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PubMed1999

A new approach to the study of ocular chromatic aberrations.

We measured the ocular wavefront aberration at six different visible wavelengths (between 450 and 650 nm) in three subjects, using a spatially resolved refractometer. In this technique, the angular deviation of light rays entering the pupil at different locations is measured with respect to a target viewed through a centered pupil. Fits of the data at each wavelength to Zernike polynomials were used to estimate the change of defocus with wavelength (longitudinal chromatic aberration, LCA) and the wavelength-dependence of the ocular aberrations. Measured LCA was in good agreement with the literature. In most cases the wavefront aberration increased slightly with wavelength. The angular deviations from the reference stimulus measured using a magenta filter allowed us to estimate the achromatic axis and both optical and perceived transverse chromatic aberration (TCA), (including the effect of aberrations and Stiles-Crawford effect). The amount of TCA varied markedly across subjects, and between eyes of the same subject. Finally, we used the results from these experiments to compute the image quality of the eye in polychromatic light.

Adult↗
PubMed1985

A survey of transforms of the CIE 1931 chromaticity diagram with some new non-linear transforms and histological illustrations of their utility.

Surveys are presented of the published data on colour matching, and of the published transforms of the CIE 1931 chromaticity diagram. All transforms are given in the form of standardized equations and tables of coefficients. Both linear and non-linear transforms are considered, although the latter are given special attention. The concept of a uniform chromaticity space (UCS) is discussed, and the published transforms are assessed for uniformity using the colour matching data. 2 series of new, non-linear transforms are presented, both based on 2-dimensional polynomial equations, and both derived using iterative optimization techniques. The 1st series attempts to approximate Farnsworth's (1961) diagram. The 2nd uses Nutting's colour matching points directly. The coefficients of these transforms are tabulated. It was found that increasing the number of coefficients in the 2-dimensional polynomial, beyond 15 each for x and y, does little to increase the uniformity of the resulting transform. The usefulness of UCS's in assessing stain performance is illustrated by examples drawn from the areas of azure B/eosin staining of blood cells and Papanicolaou staining of epithelial cells from the uterine cervix.

Blood Cells↗
PubMed2001

[Chromatic computerized analysis is an early predictor of cardiovascular risk associated to hypercholesterolemia].

INTRODUCTION AND OBJECTIVES: Early detection of cardiovascular disease is a major goal of contemporary medicine in efforts to prevent coronary heart disease. The goal of this study was to look for a number of changes that could be detected in the neurons of the 19 Brodman area by means of chromatic computerized analysis (CCA) as a consequence of a neurobiological dysfunction, which induced a failure in the chromatic perception, which, in turn, expressed the existence of hypercholesterolemia through numeric qualification and therefore, a cardiovascular risk. PATIENTS AND METHOD: . We studied 208 patients (Group 1) (153 men and 55 women) with pre-study plasma cholesterol levels in excess of 200 mg/dl. The control group (Group 2) also consisted of 208 subjects (153 men and 55 women) but with a cholesterol level below 200 mg/dl. They were performed by CCA, previously ruling out any systemic or ophthalmological pathology. RESULTS: All global indexes were highly correlated in both groups. The direct relation between cholesterol levels and 19 area, reached a canonical correlation of 0.825 with a sensitivity of 90% and especifity of 93%. The results of the multiple regression taking total cholesterol as a dependent variable and the most significative parameter of CCA, as an independent variable was R = 0.89 (p < 0.001), with a test variability of 81%. CONCLUSIONS: This study determines a strong association between hypercholesterolemia and the visual areas of the cerebral cortex.

Adult↗
PubMed2002

[Comparative study of the impact of diet versus pravastatin on color vision in Brodman area 19 detected by computerized chromatic analysis (CARDIOCOLOUR Study)].

