Clinical Studies in Scanning Laser Polarimetry

Glaucoma is the second leading cause of irreversible blindness worldwide. When left untreated, glaucoma results in visual field loss and eventually in blindness. In considering the diagnosis of glaucoma, the physician will evaluate the intraocular pressure, the optic nerve head and the visual field. This seems to be a straightforward diagnostic process, but, surprisingly, there is still no consensus on the criteria for the signs on which the diagnosis is based. Glaucoma is a progressive optic neuropathy characterized by death of retinal ganglion cells. The course of events that eventually leads to death of these cells is not exactly known, but the retinal nerve fiber layer, which is made up of the axons of the retinal ganglion cells, thins. Scanning laser polarimetry is an imaging technique that can detect glaucoma by assessing the thickness of the retinal nerve fiber layer. Scanning laser polarimetry came onto the market in 1993. The working principle is based on the fact that in the nerve fiber layer a phase shift occurs in polarized laser light that is sent through the nerve fiber layer. This so called retardation is thought to be linearly correlated with nerve fiber layer thickness. In the past, scanning laser polarimetry has shown to discriminate well between normal and glaucomatous eyes. The goal of this thesis was to investigate the clinical performance of the GDx (a revised version of the first scanning laser polarimeter, the Nerve Fiber Analyzer). In summary, the GDx provides fast, objective and quantitative data on nerve fiber layer thickness. The applicability and reproducibility of measurements are high and the image acquisition is user and patient friendly. The GDx yields useful sensitivity and specificity values for the detection of glaucoma, whereas its role in follow-up remains to be investigated. As it stands, the GDx holds insufficient validity to serve as a single test for glaucoma. It does, however, provide a very useful addition to the existing tests we run in patients to make the correct diagnosis.

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