What is glaucoma?
Glaucoma is the name given to a group of eye diseases where vision is lost due to damage to the optic nerve. Approximately 300,000 Australians have glaucoma. Generally there are no symptoms or warning signs in the early stages of this eye condition. The loss of sight is usually gradual and a considerable amount of peripheral (side) vision may be lost before there is an awareness of any problem. The best way to protect your sight from glaucoma is to have your eyes tested.
Glaucoma cannot be self-detected, and many people affected by glaucoma may not be aware of any vision loss. It is important to remember that while it is more common as we get older, glaucoma can occur at any age. Unfortunately there is currently no cure for glaucoma and vision cannot be regained, although early detection and adherence to treatment can halt or significantly slow progression.
The eye works very much like an old-style camera. In the camera, the light comes in through the shutter, is focused by the lens, falls onto the film and then we take it to be processed.
In the eye, light comes in through the cornea and pupil. It is focused by the lens, falling onto the film in the eye (the retina) and then goes, via the optic nerve (the nerve of sight), to the brain (the processor) for developing. In people with glaucoma there is damage to the optic nerve, therefore not all the image captured by the eye will reach the brain, which can result in progressive vision loss.
Although damage to the optic nerve can be caused by injury or by poor blood flow, the most common cause of optic nerve damage is increased pressure within the eye (referred to as intraocular pressure or IOP). IOP is generally controlled by the circulation of aqueous, a fluid which bathes and nourishes the eye, keeping it firm and maintaining optimal eye pressure.
Aqueous flows from the ciliary body, through the anterior chamber and drains out of the eye via the trabecular meshwork. If this draining process becomes blocked, the aqueous fluid level within the eye can build-up, resulting in increased eye pressure. This increased eye pressure can cause ongoing damage to the optic nerve leading to vision loss and blindness seen in glaucoma.
Glaucoma treatments (eye drops, laser surgery, and conventional surgery) aim to reduce pressure in the eye, click here for more information on glaucoma treatment.
Note that eye pressure varies from person to person; what is high pressure for one person may not be for another. Many people may have normal pressure inside the eye and still have glaucoma.
The above information is a general overview of glaucoma - different types of glaucoma can have more specific causes. Click here for detailed information on the different types of glaucoma.
Effects of Glaucoma
While there are different types of glaucoma, Primary Open-Angle Glaucoma (POAG) is the most common, accounting for 90% of glaucoma cases in Australia. POAG generally has no warning signs in the early stages of development. Damage progresses slowly and destroys vision gradually, starting with peripheral vision. This early vision loss often goes undetected since the other eye can initially cover for the loss, and the effects of glaucoma may only be noticed when a significant amount of nerve fibres have been destroyed.
Damage caused is irreversible and will progress unless treated. Treatment cannot restore lost vision but it can halt or at least slow down the damage process. Early detection of glaucoma means that treatment can commence before a significant loss of vision occurs.
Images courtesy of Dr. Anne Hoste