RONALD L. FELLMAN and GEORGE L. SPAETH
Table Of Contents
CLASSIC GONIOSCOPY AND ADJUNCTIVE METHODS OF CHAMBER EVALUATION
UNDERSTAND WHY THE ANTERIOR CHAMBER ANGLE CANNOT BE SEEN ROUTINELY: GEOMETRIC OPTICS AND SNELL'S LAW ARE THE ANSWER
LEARN THE NORMAL ANGLE LANDMARKS
NORMAL VARIABILITY OF THE CHAMBER ANGLE
ANTERIOR CHAMBER DEPTH
ESTIMATE OF PERIPHERAL ANTERIOR CHAMBER DEPTH
GONIOSCOPIC CLASSIFICATION SYSTEMS
GONIOSCOPY: INDICATIONS AND TECHNIQUES
EVALUATION OF THE NARROW-ANGLED EYE
GONIOSCOPY MYSTERY CASES
|Routine gonioscopy is an essential component of vision care. It remains
a tremendously valuable diagnostic and therapeutic adjunct to ophthalmic
care and is vital in order to classify glaucoma. With this is mind, the
practice of gonioscopy should be at an all-time high considering
angle-closure glaucoma causes blindness in more people
worldwide than open-angle disease.1,2 However, a recent study of initial office visits for glaucoma in the United States found gonioscopy documented in only 46% of cases while
evaluation of the disc was noted in 94%.3 A similar study in Britain documented gonioscopy in only 23% of
subjects with glaucoma even though the majority of ophthalmologists thought
it was necessary.4|
Why is gonioscopy underutilized? Gonioscopy remains a lost art because there are typically no signs or symptoms associated with early angle compromise that prompt an angle examination. For example, in early angle-closure disease, the patient has no complaints, the slit-lamp examination usually appears normal and there is nothing to prompt the ophthalmologist to look at the angle. This is best exemplified by the fact that 80% of angle-closure glaucoma cases are asymptomatic: only 20% have the acute variant.5 The eye has an astounding anterior chamber angle reserve that may hide disease for years. However, when that is exhausted, glaucomatous field loss and elevated intraocular pressure (IOP) may rapidly progress.
Lack of routine gonioscopy often culminates in misdiagnosis, maloccurrence, and maltreatment. Routine gonioscopy detects early angle compromise in time to preserve vision in countless patients. This chapter is dedicated to that mission.
|CLASSIC GONIOSCOPY AND ADJUNCTIVE METHODS OF CHAMBER EVALUATION|
|Classically, gonioscopy involves viewing the chamber angle through a goniolens
or gonioprism. Twenty-first century gonioscopy offers much
more. There are a plethora of gonioprisms and goniolenses to fit a
variety of diagnostic and therapeutic tasks. In addition, the technological
advances of ultrasound biomicroscopy (UBM), Scheimpflug
photography, optical coherence tomography, and ophthalmic endoscopy
augment our understanding of angle mechanics (Table 1). The ability to correlate classic gonioscopy with new imaging techniques
of the chamber angle facilitates a better understanding of chamber
angle anatomy, physiology, and pathophysiology.6|
EUA, examination under anesthesia; UBM, ultrasound biomicroscopy; ACD, anterior chamber depth.
These new clinical modalities inspire a modern-day definition of gonioscopy, namely: the evaluation and management of the eye based on the visualization of the anterior chamber angle constitute the field of gonioscopy. Gonioscopy currently consists of direct and indirect gonioscopic techniques performed with variable-sized gonioprisms, goniolenses, and viewing devices. Ophthalmic endoscopy is a relatively new technique that allows the surgeon to view the chamber angle directly during surgery. Imaging of the chamber angle with UBM and photography adds valuable angle information that is correlated with gonioscopy. Ophthalmologists who take advantage of these techniques and devices provide superior care through a rapid assessment of the angle situation. The focus of this chapter is classic gonioscopy, the benefits of which are currently the greatest for practitioners on a day-to-day clinical basis.
