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PURPOSE: To establish a virtual device that can predict the effect of facial features on the visual field of humans and primates. METHODS: Virtual masks were obtained from human subjects, and macaque, chimpanzee and baboon taxidermic specimens, and aligned with upright head orientation at the center of a virtual perimeter-like dome (radius = 50 m) developed with Cinema 4D. Virtual searchlights positioned at the masks' pupils were then allowed to 'paint' facial elements obstructing their path, and demarcate the unobstructed rays at the perimetric surface and on a virtual ground floor related to eye level. Searchlight positions along the human mask's pupillary axis were identified by maximum congruence to Goldmann visual field limits. RESULTS: The human contours largely concur with large-stimulus isopters displaying the limiting role of the nasal ridge, and the relatively extended ventral and temporal limits. In contrast, the facial design of chimpanzees and baboons obstructs significant portions of the ventral foreground (>2 m cf < 0.5 m in human), while there appear to be larger binocular overlaps (125 degrees in chimp cf 90 degrees in human). CONCLUSIONS: The model provides information on anatomical constraints for monocular and binocular visual field extensions including projection of the ventral field on a virtual floor.

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Noncontact, depth-resolved, optical probing of retinal response to visual stimulation with a <10-microm spatial resolution, achieved by using functional ultrahigh-resolution optical coherence tomography (fUHROCT), is demonstrated in isolated rabbit retinas. The method takes advantage of the fact that physiological changes in dark-adapted retinas caused by light stimulation can result in local variation of the tissue reflectivity. fUHROCT scans were acquired from isolated retinas synchronously with electrical recordings before, during, and after light stimulation. Pronounced stimulus-related changes in the retinal reflectivity profile were observed in the inner/outer segments of the photoreceptor layer and the plexiform layers. Control experiments (e.g., dark adaptation vs. light stimulation), pharmacological inhibition of photoreceptor function, and synaptic transmission to the inner retina confirmed that the origin of the observed optical changes is the altered physiological state of the retina evoked by the light stimulus. We have demonstrated that fUHROCT allows for simultaneous, noninvasive probing of both retinal morphology and function, which could significantly improve the early diagnosis of various ophthalmic pathologies and could lead to better understanding of pathogenesis.

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The tuatara Sphenodon punctatus, restricted to a few New Zealand offshore islands and now strictly protected, belongs to the Rhynchocephalia, the smallest order of extant reptiles. Earlier light microscopical studies on the retina of this species described photoreceptors with both rod- and cone-like features and the presence of a fovea. A limited amount of retinal material from S. punctatus has now allowed us to prepare the first-ever electron microscopic observations on the eye of this reptile. We were able to distinguish three types of photoreceptor, all with fine structural features characteristic of cone cells. Large single cones as well as double cones had open discs in their outer segments and straight axons with pedicle-type terminals. An additional cone type, characterized by somewhat more slender inner and outer segments, vitreally-displaced cell bodies and oblique axons, resembled short-wavelength cones known from other sauropsids. No cells with rod characteristics could be confirmed in the samples, although they might occur in retinal regions not available for this study. We conclude that the tuatara has cone-like photoreceptors, which-as in other crepuscular or nocturnal reptiles-have acquired rod-like features. The phenotypic adaptations notwithstanding, the set of photoreceptor types is quite typical of the reptilian eye and in some respects reminiscent of those seen in lizards and turtles.

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The morphology and distribution of normally placed and displaced A horizontal cells were studied in the retina of a diurnal hystricomorph rodent, the agouti Dasyprocta aguti. Cells were labeled with anti-calbindin immunocytochemistry. Dendritic-field size reaches a minimum in the visual streak, of about 9,000 microm(2), and increases toward the retinal periphery both in the dorsal and ventral regions. There is a dorsoventral asymmetry, with dorsal cells being larger than ventral cells at equal distances from the streak. The peak value for cell density of 281 +/- 28 cells/mm(2) occurs in the center of the visual streak, decreasing toward the dorsal and ventral retinal periphery, paralleling the increase in dendritic-field size. Along the visual streak, the decline in cell density is less pronounced, remaining between 100-200 cells/mm(2) in the temporal and nasal periphery. Displaced horizontal cells are rare and occur in the retinal periphery. They tend to be smaller than normally placed horizontal cells in the ventral region, whilst no systematic difference was observed between the two cell groups in the dorsal region. Mosaic regularity was studied using nearest-neighbor analysis and the Ripley function. When mosaic regularity was determined removing the displaced horizontal cells, there was a slight increase in the conformity ratio, but the bivariate Ripley function indicated some repulsive dependence between the two mosaics. Both results were near the level of significance. A similar analysis performed in the capybara retina, a closely related hystricomorph rodent bearing a higher density of displaced horizontal cells than found in the agouti, suggested spatial independence between the two mosaics, normally placed versus displaced horizontal cells.

