Glaucoma Classifications

There are several specific types of glaucoma. Some of these are:

Primary open angle glaucoma

In this type of glaucoma the optic nerve damage resulting from increased pressure in the eye is caused by trabecular blockage which is where the aqueous humor in the eye drains out. All patients with open angle glaucoma do not have eye pressure that is elevated beyond normal, but decreasing the eye pressure further has been shown to stop progression of loss of vision. Vision loss is a gradual process and peripheral vision is affected first, however, eventually the entire vision will be lost if not treated. Diagnosis is made by looking at changes in the optic nerve cup. Prostoglandin agonists like lataniprost and parasympathetic analogs like pilocarpine help by opening uveoscleral passageways for drainage. Beta blockers such as timolol and Alpha 2 agonists (brimonidine, apraclonidine), are also beneficial by decreasing aqueous formation. Similarly Carbonic anhydrase inhibitors like dorzolamide and acetazolamide help in decreasing bicarbonate formation from ciliary processes in the eye, thus decreasing formation of Aqueous humor.

Angle-closure glaucoma

This type of glaucoma occurs due to narrowing of the angle between the iris and trabecular meshwork, which in turn obstructs outflow of the aqueous humor from the eye. This narrowing damages the function of the meshwork until it fails to keep pace with aqueous production, and the pressure rises. In some cases, pressure may rapidly build up in the eye causing pain and redness. This is called acute angle closure glaucoma. In this situation the vision may become blurred, and halos may be seen around bright lights along with severe headache and vomiting. After initial treatment with medications definitive treatment is laser iridotomy. This may be performed using either Nd:YAG or argon lasers, or in some cases by conventional incisional surgery.

Normal tension glaucoma (low tension glaucoma)

Glaucoma occurs in absence of a raised mean IOP on diurnal testing. There may be presence of optic nerve damage and an open angle between the iris and the cornea. Elderly and females are usually prone to this type of glaucoma. May be associated with the Raynaud's phenomenon, migraines, paraproteinaemia. Treatment is by reducing intraocular pressure as for open angle glaucoma. The aim is to reduce IOP by 30%. It is also recommended that systemic blood pressure be monitored over 24 hours, as normal tension glaucoma may be associated with nightly low blood pressure. There is often a delay in diagnosis, resulting in more advanced visual field defects. Patients with defects in one eye have a 40% chance of developing defects in the fellow eye over 5 years.

Secondary glaucomas

These are caused as a result of blockage of the aqueous outflow system due to other eye diseases. Types include:

• Pseudoexfoliative glaucoma – Secondary to pseudoexfoliation syndrome. A dusty grey deposit of extracellular amyloid-like material is deposited on the anterior lens capsule, the zonules, the ciliary body and in the trabecular network. This clogs up the drainage of the fluid. It is common among elderly and females. Treatment is with medications and laser surgery.
• Pigmentary glaucoma – Here a pigment deposits from the posterior surface of the iris to block the drainage system. Common among young (20-40 year-old), male, Caucasians with high myopia. Treatment is with medications and laser surgery.
• Neovascular glaucoma – This occurs due to iris neovascularisation (rubeiosis iridis). This can occur after ischaemic retinal vein occlusion, advanced diabetic eye disease, central retinal artery occlusion, intraocular tumours, long-standing retinal detachment and where there has been chronic intraocular inflammation. Treatment is with panretinal photocoagulation and possibly retinal surgery.

Primary congenital glaucoma

This includes types like infantile glaucoma and glaucoma associated with hereditary of familial diseases.

Other types of glaucoma

• Inflammatory glaucoma – There may be fluctuating IOPs and a ciliary body closure. It is the most common cause of blindness in children and young adults with chronic anterior uveitis. Treatment is mainly with medications but severe cases may require surgery too.
• Lens-related glaucoma – The lens may cause phacolytic glaucoma due to a hypermature cataract leading to shedding of proteins which clog up the drainage system or phacomorphic glaucoma where the lens swells and bulges forward, compressing the trabecular meshwork. Both need prompt cataract surgery.
• Traumatic glaucoma – Here glaucoma occurs secondary to eye injury. The red blood cells can block the trabecular meshwork. It is seen in 6-9% of patients over a 10-year period.
• Iridocorneal endothelial (ICE) syndrome – Affects one eye in young- to middle-aged women. There are iris abnormalities which are associated with glaucoma in 50% of cases. Treatment is medical and surgical.
• Glaucoma in ciliochoroidal detachment – This is seen after a detachment of the ciliary body or choroid that leads to displacement of the lens-iris complex resulting in shallow iridocorneal angles which may close off.
• Glaucoma in epithelial ingrowth – This is seen after anterior segment trauma or surgery. Conjunctival and corneal epithelial cells migrate from the external surface of the eye and may block off the aqueous outflow. Treatment involves surgery and cryotherapy.
• Sturge-Weber syndrome is associated with early presentation of patients with glaucoma (60% within the first 2 years of life).
• Neurofibromatosis-1 patients may also (uncommonly) present with unilateral, congenital glaucoma.
• Iridocorneal dysgenesis is seen in conditions like Axenfeld-Rieger syndrome, Peters' anomaly, aniridia and is associated with glaucoma.
• Glaucoma in cavernous-sinus fistula – This is caused due to raised episcleral venous pressure that impairs the aqueous outflow. Medical treatment is required until the shunt resolves or is treated.
• Glaucoma in intra-ocular or eye tumours – The glaucoma depends on the site of the tumour but it occurs in about 5% of affected eyes.
• Glaucoma in iridoschisis – There is iris atrophy which is associated with glaucoma in 90% of cases. Laser treatment followed by drug treatment is necessary.