The ultimate goal of gonioscopy is to preserve or improve vision through the systematic evaluation and management of the anterior chamber angle. This requires the skill necessary to use a variety of instruments in order to accomplish a specific gonioscopic task (Fig. 1). In addition, the accurate recording and classification of visualized structures is imperative to document angle structures and note their changes over the lifetime of the patient. Physicians who integrate gonioscopy into their practice are able to examine, evaluate, document, and appreciate the appearance of the normal angle and its immense variability. A thorough understanding of normal is imperative in order to recognize and treat angle pathology.
|UNDERSTAND WHY THE ANTERIOR CHAMBER ANGLE CANNOT BE SEEN ROUTINELY: GEOMETRIC OPTICS AND SNELL'S LAW ARE THE ANSWER|
|A refresher course in geometric optics7 and limbal anatomy is a must for ophthalmologists who want to understand
the inability to see the chamber angle. Understanding why the angle
is ordinarily hidden should increase the desire to view it.|
The optics of gonioscopy centers on the following point: how much and in which direction will a light ray bend as it emerges from the anterior chamber into air? Geometric optics revolves around constructing a normal to the interface; the normal is 90 degrees to the boundary interface. All the ray racings are based on the construction of this normal (Fig. 2).
|LEARN THE NORMAL ANGLE LANDMARKS|
|Each and every angle is like a fingerprint, unique yet ordinary. It is
imperative to understand the normal angle thoroughly. A comprehensive
understanding of normal is mandatory in order to differentiate peripheral
anterior synechiae (PAS) from iris processes, normal angle
vessels from new angle vessels, plateau iris, a narrow angle, angle
recession, a small cleft that causes hypotony, and countless others. The
physician must appreciate normal angle variability in order to find
early disease, yet at the same time avoid misdiagnosis and unnecessary
treatment based on gonioscopic findings.|
Gonioscopy requires a fusion of higher level skills including: hand–eye coordination, angle anatomy, physiology and pathophysiology of outflow structures and disease correlates, to name a few. There are several key landmarks that guide the gonioscopist through the iridocorneal angle in a systematic way; otherwise the angle loses its unique identity. The scleral spur is the visual landmark for maximum angle orientation. If the scleral spur is not located, suspect an abnormal angle or at least an unusual one. All outflow anterior to the spur is trabecular and the remaining uveoscleral outflow is posterior. Initially it is helpful to visualize the angle from a diagram that is correlated with a goniophotograph and then histophotograph (Fig. 3).
Initially gonioscopy should be performed in every apparently normal eye until familiar with normal. Physicians who look at the angle daily will rapidly become proficient at differentiating normal from abnormal in a matter of seconds. Others who only look at the angle when abnormality is suspected will take much longer and may never become efficient gonioscopists.
If possible, first find the scleral spur for rapid orientation. Then, to avoid confusion, observe the six structures in order from the iris to the cornea. If unable to find recognizable landmarks, look in another region of the angle.
A scan across the chamber into the iridocorneal angle starts by looking for blood vessels, iris cysts, and dandruff-like particles in the pupillary border. If posterior chamber pathology such as misdirection, tumors, or cyclitic membranes is suspected, the pupil is dilated and gonioscopy repeated. The anatomy of the posterior chamber is easier to visualize with a gonioprism while the pupil is dilated. The fundus can also be viewed through the contact lens.
Where the iris inserts onto the inner wall of the eye is identified, then the peripheral configuration of the iris is described and the angular approach of the iris to the cornea characterized. The peripheral iris may be flat, steep, or bow posterior; insertion is made anywhere from ciliary body to cornea with an angular approach of 0 degrees to 45 degrees.
Ciliary Body Band
The ciliary body band is that portion of the ciliary body muscle seen on gonioscopy (see Fig. 3D). The band is usually tan, gray, or dark brown, and typically narrow in hyperopes and wide in myopes. The root of the iris normally inserts onto the ciliary body band. If the iris inserts directly into the scleral spur, the ciliary body band is not seen easily.
The scleral spur is consistently the most notable landmark in the chamber angle (see Fig. 3E). Inability to locate the scleral spur is a cause for concern because obfuscation of the spur especially due to the peripheral iris is a tell tale sign of angle closure disease. The scleral spur appears as a white circumferential band. This white band represent the attachment of the ciliary body to the sclera and if found, the trabecular meshwork is directly anterior. The scleral spur separates conventional trabecular outflow from uveoscleral outflow and cyclodialysis clefts appear posterior to the spur.
The trabecular meshwork extends from the scleral spur to Schwalbe's line and typically has a ground-glass appearance best seen with sclerotic scatter. Pigment in the meshwork usually accumulates in the posterior division and facilitates identification. However, any angle structure may accumulate pigment. The junction of the mid and posterior meshwork is the favored location for trabeculoplasty. When there is no pigment in the meshwork, the ground-glass appearance is essential to define the outflow system and the corneal optical wedge is helpful in delineating nonpigment outflow systems (best seen with the Goldmann gonioprism).
