The glaucomatous visual field.

The characteristic visual field defect in chronic simple glauconma occurs as a result of damage to individual bundles of nerve fibres in the optic nerve head.Chronic simple glaucoma, while the most frequent cause, is not the only cause of nerve fibre bundle defects.The causes ofsuch defects were divided by Harrington (i 965) into those occurring at the disc, those resulting from lesion of the anterior nerve, and those due to lesions of the posterior nerve and chiasm (Table ).Table Lesions producing arcuate scotomata (Harrington, I965) Lesions at the disc i. Juxtapapillary choroiditis 2. Myopia and peripapillary atrophy 3. Colobomata and pits of the optic nerve head 4. Drusen on the optic nerve 5. Papilloedema with increased intracranial pressure 6. Secondary optic atrophy to papilloedema 7. Papillitis 8. Retinal arterial plaque on the disc 9. Papilloedema in malignant hyper- tension 1o.Occlusion of central retinal artery Lesions of the anterior nerve i.Ischaemic infarct and segmental atrophy in the optic nerve due to arterial occlusion 2. Carotid and ophthalmic artery occlusion 3. Cerebral arteritis 4. Retrobulbar neuritis 5. Electric shock 6.Exophthalmos Lesions in the posterior nerve and chiasm i. Meningioma at the optic foramen 2. Meningioma of the dorsum sellae 3. Pituitary adenoma 4. Opticochiasmatic arachnoiditis Knowledge of the visual field changes and their progression is essential so that perimetric techniques can: (i) Delineate the earliest characteristic nerve fibre bundle defects which indicate glau- comatous damage.(2) Plot the size and density of the defects, so that changes indicating progression can be recorded accurately and reproducibly. SIGNIFICANCE OF BARING OF THE BLIND SPOTBaring of the blind spot has been described as one of the early changes of the glaucomas (Traquair, I93I).In most normal individuals, there is a difference in the sensitivity of the retina above and below the disc.The portion of the visual field below the blind spot has a slightly iower differential threshold and is slightly more sensitive to light than the corresponding area above the blind spot.The profile of the field above the blind