Chronic Open Angle Glaucoma

Glaucoma is where there's optic nerve damage due to a rise in intra-ocular pressure, which is caused by a blockage in the drainage of aqueous humour. In Chronic/open-angle glaucoma, there's a gradual increase in the resistance of the trabecular meshwork, therefore making it harder for the aqueous humour to flow through it and drain out, leading to a slow increase in pressure.

Risk factors:

• Raised IOP

• Near-sightedness (Myopia)

• DM

• HTN

• Increasing age

• FHx

Presentation

• Gradual loss of peripheral vision, which eventually becomes tunnel vision

  • Most are unaware of this visual field defect in the early stages as their other eye usually compensates quite well

• Gradual onset of fluctuating pain

• Headaches

• Blurred vision

• Halos around lights

• O/E - Pale optic disc (optic nerve atrophy), Optic disc cupping

Optic disc cupping is a sign of of Raised Intraocular Pressure. The optic cup is the small indent in the optic disc. When there’s increased pressure, the size of this cup increases as it becomes wider and deeper (An optic cup > 50% of the optic disc is abnormal).

N.B. Usually asymptomatic for a long time, therefore diagnosed during routine eye tests.

Measuring Intraocular Pressure

The gold standard tool for this is the Goldmann Applanation Tonometry. With this, pressure is directly applied to cornea, therefore giving a more accurate reading.

Non-contact Tonometry can also be used. This is where a puff of air is shot at the cornea and measuring the corneal response to it. This is less accurate but gives a helpful estimate during general screening.

Investigations

• Goldmann Applanation Tonometry – Check IOP

• Fundoscopy – Check for cupping

• Eye examination – Check for peripheral vision loss

Management

Treatment is usually started when IOP is > 24 mmHg and there's a risk of visual impairment.

1st line - Selective Laser Trabeculoplasty (SLT). With this, a laser is directed at certain cells in the trabecular network, therefore improving drainage.

2nd line options:

• Prostaglandin eye drops (e.g. Latanoprost)

• B-blockers

• CA inhibitors

  
  

N.B. One SE of Latanoprost is increased eyelash growth.