Schwalbe's line is the termination of Descemet's membrane and is the most anterior angle structure identifiable. Schwalbe's line marks the forward limit of the trabecular meshwork and is easily identified where the anterior and posterior reflections of the corneal optical wedge meet.
|NORMAL VARIABILITY OF THE CHAMBER ANGLE|
There are certain features that differentiate normal from abnormal angle vessels. Normal angle vessels rarely bridge the scleral spur and do not branch. They are usually single vessels without arborization (Fig. 4). Normal angle vessels are seen in 62% of individuals with blue eyes and only 9% with brown eyes.8
The canal (Fig. 6) is located directly anterior to the scleral spur and is normally not seen. However, during gonioscopy, blood may reflux in to the canal exposing its dimensions. The canal is approximately 300 μm in width, 36 mm in length, and 30 μm in height.
A minimal amount of angle pigment is expected but excessive angle pigmentation should prompt the examiner to search for its cause (Fig. 7). This may be caused by pigmentary glaucoma, pseudoexfoliation, trauma, uveitis, or tumors.
|ANTERIOR CHAMBER DEPTH|
|If the central anterior chamber depth is very shallow, the patient is more
likely to have an occludable angle. An anterior chamber depth less
than 2.22 mm measured by optical pachymetry is significant.10 However, many patients who develop angle-closure glaucoma do not
have overly shallow anterior chambers as seen during routine slit lamp
exam. The depth of the anterior chamber is highly variable and dependent
on multiple factors.|
Family members of patients with angle-closure glaucoma are more likely to have occludable angles especially noted by a marked anterior convexity that is five times greater than that of controls. In addition, patients with angle closure disease have a higher insertion of the iris, shallower recess, and greater iris convexity than controls.11 Ethnicity creates gonioscopic expectations. The iris is more likely to insert anteriorly and the chamber is shallower in Eskimos-Inuit, Asians, blacks, and whites. Why is the prevalence of angle-closure glaucoma so much greater in Asians and Alaskans?12,13 Studies show the iris inserts more anteriorly in these individuals, which may be one factor that predisposes to angle closure disease (Fig. 8). In high-risk populations, gonioscopy is essential in screening for glaucoma and has a higher yield than applanation tonometry.14
Hyperopic individuals are well known to be more prone to angle-closure disease. Nanophthalmos is the extreme form of a “dwarf eye” with axial length below 18 mm, high hyperopia, shallow anterior chamber and angle closure disease. Every ophthalmologist should be an angle-closure detective in all hyperopes.
Anterior chamber depth definitely decreases with age, further decreasing angle width. Phacomorphic changes also influence this relationship.
Women have slightly smaller ocular dimensions than men. This may partly explain why their incidence of angle-closure glaucoma is greater than men.
Patients with thicker lenses are more likely to have shallow anterior chambers. The depth of the anterior chamber may vary depending on time of day. In the initial evaluation of narrow angles, it is helpful to reevaluate at different times of day. The depth of the chamber also has a diurnal variability.15
A recent population-based study from India16 revealed patients with occludable angles had the following: (1) shorter axial length, (2) shallower anterior chamber depth, and (3) increased lens thickness. This seems to hold true for most populations at high risk for angle-closure disease.
|ESTIMATE OF PERIPHERAL ANTERIOR CHAMBER DEPTH|
Many ophthalmologists use the van Herick17 test to estimate depth of the peripheral anterior chamber (Table 2). It is a screening tool designed to estimate depth of the iridocorneal angle but not a substitute for gonioscopy.18 A thorough understanding and review of limbal anatomy reveals why the van Herick test is not always what it seems. Surgeons who perform angle surgery realize the immense variability of the region surrounding the scleral spur (Fig. 9).
vH, van Herick, ACD, anterior chamber depth, CT, corneal thickness.
The van Herick test is a slit-lamp screening tool and the Shaffer system requires gonioscopy. The areas in green represent deep angles that are unlikely to close. The yellow zone is more worrisome and the red zone represents a very high likelihood of angle-closure disease. The grading system is correlated with two populations emphasizing the increased prevalence of angle-closure disease in Japanese patients.
