Abstract

Glaucoma can be defined as an optic neuropathy where the clinical features include optic disc cupping and pallor, a characteristic pattern of mid-peripheral visual field loss and intra-ocular pressure which may be elevated or, less frequently, within the normal range.

The underlying hypothesis in glaucoma is that, following a period of raised ocular pressure there is loss of retinal ganglion cells which leads to a change in the appearance of the optic nerve head and which ultimately will result in irreversible visual field loss. This model of the disease is the basis upon which treatment of glaucoma is organised, i.e. lowering of intra-ocular pressure is the mainstay of treatment.

The fact that optic disc damage precedes loss of visual function in glaucoma emphasises the importance of being able to recognise the characteristic features of the glaucomatous optic nerve head. The clinical appearance of the optic disc in end-stage disease is easily recognised. However, the changes of early and moderate glaucoma can sometimes be difficult to evaluate.

The use of traditional terms, such as cup-to-disc ratio, cupping and pallor, and nasal displacement of vessels, helps to describe some well recognised features. Other aspects, including the presence of peripapillary atrophy, visibility of the lamina cibrosa, and thinning of the neuro-retinal rim provide further additional information. Frequently it is a combination of several features, rather than any one single feature, which forms the basis of the diagnosis. The size and shape of the optic disc influence the extent of disc cupping, and because the relevance of the cup to disc ratio depends on optic disc size it is important to have accurate measurements of disc size. It is essential also that the disc appearance coincides with the visual field result.

Because of the poor intra- and inter-observer agreement at describing the features of optic disc damage in glaucoma, photographic documentation is a valuable aid in clinical management. Recent advances in image analysis techniques, including confocal laser scanning and optic coherence tomography, may, in the future, provide objective and reproducible quantitative data of optic disc cupping and retinal nerve fibre layer thickness. For the time being, careful clinical examination of the optic disc remains a vital part of the assessment of the glaucoma patient.