production and resorption, and maintenance of the lens zonules for the purpose of anchoring the lens in place. Accommodation Accommodation essentially means that when the ciliary muscle contracts, the lens becomes more convex, generally improving the focus for closer objects. When it relaxes, it flattens the lens, generally improving the focus for farther objects. Aqueous humor The ciliary epithelium of the ciliary processes produces aqueous humor, which is responsible for providing oxygen, nutrients, and metabolic waste removal to the lens and the cornea, which do not have their own blood supply. Eighty percent of aqueous humor production is carried out through active secretion mechanisms (the Na+K+ATPase enzyme creating an osmotic gradient for the passage of water into the posterior chamber) and twenty percent is produced through the ultrafiltration of plasma. Intraocular pressure affects the rate of ultrafiltration, but not secretion. Lens zonules The zonular fibers collectively make up the suspensory ligament of the lens. These provide strong attachments between the ciliary muscle and the capsule of the lens. Clinical significance Glaucoma is a group of ocular disorders characterized by high intraocular pressure-associated neuropathies. Intraocular pressure depends on the levels of production and resorption of aqueous humor. Because the ciliary body produces aqueous humor, it is the main target of many medications against glaucoma. Its inhibition leads to the lowering of aqueous humor production and causes a subsequent drop in the intraocular pressure. There 3 main types of medication affecting the ciliary body: Beta blockers, the second most common treatment method for glaucoma, reduce the production of aqueous humor. They are relatively inexpensive and are available in generic form. Timolol, Levobunolol, and Betaxolol are common beta blockers prescribed to treat glaucoma. Alpha-adrenergic agonists work by decreasing production of fluid and increasing drainage. Brimonidine and Apraclonidine are two commonly prescribes alpha agonists for glaucoma treatment. Alphagan P uses a purite preservative, which is better tolerated those who have allergic reactions than the older BAK preservative in other eye drops. Furthermore, less selective alpha agonists such as [epinephrine] may decrease the production of aqueous humor through vasoconstriction of the ciliary body (only for open-angle glaucoma). Carbonic anhydrase inhibitors also decrease fluid production. They are available as eye drops (Trusopt and Azopt) and pills (Diamox and Neptazane). This may be helpful if using more than one type of eye medication. See also Intraocular pressure Iridodialysis Glaucoma Cyclodestruction References External links - "Sagittal Section Through