What is glaucoma?
Glaucoma is the name used for the group of eye conditions which cause damage to the optic nerve. This damage can ultimately cause sight loss. Our optic nerve is the wire that connects the brain and the eye together. It sends visual information from one to the other.
There is a misconception that glaucoma is one disease, when actually there are many different types. I will touch upon a few below.
Types of glaucoma
Primary open angle glaucoma (POAG)
This is the most common type of glaucoma, characterised by elevated intraocular pressure and an open anterior chamber angle with no other underlying pathology. Some of the risk factors for this include; increasing age, higher intraocular pressures (checked with the puff of air test), being of Afro-Caribbean descent, being short sighted and having a family history of POAG.
In early stages, most people with POAG don’t have any symptoms. They are only diagnosed as part of their routine sight test, which is why it is important to keep up to date with regular sight checks. Those in late stages of POAG may notice a restricted visual field and blurred vision.
Normal Tension Glaucoma
This is a type of POAG, however in this type of glaucoma, there are no raised intraocular pressures (IOP). Although there are no raised IOPS, there is still damage to the optic nerve, retinal nerve fibre layer thinning and visual field loss ( we can use the OCT machine and the visual field screener, along with ophthalmoscopy to help identify this). Some of the risk factors for this type of glaucoma include; those with the higher-normal level IOPS; those patients with history of stroke or diabetes (any ischemic vascular disease) and those with Raynaud syndrome – this is commonly linked to migraine.
This is high IOP within the first year of life. Blindness occurs in 5/50 of all cases and reduced vision in 20/50 of all cases, it is rare, and only occurs in 1/10,000 births.
This is a very rare type of glaucoma in those individuals aged between 3 and 40. It is genetic and early onset in nature. It is not very responsive to medication and often requires surgical intervention, as it has a very rapid progression
Acute Angle Closure Glaucoma ( AACG)
Closed angle glaucoma, this happens when there is a sudden rise of intraocular pressure, which can cause damage to the optic nerve. This is usually caused by the pupil blocking the drainage channel of the eye ( in most cases), and in the case of Primary AACG, eyes which suffer from this type of condition are anatomically different from those which don’t, putting them at a much higher risk. They tend to be shorter, have thicker lenses – which are positioned further forward in the eye, and the cornea ( the window which covers the coloured section of the eye), tends to be flatter.
Some other risk factors for this type of glaucoma include; being long sighted, having a family history of this type of glaucoma, increase in age, being female, being of Asian or Inuit descent.
Secondary AACG is when trauma or eye disease can cause the pressure in the eye to raise.
This occurs secondary due to an underlying healthy or eye condition. Types of secondary glaucoma can include –
Pigment dispersion syndrome and pseudoexfoliation
this is where the pigment from the back of the iris, is rubbed off by the front of the lens. This pigment then deposits itself in the drainage channel, eventually blocking the outflow of the fluid in the eye ( aqueous humour ), this leads to high pressure. In pseudoexfoliation, the drainage channel is blocked with a dust like substance. The dust comes from the surface of the lens capsule which is rubbed off by the continuous movement of the iris, when the pupil changes size.
Iatrogenic means caused by a medical professional, for example during surgery, or due to steroid use.
Uveitis is when the pigmented tissues of the eye ( the Uvea) become inflamed. It usually affects those from ages 20-59. There are different types of uveitis Anterior, Posterior and Intermediate all categorised based on which part of the uveal tract is being affected. The way in which uveitis can cause glaucoma is numerous; the inflammatory byproducts of fluid and protein may leak into the drainage channel and block fluid outflow; Uveitis can cause secondary angle closure glaucoma due to the inflammation in the front part of the eye; Uveitis is often treated with steroids. It is this steroid use which can lead to high IOPS and damage to the optic nerve.
When cataracts become very advanced, they can swell and block the outflow of fluid through the eye, and cause a secondary angle closure effect.
Being hit in the eye may cause high pressure though inflammation ( uveitis ), Bleeding ( haemorrhage blocking the drainage channel), dislodging of the lens in the eye.
Chemical burns can cause inflammation uveitis)
Blunt force trauma can cause the drainage angle to be pushed backwards, and over a number of years, there is a pressure build up/ development of high pressure.
Steroids cause the pressure in the eye to raise, and although they can be injected, inhaled, taken orally, used topically on the skin or eye, the most common way to cause IOP raise is by application locally to the eye. This is when a steroid is applied onto or around the eye, either by injection, or eye drop. This is why those people who are using eye treatment containing a steroid, should have their eye pressures checked on a regular basis.
this can occur when due to certain eye conditions ( such as diabetic retinopathy ), new blood vessels are created. These are small and leaky. They can grow into the surface of the eye, but also into the drainage channel, and block it, causing a raise in IOPS
There are several other reasons for secondary glaucoma, but these are just a few examples.
Are there any signs of glaucoma?
For NTG and PAOG usually no, not in the early stages. AACG does cause symptoms and can be extremely uncomfortable. I have listed some of the glaucoma warning symptoms below
- Gradual blurred vision, starting in the periphery ( outer edges)
- Seeing halos around bright lights
- Severe pain in the eye and frontal headache, a very red, sore eye, and nausea/vomiting
How is glaucoma detected?
Glaucoma is detected usually following a routine sight test. We check intraocular pressures using our pressure test, we can check the peripheral field of vision using our field screening test, we do a thorough examination using the slit lamp of the front and the back of the eye to look at the drainage channel and at the optic nerve using volk. We also carry out a OCT 3D scan if requested, and this can detect glaucoma up to 4 years early.
If raised IOPS are suspected we carry out repeat pressure reading; as checking pressures at a different time of day, on a different day, can also affect the measurement of IOP we obtain.
If glaucoma is suspected, an onward referral to the hospital eye clinic for further investigations
How is it treated?
The aim of the ophthalmologist and hospital optometrist is then to manage the underlying cause and prevent any further damage to the optic nerve. Some of these treatments include:
- Eye drops
- Laser treatment – iridotomy, a small hole is made in the iris to help with drainage of fluid
- Trabeculectomy – this is where a new drainage channel is made to improve fluid outflow
… and Finally
Damage to the optic nerve can not be reversed, and glaucoma is the second leading cause of blindness worldwide, with around 60 million people living with it.
Damage to the optic nerve can however, be prevented if detected and treatment is sought at an early stage. Make sure you attend your regular sight tests, and if you have any concerns ring your optometrist for advice.