Retinal Topographic Maps: A Glimpse into the Animals’ Visual World

The vertebrates’ retina has a highly conserved laminar organization of 10 alternating nuclear and plexiform layers. Species differences in the retinal specializations, i.e., areas of higher cell density, among the species, represent specific regions of the visual field of higher importance for a better spatial resolution and indicate distinct evolutionary pressures on the structures of the visual system, which can be related to many aspects of the species evolutionary history. In this chapter, we analyzed the density and distribution of cells of the retinal ganglion cell layer (GCL) and estimated the upper limits of the spatial resolving power of 12 species of snakes from the Colubridae family, 6 diurnal and 6 nocturnal, which inhabit different habitats. Our results revealed lower visual acuity in nocturnal species, compared to diurnal, and we observed different types of retinal specialization, horizontal streak, area centralis, or scattered distribution, with higher cell density in different retinal regions, depending on the species. These variations may be related to ecological and behavioral features, such as daily activity pattern, habitat, and substrate preferentially occupied, hunting strategies and diet. This comparative study indicates the complexity of the adaptive strategies of the snakes’ visual system

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Color space distortions in patients with type 2 diabetes mellitus

Color vision impairment was examined in patients with type 2 diabetes mellitus (DM2) without retinopathy. We assessed the type and degree of distortions of individual color spaces. DM2 patients (n = 32), and age-matched controls (n = 20)were tested using the Farnsworth D-15 and the Lanthony D-15d tests. In addition, subsets of caps from both tests were employed in a triadic procedure (Bimler & Kirkland, 2004). Matrices of inter-cap subjective dissimilarities were estimated from each subject’s “odd-one-out” choices, and processed using non-metric multidimensional scaling. Two-dimensional color spaces, individual and group (DM2 patients; controls), were reconstructed, with the axes interpreted as the R0G and B0Y perceptual opponent systems. Compared to controls, patient results were not significant for the D-15 and D-15d. In contrast, in the triadic procedure the residual distances were significantly different compared to controls: right eye, P 0.021, and left eye, P 0.022. Color space configurations for the DM2 patients were compressed along the B0Y and R0G dimensions. The present findings agree with earlier studies demonstrating diffuse losses in early stages of DM2. The proposed method of testing uses color spaces to represent discrimination and provides more differentiated quantitative diagnosis, which may be interpreted as the perceptual color system affected. In addition, it enables the detection of very mild color vision impairment that is not captured by the D-15d test. Along with fundoscopy, individual color spaces may serve for monitoring early functional changes and thereby to support a treatment strategy

Saturation-specific pattern of acquired colour vision deficiency in two clinical populations revealed by the method of triads

Subjective colour spaces were reconstructed for persons occupationally exposed to mercury (Hg) and patients with diabetes mellitus type 2, two groups at risk for acquired colour-vision deficiency, and compared with healthy normal trichromats. Judgments of colour dissimilarity were collected with the method of triads, applied to a composite assortment of colour samples. These were drawn from two widely used colour arrangement tests—10 hues from the Farnsworth D-15 test and five from the Lanthony Desaturated D-15d test, ensuring that the assortment sampled two levels of lightness and saturation. The data were analyzed with maximum-likelihood multidimensional scaling (MDS) and within a novel individual-differences MDS model to estimate subject-specific parameters. The MDS solutions for the two clinical groups showed a compression along a blue-yellow axis, limited however to desaturated hues. This result was confirmed by the individual-differences model. In addition, the clinical groups were found to place significantly higher weights on the lightness differences between stimuli, conceivably to compensate for their reduced chromatic discrimination. The specific form of colour-space distortion in the clinical groups indicated an increase in their thresholds for blue-yellow signals, providing insights into the nature of impairment mechanisms. The results have implications for stimuli and diagnostic procedures for testing individual differences in color vision, and for analyzing the responses. This approach is sensitive to distinctive patterns of subtle colour-vision impairment underestimated by the conventional D-15d test

Evaluation of Glaucomatous Damage via Functional Magnetic Resonance Imaging, and Correlations Thereof with Anatomical and Psychophysical Ocular Findings

PurposeTo evaluate the functional magnetic resonance imaging (fMRI) response to binocular visual stimulation and the association thereof with structural ocular findings and psychophysical test results in patients with glaucoma, and controls.MethodsCross-sectional study. Participants underwent a complete ophthalmic examination, including Humphrey 24-2 visual field (VF) testing and optical coherence tomography. Binocular VF in each quadrant was determined using an integrated method. Patients with glaucoma were assigned to three subgroups: initial, asymmetrical and severe glaucoma. Regions of interest (ROIs) were determined anatomically. fMRI (3 T) was performed using a bilaterally presented polar angle stimulus, and the accompanying changes in blood oxygen level-dependent (BOLD) signals were obtained from the occipital poles and calcarine ROIs. We used generalized estimation equation models to compare anatomical and functional data between the groups.ResultsA total of 25 subjects were enrolled, of whom 17 had glaucoma and 8 were controls. Significant associations between quadrant binocular VF sensitivities and fMRI responses were found in the occipital pole ROIs (p = 0.033) and the calcarine ROIs (p = 0.045). in glaucoma severity subgroup analysis, retinal nerve fiber layer (RNFL) thickness was associated with the BOLD response of the calcarine and occipital pole ROIs (p = 0.002 and 0.026, respectively). the initial and asymmetrical glaucoma subgroups had similar binocular VF sensitivities and RNFL thicknesses, but distinct BOLD responses.ConclusionsThe response of the visual cortex to binocular stimulation was associated with binocular VF sensitivity. RNFL thickness was associated with the BOLD response of the calcarine and occipital pole ROIs.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Universidade Federal de São Paulo, Dept Ophthalmol, São Paulo, BrazilHosp Israelita Albert Einstein, São Paulo, BrazilUniv São Paulo, Inst Psychol, Dept Expt Psychol, São Paulo, BrazilUniversidade Federal de São Paulo, Dept Ophthalmol, São Paulo, BrazilFAPESP: 2007/07339-2Web of Scienc