A B C D E F G H I J K L M N O P R S T U V W

GLAUCOMA : CHRONIC

What is Chronic Glaucoma ?

Glaucoma is a condition which affects the main nerve of the eye, the optic nerve. The optic nerve transmits the focused images from the eye to the brain. There are different types of chronic glaucoma, the most common is chronic open angle glaucoma. This affects approximately 1% of the population over the age of 40. In this condition the pressure within the eye is abnormally high often above 30 mm Hg (the normal pressure range is between 10-21 mm Hg. Normal tension glaucoma is a condition when optic nerve damage occurs even though the eye pressure is not abnormally high. Pigmentary glaucoma (or pigment dispersion syndrome) occurs due to the shedding of pigment cells of the coloured iris (usually in the dark pupils) which then obstructs the drainage channels. There are other causes of raised pressure called secondary glaucoma,. For example as a result of eye injury or when the eye has been chronically inflamed. In all forms of chronic glaucoma the loss of vision which occurs is slow and often unnoticed. It can become slowly progressive if not arrested by treatment. The loss of vision occurs first in the outer part of the field of vision. The detailed visual acuity is not affected until much later in the process when the glaucoma is advanced. For this reason glaucoma can progress undiagnosed in many people before they are aware of any real problem. This is the reason why screening for the condition by examination with an Optometrist is so important. The condition is uncommon before the age of 50 and becomes more common with increasing age. The condition runs in families, particularly the open angle type. Certain eye drops containing cortisone, (steroid) can cause glaucoma in certain susceptible individuals called "steroid responders". Chronic use of steroid drops for conditions such as allergic conjunctivitis can result in secondary glaucoma if treatment is not monitored.

How does Chronic Glaucoma occur ?

In the common form high pressure within the eye over many months or years. This eventually causes irreversible damage to the nerve fibres within the optic nerve. This is considered to be due to disturbance to the blood supply to the optic nerve within the eye. It results in lack of oxygen (ischaemia) to the nerve which causes damage. In normal tension glaucoma there is an abnormality of the blood supply to the nerve and progressive damage may occur without high eye pressure. The end result is the same that unchecked progressive loss of the visual field results which may eventually lead to blindness.

Why does Chronic Glaucoma occur ?

In open angle glaucoma and pigmentary glaucoma there is a disturbance of the flow of fluid out of the eye resulting in high pressure. The reason for this is that the drainage angle becomes narrow in normal individuals with age due to increasing size of the crystalline lens of the eye. This in part explains the increase in pressure of the eye which occurs with ageing. In normal tension glaucoma there is a reduced blood supply to the nerve. Patients often have evidence of blood vessel problems in the hands and feet (Raynaud's Phenomenon) or migraine. Blood flow becomes less effective with increasing age in part explaining the fact that glaucoma is much more common in the older age group.

Treatment Involved for Chronic Glaucoma

The condition is diagnosed often at a routine examination for glasses by an optometrist. An examination for spectacles in any one over the age of 40 should always include an assessment of the intraocular pressure. This is usually done with a "puff air" tonometer. A small puff of air is directed at the front of the eye which indirectly assesses the pressure. The eye is examined internally with an instrument called an ophthalmoscope. This will detect any abnormality of the nerve of the eye. Classically the nerve in glaucoma is described as being "cupped". In this way normal tension glaucoma can be suspected. The condition is confirmed by an assessment of the field of vision. This is done with a computerised analysis which will show up an area of missing or reduced sensitivity in the visual field. A new technique of assessing a nerve is with a scanning laser which documents on digital image the appearance of the nerve. Any change in the cupping which would indicate progression of the glaucoma can be detected. Treatment for raised pressure can either be directed at reducing the production of aqueous fluid in the eye or by increasing the outflow or drainage of fluid from the eye. Betablocker eye drops are often given as the first line treatment for glaucoma. These work by reducing the production of fluid resulting in reduced pressure. These drops however are not suitable for people who have asthma as they can cause a severe asthmatic attack. Elderly patients who have slow heart beat are also not suitable for this treatment. A group of drugs called Carbonic Andydrase Inhibitors also work by reducing fluid production. These can be in either tablet or capsule form. The tablet form is useful for short term treatment of pressure only. The eye drops can be combined with the betablocker for additive effect to reduce pressure. Outflow of fluid can be improved by adrenaline type drugs and by a new type of drug which is a Prostaglandin Analogue. The Prostaglandin Analogue may have a particular role in normal tension glaucoma as it is possible to reduce normal pressure to a lower level. Drops can control glaucoma in many people with the condition. However surgery to reduce the pressure may be necessary. The standard operation used in glaucoma is a trabeculectomy. This involves making a surgical opening in the eye for fluid to drain out. The fluid drains out under the conjunctival layer controlled by a small flap of sclera, (the white part of the eye). In some cases a drug called an Antimetabolite (used in some cancer treatments), is used to reduce scarring after the operation. This is applied to the operation site and occasionally it is necessary to inject into the operation area after the operation. The operation is generally advised when the intraocular pressure is not well controlled with eye drops or the glaucoma condition is worsening despite good pressure control. However some specialists will recommend the operation as the first line treatment avoiding use of drops. The operation has generally good success rate but there are risks which the eye surgeon will discuss fully with the patient. YAG laser is used for the treatment of narrow angle glaucoma. The Argon laser is occasionally used in a procedure called Argon Laser Trabeculoplasty. The procedure although useful in reducing pressures does not have a lasting effect and if not often advised.

After Treatment for Chronic Glaucoma

Treatment of chronic glaucoma is given only to prevent it from getting worse or at least to slow it down. The drops used may have side-effects. Pilocarpine makes the pupil small and vision goes rather dark. Adrenaline may make the eye red and sore. Beta-blockers can worsen asthma- type breathing difficulties. Carbonic Andydrase Inhibitors tablets may cause pins and needles in the hands and feelings of sickness and depression. Following operations, the eye is more susceptible to infections. You should notify the development of a red, sticky eye to your doctor immediately.

If Chronic Glaucoma is Left Untreated

Regular use of the prescribed treatment and attendance at eye clinic appointments is very important. The condition can progress seriously without the patient being aware of visual deterioration. Untreated Glaucoma can result in serious loss of vision and even blindness.

Effects on Family of Chronic Glaucoma

Screening of family members over the age of 40 is important. This of course includes brothers and sisters. Support for attendance to eye clinic appointments is helpful. Many people with glaucoma are eligible to be registered as partially sighted or blind due to the extensive loss of visual field even if they still have good acuity. This should be discussed with the eye specialist. Unfortunately for this reason many people with glaucoma are not eligible to drive due to the loss of visual field despite the fact that they may have a level of acuity allowing them to read a number plate at the required distance.