How is glaucoma diagnosed?

The typical feature in glaucoma is that there is progressive damage to the nerve of the eye, usually associated with high eye pressure and a defect in the field of vision. Diagnosis therefore requires assessment of several parameters, including the eye pressure, the drainage part of the eye, the nerve of the eye (including scans) and the field of vision. However, diagnosis is sometimes not entirely straightforward. Examples include low pressure glaucoma and short-sighted eyes.

The most common type of glaucoma is usually without symptoms, especially in its early stages. Therefore it requires an eye examination to diagnose or assess the risk of developing it.

Glaucoma is assessed mainly by measurement of the pressure inside the eyes, the appearance of the optic nerve and visual field evaluation. Another worthwhile procedure involves scanning of and around the optic nerve to further aid in detecting abnormality.

Risk factors in the development of glaucoma include age, family history, high pressure inside the eye, myopia (“shortsightedness”), thin cornea, abnormal blood pressure, diabetes, smoking, migraine, Raynaud's disease (inflammation of tongue, lips, fingers or toes when exposed to cold), sleep apnoea, thyroid gland disease.    

I agree with the information provided by Glaucoma Australia. As with any disease or condition, diagnosis is made with a combination of history, examination findings and the results of tests. When considered together, these will indicate a probability of having glaucoma.

The history will provide information about symptoms which may be attributed to glaucoma as well as well as any risk factors for developing it. Some risk factors have a proven association with glaucoma. These include elevated intraocular pressure, increasing age, short sightedness or long sightedness, Afro-Carribean ancestry, Asian ancestry, below average central corneal thickness, ocular trauma or inflammation, previous ocular surgery and vasospastic disorders such as migraine and Raynaud's Phenomenon. Individuals on blood pressure treatment may be at risk due low perfusion pressure to the optic nerve overnight. However, there is no consistent evidence to support an increased risk of glaucoma due to high blood pressure, smoking, diabetes or thyroid eye disease.

Examination focuses on detecting glaucoma and understanding the mechanism for its development. Examiners will assess vision, intraocular pressure, corneal thickness, the shape of the front of the eye, the angle between the cornea and iris, the presence of cataract, the shape and size of the optic nerve, the health of the retinal nerve fibre layer.

Tests include a measure of peripheral visual function (perimetry), imaging of the optic nerve head (photography, OCT, HRT), measurement of the retinal nerve fibre layer (OCT, GDx) and measurement of the angle between cornea and iris (Pentacam, OCT). Not all these tests are indicated in all patients and there is a tendency by some to use too many tests and rely too heavily on their results. The most important aspect of assessment is the history and examination findings. Test results compliment these findings and help monitor the health of the optic nerve over time.

There are several tests to detect Glaucoma. The most common measurement is called Tonometry which measures the pressure inside the eye. This can be either the applanation which touches the eyes surface or an air puff on non contact. Newer methods also include electronic indentation and uses a digital pen like instrument. Visual fields testing is vitally important and the newer machines detect very early field loss before any pressure issues arise. Also important is Gonioscopy which allows us to look at the angle of the iris at the front of the eye. Digital techniques include optical nerve imaging which follow nerve changes over a particular time period. Some of these include an OCT and a GDx, these machines are fully automated and are very important for assessing the structure and layers of the optic nerve head. Pachymetry or measurements of your corneal thickness is paramount in evaluating the correct eye pressure as a thicker cornea can cause a higher reading when we perform Tonometry.