Gonioscopy

From EyeWiki


History

  • Alexios Trantas first used the word “gonioscopy”, from the Greek origins on gonia meaning “angle” and skopein to “observe”.
  • He described the anterior chamber angle using a direct ophthalmoscope and simultaneous digital pressure on the limbal region.
  • Years later Maximilian Salzmann would be the first to use a contact lens and indirect gonioscopy for examination of the angle. Both are regarded as the “fathers of gonioscopy”. [1]
  • There are many great resources available for learning gonioscopy. The website www.gonioscopy.org is a recommended starting point with excellent videos and narration.[2]

How to Perform Gonioscopy

  • Gonioscopy is usually performed at the slit lamp.
  • It can also be used during examination under anesthesia in children and also in glaucoma surgery.
  • With the increasing emphasis on Micro-invasive Glaucoma Surgery (MIGS), intraoperative gonioscopy has become even more frequent.
  • Gonioscopy should be performed in a relatively dark room. A brightly lit room will constrict the pupil, opening the angle, and possibly missing ITC and apposition. Likewise, a shorter and less bright slit beam should also be used.

Lenses

  • Gonioscopy is required to visualize the chamber angle because under normal conditions light from the angle structures undergoes total internal reflection at the tear-air interface.
  • To overcome this, a lens must be placed against the eye.
  • Depending on the type of lens used, the angle can be examined either directly or indirectly.

Direct gonioscopy

  • Allows for direct visualization of the chamber angle. Examples of direct goniolenses include Koeppe, Barkan, Wurst, Swan-Jacob, or Richardson lenses.
  • During direct gonioscopy, the viewer has an erect view of the angle structures.
  • Direct gonioscopy is most easily performed with the patient supine and in the operating room for an exam under anesthesia or a MIGS procedure.

Indirect gonioscopy

  • More commonly used in the clinic setting. Examples of indirect gonioscopy lenses include the Posner, Sussman, Zeiss, and Goldmann lenses.
  • The viewer in indirect gonioscopy will have an inverted and slightly foreshortened image of the opposite angle because the light from the angle is reflected off of a mirror and directed towards the viewer.
  • The Posner, Sussman, and Zeiss lenses have a smaller area of contact than the Goldmann-type lenses, and allow the examiner to apply pressure to the cornea, which may cause Descemet’s membrane folds, and falsely open the angle. This also allows the examiner deepen the angle, which is discussed more below in the dynamic gonioscopy section.
  • The Goldmann lens does not allow for this indentation because of the size of the lens. [3]

Procedure

Indirect Gonioscopy

  • As with any procedure, the patient and the examiner must be positioned in a comfortable fashion.
  • A drop of topical anesthetic is then applied to the conjunctiva of both eyes.
  • If using the Goldmann lens, contact gel is placed in the concave part of the lens.
  • If using a Posner or similar type lens, a drop of artificial tears can be placed on the concave surface.
  • The patient is then asked to open both eyes and look upwards.
  • The examiner can then pull down slightly on the lower lid and places the lens on the surface of the eye.
  • The patient is then asked to look straight ahead.
  • Most examiners choose to start with the inferior angle as it is usually a bit more open, and the pigmentation of the trabecular meshwork is slightly more prominent, allowing for easier identification of the angle structures.
  • Continue identifying all angle structures in all 4 quadrants, and then repeat with the other eye.

Dynamic Gonioscopy

  • In eyes with a closed angle, one must distinguish between an anatomically closed angle with iridotrabecular contact (ITC, apposition) and peripheral anterior synechiae (PAS).
  • To perform dynamic or compression gonioscopy, you will need to be using either the Posner, Sussman, or Zeiss style lens.
  • The patient is positioned as noted above. Gentle pressure is placed on the cornea, and aqueous humor is forced into the chamber angle.
  • If there is ITC or apposition, the angle will open and the structures should become more visible.
  • If PAS is present, the angle will stay the same in the affected areas. Examine all areas of the angle and repeat on the other eye.

Direct Gonioscopy

  • Direct gonioscopy is most easily performed with the patient in a supine position and is commonly used in the operating room for examination of the eyes of infants under anesthesia.
  • It can be performed using a direct goniolens and either a binocular microscope or a slit-pen light.
  • Examples of direct goniolenses include Koeppe, Barkan, Wurst, Swan-Jacob, or Richardson lenses.
  • The lens is positioned after saline or viscoelastic is placed on the eye, which can act as a coupling device.
  • The lens provides direct visualization of the chamber angle (ie, light reflected directly from the chamber angle is visualized) in an erect position.
  • This is essential for performing goniotomies or other angle-based surgeries, including MIGS.

Anatomical Structures of the Normal Angle

The most important part of gonioscopy is identification of the anatomical landmarks. There are also many normal variations that one must be aware of. A clinician must possess this knowledge in order to properly manage his or her patients. We will discuss these below, moving from most anterior to posterior.

