Colour Vision Impairment in Young Alcohol Consumers.

Alcohol consumption among young adults is widely accepted in modern society and may be the starting point for abusive use of alcohol at later stages of life. Chronic alcohol exposure can lead to visual function impairment. In the present study, we investigated the spatial luminance contrast sensitivity, colour arrangement ability, and colour discrimination thresholds on young adults that weekly consume alcoholic beverages without clinical concerns. Twenty-four young adults were evaluated by an ophthalmologist and performed three psychophysical tests to evaluate their vision functions. We estimated the spatial luminance contrast sensitivity function at 11 spatial frequencies ranging from 0.1 to 30 cycles/degree. No difference in contrast sensitivity was observed comparing alcohol consumers and control subjects. For the evaluation of colour vision, we used the Farnsworth-Munsell 100 hue test (FM 100 test) to test subject's ability to perform a colour arrangement task and the Mollon-Reffin test (MR test) to measure subject's colour discrimination thresholds. Alcohol consumers made more mistakes than controls in the FM100 test, and their mistakes were diffusely distributed in the FM colour space without any colour axis preference. Alcohol consumers also performed worse than controls in the MR test and had higher colour discrimination thresholds compared to controls around three different reference points of a perceptually homogeneous colour space, the CIE 1976 chromaticity diagram. There was no colour axis preference in the threshold elevation observed among alcoholic subjects. Young adult weekly alcohol consumers showed subclinical colour vision losses with preservation of spatial luminance contrast sensitivity. Adolescence and young adult age are periods of important neurological development and alcohol exposure during this period of life might be responsible for deficits in visual functions, especially colour vision that is very sensitive to neurotoxicants.

Influence of retinopathy on the achromatic and chromatic vision of patients with type 2 diabetes.

BACKGROUND: Luminance contrast sensitivity and colour vision are considered to have great predictive value in the evaluation of type 2 diabetic retinopathy. However, these two visual characteristics have seldom been investigated in the same group of patients. In the present study we measured contrast sensitivity and colour vision in a group of patients with type 2 diabetes and correlated the results with estimates of common metabolic markers for the disease. A subgroup of the patients had no clinical signs of retinopathy. METHODS: The vision of 27 patients (n = 50 eyes) with type 2 diabetes, with retinopathy (n = 20 eyes), or without retinopathy (n = 30 eyes) were evaluated using two psychophysical tests, the Farnsworth-Munsell 100 hue test (FM 100), and measurements of the luminance contrast sensitivity at 11 spatial frequencies. The results were compared with measurements obtained from an age-matched control group (n = 32), and were correlated with the level of glycated haemoglobin, glycaemic level, and time of disease onset. Signs of retinopathy were identified during the ophthalmological examinations. RESULTS: Contrast sensitivity and colour vision impairments were present at different levels in diabetes patients. Eyes with retinopathy showed more severe vision loss than eyes without retinopathy. The FM 100 test was more sensitive for separation of patients from controls. Colour vision loss had no colour axes preference. The contrast sensitivity test appeared to have some advantage in differentiating patients with retinopathy from patients without retinopathy. CONCLUSIONS: Both methods can be useful to follow the visual function of diabetic patients and should be used together to discriminate patients from controls, as well as to identify early signs of retinal damage.

Evidence for two types of lateral interactions in visual perception of temporal signals.

The aim of this work was to investigate the mechanisms of lateral interactions involved in flicker perception. Furthermore, the spatial properties of the monoptic and dichoptic components of these mechanisms were studied. We quantified the perceived flicker strength (PFS) in the center of a test stimulus, which was simultaneously modulated with a surround stimulus of variable size. The modulation depth of a separate stimulus, identical to the center test stimulus but without the surround, was determined using a two-alternative forced choice procedure. Using LCD goggles synchronized to the frame rate of a CRT screen, the center and surround of the test stimulus were presented either monoptically or dichoptically. In the monoptic condition, center-surround interactions have subcortical and cortical origins. In the dichoptic condition, center-surround interactions must have a cortical origin. The difference between the dichoptic and the monoptic data is an estimate of the contribution of the subcortical mechanisms. At each condition (surround stimulus size; monoptic or dichoptic presentation), the PFS was measured for phase differences between center and surround stimuli. The PFS changed systematically with phase difference. It also was observed that the PFS in the center stimulus changed merely be the presence of a surround stimulus independently of the center-surround phase difference. We propose that this is a phase-independent mechanism related to contrast adaptation owing to the presence of surround modulation. Our data suggest that both phase-dependent and -independent mechanisms have cortical and subcortical origins. There were no systematic differences between the spatial properties of subcortical and cortical components involved in PFS modulation.

Spatial distributions of on- and off-responses determined with the multifocal ERG.

