Open Angle Glaucoma

Glaucoma is a disease of the optic nerve usually caused by increased intraocular pressure. When some of the nerve fibres that make up the optic nerve itself are damaged, visual field defects (or blind spots) develop. Initially the damage causes subtle changes in the peripheral or side vision but eventually the optic nerve is significantly damaged, tunnel vision and blindness can result.

Primary open angle glaucoma is the most common form of glaucoma. In this condition there is no specific cause of the increased pressure (such as other disease or injury), but the balance between intraocular fluid production and drainage gradually changes over time and the pressure in the eye gradually increases. The result is gradual and painless loss of nerve fibres in the optic nerve over time. It should be noted that some eyes appear to have different abilities to withstand eye pressure, such that some people develop glaucoma changes at “normal” intraocular pressures, while others may not develop damage at pressures considered to be “above normal”.

Glaucoma is often called “the sneak thief of sight”, as there are no symptoms early in the disease. As the initial damage is to the peripheral vision, it may not be noticed until the disease is advanced, and this vision loss is not reversible. For this reason it is important that all patients over the age of 40 years old be screened regularly (every 2-3 years, or more frequently as recommended) by their Optometrist. Glaucoma is a condition best identified before a patient has symptoms and in its very early stages.

An increased risk for glaucoma may be associated with older age, a positive family history of glaucoma, diabetes, being very myopic (near sighted) and previous trauma or surgery to the eye.

A routine eye examination will assess your vision, intraocular pressures, and optic nerve appearance, and your family history risk for glaucoma will be assessed. If a patient is considered to be at risk further testing may include gonioscopy, visual field testing and optic nerve assessment via optical coherence tomography (OCT).
In the early stages, diagnosis of glaucoma can be challenging, and several tests are generally required. Sometimes patients are monitored closely for some time before the decision is made to commence treatment.

The treatment approaches for glaucoma aim to lower intraocular pressure to prevent further progression. It is important to realise that there is no treatment that can reverse damage to the optic nerve and return the visual field to normal.

Eye drops
Most patients are commenced first on eye drops to reduce intraocular pressure. Most glaucoma medications are well tolerated, safe and have minimal ocular or systemic side effects. For many patients a drop taken once daily is adequate to control their intraocular pressure. Some patients will require additional topical treatments and may require drops several times a day, and some need more than one type of anti-glaucoma drop. Treatment is life-long, and there is no cure for glaucoma.

Laser
For some patients selective laser trabeculoplasty (SLT) is a better option, and involves applying a special laser to the trabecular meshwork (drainage area) to improve the outflow of intraocular fluid. This treatment is considered if a poor response to topical glaucoma drops has been seen or if a patient does not tolerate the eye drops. Some patients require both eye drops and SLT to control their intraocular pressures. SLT is well tolerated, safe and painless, but may require several treatments for best effect, and also the pressure lowering effect of SLT can lessen over time. Retreatment is usually needed each two to 10 years.

Surgery
In advanced cases of glaucoma, surgery may be required. It is usually only considered where neither eye drops nor laser has sufficiently stopped the progression of optic nerve damage and visual loss. Surgery aims to form a new drainage channel to improve fluid outflow from the eye and so reducing intraocular pressure.

Microinvasive glaucoma surgery (MIGS)
A relatively recent addition to glaucoma control is the use of microinvasive glaucoma surgery (MIGS) which use tiny devices to improve drainage of fluid out of the eye. While MIGS is not as effective at achieving very low pressure goals as traditional glaucoma surgery, it has a much better safety profile and faster visual recovery. MIGS is often coupled with cataract surgery.