Part 2 book “ABC of eyes” has contents: Glaucoma, age-related macular degeneration, squint, general medical disorders and the eye, the eye and the nervous system, global impact of eye disease. | 9 Glaucoma The glaucomas are a range of disorders with a characteristic type of optic nerve damage. The glaucomas are the second commonest cause of blindness in the world, and the commonest cause of irreversible blindness. The most effective way of preventing this damage is to lower the intraocular pressure. Normally the ciliary body secretes aqueous, which flows into the posterior chamber and through the pupil into the anterior chamber. It leaves the eye through the trabecular meshwork, flowing into Schlemm’s canal and into episcleral veins. The flow and drainage can be obstructed in several ways. Block in flow through meshwork Raised episcleral venous pressure Symptoms and signs A patient with primary open angle glaucoma (also known as chronic open angle glaucoma) may not notice any symptoms until severe visual damage has occurred. This is because the rise in intraocular pressure and consequent damage occurs so slowly that the patient has time to compensate. In contrast, the clinical presentation of acute angle closure glaucoma is well known, as the intraocular pressure rises rapidly and results in a red, painful eye with disturbance of vision. Block in flow between iris and lens Flattening of iris against trabecular meshwork Normal aqueous drainage and possible sites of obstruction The clinical signs of raised intraocular pressure depend on both the rate and degree of the rise in pressure Raised intraocular pressure Most patients with raised intraocular pressure (IOP) are unaware that they have a problem. Raised IOP is detected most commonly through screening as part of a routine eye test by an optometrist. The IOP is determined by the balance between aqueous production inside the eye and aqueous drainage out of the eye through the trabecular meshwork. Each normal eye makes about 2 l of aqueous a minute—that is, about 70 litres during the course of a lifetime. In a British Caucasian population, 95% of people have an IOP between 10 and 21 mm Hg, but IOP .
