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INDICATIONS
Gonioscopy is indicated prior to pillary dilation when the anterior chamber angle appears narrow (less than 1/4:1 ) by the van Herick slit lamp estimation technique. Other indications include glaucoma or suspected glaucoma, any condition that predisposes the patient to iris neovascularization, syndromes associated with glaucoma (eg, pigment dispersion or pseudoexfoliation), history of blunt trauma, and suspicious iris lesions.
EQUIPMENT
·Goldmann 3-mirror lens, cleaned and disinfected.
·Biomicroscope.
·Gonioscopy fluid (1% or 2% methylcellulose).
·Topical anesthetic (0.5% proparacaine).
·Sterile saline irrigating solution.
Note: Numerous indirect (mirrored) gonioscopic lenses are available, varying in size, shape, and number of mirrors. The Goldmann 3-mirror lens is commonly used because it is versatile, allowing for observation of the entire retina as well as the anterior chamber angle. The procedure described here assumes use of the 3-mirror lens but, with minor modifications, will apply to all indirect goniolenses.
SET-UP
·Adjust the slit lamp so it is comfortable for both the patient and the examiner.
·Focus the oculars, set the PD, remove all filters, and set the magnification on the lowest setting.
·Adjust the slit beam to a medium width parallelepiped and set the illumination arm of the biomicroscope in the straight ahead position (zero degrees).
·Prepare the gonioscopy lens by filling the concave face of the lens with 2 to 3 drops of gonioscopy fluid. Take care to avoid bubbles in the solution. The first drop from the bottle should be dropped onto a tissue. The bottle should be stored side down.
·Scan the anterior segment of the patient’s eye with the biomicroscope to rule out conditions that would contraindicate gonioscopy, such as, severe corneal trauma or a red eye of infectious etiology.
·Instill a single drop of a topical anesthetic in the eye to be examined.
STEP-BY-STEP PROCEDURE
INSERTION OF THE GONIOSCOPY LENS
1. Position the patient in the slit lamp. It is helpful to lower the chin rest slightly, so the patient’s lateral canthus falls slightly below the alignment mark. This ensures that the slit beam can reach the gonioscopy mirror when the mirror is in the serior position.
2. Holding the gonioscopy lens in your dominant hand between your thumb and index finger, instruct the patient to look down. Grasp the patient’s per lid firmly with your nondominant hand.
3. Instruct the patient to look and pull down the patient’s lower lid with the middle or fourth finger of the hand holding the lens. At the same time, firmly hold his per lid against the serior rim of his orbit.
4. Insert the lower edge of the lens into the inferior cul-de-sac (see Figure 5-16). Rotate the lens ward until the entire lens is firmly in contact with the globe as shown in Figure 5-17. Look through the central lens of the Goldmann 3-mirror to tell when the lens is in contact with the globe.
5. Instruct the patient to slowly look down until he is fixating straight ahead. Slowly release the patient’s lids. Continue holding the lens throughout the entire procedure, but do not push the lens forward against the patient’s cornea.
OBSERVATION OF THE ANTERIOR CHAMBER ANGLE
6. Rotate the lens until the gonioscopy mirror (the thumbnail shaped mirror) is located in the 12 o'clock position. This permits you to observe the inferior angle first. The inferior angle is usually the most open and the most pigmented, so it is easier to identify the angle structures.
7. Looking outside the oculars, position the vertical slit beam in the gonioscopy mirror.
8. Look through the oculars and focus on the angle structures. Once the angle is in focus, increase the width of the slit beam or increase the magnification to enhance your view. If glare from the mirror or lens surface interferes with your view, it can be eliminated by altering the angle of the illumination arm slightly (5 to 10°).
9. Begin eva luation of the anterior chamber angle at the pil. Glance across the iris, noting any elevations or abnormalities. Note where the iris inserts. This is the posterior border of the anterior chamber angle. Identify the structures visible in the angle and note any unusual or abnormal findings (see Figure 5-18).
10. If you have difficulty identifying the structures, narrow your beam to an optic section and increase the angle of the illumination arm to approximately 20°. The beam should appear as two focal lines along the corneal dome, intersecting and merging into one at Schwalbe's line as shown in Figure 5-19. Because Schwalbe's line is actually a ledge, you should also appreciate that the optic section curves out slightly as it passes over this structure.
11. Rotate the lens 90°to observe one of the lateral angles. Use two hands to rotate the lens. One is used to hold the lens firmly against the globe to maintain contact, and the other turns the lens.
12. Rotate the slit beam to the horizontal position and repeat steps 7 through 9.
13. Rotate the lens two more times, turning it 90°each time, to observe the entire 360°angle. Each time the lens is rotated, the slit beam is also rotated to correspond to the position of the mirror. The beam should be oriented vertically when the mirror is in the serior or inferior positions and oriented horizontally when the mirror is in the nasal or temporal positions.
REMOVAL OF THE GONIOSCOPY LENS
14. Remind the patient to keep his forehead pressed firmly against the forehead rest, and instruct him to look slowly.
15. Hold the lens loosely with one hand. With the index finger of your other hand, apply firm pressure against the lower lid at the edge of the lens to break the suction between the lens and the cornea. Do not pull the lens forward! If you have difficulty removing the lens, ask the patient to blink forcefully as you press against the lid. You may also try rocking the lens slightly or down (see Figure 5-20).
16. Wipe the gonioscopy solution from the lens with a tissue. The lens is cleaned with a nonabrasive rigid contact lens cleaner and disinfected following the Centers for Disease Control guidelines.
17. Gently irrigate the patient’s eye with sterile saline solution to remove residual gonioscopy solution which may cause irritation.
RECORDING
·Draw a large “×.” Each compartment within the × represents a quadrant of the angle.
·In each compartment, record the most posterior angle structure observed.
The following abbreviations are commonly used:
“CBB” ciliary body band
“SS” scleral spur
“TM” trabecular meshwork
“SL” Schwalbe's line
Systems are available that grade the angle from 0 to 4 based on the openness of the angle. However, these grading systems are not standardized and can be confusing.
·Unusual or abnormal findings are also recorded for each quadrant. Pigmentation of the trabecular meshwork is usually graded on a scale of 0 to 4, where 0 is no pigment and 4 is darkly pigmented.
·Remember that your view through the gonioscopy mirror is reversed. Recording should be anatomically correct.
EXAMPLE
An example of recording the findings of gonioscopy is shown in Figure 5-21.
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