Monday, August 28, 2006

Section 6-C: The drainage angle

Examination of the drainage angle is referred to as gonioscopy. The drainage angle is examined to determine if it is open or closed. To visualize the angle, an anesthetic eye-drop is applied to the eye and a special contact lens (gonioscopy lens, Figure 6-8) is placed against the cornea (Figure 6-9). This lens allows an examiner to see into the drainage angle using a slit lamp biomicroscope. This examination is usually painless; however, the anesthetic drop may cause a minor burning sensation that lasts a few seconds.



Figure 6-8. A Posner Gonioscopy contact lens. The smooth surface of this contact lens is placed against the cornea to allow the examiner to see the drainage angle.
Figure 6-9. Gonioscopy. An examiner gently places the gonioscopy lens (arrow) against the cornea and examines the eye with a slit lamp biomicroscope.



The goal of gonioscopy is to visualize the structures of the drainage angle including the trabecular meshwork (see Chapter 3). Fluid exits the eye through the drainage angle by passing through the trabecular meshwork. If the trabecular meshwork can be seen the drainage angle is said to be open. If the drainage angle is obstructed and the trabecular meshwork cannot be visualized, the angle is said to be closed.


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