One can liken the eye to a TV Camera. Lenses in the front portion of the TV camera focus light onto photosensitive diodes in the back of the camera. Here the light is transformed into electrical signals and the camera cable carries these impulses to the studio.
In the front portion of the eye the cornea and lens focus light on the retina, which in the back of the eye. The retina transforms this focused light into electrical impulses. Nerve fibers accumulate these signals and merge at the back of the eye to form the optic nerve. This nerve exits the eye and goes to the brain. Where the nerve leaves the eye is a vulnerable region, and if pressure in the eye becomes too high nerve damage results. A healthy optic nerve has about 1.3 million fibers and the loss of these fibers through the above process is called glaucoma.
There are different types of glaucoma. In the common variety, pressure slowly increases in the eye over the months and years, and gradually optic nerve fibers are destroyed. In certain individuals, the glaucomatous process is due more to the intrinsic health of the optic nerve and its vascular supply as opposed to a significantly high intraocular pressure. In either case the most vulnerable optic nerve fibers are those that serve peripheral vision. As damage progresses side vision is lost. This is often not noticed by the patient as it is gradual and reading and straight-ahead vision remains intact until the disease is in its very late stages.
One can diagnose glaucoma long before this point by a combination of looking at the optic nerve in the back of the eye with an ophthalmoscope, detecting any visual field loss by careful visual field testing, and measuring the internal eye pressure with an instrument called a tonometer. As the tonometer reports a pressure measurement that is lower than the true intraocular pressure if the cornea is thin, and reports a higher value than the true pressure if the cornea is thick, measuring the central corneal thickness with an instrument called a pachymeter is also useful. This ability to correct the intraocular pressure for unusually thick or thin corneas allows one to more precisely know the actual intraocular pressure, and in some patients this can help predict the probability of developing glaucoma.
Once the disease is diagnosed, vision that has been lost cannot be restored, as optic nerve fibers do not regenerate. This is why it is important to diagnose and institute treatment at an early stage when visual loss is not significant. In most individuals eye drops, lasers or surgery will control the progression of the disease. Periodic visits to an Ophthalmologist or Optometrist are important especially if you are in a high-risk group. This includes blacks over the age of forty, everyone over the age of sixty, individuals with a history of ocular trauma, those who must use anti-inflammatory steroids for medical conditions such as asthma, and people with a family history of glaucoma.
For more information. . .
National Eye Institutes
has pamphlets on common ocular conditions and their one on glaucoma provides an
easily read synopsis. It provides very basic information about what
the disease is, risk factors, diagnosis, treatment, and a short reference
section to other sites.
The Glaucoma Research Foundation is
an in depth site and has won several Internet web site awards. There are a
variety of fact sheets, speaker's bureau, newsletters, information on research,
and a patient support section. Two mini books: Understanding and
Living with Glaucoma, which is for adults, and a second book: Childhood
Glaucoma, which is targeted toward families who have a child with this
disease, are free and may be ordered from the website. Both references
offer in-depth information on their respective subjects. A new
section on Alternative Medicine discusses the role of unconventional therapies
in glaucoma treatment. The site has links to other web sources, and an easily
found privacy statement.
Glaucoma Foundation has
an online Patient
Guide that gives detailed information about glaucoma. There are
support groups, links to current news articles, a newsletter and information
on research projects and grants. A limitation of the site was
that technical information generally did not contain any publication or revision
dates. As of