We studied the contribution of retinal on and off-mechanisms in the multifocal electroretinogram (mfERG) by measuring responses to saw tooth stimuli. Six healthy subjects participated in this study. Rapid-on and rapid-off sawtooth stimuli with a period of 427 ms were presented in a multifocal pattern composed of 19 hexagons. The stimuli were interleaved with a blank field of the mean luminance and chromaticity. On- and off-responses were added to extract response asymmetries. The amplitudes of on-, off-, and added-responses were determined for different eccentricities relative to a signal baseline that was defined as the average of the electrical level recorded in two different time windows in which no responses were present. Measurements were repeated with eight different stimulus stretch factors to account for changes in retinal cell density as a function of eccentricity. The amplitudes of all ERG components decreased with increasing eccentricity for all stretch factors. For stretch factors between 0 and 20, responses to the central and immediately adjacent hexagons were large in amplitude. For more peripheral hexagons, the responses were very small or absent. Three components were identified in the on-responses (N20(on), P46(on) and N100(on)). In the offresponses, we found one positive (P20(off)) and one negative (N90(off)) component, whereas in the addition, three components (N20(add), P46(add) and N100(add)) could be observed. The N20(on) and P46(on) amplitudes decreased less steeply with eccentricity than the N100(on) amplitude, whilst the P20(off) and N90(off) amplitudes exhibited a similar decrease with eccentricity. In the addition, the two negative components exhibited a similar decrease in amplitude as a function of eccentricity and decreased more steeply than the positive component. The number of stimulated cones and retinal ganglion cells was estimated from anatomical data and compared with the responses. The spatial properties of the amplitudes of N20(on), P46(on), P20(off), and N90(off) and P46(add) were similar to those of the stimulated cone numbers. The remaining components had spatial characteristics that resembled those of the retinal ganglion cells. It is proposed that the ERG asymmetries revealed in the summed responses have post-receptoral origins, some of them reflecting the activity of the ganglion cell population. The use of sawtooth stimuli provide, similar to the pattern ERG, a way to record the ERG asymmetries.

Rod bipolar cells in the retina of the capuchin monkey (Cebus apella): characterization and distribution.

Rod bipolar cells in Cebus apella monkey retina were identified by an antibody against the alpha isoform of protein kinase C (PKCalpha), which has been shown to selectively identify rod bipolars in two other primates and various mammals. Vertical sections were used to confirm the identity of these cells by their characteristic morphology of dendrites and axons. Their topographic distribution was assessed in horizontal sections; counts taken along the dorsal, ventral, nasal, and temporal quadrants. The density of rod bipolar cells increased from 500 to 2900 cells/mm2 at 1 mm from the fovea to reach a peak of 10,000-12,000 cells/mm2 at 4 mm, approximately 5 deg of eccentricity, and then gradually decreased toward retinal periphery to values of 5000 cells/mm2 or less. Rod to rod bipolar density ratio remained between 10 and 20 across most of the retinal extension. The number of rod bipolar cells per retina was 6,360,000 +/- 387,433 (mean +/- s.d., n = 6). The anti-PKCalpha antibody has shown to be a good marker of rod bipolar cells of Cebus, and the cell distribution is similar to that described for other primates. In spite of the difference in the central retina, the density variation of rod bipolar cells in the Cebus and Macaca as well as the convergence from rod to rod bipolar cells are generally similar, suggesting that both retinae stabilize similar sensitivity (as measured by rod density) and convergence.

Color discrimination ellipses of trichromats measured with transient and steady state visual evoked potentials.

The purpose of this work is to investigate the use of different forms of visual evoked potentials (VEPs) to measure color discrimination thresholds and to plot color discrimination ellipses (MacAdam, 1942). Five normal trichromats (24.5 +/- 2.6 years-old) were monocularly tested. Stimuli consisted of sinusoidal isoluminant chromatic gratings made from chromaticity pairs located along four different color directions radiating from one reference point of the CIE 1976 chromaticity diagram (u' = 0.225; v' = 0.415). Heterochromatic flicker photometry (HFP) was used to obtain the isoluminance condition for every subject and for all chromaticity pairs. VEPs were elicited using two cycles per degree grating stimuli at three different temporal configurations: transient, onset (300 ms)/offset (700 ms), 1 Hz fundamental frequency; steady-state, onset (50 ms)/offset (50 ms), 10 Hz fundamental frequency; and steady-state pattern reversal at 5 Hz fundamental frequency (10 Hz phase reversal). VEP amplitude was measured using transient VEP N1-P1 components and steady state VEP first (10 Hz) and second (20 Hz) harmonics. VEP amplitude was plotted as a function of chromatic distance in the CIE 1976 color space and the data points were extrapolated to zero amplitude level to obtain chromatic discrimination thresholds. The results were compared with psychophysical measurements performed using the same stimulus configurations and with the pseudoisochromatic method of Mollon-Reffin (one-way ANOVA). For all subjects and all stimulation methods, the ellipses showed small sizes, low ellipticities, and were vertically oriented. Despite some consistent differences in the results obtained with different procedures, there was no statistical difference between ellipses obtained electrophysiologically and psychophysically. For steady state VEPs, ellipses obtained from second harmonic amplitudes were larger and more elongated in the tritan direction than those obtained with first harmonic amplitudes.

