Introduction to Gonioscopy

Gonioscopy is a valuable diagnostic technique for many clinical situations including evaluation of iris lesions such as nevi and determining the presence of neovascularization of the angle in patients with proliferative diabetic retinopathy or ischemic central retinal vein occlusion. Still, the most common use of gonioscopy is for the evaluation of glaucoma patients and suspects as well those with anatomically narrow angles.

Gonioscopy is indicated at least once during the initial glaucoma evaluation process and thereafter as indicated by the clinical circumstances. It is required to evaluate and document the angle as being open or closed. The common diagnosis of Primary Open Angle Glaucoma cannot be made without the information obtained with gonioscopy as well as forms of chronic angle closure may only be diagnosed with gonioscopy. Additionally, the diagnosis of various secondary causes of glaucoma or elevated intraocular pressure can be identified with gonioscopy. In spite of recommended practice guidelines such as those from the American Optometric Association, the European Glaucoma Society and the American Academy of Ophthalmology, gonioscopy is not routinely performed (Freemont et al). The object of this piece is to review the anatomy, technique and interpretation of this important technique with the goal of enhancing the clinician's comfort and utilization.

Review of Anatomy

The ciliary body band is that portion of the ciliary body visible anterior to the insertion of the iris. It is the most posterior structure in the normal angle. There is inter-individual variability in its width and color but is typically fairly uniform throughout the angle and symmetric between the two eyes. The scleral spur is a white structure anterior to the ciliary body. In cases of more anterior insertion of the iris it may be the most posterior structure visible. The trabecular meshwork is seen anterior to the scleral spur. This structure is responsible the majority of aqueous outflow. It may vary in degree of pigmentation. Anatomically there are three layers (uveal, corneoscleral, and juxtacanalicular). Clinically the trabecular meshwork can be divided into two layers (anterior or non-pigmented and posterior or pigmented). Aqueous flows through the posterior pigmented portion. Schlemm's canal is deep to the trabecular meshwork and may be visible if blood is present. Schwalbe's line is the most anterior structure in the anterior chamber angle. It may have variable prominence among individuals. In an eye where it is difficult to identify, the clinician may be aided by the corneal wedge technique (see Figure 1). A thin, sharply focused beam is directed obliquely across the iris into the angle. This beam will be single across the iris and up the angle wall but will split into a wedge of two beams, the apex of which rests on Schwalbe's line. Optimal focus of this wedge may be obtained by pulling back slightly from the optimal focus for the more posterior structures in the angle. Examples of when the precise identification of Schwalbe's line is critical will be discussed below.

Figure 1

Figure 1. Corneal wedge in gonioscopic view of angle. Reflections from inner and outer corneal surface can be seen coming together at Schwalbe's line (photo courtesy of M. Johnson).

Examination Technique

One of the keys to successful gonioscopy is that the clinician and patient be in a correct and comfortable position. The hints offered in this section are meant as suggestions. Individuals will investigate and adapt techniques that work best in their hands in the various clinical circumstances they encounter. This author prefers the four-mirror type lenses. While they present a greater initial challenge to developing proficiency, these lenses are more convenient and allow for a more dynamic examination. Clinicians are encouraged to use the lenses with which they are most comfortable as all types provide useful information.

Figure 2

Figure 2. Posner-type four mirror (front) and Magnaview (rear) goniolenses. The Posner lens has the advantage that it can be used without coupling solution and may be used for rapid indentation gonioscopy. Although the Magnaview lens requires coupling solution, this lens has the advantage of providing a high level of magnification.

Most three-mirror type lenses require a coupling agent such as goniosolution or a thick methylcellulose tear preparation. The patient is often in position in the slit lamp when the lens is placed on the eye by the doctor outside the slit lamp. The doctor then approaches the oculars of the slit lamp while holding the lens and proceeds with the exam. The four-mirror type lenses can be gently brought into contact with the precorneal tear film under direct visualization in the slit lamp. No coupling agent is required although many clinicians will use an artificial tear preparation on the lens as additional protection for the corneal epithelium. This may be particularly prudent in patients with dry eyes or blepharitis. Stability of views is essential and is best accomplished if the doctorss arm and hand holding the lens are supported. Many clinicians will support the arm with a tissue box or a case for their fundus lenses. Additional stability is achieved by allowing the fingers of the hand holding the goniolens to gently rest on the patientss cheek or temporal orbital rim. The angle is then examined in a systematic fashion. For example, each time the order would be the same, superior, inferior, nasal, temporal. While one recommendation is to perform the exam with medium magnification and the moderately thin beam of light angled out 10-25 degrees, it is important to remember that gonioscopy is a dynamic exam. The angle, height and width of the beam as well as the magnification will be adapted during the examination to provide the optimal views. During the exam it may be necessary to re-orient yourself particularly if the view seems inadequate. The view may be influenced by the improper gaze position on the part of the patient. Light may reflect off a mirror surface, or front surface of the lens and result in a level of glare that interferes with the view. The simplest solution is to slightly change the angle of illumination and perhaps tilt the lens very slightly. Corneal folds may be induced if too much pressure is applied or if the lens is tilted excessively. If the examiner encounters folds, he or she may find help in reducing the amount of pressure applied to the eye and recentering the lens. There should be just enough pressure to maintain the lens in contact with the tear film. This is seen with the 4 mirror type lenses just when the tear film uniformly disperses as the lens comes in contact. Folds induced with indentation gonioscopy will be further discussed below.

