Electrodiagnosis of red-green colour deficiency

The electroretinographic rapid off-response and the early receptor potential were studied in congenital red-green colour deficiency. The sensitivity of the rapid off-response was low in protans and high in deutans at long wavelengths, and high in protans and low in deutans at short or medium wavelengths, as compared with normal subjects. The ratio of the sensitivity at 480 nm to the sensitivity at 620 nm (S480/S620) was higher in all cases of protans and lower in all cases of deutans so far tested than in normal subjects. The amplitude of the rapid off-response to white stimulus light did not differ among normals, protans and deutans. The S480/S620 was abnormal in some protan-carriers, deutan-carriers and Farbenamblyopie. The mean amplitude of the early receptor potential (R2) was small in protans at long wavelengths, and small in deutans at short or medium wavelengths. A significant correlation was found between the amplitude ratio of the R2 and the sensitivity ratio of the rapid off-response at short and long wavelengths.     

Spectral characteristics of electroretinography in congenital red-green color blindness

There are few conclusive electroretinography (ERG) studies comparing the spectral characteristics in deutans and normals in contrast to protans and normals. The difficulties of research on deutans were thought to be due to problems in detecting the very slight differences in the spectral characteristics between deutans and normal subjects. To record monochromatic ERG responses accurately in deutans, our time-locked scanning method was improved as follows: We used 12 interference filters for stimulus lights with narrow half widths (4-6 nm) and wavelengths of peak transmission arranged at intervals of 10 nm between 520 nm and 600 nm. Each stimulus light was strictly adjusted to an equal energy and checked simultaneously with ERG recordings. Contact lens electrodes were reformed for comfortable fitting to subjects' corneas. The time interval between each stimulation was set at 300 msec and one scanning of all stimulations took only 3.9 sec. ERG bp-waves were recorded in congenital color blindness by scanning monochromatic light stimuli, and spectral responses obtained could be evaluated as a spectral pattern. Different spectral patterns of responses from those of normal subjects and shift of the peak in the spectral response curves were obtained for congenital color blind subjects. The maximal responses were recorded at around 540 nm in protans and at 570-580 nm in deutans under white adaptation. Differences in the response curves were not found between dichromats and anomalous trichromats. Moreover, selective chromatic adaptation disclosed the separate responses of green cone and red cone systems. In normal subjects the peak of the spectral response curves was shifted to around 540 nm by red adaptation and to around 580 nm by blue adaptation. The spectral patterns changed so that they looked like the patterns under white adaptation of protans and deutans, respectively. But in protans and deutans the same spectral response patterns and almost the same wavelengths of the peak in the spectral response curves as those obtained under white adaptation were recorded under chromatic adaptation. This method provides the possibility of differentiating between red and green color blind subjects and normal subjects by the ERG. Defects or marked abnormality in the red cone system in protans and the green cone system in deutans can also be detected. Monochromatic ERGs of deutans were recorded under more intense red adaptation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Electroretinographic off-response in congenital red-green color deficiency and its genetic carrier

The spectral sensitivity of the rapid off-response in the electroretinogram is found to be abnormal in all protans and deutans so far tested, and in some of their genetic carriers. The rapid off-response is an objective means of assessing the x-linked recessive color deficiencies and their carrier state.     

Empirical detection of congenital dyschromatopsia by electroretinography

The electroretinographic rapid off-response, composed mainly of the late receptor potential of cones, is found to be abnormal in all protans and deutans so far tested. The rapid off-response can thus be used as an objective measure in the diagnosis of congenital red-green colour defect.     

Spectrally selective flash early receptor potential (ERP) in dichromats

The human spectrally selective flash early receptor potential (ERP) was studied in 12 dichromats: 6 protanopes (12 eyes) and 6 deuteranopes (12 eyes). Color filters used were Kodak Wratten filters No.23A, No.57, and No.47 for the red, green, and blue flash ERPs, respectively. The ERP amplitude was measured between the summits of R₁ and R₂.Mean amplitudes of the red flash ERP and green flash ERP were highly significantly decreased in the protanopes (p < 0.001) and deuteranopes (p < 0.01) as compared with the corresponding data in 10 normal subjects (20 eyes). The mean amplitude of the blue flash ERP was significantly lower than normal (p < 0.001) in the deuteranopes. The mean ratio of the blue flash ERP amplitude to the red flash ERP amplitude showed a highly significant increase in the protanopes (p < 0.001) and a highly significant decrease in the deutoranopes (p < 0.001) compared with the mean ratio in the normal subjects, indicating a new, useful index for the objective clinical detection of congenital color defects.     

