Open angle

• Glaucoma is a group of eye diseases which cause progressive optic neuropathy commonly associated with raised intraocular pressure (IOP)
• Primary open-angle glaucoma (POAG) is the most common type associated with an open anterior chamber angle of the eye. 
• Aqueous humour:

  • Clear fluid
  • Supplies nutrients to the cornea and lens
  • Produced by the ciliary body
  • Travels from the posterior chamber through the pupil into the anterior chamber
  • Constant production and drainage helps maintain eye pressure 12-21 mmHg
• The aqueous humour then drains out of the anterior chamber through two independent pathways:

  • The trabecular meshwork into the canal of Schlemm in the iridocorneal angle
  • The uveoscleral pathway 
• Pathophysiology:

  • Increased resistance to outflow of aqueous humour through the trabecular meshwork
  • Causes intraocular pressure to rise - retinal ganglion cell death
  • Loss of retinal ganglion cells and nerve fibre layer usually follows a pattern of inferior loss occurring before superior loss
• Risk factors for POAG include:

  • Myopia (short-sightedness)
  • Increased age particularly after 65 years
  • Family history
  • African-Caribbean ethnic origin
  • Untreated ocular hypertension (raised IOP)
  • Cardiovascular disease
  • Type two diabetes (this is a secondary glaucoma)
• POAG is typically insidious in onset, following a slow and chronic course. It is usually adult onset and affects both eyes.
• History:

  • Most patients will be asymptomatic
  • Initially causes loss of peripheral vision usually in the superior visual field
  • Central vision loss occurs at the end stage
  • Important to check if there is a family history of glaucoma
• Typical clinical findings in POAG include:

  • Increased IOP
  • Visual field defects
  • Fundoscopy: cupped optic discs
• Investigations:

  • Measure intraocular pressure - Goldmann applanation tonometer
  • Optic nerve assessment via fundoscopy
  • Visual field assessment - loss of peripheral vision
  • Gonioscopy - assessing the drainage angle of the anterior chamber between the iris and cornea (angle is open in POAG)
• Optic disc examination is a direct marker of the disease progression. Damage is assessed by looking at the vertical optic cup-to-disc ratio, which will increase in glaucoma. A normal ratio is less than 0.5 though disc asymmetry is important too.
• Glaucoma will cause death of nerve fibres within the optic nerve and gives the appearance of a pale optic disc
• Glaucoma is suggested by an increased ‘cupped’ appearance of the optic disc over time.
• Management:

  • Usually started when IOP >24
  • Laser management
  • Medical management
  • Surgical management
• Laser management:

  • Offer all newly diagnosed patients 360 selective laser trabeculoplasty
  • Short pulses of low-energy light - triggers processes within the eye to remove and rebuild a meshwork that will function effectively and reduce IOP
• Medical management:

  • Variety of eye drop preparations that either reduce the production or increase the outflow of aqueous humour
  • First line - generic prostaglandin analogue (GPA) eye drops e.g. latanoprost
  • Others - beta blockers, carbonic anhydrase inhibitors (acetazolamide) and parasympathomimetics (pilocarpine)
• Surgical management:

  • Trabeculectomy - creating a channel in the sclera
  • Surgery offered with pharmacological augmentation using mitomycin C - prevents excessive postoperative scarring
• The main complication of untreated glaucoma is the irreversible loss of vision. It is important to seek early advice and management to optimise vision as this can have a significant impact on a patient’s quality of life.
• In the United Kingdom, the Driver and Vehicle Licensing Agency (DVLA) requires patients to inform them of a new diagnosis of glaucoma if it affects both eyes (group 1/car drivers) or one eye (group 2/commercial drivers). This is a legal responsibility.