Glaucoma

Glaucoma

At Sapphire, we often describe the eye as being like a camera.

Glaucoma is a serious eye condition that involves a build-up of pressure within the eye. Since it often occurs without obvious symptoms, it’s very important to keep yourself up to date with regular eye examinations. Thanks to an array of excellent modern treatments, glaucoma is no longer the unavoidable threat to sight that it once was. But early intervention and careful monitoring is vital in preventing the damage from turning into permanent loss of vision.

Glaucoma is a group of eye diseases that affects the optic nerve in the eye. The optic nerve takes the visual information from the eye to the brain. Glaucoma damages this nerve, which results in vision loss.

When the nerve fibres in the optic nerve are damaged, they cannot recover – which also means that any vision lost can’t be recovered. For this reason it’s important to get an early diagnosis for glaucoma. The condition needs to be monitored and treated carefully so that you can keep your sight. The good news is that with early diagnosis, regular monitoring and correct treatment, the majority of patients are able to maintain useful vision.

Your eyes contain aqueous humour, a clear fluid which allows them to function properly and maintain their shape. This requires a certain amount of pressure within the eye, which is known as intraocular pressure. In glaucoma, damage to the optic nerve usually occurs if the intraocular pressure rises to an excessive level. This kills the nerve fibres and leads to sight loss. But high pressure does not always cause glaucoma. Some patients can experience glaucoma damage to their optic nerve even though their eye pressure is within the “normal range”: we call this normal tension (or low tension) glaucoma. Conversely, some patients whose intraocular pressure is above the “normal range” won’t go on to experience damage to their optic nerve: this is known as ocular hypertension. Patients with ocular hypertension need to be monitored for signs of glaucoma, and may need treatment to prevent glaucoma from developing.

Understanding the structure of the eye

The front of the eye, which is clear, is known as the cornea. The coloured part of the eye is called the iris and is found behind the cornea. The hole within the iris is the pupil, and behind this is the lens of the eye. Between the iris and the cornea is something we call the drainage angle of the eye; this contains a sieve-like structure that’s made up of tiny drainage channels, known as the trabecular meshwork. Behind the iris is a ring-like structure called the ciliary body. This is where aqueous humour (the fluid within the eye) is made. It flows between the lens and under the iris, then passes through the pupil and drains out through the drainage angle and trabecular meshwork. The intraocular pressure is a balance between the production of fluid in the eye and the drainage out of the eye. In glaucoma, this balance becomes upset: the fluid outflow is usually restricted, resulting in a rise in the eye pressure. At the back of the eye is the retina, where light is focused by the cornea and lens. The sharpest, most detailed vision is found at the macula, in the central retina. The visual information is sent from these retinal areas to the optic nerve. The optic nerve then takes this information to the brain. The structure attached under the retina is the choroid; it provides the blood supply to the eye.

While there is no single cause of glaucoma, there are certain risk factors for the condition, which have a cumulative effect. These risks include a raised intraocular pressure.

Other risk factors are:

Age: The incidence of glaucoma increases as we get older.

Family history: You’re at increased risk of glaucoma if you have a family member with condition. If you have a first-degree relative (a mother, father, sister, brother or child) with glaucoma, you are at least four times more likely to develop glaucoma yourself.

Ethnicity: People from certain ethnic backgrounds have a higher risk of developing certain forms of glaucoma. Afro-Caribbean populations are at higher the risk of primary open angle glaucoma. People of South East Asian ethnicity are at increased risk of developing primary angle glaucoma (see also ‘What kinds of glaucoma are there?’).

Short-sightedness (myopia): Short-sighted (myopic) patients are at higher risk of developing the condition.

Long-sightedness (Hypermetropia): Long-sighted patients are at increased risk of developing angle closure.

Diabetics: Diabetics may be at higher risk of developing glaucoma.

