There are dozens of types of glaucoma. The most common form is "POAG" or primary open angle glaucoma. This is distinct from another major type of glaucoma - angle closure glaucoma. Some glaucomas arise secondary to other eye conditions, for example, pseudoexfoliation syndrome or pigment dispersion syndrome.

Primary angle closure glaucoma is caused by contact between the iris and the drainage angle, which in turn blocks outflow of the fluid from the eye. This contact between iris and drainage angle is believed to gradually damage the function of the drain (the "trabecular meshwork") until it  is unable to drain fluid effectively, and then the eye pressure rises. In many cases, contact between iris and the meshwork causes the formation of scar tissue. These can cause permanent obstruction of aqueous outflow, and in some cases, the pressure may build up in the eye very rapidly causing pain and redness. The treatment for angle closure is initially for YAG iridotomy. Sometimes, laser iridoplasty may be performed, and otherwise rarely a surgical iridectomy is required for those with no cataract. Angle closure is often dealt with very effectively nowadays with cataract surgery as this procedure definitively opens up the drainage angle.

Developmental glaucoma

* Primary congenital glaucoma
* Infantile glaucoma
* Glaucoma associated with hereditary of familial diseases

Secondary glaucomas

* Inflammatory glaucoma
* Uveitis of all types
* Fuchs heterochromic iridocyclitis

* Phacogenic glaucoma
* Angle-closure glaucoma with mature cataract
* Phacoanaphylactic glaucoma
* Phacolytic glaucoma
* Subluxation of lens

* Glaucoma secondary to intraocular hemorrhage
* Hyphaema
* Haemolytic glaucoma

* Traumatic glaucoma
* Angle recession glaucoma: Traumatic recession on anterior chamber angle
* Postsurgical glaucoma
* Aphakic pupillary block
* Ciliary block glaucoma

* Neovascular glaucoma (see below for more details)
* Drug-induced glaucoma
* Corticosteroid induced glaucoma

Neovascular glaucoma is an uncommon type of glaucoma that is more difficult to treat. This condition may be caused by proliferative diabetic retinopathy (PDR) or central retinal vein occlusion (CRVO).

Prism used to measure eye pressure (Goldmann tonometry).