INTRODUCTION AND OBJECTIVES: Hypercholesterolemia causes important neurodegenerative changes in the cerebral cortex, which are manifested by defects in the color perception by the neurons of Brodman area 19. Extensive interventional epidemiological data from both primary and secondary-prevention clinical trials indicate that cardiac ischemic events decrease when total cholesterol or LDL-C is reduced. Our goal was to elucidate the effects of diet compared with a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor (pravastatin) on color perception using computerized chromatic analysis (CCA) and plasma cholesterol levels. PATIENTS AND METHODS: We studied 191 normotensive patients (133 men and 58 women) with pre-study plasma cholesterol levels in excess of 200 mg/dl. Seventy of these patients were treated with the American Heart Association Step II diet for six months. The remaining 121 were treated with pravastatin, 61 patients with 10 mg and 60 patients with 40 mg. They were examined by CCA after excluding any general or ophthalmological pathology. RESULTS: Chromatic vision recovered by 23% with diet, 38% with pravastatin 10 mg and 92% with pravastatin 40 mg. CONCLUSIONS: This study confirmed a strong association between therapeutic intervention with either diet or pravastatin and improved color vision.

Adult↗
PubMed1990

A new technique for estimating chromatic isoluminance in humans and monkeys.

Current approaches to the problem of equating different colors for luminance (chromatic isoluminance) rely upon human reports of perceptual events that are reduced at some luminance ratio. In this report, a technique is described that evokes a vivid percept of motion of a textured pattern only at isoluminance. Furthermore, in both humans and monkeys, the moving stimulus produces a striking optokinetic response in the same direction as the perceived motion. If used in this manner, the technique can provide an estimate of chromatic isoluminance in a variety of species and be used to corroborate a human subject's perceptual judgement.

Animals↗
PubMedDate not supplied

Short-term effects of dopamine on photoreceptors, luminosity- and chromaticity-horizontal cells in the turtle retina.

The effects of dopamine on luminosity-type horizontal cells have been documented in different vertebrate retinas, both in vivo and in vitro. Some of these effects may reflect direct action of dopamine onto these cells, but indirect effects mediated by presynaptic neurons cannot be ruled out. Furthermore, direct effects of dopamine on horizontal cells may affect other, postsynaptic neurons in the outer plexiform layer. To test these possibilities, we studied the effects of dopamine on photoreceptors and all types of horizontal cells in the turtle (Pseudemys scripta elegans) retina. Receptive-field properties, responsiveness to light, and time course of light responses were monitored with intracellular recordings. Dopamine at a concentration of 40 microM exerted effects with two different time courses. "Short-term" effects were fully developed after 3 min of dopamine application and reversed within 30 min of washout of the drug. "Long-term" effects were fully developed after about 7-10 min and could not be washed out during the course of our experiments. Only the "short-term" effects were studied in detail in this paper. These were expressed in a reduction of the receptive-field size of all types of horizontal cells studied; L1 and L2 luminosity types as well as Red/Green and Yellow/Blue chromaticity types. The L1 horizontal cells did not exhibit signs of reduced responsiveness to light under dopamine, while in the L2 cells and the two types of chromaticity cells responsiveness decreased. None of the rods, long-wavelength-sensitive, or medium-wavelength-sensitive cones exhibited any apparent reduction in their receptive-field sizes or responsiveness to light. The present results suggest that the "short-term" effects of dopamine are not mediated by photoreceptors and are probably due to direct action of dopamine on horizontal cells.

Animals↗
PubMedDate not supplied

Rearing in different photic and chromatic environments modifies spectral responses of cone horizontal cells in adult fish retina.

We investigated chromatic processing in the outer retina of the cichlid fish Aequidens pulcher. Intracellular recordings from cone-specific horizontal cells (CHCs) revealed that the two morphologically identified types (H1 and H2) also have different spectral responses. H1-L cells hyperpolarize to all wavelengths ("luminosity"). H2-Cb cells depolarize to long wavelengths and hyperpolarize to short wavelengths ("chromaticity", biphasic). Furthermore, we verified by immunocytochemistry that H2-Cb cells of A. pulcher predominantly contact the middle-wavelength-sensitive (MWS) members of double cones. Developmental plasticity in the cone-CHC networks was induced by rearing fish under conditions of spectral deprivation and different levels of white light. H1-L spectral responses were unaffected by the rearing conditions. Different intensity levels of white light and deprivation of long wavelengths during rearing both induced changes in the spectral responses of H2-Cb. Deprivation of short and middle wavelengths had no effect. Our results indicate that spectral processing in the outer retina of fishes can be modulated in response to different visual experiences and suggest that developmental fine tuning of the color-vision system occurs at early levels of visual processing.

