Glaucoma Information

The Structure of the Eye and its relation to Intraocular Pressure

The ciliary body, situated at the root of the iris, continually produces a fluid called aqueous humour. This is a clear, watery fluid that helps to maintain the normal shape of the eyeball. The nutrients in the Aqueous help sustain the structures within the eye that do nod have a copious blood supply.

At the same time the aqueous humour is also draining from the eye via 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.

The Inflation pressure within the eye is the result of the difference between the rate of fluid being secreted by the ciliary processes and the rate of drainage through the trabecular meshwork.

The inflation pressure or "intra-ocular pressure" or IOP, varies considerably within the normal population, between about 8mm.Hg. (soft) and 21 mm. Hg. (hard).

Glaucoma

Glaucoma is the name given to a group of conditions in which the pressure within the eye builds up to a level such that it compresses the blood vessels supplying the optic nerve, causing nerve fibres to die off irreversibly.

Progressive loss of the patient's field of vision may not be noticed by the patient for years in the slowly developing, chronic form of glaucoma.

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.

If the iris blocks off the fluid suddenly, this is acute glaucoma (acute - sudden).
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.

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.

Are there other types of glaucoma?

Yes. It can be due to inflammation or other trouble in the eye which obstructs the normal flow of fluid through the eye (secondary glaucoma). It can also occur in babies due to the eye not forming properly.

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.

Is it hereditary?

Yes, chronic glaucoma is about 10 times as common in near blood relations, so all those relative from the age of about 35 should have their eye pressures measured and their optic nerves viewed with an ophthalmoscope. If these tests are abnormal an examination of the visual fields becomes essential. These measures should make sure that the presence of glaucoma is not being overlooked.

Can it be successfully treated?

Yes, it can be controlled and further loss of sight prevented in the majority of patients. Treatment is by eyedrops, tablets, laser light beam, or operation.

a) 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.
b) In the 'slow' type of glaucoma, treatment aims to prevent further loss of sight because as a rule what has been lost is not recovered. Early diagnosis is therefore of crucial importance.

Why do the persons with the 'slow' type of glaucoma not notice that there are black patches in their vision?

There are two reasons:

a) Because most people use both eyes together and one of 'fills in for the other.
b) Because the blank patches are not at first in the centre of their sight.

There is a loss of 'all round' vision and in some cases it is so restricted that it is like 'looking through a tube'. Frequently even this is not noticed until a very late stage.

Will I have it for life?

Usually the glaucoma tendency is always present and requires treatment but occasionally treatment can be discontinued gradually. This can only be decided by the ophthalmologist.

What happens if it is untreated?

Eventually, you may only see the Centre of what you are looking at, making it difficult to get about despite the sight being clear in the Centre. Later even this sight may be lost.

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.

There is little risk to sight if treatment is regularly given and adjusted to requirements, especially if detected early. Very advanced cases may be difficult to arrest and require energetic treatment and close supervision.

In cases of severe glaucoma, usually secondary to other eye disease, the high pressure can cause the cornea to loose its transparency. This is called corneal decompensation.

Is it common?

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.

Chronic glaucoma is about 10 times as common in near blood relations, so all those relative from the age of about 35 should have their eye pressures measured and their optic nerves viewed with an ophthalmoscope. If these tests are abnormal an examination of the visual fields becomes essential. These measures should make sure that the presence of glaucoma is not being overlooked.

How do the drops work?

Some types reduce the fluid entering the eyes and others help it escape more easily. Some act in both ways.

How do the tablets work?

They reduce the amount of fluid entering the eye.

The tablets of acetazolamide (Diamox) or dichlorphenamide (Daranide, Oratrol) directly affect the eye by reducing fluid going into it. They may be undesirable in patients with kidney trouble.

Eyedrops sometimes sting a little this may vary for no obvious reason. Pilocarpine (Isoptocarpine, Sno-pilo) or carbachol tend to make the eyes focus close-up and cut down the light by making the pupils small. Adjustment is then slower when going into a darker place from the light.