There are actually several different kinds of glaucoma:

Primary open angle glaucoma

This is the most common form of glaucoma in the UK. Although the drainage angle is open, there is microscopic damage to the trabecular meshwork within the eye, which means the fluid does not properly drain out of the eye. The eye pressure slowly rises, and although it doesn’t cause symptoms in the patient, the optic nerve is still damaged. Damage to the optic nerve results in visual field loss – but you may not be aware of this, since the field loss in one eye may be compensated by the other eye, so “filling in” the loss in the visual field. This means that some patients don’t realise they have a problem until extensive damage has occurred. This is why glaucoma is sometimes known as the “silent thief of sight” and it’s the reason why it’s very important to diagnose and treat glaucoma early.

Primary angle closure glaucoma

In primary angle closure glaucoma, the drainage angle in the eye is ‘occludable’. This means that the aqueous fluid cannot drain through the trabecular meshwork. Since the fluid cannot drain, the pressure in the eye rises. This can happen very quickly, resulting in a very high intraocular pressure and, usually, pain in the eye. The eye can also become red. Vision may also become blurred, with halos appearing around bright lights. The pain can be so bad that it causes nausea and vomiting. This condition is known as acute angle closure. It can result in permanent vision loss, especially if treatment is delayed. However, if the angle closure attack is treated promptly, the vision recovers.

Sub acute angle closure glaucoma

Sub acute angle closure attacks occur when patients experience mild instances of raised pressure, resulting in blurring of vision, some pain and redness. This then resolves. But if you do experience these symptoms, you should get yourself checked immediately. A more chronic, or slow-developing form, of the disease is primary angle closure glaucoma (see above). This is where the intraocular pressure rises to a level that causes damage to the optic nerve but without any noticeable symptoms. The aim of treatment for this condition is to lower the intraocular pressure and open the drainage angle.

Normal tension glaucoma (also known as low tension glaucoma)
In this condition, the intraocular pressure remains within the normal range (between 10-20mmHg); however, there is still damage to the optic nerve. It is thought that poor blood flow to the optic nerve contributes to its damage. Patients with Raynaud’s Syndrome (a condition that affects blood circulation, causing cold hands and feet) and migraines have a high risk of normal tension glaucoma. This contributes to the theory that blood flow is important in normal tension glaucoma. If blood pressure is too low, it can result in worsening of the disease. For this reason, you may need to have your blood pressure control reviewed. Normal tension glaucoma is treated by lowering the intraocular pressure. This is usually done with pressure-lowering drops, in the first instance.

Ocular hypertension

In this condition, the intraocular pressure is raised but there is no damage to the optic nerve and no visual field loss. There is, therefore, no detectable glaucomatous damage. However, since patients with ocular hypertension have a raised intraocular pressure, they are at increased risk of glaucoma. These patients may need to be treated to reduce their risk of developing glaucoma, or monitored so they can start treatment as early as possible if glaucoma does develop.

Secondary glaucoma

With secondary glaucoma, the raised intraocular pressure does have a specific cause. This might be trauma to an eye, previous surgery or neovascular glaucoma (a condition where blood vessels grow in the drainage angle of the eye because of conditions like diabetic eye disease). Here the glaucoma will need to be treated; the original cause of the glaucoma may need to be treated, too.

Congenital Glaucoma

This is a rare condition where developmental abnormalities in the eye cause raised intraocular pressure.

The diagnosis of glaucoma can be difficult and requires several tests. It may not be possible to give a definitive diagnosis at the first consultation.

Tests for glaucoma include:

Tonometry

This measures the intraocular pressure of your eyes. It’s performed by Goldman Applanation Tonometry, not the ‘air puff’ that you may have experienced at the opticians.

Slit lamp examination

A slit lamp allows us to examine the eye in detail, especially the optic nerve.

Goniscopy

This test enables us to examine the drainage angle. It’s performed using a special contact lens on the eye.

Pachymetry

Pachymetry is a test that allows us to measure the thickness of your cornea. This is important, since a thicker-than-average cornea could lead to an overestimated intraocular pressure while a thinner-than-average cornea could result in an underestimated pressure reading. So it’s important to get a very accurate measurement.

