Glaucoma is the gradual loss of nerve cells in the eye, mainly caused by raised eye pressure. This occurs when fluid outflow becomes obstructed over time, so that the correct amount of fluid cannot drain out of the eye (see How the eye works). Glaucoma generally develops when eye pressure surpasses 21 mm Hg (millimeters of mercury).

Some people with eye pressures above 21 mm Hg will never develop glaucoma because their nerve cells are very resistant to eye pressure increases. Obviously these people do not require therapy. Your eye doctor can determine whether or not you already need a treatment. If not, you should still receive regular (usually yearly) check-ups.

Most people with eye pressures below 21 mm Hg will never have glaucoma, although some people will. This happens when the nerve cells are unusually sensitive to minor eye pressure increases. This is most often the case when blood flow through the eye is impaired.
Therefore eye pressure measurements alone, cannot exclude with certainty the possibility that you have glaucoma. Only your eye doctor can with additional tests, detect so-called normal pressure glaucoma.

In plain English: no it isn’t!