Adrenaline (eppy, Simplene, Isopto EpinalO may give an ache in the forehead which usually becomes less troublesome if continued. The eyes also tend to get a little red and watery. Timolol (Timoptol) is usually free of local effects on the eye, which is very satisfactory, but occasionally in patients with asthma, difficult breathing, or certain types of heart trouble, timolol drops may aggravate the condition so that such patients may not be suitable for this type of treatment.

Surgery For Glaucoma

For some people, surgery might be the best treatment for glaucoma. Your ophthalmologist may suggest surgery as a first treatment, or after trying medication to lower your IOP.

There are several different types of surgery for glaucoma. The kind of surgery you and your ophthalmologist decide is right for you depends on many factors, including the type and severity of your glaucoma, and other eye problems or health conditions.

Glaucoma surgery may be performed using a laser (a concentrated beam of light) or conventional surgical instruments.

Laser Surgery

Trabeculoplasty is used most often to treat open-angle glaucoma. In trabeculoplasty, a laser is used to place "spot welds" in the drainage area of the eye-- also known as the trabecular meshwork -- that allow the aqueous to drain more freely.

Iridotomy is another kind of laser surgery used in treating glaucoma. It is frequently used to treat angle-closure glaucoma. In this procedure, the surgeon uses the laser to make a small hole in the iris-- the colored part of the eye -- which allows the aqueous to flow more freely within the eye so the iris doesn't plug up the trabecular meshwork.

In cyclophotocoagulation, a laser beam is used to freeze selected areas of the ciliary body -- the part of the eye that produces aqueous humor -- to reduce the production of fluid. This procedure may be used to treat more advanced or aggressive cases of glaucoma.

Most laser surgeries for glaucoma can be performed in the ophthalmologist's office or an outpatient surgical facility. Eye drops are used to numb the eye for the duration of the procedure. Because there is usually little discomfort during glaucoma surgery, this is often the only anesthesia needed

Little recuperation is needed after laser eye surgery. Patients may experience some local eye irritation, but can usually resume their normal activities a day or two after surgery.

In some cases, laser surgery is not the preferred surgical treatment for glaucoma. Sometimes, when vision loss is rapid, or medication and/or laser surgery fails to lower IOP sufficiently, "conventional" incisional surgery is the best option.

Incisional Surgery

Filtering surgery is usually done in a hospital or outpatient surgery center, with local anesthesia, and sometimes, sedation. The surgeon uses very delicate instruments to remove a tiny piece of the wall of the eye (the sclera), leaving a tiny hole. The aqueous can then drain through the hole, reducing the intraocular pressure, and be reabsorbed into the bloodstream.

In some cases, the surgeon may place a small tube or valve in the eye through a tiny incision in the sclera. The valve acts a regulator for the buildup of aqueous within the eye. When the intraocular pressure reaches a certain level, the valve opens, allowing the fluid to flow out of the eye's interior, where it can be reabsorbed by the body. The procedure may take place in the ophthalmologist's office or outpatient surgical center, and can be done under local anesthesia.

The recuperative period following incisional glaucoma surgery is usually short. You may need to wear an eye patch for a few days after surgery, and to avoid activities which expose the eye to water, such as showering or swimming. The ophthalmologist may recommend you refrain from heavy exercise, straining or driving for a short time after surgery, to avoid complications.

Possible Complications

As with all surgery, there are risks associated with glaucoma surgery. Complications are unusual, but can include:

oinfection obleeding oundesirable changes in intraocular pressure oloss of vision

Sometimes, a single surgical procedure is not effective in halting the progress of an person's glaucoma. In these cases, repeat surgery, and/or continued treatment with topical or oral medications may be necessary.

Your age, eye structure, type of glaucoma, and other medical conditions are all considerations when deciding how to treat your glaucoma.

Although angle-closure glaucoma is unusual, people of Asian or Eskimo ancestry are at higher risk of developing it. As with other forms of glaucoma, age and family history are also risk factors, and the problem seems to occur in older women more often than others.

Both open-angle and angle-closure glaucoma can be primary or secondary. A primary condition is one that cannot be attributed to any known cause. A secondary condition can be traced to another cause, such as previous injury or illness.

