Glaucoma Suspect

The terminology in glaucoma can be confusing. There are open and closed angle varieties; high and normal pressure varieties; secondary glaucomas; early and advanced glaucomas and ocular hypertension – which is not yet glaucoma.

It is no wonder that many patients are confused by this condition, which in most cases does not even cause symptoms, particularly in the earlier stages.

Being a glaucoma suspect can be frustrating, as after a wait and several tests in the eye clinic (that is; after negotiating the car parking), you have still not been given a definitive diagnosis.

To start from the beginning, glaucoma is a condition of the optic nerves. Damage to the optic nerves is the underlying pathology. Each optic nerve at birth has around 1.2 million nerve fibres at birth and this number declines with age. If there is sufficient damage to the optic nerves, the field of vision may become affected. However, in the earlier stages, there is often no change in visual field.

The normal (intraocular) eye pressure is in the range 11-21mmHg. Glaucoma is usually associated with a high intraocular pressure (IOP) although it can occur at a normal IOP. This is the case in 10% of people with glaucoma, and this is termed normal pressure/tension glaucoma (NTG).

In cases where the pressure in the eye is normal and the visual fields are normal, but the optic nerve looks suspicious of glaucoma, it may not be possible to make a concrete diagnosis. The optic nerve features of glaucoma are variable and often subtle. The whole nerve, when observed head on in the eye clinic measures between 1 and 2 mm in diameter.

When looking at the optic nerve, we measure the thickness of nerve fibre layer. As you look at the nerve, it looks a bit like a ‘polo mint’ with the nerve fibres arranged around the perimeter of the nerve. As the damage from the glaucoma gets worse, the central hollow gets larger and the rim gets thinner.

The thickness of the optic disc rim of each person varies, as with every other biological variable. It is difficult therefore at one visit to know if the optic disc is glaucomatous or if it is a normal but thin rim. It is the case that if the optic disc rim is thin but remains unchanged over time, then there is no diagnosis of glaucoma. However, if the optic disc rim becomes thinner over time, then a diagnosis of glaucoma can be made.

In the period of observation where the doctor is unsure whether the optic disc rim is thin but normal and not changing or whether this is a case of glaucoma, there is no certain diagnosis. ‘Glaucoma suspect’ is the term used describe the diagnostic conundrum in which we do not have a firm diagnosis but are waiting to see if time confirms the diagnosis.