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Glaucoma awareness, what is it and how does it affect the eye?

Posted on 09 February 2021


Low vision awareness month; Glaucoma.

Glaucoma, What is it and how does it effect sight?

Glaucoma is a group of eye diseases that affect the optic nerve, the nerve which connects the eye to the brain. The damage is caused by an increase in pressure inside the eye (intra ocular pressure or IOP).
It often affects both eyes, usually to varying degrees. It affects the most peripheral vision first gradually working its way to the central vision area and for that reason the effects often go unnoticed until it can be quite advanced. In most cases it is asymptomatic and is hence know as a silent blinder of sight conditions. It is treatable but best managed if detected early, something which can be done through a routine eye test.

What causes Glaucoma?

Inside the eye, a continuous production of fluid occurs called the aqueous humour. This fluid has a very important job of maintaining the shape of the eye as well as keeping the back of the eye pressed down so it can function correctly. Normally as new fluid is produced, old fluid makes its way to drainage tubes where it leaves the eye. In glaucoma this drainage is damaged or blocked somewhere along the fluids pathway causing a build up of fluid and an increase in pressure. Imagine a sink with the tap on, glaucoma is either the plug being closed or partially closed or the pipes under the sink being blocked.

There are 2 main subtypes of glaucoma, Chronic and Acute.

Chronic is the most common type which develops very slowly. It is painless and will effect the vision slowly from the outside in and therefore needs detecting through a sight test.
Acute Glaucoma is painful and has a sudden onset due to a rapid increase in IOP. The pain is usually extreme and not something you may ignore with blurred vision and halo’s around light also noticed. In this instance you should go immediately to a hospital with an eye A+E department. In our practice areas this would be Burton Queens, Birmingham City or Wolverhampton New cross hospitals.
In my earlier comparison, Chronic glaucoma is either the plug being slightly covered or the pipes being slightly blocked so the water doesn’t run away quite as efficiently, Acute is where the plug is in or the pipes are blocked so the sink fills with water and has nowhere to go.

The most common types are:
• Primary open angle glaucoma, the most common type of glaucoma in the UK. It’s also known as chronic open angle glaucoma which means the damage to your optic nerve and changes to your sight happen very slowly over time.

• Closed angle glaucoma, where damage to the optic nerve can happen very quickly due to a sudden rise in eye pressure.

• Normal tension glaucoma, when an eye pressure within the normal range still causes damage to the optic nerve.

• Secondary glaucoma, which occurs as a result of another eye condition, an injury to the eye or due to medication.

• Congenital glaucoma, when a baby is born with glaucoma.

What factors increase your risk?

Risk factors for glaucoma include:
• increasing age,
• high pressure in the eye,
• a family history of glaucoma,
• being short sighted (myopic)
• use of steroid medication.
You are also at increased risk of developing chronic glaucoma if you are of black-African or black-Caribbean origin, whereas people of Asian origin are more at risk of getting acute glaucoma compared with those from other ethnic groups.
Because Family history is such an important risk factor, anyone over the age of 40 directly related to someone with glaucoma can have NHS sight tests, either every 12 months or 2 years depending on what is found on the sight test.

Testing for glaucoma.

Eye pressure test (tonometry)

An instrument called a tonometer is used to measure the pressure inside your eye – intraocular pressure. Tonometry can be useful to identify ocular hypertension (OHT – raised pressure in the eye). In some opticians this device produces a puff of air into the eye. In all of our practices we have non puff tonometer’s.

Visual field test

By staring straight at a central light/target throughout, You will be shown a sequence of lights and asked to respond by pressing a button when you notice a light flash in your peripheral vision. If you can’t see the spots in your peripheral vision, it may indicate the glaucoma has damaged part of that area of vision.

Optic nerve assessment

Your optic nerve connects your eye to your brain. This can be assessed in a variety of ways during your examination. We are interested in the cup to disc ratio or in other words the size it is round by how deep it appears like a tea cup. Too much pressure forces to cup to become deeper.

OCT (Optical Coherence Tomography)

OCT scans are similar to MRI and ultrasound scans and can help opticians detect signs of glaucoma and other conditions up to four years earlier than more traditional imaging methods. The scan produces a 3D-like image that allows us to see the structures of your eye in even greater detail. Over time, your optician will be able to spot the changes that indicate the start of glaucoma. Ask your local store if they offer OCT and you can add it to your eye test for an additional fee.

Treatment

Glaucoma cannot be cured but in many cases it can be managed to slow the progression to avoid glaucomatous damage and nerve damage, which will preserve the visual field and provide total quality of life for patients, with minimal side-effects. Sadly however there are some people less fortunate or those with rarer strains of the condition who are left visually impaired.

Glaucoma can be treated:
• Medication; Using eye drops to either help the flow of fluid in the eye or slow its production.
• Laser; Laser can be used to create a hole allowing fluid to leave the eye or to remove a source of blockage in effect.
• Surgery; Implants can be put in to bisect a blocked area.

Low vision considerations

Ophthalmologists can refer patients with low vision caused by any eye condition to a low vision clinic where assessments can be conducted to determine if any devises can improve everyday life for someone living with an eye condition. With glaucoma the peripheral vision is damaged first leaving the central area of vision functional or partially functional.
To empathise how this would feel close one eye and look through a toilet roll tube or tube made from your fist.

Spectacle lenses are designed to focus light entering the eye as sharply as possible into the back of the eye. They unfortunately cannot be used to improve lost field of vision, only make the image as sharp as possible on the non damaged area's.

Low vision therapy can be anything from teaching someone how to use their functional areas of vision to the use of telescopes or magnifiers to ensure an image falls on the functional area of vision. Low vision aids can be quite expensive so these are loaned to patients from the hospital/social services or purchased privately direct from source.

Central vision is more sensitive to colour vision, whereas peripheral cells are more tuned to black and white so night time can be an issue as well as black and white images, filters and adequate lighting are key to successfully using functional retained/residual vision.

There are many support groups and networks for either people living with low vision or specifically glaucoma. These are excellent resources as no one can understand the challenges and how to overcome them better than someone who also has the condition. You cannot learn that form of experience through reading.

Modern technology is always producing new and exciting low vision aids, some which we couldn't have imagined possible one generation ago. If you know someone with low vision needs, there are yearly shows put on in places like the NEC where the latest tech is on show to trial and see if it may be of benefit.


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