Eye clinic - primary open-angle glaucoma
Consultant ophthalmologist Dr Mark Llewellyn gives an update on an often incidental finding
This 68-year-old retired nurse presents to her GP complaining that she has been suffering headaches two to three times a week for the past fortnight.
As part of the work-up, the GP carries out fundoscopy and notices cupping of the optic disc in both eyes, particularly pronounced in the left (pictured). When asked, the patient says she has not visited an optician in over 10 years but needs reading glasses, which she buys from her local supermarket.
She is referred to ophthalmology where her intraocular pressure (IOP) is found to be 27mmHg in the left eye and 25mmHg in the right eye, and the cup-to-disc ratio 0.4 and 0.3 respectively. Visual field testing suggests some loss of peripheral vision. She is diagnosed with primary open-angle glaucoma. Her presenting symptoms are thought to be a primary headache and unconnected with the glaucoma.
Treatment with ß-blocker eye drops (timolol) is started, but after six months pressures have reduced to just 25mmHg and 23mmHg respectively – so a prostaglandin analogue (bimatoprost) is added in. She is due to be reviewed again in two months.
- Glaucoma is a family of conditions characterised by atrophic changes in the optic nerve usually – but not always – associated with raised IOP. This is the only modifiable risk factor and so the target for treatment.
- Primary open-angle glaucoma is the most common form and is a progressive, chronic condition caused by impaired aqueous humour drainage through the angle where the iris meets the cornea, resulting in raised pressures. It is often asymptomatic.
- Less than 10% of glaucoma is angle-closure glaucoma where drainage through the iridocorneal angle is blocked and the IOP rises suddenly, usually causing pain.
- Around 2% of people older than 40 years of age have open-angle glaucoma, rising to almost 10% in people older than 75 years of age – but the prevalence is higher in people of African descent.1
- It is asymptomatic in many cases and up to 50% of cases are undiagnosed – most cases are picked up during a routine eye check.
- Most commonly presents after 65 years of age and rarely before 40.
- There is a clear family history in some cases – with IOP and aqueous outflow rates having a hereditary influence.
- Generally bilateral, although not always symmetrical.
GPs and opticians usually pick up cases by spotting the characteristic cupping of the optic disc on fundoscopy – opticians may note a high IOP. Visual fields may also be abnormal. On referral to ophthalmology, patients will have the following investigations as well:
- gonioscopy – measurement of the angle between the cornea and the iris
- corneal thickness
- optic disc examination to measure cup-to-disc ratio
- detailed visual field assessment
- slit-lamp examination of the optic nerve head.
If the disease is obvious and advanced, treatment should start immediately – if not, serial IOPs should be taken.
NICE defines the treatment target as ‘the level of IOP sufficient to minimise or arrest disease progression', but as a rule of thumb an initial goal should be around a 30% drop – this should be higher in those with higher pressures and multiple risk factors.
No single treatment stands out as being better than another,2 but topical ß-blockers and prostaglandin analogues are first-line options. Treatment can be confined to one eye if clinically appropriate.
Drugs should be initiated one at a time, but combine as necessary – pairing a ß-blocker with a prostaglandin analogue before trying a sympathomimetic, carbonic anhydrase inhibitor or pilocarpine.
Laser and surgical treatments should be considered when at least two pharmacological treatments have not been effective, but it is worth checking compliance and making sure patients are getting the drops onto the surface of the eye.
Dr Mark Llewellyn is consultant ophthalmologist at the Powys Teaching Health Board in Brecon
1 NICE. Diagnosis and management of chronic open-angle glaucoma and ocular hypertension. CG85. March 2009.
2 Vass C, Hirn C, Sycha T et al. Medical interventions for primary open- angle glaucoma and ocular hypertension. Cochrane Database of Systematic Reviews 2007;4:CD003167