Adaptation, Physiological↗
PubMedDate not supplied

Spatial-chromatic interactions in C-type horizontal cells of the turtle (Mauremys caspica) retina.

Horizontal cells are second-order retinal neurons that play a key role in spatial information processing. In some cold-blooded vertebrates such as turtles, a subtype of these cells, the chromaticity horizontal cells exhibit color-opponent responses and therefore are considered to be important also for color information processing. To reveal spatial and color interactions, the receptive-field properties of Red/Green and Yellow/Blue chromaticity horizontal cells in the retina of the turtle Mauremys caspica were studied by intracellular recordings from the everted eyecup preparation. We found that the polarity of the photoresponses depended not only upon the wavelength and intensity of the stimulus, but also upon its spatial configuration. Thus, a hyperpolarizing photoresponse that was elicited by full-field stimulation with bright light of wavelength close to the "neutral" one was reversed in polarity to a pure depolarizing one when a small spot or a thin annular pattern were used for stimulation. This finding could not be explained either by different balances between depolarizing and hyperpolarizing inputs to different cells or by stray light that effectively reduced the light intensity in the center of the small spot. Rather, it was found that the depolarizing and hyperpolarizing components were characterized by different receptive-field size and that these differences could account for the dependency of response polarity upon the spatial pattern of the stimulus. These findings indicate that color information processing in turtle C-type horizontal cells is a complex process that depends upon the wavelength and intensity of the light stimulus as well as upon its spatial properties.

Animals↗
PubMedDate not supplied

Long-term renormalization of chromatic mechanisms following cataract surgery.

The optical density of the human crystalline lens progressively increases with age, the greatest increase in the visible spectrum being at short wavelengths. This produces a gradual shift in the spectral distribution of the light reaching the retina, yet color appearance remains relatively stable across the life span, implying that the visual system adapts to compensate for changes in spectral sensitivity. We explored properties of this adaptive renormalization by measuring changes in color appearance following cataract surgery. When the lens is removed, cataract patients often report a large perceptual shift in color appearance that can last for months. This change in color appearance was quantified for four cataract patients (63-84 years) by determining the chromaticity of stimuli that appeared achromatic before surgery, and at various intervals after surgery for up to 1 year. Stimuli were presented on a calibrated CRT as 9.5-deg spots, with 3-s duration and 3-s interstimulus intervals (ISIs). Chromaticity was adjusted by the subjects in CIE L*a*b* color space with luminance fixed at 32 cd/m2, on a dark background. We also estimated the optical density of the cataractous lens by comparing absolute scotopic thresholds from 410 nm to 600 nm before and after surgery. The results demonstrated that immediately following surgery there is a large increase in the short-wave light reaching the retina, mainly below 500 nm. The achromatic settings generally showed an initial large shift in the "yellow" direction after surgery that gradually (but never fully) returned to the original achromatic point before surgery. The shifts in the achromatic point occur over a number of months and appear to occur independently of the fellow eye.

Adaptation, Ocular↗
PubMed2001

Modulating artificial membrane morphology: pH-induced chromatic transition and nanostructural transformation of a bolaamphiphilic conjugated polymer from blue helical ribbons to red nanofibers.

Design and characterization of helical ribbon assemblies of a bolaamphiphilic conjugated polymer and their color-coded transformation into nanofibers are described. An L-glutamic acid modified bolaamphiphilic diacetylene lipid was synthesized and self-assembled into right-handed helical ribbons with micron scale length and nano scale thickness under mild conditions. The ribbon structures were further stabilized by polymerizing well-aligned diacetylene units to form bisfunctional polydiacetylenes (PDAs). Transitions from flat sheets to helical ribbons and tubes were observed by transmission electron microscopy. The helical ribbons appear to originate from the rupture of flat sheets along domain edges and the peeling off between stacked lipid layers. These results point to the applicability of chiral packing theory in bolaamphiphilic supramolecular assemblies. Contact mode atomic force microscopy observations revealed that high order existed in the surface packing arrangement. Hexagonal and pseudorectangular packings were observed in flat and twisted regions of the ribbons, respectively, suggesting a correlation between microscopic morphologies and nanoscopic packing arrangements. The tricarboxylate functionalities of the bolaamphiphilic lipid provide a handle for the manipulation of the bisfunctional PDAs' morphology. Increasing solution pH caused the fraying of helical ribbons into nanofibers accompanied by a sharp blue-to-red chromatic transition. A dramatic change in circular dichroism spectra was observed during this process, suggesting the loss of chirality in packing. A model is proposed to account for the pH-induced morphological change and chromatic transition. The color-coded transition between two distinct microstructures would be useful in the design of sensors and other "smart" nanomaterials requiring defined molecular templates.

