Histologically, there are remarkably few changes to account for the raised intraocular pressure, at least in the early stages of the disease. Subsequently, degenerative changes have been described in the juxtacanalicular trabecular meshwork, with endothelial thickening and oedema in the lining of Schlemm's canal. It has been shown that in the majority of cases the problem is one of inadequate drainage rather than excessive secretion of aqueous. In the untreated patient, the chronically raised pressure leads to progressive damage to the eye and eventual blindness. The rate of progress of the disease varies greatly from individual to individual. It is possible for gross visual loss to occur within months, but the process may take five years. Younger eyes survive a raised pressure rather better than older eyes, which could already have circulatory problems. Few eyes can withstand a pressure of 50mmHg for more than a week or two or a pressure of 35 mmHg for more than a few months.
Primary open-angle glaucoma is nearly always bilateral, but often the disease begins in one eye, the other eye not becoming involved immediately. It is important to realise that the progress of chronic glaucoma can be arrested by treatment, but unfortunately, many ophthalmologists experience the natural history of the disease by seeing neglected cases.
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