"Normal (or low) tension" glaucoma is an unusual and poorly understood form of the disease. In this type of glaucoma, the optic nerve is damaged even though the patient's intraocular pressure is consistently within a range usually considered normal.

Childhood glaucoma is rare, and starts in infancy, childhood or adolescence. Like open-angle glaucoma, there are few, if any, symptoms in the early stage, and blindness can result if it is left untreated. Like most types of glaucoma, this type of glaucoma is thought to have a hereditary component.

Congenital glaucoma is a type of childhood glaucoma that usually appears soon after birth, although it can become apparent later in the first year of life. Unlike other childhood glaucomas, congenital glaucoma often has noticeable signs, including tearing, light sensitivity, and cloudiness of the cornea. This type of glaucoma is more common in boys, and can affect one or both eyes.

Elevated IOP is sometimes called ocular hypertension. This means that your IOP is higher than what is considered "normal." A diagnosis of ocular hypertension does not mean you have glaucoma, but it does mean you're at increased risk, and should probably have frequent medical eye examinations. Sometimes your ophthalmologist will recommend medication to lower your IOP.

Treatment for glaucoma may include medication and/or surgery.

Ophthalmologists used to think that high intraocular pressure was the main cause of optic nerve damage in glaucoma, however we now know that even people with "normal" IOP can experience vision loss from glaucoma -- so-called "normal tension glaucoma". Some people with high intraocular pressure (also known as ocular hypertension) never develop the optic nerve damage of glaucoma. (These people need to be followed carefully by an ophthalmologist, because they are considered "glaucoma suspects.")

There may be other factors which affect the optic nerve, even when IOP is in so-called "normal" range. Elevated IOP is still considered a major risk factor for glaucoma, though, because studies have shown that the higher the IOP is, the more likely optic nerve damage is to occur.

Where should glaucoma drops be kept and for how long?

In a refrigerator (not in the ice box) or in a cool place, and if opened they will then last about four weeks. If they become discoloured they should be renewed. The unopened bottle will have an expiry date.

Why does the glaucoma patient have to see the optometrist regularly?

So that field of vision tests can be carries out and the pressure in the eye measured. In this way the treatment can be altered as necessary to prevent any deterioration.

Are there any signs to watch for which indicate that I need to see the specialist?

Increasingly blurred vision or undue redness or pain in the eyes.

What is meant by 'phasing'?

Measuring the eye pressure at intervals during the day, because it varies and the variability may effect the decisions about treatment.

What is 'field testing'?

Mapping out the blank area, if any, in the field of vision, so that the progress of the glaucoma can be accurately assessed and followed.

Is it important for relatives to be tested for glaucoma?

Yes, this is very important and sometimes may allow the condition to be detected at an early stage, when treatment is most effective.
Particularly brothers and sisters, parents, uncles and aunts, also children and nephews and nieces ages 35 years and over, or at any age if there are ocular symptoms.

Can a patient with glaucoma wear contact lenses?

There is no reason why not, except in the case of soft contact lenses and it is then best to ask advice.

Can strong sunlight affect glaucoma?

No, but if eyes are sensitive to strong light, then in these conditions there is no objection to dark glasses being worn.

Can the glaucoma patient drive a car?

Yes, if you reach the statutory standard of vision, but safety should be considered if the field of vision is restricted. In the UK the DVLA regularly assesses the visual field and corrected acuity in glaucoma sufferers to ensure safety on the road. The visual field test used is called the "Estermann" visual field test. This is a binocular, or both eyes together test, which many glaucoma sufferers pass despite having visual field loss in one or both eyes, due to binocular overlap.

Because visual fields are slightly variable from visit to visit, if you preform poorly on your first attempt we allow you to have a second go before we send the results off to the DVLA medical examiner.

At Matheson Optometrists we use the hospital standard, Humphrey 7-series Visual Field Analyser both for our Co-managed Ophthalmology clinics and when providing DVLA services.

Our private fees for Humphrey 24-2 visual field testing are currently £24.00 (01/01/05) and Estermann £38.00. These services can be provided often through private medicine as Andrew Matheson is registered with BUPA (id number 30015547) and other health care providers, as an "umbrella" practitioner to Ophthalmology.