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Fundamentals of Gonioscopy
- Indications for Performing Gonioscopy
- Contraindications and Relative Contraindication to Performing Gonioscopy
- Anterior Chamber Anatomy
- Gonioscopy Lenses
- Gonioscopy Procedure
- Common Errors While Performing Gonioscopy
- Recording and Coding for Gonioscopy
- Anterior Chamber Angle Grading Considerations
- Common Gonioscopy Findings
There are several methods of recording gonioscopy findings. The following is a clinically useful way of recording information from the gonioscopy examination. Because it is descriptive, other practitioners that read your chart notes will be able to easily interpret the findings. See Figure 19 for an example of recording gonioscopy findings.
Each quadrant of an “X” represents one quadrant of the anterior chamber angle. For each quadrant a minimum of three features should be recorded. First, record the abbreviation of the most posterior structure that is visible: ciliary body (CB), scleral spur (SS), trabecular meshwork (TM), or Schwalbe’s line (SL). All structures that are anterior to that recorded can be assumed to be present. For example, if scleral spur is the most posterior structure seen in the superior quadrant, record SS in the superior quadrant. It is assumed that trabecular meshwork and Schwalbe’s line are also visible.
Second, it is important to make note of the pigment in the trabecular meshwork. The pigment is typically graded on a scale of 0 (no pigment in the trabecular meshwork) to 4 (extremely dense pigment in the trabecular meshwork).
Finally, the third item that needs to be recorded is the topography of the iris. Is should be documented whether the iris has a flat, convex, or concave appearance. In addition to these three features, it is also important to record any abnormalities seen within the anterior chamber angle.
Gonioscopy is not bundled with the office visit. This bilateral procedure should be billed with the following CPT code: 92020. Common billable diagnoses include all types of glaucoma except steroid induced glaucoma, potential angle-closure, pigment dispersion syndrome, central retinal artery occlusion, central retinal vein occlusion, uveitis, angle recession, rubeosis, anterior or posterior synechiae, diabetic retinopathy, neoplasm, retinal vasculitis, retinal detachment, and iris lesions. Proper documentation includes a diagram including angle structures, pigment in the trabecular meshwork, and other angle abnormalities.
The position of the gonioscopy lens, as well as the type of gonioscopy lens being used, can affect the appearance of the angle. In a patient with a convex iris, the angle may appear deeper when using a gonioscopy lens with a higher vantage point or angling the gonioscopy lens so light if reflected over the obstruction of the iris (See Figure 20).
As shown in Figure 20A the mirrors of the smaller 1 or 2-mirror gonioscopy lenses are closer to the apex of the cornea than the larger 3-mirror gonioscopy lenses. This causes the light to be reflected differently. A view with a bigger gonioscopy lens may be obstructed by a convex iris, whereas the angle may be visible when viewing through a more centrally placed mirror.
If a patient appears to have a closed angle, have the patient move their fixation to look in the direction of the mirror being observed. Alternatively, tilt the gonioscopy lens away from the observation mirror. This will permit the examiner to look over the convex iris into the anterior chamber angle (See Figure 20B). If anterior angle structures are visible following refixation, this indicates that the patient has a convex iris configuration rather than an appositionally closed angle. If additional structures are not visible after the patient refixates, the iris is in contact with the angle structures. Indentation gonioscopy should then be performed to determine if the iridotrabecular contact is appositional in nature or caused by anterior synechiae.
Pushing too hard with a non-suction gonioscopy lens will cause aqueous to move to the peripheral portion of the angle. This pushes the iris back causing the angle to appear wider than under normal conditions. This technique, indentation gonioscopy, can be useful if attempting to differentiate between appositional angle closure and synechiae in the anterior chamber.
When examining potentially narrow angles, the patients should be examined in a dark room with a narrow beam of light to minimize pupillary constriction and corresponding narrowing of the angle. The anterior chamber angle is significantly narrower in dark versus light due to peripheral iris thickening and the iris assuming a more convex configuration.Angle closure is also more likely to occur when a patient is in a dim environment such watching a movie at the theater. Dim illumination while performing gonioscopy increases the likelihood of correctly diagnosing a patient that is at risk for angle closure. In addition to angle closure, it is important to look for pigment in the trabecular meshwork, neovascularization of the angle, anterior synechiae, angle recession, and peripheral iris and ciliary abnormalities. These may be more easily seen if the pupil is smaller creating a wider view of the anterior chamber angle.