Acetylene↗
PubMed2001

Direct oxidation of guanine and 7,8-dihydro-8-oxoguanine in DNA by a high-valent chromium complex: a possible mechanism for chromate genotoxicity.

Intracellular reductive activation of the human carcinogen chromate, Cr(VI), is a necessary step in the formation of DNA lesions that lead to cancer. Reductive activation forms the transient metastable high-valent oxidation state of Cr(V) as a precursor to the final intracellularly stable oxidation state, Cr(III). In this study, we have used a model high-valent Cr(V) complex, N,N'-ethylenebis(salicylideneanimato)oxochromium(V), Cr(V)-Salen, to probe the mechanism of interaction between this oxidation state of chromium and DNA. This interaction was found to be specific toward the oxidation of the nucleic acid base guanine in unmodified single- and double-stranded oligonucleotides as measured by an increased level of DNA strand cleavage at these sites following piperidine treatment. Replacement of a single guanine residue in DNA with a more readily oxidized 7,8-dihydro-8-oxoguanine (8-oxo-G) base allowed for site-specific oxidation at this modified site within the DNA strand by the Cr(V)-Salen complex. HPLC and ESI-mass spectrometry were used to identify the modified guanine base lesions formed in the reaction of this high-valent chromium complex with the 8-oxo-G-containing DNA substrate. Two of these modified base lesions, identified as guanidinohydantoin and spiroiminodihydantoin, were found in the reaction of the Cr(V)-Salen complex with 8-oxo-G-modified DNA, while only one, spiroiminodihydantoin, was formed from oxidation of the 8-oxo-G nucleoside. A primer extension assay using the exo(-) Klenow fragment demonstrated polymerase arrest at the site of these base modifications as well as a high degree of misincorporation of adenine opposite the site of modification. These results suggest that mutations arising from G --> T transversions would predominate with these lesions. The mechanism of damage and base oxidation products for the interaction between high-valent chromium and DNA described herein may be relevant to the in vivo formation of DNA damage leading to cancer in chromate-exposed human populations. These results also suggest how high-valent chromium can act as a cocarcinogen with 8-oxo-G-forming xenobiotics.

Carcinogens, Environmental↗
PubMed1997

Use of a luminescent bacterial biosensor for biomonitoring and characterization of arsenic toxicity of chromated copper arsenate (CCA).

An arsenic oxyanion-inducible Escherichia coli chromosomal operon (arsRBC) has been previously identified. Construction of a luciferase transcriptional gene fusion (arsB::luxAB) showed that ars operon expression, plus concomitant cell luminescence, was inducible in a concentration-dependent manner by arsenic salts. The present study was conducted to evaluate the potential of the arsB::luxAB transcriptional gene fusion for use as a biosensor in monitoring the toxicity of arsenic compounds. Cultures from this gene fusion strain were exposed to increasing concentrations of the wood preservative chromated copper arsenate (CCA), as well as its constituents, sodium arsenate and chromated copper solution (CC). Analysis of luciferase activity revealed that the arsB::luxAB gene fusion was expressed in response to CCA and sodium arsenate, but not to the CC solution. The detection limit of arsenic was found to be 0.01 microgram As/ml (10 parts per billion, 10 ppb) and therefore well within the range of environmental concerns. A greater induction of luminescence by arsenate was observed when cells were limited for phosphate, as phosphate can act as a competitive inhibitor of arsenate ions. Our results suggest that the E. coli arsB::luxAB fusion strain has a promising future as a specific and sensitive biosensor for monitoring bioavailable levels and toxicity of arsenic near sites where CCA-treated wood has been used.

Arsenates↗
PubMed2003

A molecular understanding of complementary chromatic adaptation.

