Glaucoma is the name given to a group of eye conditions which causes optic nerve damage and in turn can permanently affect vision. Glaucoma damages the optic nerve at the point where it leaves the eye.
Glaucoma damage may be caused by raised eye pressure or a weakness in the structure surrounding in the optic nerve. Our eye pressures may be within normal limits but damage occurs because there is a weakness in the optic nerve which in turn affects blood flow to the nerve.
NOTE: Eye pressure is not connected to your blood pressure.
Diagnosis of Glaucoma
A thorough consultation is required if there is any suspicion that you might have glaucoma. The examination involves measuring the intraocular pressure (IOP), Center corneal thickness, Gonioscopy(measurement of anterior chamber angle) as well as evaluation of the optic nerve, specifically the cup/disk ratio which provides an indication if there has been any damage.
Specific investigations are performed and includes a Visual field Test and an Ocular Coherence Tomographic (OCT) evaluation of the Retinal Nerve Fibre Layer (RNFL).
The visual field test is checked on a sophisticated machine that using patient feedback measures the the peripheral vision. Subtle changes can be picked up and monitored over time.
A RNFL OCT measures the thickness of the nerve fibre layer surrounding the optic disc. Nerve damage results in loss of nerve fibre layer thickness. Again the areas of damage which often match up with the visual field can be documented and followed over time.
Treatment of Glaucoma
Drops are usually the first line of treatment for Glaucoma. If the intraocular pressure cannot be reduced to an appropriate level, further drops may be added.
Some cases of glaucoma, e.g. narrow angle glaucoma can benefit from a YAG peripheral iridotomy. This is where the YAG laser is used to create a small opening in the iris to allow fluid to pass through from the back of the eye to the draining area (Trabecular meshwork) at the front.
Another laser treatment is Selective Laser Trabeculoplasty (SLT) which is used to try and promote outflow of fluid from the eye.
When medical and laser treatments fail or if there is poor compliance to the medical treatment then surgery may be required.
A filtering procedure to allow fluid to drain from the eye is called a Trabeculectomy. A small opening valve is created which allows fluid to drain from the eye to the outer mucous lining covering of the eye.
A variety of microincisional glaucoma devices have recently become available. These work through a variety of mechanisms and essentially make use of a device or shunt which is implanted into the eye allowing fluid to escape by an alternate route. These procedures have the advantage of being minimally invasive with minimal complications.