The aqueous humor pressure of the eye enables symptom-free and optimal vision. However, if something in the sensitive interaction is disturbed, serious visual disturbances can occur.
What is aqueous humor pressure?
The aqueous humor pressure of the eye allows for symptom-free and optimal vision. The aqueous humor is a clear fluid containing nutrients in the anterior and posterior chambers of the eye. Aqueous humor has a similar consistency to blood serum, but contains less protein and no bilirubin. It consists of about 98 percent water, in which mainly amino acids, ascorbic acid, electrolytes, lactic acid and immunoglobulin G are dissolved. Furthermore, traces of hydrogen peroxide are present. A human eye produces about three to nine milliliters of aqueous humor in a day. This production is somewhat reduced at night. Comparatively, the eyeball has a volume of about 6.5 milliliters. The aqueous humor is continuously formed from the carbonic acid of the blood in the ciliary body (ray body) at the medial eye surface and is discharged from there into the posterior chamber of the eye. Through a tiny gap between the lens and the iris (iris skin), it eventually also enters the anterior chamber of the eye. Most of the aqueous humor flows through the angle of the chamber and Schlemm’s canal through the veins of the conjunctiva back into the bloodstream.
Function and purpose
With the circulation described above, aqueous humor supplies nutrients to the lens and the innermost layer of the cornea. In addition, with its content of immune substances and constant circulation, it has the task of banishing pathogens and toxins from the interior of the eye. The production and subsequent outflow of aqueous humor are always balanced in a normally functioning eye. In this case, both eye chambers are filled with aqueous humor at all times. This also stabilizes the shape of the eye and the curvature of the cornea. However, as soon as the outflow is obstructed or more aqueous humor has formed than can flow out, the internal pressure in the eye chambers as well as in the vitreous body increases. This space between the lens and the retina, which is filled with a gel-like substance, bears down on the head of the optic nerve in the event of increased pressure. This is an extremely fine-nerved and sensitive area of the eye. Because of the increased intraocular pressure, the very sensitive fibers of the optic nerve head can be crushed.
Diseases and complaints
If the optic nerve fibers begin to die, glaucoma (glaucoma) forms. This results in a reduced field of vision for the affected person. This process is slow and is not noticeable at first. At the beginning of the glaucoma, the restrictions also only affect the edge of the visual field. However, if the pressure remains high, the visual field gradually narrows further. Eventually, the limitations affect the center of the field of vision, although there is usually no pain. Thus, if left untreated, glaucoma can lead to loss of vision. It is estimated that in Germany about 2000 people per year go blind from glaucoma. Timely consultation with an ophthalmologist for effective treatment of developing glaucoma is highly recommended. He will measure the intraocular pressure by simple means to determine the extent of a possible glaucoma disease. The harmless intraocular pressure ranges from 10 to 30 mmHg (millimeter mercury column, formerly Torr) depending on age. One mmHg is defined as the static pressure exerted by a column of mercury one millimeter high. A healthy middle-aged adult has an intraocular pressure of about 21 mmHg. In older people, the intraocular pressure often increases somewhat. If there is a severe case of glaucoma, the pressure reaches up to 70 mmHg. This serious event is accompanied by headache, eye pain, and often nausea and vomiting. The patient suddenly suffers from severe sensitivity to light and the affected eye feels very rigid. Immediate medical attention is needed in this emergency. For a certain time, the eye is able to withstand a slightly increased pressure. Medically, this property is called tension tolerance. However, if the pressure increases significantly over a longer period of time, there is a risk of permanent injury to the visual apparatus. The aqueous humor pressure value can also be too low if the formation of aqueous humor is reduced.The dangers then lie in the threat of retinal detachment, which can lead to blindness. This is because only when the intraocular pressure is in the right range can it fix the retina in its intended position. Excessive intraocular pressure that is detected in time can first be lowered with special eye drops or other medications that reduce the formation of aqueous humor. In order to improve the difficult outflow of the aqueous humor, especially in older people, a small surgical intervention is often sufficient to cut the so-called trabecular meshwork in the chamber angle. It can become stiff over time and thus block the outflow of the aqueous humor. A larger intervention is the so-called trabeculectomy. Here, the conjunctiva is cut open extensively and an artificial drain for the aqueous humor is created. However, this operation requires a very complex follow-up treatment. Procedures such as laser treatment of the chamber angle or sclerotherapy of the ciliary body are only considered for patients with far advanced disease.
