What is chronic open angle glaucoma?
Chronic open angle glaucoma (COAG) affects approximately 1-2% of the white population of the UK over 40 years of age, increasing to 4-5% of those over 80 years. It is more likely to affect people with a family history of the same condition, and people of West African ancestry, including African-Caribbean. The condition is not painful and patients may be unaware that they have it until they have started to lose vision.
The optometrist examining a patient for COAG, will look for the characteristic appearance of ‘cupping’ of the optic disc (the head of the optic nerve at the back of the eye). The optic nerve transfers visual information from the eye to the brain, and can be examined with various special instruments. On testing the patient’s fields of vision, defects may be found that are typical of glaucoma. The pressure of the fluid inside the eye (known as the intraocular pressure) must be measured as it is usually raised in glaucoma. In a small proportion of patients, however, the pressure is within the normal range.
The eyeball is a sphere kept inflated by fresh clear fluid formed within the eye. This fluid drains away through a fine ring-shaped sieve of tissue, known as the drainage angle (or simply angle), situated within the eye at the edge of the cornea (the clear window of the eye) and from there into the bloodstream. This sieve is not directly visible but it can be seen through a special contact lens containing a mirror. In COAG the fluid is unable to escape normally because the meshwork has become blocked. The blockage causes the pressure inside the eye to rise, and in time this can damage the optic nerve, causing loss of visual field and even blindness if the condition is not treated.
How is chronic open angle glaucoma managed?
Treatment is usually with eye drops, or with a laser procedure called selective laser trabeculoplasty (SLT) which lower the intraocular pressure. If these treatments are inadequate a separate operation may be needed.
The optometrist who discovers COAG will usually refer the patient routinely to the hospital eye service.
Sometimes COAG develops out of another condition called Ocular Hypertension, for which a separate Clinical Management Guideline has been written.