Various grading and recording systems exist. A complete review of these systems is not in the scope of this article. One suggestion is to deliberately consider and record the most posterior structure visible, the angle width or approach, the degree of pigmentation in the trabecular meshwork and any additional findings of interest. An alternative simple but effective approach, in the context of baseline glaucoma assessment is to grade the angle as open, occludable (anatomically narrow) or closed. Several considerations may be helpful when evaluating a patient with a narrow angle. It is important that gonioscopy be done in a dark room with a small beam. Constriction of the pupil will pull the iris centrally and away from the angle. In narrow angles it is advisable to examine the angles with lower levels of light including shortening the vertical height of the beam and using care to avoid shining the light directly into the pupil. It is possible for an angle to appear to be open to the scleral spur under bright illumination but narrow to appositional closure without the light induced constriction of the pupil. The degree and location of trabecular meshwork pigmentation may provide insight also. Typically the degree of pigmentation is fairly uniform throughout the angle or more pronounced inferiorly. Areas of intermittent apposition may contribute to a deposition of pigment on the angle wall, particularly the trabecular meshwork as a result of contact with the iris. If any angle is more narrow it is usually the superior angle. A narrow angle with more intense pigmentation of the superior angle (sometimes referred to as inversion of pigment) should be viewed with suspicion. The potential for multiple pigment lines in the angle makes the identification of Schwalbe's line important as the misidentification of a pigmented area as trabecular meshwork may occur.

Figure 3a

Figure 3a. Gonioscopic view of an open angle with ciliary body band easily visible and trace+ trabecular meshwork pigment

Figure 3b

Figure 3b. A widely open angle with ciliary body band visible and moderate + trabecular meshwork pigment (2+ -3)

Indentation gonioscopy is another important method used when performing gonioscopy. This is best accomplished with the smaller diameter, flatter base curve of the 4-mirror type lenses. Gently applying pressure with the lens displaces aqueous toward the peripheral part of the angle. This also increases the diameter of the limbus pulling structures peripherally and posteriorly. Corneal folds may be induced but with some slight modification of technique can be minimized or eliminated. A helpful suggestion is to pull or tilt slightly away from the angle you are viewing while pushing slightly in with the mirror you are using to view. For example, if the goal is to indent the superior angle, the doctor can tilt the lens away from the patient superiorly while gently pushing up and in inferiorly. With some practice this allows for a more selective indentation and produces minimal if any corneal folds. Palmberg and Forbes provide a more detailed review of this topic (Palmberg , Forbes)

Peripheral anterior synechiae (PAS) are adhesions of the peripheral iris to the angle wall (see Figure 4). These suggest contact of the iris with the angle and/or inflammation having occurred. PAS may occur at any level, from isolated, thin high adhesions to low broad ones.

Figure 4

Figure 4. Peripheral anterior synechiae (PAS)

There is also the potential for appositional closure. This involves the peripheral iris being in contact with the angle, particularly the trabecular meshwork, but not adherent to it. Indentation gonioscopy (see Figure 5) can help differentiate between appositional and synechial closure. It is helpful to distinguish between peripheral anterior synechiae and iris processes. Iris processes commonly occur in normal angles. These are extension of the peripheral iris along the angle wall. These may also bridge the angle recess. They do not distort the iris. The adhesions of PAS will cause the adjacent iris stroma to distort or stretch slightly on indentation.

Figure 5a

Figure 5a. Gonioscopic view of narrow angle. No angle structures are evident.

Figure 5b

Figure 5b. Gonioscopic view of same angle as Figure 5a but with indentation. Note that the iris configuration has changed and that the pigmented trabeculum is now visible.

Angle closure may be primary or secondary. Primary angle closure is the result of an anatomic predisposition. The more common of these is pupillary block or relative pupillary block. Iridolenticular contact near the pupil contributes to a build up of aqueous in the posterior chamber. This gives rise to an anterior bowing of the iris commonly referred to as iris bombé. This forward bowing of the iris narrows or closes the angle. The slit lamp appearance is one of a convex iris and an angle that is shallow peripherally and mid-peripherally but is deeper centrally. It has been this author's observation that lighter colored iris is associated with a more dramatic convexity of the iris. Darker iris color may have less iris bombé, in fact the chamber may only appear narrow in the periphery. This again underscores the importance of gonioscopy in these patients.

