chronic open angle glaucoma (COAG)

Last edited 02/2022 and last reviewed 06/2022

Chronic simple glaucoma (chronic open angle glaucoma (COAG)) occurs when the intra-ocular pressure is raised over several months. The eye remains white and painless but there is insidious damage to the retina and optic fibres.

COAG is glaucoma without evident secondary cause, which follows a chronic time course and occurs in the presence of an open anterior chamber angle (the trabecular meshwork is visible on gonioscopy)

• COAG is categorised as early, moderate and advanced
  • definitions are based on the Hodapp classification of visual field loss for the stages of glaucoma
    • in terms of mean defect (MD):
      • early, MD greater than -6 dB;
      • moderate, MD -6 dB to greater than -12 dB;
      • advanced, MD -12 dB to greater than -20 dB
      • severe visual impairment (blindness) is defined as MD -20 dB or worse

It affects approximately 2% of the population over the age of 40 years

• approximately 10% of UK blindness registrations are attributed to glaucoma
  • around 2% of people older than 40 years have chronic open angle glaucoma (COAG), rising to almost 10% in people older than 75 years in white Europeans
    • prevalence may be higher in people of African/Caribbean descent or who have a family history of glaucoma
  • estimated that 480,000 people are currently affected by COAG in England

The majority of patients found to have increased intraocular pressures on screening do not have glaucoma when their peripheral fields and fundi are checked. Patients with raised intraocular pressure who do not have glaucoma require life-long follow-up in case of subsequent development of glaucoma.

Notes:

• the term suspected COAG is used when there are changes in the optic nerve head suggestive of COAG but the visual field appears normal or vice versa.
• people with a diagnosis of ocular hypertension (OHT), suspected COAG or COAG should be monitored and treated by a trained healthcare professional who has all of the following:
  • a specialist qualification (when not working under the supervision of a consultant ophthalmologist)
  • relevant experience
  • ability to detect a change in clinical status
• knowledge of corneal thickness is no longer needed to decide whether or not to treat OHT and a single threshold of 24 mmHg is now recommended for both onward referral and treatment (1)
  
  
• the NICE committee agreed that the key outcome for adults with ocular hypertension (OHT) or chronic open angle glaucoma (COAG) was visual field progression that, in the long-term, could affect people's vision (1)
• intraocular pressure (IOP) was considered to be a relevant surrogate outcome because lowering IOP can prevent the risk of optic nerve damage and sight loss
• high-quality evidence showed that there is no meaningful difference between 360 degrees selective laser trabeculoplasty (SLT) and eye drops in achieving a target IOP, health-related quality of life, risk of total adverse events, and treatment adherence
• highlighted that there are rare complications associated with SLT
  • while rare events were not highlighted in the evidence, corneal failure is possible after SLT procedures
• in people who have first-line treatment with eye drops compared with first-line 360 degrees SLT, more people used eye drops and more people have more than 1 eye drop medication at 12 months
• cost-effectiveness evidence showed that first-line treatment with 360 degrees SLT was more effective and less costly compared with eye drops, with at least 90% probability of being the more cost-effective option
• based on this evidence and their clinical experience, the committee recommended 360 degrees SLT as first-line treatment for people with newly diagnosed OHT or newly diagnosed COAG
  • recommendation excludes cases associated with pigment dispersion syndrome
    • was because there was no evidence on the use of 360 degrees SLT in people with pigment dispersion syndrome and the committee agreed that eye drop treatment is more suitable for those people

Reference:

• 1.NICE (January 2022).Glaucoma: diagnosis and management
• 2. Pulse (6/5/2000), What's New in Ophthalmology, 69.