Anterior Chamber Aqueous and Angle

The anterior chamber of the eye is filled with a clear fluid called aqueous. The normal anterior chamber is optically empty.

The aqueous that fills the anterior chamber is constantly being formed and drained out. The aqueous drainage area is found in the angle, the area formed where the posterior corneal surface meets the anterior iris root. (The angle itself cannot be viewed directly unless a gonio lens is used.) This dynamic creates a pressure within the eye, the IOP. Average IOP is around 15, ranging from 8 to 21. (Opinions vary as to what is normal.) IOP is measured using a tonometer, which may be attached to the slit lamp. If the IOP is abnormally high and continues to be high, the optic nerve may be damaged, which, in turn, can reduce the visual field. This condition is called glaucoma.

OphA

OptA

OptT

Anterior 1 Posterior segment segment

Anterior 1 Posterior segment segment

Anterior chamber

Anterior chamber

Figure 3-4. The anterior and posterior segments of the globe. (Reprinted with permission from Medical Sciences for the Ophthalmic Assistant, SLACK Incorporated.)

The depth of the anterior chamber is clinically significant. In a shallow chamber, the dilated iris may bunch up and block off the angle. This covers the aqueous drainage system, and the pressure of the stagnant (and continually forming) aqueous begins to build up. The pressure causes corneal edema (swelling that clouds the cornea), blurred vision (secondary to the edema), redness, pain, and optic nerve damage. This entire scenario is called angle closure glaucoma or a glaucoma attack. The likelihood of angle closure is related to the depth of the anterior chamber. If the chamber is deep, angle closure is unlikely to occur. Myopes, with their longer eyeballs, generally have a deep anterior chamber. The shorter eye of a hyperope is more likely to be shallow.

Estimating the depth of the anterior chamber is an important aspect of the slit lamp exam. To evaluate the chamber depth of the right eye, turn the lamp so that the light is coming at the temporal limbus at an angle of 60 degrees (Figure 3-5A). Change the slit to its most narrow setting, and direct the beam onto the cornea, just barely to the right of the limbus. You should see three things: the beam of light sharply focused on the cornea in a thin slit, the light falling on the iris (unfocused), and a dark interval in between (Figure 3-5B). The dark interval is the area of interest, as it represents the chamber's depth. If this shadow is one-quarter to one-half the width of the illuminated corneal section, the angle is open. If the dark section is less than one-quarter the width of the corneal beam, the chamber is narrow. If there is no dark interval (ie, the corneal and iris beams meet), the angle is extremely narrow or closed. The chamber is graded from 1 to 4 or labeled as closed, open, shallow, or moderate. (See Chapter 5 regarding subjective grading.) The nasal angle should be checked as well by swinging the beam to the right. The left eye is examined in the same way.

Documentation: anterior chamber deep and clear, angles open, grade 4

Figure 3-5A. Overhead schematic of angle estimation. (Drawing by Edmund Pett.)

Figure 3-5A. Overhead schematic of angle estimation. (Drawing by Edmund Pett.)

Slit Lamp Angle Estimation

Figure 3-5B. Straight-on view of estimating chamber depth with the slit lamp. (Reprinted with permission from Medical Sciences for the Ophthalmic Assistant, SLACK Incorporated.)

Dark Interval should be At least V, of the corneal thickness to establish an angle incapable of closure.

Dark Interval should be At least V, of the corneal thickness to establish an angle incapable of closure.

Open Angle Slit Lamp

A. Open B. Shallow angle angle

A. Open B. Shallow angle angle

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  • mildred theobald
    What is the normal angle for slit lamp eye?
    7 months ago
  • Filippa
    How to check the angle closure on slit lamp?
    5 months ago
  • carita
    How to PROPERLY check eye angles in the slit lamp?
    1 month ago

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