Aerospace medicine and biology: A continuing bibliography with indexes, supplement 125

This special bibliography lists 323 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1974

Aerospace medicine and biology: A continuing bibliography with indexes, supplement 218, April 1981

This bibliography lists 161 reports, articles, and other documents introduced into the NASA scientific and technical information system in March 1981

An electrophysiological study of chromatic processing in the human visual system. Using visual evoked potentials and electroretinograms to study cortical and retinal contributions to human trichromatic vision.

The work in this thesis is concerned with examining the retinal and cortical contributions to human trichromatic colour vision. Chromatic processing at the cortex level was examined using visual evoked potentials (VEPs). These responses were elicited by chromatic spot stimuli, which were manipulated in order to selectively activate the chromatic processing system. Chromatic processing at the retinal level was examined using the electroretinograms (ERGs) for which cone isolating stimuli were used to assess the nature of L and M cone inputs to cone-opponent mechanisms. The results from the VEP experiments suggest VEP morphology is dependent upon 1) chromatic and or luminance contrast content of the stimulus, 2) stimulus size, and 3) extent to which the chromatic stimulus activates either the L/M or S/(L+M) opponent mechanism. The experiments indicate that chromatic stimulation is indexed by large N1 component and small offset responses. Optimal stimulus size for chromatic isolation is 2-4 ° along L/M axes and 6° along S/(L+M) axis. From the ERG experiments, It has been shown that the low (12Hz) and high (30Hz) temporal frequency flickering stimuli can isolate the chromatic and luminance processing mechanisms in the retina. For low temporal frequency ERGs, the L:M ratio was close to unity and L/M phase difference was close to 180°. For high temporal frequency ERGs, the L:M ratio was more than unity and L/M phase difference was close to 90°. In addition to this, the variation in L:M ratio across the retinal eccentricity was also examined. These results suggest, for the chromatic processing, L:M ratio is close to unity independent of retinal eccentricity and individuals. For the luminance processing, L:M ratio is more than unity and depends upon the region of the retina being stimulated. These findings indicate the maintenance of cone selective input for the chromatic processing across the human retina

Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 152, March 1976

This bibliography lists 252 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1976

Developing a new generation of neuro-prosthetic interfaces: structure-function correlates of viable retina-CNT biohybrids

PhD ThesisOne of the many challenges in the development of neural prosthetic devices is the choice of electrode material. Electrodes must be biocompatible, and at the same time, they must be able to sustain repetitive current injections in a highly corrosive physiological environment. We investigated the suitability of carbon nanotube (CNT) electrodes for retinal prosthetics by studying prolonged exposure to retinal tissue and repetitive electrical stimulation of retinal ganglion cells (RGCs). Experiments were performed on retinal wholemounts isolated from the Cone rod homeobox (CRX) knockout mouse, a model of Leber congenital amaurosis. Retinas were interfaced at the vitreo-retinal juncture with CNT assemblies and maintained in physiological conditions for up to three days to investigate any anatomical (immunohistochemistry and electron microscopy) and electrophysiological changes (multielectrode array stimulation and recordings; electrodes were made of CNTs or commercial titanium nitride). Anatomical characterisation of the inner retina, including RGCs, astrocytes and Müller cells as well as cellular matrix and inner retinal vasculature, provide strong evidence of a gradual remodelling of the retina to incorporate CNT assemblies, with very little indication of an immune response. Prolonged electrophysiological recordings, performed over the course of three days, demonstrate a gradual increase in signal amplitudes, lowering of stimulation thresholds and an increase in cellular recruitment for RGCs interfaced with CNT electrodes, but not with titanium nitride electrodes. These results provide for the first time electrophysiological, ultrastructural and cellular evidence of the time-dependent formation of strong and viable bio-hybrids between the RGC layer and CNT arrays in intact retinas. We conclude that CNTs are a promising material for inclusion in retinal prosthetic devices

Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 178

This bibliography lists 230 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1978

