The Science of Glaucoma and the Types of Glaucoma
Aqueous Fluid & Intraocular Pressure (IOP)
Aqueous fluid is a clear and watery ultra-filtrate of blood that fills the anterior and posterior chambers of the eye. Flowing more at night than in the day, it is a source of nourishment for the eyes and plays a part in waste removal. The eye forms and reabsorbs aqueous fluid continuously. The regulation of intraocular pressure (IOP) is in part a result of the flow of aqueous fluid. IOP can be determined by comparing the inflow versus the outflow of aqueous fluid in the anterior segment (the chamber on the front of the eye covered by the cornea) IOP remains constant if the outflow is equal to the inflow. If outflow is less than flow, the IOP rises.
Most people with glaucoma suffer from one of two major types of the disease, "open angle" and"closed angle" glaucoma.
What is the Angle?
To better understand these two types of glaucoma we first have to explore why the term"angle" is used to describe them. The anterior chamber is the fluid-filled space inside the eye between the iris and the cornea's innermost surface, the endothelium. Aqueous fluid fills the anterior chamber. In differentiating between open angle and closed angle glaucoma experts use the iris, the corneal endothelium and the trabecular meshwork as points of reference. The anterior chamber angle is often referred to as "the angle". The base of the angle is the iris. The apex of the angle is the trabecular meshwork. The top of the angle is the corneal endothelium. If a miniature protractor could be placed on the base of the angle (the iris) to determine the width of the anterior chamber angle in degrees. a 45 degree angle would be considered wide (or "Open"), and a ten degree angle would be considered narrowed (or "Closed").
Chronic open angle glaucoma progresses at a slower rate and is often not noticed until there is a significant loss of vision. On the part of doctors, being vigilant and asking patients questions can uncover underlying risk factors. Eye pressure being above normal levels is not the reason all people have open angle glaucoma, however decreasing eye pressure has been proven to forestall the progression of glaucoma even in the cases where elevated pressure does not occur. Peripheral vision tends to be affected first, and if not treated, open angle glaucoma will lead to a total loss of entire vision.
Closed angle glaucoma is often painful and sudden, characterized by visual loss (that progresses quickly) and discomfort (that often leads people to seek medical attention before permanent damage occurs). Closed angle glaucoma is diagnosed when aqueous fluid cannot reach the anterior chamber angle. It accumulates and forces the iris to obstruct the trabecular meshwork. Contact between the iris and the trabecular meshwork may ultimately damage the function of the meshwork so that it fails to respond to aqueous fluid production leading to an increase of IOP (intraocular pressure). Scars called synechiae form, causing an irreversible block in aqueous outflow. Most cases of closed angle glaucoma do not reveal themselves through symptoms. In the cases where symptoms do occur patients experience eye pain and redness, blurred vision, headaches, vomiting, and the appearance of halos. In addition to these symptoms doctors look for mid-dilated pupils, lack of response to light, cloudy corneas and reduced vision to diagnose closed angle glaucoma.
Less common and less treatable types of Glaucoma
Forms of developmental glaucoma include; congenital, infantile and hereditary/familial disease. Forms of secondary glaucoma include: inflammatory, phacogenic, intraocular hemmorhage, traumatic glaucoma, neovascular glaucoma, drug-induced glaucoma, and glaucoma of miscellaneous origin. Both developmental and secondary glaucoma groups respond to treatment but resulting outcomes vary.
Individuals with poor blood flow are at high risk for neovascular glaucoma which is rare, untreatable, and characterized by the development of abnormal vessels that block fluid drainage in the eye. Toxic glaucoma which is also untreatable results from an unexplainable rise in intraocular pressure.
Absolute glaucoma is the final stage of glaucoma, no vision, pain, a stone-like appearance of the eye, and treatment is based on the destruction of the eye.
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