Aqueous humor and intraocular pressure !
- Regulation
- Exam priority: medium
The eye makes and drains a clear fluid all the time; if drainage fails, pressure rises and can harm the optic nerve.
Updated 2026-11-01
Also called: IOP, Trabecular outflow
See it in 3D: Ciliary body · Drainage angle · Anterior chamber · Iris · Optic disc
What it is
Aqueous humor is secreted by the ciliary processes into the posterior chamber, flows through the pupil into the anterior chamber and leaves through the trabecular meshwork and Schlemm's canal, with a smaller uveoscleral route. Intraocular pressure is set by the balance between production and outflow resistance. Glaucoma is an optic neuropathy, often but not always linked to high pressure.
Reference values
| Parameter | Value | Note |
|---|---|---|
| Intraocular pressure | ≈10–21 mmHg | mean ≈15 mmHg |
| Aqueous production | ≈2–3 µL/min | |
| Trabecular share of outflow | most of it (≈70–90%) | the rest uveoscleral; varies with age |
Approximate values for a healthy adult at rest; each laboratory sets its own ranges.
Regulation
- +β-adrenergic stimulation of ciliary epithelium: Increases aqueous production; β-blockers lower IOP this way.
- +Carbonic anhydrase: Supplies bicarbonate for secretion; its inhibitors reduce production.
- −Ciliary muscle contraction (muscarinic): Pulls on the scleral spur and opens the trabecular meshwork, increasing outflow.
- −Prostaglandin F receptor signalling: Remodels the ciliary muscle matrix and increases uveoscleral outflow.
- −α2-adrenergic stimulation: Reduces production and adds some uveoscleral outflow.
Clinical notes
- Glaucoma is a leading cause of irreversible blindness; in Colombia it is often found late because early field loss is silent.
- Acute angle-closure: sudden eye pain, headache, nausea, halos, a hard eye and a mid-dilated, unreactive pupil; an emergency.
- Glucocorticoids, topical or systemic, can raise IOP in susceptible people.
Test yourself
Think of the answer, then tap the question to see it.
How do topical β-blockers lower intraocular pressure?
They block β-adrenergic signalling in the ciliary epithelium and reduce aqueous production; outflow is not the main target.
Why can dilating the pupil precipitate acute angle-closure glaucoma?
In a narrow angle, the thickened, relaxed peripheral iris folds into the angle and blocks the trabecular meshwork, so outflow stops while production continues.
How do muscarinic agonists improve aqueous outflow?
Contracting the ciliary muscle pulls on the scleral spur and opens the trabecular meshwork; constriction of the pupil also pulls the iris away from the angle.
Why is open-angle glaucoma often found late?
Optic nerve damage starts in the peripheral field, which the other eye and the brain compensate for, and the raised pressure causes no pain.
See it in 3D
The structures of Durgical's 3D anatomy where it happens.
Related topics
- Optics of the eye, accommodation and refractive errors
- Sympathetic and parasympathetic effects on each organ
- Adrenergic and cholinergic receptors
Related conditions
In Pharmacology
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: Physiology, Aqueous Humor Circulation (StatPearls (NCBI Bookshelf), 2024); Open Angle Glaucoma (StatPearls (NCBI Bookshelf), 2024); Acute Angle-Closure Glaucoma (StatPearls (NCBI Bookshelf), 2024); 14.1 Sensory Perception (OpenStax (Rice University), 2022); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 50). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).
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Representative model, for educational purposes only.