D Max Snodderly - US grants

The pigmentation and geometry of the primate fovea are prominent features thought to be associated with high acuity. We propose to measure the spatial distribution of the macular pigment in the foveal region and relate it to the width of the fovea, especially the avascular zone. Entoptic phenomena caused by macular pigmentation, retinal vasculature, and foveal geometry will be studied in the same subjects. Visual acuity at different eccentricities within the fovea will be measured in human subjects with dense or slight pigmentation and small or large avascular zones. This will test whether the pigmentation and foveal size are tightly linked with visual acuity. The macular pigment will be visualized in vivo in human and monkey eyes by monochromatic fundus photography and the pigment density distribution will be estimated. The avascular zone of the fovea will be measured by fluorescein angiography in the same monkey eyes and a few human eyes for which pigment measures were made. Some of the monkey eyes that were photographed will be excised and the Pigment density will be measured by microspectrophotometry and densitometry to establish the limits of precision of the in vivo technique. Two-dimensional plots of the pigment distribution will be obtained by image analysis. This project will combine the resources of three different laboratories in the Boston area. The long-term objectives of the project are to characterize the natural variations in macular pigmentation and foveal geometry that occur in a representative population of normal human subjects. Our research will establish techniques to estimate macular pigmentation and foveal size in vivo. It will link physical measurements with entoptic phenomena. These phenomena may be useful in obtaining information about the state of the macula in older patients with poor optic media. The availability of the methodology will also make it possible to study whether particular types of foveal pigmentation or foveal geometry are associated with the development of macular degeneration or other disorders of the macula.

Primate foveas have a distinctive yellow macular pigment that is one of their recognized specializations. The long-term objectives of this application are to test two major nonexclusive hypotheses about the functional roles of the macular pigment. The first hypothesis states that the macular pigment aids in visual resolution in the fovea by absorbing scattered or poorly focussed blue light. A parallel series of experiments will be done with monkeys and humans to examine the relationship of the foveal pigmentation to visual resolution. Monkey retinas will be studied by densitometry, microscopy and image analysis. The macular pigment density distribution, and other foveal features will be characterized. These data will be used to refine monochromatic fundus photography for measuring the macular pigment density in vivo. Humans with high and low amounts of macular pigment measured by the in vivo technique will be compared on a demanding test of visual acuity. The test stimulus will be placed precisely at closely spaced intervals within the foveal avascular zone by image stabilization. An accurate profile of visual acuity in the fovea will be determined. If the resolution hypothesis is correct, humans with higher amounts of macular pigment should have better visual resolving power. The second hypothesis states that the macular pigment protects the fovea from damage by light and oxygen. Protection could occur by absorption of light, quenching of radicals, or breaking chain reactions leading to lipid oxidation. Absorption of light will be measured optically by microdensitometry and image analysis. In the same retinas the concentrations of lutein and zeaxanthin, the carotenoids that comprise the macular pigment, will be measured by high performance liquid chromatography. Serum and other tissues of the same individuals will also be analyzed for carotenoid concentrations. Retinas of monkeys with high and low amount of macular pigment will be assayed for lipid oxidation products. If macular pigment is protective, the retinas low in macular pigment should be subject to more oxidative damage and be higher in lipid peroxides. Two health-related results are expected. One is a description of visual acuity in the avascular zone of the fovea. This may be useful for establishing treatment criteria for mascular disease. The other outcome will be better understanding of one of the key factors that is thought to protect the macula from damage.

Long-term objectives: Describe the anatomical variations of the vasculature of primate retinas, with special emphasis on the fovea. Relate the geometry of the vasculature to the structure of the neural layers. Compare the chacteristics of the vascular patterns at different retinal loci. Specific Aims: Study the retinal vasculature of primate retinas in histological preparations. Describe the laminationof retinal capillaries and their relationships to the planes established by the neural layers. Compare the capillary planes to planes of high metabolic activity. Build solid models of the vascular networks using computer image analysis techniques to obtain a three- dimensional view of the interconnections betwee the capillary planes at selected retinal loci. Determine which anatomical features of the vasculature are readily observed in vivo by fluorescein angiography. Characterize unusual patterns of the foveal vasculature, such as vessels crossing the foveola and relate them to any concomitant anatomical anomalies of the retina. Methods: Monkeys will be studied by fuundus photography and fluorescein angiography. Retinas from the same animals will be prepared as whole mounts and a continuity diagram of the vessels will be drawn at high magnification. The depth planes of the vessesl will be coded on the drawings and enterd into an image analysis systems to build a three-dimensional model. The retinas will be sectioned to relate the vessel planes to the neuronal bujndary planes and planes of high cyutochrome oxidase activity. The detail available in the histological preparations will be compared with fundus photos and fluorescein angiograms. Significance and Helath Relatedness: The literature on the retinal vasculature, particularly in the fovea, is full of contradictions and errors. By relating the vasculature to the neural layers, many of the issues can be resolved. It will then be possible to interpret clincial tests such as fluorescein angiograms with more confidence and precision. The results may assist in understanding the changes in the retina that occur in patients with diabetes, macular degeneration, and other conditions.

