[Uveitis as a presenting manifestation of sarcoidosis: clinical characteritics of a series of 23 cases]. / Uvéites révélant une sarcoïdose : caractéristiques cliniques à propos de 23 cas.

PURPOSE: Uveitis may rarely reveal sarcoidosis in Caucasian patients. Our objective was to analyze the clinical manifestations, and the outcome in a group of patients in whom uveitis was the presenting manifestation of sarcoidosis. METHODS: Retrospective study including 23 patients (mean age: 50.3±14.5 years) diagnosed with sarcoidosis after an episode of uveitis. Granulomatous lesions were documented in 14 patients. RESULTS: Ophthalmological examination revealed anterior uveitis (n=5), intermediate uveitis (n=2), posterior uveitis (n=25) and panuveitis (n=11). Ocular inflammation was bilateral in 16 patients (69,6%), typical aspects of granulomatous uveitis were found in only 16 eyes over 39 (41%), posterior uveitis was found in 18 eyes (46.2%), with an averaged visual acuity of 5/10. Macular oedema was noted in five patients. Suggestive signs of ocular sarcoidosis were present in 43% of the patients. Stage 1 or 2 pulmonary involvement (n=22), musculoskeletal (22%), skin (13%), or spleen (9%) involvements were the most common findings. Oral corticosteroids were necessary in 91.3% of the patients, immunosuppressive agents in 26.1%, with a prolonged treatment greater than two years in 58%. The visual prognosis was good, with visual acuity greater than 6/10 in 96% of the cases if the ocular inflammation spared retina and choroid. However, a visual acuity less than 6/10 was observed in 44% of the cases when the posterior segment was involved. CONCLUSION: Sarcoidosis may be revealed by an intraocular inflammation, with typical patterns in only 43% of the cases. Sarcoidosis should therefore be included in the differential diagnosis of every uveitis. Oral corticosteroids are required in almost all cases, owing to ocular involvement rather than visceral involvement.

[Which epiretinal membranes should be operated?]. / Quelles sont les membranes épimaculaires qu'il faut opérer?

Epimacular membrane (ERM) formation is an age-dependent more or less vision-threatening finding. Increased life expectancy and patient demand for better vision have led to increasing numbers of patients seeking therapy, making selection for surgery mandatory. The impressive improvements in macular hole surgery have influenced the epiretinal membrane and have renewed its therapeutic approach. Disturbing metamorphopsia, visual deterioration under 5/10, especially near-vision alteration and binocular disturbance, are major symptoms to motivate surgery. As epiretinal membrane removal can be considered a relatively safe and effective procedure today, with ILM peeling and simultaneous cataract surgery, visual acuity alone is no longer the single criterion. The patient's demands regarding vision in daily life should be taken into account. Patients with moderate visual loss, recent onset of symptoms, or progression are the best candidates for ERM surgery. Functional outcome in patients with poor initial visual acuity or long-standing disease is unsatisfactory. The OCT macular profile helps detect the best candidates with thickening between 300 and 450 microns. The presence of a pseudo hole, traction, or an intraretinal cyst does not impair functional results. Complete traction relief during pucker surgery is believed to be a precondition for good functional results. Intended ILM peeling is a tool to achieve this goal.

Color signals in human motion-selective cortex.

The neural basis for the effects of color and contrast on perceived speed was examined using functional magnetic resonance imaging (fMRI). Responses to S cone (blue-yellow) and L + M cone (luminance) patterns were measured in area V1 and in the motion area MT+. The MT+ responses were quantitatively similar to perceptual speed judgments of color patterns but not to color detection measures. We also measured cortical motion responses in individuals lacking L and M cone function (S cone monochromats). The S cone monochromats have clear motion-responsive regions in the conventional MT+ position, and their contrast-response functions there have twice the responsivity of S cone contrast-response functions in normal controls. But, their responsivity is far lower than the normals' responsivity to luminance contrast. Thus, the powerful magnocellular input to MT+ is either weak or silent during photopic vision in S cone monochromats.

Color signals in area MT of the macaque monkey.

