Pressure in the eye is usually balanced and plays an important part in the functioning of the eye. This pressure is created when a fluid (known as aqueous) produced by cells behind the iris, passes through the pupil to be drained away by drain tunnels in the angle of the eye (gap between the cornea and the iris). Pressure increases if the angle becomes blocked and the aqueous can not drain away fast enough, or if too too much aqueous is produced.
Chronic glaucoma is more common in Western countries than acute glaucoma, but is easier to treat. This form of glaucoma causes no pain, and your eyesight seems normal, despite the damage being done to your optic nerve. Many people who have had chronic glaucoma for a long time before diagnosis complain of one eye's vision being worse than the others, or a loss of field vision in the shape of an arc above or below the center of their vision. If left untreated, it can result in "tunnel-vision", and in time, this too is lost. It is more common in people over the age of 40, and it affects 5% of the population over the age of 65. People of African origin are said to be more prone to glaucoma, as well as those with a high degree of short sightedness . Treatment includes eye drops (to reduce the amount of aqueous you produce, and to unblock the drainage tunnels) and laser surgery, to improve drainage.
Acute glaucoma is characterized by sudden pain in the eye, as well as the appearance of misty rainbow colored circles surrounding white lights. This may be followed by complete loss of sight and nausea and vomiting. Typically, people experience a series of mild attacks in the evenings, and with routine inspection at the hospital or GP's surgery, acute glaucoma is diagnosed. It is initially treated with drops to reduce the amount of aqueous produced, and then a small hole is made in the iris to remove the blockage in the angle. It is recommended that this is done to both eyes, as if you suffer with acute glaucoma in one eye, it is highly likely that you will contract it in the other.
It is important to attend your optician appointments, because even if you feel as though your eyesight is fine, there may be damage to your optic nerve, which will reduce your quality of vision in the long run. While this condition is not common, neither is rare and quick diagnosis is important to maintaining healthy eyesight.