Glaucoma is a group of conditions in which the optic nerve is damaged in a characteristic way. This is often associated with a raised intraocular pressure. The intraocular pressure is the pressure of the fluid within the eye that keeps the eye inflated into its normal spherical shape. It is the balance between the rate of fluid secretion into the eye to that of the fluid draining from the eye that determines the pressure inside the eye, the intra-ocular pressure. Some type of glaucoma occurs in about 2% people over the age of 40. Most cases in the western world are of the chronic type.
The nutrients in the aqueous humour help sustain the structures within the eye that do not have a copious blood supply. The aqueous humour drains from the eye at a point called the angle - situated where the back of the cornea meets the anterior surface of the iris. In the angle is situated the trabecular meshwork. This is analogous to the plug-hole in a bath, letting the fluid drain away.The inflation pressure or "intra-ocular pressure" or IOP, varies considerably within the normal population, between about 10mm.Hg. (soft) and 21 mm. Hg. (hard).
The optic nerve damage causes a reduction in the sensitivity that varies in severity from patient to patient. It usually does not affect the central vision. There is not usually any pain or discomfort with chronic glaucoma. Also because the reduction in vision is usually slow and "patchy" and the visual field loss between the eyes is not usually symmetrical, it often goes undetected until an eye examination at your optometrist shows its presence.
The centre of the optic nerve head becomes damaged when the intra-ocular pressure remains high enough to cut of the blood supply to it. The exact pressure that this occurs at varies from individual to individual. As the normal tissue dies off the disc looses its normal healthy colour and becomes much paler. An interesting fact is that this appearance in itself is not diagnostic as several normal, non-glaucomatous people, especially short-sighted ones, can have an optic disc appearance which mimicks that seen in glaucoma.
An optic Nerve showing possible signs of Glaucoma
Without treatment, the loss of vision usually gets worse over the course of many months or several years. The loss of vision in glaucoma is permanent, but with early treatment, the damage to vision can be minimised.
Most patients with glaucoma are not aware of problems with their vision. This is because the central vision (for reading and recognising people) is only affected when glaucoma has advanced to a late stage. This is why a regular eye examination by your optometrist is so important.
Even when central vision is still good, glaucoma may affect the vision needed for driving and getting about (for instance, seeing steps). Blindness from glaucoma is rare. If blindness does occur, it is usually because the glaucoma is already advanced when it is first diagnosed, because the eye pressure has not responded well to treatment or because patients have not taken their drops regularly.
For most glaucoma patients, the main effect of the condition is the inconvenience of taking eye drops. Caught early the loss of vision is often minimal and the treatment is usually simply taking an eyedrop at bedtime.
Adult glaucoma falls into two categories – open angle glaucoma and closed angle glaucoma.
Primary open angle glaucoma (POAG), also known as chronic glaucoma, is the most common. It has no symptoms in the early stages, but slowly and painlessly destroys sight if it is not detected and treated. The loss of vision cannot be reversed. It mainly affects middle aged and elderly people, although it can develop in younger people. The earlier glaucoma is detected, the more successful the treatment. Chronic glaucoma is about 10 times as common in near blood relations, so all those relative from the age of about 35 should be evaluated for glaucoma. The english NHS pays for a basic eye examination for those patients with an immediate family history of glaucoma.
If the hardness happens slowly by 'silting up' of the sieve tissue, this is chronic open angle glaucoma (chronic - slow). The eye adjusts partially to the raised eye pressure and the patient may not notice anything wrong until blood supply of the nerve of sight (the optic nerve) is slowly cut off by the pressure on it, causing blank patches in the field of vision. Occasionally, certain eyes may not tolerate even average pressures, such patients my require treatment to reduce their eye pressures to even lower levels. This is called 'low tension' glaucoma. By contrast some eyes tolerate higher than average pressures without loss of visual field. This is called 'ocular hypertension'. It does not usually require treatment but should be carefully reviewed at intervals.
Even if you seem to have excellent sight, this doesn't rule out glaucoma because:
Glaucoma initially destroys the off centre vision, leaving the central detailed vision unaffected until a later stage.Blank patches in the field of vision may go unnoticed as the less affected eye 'completes the picture'.Glaucoma does not affect the ability of the eye to focus and the condition may be present even though vision seems fine without the need for glasses. There is no pain felt in chronic Glaucoma. The retina and optic nerve have no pain receptors.You could lose a considerable amount of sight irretrievably before you are aware of a problem.
In the rarer acute form, because the patient experiences symptoms such as a painful red eye, haloes round lights and nausea, it is usually detected soon after onset.
The hard eye gets very painful and red with a hazy surface and misty vision. The mistiness may cause coloured haloes to be seen around lights. This condition is very dangerous and can take away a patient's sight in hours or days. It can be treated, by the urgent treatment with tablets, injections and eye drops, followed usually by laser surgery. The 'sudden' type of glaucoma requires urgent hospital treatment and a small operation or laser treatment but if there is no delay in starting treatment, restoration of sight may be almost complete. Delay may be disastrous.
What are the glaucoma tests?
The only way you can know for certain whether or not you have glaucoma is to arrange to have an eye examination (sight test) which includes all the glaucoma tests. These tests are rapid and painless. They are: optic disc assessment, tonometry, gonioscopy and visual field testing. Ideally corneal centre thickness should be assessed in all suspicious cases, by ultrasonic pachymetry or OCT corneal thickness measurement. Matheson Optometrists recommend all older patients to have periodic OCT scans that include optic nerve fibre analysis and Corneal Centre Thickness assessment in addition to macular degeneration evaluation..
Be aware that the likelihood of developing glaucoma and other eye diseases increases with age, so regular eye tests (at least every 2 years if you are under 70 years of age) are essential to ensure early diagnosis and optimum eye health. In England the NHS will pay for a 2 year eye examination by an optometrist if you are over 60 but under 70, and an annual exam if you are over 70. If you have an immediate family member with glaucoma the NHS pays for a basic examination as frequently as every year. There may be additional charges for some tests not covered by the NHS eye exam.
How is glaucoma treated?
Treatment for chronic glaucoma is usually with eye drops. Laser treatment or surgery may be necessary in some cases. The good news is that once it is detected and treated, most people retain useful vision for a lifetime.
Glaucoma left untreated may lead to tunnel vision and, eventually, to blindness. It is estimated that approximately 2% of people over the age of 40 will have glaucoma. 13% of those on the blind register have glaucoma of some type.
Don't be a statistic – give yourself peace of mind.
