Introduction to Glaucoma
The optic nerve is only 1.5 mm in size. It consists of two portions, and inner part called the cup, and an outer part called the disk. The cup/disk ratio is used to assess risk for glaucoma. An optic nerve with a vertical cup/disk ratio greater than 0.6 may be at high risk for glaucoma.
In addition to using the cup/disk ratio and other contour features of the optic nerve to assess the presence or absence of glaucoma, the cup/disk ratio can be followed over time. If the cup enlarges or deepens, that is a danger sign and suggests that the current level of treatment is NOT working. Changes in the cup disk ratio are often associated with visual field loss.
The peripheral vision in a normal person extends 40 degrees nasally and 70 degrees temporally in each eye. Even while you gaze straight ahead a lot of visual information is coming in subliminally from the side. This is a carryover from the days when man existed by hunting, fishing and gathering, and needed peripheral vision to protect from predators. Now we still use our side vision for driving, sports and a host of other activities.
In glaucoma, side vision is lost. The central portion of the vision remains normal until the very late stages. Thus, the majority of glaucoma patients have normal central vision: 20/20 vision.
Vision loss in glaucoma is thus best determined by taking measurements of the side (peripheral) vision. The test that your doctor might order is called a visual field test.
There are different types of visual field tests. Some are used to detect early glaucoma; others are used for later stage glaucoma to follow for visual field loss progression.
An adage with glaucoma is to make the diagnosis by assessing the optic nerve and follow the course of the disease by frequent visual field and intraocular pressure testing. At our clinic, we believe that BOTH visual field testing and optic nerve assessment can be useful at all stages of the disease to best manage your glaucoma.
Treatment consists of eye drops, laser treatments or eye surgery for more advanced cases.
Glaucoma almost always starts WITHOUT any symptoms. Often patients have silent glaucoma for up to 8 years before patients notice problems with vision.
Because the vision loss is irreversible it is critical that it be detected as early as possible.
Early detection not only prevents vision loss, but it also makes treatment easier. The more advanced the disease when it is first diagnosed the more difficult it is to prevent further vision loss.