What is glaucoma?

• A progressive loss of optic nerve tissue leading to loss of peripheral vision and eventually blindness. Often, but not always associated with high eye pressure (Intraocular pressure or IOP).
• There are usually no symptoms.
• Known as the “silent thief of sight”
• Glaucoma affects around 1% of the global population.
• More than 300,000 Australians are estimated to have glaucoma, yet 50% are unaware of it.

What are optic nerves?

• They can be thought of as the ‘cable’ connecting the camera (eye) to the computer (brain).
• Parts of central nervous system (CNS).
• Composed of bundles of around 1 million nerve fibres.
• Ganglion Cells around the macula provide most of these fibres.
• They transmit all visual signals from the retina/macula to the brain.

What is eye pressure?

• The eyeball is a little like a soccer ball filled with an aqueous fluid and a gel-like substance called the vitreous.
• Aqueous fluid provides nutrients and oxygen to the cornea and the lens.
• The ciliary body (CB) acts like an inflow pump, constantly producing the fluid.
• The trabecular meshwork (TM) acts like an outflow filter, draining the fluid.
• The TM is bound by the angle formed between the cornea at the front and the iris at the back.
• The normal angle is around 40˚.
• The cycle and balance between the inflow and outflow provides the internal tension, hence the term eye pressure or intraocular pressure (IOP).
• Almost all high IOPs are caused by reduction of the outflow filter i.e. blockage of the TM.

What is normal eye pressure/IOP?

•  There is actually no universally “normal” eye pressure.
• Average eye pressure ranges from 12-22 mmHg (millimetres of mercury).
• Individual IOP levels fluctuate throughout the day.
• Measurements may vary depending on the instruments used.
• Corneal thickness also affects IOP levels.
  • Thin cornea <555 µm —- artificially lowers IOP
  • Thick cornea >555 µm —- artificially increases IOP
• The most important factor is whether your current IOP is at a sufficiently low level to slow or prevent glaucoma damage to your optic nerve.

What is an abnormal eye pressure/IOP level?

• Anything over 22 mmHg (after adjustment for corneal thickness) is considered high.
• Sometimes it is called Ocular Hypertension (OHT).
• It may not become glaucoma but does increase the risk -especially when you are getting older or other risk factors emerge.
• Anything under 6mm (after adjustment for cornea thickness) is considered low.
• It is called hypotony.
• It usually only occurs after having glaucoma filter operation.

How does glaucoma cause optic nerve damage?

• Mechanical pushing on the nerve
  • High eye pressure
• Ischaemic
  • Lack of oxygen and blood supply
• Neuro-degenerative
  • Programmed cell death from ageing
• Others
  • Inflammation
  • Trauma

What else can cause optic nerve damage apart from glaucoma?

• Severe head trauma or blood loss
• Neurological diseases
• Compression from brain or orbital lesions

Sometimes an MRI is needed to rule out these conditions.

What are the risk factors of glaucoma?

• Its degenerative nature has multiple risk factors. Most are not readily treatable:
  • Advancing age
  • Family history of glaucoma
  • Poor cardiovascular status
• The main treatable risk factor is:
  • High eye pressure (intra-ocular pressure IOP)
• Other risk factors may contribute:
  • High-level myopia
  • Ethnicity – higher risk for those of African or Asian descent
  • Previous eye trauma
  • Previous eye inflammation
  • Chronic steroid use
  • Low blood pressure
  • Sleep apnoea
  • Migraine
  • Smoking