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Fundamentals of Gonioscopy
Denise Goodwin, OD, FAAO
Contents
- Introduction
- 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
- Conclusion
- References
- Exam
Introduction
Evaluating the anterior chamber angle with gonioscopy is an essential part of evaluating patients at risk for glaucoma and neovascularization. It is also useful for patients with iris abnormalities or a history of trauma or ocular inflammation. Unfortunately, gonioscopy is underutilized by both optometrists and ophthalmologists.[1,2] Coleman, et al. found that less than half of Medicare beneficiaries underwent gonioscopy during a 4-5 year period prior to glaucoma surgery.[3] It is critical to our patient’s ocular health that this change.
This article discusses the indications and contraindications to performing gonioscopy. Anterior chamber angle anatomy, types of gonioscopy lenses, a review of the procedure, and proper recording and insurance coding will also be covered. Finally, we will describe common variations of normal anterior chamber angles and angle abnormalities that are commonly seen in an eye care setting.
Indications for Performing Gonioscopy
There are many indications for performing gonioscopy. One of the most common reasons to do gonioscopy is if you suspect a patient is at risk for angle closure with pupil dilation.
The Van Herrick procedure is routinely used to estimate the depth of the anterior chamber and is a useful way to determine if gonioscopy is necessary prior to dilating the patient’s pupils. Van Herrick angle estimation is performed in the biomicroscope by creating a 60° separation between the illumination and the magnification arms. A narrow beam of light is placed at the peripheral edge of the cornea. The size of the shadow between the posterior cornea and the iris is then compared to the size of the optic section (See Figure 1). A shadow that is greater than ½ the width of the optic section is considered a grade 4. A shadow ¼ to ½ the size of the optic section is a grade 3. A shadow equal to ¼ of the optic section is a grade 2, and a shadow less than ¼ the size of the optic section is a grade 1. A grade of 3 or 4 with Van Herrick is considered safe for dilation. All patients with a Van Herrick grade 2 or less should have gonioscopy performed prior to dilation.
Another important indication for gonioscopy is to determine the cause of intraocular pressure (IOP) elevation. Gonioscopy should be performed on all patients that are suspected or known to have glaucoma. Gonioscopy is not only used to differentiate between open and closed angle glaucoma by determining the accessibility of the trabecular meshwork, it aids in determining the cause of open angle glaucoma.
Patients with pigment dispersion syndrome (PDS) are likely to have a posterior insertion of the iris root and a concave iris configuration causing increased contact between the posterior iris and the anterior zonules.[4] Contact with the zonules causes release of pigment from the posterior iris. The pigment is then deposited throughout the anterior segment. Transillumination in the midperipheral area of the iris, pigment on the posterior surface of the cornea (Krukenberg spindle), and increased pigment in the trabecular meshwork are hallmark sign of PDS (See Figure 2). Pigment in the trabecular meshwork causes a rise in IOP (pigmentary glaucoma) in as high as 25% of patients with PDS.[5] It is, therefore, critical that gonioscopy is performed in all patients with iris transillumination, pigment on the posterior cornea, or pigment on the anterior lens.
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Exfoliation syndrome can result in severe chronic open angle glaucoma. Here, abnormal fibrillar deposits are seen on anterior segment structures including the anterior lens capsule, pupillary margin, and trabecular meshwork (See Figure 3). It is important to perform gonioscopy in patients suspected of having exfoliation syndrome looking for evidence of the exfoliative material in the trabecular meshwork and along the pupil border. Patients with a history of blunt ocular trauma should be evaluated for evidence of angle recession, tears between the longitudinal and circular muscles of the ciliary body. It is also common to see pigmentation of the trabecular |
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meshwork and foreign bodies in the anterior chamber while performing gonioscopy on patients with a history of ocular trauma. Gonioscopy is a good way to examine abnormalities of the iris. The view with gonioscopy is as if you are looking at the iris while you are standing on the crystalline lens and sticking your head up through the pupil. Therefore, gonioscopy makes it very easy to see elevation of an iris lesion (See Figure 4). Patients with a history of ocular inflammation should have gonioscopy performed. Anterior synechiae and inflammatory debris in the trabecular meshwork can cause a rise in IOP. |
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Gonioscopy should be performed on all patients with a compromised vascular system. This includes conditions such as diabetes (See Figure 5), carotid artery disease, and a history of central retinal artery occlusion or central retinal vein occlusion. Neovascularization of the angle can cause severe glaucoma. It is critical that this is recognized and treated early.
Figure 5: |
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