Glaucoma occurs when the pressure inside the eye increases and causes damage. Glaucoma may lead to permanent vision loss, including blindness, if left uncontrolled. The effects of glaucoma happen slowly, and in the early stages, a person with the condition will not notice any symptoms. A routine eye exam will often lead to clinical findings or warning signs of damage from glaucoma.
Increased Eye Pressure
As part of a regular eye exam, eye doctors check the patient's eye pressure. They will do this with a painless puff of air in the eye, or they may place a numbing drop in the eye and gently touch an instrument against the eye's surface. For most people, a normal eye pressure will measure between 10 to 20 mm Hg, according to the Glaucoma Research Foundation. Most people with a pressure in this range do not have damage from glaucoma. If the eye pressure measures above this range, the doctor will evaluate further. A clinical finding of a high eye pressure does not, in itself, indicate glaucoma, although this can be a warning sign.
Optic Nerve Damage
In order to examine the back of the eye, the eye doctor will put drops in the eyes to dilate both pupils. He will then use a special microscope designed for the eyes, called a slit lamp, to complete the examination. The doctor may suspect glaucoma if he sees damage to the optic nerve. The optic nerve sits at the back of the eye and passes visual information to the brain. Damage to the optic nerve happens gradually, and the doctor may not detect changes in the optic nerve between visits. To help monitor changes, he may recommend taking photos of the optic nerve, which will allow him to compare the nerve at different times and to look for signs of damage.
Decreased Peripheral Vision
Damage to the optic nerve occurs slowly, which means that vision damage happens at such a slow rate that a person may not know she lost any part of her vision. To determine changes in side vision, the doctor will often have the patient cover one eye and test peripheral vision by putting a hand off to the side of the patient's eye. If a person has difficulty seeing in a particular area, the doctor will note this as an abnormal finding. To monitor exact vision changes, the doctor will often order a visual field test. For this, the person sits with her chin on a chin rest, staring at a light straight ahead. When she sees a blinking light, she presses a button. At the end of the test, the machine will show the areas of vision that have deteriorated, according to the U.S. National Library of Medicine.
