Overview of Glaucoma
Glaucoma is an umbrella term for optic nerve pathologies (diseases) characterised by progressive degeneration of retinal ganglion cells in the nerve fibre layer of the retina.
The optic nerve is a bundle of over one million nerve fibres (extensions from the retinal ganglion cells) at the back of the eye that carry visual messages from the retina to the brain. These nerve fibres exit the eye through a hole in the sclera called the lamina cribrosa. The lamina cribrosa is the weakest point of the wall of the pressurised eye. Intraocular pressure-induced stress and strain can disrupt this area causing damage to the nerve fibres.
Glaucoma is the result of retinal ganglion cell death and damage which is characterised by thinning of the nerve fibre layer. With retinal ganglion cell death and optic nerve fibre loss in glaucoma, characteristic changes referred to as “cupping” in the appearance of the optic nerve head and retinal nerve fibre layer occur.
Figure 1 (a) shows a normal, healthy optic nerve head fundus image on the left, and the cupping of the optic nerve head in an eye with glaucoma on the right, the diameter of the optic cup is indicated by a double ended arrow, the optic disc is indicated by a single ended arrow. Figure 1 (b) provides an illustration of the changes in the optic cup and disc of a normal healthy eye on the left, compared to the glaucomatous cupping on the right. This image was adapted from Marais, Andre & Osuch, Elzbieta. (2017). The medical management of glaucoma. South African Family Practice. 59. 6-13.