Trabecular meshwork

FIGURE 24-1. In the normal eye, aqueous humor flows through the ciliary body into the posterior chamber, through the pupil into the anterior chamber, and out through the trabecular meshwork to the canal of Schlemm into the venous drculation. 

As noted above, the presence of Met(O) in proteins would go undetected after acid hydrolysis and subsequent amino acid analysis. Thus, since this method of hydrolysis is most commonly used, it is impossible to ascertain from the literature the abundance of Met(O) residues normally present in proteins. However, a number of studies have reported the presence of Met(O) residues in various proteins using one of the appropriate procedures described above. It has been found that Met(O) residues comprise 30% of the total Met in proteins isolated from bovine glomerular basement membranes and anterior lens . Other investigators have reported that the levels of Met(O) in proteins of the trabecular meshwork of human eyes increased with the age of the donor . The amount of Met(O) detected ranged from 15% (10 years old) to 55% (79 years old) of the total methionine content found in the tissue samples. Other studies have shown that in certain species of clams the proteins of the hinge ligament contain only Met(0) residues and no Met . In addition, it has also been reported that as much as 18% of the Met residues in pea seed proteins is in the form of Met(O) . Lastly, Met(O) residues have been found in... 

After the transport of aqueous humor into the posterior chamber, it flows through the pupil into the anterior chamber where it provides oxygen and nutrition to the avascular lens and cornea. Aqueous humor then exits the anterior chamber through the trabecular meshwork and drains into Schlemm s canal which drains aqueous humor into the episcleral venous system. 

Eighty percent of aqueous humor drains through the trabecular meshwork, which is a lattice of connective tissue that surrounds the anterior chamber. The size of the trabecular meshwork can be altered by the contraction or the relaxation of the ciliary muscle. Stimulation of muscarinic receptors on the ciliary muscle causes contraction, which in turn causes the pores of the trabecular meshwork to open, increasing aqueous humor outflow. 

Laser trabeculoplasty uses laser energy aimed at the trabecular meshwork to improve the outflow of aqueous humor and can be used as first-line therapy, especially in patients unable or unwilling to adhere to medical therapy. Laser trabeculoplasty may be used as bridge therapy between medical and surgical intervention, and approximately 50% of laser trabeculoplasty procedures will fail at 10 years. Trabeculectomy is the removal of a portion of the trabecular meshwork to improve aqueous... 

Pilocarpine directly stimulates the muscarinic (M3) receptors of the ciliary body which causes contraction of the ciliary muscle. This results in widening of the spaces in the trabecular meshwork, which causes an increase in aqueous humor outflow and reduces IOP by 20% to 30%. 

Synechia Adhesions or the abnormal attachment of the iris to another structure. Peripheral anterior synechia refers to occurrence of synechia with the trabecular meshwork. 

A recent publication by Millar has shown that NO concentrations can be measured in bovine eyes trabecular meshwork in situ using an ISONOP200 electrode from WPI [79], For this study, the tip of the 200 pm diameter electrode was inserted... 

J.C. Millar, Real-time direct measurement of nitric oxide in bovine perfused eye trabecular meshwork using a Clark-type electrode. J. Ocular Pharmacol. Ther. 19, 299-313 (2003). 

Closed-angle glaucoma occurs when there is a physical blockage of the trabecular meshwork, resulting in increased IOP. 

Alexander, J., Samples, J., and Acott, T., Growth factor and cytokine modulation of trabecular meshwork matrix metalloproteinase and TIMP expression, Curr. Eye Res., 17, 276, 1998. 

Structures of the anterior chamber of the eye. Tissues with significant autonomic functions and the associated ANS receptors are shown in this schematic diagram. Aqueous humor is secreted by the epithelium of the ciliary body, flows into the space in front of the iris, flows through the trabecular meshwork, and exits via the canal of Schlemm arrow). Blockade of the 13 adrenoceptors associated with the ciliary epithelium causes decreased secretion of aqueous. Blood vessels (not shown) in the sclera are also under autonomic control and influence aqueous drainage. 

Muscarinic agonists instilled into the conjunctival sac cause contraction of the smooth muscle of the iris sphincter (resulting in miosis) and of the ciliary muscle (resulting in accommodation). As a result, the iris is pulled away from the angle of the anterior chamber, and the trabecular meshwork at the base of the ciliary muscle is opened. Both effects facilitate aqueous humor outflow into the canal of Schlemm, which drains the anterior chamber. 

Pilocarpine, carbachol, physostigmine, echothiophate, demecarium Ciliary muscle contraction, opening of trabecular meshwork increased outflow Topical drops or gel plastic film slow-release insert... 

Bimatoprost is an analogue of PGF, used to treat glaucoma. It is believed to lower intraocular pressure by increasing the outflow of aqueous humor through both the trabecular meshwork and uveoscleral routes. 

Muscarinic cholinomimetics mediate contraction of the circular pupillary constrictor muscle and of the ciliary muscle. Contraction of the pupillary constrictor muscle causes miosis, a reduction in pupil size. Miosis is usually present in patients exposed to large systemic or small topical doses of cholinomimetics, especially organophosphate cholinesterase inhibitors. Ciliary muscle contraction causes accommodation of focus for near vision. Marked contraction of the ciliary muscle, which often occurs with cholinesterase inhibitor intoxication, is called cyclospasm. Ciliary muscle contraction also puts tension on the trabecular meshwork, opening its pores and facilitating outflow of the aqueous humor into the canal of Schlemm. Increased outflow reduces intraocular pressure, a very useful result in patients with glaucoma. All of these effects are prevented or reversed by muscarinic blocking drugs such as atropine. 

M. Hangai, H. Tanihara, Y. Honda, and Y. Kaneda, Introduction of DNA into the rat and primate trabecular meshwork by fusogenic liposomes. Invest. Ophthalmol. Vis. Sci. 39 509 (1998). 

Primary open-angle glaucoma is a very common form (also known as chronic simple or wide-angle glaucoma). It results from obstruction in the trabecular meshwork which acts as the drainage system for the aqueous humour. 

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