Tests for glaucoma

Intraocular pressure measurement
Many opticians use the dreaded air-puff technique, which is simple and convenient but somewhat over sensitive. The most accurate method is use Goldman tonometry, in which the eye is first anaesthetised and then mildly stained with fluorescein. A small plastic prism is advanced towards the eye and touches it. The pressure can be deduced from the amount of force required to gently alter the shape of the cornea.

Corneal thickness
We may measure the thickness of your cornea, as this measurement can affect IOP measurements. In general, thicker corneas are associated with exaggerated IOP’s, whereas IOP measurements in patients with thinner corneas are artificially lower.

A contact lens with an internal mirror is placed on the surface of your cornea, to allow us to see around the cornea into the trabecular meshwork. This allows open angles to be distinguished from closed angles.

Examination of the optic disc
i) Clinical
This is done at the slit lamp and allows a 3-D view of the optic disc. In patients with glaucoma, particular patterns of optic disc damage are recognised, which usually correspond to changes in the patients peripheral vision.

ii) Photography, ocular coherence tomography and Heidelburg Retinal Tomography
Technological advances in imaging of the optic disc has spawned machines such as the OCT (ocular coherence tomography) and HRT (Heidelburg Retinal Tomography), which create maps of the surface of the optic disc. These are very useful when first diagnosed, as subsequent images to can compared to those obtained at the first visit to detect progression, which is the hallmark of glaucoma.

Visual field testing
Perimetry or computerised visual field testing determines to what extent you, the patient are practically affected by glaucoma. This measures the problem we are trying to avoid and means that, if you have visual field defect, you have relatively advanced disease. The test is done by looking into a white bowl in a dark room, and pressing a button every time you see a light flash in the corner of your vision.  It does require a lot concentration, but for most patients only takes about 5-10 minutes per eye. Repeat visual field tests allow us to determine if your glaucoma is relatively stable or progressing rapidly.