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Novel ultra-broad bandwidth light sources enabling unprecedented sub-2 microm axial resolution over the 400 nm-1700 nm wavelength range have been developed and evaluated with respect to their feasibility for clinical ultrahigh resolution optical coherence tomography (UHR OCT) applications. The state-of-the-art light sources described here include a compact Kerr lens mode locked Ti:sapphire laser (lambdaC = 785 nm, delta lambda = 260 nm, P(out) = 50 mW) and different nonlinear fibre-based light sources with spectral bandwidths (at full width at half maximum) up to 350 nm at lambdaC = 1130 nm and 470 nm at lambdaC = 1375 nm. In vitro UHR OCT imaging is demonstrated at multiple wavelengths in human cancer cells, animal ganglion cells as well as in neuropathologic and ophthalmic biopsies in order to compare and optimize UHR OCT image contrast, resolution and penetration depth.

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A compact, low-cost, prismless Ti:Al2O3 laser with 176-nm bandwidth (FWHM) and 20-mW output power was developed. Ultrahigh-resolution ophthalmic optical coherence tomography (OCT) ex vivo imaging in an animal model with approximately 1.2-microm axial resolution and in vivo imaging in patients with macular pathologies with approximately 3-microm axial resolution were demonstrated. Owing to the pump laser, this light source significantly reduces the cost of broadband OCT systems. Furthermore, the source has great potential for clinical application of spectroscopic and ultrahigh-resolution OCT because of its small footprint (500 mm x 180 mm including the pump laser), user friendliness, stability, and reproducibility.

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In this article the ability of ultrahigh resolution ophthalmic optical coherence tomography (OCT) to image small choroidal blood vessels below the highly reflective and absorbing retinal pigment epithelium is demonstrated for the first time. A new light source (lambdac= 1050 nm, Deltalambda = 165 nm, Pout= 10 mW), based on a photonic crystal fiber pumped by a compact, self-starting Ti:Al2O3 laser has therefore been developed. Ex-vivo ultrahigh resolution OCT images of freshly excised pig retinas acquired with this light source demonstrate enhanced penetration into the choroid and better visualization of choroidal vessels as compared to tomograms acquired with a state-of-the art Ti:Al2O3 laser (Femtolasers Compact Pro, lc= 780 nm, Deltalambda= 160 nm, Pout= 400 mW), normally used in clinical studies for in vivo ultrahigh resolution ophthalmic OCT imaging. These results were also compared with retinal tomograms acquired with a novel, spectrally broadened fiber laser (MenloSystems, lambdac= 1350 nm, Deltalambda= 470 nm, Pout = 4 mW) permitting even greater penetration in the choroid. Due to high water absorption at longer wavelengths retinal OCT imaging at ~1300 nm may find applications in animal ophthalmic studies. Detection and follow-up of choroidal neovascularization improves early diagnosis of many retinal pathologies, e.g. age-related macular degeneration or diabetic retinopathy and can aid development of novel therapy approaches.

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Unlike in birds and cold-blooded vertebrates' retinas, the photoreceptors of mammalian retinas were long supposed to be morphologically uniform and difficult to distinguish into subtypes. A number of new techniques have now begun to overcome the previous limitations. A hitherto unexpected variability of spectral and morphological subtypes and topographic patterns of distribution in the various retinas are being revealed. We begin to understand the design of the photoreceptor mosaics, the constraints of evolutionary history and the ecological specialization of these mosaics in all the mammalian subgroups. The review discusses current cytological identification of mammalian photoreceptor types and speculates on the likely "bottleneck-scenario" for the origin of the basic design of the mammalian retina. It then provides a brief synopsis of current data on the photoreceptors in the various mammalian orders and derives some trends for phenomena such as rod/cone dualism, spectral range, preservation or loss of double cones and oil droplets, photopigment co-expression and mono- and tri-chromacy. Finally, we attempt to demonstrate that, building on the limits of an ancient rod dominant (probably dichromatic) model, mammalian retinas have developed considerable radiation. Comparing the nonprimate models with the intensively studied primate model should provide us with a deeper understanding of the basic design of the mammalian retina.

