Glaucoma
GLAUCOMA
WHAT IS GLAUCOMA?
Glaucoma is a group of eye conditions that damage the optic nerve. The damage that occurs is irreversible and glaucoma cannot be cured, however, it can be detected early through regular check-ups with your Optometrist. It is an eye condition that can be easily managed and with timely treatment, individuals with glaucoma can retain excellent vision their entire life.
WHY IS THE OPTIC NERVE IMPORTANT AND HOW DOES GLAUCOMA AFFECT IT?
The optic nerve is a structure at the back of the eye composed of nerve fibres that carry information from all parts of the retina to the brain so that you can see.
The most common cause of damage to the optic nerve is due to eye pressure being too high, resulting in compression of the optic nerve and permanently damaging the nerve fibres, leading to loss of your peripheral vision. Depending on which nerve fibres are affected, this will correlate to where in your visual field vision loss occurs.
HOW CAN I TELL IF I HAVE GLAUCOMA?
Glaucoma is a slow, progressive, silent disease and symptoms are often not experienced until the later stages of the disease. It begins with gradual peripheral vision loss and only in the later stages affects your central vision. Once this vision has been lost, unfortunately, it cannot be regained.
The best way to detect Glaucoma is to have regular check-ups with your Optometrist where the optic nerve, eye pressure and visual field of the eye can be assessed.
ANATOMY OF THE EYE
A small structure called the Ciliary Body near the front of the eye acts as a fluid generator, constantly producing fluid that is essential to prevent the eyes from collapsing. The Anterior Chamber Angle of the eye contains a drainage system that prevents too much fluid from building up, maintaining a steady pressure in the eye. Any issue with this drainage system can cause eye pressure to rise and the risk of optic nerve damage to increase.
TYPES OF GLAUCOMA
The most common form of glaucoma is Primary Open Angle Glaucoma (POAG). This form of glaucoma occurs when the drainage channels of the eye become blocked so the fluid cannot easily drain from the eye. The imbalance of fluid generation and drainage causes an increase in eye pressure and can result in damage to the optic nerve.
Secondary Open Angle Glaucoma (SOAG) occurs when there is an identifiable cause of increased eye pressure. Glaucoma will occur secondary to another condition that is present and prevents proper drainage of fluid out of the eye despite the angle being open. A common example of this is Pigment Dispersion Syndrome where pigmented cells from the iris deposit over the drainage angle preventing outflow of fluid.
Primary Angle-Closure Glaucoma (PACG) is another form of glaucoma that involves the depth of the drainage angle. The iris of the eye is attached next to the drainage system of the eye and determines the depth of the angle where fluid drains out. When the drainage angle is narrow, angle-closure may occur when the iris begins to block the outflow pathway. This can occur suddenly (Acute Angle-Closure Glaucoma) where there is a rapid increase in eye pressure which usually results in a painful red eye and blurred vision. This is a sight-threatening emergency and must be seen by an eye specialist immediately.
Secondary Angle-Closure Glaucoma (SACG) can also occur where, similar to SOAG, an identifiable cause of angle closure is present that leads the drainage angle to close and pressure in the eye to spike.
TREATMENT
Treatment for glaucoma varies depending on the type of glaucoma that is present. This eye condition is managed through a variety of medical and surgical procedures.
In the case of narrow angles, laser Peripheral Iridotomy can be performed. With a laser, a small opening is made in the edge of the iris allowing fluid to pass directly to the anterior chamber, releasing the build-up of pressure behind the iris and preventing the iris from blocking the drainage angle. Early cataract surgery has also been shown to be effective in the treatment of narrow angles. A study that has arisen (called the EAGLE study) concluded that cataract surgery showed greater efficacy and was more cost-effective than laser peripheral iridotomy, and should be considered as an option for first-line treatment for narrow angles. [2]
Medical treatment for glaucoma is usually in the form of eye drops and includes medications that either reduce the production or increase the drainage of fluid out of the eye. These medications include prostaglandin analogues (e.g. Latanoprost) and beta-blockers (e.g. Timolol). Other medications that are also used include alpha-agonists (e.g. Brimonidine), carbonic anhydrase inhibitors and combination drops. Glaucoma medication can come in different strengths and combinations. The aim is to use the least amount of medication to get the best control of eye pressure while minimising the number of side effects.
When medical intervention is not enough further surgical treatment is an option. Surgeries include selective laser trabeculoplasty (SLT) whereby a laser is used to alter the biochemical composition of the drainage angle allowing for greater outflow of fluid. Another common surgery is a trabeculectomy, where a new passageway is created to bypass the blocked natural drainage angle. The fluid forms a ‘bleb’ between the conjunctiva and sclera of the eye and is eventually absorbed by blood vessels in the eye.
IMPORTANCE OF REGULAR EYE EXAMINATIONS
Glaucoma is a slowly progressive disease that is not often diagnosed on the spot. Regular checkups are required to pick up on subtle changes to eye health and function to catch the disease early and prevent further damage from occurring.
REFERENCES
Glaucoma NZ - Reference here
Azuara-Blanco A, Burr J, Ramsay C, Cooper D, Foster PJ, Friedman DS, Scotland G, Javanbakht M, Cochrane C, Norrie J; EAGLE study group. Effectiveness of early lens extraction for the treatment of primary angle-closure glaucoma (EAGLE): a randomised controlled trial. Lancet. 2016 Oct 1;388(10052):1389-1397. doi: 10.1016/S0140-6736(16)30956-4. PMID: 27707497.