Section 3-B: Aqueous fluid production and drainage angle.
The cornea and the lens have no blood supply. They receive nourishment from nutrients in the aqueous fluid that fills the eye. The aqueous fluid is produced by the ciliary body, which is located behind the iris (Figure 3-2). The aqueous fluid enters the eye through the ciliary body and flows between the iris and lens through the pupil. The fluid passes out of the eye through a tissue called the trabecular meshwork, which is at the drainage angle (at the junction of the cornea and the iris). As the aqueous fluid passes through the eye, it supplies the lens and cornea with nutrients and carries away waste products.
Figure 3-2. Aqueous Fluid Flow in the Eye. The aqueous fluid that fills the eye is produced by the ciliary body and flows between the iris and lens, through the pupil and to the drainage angle at the junction of the iris and the cornea. Aqueous fluid exits the eye through a tissue called the trabecular meshwork in the drainage angle.
The pressure of the fluid in the eye (intraocular pressure) is determined by the amount of fluid entering the eye through the ciliary body and exiting the eye through the trabecular meshwork. In most people, the balance between the fluid coming in and going out of the eye results in an eye pressure between 10 and 21 mm of Hg. In patients with glaucoma, fluid drains from the eye through the trabecular meshwork at a slower rate causing the pressure in the eye to rise.
Eye doctors regularly examine the drainage angle to see if there is any visible obstruction to fluid leaving the eye through the trabecular meshwork. A special lens (gonioscopy lens) is needed to examine the trabecular meshwork (Figure 3-3A – 3-3B). The gonioscopy lens is gently placed against the surface of the cornea and allows eye doctors to see the trabecular meshwork in the drainage angle (Figure 3-3C).
There are two major types of glaucoma. In open-angle glaucoma, the drainage angle between the cornea and the iris is wide open and allows the aqueous fluid of the eye to make its way to the trabecular meshwork – the chief site for fluid drainage from the eye. In patients with open-angle glaucoma, abnormalities in the trabecular meshwork reduce the outflow of aqueous humor (Figure 3-4A). In angle closure glaucoma the trabecular meshwork is visibly obstructed and the aqueous humor is prevented from draining out of the eye (Figure 3-4B).
Figure 3-4. Open and closed drainage angles. A. The drainage angle formed between the cornea and the iris is wide open to about 40˚. Aqueous fluid flows freely to the trabecular meshwork and out of the eye. B. The drainage angle is closed. The iris and the cornea are in contact (*) and block the flow of aqueous fluid to the trabecular meshwork. The fluid is trapped in the eye causing intraocular pressure to rise.
Figure 3-2. Aqueous Fluid Flow in the Eye. The aqueous fluid that fills the eye is produced by the ciliary body and flows between the iris and lens, through the pupil and to the drainage angle at the junction of the iris and the cornea. Aqueous fluid exits the eye through a tissue called the trabecular meshwork in the drainage angle.
The pressure of the fluid in the eye (intraocular pressure) is determined by the amount of fluid entering the eye through the ciliary body and exiting the eye through the trabecular meshwork. In most people, the balance between the fluid coming in and going out of the eye results in an eye pressure between 10 and 21 mm of Hg. In patients with glaucoma, fluid drains from the eye through the trabecular meshwork at a slower rate causing the pressure in the eye to rise.
Eye doctors regularly examine the drainage angle to see if there is any visible obstruction to fluid leaving the eye through the trabecular meshwork. A special lens (gonioscopy lens) is needed to examine the trabecular meshwork (Figure 3-3A – 3-3B). The gonioscopy lens is gently placed against the surface of the cornea and allows eye doctors to see the trabecular meshwork in the drainage angle (Figure 3-3C).
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| Figure 3-3. Gonioscopy. A and B. The drainage angle is examined using a special lens (gonioscopy lens). C. The gonioscopy lens is gently held against the cornea. Eye doctors look through the gonioscopy lens to see the drainage angle. |  |
There are two major types of glaucoma. In open-angle glaucoma, the drainage angle between the cornea and the iris is wide open and allows the aqueous fluid of the eye to make its way to the trabecular meshwork – the chief site for fluid drainage from the eye. In patients with open-angle glaucoma, abnormalities in the trabecular meshwork reduce the outflow of aqueous humor (Figure 3-4A). In angle closure glaucoma the trabecular meshwork is visibly obstructed and the aqueous humor is prevented from draining out of the eye (Figure 3-4B).
Figure 3-4. Open and closed drainage angles. A. The drainage angle formed between the cornea and the iris is wide open to about 40˚. Aqueous fluid flows freely to the trabecular meshwork and out of the eye. B. The drainage angle is closed. The iris and the cornea are in contact (*) and block the flow of aqueous fluid to the trabecular meshwork. The fluid is trapped in the eye causing intraocular pressure to rise.
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