Normal and dichromatic color discrimination measured with transient visual evoked potential.

It would be informative to have an electrophysiological method to study, in an objective way, the effects of mercury exposure and other neurotoxics on human color vision performance. The purpose of the present work was to study human color discrimination by measuring chromatic difference thresholds with visual evoked potential (VEP). Six young normal trichromats (24 +/- 1 years old) and one deutan (26 years old) were tested. The stimuli consisted of sinusoidal isoluminant chromatic gratings made from chromaticity pairs located along four different color directions centered on two reference points. Heterochromatic flicker photometry (HFP) protocol was used to obtain the isoluminance condition for every subject and for all chromaticity pairs. Spatial frequency was 2 cycles/deg. Presentation mode comprised onset (300 ms)/offset (700 ms) periods. As previously described, we found a negative deflection in the VEP which was related to the chromatic difference: as chromatic difference increased, amplitude increased and latency decreased. VEP response amplitude was plotted against distance in the CIE 1976 color space between the grating chromaticities and fitted with a regression line. We found color thresholds by extrapolating the fitting to null amplitude values. The thresholds were plotted in the CIE 1976 color space as MacAdam ellipses. In normal trichromats the ellipses had small size, low ellipticity, and were vertically oriented. In the deutan subject, the ellipses had large size, high ellipticity, and were oriented towards the deutan copunctal locus. The VEP thresholds were similar to those obtained using grating stimuli and psychophysical procedures, however smaller than those obtained using pseudoisochromatic stimuli (Mollon-Reffin method). We concluded that transient VEP amplitude as a function of contrast can be reliably used in objective studies of chromatic discrimination performance in normal and altered human subjects.

Visual impairment on dentists related to occupational mercury exposure.

A detailed assessment of visual function was obtained in subjects with low-level occupational mercury exposure by measuring hue saturation thresholds and contrast sensitivity functions for luminance and chromatic modulation. General practice dentists (n=15) were compared to age-matched healthy controls (n=13). Color discrimination estimated by the area of Mac Adam ellipses was impaired, showing diffuse discrimination loss. There was also reduction of contrast sensitivity for luminance and chromatic (red-green and blue-yellow) modulation, in all tested spatial frequencies. Low concentrations of urinary mercury (1.97±1.61µg/g creatinine) were found in the dentists group. Color discrimination as well as contrast sensitivity function, assessed psychophysically, constitutes a sensitive indicator of subtle neurotoxic effect of elemental mercury exposure.

Color vision loss in patients treated with chloroquine

Patient that make use of chloroquine or hydroxychloroquine, drugs which are frequently administered for treatment of rheumatoid arthritis, lupus erithromatosus or malaria, may suffer alterations in color vision and in contrast sensitivity. The present work evaluates the visual functions of these patients in a joint study of the University of São Paulo (USP), in São Paulo, and of the Federal University of Pará (UFPA), in belém. Thirty two chloroquine user patients without alterations in the eye fundus exam were evaluated in São Paulo (n=10; aged 38 to 71 years; mean=55,8 years) and in Belém (n=22; aged 20 to 67; mean=40 years). The described accumulated chloroquine dose was 45 to 430g (mean=213g; as=152g) for the São Paulo group, and 36 to 540g (mean=174g; sd=183g) for the Belém group. Tests were performed monocularly corrected eye refractive state. Color discrimination was evaluated using the Cambridge Colour Test (CCT): the color discrimination threshold was measured first in the protan, deutan and tritan axes and , in succession, three MacAdamÆs ellipses were determined. The patientÆs color vision was also evaluated with color arrangement tests: the Farnsworth-Munsell 100 Hue (FM100), the Farnsworth-Munsell D15, and the Lanthony Desaturated (D15d) tests. We also measured the contrast sensitivity for black-and-white sine wave grating of twenty two patients. The results were compared with control without ophthalmologic or neuro-ophthalmologic pathologies. Twenty four patients presented acquired dyschromatopsia. There were cases of selective loss (11 patients) and of diffuse loss (13 patients). Although losses were present in the FM100 there was no correlation between the FM100 error score and the ellipse area measured by the CCT. Moreover, three patients that scored normal in the FM100, failed to reach normal threshold in the CCT. The Lanthony test was less sensitive than the other two tests, since it failed to indicate loss in about half the patients, and the D15 was the least sensitive test, having failed to indicate loss in 9 out of 10 patients. Contrast sensitivity was within normal values for patients submitted to this test. The extent of losses in color discrimination was positively correlated with the accumulated dose. The CCT is recommended for follow up since it provides quantitative data that can be directly interpreted in CIE (Commission Internationalle dÆÉclairage) color space.