The range of eye pressure found in approximately 90 percent of the general population is between 8-21 mm Hg (millimeters of mercury). Low eye pressure may therefore generally be defined as less than 8 mm Hg. In general, the eye can see fine still at these low pressures, though the risk of blurred vision increases significantly with eye pressures under 6 mm Hg.

Rather than the pressure number, the primary issue is whether the low eye pressure is causing any problems for the eye or for the vision. What pressure an eye can tolerate varies greatly among different individuals. When the eye pressure is lower than the eye can tolerate it is like a ball that is low on air where part of the ball can begin to collapse. For some individuals that can begin to happen with an eye pressure of even 10 mm Hg, while someone else may be perfectly fine without visual symptoms with a pressure of 2 mm Hg. If you have low eye pressure or are concerned about your vision you should discuss this with your ophthalmologist.