What is glaucoma?
The glaucomas are a group of diseases which, if untreated, lead to damage to the optic nerve and eventually to blindness.The commonest type of glaucoma is primary open angle glaucoma (POAG) which occurs in about 2% of the adult population in the UK. Older people, British Africans, and people with other family members who have glaucoma are more at risk.
What are the symptoms of primary open angle glaucoma?
This type of glaucoma generally does not cause any symptoms until late on in the disease process. This is different to Acute or Closed Angle Glaucoma which often causes eye pain and visual disturbances. It is possible to be at risk from a combination of both types of glaucoma at the same time.
What is the glaucoma test?
Eye pressure measurement is usually not an adequate glaucoma test. Many people mistakenly believe that a check of the “eye pressure” is the test for glaucoma. Actually, the modern definition of POAG does not even mention eye pressure. This is because about 40% of patients who do have glaucoma have “normal” eye pressures. Conversely, many patients with “high” eye pressure do not have glaucoma.
Why is it that it is thought that about 50% of all glaucoma sufferers in the UK are undiagnosed?
Glaucoma is not easy to detect until significant damage to sight has occurred. Diagnosis can take considerable skill. Simply checking eye pressures is not adequate.
So how is glaucoma diagnosed?
Diagnosis of POAG is made using a combination of at leasr four tests which are
1. Anterior chamber assessment
An examination of the anterior chamber to rule out other types of glaucoma such as closed angle glaucoma. This is done initially with a simple screening test. Further assessment may be carried out by gonioscopy or OCT.
2. Optic nerve assessment
A careful examination of the optic nerves with binocular slit lamp biomicroscopy lin conjunction with a lens such as the Volk 66D which provides the optometrist or ophthalmologist with a 3-D view of the optic nerve is of paramount importance. This takes significant skill particularly in the earliest stages of glaucoma where signs can be very subtle.
3. Visual field investigation
A visual field assessment with the Humphrey visual field, used routinely at Barnard Levit Optometrists on all adults.
4. Eye pressures
Measurements of eye pressure (intraocular pressure) are taken and this may need to be repeated on a different day or at a different time of the day.. An instrument that measures the eye pressure is called a tonometer. Barnard Levit Optometrists use three different types of tonometer, the “air puff” , the Goldmann applanation and the Pascal DCT.
Is there a way that glaucoma can be detected before there is a loss of visual field?
It is thought that by the time there is the first measurable loss of visual field, a large proportion of optic nerve cells have already died. A technique called optical coherence tomography (OCT) which measures the thickness of the retinal nerve fibre layer (RNFL) may provide an earlier warning of glaucomatous damage. This test may be particularly useful for ‘at risk’ patients when the test is repeated over time, for example six monthly or annually. A special computer programme then analyses the results to look for changein RNFL thickness over time. Barnard Levit Optometrists have been using this technology since 2005. Your optometrist will advise you if OCT is indicated.
Also, when eye pressures are consistently at a level that is too high for a patient's age and central corneal thickness, prophylactic treatment may be started to prevent damage to the optic nerve. There are NICE Guidelines published to provide clinical guidance in this area.