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In most mammals short-wavelength-sensitive (S) cones are arranged in irregular patterns with widely variable intercell distances. Consequently, mosaics of connected interneurons either may show some type of correlation to photoreceptor placement or may establish an independent lattice with compensatory dendritic organization. Since axonless horizontal cells (A-HC's) are supposed to direct all dendrites to overlying cones, we studied their spatial interaction with chromatic cone subclasses. In the cheetah, the bobcat, and the leopard, anti-S-opsin antibodies have consistently colabeled the A-HC's in addition to the S cones. We investigated the interaction between the two cell mosaics, using autocorrelation and cross-correlation procedures, including a Voronoi-based density probe. Comparisons with simulations of random mosaics show significantly lower densities of S cones above the cell bodies and primary dendrites of A-HC's. The pattern results in different long-wavelength-sensitive-L- and S-cone ratios in the central versus the peripheral zones of A-HC dendritic fields. The existence of a related pattern at the synaptic level and its potential significance for color processing may be investigated in further studies.

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The organisation of the human photoreceptor mosaic reflects evolutionary strategies for optimising visual information under a wide range of stimulus conditions: (1) The rod population dominates (max. 170,000/mm2 at c. 30 degrees sup.) except for the central 2 degrees and along the ora serrata. (2) Density of cone inner/outer segments reaches up to 300,000 mm2 in the fovea. A bundle of c. 300-500 foveolar cones are further distinguished by having their synaptic terminals located within the capillary-free zone. Radial displacement (> 350 microns) of foveal cone terminals may result in the lesion of two sets of cone pathways by perifoveal laser treatment. Along the ora serrata peripheral cone density (c. 4000) rises within a small rim (1 degree) to up to 20,000, but may be considerably decreased by cystoid degenerations. For the L- and M-cone subpopulations ratios of 2:1 to 1:1 and random arrangement are suggested. (3) Blue-sensitive (S-) cones constitute a regular and independent submosaic of c. 7% across the periphery. An annular maximum (1000-5000/mm2) at c. 1 degree surrounds the foveola. There density decreases and irregular zones lacking S-cones result in tritan deficiencies.

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The topography and spectral characteristics of mammalian photoreceptors correlate with both, the present ecological demands and the evolutionary history. The South American Opossum is a marsupial mammal with unspecialized habitus and crepuscular lifestyle. A sparse population of cones (max. = 3000/mm2) can be differentiated into four subtypes by morphological, topographical and immunocytochemical criteria. In spite of this unusual diversity the cone types can be split into two functional groups: The population of single cones labeled by antibody OS-2 for short wavelength sensitive pigments was ubiquitous but at very low densities (200/mm2). The single cones labeled by antibody (COS-1) against long wavelength sensitive pigments constitute the dominant population in the area centralis (2300/mm2). These two single cone types correlate with the pair typically present in placental mammals. Discrimination of spatial and color contrast may be provided by this "modern" set. The COS-1 labeled double and single cones bearing an oil droplet, display a different pattern by being restricted to the inferior (non-tapetal) half of the retina (max = 800/mm2). This additional set of cones with oil droplets and long wavelength pigments is a conservative feature of the opossum retina and other marsupials. As an accessory cone system it is possibly providing enhanced sensitivity at mesopic conditions. During the early evolution of nocturnal mammals with its prominent expansion of rod vision these cone types were conserved but then were lost in placental mammals. Thus the unique features of mammalian retinas are the result of two evolutionary steps: first a reduction of cone based vision, followed by a secondary differentiation of photopic vision and behaviour relying on the remaining set of cones.

