Understanding Glaucoma: The different types

Primary Open Angle Glaucoma (POAG) is the most common form of glaucoma.

 

In POAG, the pressure inside the eye (intraocular pressure) is higher than normal, typically above 21-24mmHg. This increased pressure leads to damage to the optic nerve, known as "cupping," which can cause a gradual loss of peripheral vision.

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In POAG, the drainage angle of the eye is open, which can be confirmed through a simple test called gonioscopy, where a lens with a small mirror is placed on the eye. The main issue in POAG is that fluid drainage from the eye’s anterior chamber is impaired due to a blockage in the drainage channels (trabecular meshwork). You can think of it like a bath where the plug is clear, but there’s a blockage further down the pipe that causes the water to rise.

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Treatment for POAG usually begins with eye drops or Selective Laser Trabeculoplasty (SLT) to lower eye pressure. If these treatments aren’t sufficient, surgery may be necessary. You can find more detailed information about surgical options in the Treatment section of this website.

In Primary Angle Closure Glaucoma (PACG), the drainage angle is closed, leading to increased eye pressure and optic nerve damage. This type of glaucoma can be identified using gonioscopy. In PACG, the iris blocks the trabecular meshwork, preventing fluid from draining properly and causing a rise in eye pressure.

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Treatment for PACG often starts with eye drops, Yag Laser Peripheral Iridotomy (PI), or cataract surgery. Yag PI involves creating a small hole in the iris to allow fluid to bypass the blockage, which helps open up the drainage angle. Cataract surgery can also help by replacing the natural lens with a thinner artificial lens, providing more space for fluid to drain. In some cases, further surgery may be required if these treatments don’t adequately control the disease.

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PACG can develop slowly or suddenly. If it occurs suddenly, it’s known as Acute Angle Closure Glaucoma (AACG). Symptoms of AACG include severe headache, eye pain, nausea, seeing halos around lights, blurred vision, and a red eye. This is an eye emergency, and if you experience these symptoms, you should go to A&E or an Eye Casualty immediately. Eye Casualties are available at Southend University Hospital and Broomfield Hospital, but you will need a referral from the main A&E or an emergency optician.

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Some patients may have narrow drainage angles without developing glaucoma. These patients may be classified as having Primary Angle Closure (PAC) if the pressure is raised without optic nerve damage, or Primary Angle Closure Suspects (PACS) if the angle is narrow but the pressure is normal. Treatment is recommended for PAC, while patients with PACS can often be monitored by their optician annually, as the risk of progressing to glaucoma is low.

In Normal Tension Glaucoma (NTG), the pressure inside the eye is within the normal range (below 21mmHg), but there is still optic nerve damage and corresponding visual field loss. The drainage angle is open, as confirmed by gonioscopy.

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In NTG, factors other than eye pressure, such as blood supply to the optic nerve, mitochondrial function (how well the cell’s energy production parts work), and the pressure of the fluid surrounding the brain and optic nerve, may contribute to optic nerve damage. However, the only proven treatment for reducing the risk of vision loss in NTG is lowering eye pressure.

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Treatment for NTG typically starts with eye drops, though SLT (laser) may also be tried. However, SLT is often less effective in NTG because it works best when eye pressure is initially raised. In some cases, surgery may be necessary. There is ongoing research into using oral nicotinamide to improve mitochondrial function, which may emerge as a new treatment for NTG.

Ocular Hypertension (OHT) is a condition where the pressure inside the eye is elevated (above 21-24mmHg) without any signs of optic nerve damage or visual field defects. About 1 in 10 patients with OHT will develop glaucoma over a 5-year period, but treatment can reduce this risk to 1 in 20.

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In OHT, the drainage angle is open, but there may be a blockage in the drainage channels that prevents fluid from leaving the eye properly.

 

Treatment for OHT is not always necessary, as not all patients will go on to develop glaucoma. The decision to treat is based on the patient’s risk factors and preferences. If treatment is recommended, it usually starts with eye drops or SLT (laser). Surgery is generally avoided in OHT unless the patient is at high risk of vision loss.

Secondary glaucoma occurs when increased eye pressure and optic nerve damage result from another eye condition or surgery. Conditions that can lead to secondary glaucoma include:

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• Vitreoretinal surgery (e.g, for retinal detachment)

• Complicated cataract surgery

• Corneal graft surgery

• Use of steroid eye drops

• Uveitis (inflammatory eye disease)

• Uncontrolled diabetic eye disease (neovascular glaucoma)

• Eye trauma or injury

• Pseudoexfoliation (PXF)

• Pigment Dispersion Syndrome (PDS)

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In secondary glaucoma, the drainage angle may be open or closed, depending on the cause. Treatment will vary based on the underlying condition and may include eye drops, laser therapy, surgery, or a combination of these approaches.

Pseudoexfoliation (PXF) involves the abnormal accumulation of protein deposits in the body, including the eyes. In some cases, these deposits block the trabecular meshwork, leading to increased eye pressure. Patients with PXF may experience faster disease progression, and surgery can be more challenging.

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Pigment Dispersion Syndrome (PDS) occurs when the lens inside the eye rubs against the iris, causing pigment to shed and potentially block the trabecular meshwork.

 

Not all patients with PXF or PDS develop glaucoma, but if pressure increases, treatment options are similar to those for open-angle glaucoma.

 

PDS patients should avoid high-impact sports, as these can increase pigment shedding. Activities like cycling and swimming are generally safer.

 

Yag Laser Iridotomy may be offered to PDS patients who haven’t developed high eye pressure, as it might reduce the risk of raised pressure. However, once pressure is elevated, Yag Laser Iridotomy is less likely to help.