Glaucoma is the name given to a group of eye diseases in which the optic nerve at the back of the eye is slowly destroyed. In most people this damage is due to an increased pressure inside the eye – a result of blockage of the circulation of aqueous, or its drainage. In other patients the damage may be caused by poor blood supply to the vital optic nerve fibres, a weakness in the structure of the nerve, and/or a problem in the health of the nerve fibres themselves.
Over 300,000 Australians have glaucoma. While it is more common as people age, it can occur at any age. As our population becomes older, the proportion of glaucoma patients is increasing.
Diagnosing glaucoma is a complex process and involves accumulating enough evidence to make a positive diagnosis and set the target intra-ocular pressure required to prevent glaucoma damage.
1) Optic disc photographs:
We have a digital non-mydriatic Kowa fundus camera which takes excellent photographs of the optic discs. This is the “gold standard” diagnostic test in diagnosing glaucoma and is an essential tool in monitoring glaucoma progression.
2) Optic disc OCT:
The OCT measures the nerve-fibre layer surrounding the optic disc as the nerve spreads out onto the retinal surface. The ganglion cells are damaged in glaucoma and this can be picked up by the OCT. This is an excellent monitor of progressive disease and a baseline OCT is done at the time of diagnosis which serves as a baseline for future reference.
3) Humphrey Visual Field:
Glaucoma is a disease of the optic nerve which leads to progressive loss of peripheral visual field. The Visual Field test is an essential part of making the diagnosis of glaucoma. The machine tries to establish the threshold level of vision within the visual field and does this by flashing faint lights which the patient responds to. The test can be very frustrating as patients often complain that they feel “tricked” by the machine. As frustrating as it can be, it is the only way of establishing the functional loss caused by the disease.
The underlying cause of glaucoma is poorly understood. What we do know is that lowering the intra-ocular pressure (IOP) reduces the rate glaucoma damage in most cases.
IOP can be reduced using either:
1) Eyedrops (Single drop or multiple drops depending on disease severity)
2) Laser (SLT)
3) Surgery- Trabeculectomy
In most cases, glaucoma is controlled with drops alone. Drops can cause irritation and discomfort and may not reduce the IOP to a satisfactory level which would be an indication to use SLT laser.
SLT laser is relatively painless and is done in 2 sittings per eye. It is successful in lowering the IOP in most cases. There are few known side-effects of the laser and is a good option for someone who is struggling with eye drops alone.
Filtering/ Trabeculectomy surgery is reserved for advanced/poorly controlled glaucoma only. A hole is made in the casing of the eye and the eye fluid drains out through the back of the eye to form a filtering bleb on the eye. Trabeculectomy surgery is successful in most cases but is an invasive procedure which can lead to early and late infection in the eye.