Visual Field Perimetry

This test measures the specific area of sight loss, especially in the peripheral vision.

Optic nerve imaging

This test measures the thickness of the nerve fibre layer of the optic nerve and can detect areas of nerve fibre loss. It can also be used to monitor any further loss.

For a helpful summary of the key medications used in glaucoma treatment, click here.

Selective Laser Trabeculoplasty (also called SLT) is a treatment aimed at lowering the pressure in the eyes if you have ocular hypertension or open angle glaucoma (see ‘What kinds of glaucoma are there?’). The laser treatment helps fluid to drain from the eye, which in turn lowers the pressure.

Some people respond better to the treatment than others. While the initial treatment may be successful, the pressure can rise again in time. If this happens, the treatment can be repeated, although the results may not be quite so effective as after the first treatment. You may also need to continue eye drop treatment. In some cases we may also recommend further treatment, including surgery, if the pressure does not return to a satisfactory level.

Complications of SLT

Complications are rare but may include inflammation, a temporary increase in eye pressure, blurred vision, headaches and corneal oedema (clouding of the clear window at the front of the eye).

How SLT works

During treatment patients are normally given drops to make the pupil smaller, which can often cause a slight headache above the eye. Once you sit in front of the laser machine, further drops are given to numb the surface of the eye.

The doctor will place a special contact lens onto the eye and aim the laser at the part of the eye where the fluid drains (known as the ‘trabecular meshwork’, in the angle between the iris and the cornea). Many patients don’t feel any discomfort from the treatment, but those that do usually describe the pain as mild. It takes about five minutes to treat one eye.

After laser treatment the eyes will temporarily be dazzled, but vision should improve over the following few hours. It may help to wear sunglasses when you go home.

There is a chance that you may experience a headache during the first few hours following the procedure. If this happens, you should take your usual painkiller. You may also need to take extra drops for a week or so after the treatment. You will probably also be advised to continue with your usual glaucoma drops until your next appointment.

Glaucoma can get worse if the pressure inside the eye is too high. If this happens and eye drops are not sufficiently lowering the pressure, and if there is a significant risk that glaucoma is going to cause further damage to your sight, we may recommend trabeculectomy surgery.

A trabeculectomy is an operation to lower the pressure inside the eye. It involves making a new channel in the white wall of the eye (the sclera), through which fluid flows out into a space underneath the outer layer of the eye (the conjunctiva). A successful trabeculectomy creates what we call a ‘bleb’ – a small elevation, which is usually covered by the upper eyelid.

Trabeculectomies are usually done as day cases, under local anaesthetic. The local anaesthetic involves an injection beside the eye a few minutes before the start of the operation. This makes the eye numb, and usually blurred as well.

What happens during a trabeculectomy operation?

The operation is performed with you lying on your back. A paper drape is placed over your face, with fresh air piped beneath it. A clip is used to keep the eye open. You may see light and shadow, but you will not see the surgery itself. It usually takes between 40 and 80 minutes to complete the operation. At the end of the procedure, a patch is taped over the eye. You will leave this on until the next day.

In many cases we will treat the area of the trabeculectomy with additional medication during the surgery, to prevent scar tissue from closing the new channel we have created. The medications we use for this include mitomicin-C and 5- fluorouracil (5-FU).

What happens after the operation?

Frequent follow-up is required in the first few weeks after this operation. You will need to be reviewed the day after surgery. If all is well, you will be reviewed a week later, and again one to three weeks after that. The exact timing of these and future reviews depends on how your eye is settling down; more frequent visits are quite often required.

The first few weeks after the operation is a very important time for checking the eye and for carrying out adjustments. Most of these adjustments are minor and will be done as part of an outpatient visit. To be on the safe side, it’s best to avoid planning any holiday within two months of the operation.

You will be given new drops (an antibiotic and steroid) to use in your eye for several weeks after the operation. You won’t need to use your previous glaucoma drops in the eye that has had the operation (although, in the longer run, some patients do need to restart these to lower the pressure sufficiently). In your other eye, you should continue with any glaucoma drops as you did before.

