name the main colours correctly under good visibility conditions. The D15 test is an imperfect predictor of those who can name surface colour codes correctly but it does provide useful information for general counselling. It is not suitable as a single test for occupational selection because it will pass 20 per cent who cannot name surface colours correctly and fail 30 per cent who can. In occupations in which recognition of surface colour codes is of critical importance, it may be best not to select people with abnormal colour vision because of the lack of a colour vision test that is a perfect predictor of the ability to recognise surface colours.     

Rapid measurement and machine learning classification of colour vision deficiency

Colour vision deficiencies (CVDs) indicate potential genetic variations and can be important biomarkers of acquired impairment in many neuro-ophthalmic diseases. However, CVDs are typically measured with tests which possess high sensitivity for detecting the presence of a CVD but do not quantify its type or severity. In this study, we introduce Foraging Interactive D-prime (FInD), a novel computer-based, generalisable, rapid, self-administered vision assessment tool and apply it to colour vision testing. This signal detection theory-based adaptive paradigm computed test stimulus intensity from d-prime analysis. Stimuli were chromatic Gaussian blobs in dynamic luminance noise, and participants clicked on cells that contained chromatic blobs (detection) or blob pairs of differing colours (discrimination). Sensitivity and repeatability of FInD colour tasks were compared against the Hardy–Rand–Rittler and the Farnsworth–Munsell 100 hue tests in 19 colour-normal and 18 inherited colour-atypical, age-matched observers. Rayleigh colour match was also completed. Detection and discrimination thresholds were higher for atypical than for typical observers, with selective threshold elevations corresponding to unique CVD types. Classifications of CVD type and severity via unsupervised machine learning confirmed functional subtypes. FInD tasks reliably detect inherited CVDs, and may serve as valuable tools in basic and clinical colour vision science.     

Vision evaluation in people with Down's syndrome

We tested the colour vision of 72 people with Down's syndrome using the Ishihara test and an anomaloscope. We found that 13 of the subjects, 6 males and 7 females, had defective colour vision according to Pickford's classification. In monocular vision 10 eyes were protan (five simple, three extreme and two deviant), one eye was simple deuteranomalous and the remaining eyes were normal: in binocular vision four of the subjects were protan (two simple and two deviant), two subjects were deutan (one simple and one deviant) and the rest were normal. Many of our subjects had lens opacities, strabismus, nystagmus, hypermetropia, high myopia and astigmatism, confirming literature reports. The contrast sensitivity function measured with the VCTS test showed a considerable toss of low-frequency sensitivity in our subjects compared to a normal population, which was more marked in the more severely impaired subjects.     

Colour rendering of indoor lighting with CIE illuminants and white LEDs for normal and colour deficient observers

The goal of this work was to evaluate the colour rendering of indoor lighting with CIE illuminants and white LEDs by estimating the chromatic diversity produced for normal and colour deficient observers. Reflectance spectra of a collection of scenes made of objects typically found indoors were obtained with hyperspectral imaging. Chromatic diversity was computed for 55 CIE illuminants and five LED light sources by estimating the number of different colours perceived in the scenes analysed. A considerable variation in chromatic diversity was found across illuminants, with the best producing about 50% more colours than the worst. For normal observers, the best illuminant was CIE FL3.8 which produced about 8% more colours than CIE illuminant A and D₆₅; for colour deficient observers, the best illuminants varied with the type of deficiency. When the number of colours produced with a specific illuminant was compared against its colour rendering index (CRI) and gamut area index (GAI), weak correlations were obtained. Together, these results suggest that normal and colour deficient observers may benefit from a careful choice of the illuminant, and this choice may not necessarily be based only on the CRI or GAI.     

The new Richmond HRR pseudoisochromatic test for colour vision is better than the Ishihara test

Aim: The Hardy‐Rand‐Rittler (HRR) pseudoisochromatic test for colour vision is highly regarded but has long been out of print. Richmond Products produced a new edition in 2002 that has been re‐engineered to rectify shortcomings of the original test. This study is a validation trial of the new test using a larger sample and different criteria of evaluation from those of the previously reported validation study. Methods: The Richmond HRR test was given to 100 consecutively presenting patients with abnormal colour vision and 50 patients with normal colour vision. Colour vision was diagnosed using the Ishihara test, the Farnsworth D15 test, the Medmont C‐100 test and the Type 1 Nagel anomaloscope. Results: The Richmond HRR test has a sensitivity of 1.00 and a specificity of 0.975 when the criterion for failing is two or more errors with the screening plates. Sensitivity and specificity become 0.98 and 1.0, respectively, when the fail criterion is three or more errors. Those with red‐green colour vision deficiency were correctly classified as protan or deutan on 86 per cent of occasions, with 11 per cent unclassified and three per cent incorrectly classified. All those graded as having a ‘mild’ defect by the Richmond HRR test passed the Farnsworth D15 test and had an anomaloscope range of 30 or less. Not all dichromats were classified as ‘strong’, which was one of the goals of the re‐engineering and those graded as ‘medium’ and ‘strong’ included dichromats and those who have a mild colour vision deficiency based on the results of the Farnsworth D15 test and the anomaloscope range. Conclusions: The test is as good as the Ishihara test for detection of the red‐green colour vision deficiencies but unlike the Ishihara, also has plates for the detection of the tritan defects. Its classification of protans and deutans is useful but the Medmont C‐100 test is better. Those graded as ‘mild’ by the Richmond HRR test can be regarded as having a mild colour vision defect but a ‘medium’ or ‘strong’ grading needs to be interpreted in conjunction with other tests such as the Farnsworth D15 and the anomaloscope. The Richmond HRR test could be the test of choice for clinicians who wish to use a single test for colour vision.     

