What is the critical period of intraocular pressure?

Nowadays, people are exposed to more electronic products, and many young people have symptoms of high intraocular pressure. The level of intraocular pressure represents whether the eyes are normal or not. The normal range of intraocular pressure is between 10mmHg and 21mmHg. If it exceeds this range, it means that the intraocular pressure is too high. High intraocular pressure can lead to glaucoma. In order to prevent high intraocular pressure, we should spend less time watching mobile phones, computers, televisions and other electronic products that irritate the eyes.

Intraocular pressure is the pressure inside the eyeball , which is referred to as IOP. It is the balanced pressure exerted by the contents of the eye on the walls of the eye. The intraocular pressure of a normal person is stable within a certain range to maintain the normal shape of the eyeball and keep the interfaces of each refractive medium in a good refractive state. The normal intraocular pressure ranges from 10 mmHg to 21 mmHg (1.33 kPa to 2.80 kPa).

The contents of the eye include aqueous humor, lens, and vitreous body, among which the aqueous humor has the greatest impact on intraocular pressure. The total volume of aqueous humor is 0.13mL~0.3mL. Its main component is water. In addition, there are proteins, electrolytes, ascorbic acid, lactic acid, glucose, lipids, enzymes, etc. The pH value is 7.3~7.5. The aqueous humor is produced by the ciliary processes in the ciliary body, then enters the posterior chamber, flows into the anterior chamber through the pupil, and then is discharged to the outside of the eyeball through some channels through the anterior chamber angle. Under normal circumstances, the production and excretion of aqueous humor maintain a dynamic balance, that is, within a certain period of time, the amount of aqueous humor produced and discharged is equal. If the drainage channel of aqueous humor is blocked, or the amount of aqueous humor produced increases for some reason, it can lead to accumulation of aqueous humor and increase intraocular pressure. If the amount of aqueous humor produced is too little and the accumulation of aqueous humor does not reach a certain amount, the intraocular pressure will be too low.

From a clinical perspective, normal intraocular pressure should be defined as 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. 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. 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 develop typical glaucomatous optic nerve atrophy and visual field defects, 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.

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