|GONIOSCOPIC CLASSIFICATION SYSTEMS|
|Early classification systems were designed specifically to evaluate the
risk for angle-closure glaucoma. The angle was judged open or
capable of closure. Each system built on its predecessor. Scheie designed
the first system around visible posterior angle structures and the
amount of pigmentation in the posterior trabecular meshwork. The Shaffer
system, still popular today, revolves around the width of the recess. Spaeth
thought the chamber angle too complex to describe with one
variable. This system requires the observer to evaluate not only the angular
approach as in the Shaffer system, but in addition the site of
insertion of the iris onto the inner wall of the eye and the peripheral
configuration of the iris. Indentation gonioscopy is an integral part
of the Spaeth classification system. The implications of the Shaffer
system are the angle is open, capable of closure or closed. The Spaeth
system is designed purely around the description of the angle. The management
of what is seen is a separate issue.|
There are three available alphanumeric grading systems to record angle findings (Table 3). It is insufficient only to use the terms open or closed because this does not communicate enough useful information to make meaningful clinical decisions. Biometric gonioscopy is an attempt to quantitate gonioscopy but has not gained widespread acceptance.19 The Scheie system is based on visible angle structures (Fig. 10A).20
The Shaffer system is based on the width of the angle recess (see Fig. 10B and Table 2).21 The Spaeth nomenclature is a hybrid alphanumeric arrangement (see Fig. 10C to 10F).22 This system prompts the examiner to describe the angle in a three-dimensional manner. This allows total reconstruction of the angle by anyone who understands the nomenclature. For example, a grade IV Shaffer angle is wide open and a Spaeth D40p is also wide open. However, even though they are both wide open, the Spaeth system reveals a plateau configuration that requires closer scrutiny. Grade the following angles (Fig. 11).
|GONIOSCOPY: INDICATIONS AND TECHNIQUES|
|Learning how to incorporate gonioscopy into a busy practice takes planning
and commitment. In a glaucoma clinic, all established and especially
new patients undergo repeated gonioscopy. In a general ophthalmology
clinic, optimally all new patients should undergo gonioscopy. It is
good medical care to examine all compartments of the eye for a baseline. Ophthalmologists
skilled in Zeiss gonioscopy can rapidly describe the
angle. Examiners who use the Goldmann lens are less likely to view
every angle because of the extra work and patient discomfort. In a general
ophthalmology clinic, at minimum, gonioscopy should be performed
under the following circumstances:|
This is not meant to be an all-inclusive list, only a start. The point is that gonioscopy is underutilized and its use should be increased. Ophthalmologists often dictate instructions for diagnostic tests on return visits. Gonioscopy should be added to that list, especially with any of the elements noted on the above list. Physicians who train their technicians about gonioscopy will find it easier to integrate gonioscopy into their practices.
Office-based Koeppe gonioscopy is no longer performed. The demands placed on busy ophthalmologists make this technique impossible to use in the office. However Koeppe gonioscopy is an unsurpassed method for viewing the chamber angle in the operating room (Fig. 12A and 12B). If desired, a Koeppe lens is placed on each eye and the angles are viewed in tandem. The Koeppe lens comes in three sizes: small, medium, and large. Saline bridges the Koeppe cornea interface. Utilization of the proper size provides an excellent undistorted view and goniophotography is easiest with this lens. The Koeppe hand-held slit-lamp system is an elegant method of angle visualization but is not conducive to office-based gonioscopy. The best, most stable, affordable view of the angle remains the Koeppe lens as seen through the hand-held slit lamp.
The Goldmann three-mirror lens is designed for indirect viewing at the slit lamp and allows an excellent view of the angle. This lens is the classic time-honored gonioprism with which most ophthalmologists learn to recognize angle structures. If all the mirrors are used, the three-mirror lens facilitates a view of the angle, ciliary body area, peripheral retina and the fundus through the central portion. With this lens, practically all areas of the interior of the eye can be visualized. A methylcellulose viscous bridge is necessary to obtain an optimal image. The gel causes blurred vision and may interfere with further ocular testing (see Fig. 12C and 12D). Placing the device on the eye in a comfortable fashion requires practice and hand–eye coordination (see Fig. 12E to 12G). Patients do not like gonioscopy especially when gel is required, their eye is tender, or they have blepharospasm. The methylcellulose may blur their vision and inhibit further testing. Trying to manipulate the Goldmann lens to view a narrow angle causes distortion of angle structures. Pressure on the globe at the temporal limbus is usually needed to easily release the lens from the globe.
