Clinical indicators / risk factors for glaucoma
The clinical indicators of glaucoma are many, although there is no definitive sign that makes diagnosis certain. At best, optometrists and ophthalmologists can build up a picture of an individual’s likelihood of having this disease – a bit like solving a jigsaw puzzle. While progressive visual field loss (i.e. peripheral vision loss increasing over time) is a strong indicator of this disease, it can also be present in other eye conditions and neurological diseases.
Here are some of the clinical indicators your optometrist will look for in assessing your risk:
Ocular hypertension – IOP readings higher than 21mmHg. While this is not the same as glaucoma, it is a risk factor and chances are higher of developing the disease compared to someone with IOP in the normal range.
A peripheral field defect – which means a problem with your peripheral vision, as mapped by a visual field analyser. Glaucoma causes a classic field defect which is one of the strongest indicators of the disease. A conclusive diagnosis can only occur if this defect worsens over time, meaning you have permanently lost even more retinal nerve fibres. For this reason, treatment may begin in glaucoma suspects before there is conclusive evidence of progressive field loss.
Optic disc cupping – this is where the optic nerve becomes hollowed out, due to loss of retinal nerve fibres. If you picture the optic nerve as a thick cable made up of hundreds of thousands of thin wires (the individual nerve fibres) then, as the fibres die off, the cable becomes hollow. This information can be visualised by examining your retina or taking a photo, but is best assessed using Optical Coherence Tomography (or OCT), which will be recorded for comparison to future test results to look for progression (or worsening) of the disease.
Optic disc haemorrhage – these are transitory little bleeds close to the optic nerve head. They are suspicious for normal tension glaucoma. Note: you cannot see these yourself. Nor can they normally be seen by looking directly at the optic nerve with an ophthalmoscope.
Narrow angles – the space between the inside surface of your cornea and the periphery of your iris (the coloured part of your eye) is called the angle. Wide open angles facilitate good outflow of intraocular fluid. Narrow angles impede outflow and can gradually lead to glaucoma or can suddenly become closed in an acute angle-closure attack. Your angles will be assessed by your optometrist using a slit-lamp biomicroscope.
Central corneal thickness – a thinner than normal cornea can be a clinical sign of this disease. Not only do thin corneas result in falsely low intraocular pressure measurements, but they can also indicate thinner, more fragile structures in other parts of the eye – including the optic nerve – making it more prone to damage from intraocular pressure. A comprehensive test for glaucoma should include a measurement of central corneal thickness (CCT) using a pachymeter (an instrument for measuring corneal thickness). A CCT of less than 555 μm is associated with an annual risk of 3.4% of developing the disease.
Your optometrist or ophthalmologist will also factor in non-clinical risk factors such as age, race, family history and medical history in determining if you are a suspect for this disease.