Glaucoma is a disease in which there can be irreversible damage to the optic nerve, resulting in loss of peripheral vision that eventually progresses to involve central vision if left untreated. This disease is often associated with increased pressure inside the eye. The ophthalmologist (Eye M.D.) can look inside the eye to see the damage to the optic nerve and can perform visual field testing to assess the extent of visual loss. However, a significant amount of damage must occur to the optic nerve before visible changes occur, and before loss of vision appears on the visual field test. Fortunately, new methods of diagnosis have evolved that allow earlier detection of optic nerve damage.

The nerve cells that are lost in glaucoma are called ganglion cells. There are over 1 million of these cells in the retina of each eye. Each cell has a long fiber that connects it to the brain. The fiber of all the cells travel in the nerve fiber layer of the retina, and exit the eye via the optic nerve. The optic nerve consists of all these fibers, and connects the eye to the brain to allow us to see. As these ganglion cells die, the nerve fibers are lost, the nerve fiber layer becomes thinner, and an empty space in the optic nerve called the "cup" of the optic nerve becomes larger and larger until the nerve is essentially gone. It is this cup in the optic nerve that the ophthalmologist uses to gauge the extent of damage from glaucoma.

Ganglion cell loss begins in the peripheral retina, and so loss of vision begins in the peripheral visual field. This is why visual field testing can help evaluate damage before it affects central visual acuity (reading vision). However, over half of the ganglion cells may be lost before any abnormality shows up on visual field testing.

Furthermore, many people may not realize that 30 to 50 percent of eyes with glaucoma may not have pressure that is higher than "normal". In normal pressure glaucoma, and in early glaucoma without visual field abnormalities, it may be difficult for the ophthalmologist to make the diagnosis of glaucoma and recommend appropriate treatment.

Fortunately, a new technology is evolving that may assist the ophthalmologist to diagnose glaucoma. This technology allows the ophthalmologist to directly measure the thickness of the layer of nerves that is damaged in glaucoma, therapy determining if the disease is stable, or if progression is occurring. Direct measurement of the nerve fiber layer thickness is a more sensitive indicator of glaucoma damage, and may allow intervention before so much damage has occurred that the optic cup enlarges or loss of visual field occurs.

This new technology utilizes the principle of polarimetry, which measures the change in direction of alignment of light (polarization) after it passes through tissue, in this case the retinal nerve fiber layer of the eye. It has been shown experimentally that the amount of change in polarization correlates to the thickness of the retinal nerve fiber layer. The GDx Nerve Fiber AnalyzerTM calculates the thickness of the nerve fiber layer, based on the amount of change in polarization of the laser light.

The ophthalmologist can determine if a person's nerve fiber layer thickness is less than normal, indicating a diagnosis of glaucoma. This examination is performed in the office, and it takes about 10 minutes for both eyes and dilation is not required. This is a promising instrument because it potentially may allow us to diagnose glaucoma before any significant damage has occurred.

Normal white visual field test result abnormal	Blue-yellow field test result (same patient)