Schwalbe’s Line

  • Schwalbe’s line is a condensation of collagen tissue and notes the edge of Descemet’s membrane.
  • It is an important landmark to identify because normal vessels and tissue will not cross it. Neovascularization or PAS may pass Schwalbe’s line anteriorly.
  • A prominent Schwalbe’s line is also called a “posterior embryotoxon” and can be found in normal individuals. There is no increased risk of glaucoma in these eyes.
  • An important technique in identifying Schwalbe’s line is the corneal light wedge, which allows the observer to determine the exact junction of the cornea and trabecular meshwork.
    • To perform this technique, the examiner must use a narrow slit beam. They will see 2 reflections, one on the external surface of the cornea and the other on the internal surface indicating the corneal epithelium and endothelium, respectively. They will meet at Schwalbe’s line making it easier to identify the important landmarks.

Trabecular Meshwork

The trabecular meshwork is a very important landmark for diagnostic purposes, incisional surgery, and laser surgery. The amount of pigmentation may vary from person to person, and even from quadrant to quadrant as noted above. The amount of pigmentation should be included in the grading of an angle

Schlemm’s Canal

Schlemm’s canal drains the aqueous humor after passing through the trabecular meshwork. It is only visible when there is blood in the canal. It is an important structure as many surgical procedures target this area, especially many of the new MIGS devices.

Scleral Spur

The scleral spur is made up of a ridge of collagen tissue. This is noted by its white color during gonioscopy. Identifying this structure helps to differentiate open angles from closed angles. It is possible for the scleral spur to be covered by small sharp-ended iris processes that reach up to the trabecular meshwork. They do not cross the trabecular meshwork and have no pathologic consequence.

Ciliary Muscle Band

The anterior ciliary body band can be seen in eyes with deeper angles. It represents the longitudinal fibers of the cilary muscle. This is the site of nonconventional or suprachoroidal outflow and is also a landmark for newer surgical procedures.

Iris Root and Iris

The insertion of the iris is an important part of the classification of angle anatomy. The configuration of the peripheral iris is also important to note when studying angle structures. Pathology that exists in this part of the angle includes ITC or apposition and PAS, which should be noted.

Grading Systems

Gonioscopy grading systems were established to provide a standardized description of the anatomy of the anterior chamber angle. There are many grading systems used today. We will discuss them below.

Scheie

The Scheie system is based upon visibility of the anatomical structures of the angle. They are graded Wide through IV, with Wide being the most open. See Table 1 for an in depth description of the Scheie system.

Table 1. The Scheie Classification System
Grade Visibility Interpretation
Wide Wide Open, all structures visible
I Slightly Narrowed Ciliary body visible, but recess obscured by the last roll of the iris
II Apex not visible Ciliary body not visible
III Posterior half of trabecular meshwork not visible Ciliary body, scleral spur, and posterior half of the trabecular meshwork not visible
IV None of the angle structures visible Cliary body, scleral spur, and trabecular meshwok not visible

Shaffer

The Shaffer system is based on angularity. It also uses a number system, but is in reverse of the Scheie system. For example, a Grade 4 angle in the Shaffer system is wide open, while a Grade IV in the Scheie system is anatomically closed with no structures visible! See Table 2 for detailed description of the the Shaffer classification system.

Table 2. The Shaffer Classification System
Angular Grade Width (in degrees) Grade Clinical Interpretation
Wide Open Angle 45-35 4 Angle closure impossible in both Grades 3 and 4
35-20 3
Narrow Angle 20 2 Angle closure possible
Narrow Angle, extreme 10 or less 1 Angle closure probable, eventually
Narrow Angle, slit Critically narrowed angle, quite possibly against the trabecular meshwork beyond Schwalbe’s line - -
Narrow angle, partial or complete closure 0 0 Angle closed in part or all of circumference

Spaeth

The Spaeth system is much more complex and describes each detail of the anatomic angle. This system describes the iris insertion, angularity, configuration, and pigmentation of the posterior trabecular meshwork. We will illustrate this detailed description below.

Iris Insertion

Designated by letter A-E. A is anterior to Schwalbe’s line, B is between Schwalbe’s and the scleral spur, C is at the scleral spur, D is deep, E is extremely deep.

Iris Angularity

The angle of the iris is defined as the angle between two lines. The first line is parallel to the trabecular meshwork and the second a tangent to the anterior iris surface approximately 1/3 of the distance from the most peripheral portion of the iris. It is usually noted between 10 and 40 degrees.

Iris Configuration

This is named for the configuration or shape of the iris as it runs from the papillary margin to the insertion. S is for steep, B for bowing anteriorly, P for plateau, R or F for regular or flat, respectively, and C for concave posteriorly.

Pigmentation

This is graded on a 0 to 4 scale noting the amount of pigmentation in the posterior trabecular meshwork.

