Garway-Heath, David F.; (2001) Correlation of structural and functional measurements in primary open angle glaucoma (optic disc morphology and psychophysics). Doctoral thesis (M.D), UCL (University College London).

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Abstract

Background: Primary open angle glaucoma (POAG) is the term given to a progressive optic neuropathy for which the major risk factors are raised intraocular pressure and older age. The presence of glaucoma is defined by functional (visual field) defects that are associated with loss of retinal ganglion cells and neuroretinal tissue at the optic nerve head (ONH). The relationship between the functional and structural changes is, therefore, of great importance to the understanding of the disease process, and to the clinician's interpretation of the state of the disease. This thesis sets out to define the relationship between retinal function, as measured by conventional white-on-white perimetry, and optic nerve head structure, as measured by scanning laser ophthalmoscopy. Plan of research: The investigations are divided into four parts. Firstly, the ONH structural measurements that best distinguish glaucomatous from normal eyes are determined. This includes an analysis of the relationship between the optical components of the eye and image magnification. Secondly, an analysis of the physiological relationship between ganglion cell numbers and retinal function. Thirdly, the establishment of the anatomical relationship between visual field locations and the ONH (a map relating the visual field to the ONH). And fourthly, the investigation of the correlation between structural and functional measurements in POAG. Results: Neuroretinal rim area in relation to optic disc size is the best parameter to distinguish glaucomatous from normal eyes. The physiological relationship of ganglion cell numbers to decibel light sensitivity (10*log[1/light intensity]) is curvilinear and to light sensitivity (1/light intensity) is linear. The visual field/ONH map allows a correlation of sectoral ONH and regional visual field sensitivity. Analyses demonstrate that the relationship of neuroretinal rim area to decibel light sensitivity is curvilinear in glaucoma. Clinical significance: The curvilinear relationship between decibel light sensitivity and neuroretinal rim area indicates that staging of glaucoma by decibel summary indices may underestimate the amount of structural damage in early disease. In addition, the analysis of disease progression by linear modelling of decibel light sensitivity over time may need re-evaluation.

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