An eye pressure reading that is above 21 ml of mercury is considered higher than normal, according to the All About Vision website. Increased eye pressure can lead to optic nerve damage and vision loss; this can happen immediately or gradually depending on the level of eye pressure. Several diseases and medications can cause high intraocular pressure.
Ocular Hypertension
Ocular hypertension occurs when the intraocular pressure in the eye is higher than normal. In this condition, there is no actual damage to the optic nerve; however, people with ocular hypertension are at a higher risk of developing glaucoma. The eye doctor should monitor the eye pressure in these patients regularly.
Open-angle Glaucoma
In open-angle glaucoma, the intraocular pressure increases above normal because the fluid inside the eye is unable to drain out of the eye appropriately and gradually causes vision loss. This condition affects 3 million Americans, according to the Glaucoma Research Foundation.
Angle-closure Glaucoma
In angle-closure glaucoma, the eye pressure rises rapidly because of a blockage of the drainage channel of the eye. This can happen in a person whose drainage angle is not as wide or open as it should be, which can make it easier for the iris to block the channel. As noted by MayoClinic.com, this can happen gradually or rapidly--for example, when a person enters a dark room. This can quickly cause optic nerve damage and vision loss if not treated.
Inflammation
When a patient develops uveitis, or an inflammation in the eye, the intraocular pressure may also become high. The inflammatory cells inside of the eye can block the drainage channel and cause the eye pressure to rise, according to the Handbook of Ocular Disease Management.
Medications
Various medications have been found to raise the intraocular pressure in some patients; some of these medications are topical eye drops; others are taken by mouth. Some of these medications include corticosteroids like prednisone, antidepressants like amitriptyline, fluoxetine, or Prozac, and phosphodiesterase type 5 inhibitors such as tadalafil, or Cialis, and sildenafil, also known as Viagra, according to Glaucoma-Eye-Info.com
Trauma
Any type of injury to the eye can cause an elevation of eye pressure--either immediately after the injury or at a later date, according to the Glaucoma Research Foundation. Right after the injury, the intraocular pressure may increase because of bleeding inside of the eye that blocks the drainage channel. Eye pressure can increase years after the trauma because of damage to the drainage channel that was sustained during the initial injury.
