Introduction to glaucoma
Glaucoma is a disease of the optic nerve, the nerve at the back of the eye that carries information about sight from the eye to the brain. Most often the damage to the optic nerve is caused by high pressure in the eye itself.
Inside the eye there is a circulation of fluid called Aqueous Humour, which provides nourishment to the structures of the eye. This fluid is made by one part of the eye (the ciliary body) and drains back into the blood-stream via another part (the trabecular meshwork or 'the angle'). Sometimes the drain of the eye becomes blocked (often for no clear reason). Therefore pressure builds up in the eye and presses on the sensitive optic nerve. The damage that results from this usually take many months or even years to develop. But it is permanent and without treatment, blindness can occur. In fact, glaucoma is one of the leading causes of blindness in the world, but most of this occurs in developing nations with poor access to healthcare. Thankfully with early diagnosis and treatment the damage can usually be minimised.
Most patients with glaucoma are not aware of problems with their eye-sight. This is because the damage occurs very slowly and central parts of the vision are only affected when the glaucoma is very advanced. However, even when central vision is still good, glaucoma may affect the peripheral vision, which is vital for driving.
In the UK, blindness from glaucoma is rare and usually occurs because the disease has been picked up late, the pressure has not responded well to treatment or the patient has not taken their eye drops regularly.
Who Gets Glaucoma?
Glaucoma can affect anyone but is more common with age. 2% of the population over the age of 40 have glaucoma but this rises to 10% by the age of 90. Rarely children or young adults may get it. There may be a family history and those who have a parent with glaucoma have double the risk of getting glaucoma and those with a brother or sister have four times the risk. People from families in which a member has glaucoma should be tested for glaucoma from the age of 35 onwards.
In the UK, the great majority of those with glaucoma have a chronic (slowly developing) form of the condition, primary open angle glaucoma (POAG), and studies have demonstrated that up to half of all cases remain undiagnosed.
Adult glaucoma falls into two categories -open angle glaucoma and closed angle glaucoma. These categories are subdivided, according to whether the cause is unknown (primary glaucoma) or known i.e. the high eye pressure is caused by other conditions of the eye (secondary glaucoma). The drainage angle of the eye is located between the cornea and the iris and it can be described as 'open' or 'closed'.
The most common type of glaucoma seen in the UK is primary open angle glaucoma. Here the drainage angle looks open but it is no longer functioning well. Therefore, as the aqueous is still being made, pressure builds up slowly inside the eye without causing any obvious symptoms.
Closed (or 'narrow') angle glaucoma is less common in the Western world. It can be either acute (sudden onset) or chronic (slowly developing). The acute form produces a sudden dramatic rise in eye pressure, associated with severe pain in the eye and blurred vision. This needs urgent treatment at a hospital.
Unfortunately the common form of glaucoma, primary open angle glaucoma, does not cause symptoms until the very end stage of the disease when serious, irreversible visual loss happens. This is because the central parts of the vision are sparred initially, but also, the brain adapts to the visual loss in the early/middle stages and compensates by filling in the missing parts of the vision. This is similar to how we are not aware of the naturally occurring blind spot. This is why regular eye test with an optician are extremely important.
On the other hand, acute angle closure glaucoma is sudden in its onset and causes a severely painful eye and blurred vision.
As stated, persons over 35 years of age with a family history of glaucoma should have regular examinations at an optician which are free from the age of 40. All individuals over 60 years of age are eligible for free eye tests.
No single test accurately detects glaucoma and the optician should perform the three glaucoma tests as follows:
1) Tonometry - This is the measurement of eye pressure. Commonly done by the 'air-puff' technique.
2) Visual field test (perimetry) - this is the formal mapping of the field of vision by a computerized technique. This can identify damage caused by glaucoma and in fact can detect very early changes.
3) Optic disc examination - The nerve tissue at the back of the eye should be examined with a special instrument to look for signs of damage.
There are a number of different eye drops which can be used for glaucoma and the vast majority of people in the UK will be treated with these. Drops can be used in combination if necessary. It is possible for these medicines to loose their effect over time and switches in eye drops may be necessary. Occasionally they do not lower the eye pressure satisfactorily or they can cause intolerable side-effects and either laser or surgical treatments may be recommended
Selective laser trabeculoplasty (SLT) is available with Mr Rossiter at the Nuffield Taunton. This treatment uses a 'cold' laser to stimulate the natural drainage channel to work better. This has recently been proven to be as effective as eye drops in the early stages of glaucoma meaning that you can be free from the burden of having to remember to use eye drops every day. SLT can also be used to delay or prevent the need to have surgery when drops are not working.
Laser iridotomy is recommended for individuals at risk, or who have, closed angle glaucoma
Selective laser trabeculoplasty is available with Mr Rossiter at the Nuffield Taunton. This treatment uses a 'cold' laser to stimulate the natural drainage channel to work better. There is considerable interest in this laser as it may be used in place of eye drops and therefore may free patients of the burden to remember to use their eye drops regularly. Laser treatment in the form of laser iridotomy is used in closed angle glaucoma.
About 20% of glaucoma patients may need surgery ultimately. There is a considerable amount of interest into new minimally invasive operations and Mr Rossiter has already developed some expertise in these new technologies
Overall treatment for glaucoma is effective and, providing patients use their treatment as instructed and attend their eye clinic appointments for monitoring, the vast majority will retain useful vision for the whole of their life.