Glaucoma

Glaucoma is a group of diseases with characteristic optic nerve damage, resulting in irreversible vision loss. It is the leading cause of blindness, especially in the elderly. It can cause irreversible loss of vision and even blindness. Most, but not all of these diseases are characterised by raised pressure in the eye (intraocular pressure). The level of pressure that causes damage can vary in different individuals and the resistance level of the optic nerve.

Glaucoma is known as the ‘silent thief of sight’ as the initial vision loss is mainly peripheral and not readily noticeable. Central vision and reading vision are usually spared until later. The patient may not experience any symptoms until late in the disease when most of the vision has already been irreversibly lost.

Causes and Risk Factors

What causes glaucoma?

Glaucoma is usually caused by fluid pressure in the eyeball that is too high for the optic nerve to tolerate. The optic nerve carries visual impulses from your eye to the brain. This pressure build-up occurs because of an imbalance between the production and drainage of fluid within the eyeball.

Who is at risk of glaucoma?

Risk factors for glaucoma include:

• Age – your risk increases when you are over 80 years old
• Chronic diseases – you are at increased risk if you have diabetes or high blood pressure
• Ethnicity – Asians are more susceptible to angle-closure glaucoma than Caucasians
• Eye injuries
• Family history
• Use of corticosteroid
• Inherently high pressure inside the eye
• Refractive error (short-sightedness or myopia is a risk factor for open-angle glaucoma; long-sightedness or hyperopia is a risk factor for closed-angle glaucoma)

What are the different types of glaucoma?

Open-angle glaucoma

Open-angle glaucoma accounts for the majority of glaucoma. It often has no symptoms and progresses slowly. The rise in intraocular pressure (eye pressure) is slow and painless.

• ​​Drainage angle is not efficient to remove the aqueous humour of the eye
• Risk increases with the age
• Risk increases with a family history of glaucoma
• In the early stages with eye pressure in the range of 20-30 mmHg, the patient has no symptoms
• With time the same eye pressure may cause blank spots or loss of field
• It is difficult to detect field loss by the patient unless it is advanced

Closed-angle glaucoma

The drainage angle is mechanically closed. These patients usually have short eyes and are far-sighted. The iris mechanically blocks the drainage area akin to a traffic block. In turn, the fluid leads to build-up within the eye and it can raise up to 3-4 times from normal and subsequently cause optic nerve damage. Pressure may depend on the amount of angled closed.

Angle-closure glaucoma can either be acute or chronic. Acute angle-closure glaucoma is characterised by a sudden, dramatic increase in intraocular pressure. This can cause severe eye pain, redness, blurred vision and the appearance of haloes around lights. Headaches, nausea and vomiting may follow. This is an emergency and requires prompt treatment. The chronic form may show no symptoms, as in open-angle glaucoma.

Congenital glaucoma

Congenital glaucoma is rare and occurs at birth. Enlargement of the infant’s eyes, corneal haze, tearing and unusual light sensitivity are symptoms that warrant an eye examination.

Secondary glaucoma

Secondary glaucoma may be caused by conditions such as 

• Uncontrolled diabetes
• Inflammation of the eye
• Use of steroid medications
• Previous eye surgery 
• Cataracts in their advanced stages on the eye
• Trauma
• Tumours

How to prevent?

Most risk factors of glaucoma such as age, genetic risk and race cannot be prevented. If you have a family history of glaucoma or are taking medications that put you at risk, regular eye examinations are essential. Early diagnosis is the key to preventing blindness as glaucoma nerve damage is irreversible.

Diagnosis

Glaucoma is diagnosed by measuring the intraocular pressure of the eye and assessing the optic nerve at the back of the eye for any damage. 

• Intraocular pressure is measured by using an applanation tonometer
• Optic Nerve assessment is done by visual field test (perimetry) and OCT RNFL

Visual field test assesses the function of the optic nerve by checking if you can see spots of light of different intensities at different locations inside a visual field machine. It is a subjective test and helps the ophthalmologist determine if your disease is worsening or stable.

OCT RNFL helps in objectively measuring the retinal nerve fibre layer thickness and thus helps in monitoring glaucoma progression.

Treatment

Glaucoma cannot be cured, but it can be successfully controlled in most cases.

Treatment depends on the type of glaucoma you are diagnosed with. Treatment modalities include:

• Eye drops
• Oral medications
• Laser surgery
• Filtering surgery
• Drainage implants

All these treatments lower the intraocular pressure to a safe level for the eye. Your ophthalmologist will be able to advise on individualised treatment options. Even after successful control of the pressure, regular monitoring is still required.

Glaucoma is a chronic condition requiring lifelong review. The aim of treatment is to preserve the remaining vision. Damage from glaucoma cannot be reversed, hence the importance of early diagnosis.