Use of photographs for measuring cupping in the optic disc.

Our ability to diagnose chronic glaucoma and to control the disease still depends to a great extent on the observations that we can make on the intraocular pressure, the visual field, and the optic disc. In recent years the accuracy of tonometry has been improved and more efficient apparatus for testing visual fields has been produced, although it is common experience that the value of visual field testing may be limited by the subjective element in the procedure. It is now widely appreciated that solving the problem of accuracy of measurement of intraocular pressure does not solve all the problems of the diagnosis and management of glaucoma, because there is no simple relationship between the level of that pressure and the degree or the progression of visual damage. By contrast, it might be expected that the appearance of the optic disc should be closely related to the degree of visual damage and should be amenable to objective assessment. In practice, however, most of us find that although we can often confidently recognize an optic disc as glaucomatous or non-glaucomatous, there are also some discs which cause us great difficulty when we try to make this differentiation. Furthermore, there is sometimes a discrepancy between the amount of recognizable glaucomatous change in the disc and the degree of associated visual field change. These considerations, and others, suggest either that our present methods of observing the disc do not reveal the early features of glaucomatous damage, or that we are not yet aware of the earliest changes, or that, although we recognize certain features as pathological, we do not observe them with sufficient precision.