Glaucoma
Background Information
Glaucoma is the name for a group of eye conditions in which the optic nerve becomes damaged by raised pressure within the eye. The eye constantly produces aqueous, the clear fluid that fills the anterior chamber (the space between the cornea and iris). The aqueous filters out of the anterior chamber through a complex drainage system. The delicate balance between the production and drainage of aqueous determines the eye's intraocular pressure (IOP). Most people's IOPs fall between 8 and 21. However, some eyes can tolerate higher pressures than others. That's why it may be normal for one person to have a higher pressure than another.
In some eyes, nerve damage can occur in the presence of relatively normal pressure, probably due to reduced blood flow within the optic nerve.
Aqueous humour is made in the eye, circulates around the tissues and drains through outflow channels towards the front of the eye. Normal eye pressure is maintained when the amount of aqueous produced balances the amount draining away. If it cannot escape, or if too much is produced eye pressure rises and eventually this may damage the optic nerve. This can result in defects in the field of vision, which are not often perceived until they become severe and begin to affect central vision.
Glaucoma is one of the world's leading causes of blindness. In the UK, about 1% of people over 40 and about 5% of people over 65 develop glaucoma.
Common Types of Glaucoma
Open Angle - also called chronic open angle or primary open angle - is the most common type of glaucoma. With this type, even though the anterior structures of the eye appear normal, aqueous fluid builds within the anterior chamber, causing the IOP to become elevated. Left untreated, this may result in permanent damage of the optic nerve and retina. Eye drops are generally prescribed to lower the eye pressure. In some cases, surgery is performed if the IOP cannot be adequately controlled with medical therapy.
Acute Angle Closure - Only about 10% of the population with glaucoma has this type. Acute angle closure occurs because of an abnormality of the structures in the front of the eye. In most of these cases, the space between the iris and cornea is more narrow than normal, leaving a smaller channel for the aqueous to pass through. If the flow of aqueous becomes completely blocked, the IOP rises sharply, causing a sudden angle closure attack. While patients with open angle glaucoma don't typically have symptoms, those with angle closure glaucoma may experience severe eye pain accompanied by nausea, blurred vision, rainbows around lights, and a red eye. This problem is an emergency and should be treated by an ophthalmologist immediately. If left untreated, severe and permanent loss of vision will occur in a matter of days.
Secondary Glaucoma - This type occurs as a result of another disease or problem within the eye such as: inflammation, trauma, previous surgery, diabetes, tumour, and certain medications. For this type, both the glaucoma and the underlying problem must be treated.
Congenital - This is a rare type of glaucoma that is generally seen in infants. In most cases, surgery is required.
Signs and Symptoms
Glaucoma is an insidious disease because it rarely causes symptoms. Detection and prevention are only possible with routine eye examinations. However, certain types, such as angle closure and congenital, do cause symptoms.
Angle Closure (emergency)
- Sudden decrease of vision
- Extreme eye pain
- Headache
- Nausea and vomiting
- Glare and light sensitivity
Congenital
- Tearing
- Light sensitivity
- Enlargement of the cornea
Detection and Diagnosis
Because glaucoma does not cause symptoms in most cases, those who are 40 or older should have an annual examination including a measurement of the intraocular pressure. Those who are glaucoma suspects may need additional testing.
The glaucoma evaluation has several components. In addition to measuring the intraocular pressure, the doctor will also evaluate the health of the optic nerve, test the peripheral vision and examine the structures in the front of the eye with a special lens before making a diagnosis.
The doctor evaluates the optic nerve and grades its health by noting the cup to disc ratio. This is simply a comparison of the cup (the depressed area in the centre of the nerve) to the entire diameter of the optic nerve. As glaucoma progresses, the area of cupping, or depression, increases. Therefore, a patient with a higher ratio has more damage.
The progression of glaucoma is monitored with a visual field test. This test maps the peripheral vision, allowing the doctor to determine the extent of vision loss from glaucoma and a measure of the effectiveness of the treatment. The visual field test is periodically repeated to verify that the intraocular pressure is being adequately controlled.
The structures in the front of the eye are normally difficult to see without the help of a special lens. This special mirrored contact lens allows the doctor to examine the anterior chamber and the eye's drainage system.
Treatment
Glaucoma cannot be cured but may be controlled, usually by eye drops, sometimes by laser, and occasionally by operations to improve the drainage from the eye. Most patients with glaucoma require only medication to control the eye pressure. Sometimes, several medications that complement each other are necessary to reduce the pressure adequately.
Surgery is indicated when medical treatment fails to lower the pressure satisfactorily. There are several types of procedures, some involve laser. The objective of any glaucoma operation is to allow fluid to drain from the eye more efficiently.
Due to the reduced field of vision, steps and low obstacles can be a hazard to Glaucoma sufferers. Items such as televisions, shelves and fire hoses can also be a problem if placed on the wall at head height.
Mobility will be affected and mobility training may be useful with a long cane. Glaucoma Support groups meet around the country and Henshaws Society for Blind People hosts a group in Manchester.
Disclaimer of Medical Liability
Whilst we have taken great care to gather correct information and to keep it current, we cannot guarantee its accuracy and completeness.
The information provided should never be considered a substitute for professional health care by a qualified doctor or other health care professional, which will be tailored to the patient's individual circumstances. Henshaws cannot take responsibility if you rely on this information alone.