Glaucoma: Diagnosis and Treatment

Diagnosis

POAG is generally asymptomatic, and major visual field loss can occur prior to any visual symptoms.

Fundus examination is required for diagnosis, along with visual field testing (confrontational visual field testing is not sufficiently accurate to diagnose glaucoma) and measurement of intraocular pressure. Most persons with POAG will have an untreated intraocular pressure above 21 mmHg at some point in the disease,¹¹ compared with a normal intraocular pressure of about 15.3 for women and 15.5 for men.¹³

The American Academy of Ophthalmology describes POAG as chronic, generally bilateral, often asymmetrical, and with all of the following in one or both eyes:¹¹

• Optic nerve or retinal nerve fiber layer damage (including thinning or notching in the optic disc rim, defects in the nerve fiber, or progressive change), or characteristic visual field abnormalities without other explanation
• Adult onset
• Normal anterior angles
• No factors known to cause secondary open–angle glaucoma.

Treatment

Lowering intraocular pressure is effective for reducing visual field loss in many patients.^14,15 More evidence is needed to confirm that these results translate to other patient populations, such as individuals with severe POAG.

The target for intraocular pressure is individualized. Pressure must be lowered until no further damage occurs. Because the disease is generally asymptomatic until severe damage has occurred, many patients do not use their medicines or follow up as recommended. Compliance should be monitored closely.

Methods of lowering intraocular pressure include eye drops, systemic medications, laser treatment, and surgery.

Topical Medication

Beta–blockers and carbonic anhydrase inhibitors decrease aqueous production.

• Beta–blockers are first–line drugs, unless contraindicated for pulmonary or cardiovascular reasons.
• Topical carbonic anhydrase inhibitors are preferred because of multiple adverse side effects with systemic use.

Prostaglandins, alpha–adrenergic agonists, and cholinergic agonists increase aqueous outflow.

• Prostaglandins are also first–line agents or are used in conjunction with beta–blockers.
• Adrenergic agonists (ie brimonidine) have potential (although uncommon) adverse ocular/systemic side effects.
• Cholinergic agonists have adverse ocular side effects.

Systemic Therapy

Gingko biloba has improved visual field test results in patients with normal–tension glaucoma,¹⁶ but requires cautious use because of its anticoagulant effect.

Other systemic medications, such as carbonic anhydrase inhibitors, are associated with many adverse side effects and are second–line agents.

Laser Therapy

Trabeculoplasty (laser application to tissues for aqueous absorption in the angle between the cornea and iris) is effective in the short term, but repeat therapy is usually needed, and the laser may cause new damage.  

Laser therapy or cryotherapy can also be used to destroy the ciliary body.

Surgery

Surgery creates an alternative pathway for aqueous flow, but there is no clear advantage of early surgery over medical therapy.^17,18 Surgery is generally reserved for patients with severe disease and can be associated with blinding complications, particularly infection.