Cone interaction and color substitution as revealed by pattern ERG

Transient electroretinograms to a reversing color-contrast checkerboard pattern (P-ERG) were recorded in a protanomalous, a deuteranomalous, and a normal observer. Alternate monochromatic checks were of constant wavelength (630 rim. red - 531 nm green), while the relative energies were varied systematically. When changing the radiance ratio 630 nm-531 nm of the stimulus, the normal subject exhibited a P-ERG to all stimuli with only a relative amplitude minimum at a distinct radiance ratio, whereas the color-deficient observers failed to show a P-ERG at some color contrast 630 nm-531 nm, the radiance ratio of which was different in the protan and deutan. From the radiance ratio of color contrast for the smallest potential in the normal observer, we conclude that the green- and red-sensitive cone mechanism provides a difference signal which generates the response. The data from the color-deficient observer support the view that color discrimination in protans and deutans is reduced because the input of one type of photoreceptor is missing.     

Color Vision Defects with Variation in the Exon 5 of Red and Green Pigment Genes

Purpose : To investigate correlation of variation in the exon 5 of red and green pigment genes with color vision defects.Methods : Exon 5 of the red and green pigment genes in 11 protans, 19 deutans and 38 normal controls were analyzed by heteroduplux-SSCP analysis.Results : In all 11 protans and 8 of the 19 deutans, defects of the red or green pigment gene could be identified. The C polymorphism (A/C at codon 283) in green pigment gene was present in 8 of 44 trichromats and 5 of 24 dichromats. Specific electrophoretic bands were found in 2 normal controls and a deutan.Conclusions: Variation in the exon 5 of the red and green pigment genes is the most common cause for color vision defects. Heteroduplex-SSCP analysis is a suitable way in screening specific variation in visual pigment genes. Eye Science 1998; 14 : 130 - 133.     

Molecular basis of congenital color vision defects in Chinese patients.

Applying Southern blot hybridization, the structures of the red pigment gene (RPG) and the green pigment gene (GPG) were analyzed in 43 Chinese patients with red-green color vision defects, including 3 female cases of deuteranopia. The same analysis was carried out in 4 normal relatives and 3 carriers from 3 affected families, as well as in 11 normal controls. Among the 43 patients, abnormalities of the RPG were detected in all 19 protans, and abnormalities of the GPG were found in 14 of the 24 deutans. In about 80% of the protans and deutans, an alteration of exon 5 in RPG or GPG was discovered. All 19 protans had anomalous RPG and in one protan the normal RPG was replaced by a 5' red-3' green hybrid gene. However, no protans showed deletion of the whole RPG. Some deutans had no GPG; some had a 5' green-3' red hybrid gene with or without the GPG. The exon 5 of RPG and GPG was amplified by polymerase chain reaction (PCR) and the amplified fragments were further analyzed by RsaI digestion. The results of PCR were identical to those of nucleic acid hybridization. PCR will be a useful tool in prenatal diagnosis and genetic counseling.     

Abnormal spectral sensitivity of the electroretinographic off-response in protanopia and protanomalia

The mean of the spectral sensitivity of the rapid off-response in the ERG is significantly lower at 560 nm and longer wavelengths (p < 0.005) in protanopia and protanomalia, as compared with normal control subjects.     

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.     

Spectral characteristics of rapid off-response in congenital deuteranomaly in one of monozygotic female twins

The spectral sensitivity of the rapid off-response in the electroretinogram was studied in monozygotic female twins. One case was diagnosed as congenital deuteranomaly, and the other was normal. The log ratio of the sensitivity at 480 nm to the sensitivity at 620 nm (log S480/S620) was within the deutan range in the first case and within the normal range in the second. The two cases were determined to be different at the retinal receptor level by study of the rapid off-response. This result of the rapid off-response was consistent with the results of the psychophysical examinations.     