Photosynthetic activity and the composition of the photosynthetic apparatus are strongly regulated by environmental conditions. Some visually dramatic changes in pigmentation of cyanobacterial cells that occur during changing nutrient and light conditions reflect marked alterations in components of the major light-harvesting complex in these organisms, the phycobilisome. As noted well over 100 years ago, the pigment composition of some cyanobacteria is very sensitive to ambient wavelengths of light; this sensitivity reflects molecular changes in polypeptide constituents of the phycobilisome. The levels of different pigmented polypeptides or phycobiliproteins that become associated with the phycobilisome are adjusted to optimize absorption of excitation energy present in the environment. This process, called complementary chromatic adaptation, is controlled by a bilin-binding photoreceptor related to phytochrome of vascular plants; however, many other regulatory elements also play a role in chromatic adaptation. My perspectives and biases on the history and significance of this process are presented in this essay.

Journal Article↗
PubMed2003

Large shifts in color appearance from patterned chromatic backgrounds.

The perceived color of a light varies with the background on which it is seen. In the present study, patterned backgrounds composed of two different chromaticities caused larger shifts in perceived color than did a uniform background at either chromaticity within the pattern. Cortical receptive-field organization, but not optical factors or known retinal neurons, can account for the color shifts from patterned backgrounds.

Color Perception↗
PubMed1999

A method for characterizing longitudinal chromatic aberration of microscope objectives using a confocal optical system

We describe a novel method of characterizing the longitudinal chromatic aberration of microscope objectives by recording a series of axial responses as a function of wavelength as a plane reflector is scanned through the focal region of a confocal microscope. Measurements are presented for a variety of objectives with differing degrees of correction. The use of the chromatic focal shift to measure surface profiles is also discussed.

Journal Article↗
PubMed1999

Accommodation to static chromatic simulations of blurred retinal images.

The eye's longitudinal chromatic aberration (LCA) is known to drive 'reflex' accommodation to moving objects, but the evidence is not as clear for stationary objects. The present study examined whether accommodation can be driven by static simulations of the effects of defocus and LCA. Accommodation was recorded continuously while each of 12 subjects viewed images (through a 0.75 mm pinhole) that simulated the appearances of blurred sine wave gratings (3.9 c.p.d.). In two experimental conditions, an eye with normal LCA was assumed and defocus of +1 D or -1 D was simulated. In a control condition, an eye with neutralised LCA was assumed and target defocus of 1 D was simulated. Subjects' accommodation responses were consistent with the hypothesis that LCA provides a stimulus to accommodation. Chromatic aberration drives accommodation to both moving and stationary objects, and thus is an important stimulus for accommodation in everyday situations. The study findings are discussed in relation to colour vision, visual display terminals and emmetropization.

Accommodation, Ocular↗
PubMed1995

Solving occlusion indeterminacy in chromatically homogeneous patterns.

Overlapping figures can produce consistent depth stratification even when chromatically homogeneous. Since neither T-junctions nor X-junctions are present in these patterns, the problem arises of what rules determine the direction of depth stratification, ie which surfaces appear in front and which behind. In a series of demonstrations and formal experiments involving perception of stereopsis, motion, transparency, motion in depth, and reversible figures, the validity of the principle that the visual system tends to minimise the formation of interpolated modal contours was tested. The reason why larger surfaces tend to be seen modally in front, rather than behind, would reflect the geometrical property that when, in overlapping objects, larger surfaces are closer there will be shorter occluding boundaries than when smaller surfaces are closer. It is shown that this constraint is independent of the empirical depth cue of relative size. An example is also given of a simple computational strategy that extracts, from chromatically homogeneous patterns, occluding subjective contours corresponding to those perceived by human observers.

Attention↗
PubMed2005

Chromatic masking revealed by the standing wave of invisibility illusion.

We have used the standing wave of invisibility illusion (Macknik and Livingstone, 1998 Nature Neuroscience 1 144-149) to examine the masking effects produced by a range of stimuli of varying chromatic and luminance contrast content. The pattern of masking was highly selective. Maximum effects were always obtained when the target and mask were identical in terms of their chromatic and/or luminance contrast composition, but were reduced as the angular separation in colour space between them was increased. Masking was of a monopolar nature, indicating the operation of rectified mechanisms selective for different combinations of colour and luminance contrast.

Color Perception↗