Description, Symptoms, Classification and signs
see: Glaucoma – Classification
Prevalence and Significance
Glaucoma is one of the leading causes of visual disability in western countries, along with macular degeneration, diabetic retinopathy and cataract. One study of elderly Australians estimated the prevalence of Glaucoma at 3.5%.
Differential Diagnosis and other optic neuropathies
- Other optic neuropathies – Arteritic Ischemic Optic Neuropathy AION (giant cell arteritis), Nonarteritic Ischemic Optic Neuropathy (NAION)
- Compression of visual pathways e.g. pituitary tumor
- Congenital anomalies – Optic nerve pit, Optic nerve drusen, Coloboma, Morning glory syndrome, Tilted disc, Physiological cupping
Glaucoma – Visual Field Assessment, Glaucoma – Neuroretinal Rim Assessment, Glaucoma – Vascular And Nerve Fibre Layer Signs, Glaucoma- tonometry
The presence of glaucomatous signs is an indication for treatment, whereas the presence of risk factors is an indication for advice and review. Glaucoma is most often treated by a therapeutic reduction in intraocular pressure (IOP).
(a) Angle closure glaucoma with excessive IOP is a medical emergency, requiring treatment within hours. If IOP is over 40mmHg, then IOP reduction is urgent and all topical glaucoma medications should be used, subject to the medication contraindications and precautions. Check IOP every 10-20 minutes and treat both eyes. In acute angle closure, with IOP over 45 to 50mmHg, oral or intravenous (IV) agents may be helpful in treatment, such as carbonic anhydrase inhibitors e.g. acetazolamide 500mg and IV hyperosmotics such as mannitol. Systemic contraindications and precautions must be observed.
(b) Open angle glaucoma with excessive IOP requires evaluation as to causation. Diagnosis and treatment the same day is indicated.
Ocular hypertension with IOP of 21 – 24mmHg, or pseudoexfoliation syndrome without glaucoma, may only require close observation. Treatment of ocular hypertension may be started with IOP in the range of 24–30mmHg, although the more recent guidelines favor the lower end of the range, particularly when other risk factors are present, including positive family history, increased optic disc cupping, systemic risk factors, or a thin cornea (Ocular Hypertension Treatment Study).
The Early Manifest Glaucoma Trial (EMGT) had an untreated control arm and proved conclusively that medical treatment delays glaucomatous progression. First line medical treatment in recent years has become the prostaglandin-analogues e.g. Bimatoprost, Latanoprost or Travoprost q.d. nocte or Unoprostone b.i.d.. Prior to this the beta-blockers, e.g. Timolol maleate, Betaxolol, Carteolol, Levobunolol, Metipranolol q.d. mane or b.i.d. were the mainstay of treatment, although caution was required in patients with systemic conditions, including cardiac and pulmonary disease. Other topical drug categories available include adrenergic agonists, carbonic anhydrase inhibitors and cholinergic (miotic) medications. See the appendix for more details. Secondary glaucomas are usually treated according to the underlying cause.
Argon laser trabeculoplasty (ALT) is considered equally effective as medical therapy for POAG (Collaborative Initial Glaucoma Treatment Study and Glaucoma Laser Trial). Its efficacy depends on the degree of pigment in the angle. Furthermore, ALT has a higher initial success rate than medical therapy in pseudoexfoliation glaucoma. However the improvement may not be permanent and continued observation will be necessary. Selective laser trabeculoplasty (SLT) is a newer technique than ALT, but with less data available. A YAG laser peripheral iridotomy is a definitive treatment for angle closure glaucoma.
Trabeculectomy filtration surgery is beneficial in lowering IOP when medical treatment fails (Advanced Glaucoma Intervention Study, AGIS).
Refractive correction or low vision aids
Consider low vision referral for advanced glaucoma.
Fundus photos or scanning laser ophthalmoscopy can help identify optic nerve head changes. Ocular coherence tomography and nerve fiber layer analyzers enable assessment of the nerve fibre layer.
Glaucoma and glaucoma suspect patients are usually reviewed at 6 or 12 month intervals, the aim being to identify any change in the IOP, visual fields, nerve fiber layer or optic nerve.
Primary open angle glaucoma (POAG) in a 50 year old white male with a strong family history of glaucoma. There is erosion of the superior- and inferior-temporal neural rims, especially in the right eye. Note the bayoneting of the right superior vessels at the rim margin.