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Vitamin A deficiency primarily affects young children in developing countries, the symptoms of which initially present as nyctalopia, an inability of the eyes of ‘see’ in low luminance levels, specifically at twilight or at night. Vitamin A deficiency is a major cause of blindness in developing countries and is associated with significant increases in child morbidity and mortality. Nyctalopia may be examined using dark adaptometry; however, current methods of dark adaptometry have many practical limitations, including their unsuitability for use with children. This thesis reports on the design, construction, testing and evaluation of a novel automated dark adaptometer for use as a diagnostic tool in order to screen individuals and/or populations at risk from hypovitaminosis A, or other causes of night vision defects – in either third or first world situations. An instrument was devised and designed which was portable, robust, easy to use outside the clinical environment, and used solid state devices, allowing digital data capture, retrieval and display. The construction of a fully working concept prototype adaptometer model is reported, from conception phase through to data evaluation. A comprehensive description is provided on the design rationale, construction details, circuit diagrams and circuit schematics and test protocol procedures. The successful evaluation of the concept prototype adaptometer led to the development of a more sophisticated post prototype instrument which is similarly described. Repeat dark adaptation data is reported on both the concept prototype adaptometer and post prototype instrument. Data is presented on the evaluation and analysis of the concept prototype adaptometer which involved the examination of 22 healthy test volunteers. In excess of 60 repeat investigations were successfully completed on the majority of these subjects to establish the variation in subject performance and consistency of the data collected. The elevation of the rod threshold with advancing age was examined and confirmed. Results on the evaluation of the post prototype (automatic dark adaptometer) are similarly presented with the results compared to the conventional dark adaptometry methodology; specifically the Goldmann-Weekers Adaptometer. Evidence is presented on the new instrument’s repeatability and precision; and its suitability as a clinical measurement tool. Data is presented on test-retest repeatability using the new instrument on 31 subjects comprising 50 repeat investigations. The instrument described in the thesis has been successfully patented.
O'Brien, David M. C. (2009). Development and Evaluation of a Novel Automated Physchophysical Instrument for the Investigation of Nyctalopia Using Multiple Stimulus Light Emitting Diode Matrix Display Arrays. Technological University Dublin. doi:10.21427/D7GC70