Chronic Glaucoma

Definition/diagnostic criteria Chronic glaucoma, also known as primary open-angle glaucoma (POAG), is a progressive optic neuropathy characterised by the gradual loss of retinal ganglion cells, leading to structural damage to the optic nerve and visual field loss. It is typically associated with raised intraocular pressure (IOP), although IOP can be normal in some cases (normal-tension glaucoma).

Epidemiology In the UK, chronic glaucoma affects about 2% of people ged over 40 and around 10% of those over 75, making it a leading cause of irreversible blindness. The prevalence is higher in African-Caribbean populations and there is a familial predisposition.

Diagnosis
Clinical features: Patients are often asymptomatic until advanced stages. Features include gradual loss of peripheral vision, difficulty adapting to low light and, in later stages, central vision loss.

Investigations: Investigations include:

• Tonometry: Measures IOP; values over 21 mmHg are suggestive but not diagnostic.
• Ophthalmoscopy: Examines the optic disc for glaucomatous damage (increased cup-to-disc ratio).
• Visual field testing: Identifies characteristic patterns of loss.
• Gonioscopy: Assesses the anterior chamber angle.
• Optical coherence tomography (OCT): A non-invasive method to quantify the nerve fibre layer and assess progression.

Typical abnormalities include increased IOP (though not always), optic disc cupping, and visual field defects.

Treatment Treatment aims to lower IOP to slow or prevent further visual loss. Management options include:

• Medications: Topical beta-blockers (e.g. timolol) are often first-line. Other options include prostaglandin analogues (e.g. latanoprost), alpha agonists, and carbonic anhydrase inhibitors. A combination of drugs may be necessary.
• Laser therapy: Trabeculoplasty is an option when medication is insufficient or not tolerated.
• Surgery: Trabeculectomy is considered when medication and laser therapy are ineffective.

Patient adherence to medication is crucial, and side-effects should be monitored. Regular monitoring of IOP, optic nerve head and visual fields is required.

Prognosis The progression of chronic glaucoma varies; some patients may not experience significant vision loss in their lifetime, while others may have rapid progression. Early detection and treatment are key in preventing significant visual impairment. Regular follow-up and monitoring of the disease are essential for all patients.