Intensity functions of the early receptor potential and of the melanin fast photovoltage in the human eye

The early potential of the human eye is studied for a wide range of flash intensities, inducing early potentials from 0.3 to 1700 μV in amplitude. The ERP in response to white flashes begins with a cornea positive component (R₁) followed by a larger negative wave (R₂). On repetitive stimulation the ERP amplitude is progressively reduced. From the decrement of R₂ to the three first flashes it can be estimated that the destruction of 10% of the visual pigment of the dark-adapted eye produces an ERP of about 65 πV. The relation between the flash intensity and the amplitude of the early potential is linear from 0.3 (measured by averaging) to 140 μV. For higher values its amplitude is progressively saturated. An FPV of more than 100 μV amplitude leaves after bleaching an appreciable residual potential, which can be considered as a melanin FPV.     

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.     

The inter- and intraindividual variations of the early receptor potentials (ERP)

The inter- and intraindividual variations in the ERP were investigated and both shown to be remarkably large in the R₂ amplitude — like the other components (amplitudes) of the ERG. There are no evident variations in the peak time of R₂.     

Wavelength sensitivity of the two components of the early receptor potential (ERP) of the human eye

The ERP of the human eye is studied for violet, blue, green, yellow and red flashes produced with absorption filters. For isoenergetic flashes the amplitude of R₁ and of R₂ is maximum for the green flash. The R₁R₂ ratio however increases progressively from 0 to 13 from violet to red flashes. The dark-adaptation half-time of R₂ is 210 sec for violet flashes, suggesting a dominant rod contribution for this color, 90 sec for red flashes, indicating a dominant cone contribution, and 135 sec for green flashes, corresponding to a mixed origin. The dark-adaptation half-time of R₁ is about 100 sec, whatever the wavelength of the flash, which suggests a cone origin for this wave in the human eye.     

Computerized color-vision test based upon postreceptoral channel sensitivities

An automated, computerized color-vision test was designed to diagnose congenital red-green color-vision defects. The observer viewed a yellow appearing CRT screen. The principle was to measure increment thresholds for three different chromaticities, the background yellow, a red, and a green chromaticity. Spatial and temporal parameters were chosen to favor parvocellular pathway mediation of thresholds. Thresholds for the three test stimuli were estimated by four-alternative forced-choice (4AFC), randomly interleaved staircases. Four 1.5-deg, 4.2 cd/m2 square pedestals were arranged as a 2 x 2 matrix around the center of the display with 15-minute separations. A trial incremented all four squares by 1.0 cd/m2 for 133 ms. One randomly chosen square included an extra increment of a test chromaticity. The observer identified the different appearing square using the cursor. Administration time was approximately 5 minutes. Normal trichromats showed clear Sloan notch as defined by log (deltaY/deltaR), whereas red-green color defectives generally showed little or no Sloan notch, indicating that their thresholds were mediated by their luminance system, not by the chromatic system. Data from 107 normal trichromats showed a mean Sloan notch of 0.654 (SD = 0.123). Among 16 color-vision defectives tested (2 protanopes, 1 protanomal, 6 deuteranopes, & 7 deuteranomals), the Sloan notch was between -0.062 and 0.353 for deutans and was < -0.10 for protans. A sufficient number of color-defective observers have not yet been tested to determine whether the test can reliably discriminate between protans and deutans. Nevertheless, the current data show that the test can work as a quick diagnostic procedure (functional trichromatism or dichromatism) of red-green color-vision defect.     

Responses of Postreceptoral Pathways Elicited by L- and M-Cone Isolating ON- and OFF-Electroretinograms in Glaucoma Patients