Aerospace Medicine and Biology - A continuing bibliography with indexes

Annotated bibliography and indexes on Aerospace Medicine and Biology - Dec. 196

Electrophysiological investigation of age-related macular degeneration

Age-related macular degeneration (AMD) affects 12.7 million people in Europe and North America (Klein et al., 1995 Klein et al. 1999). As a combination of decreasing birth rate and increasing longevity alter the demographic of the population, the impact of this disease can only increase. This places an immense burden, not only on the individuals afflicted by the condition, but on the financial resources of society as a whole. Unfortunately, treatment for AMD is still very restricted, and even our understanding of the pathogenesis of the disease is far from complete One concern in tackling the growing problem of AMD is that methods used in the assessment of the condition are limited, usually based on fundus appearance and visual acuity. The aim of this study was to develop a battery of electrophysiological tests which would be sensitive to the most subtle changes in retinal function in AMD. Such tests may aid diagnosis, provide a more sensitive measure of disease progression, and allow an early identification of phenotypic subtypes. Protocols were included for the recording of the focal rod ERG, the focal cone ERG, the S-cone ERG and the dynamic focal cone ERG, along with psychophysical tests of colour vision and dark adaptation. These tests were then applied to 31 subjects with ARM (12 with bilateral ARM, 11 with unilateral wet AMD and 8 with unilateral dry AMD), and 28 controls. In the analysis of ERG amplitudes a ratio of focal to full-field amplitude was introduced as a novel means of reducing intersubject variability in response. This was found to increase the accuracy of all tests in distinguishing between subject groups. The greatest separation between ARM and control groups was provided by the dynamic tests of visual function i.e. rod-cone break time of the dark adaptation function, and time constant of recovery of the dynamic focal cone ERG. The time to rod-cone break also showed potential in identifying subjects at increased risk of exudative retinal changes. Subjects were assigned to groups in this study on the basis of fundus appearance. However, individuals within each subject group showed a range of retinal function which belied the homogeneity of retinal signs. This raises the question of whether 'form' or 'function' should form the basis of classification and assessment of individuals with ARM and AMD.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Electrophysiological investigation of age-related macular degeneration

Age-related macular degeneration (AMD) affects 12.7 million people in Europe and North America (Klein et al., 1995 Klein et al. 1999). As a combination of decreasing birth rate and increasing longevity alter the demographic of the population, the impact of this disease can only increase. This places an immense burden, not only on the individuals afflicted by the condition, but on the financial resources of society as a whole. Unfortunately, treatment for AMD is still very restricted, and even our understanding of the pathogenesis of the disease is far from complete One concern in tackling the growing problem of AMD is that methods used in the assessment of the condition are limited, usually based on fundus appearance and visual acuity. The aim of this study was to develop a battery of electrophysiological tests which would be sensitive to the most subtle changes in retinal function in AMD. Such tests may aid diagnosis, provide a more sensitive measure of disease progression, and allow an early identification of phenotypic subtypes. Protocols were included for the recording of the focal rod ERG, the focal cone ERG, the S-cone ERG and the dynamic focal cone ERG, along with psychophysical tests of colour vision and dark adaptation. These tests were then applied to 31 subjects with ARM (12 with bilateral ARM, 11 with unilateral wet AMD and 8 with unilateral dry AMD), and 28 controls. In the analysis of ERG amplitudes a ratio of focal to full-field amplitude was introduced as a novel means of reducing intersubject variability in response. This was found to increase the accuracy of all tests in distinguishing between subject groups. The greatest separation between ARM and control groups was provided by the dynamic tests of visual function i.e. rod-cone break time of the dark adaptation function, and time constant of recovery of the dynamic focal cone ERG. The time to rod-cone break also showed potential in identifying subjects at increased risk of exudative retinal changes. Subjects were assigned to groups in this study on the basis of fundus appearance. However, individuals within each subject group showed a range of retinal function which belied the homogeneity of retinal signs. This raises the question of whether 'form' or 'function' should form the basis of classification and assessment of individuals with ARM and AMD

Structural Integrity of Eyes Diagnosed with Amblyopia. The measurement of retinal structure in amblyopia using Optical Coherence Tomography.

Amblyopia is the leading cause of monocular visual impairment in children. Therapy for amblyopia is extremely beneficial in some children but ineffective in others. It is critical that the reasons for this discrepancy are understood. Emerging evidence indicates that current clinical protocols for the diagnosis of amblyopia may not be sufficiently sensitive in identifying individuals who, on more detailed examination, exhibit subtle structural defects of the eye. Presently, the magnitude of this problem is unknown. The aim of this study was to establish the prevalence of subtle retinal/optic nerve head defects in eyes diagnosed with amblyopia, to distinguish between possible explanations for the origin of such defects and to investigate the relationship between quantitative measures of retinal structure, retinal nerve fibre layer thickness and optic nerve head dimensions. Using the imaging technique of Optical Coherence Tomography (OCT) retinal structure has been investigated in detail, following the visual pathway across the retina from the fovea, via the paramacular bundle to the optic disc, where peripapillary retinal nerve fibre thickness has been imaged and subjected to detailed measures along with optic disc size and shape. The study formed two phases, the first imaging the eyes of visually normal adults and children, comparing them to amblyopes, both adults and children who had completed their treatment. The second phase, a longitudinal study, investigated retinal structure of amblyopic children undertaking occlusion therapy for the first time. By relating pre-therapy quantitative measures to the visual outcome the second phase of the study aimed to examine whether OCT imaging could identify children achieving a poor final outcome. The results show a clear picture of inter-ocular symmetry structure in all individuals, visually normal and amblyopic. Optic disc characteristics revealed no structural abnormalities in amblyopes, in any of the measured parameters, nor was there any association between the level of visual acuity and the measured structure. At the fovea differences were shown to occur in the presence of amblyopia, with thickening of the fovea and reduction of the foveal pit depth. The structural changes were found to be both bilateral and symmetrical with the fellow eye also affected. In the longitudinal phase of the study these changes were demonstrated to a greater extent in children who ¿failed¿ to respond to treatment. This bilateral, symmetrical structural change found at the fovea, which has not been previously reported, cannot therefore be the primary cause of the visual loss which has been diagnosed as amblyopia