Learning to use the Zeiss-type lens requires similar skills but in the long run is simpler for the patient and examiner. Regardless of type of indirect examination, the examiner and patient should be comfortable. The examiner should rest his or her elbow on the base of the slit lamp. This improves proprioceptive skills. The Zeiss lens is typically placed on the eye with the patient looking straight ahead. The patient is instructed that they will feel light pressure on their lid. The contact diameter of the Zeiss lens is 9 mm, much smaller than the Goldmann, allowing for an easier insertion (see Fig. 12H). The lens is inserted with a square orientation, which lessens lid irritation (see Fig. 12I and 12J). A methylcellulose viscous bridge is not necessary with the Zeiss lens because the contact area is small. However, it is important to learn to evenly distribute the capillary tear film. If the view is poor, look away from the biomicroscope directly at the lens and the distribution of the capillary tear film. If uneven, reapply the lens until the capillary tear film is evenly distributed (see Fig. 12K). It is important to recognize the problem of corneal striae. Ophthalmologists familiar with the mechanics of the Goldmann lens commonly complain of corneal striae when they switch to Zeiss gonioscopy (see Fig. 12L). This problem is easily overcome when the examiner is forewarned and properly instructed not to press too hard or unevenly on the cornea.
There are several acceptable methods of recording gonioscopic findings. Some physicians prefer to simply write down their angle findings. For example the angle width is 40 degrees, the iris bows slightly, the iris inserts deep into the recess, moderate trabecular pigment and there are no PAS. Others, as well as the authors, prefer to use one of the classification systems and record the angle findings in graphic form (see Fig. 12M to 12O). The ability to master a classification system allows instant communication with colleagues who know the system, saves time in recording findings, and facilitates the transfer of knowledge to advance the field of gonioscopy.
|There are a variety of methods to clean goniolenses. The simplest solution
for glass lenses is to use 70% alcohol. It is imperative to
have a system in place for cleaning lenses in order to prevent transmission
of disease, especially viruses that infect the cornea. The Zeiss
or similar glass lens lends itself to easy cleaning with alcohol. Immediately
after use, the Zeiss lens is cleaned with alcohol. It is stored
in a gonioprism holder until use for the next patient. The alcohol
dries in a matter of seconds and sterilizes the lens. The lens should
not be cleaned and then used immediately because the cleaning agent will
not have had time to vaporize and the patient will develop a severe
chemical keratitis. Therefore, the algorithm should be to use a clean
lens, immediately clean the lens after each use, and store until use
for the next patient. If the lens is cleaned and immediately applied
to the eye, keratitis is likely to develop. The cleaning instructions
from the manufacturer of the lens should always be checked. Some companies
recommend diluted bleach or hydrogen peroxide.|
Optical lens cleaners should never be used on the contact lens portion of the goniolens. These cleaner packets are abundant in ophthalmologist's office and are made to clean the surface of the contact lens that the examiner looks through, not the contact portion of the lens.
|EVALUATION OF THE NARROW-ANGLED EYE|
|On a day-by-day basis, the narrow-angled eye causes
the most concern and worry for the examiner (Fig. 13). Evaluation of the narrow-angled eye requires additional
work and skill. The expert evaluation of an eye with a shallow anterior
chamber angle is a must for all ophthalmologists and eye care professionals. The
Zeiss-type lens is the best for evaluating narrow-angled
eyes because it causes the least distortion when trying
to see what is behind the last roll of the iris. Indentation or compression
gonioscopy is extremely helpful in deciding if an eye has appositional
or synechial closure.23|
Decision-making concerning the narrow angled eye always centers on the indication of iridotomy or iridoplasty. Should the physician continue to monitor or treat? There are several key factors that should prompt the examiner to perform gonioscopy in relation to narrow angle disease: (1) hyperopia; (2) symptoms compatible with angle-closure disease; (3) shallow anterior chamber angle; (4) glaucomflecken; (5) family history of narrow angle glaucoma; and (6) sudden change in baseline IOP.
|GONIOSCOPY MYSTERY CASES (Fig. 14)|
In summary, gonioscopy is an essential ophthalmic skill necessary for the correct diagnosis and treatment of multiple eye diseases. The proficient gonioscopist will effortlessly examine, grade and treat the chamber angle. There are several excellent gonioscopy references and the serious student of gonioscopy is encouraged to explore them.24–31 Maintenance of gonioscopic skills will increase the likelihood of a lifetime of vision for patients at risk for any type of angle pathology.
4. Choong YF, Devarajan N, Pickering A, et al: Initial management of ocular hypertension and primary open angle glaucoma: an evaluation of the royal college of ophthalmologists' guidelines. Eye 17:685, 2003
18. Foster PJ, Devereux JG, Alsbirk PH, et al: Detection of gonioscopically occludable angles and primary angle closure glaucoma by estimation of limbal chamber depth in Asians: modified grading scheme. Br J Ophthalmol 84:186, 2000
30. Fellman RL, Spaeth GL, Starita RJ: Gonioscopy: Key to the successful management of glaucoma. Focal Points, 1984. Clinical Modules for Ophthalmologists, No. 7. San Francisco: American Academy of Ophthalmology, 1984