What will my vision be like?

It’s common for the eye that has had the surgery to be quite blurred for a few weeks, and sometimes longer. There’s no need to change your glasses straight away, but some patients benefit from getting new glasses sooner than they normally would (though it’s best to wait for three months while things settle).

You can resume driving if your vision is sufficient for you to meet the legal requirements. Bear in mind, however, that trabeculectomy doesn’t improve vision. Its purpose is to prevent sight loss in the future.

When can I return to work?

Most people are able to return to office-based work two weeks after the operation, although some patients need longer. It’s usually wise to wait at least a month before resuming physically strenuous work, or work in a dusty or dirty environment.

When can I get back to everyday activities?

You can use your eyes for reading, television and computers etc as soon as you wish; this won’t harm your eye. Gentle exercise such as walking is fine, but you should avoid strenuous exercise (such as running, ball sports and fitness workouts), or lifting heavy objects, for at least a month after the operation. You should avoid swimming or immersing the eye in water for at least one month. Please ask at your check-up if you’re planning to resume swimming.

How successful is trabeculectomy?

The operation helps to lower the pressure in the eye in about 80% of cases, and most patients will not need glaucoma drops in the eye that has had the operation. A lower pressure is beneficial to nearly all patients with glaucoma, but glaucoma can still progress – in some cases even after a ‘successful’ trabeculectomy.

What are the risks and complications of trabeculectomy?

It’s important to weigh up the risks as well as the potential benefits before undergoing any form of surgery. The surgeon who has recommended this operation will have judged that the risk to your sight from glaucoma without the operation is greater than the risks of the operation itself. For most patients, trabeculectomy achieves a lower pressure without any significant problems. But as with all operations, there are some risks. These include:

Reduced vision: This is very common in the first two weeks after the operation due to swings in the eye pressure, minor bleeding inside the eye and inflammation. These typically settle within the first few weeks. A small minority of patients (around five to eight percent) may have some degree of permanently reduced vision after the operation. As with all intraocular surgery, loss of all vision in the eye due to the surgery itself is possible, but it’s very unusual.

Discomfort: Any discomfort from the procedure usually settles within a few weeks, but some patients do experience long-term discomfort. However, the symptoms are usually mild and can be controlled with artificial tears.

Increased likelihood of cataracts: This is quite common within five years of the operation. If cataracts do occur, they can be treated in the normal way. In some patients, a trabeculectomy works less well if a cataract operation is performed subsequently.

Infection and loss of vision in the eye: There is a small risk of infection after any form of eye surgery, including trabeculectomy. With trabeculectomy there is also a permanently-increased risk of infection getting inside the eye. But the risk is small: roughly one in every 100 operations.

Further surgery may be required to ensure that the operation is successful, or to correct low pressure. It’s not unusual for an additional procedure of some sort to be required, but this is usually a much shorter procedure than the trabeculectomy itself.

Minimally invasive glaucoma surgery (also known as micro invasive glaucoma surgery, or MIGS) is the latest advance in surgical treatment for glaucoma. It aims to reduce intraocular pressure by either increasing outflow of aqueous humour [links to ‘Understanding the structure of the eye’], or reducing its production.

MIGS comprises a group of surgical procedures which share common features. They focus on a minimally invasive approach, often with small cuts or micro-incisions through the cornea that cause the least amount of trauma to surrounding scleral and conjunctival tissues. The techniques minimise tissue scarring, allowing for the possibility of traditional glaucoma procedures such as Trabeculectomy or glaucoma valve implantation (also known as a glaucoma drainage device) to be performed in the future if needed.

MIGS procedures reach their surgical target from an internal route, typically through a self-sealing corneal incision. This contrasts with traditional surgery, where external techniques are used. By using an internal approach, MIGS procedures often reduce discomfort and lead to more rapid recovery periods.

While MIGS procedures offer fewer side effects, they don’t tend to lower intraocular pressure to the same extent as trabeculectomy or glaucoma tube shunt implantation.

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