Primary open-angle glaucoma
Introduction
Glaucomas are optic neuropathies associated with raised intraocular pressure (IOP).
Epidemiology
- Incidence: 50.00 cases per 100,000 person-years
- Peak incidence: 70+ years
- Sex ratio: 1:1
| <1 | 1-5 | 6+ | 16+ | 30+ | 40+ | 50+ | 60+ | 70+ | 80+ |
Aetiology
Primary open-angle glaucoma (POAG, also referred to as chronic simple glaucoma) is present in around 2% of people older than 40 years. Other than age, risk factors include:
- genetics: first degree relatives of an open-angle glaucoma patient have a 16% chance of developing the disease
- black patients
- myopia
- hypertension
- diabetes mellitus
- corticosteroids
Pathophysiology
Glaucomas can be classified based on whether the peripheral iris is covering the trabecular meshwork, which is important in the drainage of aqueous humour from the anterior chamber of the eye. In open-angle glaucoma, the iris is clear of the meshwork. The trabecular network functionally offers an increased resistance to aqueous outflow, causing increased IOP. It is now recognised that a minority of patients with raised IOP do not have glaucoma and vice versa.
Clinical features
POAG may present insidiously and for this reason is often detected during routine optometry appointments. Features may include
Fundoscopy signs of primary open-angle glaucoma (POAG):
Diagnosis:
- peripheral visual field loss - nasal scotomas progressing to 'tunnel vision'
- decreased visual acuity
- optic disc cupping
Fundoscopy signs of primary open-angle glaucoma (POAG):
- 1. Optic disc cupping - cup-to-disc ratio >0.7 (normal = 0.4-0.7), occurs as loss of disc substance makes optic cup widen and deepen
- 2. Optic disc pallor - indicating optic atrophy
- 3. Bayonetting of vessels - vessels have breaks as they disappear into the deep cup and re-appear at the base
- 4. Additional features - Cup notching (usually inferior where vessels enter disc), Disc haemorrhages
Diagnosis:
- Case finding and provisional diagnosis is done by an optometrist
- Referral to the ophthalmologist is done via the GP
- Final diagnosis is done by investigations as below
Investigations
Investigations:
- automated perimetry to assess visual field
- slit lamp examination with pupil dilatation to assess optic neve and fundus for a baseline
- applanation tonometry to measure IOP
- central corneal thickness measurement
- gonioscopy to assess peripheral anterior chamber configuration and depth
- Assess risk of future visual impairment, using risk factors such as IOP, central corneal thickness (CCT), family history, life expectancy
Management
The majority of patients with primary open-angle glaucoma are managed with eye drops. These aim to lower intra-ocular pressure which in turn has been shown to prevent progressive loss of visual field.
NICE guidelines:
Reassessment
Surgery in the form of a trabeculectomy may be considered in refractory cases.
NICE guidelines:
- first line: prostaglandin analogue (PGA) eyedrop
- second line: beta-blocker, carbonic anhydrase inhibitor, or sympathomimetic eyedrop
- if more advanced: surgery or laser treatment can be tried2
Reassessment
- important to exclude progression and visual field loss
- needs to be done more frequently if: IOP uncontrolled, the patient is high risk, or there is progression
| Medication | Mode of action | Notes |
|---|---|---|
| Prostaglandin analogues (e.g. latanoprost) | Increases uveoscleral outflow | Once daily administration Adverse effects include brown pigmentation of the iris, increased eyelash length |
| Beta-blockers (e.g. timolol, betaxolol) | Reduces aqueous production | Should be avoided in asthmatics and patients with heart block |
| Sympathomimetics (e.g. brimonidine, an alpha2-adrenoceptor agonist) | Reduces aqueous production and increases outflow | Avoid if taking MAOI or tricyclic antidepressants Adverse effects include hyperaemia |
| Carbonic anhydrase inhibitors (e.g. Dorzolamide) | Reduces aqueous production | Systemic absorption may cause sulphonamide-like reactions |
| Miotics (e.g. pilocarpine, a muscarinic receptor agonist) | Increases uveoscleral outflow | Adverse effects included a constricted pupil, headache and blurred vision |
Surgery in the form of a trabeculectomy may be considered in refractory cases.