The visual field test measures central and peripheral vision sensitivity. It involves sitting in front of a dome-shaped machine. Light spots of different brightness shine on the inner surface of the dome. You are instructed to look straight ahead at a target and press a button when you can see the light spots against a bright background.

The picture shows a typical visual field defect (black area) due to glaucoma damage. Patients may not notice the visual field defects at the early stage of glaucoma because the other eye tends to compensate for losing vision in some areas. However, the loss of visual field in both eyes may affect the exact location when the disease progresses. Patients may start to notice that they are not seeing well in some areas, or objects or cars appear unexpectedly in the remaining centre of vision.

Driving can become difficult when there is significant visual field loss in both eyes. Patients must inform DVLA when they are diagnosed with suffering from glaucoma. Patients will need to complete a V1 form, and DVLA will arrange a visual field test for you to do with both eyes open. The DVLA will decide whether you meet the visual standard for driving based on the field test results.

Optic disc is the optic nerve head that we can see inside the eye with a special focusing lens. In normal people, there is a small depression on the optic disc called the optic disc cup. This is normally occupying 30% of the optuc disc area and the doctor normally measure the vertical cup-to-disc ratio during routine examination. Normal cup-disc ratio is about 0.3 to 0.6 depending on the size of the optic discs. When the cup-disc ratio is more than 0.6, this is generally considered to be abnormal and require further investigation. When this is coupled with raised eye pressure, then this is considered to be glaucoma changes on the optic discs that needs treatment to lower the eye pressure. Without treatment, the optic nerve damage will continue and the cup-disc ratio will gradually enlarged over time with result of visual loss. Some patients can develop glaucome-type optic disc changes without raised eye pressure, this is consider to be Normal Pressure Glaucoma meaning that the optic nerve damage happens even when the eye pressures are within normal limits, therefore, treatment or surgery may be require to achieve lower eye pressure to protect the optic nerve.

Optic disc imaging is a laser scan that can measure the thickness of the nerve fibre layer surrounding the optic discs. The latest Spectral Domain Optical Coherence Tomography (SD-OCT) can accurately measure the thickness of the nerve fibre layer in micrometres. The newest eye tracking technologies allow accurate scanning of the exact locations as in the previous scans, which allows precise comparison of nerve fibre layer thickness for up to 5% of changes that can be detected accurately.

The picture shows an OCT scan of an optic nerve about one year apart, demonstrating minimal nerve fibre layer thickness changes.