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Aqueous Humor

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An in-Depth Study of the Aqueous Humor

Aqueous Humor Definition 

Aqueous humor is the name given to the liquid generated by the eye. It nourishes the eye while also exerting pressure on it. Aqueous humor runs from the ciliary muscle further into the anterior aqueous humor chamber, next through the trabecular meshwork, spongy tissue at the front of the eye, and into a drainage canal (a dark blue area near to the trabecular meshwork).

In open-angle glaucoma, fluid does not flow freely through the trabecular meshwork, resulting in increased intraocular pressure, optic nerve injury, and visual loss. Glaucoma is characterized by high intraocular (eye) pressure in the majority of cases, but not all. When part of the fluid is generated by the ciliary body of the eye, aqueous humor flows freely. You will understand this when you see the diagram of aqueous humor functions.


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Composition of Aqueous Humor

Aqueous humor is an optically transparent, negligibly alkaline visual fluid that is constantly created from plasma by the ciliary body's epithelial cells. The elements helping the aqueous humor formation contain protein, γ-globulins, and albumin, relatively less than plasma. Besides this, lactic acid, immunoglobulin G, ascorbic acid and glucose are also present. 

The above-mentioned elements together form the composition of aqueous humor.

Aqueous Humor functions

The aqueous humor functions include the following points: 

  • Pumps up the sphere of the eye and sustains intraocular pressure. The eyeball is kept in an approximate sphere formed by hydrostatic pressure that maintains the eyeball's membranes tight.

  • The avascular ocular tissues, such as the posterior cornea, trabecular meshwork, lens, and anterior vitreous, get sustenance (such as amino acids and glucose).

  • Ascorbate is transported in the anterior segment and acts as an antioxidant.

  • Immunoglobulins show that they have a function in the immunological reaction to infections.

  • Inflates the cornea, increasing defence from dirt, air, pollen, and certain infections.

  • Refers to the refractive index.

  • Precludes the dryness of the eyes.

Aqueous Humor Production

The ciliary body generates 2.5L of aqueous humor every minute on typical. The following are the three processes that are involved in this  aqueous humor production:

  1. Diffusion.

  2. Ultrafiltration.

  3. The secretion that is active.

Diffusion and ultrafiltration are inert activities. However, they help gather ultrafiltrated plasma inside the ciliary body's stromal. The ciliary body epithelium then emits aqueous fluid further into the posterior aqueous humor chamber on a regular basis. In this active process, a Na⁺/K⁺- ATPase hydrolyzes ATP for energy.

It's worth noting that the sympathetic nervous system has an impact on aqueous humor production. The stimulation of beta-2 and alpha-2 adrenoceptors, accordingly, enhances and lowers the generation of aqueous humor.

Significance of Aqueous Humor

Glaucoma is a progressive optic neuropathy characterized by the death of retinal ganglion cells and their axons, resulting in a visual field deficit. High intraocular pressure (pressure inside the eye) is a significant risk factor, which can be caused by elevated generation or reduced outflow of aqueous humor. High impedance to aqueous humor flow can be caused by an aberrant trabecular meshwork or total annihilation of the meshwork as a consequence of iris damage or illness.

Aqueous Humor Drainage

The aqueous fluid drains from the aqueous chamber into the Schlemm canal, which subsequently empties to the episcleral veins via the trabecular meshwork. Schlemm's canal (SC) is a lymphatic vessel-like circular structure in the scleral sulcus, directly beyond the corneoscleral junction. The AC interacts with the interior layer of the SC, whereas the episcleral veins connect with the external perimeter.

The trabecular meshwork empties the bulk of aqueous humor, while the uveoscleral pathway drains just around 10%. The aqueous humor flows into the suprachoroidal space, which would be a gap in between the sclera and the choroid via the iris and the front side of the ciliary muscle.

Because the fluid is generally 15 mmHg (0.6 inHg) over air pressure, it flows freely when injected with a syringe. If the fluid leaks, the typical eye's hardness is undermined, causing the cornea to fold and droop.

Did You Know?

  • The ciliary body ultrafilters the aqueous humor, resulting in a practical protein-less fluid that is seamless for vision.

  • Anaerobic glycolysis by tissues of the anterior eye segment, like the lens epithelium, causes an elevated lactate level. Ascorbic acid's high quantity defends from Uv rays, which can cause the creation of free - radicals.

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FAQs on Aqueous Humor

1. What is the Difference Between Aqueous and Vitreous Humor?

Ans: The major difference between aqueous and vitreous humor are:

  • Aqueous humor is fluid, whereas vitreous humor is a jelly-like substance. 

  • The aqueous humor is found in the anterior and posterior chambers. It is found in the complete length of the cornea and the iris and serves as a reflecting medium. The vitreous humor is found between the lens and the retina and acts as a reflective medium. 

  • The aqueous humor in the eyes maintains intraocular pressure, protects the eyes by inhibiting dust, germs, and other particles, and moves because it is fluid, and on the other hand, the vitreous humor maintains the size and shape of the eyeball, protects the eye and stays in the same place since it is set in the proper position.

2. How does the Aqueous Humor Work?

Ans: The aqueous humor defined in simple terms, the ciliary body generates aqueous humor on a continuous basis (located in the anterior aqueous chamber near the lens of the eye). The output must be balanced by an equivalent rate of drainage for effective operation. Minor variations in aqueous humor production or aqueous humor flow are important as they have a major influence on intraocular pressure.

Glaucoma, a primary cause of visual loss, can develop when intraocular pressure increases. The volume of aqueous humor varies in animals and humans. The volume of the aqueous chamber is determined by the three-dimensional mapping of the anterior chamber.

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