The relationship between the neural processing of color and motion information has been a contentious issue in visual neuroscience. We examined this relationship directly by measuring neural responses to isoluminant S cone signals in extrastriate area MT of the macaque monkey. S cone stimuli produced robust, direction-selective responses at most recording sites, indicating that color signals are present in MT. While these responses were unequivocal, S cone contrast sensitivity was, on average, 1.0-1.3 log units lower than luminance contrast sensitivity. The presence of S cone responses and the relative sensitivity of MT neurons to S cone and luminance signals agree with functional magnetic resonance imaging (fMRI) measurements in human MT+. The results are consistent with the hypothesis that color signals in MT influence behavior in speed judgment tasks.

Adaptation to contingencies in macaque primary visual cortex.

We tested the hypothesis that neurons in the primary visual cortex (V1) adapt selectively to contingencies in the attributes of visual stimuli. We recorded from single neurons in macaque V1 and measured the effects of adaptation either to the sum of two gratings (compound stimulus) or to the individual gratings. According to our hypothesis, there would be a component of adaptation that is specific to the compound stimulus. In a first series of experiments, the two gratings differed in orientation. One grating had optimal orientation and the other was orthogonal to it, and therefore did not activate the neuron under study. These experiments provided evidence in favour of our hypothesis. In most cells adaptation to the compound stimulus reduced responses to the compound stimulus more than it reduced responses to the optimal grating, and the responses to the compound stimulus were reduced more by adaptation to the compound stimulus than by adaptation to the individual gratings. This suggests that a component of adaptation was specific to (and caused by) the simultaneous presence of the two orientations in the compound stimulus. To test whether V1 neurons could adapt to other contingencies in the stimulus attributes, we performed a second series of experiments, in which the component gratings were parallel but differed in spatial frequency, and were both effective in activating the neuron under study. These experiments failed to reveal convincing contingent effects of adaptation, suggesting that neurons cannot adapt equally well to all types of contingency.

A video-input device that displays high-luminance, high-resolution color images.

We describe the design and performance of a bright, full-color, video-input display monitor that can produce image luminances as high as 50,000 cd/m2 for images 15 x 10 deg in size. We have constructed this device by rearranging the components of a commercially available projection television. Our display device allows an experimenter to evaluate human visual responses to complex spectro-spatio-temporal patterns presented at naturally occurring light levels.

Pattern-color separable pathways predict sensitivity to simple colored patterns.

We have studied how contrast threshold sensitivity depends jointly on pattern and color. We measured sensitivity to colored Gabor patches from 0.5 to 8 c/deg. At each spatial frequency, we measured in many different color directions. We analyze the sensitivity measurements using a series of nested models. We conclude that a model consisting of three pattern-color separable mechanisms predicts detection performance nearly as well as fitting psychometric functions independently. We derive the pattern and color sensitivities of the separable mechanisms from the experimental data. Two derived mechanisms are spatially lowpass and spectrally color-opponent. The third mechanism is spatially bandpass and spectrally broadband.

Mapping of the RNA-binding domain of the alfalfa mosaic virus movement protein.

In-frame contiguous deletions were created in the movement protein gene of alfalfa mosaic virus by site-directed mutagenesis. The mutated movement proteins were expressed in Escherichia coli, extracted and then purified by denaturing gel electrophoresis and then renatured. Their binding ability with RNA was assayed by electrophoretic retardation and u.v.-crosslinking. Results indicated that a domain included within amino acids 36 to 81 was necessary for RNA binding.

Appearance of colored patterns: pattern-color separability.

We have measured how color appearance of square-wave bars varies with stimulus strength and spatial frequency. Observers adjusted the color of a uniform patch to match the color appearance of the bars in square-wave patterns. We used low-to-moderate square-wave patterns, from 1 to 8 cycles per degree (c/deg). The matches are not photoreceptor matches but rather are established at more central neural sites. The signals at the putative central sites obey several simple regularities. The cone contrast of the uniform patch is proportional to square-wave stimulus strength (color homogeneity) and additive with respect to the superposition of equal-frequency square waves containing different colors (color superposition). We use the asymmetric matches to derive, from first principles, three pattern-color-separable appearance pathways. The matches are explained by two spectrally opponent, spatially low-pass mechanisms and one spectrally positive, spatially bandpass mechanism. The spectral mechanisms that we derive are similar to luminance and opponent mechanisms that are derived with entirely different experimental methods.

