What does intraocular pressure mean?

If the intraocular pressure is at a normal value, some eye diseases can be avoided. Normal intraocular pressure should be within the range that does not cause damage to the optic nerve. Clinically, if the intraocular pressure is too high, ocular hypertension is very likely to occur.

1. From a clinical perspective, the definition of normal intraocular pressure should be the intraocular pressure range that does not cause optic nerve damage. Because there are great individual differences in the optic nerve's tolerance to intraocular pressure, normal intraocular pressure cannot be defined by a precise value.

2. The average intraocular pressure of normal people is 15.8 mmHg (1 mmHg = 0.133 kPa), and the standard deviation is 2.6 mmHg. From a statistical perspective, normal intraocular pressure is defined as 10~21 mmHg (mean ± 2 × standard deviation), but in reality, the intraocular pressure of the normal population is not normally distributed. Therefore, intraocular pressure > 21 mmHg cannot be mechanically considered a pathological value.

3. Clinically, although the intraocular pressure of some patients has exceeded the statistical normal upper limit, long-term follow-up does not show damage to the optic nerve and visual field, which is called ocular hypertensio. Some patients have intraocular pressure within the normal range, but typical glaucomatous optic nerve atrophy and visual field loss occur, which is called normal tension glaucoma (NTG). It can be seen from this that high intraocular pressure does not always mean glaucoma, and normal intraocular pressure cannot rule out glaucoma.