Long-term objectives: Describe the anatomical variations of the vasculature of primate retinas, with special emphasis on the fovea. Relate the geometry of the vasculature to the structure of the neural layers. Compare the chacteristics of the vascular patterns at different retinal loci. Specific Aims: Study the retinal vasculature of primate retinas in histological preparations. Describe the laminationof retinal capillaries and their relationships to the planes established by the neural layers. Compare the capillary planes to planes of high metabolic activity. Build solid models of the vascular networks using computer image analysis techniques to obtain a three- dimensional view of the interconnections betwee the capillary planes at selected retinal loci. Determine which anatomical features of the vasculature are readily observed in vivo by fluorescein angiography. Characterize unusual patterns of the foveal vasculature, such as vessels crossing the foveola and relate them to any concomitant anatomical anomalies of the retina. Methods: Monkeys will be studied by fuundus photography and fluorescein angiography. Retinas from the same animals will be prepared as whole mounts and a continuity diagram of the vessels will be drawn at high magnification. The depth planes of the vessesl will be coded on the drawings and enterd into an image analysis systems to build a three-dimensional model. The retinas will be sectioned to relate the vessel planes to the neuronal bujndary planes and planes of high cyutochrome oxidase activity. The detail available in the histological preparations will be compared with fundus photos and fluorescein angiograms. Significance and Helath Relatedness: The literature on the retinal vasculature, particularly in the fovea, is full of contradictions and errors. By relating the vasculature to the neural layers, many of the issues can be resolved. It will then be possible to interpret clincial tests such as fluorescein angiograms with more confidence and precision. The results may assist in understanding the changes in the retina that occur in patients with diabetes, macular degeneration, and other conditions.

Long-term objectives: Primate retinas have a yellow macular pigment that is thought both to enhance visual resolution and to protect the retina and retinal pigment epithelium (RPE) from oxidative damage. It is likely that some people with low pigment densities are at risk for chronic retinal damage and age-related macular degeneration. Our goal is to identify nutritional and retinal factors contributing to the protection of the retina by retinal carotenoids and Vitamin E. The idea that macular pigment contributes to refined visual resolution (acuity) in the fovea will be critically tested. Specific Aims: I. Identify factors underlying individual differences in density of macular pigmentation. Manipulate dietary levels of carotenoids while monitoring the resultant changes in the blood and the retinas of monkeys. Determine whether differences in macular pigment density are linked to differences in cone density in macaques and humans. II. Compare the spatial distributions of macular pigment carotenoids and Vitamin E. Compare the spatial distributions of the carotenoids comprising the macular pigment with the spatial distribution of Vitamin E in monkey and human retinas by microdissection and biochemical analyses. Determine whether Vitamin E is selectively associated with rod photoreceptors, which are known to be lost with aging. III. Measure the optical density profile of human macular pigment and assess its importance for visual performance. The spatial profile of human macular pigment density will be measured and compared with the spatial dimensions of the foveal depression. Noninvasive techniques will be utilized to study human macular pigment in vivo accurately and efficiently. Postmortem donor retinas will be studied in histological preparations to confirm the general features of the in vivo data. Individual differences in macular pigment density will be correlated with blood levels of macular pigment carotenoids. Subjects will include both genders and a cross section of ages and ethnic backgrounds from the local population. Visual resolution (acuity and contrast sensitivity) of subjects with high and low macular pigment will be tested to determine whether macular pigment improves visual performance. Methodology: The macular pigment carotenoids and Vitamin E will be measured in blood and retina by HPLC. In vivo measures of macular pigment in monkeys and some humans will be made by two-wavelength (photographic) reflectometry. The reflectometry data will be validated for monkeys by densitometry of retinal whole mounts, and for humans by psychophysical threshold testing. In older human subjects, much of the in vivo data will be gathered by psychophysical measurements. Retinal rod and cone distributions will be mapped by Nomarski imaging of retinal whole mounts. Health Relatedness: Older people are protected against the neovascular form of age-related macular degeneration by higher blood levels of carotenoids and other antioxidants. Thus manipulation or supplementation of the diet offers hope for preventive therapy. Our basic research project will provide essential data and techniques for deriving the maximum benefit from large, expensive clinical trials that are currently being initiated.

The goal of this research is to analyze the effects of eye movements and eye position on the electrical activity of neurons in primary visual cortex (VI) and the second visual cortical area (V2) of macaque monkeys. During the viewing of natural scenes the brain must separate the modulatory influences of eye movements from the signals that code properties of objects in the world. A major theme is the effects of the drifts and the small saccades of fixational eye movements. These miniature eye movements help to maintain the visibility of stationary visual stimuli. Some cortical cells appear to respond preferentially to the slow component of fixational eve movements (drifts) while others respond to the faster component (saccades). For comparison, the effects of larger voluntary saccades that scan the visual world will be studied. Recent psychophysical evidence indicates that voluntary saccades selectively suppress the visual input of the magnocellular system. These results imply that as saccades become larger, there may be a switch from excitatory to inhibitory effects on cortical neurons. In addition, large saccades have the consequence of taking the eye to a new position in the orbit. To judge the position of objects in the world, the brain must maintain information about the position of the eye in the orbit to combine it with location of the image on the retina. The spatial gain fields of V1 and V2 neurons that contribute to this computation will be measured. Recording sites will be localized to specific anatomical compartments to identify the regional networks and the pathways within which the recorded neurons are embedded. The results will be relevant to human visual perception, as well as in vivo imaging of human visual function.