Glaucoma
Glaucoma is a condition that affects the optic nerve at the back of the eye leading to a loss in peripheral vision and if left untreated total sight loss.
In the eye aqueous fluid, that baths the cornea and the iris, is produced behind the iris and flows forward where it is drained away at the trabecular meshwork in the angle of the anterior chamber. It is when the ability of the eye to drain away this fluid is reduced that the pressure in the eye rises and damage occurs to the optic nerve leading to visual field defects.
Aqueous fluid is produced behind the iris and flows through to the anterior chamber where it drains away at the angle
There are two types of glaucoma, open angle and closed angle. Open angle is the most common form of glaucoma and it is believed that is caused by a reduction in the ability of the eye to drain away aqueous fluid even though the angle is not blocked i.e.the angle is open. The pressure rise is gradual and there are no symptoms.
Raised pressure in the eye damages the optic nerve leading to glaucoma
There are many effective treatments for open angle glaucoma therefore it is important to catch it early so treatment can begin before too much damage occurs hence it is important to have regular eye exams. Some of the treatments involve putting drops into the eyes whilst others involve minor surgery or laser treatment to the front of the eye.
Risk factors for open angle glaucoma include: having a high pressure in the eye, old age, ethnicity (afro-caribbeans are more commonly affected) and having a family history of glaucoma. People with a first degree relative with open angle glaucoma should have an eye examination every year after the age of 45.
Closed angle glaucoma is much less common and is caused when the angle where the aqeous fluid becomes blocked or closed. This is more likely to occur in long sighted people and people of Asian oriental ethnicity as they often have smaller angles to start with. Common early symptoms are haloes around lights especially at night and if the glaucoma becomes acute then a red and extremely painful eye, blurred vision, nausea and vomiting. If you have these symptoms you should go straight to eye casualty. Treatments usually include drops and minor surgery to the iris of the eye.
Glaucoma can also be brought on by certain medications such as long term use of strong steroids and also by diseases such as diabetes and uveitis.
If you are over 45 then you will usually have the pressure of the aqueous in the eye measured using the puff of air test (non-contact tonometry) or sometimes using applanation tonometry where is a little probe is placed against the eye to measure the pressure. We will also look at the optic disc at the back of the eye for signs of glaucoma using retinal photography and the Heidelberg Retinal Tomographer. In glaucoma the optic disc becomes more cupped as nerve tissue is lost.
The Heidelberg Retinal Tomograper
The HRT ticks show a normal disc on the left and the crosses indicate a glaucomatous disc on the right
An field being taken and a plot showing a glaucomatous defect