What is Trabecular Meshwork?
The trabecular meshwork is the main pathway that allows for fluid to drain from the eye. It is a thin, porous layer containing tiny canals that drain the intraocular fluid. The trabecular meshwork is a key structure involved in the flow of aqueous humor, the fluid inside of the front part of the eye. The trabecular meshwork is responsible for maintaining the eye pressure at a normal level. If the trabecular meshwork becomes blocked, the eye pressure increases, and this can lead to glaucoma. Glaucoma is a condition that causes slow, progressive damage to the optic nerve and eventually loss of peripheral vision. High eye pressure can be associated with glaucoma.
- The Trabecular Meshwork is a spongy tissue with many tiny canals, located between the cornea and the iris. The trabecular meshwork function is to remove fluid from the eye and maintain normal intraocular pressure.
- If the trabecular meshwork is blocked or obstructed, it can increase the eye pressure and lead to glaucoma.
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Understanding Trabecular Meshwork
The Trabecular meshwork of the eye is the major route for the drainage of aqueous humor. Aqueous humor is the clear fluid that is present in the front of the eye, between the cornea and the lens, and nourishes the eye’s structures with nutrients and oxygen. The aqueous humor is also important to keep the eye inflated. If you imagine the front of the eye as a balloon, the aqueous humor is the fluid that fills up the balloon.
The trabecular meshwork is the thin layer that allows for the passage of aqueous humor from the eye. The trabecular meshwork has a network of many, tiny canals that shunt fluid from the inside of the eye to the outside of the eye. After crossing through the trabecular meshwork, the aqueous humor reaches Schlemm’s canal, which drains directly to the aqueous veins. The majority of outflow of aqueous humor through the trabecular meshwork and Schlemm’s canal is pressure-dependent. This means that the eye pressure must be greater than the episcleral venous pressure in order for the aqueous to flow out. A small percentage of aqueous humor passes through the trabecular meshwork and goes through the uveoscleral pathway, between the ciliary muscle, instead of going through Schlemm’s canal.
If the trabecular meshwork eye becomes clogged or has disrupted function, the aqueous will not drain, and the eye pressure will build up inside of the eye. This obstruction of the trabecular meshwork may cause glaucoma.
Impact of Age on the Trabecular Meshwork
Previous studies have shown that the elasticity of the trabecular meshwork decreases with age. Older people may have a thicker trabecular meshwork due to the thickening of its elastic fibers and increased extracellular matrix. This thickening could reduce aqueous drainage through the pores and enhance resistance to aqueous outflow.
It is hypothesized that this may be one factor contributing to older people’s increased risk of glaucoma. However, it is still not proven that loss of trabecular cells causes glaucoma. Further research must be done to identify why the risk for glaucoma increases with age. Although glaucoma is a disease that tends to affect older people, not all elderly people get glaucoma. The prevalence of glaucoma in the United States is approximately 2% to 3%.
Trabecular Meshwork Exam
An eye doctor can evaluate whether the trabecular meshwork of the eye is blocked, and therefore not draining properly, by doing a procedure called gonioscopy. During gonioscopy, a special lens (gonioscope) is placed on to the eye after the eye is numbed. The gonioscope allows the doctor to evaluate the structures in the iridocorneal angle, where the trabecular meshwork is present.
Conditions that can cause clogging of the trabecular meshwork include:
- Pigment Dispersion Syndrome
Anatomical configuration of the iris causes pigment to rub off the iris and deposit onto the trabecular meshwork, which blocks the fine pores of the trabecular meshwork.
- Pseudoexfoliation Syndrome
White flaky material deposits in the trabecular meshwork, clogging it.
- Neovascularization of the Iridocorneal Angle
Severe uncontrolled diabetes or hypertension can cause new blood vessels to grow on top of the trabecular meshwork, blocking its drainage route
- Uveitic Glaucoma
Scar formation, called peripheral anterior synechiae, caused by chronic eye inflammation can block the trabecular meshwork drainage.
If the doctor determines that the trabecular meshwork is blocked and causing elevated intraocular pressure, they will attempt to lower the intraocular pressure using eye drops, laser or surgery.
Topical eye drops that lower the intraocular pressure are usually the first line of treatment. The drops work by decreasing aqueous humor production or increasing aqueous humor outflow.
- Laser Surgery
Laser trabeculoplasty is a quick in-office procedure which uses laser energy to make tiny holes in the trabecular meshwork. The new holes allow for fluid to properly flow out of the trabecular meshwork again.
In cases of severe glaucoma, or when eye pressure is not controlled by eye drops and/or laser, surgery may be considered. Surgery typically creates an additional passage for aqueous humor.