Plateau iris is another consideration in the clinical spectrum of evaluating narrow angles. The slit lamp appearance is one of a deep or moderate anterior chamber. The iris plane is flat. The extreme periphery of the chamber may appear shallow with a deliberate von Herrick exam. The gonioscopic findings often make this diagnosis. The classic appearance is one of a flat iris plane leading to a prominent last roll of the iris and a crowded angle. There is often an anterior insertion of the iris. There may be areas of apposition of the iris to the angle or even peripheral anterior synechia. Indentation gonioscopy is critical for the diagnosis. The appearance with indentation is one of a concave mid peripheral iris. The peripheral iris does not move posteriorly as much as the mid-peripheral iris. The prominent last roll of iris remains anteriorly displaced relative to the rest of the iris. This peripheral aspect of the iris may appose the angle. The prominent, poorly indenting peripheral roll of iris is the result of anteriorly displaced ciliary processes that push the peripheral iris forward. This is another possible form of Chronic Angle Closure Glaucoma (CACG). As with other forms of CACG there may be multiple pigment lines on the angle wall and peripheral cornea. One of these anterior pigment lines can be falsely interpreted as trabecular meshwork, suggesting to the clinician the incorrect diagnosis of open angle glaucoma. Maintaining an index of suspicion, careful biomicroscopic exam, indentation gonioscopy and use of the corneal wedge will be particularly helpful in these cases.

Various forms of secondary glaucomas may have significant angle abnormalities. Gonioscopy is an important adjunct to a detailed history and a deliberate slit lamp examination. Pigment dispersion and pigmentary glaucoma can have abnormally dense pigmentation of all of the angle structures especially the trabecular meshwork. This pigmentation can decrease with advancing age. Pseudoexfoliation may be evident in the angle as fine flakes of pseudoexfoliative material on the peripheral iris and in the angle. The fine pigment deposition is seen primarily in the trabecular meshwork but also on Schwalbe's line and on the peripheral cornea. This pigmentation may increase with age. A nonspecific finding of pigment accumulation on Schwalbe's line, also known as a Sampaolesi's line can be seen in pseudoexfoliation. Angle recession (see Figure 6) can be seen on gonioscopy as a broadening of the ciliary body band and relative deepening of the iris insertion. It is the result of significant blunt injury to the globe. The ciliary body appears wider than other parts of the angle. This difference may only be apparent with comparison to the fellow eye. For obvious reasons, patients with bilateral injury may be more difficult to compare. There may be white linear alterations on the ciliary body in the areas in question. The insertion of the iris can appear more posteriorly displaced with some atrophic changes there as well.

Figure 6

Figure 6. Angle recession. Note the relative deepening of the iris insertion.

Peripheral anterior synechiae may be present and likely suggest inflammation associated with the inciting injury. The presence of blood vessels in the angle may pose a clinical question. Normal angle vessels may commonly occur. These are easier to appreciate in those eyes with lighter iris color. A clinician may need to differentiate between normal angle vessels and those that occur with neovascularization of the iris and angle. Normal angle vessels tend to be isolated, non-branching vessels radially oriented in the iris and circumferentially oriented at the iris insertion and on the ciliary body band. They tend not to cross the scleral spur. It is worth emphasizing these vessels are within the iris stroma. Neovascular vessels are finer and do not follow a regular pattern. They can be seen as an arborizing network of vessels that are superficial on the iris. These vessels may invade the angle and result in progressive closure. These occur in the context of ischemia of the posterior segment. Gonioscopy is a valuable diagnostic technique. Incorporation of this technique in the care of glaucoma patients and suspects will contribute to patient care.

References

1. American Optometric Association Consensus Panel on Care of the Patient with Open-Angle Glaucoma. Care of the patient with open-angle glaucoma. In: Optometric Clinical Practice Guidelines American Optometric Association, St Louis, MO 2002.

2. European Glaucoma Society Terminology and Guidelines for Glaucoma; Second edition European Glaucoma Society 2003.

3. American Academy of Ophthalmology Glaucoma Panel. Preferred Practice Pattern. Primary open-angle glaucoma. American Academy of Ophthalmology 2003.

4. Fremont AM, Lee PP, Mangione CM, et al. Patterns of care for open-angle glaucoma in managed care. Arch Ophthalmol. 2003; 121: 777-783.

5. Optometric Glaucoma Society. OGS ejournal 2006.

6. Palmberg P Gonioscopy. In Ritch R, Shields BM, Krupin T (eds). The Glaucomas. Mosby, 1996; 455-469.

7. Forbes M. Gonioscopy with corneal indentation: a method for distinguish between appositional closure and synechial closure. Arch Ophthalmol 1966; 76:488-492.

Suggested Further Reading

Alward WLM. Color Atlas of Gonioscopy, (Wolfe 1994).

Fisch BM. Gonioscopy and the Glaucomas (Butterworth-Heinemann 1993).

Palmberg P Gonioscopy. In Ritch R, Shields BM, Krupin T (eds).The Glaucomas. Mosby, 1996; 455-469.

John McSoley, OD