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The retinas of placental mammals appear to lack the large number and morphological diversity of cone subtypes found in diurnal reptiles. We have now studied the photoreceptor layer of a South American marsupial (Didelphis marsupialis aurita) by peanut agglutinin labeling of the cone sheath and by labeling of cone outer segments with monoclonal anti-visual pigment antibodies that have been proven to consistently label middle-to-long wavelength (COS-1) and short-wavelength (OS-2) cone subpopulations in placental mammals. Besides a dominant rod population (max. = 400,000/mm2) four subtypes of cones (max. = 3000/mm2) were identified. The outer segments of three cone subtypes were labeled by COS-1: a double cone with a principal cone containing a colorless oil droplet, a single cone with oil droplet, and another single cone. A second group of single cones lacking oil droplets was labeled by OS-2 antibody. The topography of these cone subtypes showed striking anisotropies. The COS-1 labeled single cones without oil droplets were found all over the retina and constituted the dominant population in the area centralis located in the temporal quadrant of the upper, tapetal hemisphere. The population of OS-2 labeled cones was also ubiquitous although slightly higher in the upper hemisphere (200/mm2). The COS-1 labeled cones bearing an oil droplet, including the principal member of double cones, were concentrated (800/mm2) in the inferior, non-tapetal half of the retina. The two spectral types of single cones resemble those of dichromatic photopic systems in most placental mammals. The additional set of COS-1 labeled cones is a distinct marsupial feature. The presence of oil droplets in this cone subpopulation, its absence in the area centralis, and the correlation with the non-tapetal inferior hemisphere suggest a functional specialization, possibly for mesopic conditions. Thus, sauropsid features have been retained but probably with a modified function.

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The relationship of primate horizontal cells (HC) to cone pedicles was assessed by superimposing the cone inner segment mosaic upon Golgi-impregnated HC dendritic terminal clusters in a light microscope (LM) study. The HI, HII, and HIII types of HC were identified, hand-drawn, photographed, and analyzed by computer graphics methods. Blue cone (B-cones) inner segments and their projected pedicles were distinguished from red (R-cones) and green (G-cones) cones on morphological criteria. Thus the inclusion or avoidance of B-cone pedicles by the various HC types' dendritic terminal clusters establishes whether there is any color specificity to their connections. In addition, we made counts of the number of dendritic terminals in the clusters going to cone pedicles in the various HCs' dendritic fields and plotted these against distances the cone pedicles lay from the cell body. In this way we could evaluate the weighting of spectral type of cone input. In general, the three HC types made the majority of their dendritic contacts with cones lying closest to their cell bodies at the center of their dendritic fields. However, HI and HIII cells, with their distinct terminal clusters, did not contact all the centrally located cones uniformly. They either avoided completely (HIII cells) or made only sparse dendritic connections (HI cells) with certain cones. The avoided or sparsely innervated cones were identified as B-cones. HII cells, on the other hand, with their more profuse and diffusely branched dendrites, appeared to contact all overlying cone pedicles and, in contrast to HI and HIII cells, directed a relatively larger number of dendrites to B-cone positions. Axon terminals of HII cells appeared to contact B-cones exclusively.

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Golgi-impregnated horizontal cells (HCs) as viewed in whole mount human retinas have been studied by light microscopic (LM) techniques. Impregnated HCs have been drawn by camera lucida and by the Eutectics neuron tracing method to provide quantitative data on dendritic tree sizes, dendritic tree shapes, and dendritic terminals for statistical treatment and cluster analysis. In addition, fractal analyses of HC dendritic branching patterns have been performed. Three significantly different HCs can be classified on both subjective and objective morphological criteria in central and peripheral human retina. In the fovea all HCs are so small that it is difficult to achieve a clear separation of the subtypes, although they can be distinguished by the experienced observer. HI types are the classic HCs of Polyak (The Retina, Chicago: University of Chicago Press, 1941) with distinct dendritic terminal clusters going to cones and a fan-shaped axon terminal consisting of large numbers of rod-destined terminals. HII cells have profusely branched, overlapping dendrites, with poorly defined terminals going to cones and a short curled axon bearing small terminals also going to cones. The HIII types exhibit larger diameter, more asymmetrically shaped dendritic trees and 30% more dendritic terminal clusters than HI cells at any location on the retina. Many HIII cells appear to emit a process from the cell body in the inner nuclear layer (INL) that descends into the outer strata of the inner plexiform layer (IPL). The axon of the HIII cell may end in a loosely organized, sprawling arborization. Fractal dimensions of the horizontal cells also show significant differences between the three groups. HII cells exhibit the highest fractal dimension followed by HI and HIII cells with lower and lowest fractal dimensions, respectively. The fractal dimension of HII cells of rhesus monkey, as determined from drawings by other authors in other publications, are the same as HII cells of human retina.

