The intraocular pressure is caused by the balance between production and outflow of the aqueous humor. This is a fluid produced by certain cells in the eye. The intraocular pressure is important for the even curvature of the cornea, as well as for maintaining the correct distance between the lens and the cornea.
The intraocular pressure can be measured. The normal value is 15.5 mmHg (millimetres of mercury), with the lower limit at 10 mmHg and the upper limit of the normal intraocular pressure range at 21 mmHg. However, the intraocular pressure also varies between 3-6 mmHg in healthy people.
Therefore, a single measurement of intraocular pressure is only a snapshot and does not necessarily rule out disease at normal values. In addition, the intraocular pressure value can be falsified by a particularly thick cornea, which an ophthalmologist should take into account. The highest values of intraocular pressure are reached around midnight and in the early morning hours, and the intraocular pressure drops slightly during the course of the day.
In addition, the intraocular pressure is generally higher in older people than in young people. If there is an outflow disorder at the angle of the chamber, where the aqueous humor can normally drain off, the intraocular pressure increases (ocular hypertension) because the fluid in the eye accumulates. If this leads to an increase in pressure to over 21mmHg, this can be harmful to the eye in the long term.
The optic nerve and the retina can be permanently damaged by the compression, resulting in vision loss or even blindness. Temporarily, the eye can withstand higher pressures without damage. This is called tension tolerance.
However, the higher the intraocular pressure is and the longer this pressure increase lasts, the higher the risk of permanent damage to the visual system. As people over 40 years of age are particularly affected by an increase in intraocular pressure, it is advisable to have the pressure checked regularly from this age. However, the intraocular pressure can also be too low (ocular hypotension).
In most cases this is due to a reduced production of aqueous humor. This is very dangerous because the intraocular pressure is necessary to fix the retina in place. If the pressure is not sufficiently high due to a lack of aqueous humor, a retinal detachment with resulting blindness may occur.
The fastest possible therapy is necessary. In glaucoma, the intraocular pressure is increased. A distinction is made between chronic glaucoma, which can develop insidiously over weeks, months or even years, and acute glaucoma.
In a glaucoma attack, the intraocular pressure suddenly rises sharply, sometimes to values of over 30 or 40 mmHg. Patients complain of a reddened, painful eye, and their vision functions only to a limited extent or even no longer at all. The pupil no longer reacts to the strength of the incident light, so the patients are also very sensitive to light.
The eye feels rock hard due to the increased intraocular pressure and very often accompanying symptoms such as headaches, nausea and vomiting occur. This is a medical emergency, where the reduction of the intraocular pressure is the first priority of the therapy. As described at the beginning, the intraocular pressure can increase either due to a disturbed production or a disturbed outflow.
It is rather rare that the ciliary body produces too much aqueous humor. In most cases, an increased intraocular pressure is due to the fact that the outflow path in the anterior chamber of the eye, through which the aqueous humor is supplied to the blood circulation, is no longer open far enough, and thus the aqueous humor accumulates in the eye. If this is the case and the patient develops glaucoma, it is called narrow angle glaucoma. The angle in the term refers to the small outflow channel of the aqueous humor.