Clinical Utility of Computerized Optic Nerve Analysis
This chapter emphasizes the point that glaucoma is a disease of retinal nerve fibers and their ganglion cells. The diagnosis and management of glaucoma requires the ability to detect the loss of retinal nerve fibers (i.e., determining if an individual has less nerve fibers than he/she is supposed to have based upon the population from which he/she comes) and to determine if the loss of retinal nerve fibers occurs at a rate greater than what is expected from normal aging. The “traditional” method for doing this has been through direct ophthalmoscopy and the determination of the cup-to-disc ratio, with the assumption that “cupping” represents the loss of nerve fibers from the neuroretinal rim. The problem with the traditional method is that it has no way of accounting for the large structural variability of human optic nerve heads. A cup-to-disc ratio of 0.6, for example, may be quite normal in an axial myope, but may be quite pathological if it was 0.3 ten years before the patient was ever seen by the eye care provider. Likewise, it may be quite normal if the disc is large, and abnormal if the disc is small. Plus, the determination of cup-to-disc ratio only provides an (subjective) indirect measure of the retinal nerve fiber layer, the tissue of interest in glaucoma. Small changes in cup-to-disc ratio may be very difficult to detect by ophthalmoscopy, and progression may go unnoticed for years. Hence, better methods are required and, as outlined in this chapter, have been developed.
KeywordsOptical Coherence Tomography Retinal Nerve Fiber Layer Optic Nerve Head Heidelberg Retinal Tomograph Computerize Scanning Imaging
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