Glaucoma: An Educational Review

Dr. Jyoti Raina

Glaucoma is one of the most common causes of incurable blindness due to damage to the optic nerve. Globally 80 million people are affected.

In the UK , 2% of population above the age of 40 years have glaucoma. In India incidence is 2.5 -4.5% of general population.

People with glaucoma do not have any complaints with sight or pain in the eye initially, as this condition progresses gradually. Problems with sight, usually described as loss of peripheral field or “tunnel vision” happen when optic nerve is already damaged irreversibly.

The loss of sight cannot be recovered and if untreated it can cause blindness.

Regular eye checks above the age of 40, by high street opticians are the only way to screen for glaucoma. If detected early, it can be treated before the nerve and the sight suffer any significant damage.

Cause

Glaucoma is a group of conditions where the common factor is the damage to the optic nerve. The optic nerve carries all the visual/sight information from the eye to the brain like an electric wire conducting energy to light a bulb. 

The common cause of nerve damaged is due high pressure (intraocular pressure [IOP]) of aqueous humour inside the eye. Aqueous humour is the name of the fluid which provides nutrition to structures inside the eye (see picture below). 

It is produced by ciliary body in the eye and drained by the trabecular meshwork in the angle of the anterior chamber. The range of normal IOP is 10-21mm Hg. 

Any gross or microscopic alterations to these structures of the eye can cause obstruction to the outflow and build-up of IOP.

This high IOP causes damage to the nerve and leads to  loss of eyesight

Diagrammatic anatomy of Eye

 

The most common types are:

Primary open angle glaucoma– commonly seen above age of 40 where no obvious reason for raised IOP. The patient usually has no eyesight complaints and is picked up in routine tests for glasses for 40 yrs. old and above.  In those where the condition is detected later, when the optic nerve damage has occurred, they have sight problems involving central and near vision (reading), mobility outside the home, difficulty in walking, stair-climbing, face recognition, and driving.

Primary closed angle glaucoma– this is less common and due to closure of the outflow channel causing high IOP of 60 -70 mm Hg. With this condition the patient present as an emergency with acute severe pain, headache, poor eyesight, and red eye.

Congenital glaucoma– rare and seen in infants and children.

Risk factors 

• Eye pressure (IOP): Above 22 Hg mm. However, this IOP is normal for some patients, and they do not develop optic nerve damage or glaucoma.
  
• Age: It occurs in up to two in 100 people over the age of 40, increasing to up to seven in 100 people over the age of 70.
  
• Sex: Closed angle glaucoma is two to three times more common in women. 
  
• Family history:  higher risk with a close blood relative (a parent, brother, sister, or child) has glaucoma. A sibling with the condition increases risk by eight times, a parent with it, increases risk by two times. If diagnosed with glaucoma, these close family members should be informed. 
  
• For blood relatives over 40, it’s recommended they should see their optometrist (also known as an optician) every year for a free NHS eye examination.
  
• Race: Primary open angle glaucoma is two to three times more common in African Caribbean ethnic backgrounds. East Asian origin can increase risk of closed angle glaucoma. 
  
• Myopia/short sightedness increases risk for primary open angle glaucoma and longsightedness/Hypermetropia for closed angle glaucoma. 
  
• Diabetes: Diabetes can increase risk of developing primary open angle glaucoma by two times.
  
• Steroid medication: Glaucoma can develop as a complication from long term use of steroid tablets, injections, or eye drops.