All About Eye Pressure
Chances are you are familiar with blood pressure and its importance as an indicator of cardiovascular health, but how familiar are you with eye pressure, also known as intraocular pressure (IOP)? Below we explain eye pressure, why it is important to your eye health, and how it can be lowered if it becomes too high.
What Causes Increased Eye Pressure?
In your eye, there is fluid between the cornea (the outside layer of your eye) and the lens of your eye, which is located behind your iris and pupil. This fluid, known as aqueous humor, helps lubricate the lens, while supplying nutrients and oxygen to the eye. It also helps maintain the shape of the eye.
The aqueous humor is produced in a structure called the ciliary body and flows through the front part of your eye before draining through a tissue called the trabecular meshwork, which is located at a point where the iris and the cornea meet.
In a healthy eye, the amount of fluid exiting is equal to the amount of fluid produced so as to create a stable system with an IOP measurement of 10 to 21 mmHg (millimeters of mercury – a scale used to record pressure). However, some people produce too much fluid or have a trabecular meshwork that does not drain the fluid properly. This can cause fluid to buildup, which can increase the pressure in the eye and cause high IOP, or ocular hypertension.
Just as high blood pressure causes damage to your heart, high eye pressure can damage the optic nerve and heighten your risk of glaucoma, one of the leading causes of blindness.
Unfortunately, ocular hypertension does not produce symptoms in most people. It can therefore go undetected for a long period of time and not be discovered until it has already damaged the optic nerve and caused irreparable vision loss. Regular comprehensive eye exams that include an eye pressure test are the best way to keep tabs on your eye pressure.
Eye Pressure Test
There are three common methods your doctor might use to measure eye pressure. One you may have experienced is the air puff test, also known as non-contact tonometry (NCT). In this test, a machine delivers a puff of air to your eye without touching it. The amount of indentation the puff of air makes to the cornea is measured and used to determine IOP.
While the non-contact tonometry test is less invasive, direct contact tonometry methods can give more accurate results. One such method is called electronic tonometry and uses a portable, handheld tonometer that resembles a writing pen to quickly check your IOP. Your eye is numbed and the device is gently placed against your eye several times in quick succession to gather data electronically. Each touch is stored and statistically analyzed to arrive at an IOP measurement.
The gold standard for measuring eye pressure is with a direct contact Goldmann applanation tonometer (GAT). The GAT is usually attached to a slit lamp microscope. Anesthetic drops along with fluorescein dye are administered to your eyes. Once your eyes are numbed, the physician or technician presses the small probe of the GAT against your cornea to flatten a small portion of it. The amount of pressure with which the cornea pushes back against the device is measured as your IOP.
Eye Pressure Range
Knowing your intraocular pressure can help eye doctors diagnose potential eye problems. Your level of eye pressure will indicate which actions may need to be taken.
Low Eye Pressure
Eye pressure below 5 mmHg is considered low eye pressure, or hypotony. While not discussed as much as high eye pressure, it can still cause issues. Hypotony can occur after eye surgery or from chronic inflammation or a detached retina and is indicative of the eye not producing enough aqueous humor or draining too much humor. The lack of adequate pressure can lead to structural changes in the eye such as chorioretinal wrinkling or swelling of the optic nerve. Such changes can lead to vision loss.
Normal Eye Pressure
Most individuals have an intraocular pressure between 12 and 21mmHg, but there is no ‘normal’ eye pressure. Rather, it is dependent on each individual patient. Additionally, pressure can vary by age (eye pressure tends to increase with age) and even by the time of day (lower in the morning and higher in the evening). It should be noted that a subset of people can have normal-tension glaucoma, which can cause glaucomatous changes in the optic nerve and visual field deficits even though IOP is within the 12-21mmHg range. Thus, simply measuring intraocular pressure is not an adequate surrogate for glaucoma screening.
Elevated Eye Pressure
Eye pressure above 21 mmHg without glaucoma signs is considered ocular hypertension.
Ocular hypertension may or may not need to be treated. Consult with your ophthalmologist about cumulative risk factors for glaucoma in order to decide if treatment is necessary. Patients with ocular hypertension need to be regularly checked for glaucoma, which is often associated with individuals with an IOP above 21 mmHg. A failure to treat glaucoma could lead to blindness.
Dangerously High Eye Pressure
Eye pressure levels between 21-30 mmHg associated with glaucoma usually cause damage over a number of years. However, an IOP in the 40-50 mmHg range can lead to retinal vascular occlusion, a potentially serious condition in which blood vessels that serve the retina are blocked. This can cause rapid loss of vision that if not treated within 24 hours can become permanent. Complications, and their severity, increase more rapidly as IOP rises above 50 mmHg necessitating aggressive intervention to lower the pressure.
How to Lower Eye Pressure
Currently there are no widely accepted lifestyle or dietary modifications known that create a continuous and sustained lower IOP; however, if an elevated IOP needs to be lowered, your doctor may turn to prescription eye drops. These eye drops either decrease how much fluid your eye produces or increase the outflow of fluid from your eye. In some circumstances, your doctor may prescribe an oral medication to supplement your eye drops.
Another initial step in lowering IOP involves laser treatments. Finally, there are a wide array of surgical options available to glaucoma patients at all stages of care. Your doctor will advise you as to when these options should be used.
Taking precautions and having regular comprehensive eye exams is even more important if your family history, age, race, or pre-existing eye conditions put you at a higher risk for developing high eye pressure. The following categories are risk factors for high eye pressure:
- Family history of glaucoma or ocular hypertension
- People with diabetes or high blood pressure
- People over the age of 40
- African Americans and Hispanics
- People with extreme nearsightedness
- People on long-term steroids
- People with a history of eye injuries, eye inflammation or surgeries