What is glaucoma?
The eyeball is a pressurised structure, like a football. At the back of the eye, there is a small circular opening or canal in the eye wall, from which stems a stalk-like structure called the optic nerve. This nerve carries all of the visual signals from the retina to the brain.
Some degree of pressure is needed in the eye, so that it can maintain its shape and structural integrity. However the pressure in the eye pushes on the nerve tissue as it exits the eye, and if the pressure is higher than normal, it can cause very slow damage of the optic nerve tissue. This pressure-related damage to the optic nerve is called glaucoma. This damage can cause loss of areas in the field of vision. Usually, the pressure needs to be high for prolonged periods of time to cause glaucoma, but some patients develop glaucoma even at normal pressure (normal tension glaucoma). Conversely, some patients’ raised eye pressures are detected before any damage has occurred – this is called ocular hypertension.
In glaucoma, the pressure in the eye causes slow damage to the delicate nerve tissue as it enters the optic nerve.
What causes raised eye pressure?
The eye constantly makes and drains fluid, and the balance between these two determines the eye pressure, known medically as the intraocular pressure (IOP). There are many individual causes of raised IOP, but in mechanical terms they must relate either to increased production of fluid or impaired drainage of fluid from the eye.
What are the symptoms of glaucoma?
In early glaucoma there is no visual deficit. Later on, parts of the visual field start to become less sensitive or even lost completely. These are often parts of the peripheral vision (away from the centre of your sight), such that people are usually unaware that they are rebelling visual field loss. Therefore in most cases, there are no symptoms until extensive parts of the visual field have been lost. At this point it is too late to recover the lost parts of vision. This is why it is so important that glaucoma is diagnosed early, as it can prevent visual loss.
I have raised blood pressure – does this affect the eye pressure?
No, there is no direct relationship between blood pressure and eye pressure, although some medications taken for elevated blood pressure (beta-blockers) can sometimes reduce eye pressure as well. In addition, some patients with very low blood pressure, or over-treated high blood pressure, may suffer from quicker progression of glaucoma damage. If you have glaucoma and take medication for blood pressure, it is important to ensure that your blood pressure is not too low on your treatment.
Am I at risk of getting glaucoma?
Risk factors include increasing age, family history (having a first-degree relative with glaucoma), and African-Caribbean ethnicity. If you have a first-degree relative with glaucoma, it is a good idea to see your community optometrist for a check-up every year.
Will I go blind from glaucoma?
The vast majority of patients diagnosed with glaucoma today will not lose all of their vision, unless they are spotted and referred very late, at an extremely advanced stage of disease. Glaucoma usually progresses slowly, and with the right treatment, its progression can successfully be slowed or delayed in most patients.
What are the different types of glaucoma?
Glaucoma is a large topic in ophthalmology and its classification is possible in several different ways. Broadly speaking, glaucoma can be divided into:
- Primary (where the eye pressure is raised without an obvious structural cause) vs Secondary (where a different eye condition eg. uveitis, diabetes, retinal vein occlusion, vitreous haemorrhage etc has directly or indirectly caused raised eye pressure)
- Congenital (where a baby is born with glaucoma) vs Acquired (where it develops in later life)
- Open angle (where the drainage angle of the eye is found to be wide open) vs Closed angle (where the drainage angle is either narrow or completely closed, in some or all quadrants)
How is glaucoma treated?
Damage done due to glaucoma cannot be reversed. Once glaucoma has been detected, we need to slow down the rate of its progression by lowering the eye pressure in order to protect the optic nerve.
The eye constantly makes and drains fluid. We can lower the eye pressure by either reducing the amount of fluid that the eye makes, or by increasing its rate of drainage from the eye. Eye pressure can be reduced with:
- Medication – given as daily eye drops; there are several types available
- Laser treatment
- Minimally Invasive Glaucoma Surgery (MIGS), eg. iStent, Cypass, Hydrus, MicroShunt, Xen, iStent supra, STARflo, Aquashunt, etc
- Traditional tube or valve implantation eg Baerveldt, Ahmed, Molteno
Does ocular hypertension need to be treated?
The answer to this depends on each patient’s specific condition, eye pressure readings, other risk factors such as family history, and of course age. This is because high pressure tends to cause very slow damage to the nerve (over years). Therefore the management of a 40-year old patient with high pressures but a healthy optic nerve (i.e. ocular hypertension) needs to be more aggressive than the same situation in a 90-year old patient, in whom significant nerve damage is very unlikely in their remaining lifetime.
What tests are used to diagnose and/or monitor glaucoma?
Because glaucoma is a disease of the optic nerve, the diagnosis and/or monitoring of glaucoma is based around recording either the structure or the function of the optic nerve.
A variety of tests are used, which include:
- Visual field test – used to see what effect the pressure has had on visual function
- Corneal pachymetry (thickness) – this helps to calibrate pressure readings themselves, and with risk stratification for glaucoma
- Anterior Chamber OCT – this can document how shallow the anterior chamber is, or how narrow the iridocorneal angle is
- Gonioscopy – this is a special diagnostic lens, used by an ophthalmologist, to directly examine the drainage angle of the eye and look for reasons for the pressure to be raised, eg. rubeosis iridis, peripheral anterior synechiae, etc.
- Retinal Nerve Fibre Layer OCT – This test measures the thickness of the nerve fibre layer around the optic nerve head, and compares it both to a database of normal people and with any previous scans of the same patient. Although false positive results are not uncommon, the real value of this test is in its ability to monitor the nerve anatomy in considerable detail for progression (as opposed to the visual field test, which monitors the nerve function, and which requires a very alert, concentrating patient)
WIll my glaucoma get worse?
There is a very slow, natural age-related decline in optic nerve tissue, and because many patients with glaucoma have already had significant damage to the optic nerve, some progression over time is almost inevitable, even with treatment. However, the treatment of glaucoma (by lowering eye pressure) will normally slow down the rate of progression.
Can I drive if I have glaucoma?
If you have been diagnosed with glaucoma in both eyes, you ought to tell your local licensing agency, responsibilities for which seem to be split in Jersey between DVS (Driver and Vehicle Standards) and the Parish Constables. Some patients with glaucoma have binocular visual field defects which mean that it would be unsafe (and unlawful) to drive. This can be formally tested using an Esterman visual field test. It is best to discuss this with your ophthalmologist who will look at your visual field results and tell you whether you remain legal to drive.
What is a ‘glaucoma suspect’?
Consider the three parameters of:
- elevated eye pressure
- abnormal optic nerve appearance that is suspicious for glaucoma
- a glaucomatous visual field defect
If an eye has all three of these, the diagnosis of glaucoma is usually straightforward. If not (eg. a suspicious nerve appearance with a normal pressure and field) then patients are sometimes labelled as a glaucoma suspect. In these circumstances, the key thing is to establish a trend, by monitoring for progression.
Should my family members be screened for glaucoma?
Glaucoma screening is a topic of some debate, since there is no single test which can definitively tell if somebody has glaucoma or not. Rather, all of the clinical and diagnostic information needs to be compiled with a good clinical opinion. We do know, however, that individuals with a first degree relative with glaucoma are at higher risk of developing the same condition, and therefore periodic eye examinations are recommended.
How should I use eye drops for glaucoma?