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Fundamentals of Gonioscopy
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.
A. B. C.
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.
Figure 3 shows exfoliative material on the lens capsule in a patient with exfoliation syndrome.
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 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).
Figure 4 demonstrates the ability with gonioscopy to appreciate elevation of iris abnormalities such as this iris cyst.
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.
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 shows a patient with diabetic retinopathy. Due to the retinal ischemia this person is at risk for neovascularization in the anterior chamber angle.
Contraindications and Relative Contraindication to Performing Gonioscopy:
There are many conditions that require that gonioscopy be performed. There are not many situations when gonioscopy should not be performed. However, if there is a worry that the patient may have lacerated or perforated the globe, gonioscopy should not be performed (See Figure 6). Putting pressure on the eye in this situation will cause aqueous to drain from the eye.
Figure 6 shows a patient with a recent corneal laceration.
Performing gonioscopy on a patient with a fresh hyphema can cause a rebleed (See Figure 7). If possible, wait a couple weeks after the hyphema has cleared to perform gonioscopy. It is important to perform gonioscopy on these patients once the eye has healed because it is common for these patients to have angle recession or other damage to the anterior chamber angle.
Figure 7 shows a patient with a hyphema. (Image from http://opt.pacificu.edu/ce/catalog/13890-AS/SteroidsAnc.html)
For patients with corneal or conjunctival surface disease such as herpes simplex keratitis or epidemic keratoconjunctivitis it is important to determine whether obtaining a view of the anterior chamber angle warrants the risk of damaging the already weakened corneal epithelium (See Figure 8). Epithelial basement membrane dystrophy also weakens the corneal epithelial attachment. It is, therefore, important to be aware of the amount of movement made with the gonioscopy lens on the cornea. Also, minimize the number of anesthetic drops you use in these patients since topical anesthetic tends to further soften the corneal epithelium.
Figure 8 shows a patient with a viral conjunctivitis.
Anterior Chamber Anatomy:
An understanding of what a normal anterior chamber angle looks like is essential to differentiating normal angle structures from abnormalities of the angle. When you first look at the anterior chamber angle it may be difficult to determine what you are seeing. Orient yourself by finding the pupil. Then follow the iris out to the ciliary body (See Figure 9A). Although the color of the ciliary body will vary depending on the color of the iris, the ciliary body will be darker in color than the iris. People with brown irises will have a dark brown ciliary body. The ciliary body may be a light brown or gray color in patient with lighter irises.
Figure 9 shows the anatomical structures of a normal anterior chamber angle: ciliary body (A), scleral spur (B), trabecular meshwork (C), and Schwalbe’s line (D).
Moving anteriorly, the next structure seen is the scleral spur (See Figure 9B). The scleral spur will be bright white because it is a projection of scleral tissue. There is little variation in the coloration of the scleral spur making this a good landmark to determine which structures are visible.
The trabecular meshwork is adjacent to the scleral spur (See Figure 9C). The trabecular meshwork can also be whitish-gray color; however, the coloration is not as bright white as the scleral spur. The trabecular meshwork will often appear gray or pink and has a meshy appearance. If there is pigment in the trabecular meshwork, the trabecular meshwork will appear to have two distinct layers as seen in Figure 9. Because the majority of aqueous is filtered through the posterior portion of the trabecular meshwork, the more posterior layer, closer to the iris, will be more pigmented. The anterior trabecular meshwork will often remain a gray or light brown color because it does not filter as much aqueous and, therefore, as much pigment or other elements in the aqueous.
Schwalbe’s line is the termination of Descemet’s membrane. It indicates the anterior border of the angle (See Figure 9D). In some patients it is not easy to identify, but you may see a white ridge in other patients. Occasionally pigment will deposit on this ridge and Schwalbe’s line will appear pigmented as seen in Figure 9. The area anterior to Schwalbe’s line is reflections off the cornea.
Figure 10 shows another normal anterior chamber angle. Again, begin by orienting yourself by finding the pupil. In this case, the iris has a concave appearance producing a very deep angle. The scleral spur is very prominent. This patient does not have much pigment in the trabecular meshwork so it does not appear to have two distinct layers. It is difficult to identify Schwalbe’s line in this patient, but it is assumed to be where the trabecular meshwork ends.
Figure 10 shows the anatomical structures of a normal anterior chamber angle: ciliary body (A), scleral spur (B), and trabecular meshwork (C). Schwalbe’s line is difficult to identify in this patient. Iris processes are also present (D).
Iris processes are visible in the angle shown in Figure 10. Iris processes are found in 35% of normal eyes.6 They typically extend from the peripheral iris to the ciliary body or scleral spur. Occasionally the iris processes extend to the posterior aspect of the trabecular meshwork or Schwalbe’s line.
Figure 11 is an image of an angle in a patient with a dark iris. The ciliary body has a very dark appearance. The scleral spur is prominent, and the trabecular meshwork appears grayish-brown. Iris processes are prominent in this patient. The image in Figure 11 appears inverted compared to Figures 9 and 10 because it is the superior angle whereas the previous angles were views of the inferior angle.
Figure 11 is an image of a superior anterior chamber angle: Ciliary body (A), scleral spur (B), trabecular meshwork (C), and iris process (D). Schwalbe’s line is difficult to identify in this patient.
Figure 12 is a gonioscopy image of a patient with a lighter iris. The ciliary body is a light brown color followed by a bright white scleral spur. There are two distinct areas of the trabecular meshwork. Schwalbe’s line is pigmented.
Figure 12 is an inferior gonioscopy view of a patient with a light iris: Ciliary body (A), scleral spur (B), trabecular meshwork (C), and Schwalbe’s line (D).