PurposeTo compare the electroretinographical (ERG) responses elicited by L- and M-cone isolating ON- and OFF-sawtooth stimuli in normal subjects and glaucoma patients.MethodsTwenty-one normal subjects and 44 primary open-angle glaucoma patients participated in the study. L- and M-cone isolating (18% cone contrast; 284 cd/m²) rapid ON- and rapid OFF-sawtooth (4 Hz) stimuli with two stimulus sizes (full-field (FF) and central 70° diameter) were generated using the triple silent substitution technique. ON- and OFF-response asymmetries were studied by adding the two (to obtain L-add and M-add responses). The initial positive (P) and subsequent late negative (LN) components of the L-add and M-add ERGs were compared between the subject groups and correlated with retinal nerve fiber layer thickness (RNFLT) and pattern ERG responses.ResultsThe responses to L-ON and to M-OFF stimuli and vice versa resembled each other particularly with 70° stimuli. The P_L-add amplitudes were not significantly different between the normal subjects and glaucoma patients, whereas the LN_L-add amplitude was significantly (P < 0.01) smaller in the glaucoma patients. Both P_M-add and LN_M-add were not significantly different between the subject groups. The PERG amplitude with 0.8° check sizes and the 0.8°/16° amplitude ratio (PERG ratio) were significantly (P < 0.05) different between the subject groups. The 70° LN_L-add amplitude and the 0.8° PERG amplitude were significantly correlated with RNFLT.ConclusionsThe ERGs to 70° cone isolating sawtooth stimuli reflect cone opponency. The cone opponent ERG responses were not significantly different between glaucoma patients and normal subjects. Luminance driven L-add responses were significantly different, indicating that central luminance signals are mainly affected in glaucoma.     

Three cone mechanisms in the primate electroretinogram: two with, one without off-center bipolar responses

We have used ganzfeld stimulation, selective chromatic adaptation and computer averaging to identify three cone mechanisms in the corneal ERG of the macaque monkey. On a strong yellow background, two cone mechanisms can be distinguished. One has a peak spectral sensitivity near 460 nm with a relatively slow b-wave to light onset and a negative wave at offset. This response is transiently reduced after a yellow background is extinguished. The second has its peak near 560 nm with a quicker b-wave at onset and a positive wave (d-wave) at offset. On a strong blue background, the ERG appears univariant from 400 to 600 nm but not at longer wavelengths (640 nm). An even brighter blue background reduces the ERG to most of the spectrum but has almost no affect on the 640 nm response. Adding an additional red background greatly reduces the 640 nm response without significantly influencing the responses to the rest of the spectrum. By Granit's terminology, the cone ERG appears to be composed of an E-like ERG of short wave cones and an I-like ERG of at least two other cone mechanisms. The difference between E and I ERGs may be due to the absence or presence, respectively, of an off-center bipolar system. The intravitreal injection of 2-amino-4-phosphonobutyric acid (APB) supports this hypothesis. APB eliminates the b-wave of all three cone ERGs and the negative off-response of the S cone ERG but releases the positive off-response of the other cone ERGs.     

On- and off-responses in the photopic electroretinogram in complete-type congenital stationary night blindness

We examined the on- and off-responses of the photopic electroretinogram in patients with complete congenital stationary night blindness. Standard flash electroretinograms as well as those produced in a ganzfeld modified for long-duration light stimuli (500 msec) permitted the separation of on- and off-responses in four patients and four normal subjects. The amplitude and latency of the electroretinogram on- response (a- and b-waves) and off-response (d-wave) in addition to the oscillatory potentials of the off-response in normal subjects and patients were compared. The abnormal on-response was demonstrated in all the patients, and the offresponse with its oscillatory potentials were preserved. We showed that the second portion of the off-response (of inner retinal origin) is normal. If congenital stationary night blindness is a defect of depolarizing bipolar cells, these results preclude input of the depolarizing bipolar cells and support the hyperpolarizing bipolar cells as the cellular origin of the off-response electroretinogram.     

Red light increment threshold as a measure of deficient color vision.

PURPOSE: People with deficient red/green color vision have both poor color discrimination and are also insensitive to colored lights, especially red, in an increment threshold situation. In this study we compare detection thresholds for a long wavelength increment to two standard color discrimination tests. METHODS: Forty-five color normal subjects and 19 color-deficient subjects (CDs) (12 deutans, 4 protans, and 3 unclassified) were tested with the Hardy-Rand-Rittler (HRR) plate test (4th edition), Farnsworth D-15 arrangement test and a long wavelength increment threshold test, i.e., the red test. RESULTS: All CDs were less sensitive to the red increment than any of the normal subjects. The red test identified all CDs. There were no significant correlations between the red test results and the HRR test or the Farnsworth D-15 test. CONCLUSIONS: The red test measures red light increment threshold, a characteristic of color vision not assessed by conventional tests of color vision which are based upon measuring loss of color discrimination. All CD observers have raised red light increment thresholds and the test clearly differentiates CD observers from those with normal color vision.