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Connections of the three human horizontal cell (HC) types with overlying cone pedicles have been studied via electron microscopy (EM). Because blue cones (B-cones) can be recognized on distinctive morphological criteria, we could determine their presence by light microscopy (LM) in the mosaic overlying HC dendritic trees. Then we could confirm the presence or absence of dendritic contacts to B-cone pedicles by examining EM serial sections and making reconstructions of examples of the three HC types. Three HI cells have been reconstructed. Their dendritic terminals ended as lateral elements of ribbon synapses in green and red cone pedicles (G- and R-cones) primarily. B-cone pedicles in HI cell dendritic fields received no more than one or two contacts. Six reconstructed HII cells were found to contact all the pedicles within their dendritic field. However, their dendrites reached especially for B-cone pedicles and innervated them with disproportionately large numbers of terminals compared with G- and R-cones. HII axons appeared to contact B-cones exclusively. The four reconstructed HIII cells were found to avoid completely B-cones in their dendritic fields. Data have been collected on synaptic ribbon lengths at HI and HII lateral elements in the B-cone as compared with G- and R-cone pedicles. HII dendritic terminals end almost exclusively at the smaller ribbons and HI dendrites at the larger ribbons. The number of dendritic terminals provided by the three HCs to G- and R-cone pedicles as compared B-cone pedicles has been more accurately quantitated than was possible in the LM analysis (accompanying paper). New findings on the morphology of B-cone pedicles in peripheral retina have revealed that 1) B-cone pedicles end further vitread in the outer plexiform layer (OPL) than other cone pedicles, thereby forming a sublayer of the OPL neuropil, here named OPLb, in comparison to OPLa, where the G- and R-cone pedicles end; 2) B-cone pedicles have very few telodendrial connections; and 3) in peripheral retina (probably beyond 8 mm from the fovea to the ora serrata), they are bi- or trilobed, with each lobe containing separate synaptic invaginations. The vitread position and unique morphology of B-cone pedicles appear to relate directly to the unique morphology and unusual connectivity patterns of both their B-cone-specific bipolar and B-cone-related horizontal cell, the HII cell.(ABSTRACT TRUNCATED AT 400 WORDS)

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This paper describes an approach to computer-assisted 3D-reconstruction of neuronal specimens based on a low cost yet powerful software package for a personal computer (Atari ST). It provides an easy to handle (mouse driven) object editor to create 3D models of medium complexity (15,000 vertices) from sections or from scratch. The models may be displayed in various modes including stereo viewing and complex animation sequences.

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The quality of the foveal cone mosaic in human and primate retinas is a basic parameter of spatial vision function. The present study uses digital-texture analysis procedures to analyze the crystalline order of inner segment sections containing the rod-free portions of foveal cone mosaics. Definition of the cone cross-sectional centers made possible by adequate preprocessing allows precise mapping of lattice vertices and differentiation of hexagonal positions by procedures for direct neighbor recognition. In a further step, the existence of subunits within the hexagonal areas is revealed by the determination of axial orientation. The lattice of the subunits is characterized by similar orientation and high positional correlation of its hexagonal units. The axial orientation of the areas differs from that of neighboring subunits by angular shifts of 10-15 deg and linear series of nonhexagonal irregularities demarcate the borders. Although larger patches with continuous hexagonal order occur in the surrounding rod-free regions, elevated degrees of disorder (30%) are found within the foveolar center (ca. 300 cones). Analysis of a mosaic showing labeled B cones (Szél et al., 1988) demonstrates that lattice disorder is in part associated with the blue cone subpopulation. The foveal mosaic from a glaucomatuous eye reveals severe lattice degradation throughout the rod-free zone, presumably due to extensive receptor loss. The low-frequency superstructure results in local sets of sampling grids (5'-8') with differing orientational bias. Besides a horizontal/vertical difference of mosaic compression (ca. 1:1.15), the present analysis gives no hints for the existence of systematic meridional anisotropies at the receptor mosaic level. The study reveals a discontinuous organization of the foveal mosaic and points to possible sources for the induction and location of lattice disorder.

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