Glaucoma is a group of eye diseases that are characterized by intraocular pressure levels that damage the optic nerve and nerve fibers that form parts of the retina in the back of the eye. The optic nerve links the light-perceiving tissues of the eye with the parts of the brain that process visual information. Glaucoma is a common cause of preventable vision loss and can be treated by prescription drugs, laser therapies, and surgery. People with glaucoma often have no symptoms until they begin to experience loss of part of their peripheral vision. It is important to note that visual loss from glaucoma is permanent and irreversible in most cases, hence the need for early diagnosis and treatment.

Visual field loss is one of the three main signs of glaucoma and is the result of damage to the optic nerve. Once damaged, visual losses are not reversible. (Photo courtesy National Eye Institute)

The ophthalmologist making a diagnosis of glaucoma will look for three conditions:

1. Higher intraocular pressures are associated with a higher risk for developing the disease. In addition, it is known that the chances of maintaining vision and side or peripheral vision are related to decreasing pressure within the eye.
2. Loss of tissue or cupping in the center of the optic nerve head or disc at the back of the eye, which suggests optic nerve damage or reduced function.
3. Visual field loss or defect of a glaucomatous type (typically a reduction of peripheral vision, or an increase in the number or size of blind spots) (see photos above).

Some or all these signs may be present if a person has glaucoma. The condition of the optic nerve head and raised intraocular pressure are only detectable during an eye examination by an ophthalmic professional.