Colour‐opponent mechanisms are not affected by age‐related chromatic sensitivity changes

The purpose of this study was to assess whether age‐related chromatic sensitivity changes are associated with corresponding changes in hue perception in a large sample of colour‐normal observers over a wide age range (n = 185; age range: 18–75 years). In these observers we determined both the sensitivity along the protan, deutan and tritan line; and settings for the four unique hues, from which the characteristics of the higher‐order colour mechanisms can be derived. We found a significant decrease in chromatic sensitivity due to ageing, in particular along the tritan line. From the unique hue settings we derived the cone weightings associated with the colour mechanisms that are at equilibrium for the four unique hues. We found that the relative cone weightings (w_L/w_M and w_L/w_S) associated with the unique hues were independent of age. Our results are consistent with previous findings that the unique hues are rather constant with age while chromatic sensitivity declines. They also provide evidence in favour of the hypothesis that higher‐order colour mechanisms are equipped with flexible cone weightings, as opposed to fixed weights. The mechanism underlying this compensation is still poorly understood.     

Colour vision defects in asymptomatic carriers of the Leber's hereditary optic neuropathy (LHON) mtDNA 11778 mutation from a large Brazilian LHON pedigree: a case-control study

AIMS: To determine if asymptomatic carriers from a previously identified large pedigree of the Leber's hereditary optic neuropathy (LHON) 11778 mtDNA mutation have colour vision deficits. METHODS: As part of a comprehensive analysis of over 200 members of a large Brazilian LHON pedigree spanning seven generations, colour vision tests were obtained from 91 members. Colour vision was tested one eye at a time using the Farnsworth-Munsell 100 (FM-100) hue colour vision test. The test was administered under uniform conditions, taking into account: ambient light levels, daylight colour temperature of 6700 kelvin, and neutral uniform background. Tests were scored using the FM-100 MS-Excel computer scoring program. Defects were determined and categorised as tritan, deutan, or protan. Categorisation of each dyschromatopsia was based on review of demonstrated axis computer generated plots and age adjusted error scores which coincided with Verriest 95% confidence intervals. Only the axis with the greatest magnitude error score was used to classify the defect. 55 of the 91 test subjects were LHON mtDNA 11778 J haplotype mutation carriers, proved by mtDNA analysis. The remaining 36 subjects were age matched non-blood relatives (off pedigree), who served as controls. RESULTS: 27 of 55 carriers (49.10%) were shown to have colour vision defects in one or both eyes. 13 of the 27 (48%) abnormal tests in the carrier group were tritan defects and the remaining 14 (52%) were deutan defects. Nine of the 27 (33%) abnormals in the carrier group were identified as having bilateral defects. Six of these were deutan, and the remaining three were tritan dyschromatopsias. Only six of the 36 (16.66%) age matched controls were found to have any type of dyschromatopsia. Five (83.3%) of these were deutan defects. The remaining one was a tritan defect. The difference between the two groups using a chi(2) test with one degree of freedom was statistically significant with a p value less that 0.001. CONCLUSIONS: Until now, LHON has always been characterised by a sudden, devastating vision loss. Asymptomatic carriers, those without vision loss, were considered unaffected by the disease. It now appears that asymptomatic carriers of the LHON mutation are affected by colour vision defects and may manifest other subtle, yet chronic, changes.     

Electronic Flight Information System displays and colour defective observers

The use of colour in the Electronic Flight Information System (EFIS) displays of modern commercial airliners has created an environment for pilots in which colour coding is used more extensively than previously. Therefore, more thorough diagnostic analysis of pilots' colour vision, before a full commercial licence is granted, has been proposed. The aim of the experiments reported here is to determine whether a reliable battery of diagnostic colour vision tests is able to predict the colour naming perforniarice of colour defective subjects when using Boeing 747–400 EFIS displays. Results show that observers with normal colour vision and those identified as hiing. mild deuteranomaly made significantly fewer errors than those with other types of defective colour vision. As protanomals, protanopes and more severe deitteranomals can only be identified reliably with a battery of colour vision tests, we propose that the lantern test be supplemented by other tests for aircrew colour vision testing.