The human eye is like a camera. It captures light information from the world and sends it to the brain. The brain then makes sense of that information so that we can observe our surroundings, recognize familiar objects and people, avoid obstacles, etc. The eye sends all the information that it captures to the brain via a small, delicate, but very important cable called the optic nerve.
The optic nerve can be damaged in many ways. Glaucoma is one of the leading causes of optic nerve damage. In fact, glaucoma is also the leading cause of incurable blindness in the world. A person who has glaucoma at first looses peripheral or side vision. If nothing is done about it, the person could keep losing more and more peripheral vision until they have only tunnel vision left. Eventually, the person could lose all their vision. Once a person loses vision to glaucoma, there is nothing doctors can do to bring that vision back.
The human eye makes fluid and drains that same fluid in a continuous cycle in order to maintain a constant shape, pressure and internal environment. Due to this continuous cycling of fluid, the pressure inside the normal human eye, also known as intraocular pressure or IOP, is normally between 9 and 21 millimeters of mercury (mmHg). As a comparison, normal blood pressure in the human body is around 115mmHg systolic, and around 75mmHg diastolic in healthy adults. From this point on, the word ‘pressure’ in this document will refer to eye pressure or IOP, unless otherwise specified.
The part of the eye that makes fluid is called the ciliary body. It sits behind the coloured part of the eye called the iris. The structure that drains the fluid is known as the angle. The angle is located in front of the iris. It is called the angle because it is located where the iris meets the clear covering of the eye called the cornea. Broadly speaking, there are two types of glaucoma: open angle glaucoma, and angle closure glaucoma. In open angle glaucoma, the angle looks open but does not function properly for a wide variety of reasons. On the other hand, in angle closure glaucoma, the angle is physically closed and therefore does not allow fluid to drain out of the eye normally. Either way, pressure builds up inside the eye.
Many people believe that glaucoma is a disease of high pressure inside the eye. Strictly speaking, this is not completely correct. While most people with glaucoma have high eye pressure, some people who develop glaucoma have always had pressures in the normal range, while other people who have high pressure never develop glaucoma!
In any case, once a person is diagnosed with glaucoma, the only way to protect them from continuing to lose vision is to reduce the IOP. Doctors do this with medications, laser, and surgery. In this document, we will cover the details of medications, lasers, and surgery for glaucoma.