Usually, your ophthalmologist will be far more worried about high eye pressure than low eye pressure. However, both eye conditions can cause serious problems for your vision. Ocular tonometry is the best way to determine if you have an eye pressure problem, so have your healthcare professional check your eyes regularly.

Hypotony

Regular eye pressure ranges from 12 to 22 mm Hg. High eye pressure can signal glaucoma, but sometimes eye pressure plummets due to certain medications and even cataract surgery. Hypotony is usually defined as eye pressure that is lower than 5 mm Hg. Low eye pressure can cause macular edema, choroidal detachment, and corneal astigmatism, among other problems. One common cause of the condition is a leaking wound after cataract surgery. Steroid drops may help along with a few other medications, but the problem can be complicated to treat. 

Measuring Eye Pressure

Problem eye pressure is determined by using one of the different types of tonometry. They include

• Non-Contact Tonometry. This test simply requires that you stare straight ahead while the instrument blows a little air into your eye. This test is used to screen for obvious abnormal pressure readings. If it registers unnaturally high or low, your doctor will use another method to get a more precise reading. 
• Applanation (Goldmann) Tonometry. This instrument flattens a part of your cornea with a probe to measure eye pressure. It also includes a "slit lamp" to further examine your eye. Your optometrist will use this machine to get a more accurate reading if the basic puff of air test delivers an abnormal measurement. 
• Electronic  Indentation Tonometry. This type of tonometry is a portable hand-held device. Your healthcare professional will gently apply the tip of the pen-like instrument to your cornea. To ensure an accurate reading, he may need to measure the pressure several times. This method is not as accurate as the Applanation (Goldmann) Tonometry but is more reliable than the air puff test. 

Low eye pressure can cause serious vision problems as can high eye pressure. Your ophthalmologist will use a variety of tonometry devices to get the most accurate eye pressure reading possible. The various instruments all have their own advantages, but if your doctor suspects you have abnormal eye pressure, he or she will probably use either electronic indentation tonometry or Applanation (Goldmann) Tonometry. Eye pressure can fluctuate due to exercise, medications, and fluid intake. The only trustworthy way to measure your pressure is by using tonometry and ophthalmic instruments.