Effect of the alfalfa mosaic virus movement protein expressed in transgenic plants on the permeability of plasmodesmata.

Symplastic transport of different sized fluorescent probes has been assessed in leaf epidermal cells of transgenic Nicotiana plants expressing the movement protein (MP) of alfalfa mosaic virus (AMV). In both N. tabacum and N. benthamiana, the size exclusion limit (SEL) of plasmodesmata increased from M(r) 1000, which represents the commonly accepted limit, to over 4.4K. However, in control plants, movement of a 3K probe was seen in 11 to 22% of the injections, indicating that plasmodesmata may on occasion allow the passage of molecules larger than was previously thought. The increase of SEL due to the presence of the AMV MP, although significant, remains insufficient to permit the passage of viral particles and the possibility of other mechanisms involved in viral cell-to-cell spread is discussed.

Task-dependent color discrimination.

When an observer's ability to discriminate colored objects is estimated from the variability in color matches, the observer inspects adjacent visual fields carefully and makes considered judgments. Color discrimination does not always take place under such viewing conditions. When color video displays are used in time-critical applications (e.g., head-up displays, video control panels), the observer must discriminate among briefly presented targets seen within a complex spatial scene. We compare color-discrimination thresholds by using two tasks. In one task the observer makes color matches between two halves of a continuously displayed bipartite field. In a second task the observer detects a color target in a set of briefly presented objects. The data from both tasks are well summarized by ellipsoidal isosensitivity contours. The fitted ellipsoids differ both in their size, which indicates an absolute sensitivity difference, and orientation, which indicates a relative sensitivity difference.

Surface characterizations of color thresholds.

We evaluate how well three different parametric shapes, ellipsoids, rectangles, and parallelograms, serve as models of three-dimensional detection contours. We describe how the procedures for deriving the best-fitting shapes constrain inferences about the theoretical visual detection mechanisms. The ellipsoidal shape, commonly assumed by vector-length theories, is related to a class of visual mechanisms that are unique only up to orthogonal transformations. The rectangle shape is related to a unique set of visual mechanisms, but since the rectangle is not invariant with respect to linear transformations the estimated visual mechanisms are dependent on the stimulus coordinate frame. The parallelogram is related to a unique set of visual mechanisms and can be derived by methods that are independent of the stimulus coordinate frame. We evaluate how well these shapes approximate detection contours, using 2-deg test fields with a long (1-sec) Gaussian time course. Two statistical tests suggest that the parallelogram model is too strong. First, we find that the ellipsoid and rectangle shapes fit the data with the same precision as the variance in repeated threshold measurements. The parallelogram model, which has more free parameters, fits the data with more precision than the variance in repeated threshold measurements. Second, although the parallelogram model provides a slightly better fit of our data than the other two shapes, it does not serve as a better guide than the ellipsoidal model for interpolating from the measurements to thresholds in novel color directions.

The ellipsoidal representation of spectral sensitivity.

When plotted in three-dimensional color-space, thresholds of colored lights fall on or near the surface of an ellipsoid. Using data reported in the literature, we estimate the deviation between sets of spectral threshold measurements and the ellipsoid that passes closest to the data. Seventy-three percent of the reported spectral thresholds fall within 0.1 log units of the best-fitting ellipsoid. Our ability to distinguish one ellipsoidal fit as significantly better than another is limited by the choice of sampling directions in color-space. Spectral lights do not provide a good set of sampling directions for reducing the uncertainty about the estimated best-fitting ellipsoid. Complete characterization of visual sensitivity requires measuring thresholds to mixtures of spectral lights.

Cone sampling array models.

A model is described for positioning cones in the retina. Each cone has a circular disk of influence, and the disks are tightly packed outward from the center. This model has three parameters that can vary with eccentricity: the mean radius of the cone disk, the standard deviation of the cone disk radius, and the standard deviation of postpacking jitter. Estimates for these parameters out to 1.6 deg are found by using measurements reported by Hirsch and Hylton [Vision Res. 24, 347 (1985)] and Hirsch and Miller [J. Opt. Soc. Am. A 4, 1481 (1987)] of the positions of the cone inner segments of an adult macaque. The estimation is based on fitting measures of variation in local intercone distances, and the fit to these measures is good.