The Spaeth system also takes into account dynamic or compressive gonioscopy. If a letter is in parentheses, this means it is the originally viewed insertion prior to compression. It is then followed by a letter without parentheses, which denotes the insertion after compression. An example is (B)D30P1. This is an angle that is thought to have an iris insertion between Schwalbe’s line and the scleral spur. After compression, it is noted that the insertion is deep, with an angle of 30 degrees and a plateau configuration with grade 1 pigmentation of the trabecular meshwork.

Becker

The Becker classification focuses on the amount of trabecular meshwork present and the distance between the scleral spur and the insertion of the iris. Numbers (0-3) are used to describe how much trabecular meshwork is present. Letters (A-C) are used to describe the level of iris insertion. Table 3 shows the details of this system.

Table 3. The Becker Classification System

0 1 2 3
0 Angle closed Small trabecular zone, iris insertion not visible Average width of trabecular zone, iris insertion not visible Broad trabecular zone, iris insertion not visible
1 Small trabecular zone, iris insertion anteriorly Average width of trabecular zone, iris insertion anteriorly Broad trabecular zone, iris insertion anteriorly
2 Small trabecular zone, iris insertion in the middle Average width of trabecular zone, iris insertion in the middle Broad trabecular zone, iris insertion in the middle
3 Small trabecular zone, iris insertion posteriorly Average width of trabecular zone, iris insertion posteriorly Broad trabecular zone, iris insertion posteriorly

Shaffer-Kanski

This system is based on the width of the angle as previously described in the Shaffer system and the risk of angle closure. See Table 4.

Grade Angle (°) Visiblity of structures Risk of angle closure
0 0 No structures visible Closed angle
1 10 Schwalbe’s line, possibly anterior trabecular meshwork visible Closure possible
2 20 Schwalbe’s line and trabecular meshwork visible Narrow, closure unlikely
3 320-35 Schwalbe’s line, trabecular meshwork and scleral spur visible Closure impossible
4 35-45 All structures visible from Schwalbe’s line to ciliary band Closure impossible
Table 4. The Shaffer-Kanski classification system

Van Herick

This is a non-gonioscopic grading system. It uses an estimation of the peripheral anterior chamber depth. It is done at the slit lamp and is most helpful before dilation. A thin slit beam is angled approximately 60 degrees and aimed at the cornea peripherally near the limbus. The corneal thicknes is compared to the anterior chamber depth. The ratio is then used to provide some information on the width of the chamber angle. Because it is done without gonioscopy, no angel structures can be identified and it does not replace gonioscopy. See Table 5.

Grade Cornea: Peripheral anterior chamber ratio Risk of angle closure Angle (°)
4 1:1 or higher Very unlikely or impossible 35-40
3 1:1/2 Unlikely or improbable 20-35
2 1:1/4 Possible 20
1 1:<1/4 Likely or probably 10
0 No anterior chamber slit visible Closed 0
Table 5. Van Herick classification system

Documentation

Proper documentation is important so that you are able to follow patients over time and so that other may interpret your findings. Both written documentation and drawings are acceptable ways of communicating findings. You can use any of the above mentioned classification systems or any drawing tool that is available in your charting system, whether they are paper or electronic.

Other Uses of Gonioscopy

As discussed above, gonioscopy is extremely useful in determining how open or narrow an angle is and the possibility of it becoming closed. There are also many other indications and uses for gonioscopy. Knowing the anatomy described above will help with identifying any pathology that may be present. Blood in Schlemm’s canal can be seen in patients with increased episcleral venous pressure such as carotid cavernous fistulas. It can also be present with hypotony. The formation of peripheral anterior synechiae and the identification of this is extremely important. Depending on the severity, this can decide a treatment approach or indication for a peripheral laser iridotomy. Neovascularization may be noted in patients with uncontrolled diabetes or a history of central retinal vein occlusions. There are other conditions that may cause neovascularization as well. Other findings that can be visible with gonioscopy include hyphemas and microhyphemas. Foreign bodies can also be found on gonioscopy. The extent of iris or uveal tumors can be evaluated. Iridodialysis or other damage to angle structures can also be noted after a history of trauma.

As you can see, the importance of gonioscopy cannot be understated and should be used routinely for evaluation and diagnosis many different ophthalmologic conditions. It is a valuable skill that should be used by all ophthalmologists, not just glaucoma specialists. In a recent study, only 45% of patients had received gonioscopy within either 12 months prior or 6 months following the initial diagnosis of POAG (Arch Ophthalmology 2003; 121:777-783)[4]

Additional Resources

References

  1. Faschinger, C; Hommer, A. Gonioscopy. Springer. Heidelberg.
  2. www.gonioscopy.org
  3. 2012 BCSC Glaucoma page 38-42
  4. Arch Ophthalmology 2003; 121:777-783