Gonioscopy
Oscar V. Beaujon-Balbi
Oscar Beaujon-Rubin
INTRODUCTION
Gonioscopy is an examination of great importance for the evaluation, diagnosis, and treatment of the patient with glaucoma. Its main purpose is visualization of the configuration of the anterior chamber angle. Under normal circumstances, the structures of the anterior angle cannot be seen directly through the cornea because of the optical phenomenon known as total internal reflection. Briefly, this phenomenon refers to optical physics, whereby light that is reflected from the anterior chamber angle is bent internally within the cornea at the cornea-air interface. The gonioscopy lens (or goniolens) eliminates this effect by placing the lens-air interface at a different angle, making it possible to observe the light reflected from the structures of the angle.
Gonioscopy can be direct or indirect, depending on the lens employed, with a magnification of 15 to 20 times normal.
DIRECT GONIOSCOPY
• Direct gonioscopy refers to a “direct” view of the angle. A lens is used to overcome the internal reflectance of light in the cornea to allow visualization of the angle. Thus, one would examine the nasal angle by looking in the same direction; this is in contradistinction to looking at a mirror to examine the angle opposite to the mirror.
• The Koeppe lens is an example of a direct gonioscopy instrument (Fig. 4-1). It requires a magnification device (microscope) and a separate light source.
• The patient needs to be in a supine position.
• Direct gonioscopy lenses are often used in the operating room for angle surgery, such as goniotomy or ab interno trabeculotomy. At the present, we are using the Volk Trascend Vold Gonio Surgical Lens. This goniolens has a grassping ring that allows the surgeon to move the eye without tilting the patients head or microscope offering a clear view of the angle structures. Its has a floating lens with a image magnification of 1.2x and contact diameter of 9 mm (Fig. 4-2).
Advantages
• Direct gonioscopy is useful in patients with nystagmus and irregular corneas.
• Direct gonioscopy is useful for examination in children at the office under topical anesthesia. If necessary, they can be sedated, and the Koeppe lens allows examination of both the angle and the posterior pole.
• Direct gonioscopy allows a wide and panoramic evaluation of the angle that enables comparison between the different sectors and between both eyes if two lenses are placed simultaneously.
• Direct gonioscopy allows retroillumination, which is of great importance in differentiating congenital and acquired abnormalities of the angle (Fig. 4-3).
Disadvantages
• Direct gonioscopy requires that the patient be in the supine position.
• It is technically more difficult to perform.
• It requires a separate light source and magnification device (microscopy) with less optic quality than the examination made at the slit lamp (Fig. 4-4).
 FIGURE 4-1. Direct gonioscopy instruments. A. Direct gonioscopy. B. Koeppe lens. |
 FIGURE 4-2. Transcend Volk Gonio (TVG) goniolens. Its grasping outer ring allows the surgeon to move the eye with minimal movement of the patient’s head or microscope tilting. A. Placement of grasping platform of 15 mm diameter at limbus. B. Movement of the goniolens with handle. C. Visualization of the angle structures. |
 FIGURE 4-3. Retroillumination. Retroillumination with the Koeppe lens. A. Light reflection from angle structures B. Internal corneal scattering of light. |
 FIGURE 4-4. Barkan’s device. Barkan’s optical and illumination device. |
INDIRECT GONIOSCOPY
• The angle is visualized with a lens that has one or more mirrors, allowing the evaluation of the structures opposite to the mirror employed. For evaluating the nasal quadrant, the mirror is placed temporally, but the superior and inferior orientation of the image is maintained. The examination is performed using the slit lamp.
• Since the introduction of Goldmann’s indirect concept with the one-mirror goniolens, multiple lenses have been developed (Table 4-1).
Lenses are available with two mirrors that enable examination of all quadrants with rotation of 90 degrees of the lens. Other lenses, with four mirrors, allow evaluation of the entire angle without rotation.
The Goldmann and similar lenses have a contact surface with a curvature radius and diameter higher than the cornea, requiring the use of a viscous coupling substance. Zeiss and similar lenses do not require any coupling substance, because the radius of curvature is similar to that of the anterior cornea. These lenses also have a smaller contact surface diameter, and the tear film fills the cornea-lens space (Fig. 4-5).
• Proper selection of the type of goniolens is crucial to perform an effective gonioscopy. To aid this selection, some aspects should be considered. Without using a goniolens, the anterior chamber depth can first be estimated using the van Herick-Shaffer method. If a wide-open angle is suspected, any lens could be employed because there is no element that would prevent visualization of the angle (Fig. 4-6).
• If a shallow angle is suspected, it is preferable to use a one- or two-mirror Goldmann or a Zeiss lens. The mirrors of these goniolenses are higher and closer to the center, enabling visualization of the structures that would be otherwise occluded by the anterior displacement of the lens-iris diaphragm.
