Malik, R; (2012) Investigation of Psychophysiological and Electrophysiological Changes in Primary Open Angle Glaucoma. Doctoral thesis , UCL (University College London).

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Abstract

The functional assessment of patients with primary open angle glaucoma (POAG) is important both for quantifying glaucomatous damage and for providing the clinician with an indication of the level of visual impairment from glaucoma. In its commonest form, perimetry is carried out using automated computerised techniques to bracket visual sensitivity (differential light sensitivity, DLS) at multiple test locations. Test parameters for contemporary standard automated perimetry (SAP) have largely been translated from the Goldmann kinetic parameter with minimal modification, with the use of an achromatic circular stimulus of a fixed size and perimetric strategies which utilise logarithmic (decibel, dB) increments of sensitivity. Perimetry is not without its problems: tests can often be unreliable and learning and fatigue effects contribute to test variability. Electrodiagnostic tests offer an alternative and objective means of functional assessment. In this regard, the photopic negative response (PhNR) is a technically easy test to perform and is not dependent on precise fixation stability or refractive correction. Following the introductory chapter (Chapter 1), the thesis consists of two broad areas of study: psychophysical (visual field) changes in POAG (Chapters 2 and 3) and electrophysiological changes in POAG (Chapter 4). Chapter 2 explores the use of linear units for the measurement of DLS, with the development of new algorithms which yielded lower perimetric bias and variability compared to conventional dBincrement algorithms. Two new stimuli for perimetry were subsequently developed with the aim of improving correlation and agreement of DLS with structural parameters in POAG (Chapter 3). The electrophysiological investigations demonstrated the PhNR to be as sensitive as global visual field measures and existing electrophysiological tests for the identification of functional loss associated with glaucomatous optic neuropathy (Chapter 4) and further refinement of this response for the diagnosis of glaucoma has been recommended (Chapter 5).

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