To better explain this concept, see Figure 4-7. Imagine an observer standing at point A who wants to see a house that is situated behind a hill. The hill in this example resembles the iris convexity. To solve the problem, the observer could go to a higher point, B, that enables him to see the house, or move closer to the center (top of the hill), point A′, or even better, go to point B′, which allows complete observation of the house and surrounding elements.
TABLE 4-1. Characteristics of Goniolenses | ||||||||||||||||||||||||||||||||||||||||||
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 FIGURE 4-5. Types of goniolenses. A. Indirect gonioscopy using a Goldmann one-mirror lens. B. Zeiss four-mirror type of indirect goniolens, which uses a handle. C. Sussman four-mirror type of indirect goniolens, which is handheld. |
 FIGURE 4-6. Diagram of an open-angle configuration. This figure shows that with an open angle, you can view any object in a reflective mirror, regardless of the height or distance from the center, because you do not have any interference. |
 FIGURE 4-7. Observer and obstacle. This figure shows that when there is an obstruction in this example, the hill in part A, resembling the convex iris of a narrow angle with gonioscopy. In this case is better to be higher as B that allows to see the tree but not the person or closer as A’or closer and higher as B’. In part B, letters A, B, C and D shows the structures saw with the mirrow.; with gonioscopy, the convex iris of a narrow angle, it is better to be higher and closer to the center. This is analogous to using a goniolens whose mirrors are higher and closer to the center. |
ESTIMATING THE ANTERIOR CHAMBER DEPTH
• Before evaluating the anterior chamber angle configuration, the van Herick-Shaffer technique is used to estimate the anterior angle depth. The procedure is performed while evaluating the patient with the slit lamp. With the thinnest slit beam possible, the cornea is illuminated perpendicularly near the temporal limbus (creating an optical section) and viewed at 50 to 60 degrees from the slit incidence. To estimate the anterior chamber depth, the ratio between the cornea-iris distance and the corneal thickness is observed.
• The angle can be graded as follows:
Grade 0 (closed)—when the iris is contacting the corneal endothelium
Grade I—when the space between the iris and the cornea is less than 25% of corneal thickness
Grade II—when the space is 25%
Grade III—when it is 25% to 50%
Grade IV—when it is higher than 50%
• This technique does not substitute gonioscopy, but it can be of great help in estimating the amplitude of the anterior chamber, especially in patients with opacities or cloudy corneas.
 FIGURE 4-8. Van Herick’s technique for angle depth estimation. A. Schematic showing proper placement of the slit beam; magnified view shows that the depth of the anterior chamber (AC) (black) is greater than 50% of the corneal slit beam (white), estimating a wide angle. B. Demonstration of the preceding placement in a live patient. In this example, the AC depth is approximately 90% of the corneal slit beam. C. Schematic showing proper placement of the slit beam; magnified view shows that the AC depth (black) is less than 50% of the corneal slit beam (white), estimating a narrow angle. D. Demonstration of the preceding placement in a live patient. In this example, the AC depth is approximately 10% to 15% of the corneal slit beam. |
ANTERIOR SEGMENT IMAGING
• The use of imaging devices, such as ultrasound biomicroscopy (UBM) and optical coherence tomography (OCT), has been of great help to evaluate the angle configuration. Both technologies allow the observer to measure the angle amplitude and offer details and relation of structures. The UBM is crucial in iris plateau diagnosis and cases of corneal edema or opacities, for example, before keratoplasty (Fig. 4-9). Even in the presence of high quality and magnification of the images, gonioscopy is still needed. These technologies should be used as complementary tests (Fig. 4-10).
 FIGURE 4-9. Optical coherence tomography on a 60-year-old woman with an occludable angle configuration. A. Arrow shows the area studied and magnified in B. B. Note apposition of the iris to the trabecular meshwork. C. Arrow shows the same area studied after laser. D. Note the widening of the angle between the iris and the peripheral cornea. |
 FIGURE 4-10. A 65-year-old woman with bullous keratopathy secondary to angle-closure glaucoma. A. Corneal fibrosis with vascularization obscures the view. In this case, gonioscopy is not suitable. B. Nasal angle closed by optical coherence tomography. C. Same angle closed as demonstrated by ultrasonic biomicroscopy. |
TECHNIQUE
• A drop of anesthetic is administered to both eyes, and the examination is performed at the slit lamp. Depending on the lens employed, a viscous coupling substance may be required. The goniolens must be placed gently on the eye, while trying to avoid distortion of the intraocular elements (Figs. 4-11 and 4-12). To obtain a good view of the angle, the incidence of the light beam must be perpendicular to the mirror of the goniolens.
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