Chapter 44
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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.

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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


TABLE 1. Clinical Methods of Viewing the Anterior Chamber Angle

Method of ViewSizesAdvantageDisadvantage
I. Refractive   
Direct view   
Small medium and largeConvenient for EUA, no angle distortion, angle magnification, able to view fundus, angle photography excellent, requires hand held biomicroscope.Patient must be in supine position, laborious examination, time consuming, patient dislikes, lid speculum required, examiner must change position.
Pediatric and adultSurgical goniolens with blunted side allows access for goniotomy.Same as Koeppe, angle photography more difficult than Koeppe.
II. Reflective   
Indirect view   
Goldmann 3-mirror
Small/medium/large No handle to hold prism
Excellent gonioprism for neophyte to learn angle anatomy, coupling gel necessary, viscous bridge creates suction effect stabilizing eye for examination and laser therapy.Goniogel required which obscures patients vision and may compromise further same-day diagnostic tests, corneal abrasion in compromised cornea, part of angle hidden in narrow angled eyes, easy to distort peripheral angle.
4-mirror lenses: Zeiss, Gaasterland, Posner
One size but variable handles to grasp the gonioprism (round, flat)
Rapid evaluation without goniogel, same day diagnostic tests not compromised, indentation or compression gonioscopy allows expert evaluation of narrow angled eyes with hidden anatomy, patient friendly, slit-lamp friendly with minimal movement to see 360 degrees.Must first master Goldmann gonioprism, more hand–eye coordination necessary than for Goldmann gonioprism, easy to apply excessive force causing corneal folds with poor view of angle.
III. Ultrasound Biomicroscopy (UBM) Imaging of anterior segment with UBM correlating ACD, iris position, lens, ciliary body and posterior chamber anatomy.Expensive equipment, not clinically available for most physicians
IV. Scheimpflug photography   High resolution photography demonstrates position of lens and irisExpensive and clinically difficult
V. Ophthalmic Endoscopy Endoscope allows direct intraoperative visualization of chamber angle, useful with cloudy cornea and to find cyclodialysis clefts.Must be performed in operating room under sterile conditions.

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.

Fig. 1 It is desirable to master more than one gonioscopic instrument to diagnose and treat the anterior chamber angle accurately. One gonioscopic device is insufficient to diagnose and treat eye diseases related to the anterior chamber angle. This figure demonstrates several instruments used in the office. For example, the Zeiss or comparable lens, number 2, (Table 1, II), is best for obtaining a rapid painless view of the angle and is especially helpful for evaluating eyes with narrow angles; lens number 5 (Magna View lens, Ocular Instruments, Bellevue, WA) allows a magnified view of the angle greater than a Goldmann for trabeculoplasty (magnification 0.93 versus 1.3); the classic Goldmann lens, number 1, is excellent for residents learning gonioscopy because the lens allows a large 140-degree field of view and stabilizes the globe better than a Zeiss-type lens. Because of anatomic variation of the width of palpebral fissures, the construction and size of the contact diameter of the Goldmann lens varies from 13 to 18 mm. The smaller lenses have one or two mirrors. The authors typically use the following gonioscopy lenses: a Zeiss or equivalent lens, Goldmann lens (13 mm, 15 mm, 18 mm) and Magnaview lens (trabeculoplasty) in the clinic and a Koeppe (magnified view), Barkan (goniotomy), and Posner (able to autoclave) in the operating room. This totals eight different gonioscopy devices to perform the specific functions necessary to examine and treat the chamber angle on a daily basis.

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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).

Fig. 2 Geometrical optics: why you cannot normally see the anterior chamber angle. A. Despite much effort, it is impossible to see into the chamber angle without additional means. This figure is an eye with a very deep anterior chamber and wide-open angle, but without gonioscopy the angle cannot be seen because of the total internal reflection of light rays that originate from the far recesses of the chamber angle. Every ophthalmologist is a lifetime student of optics and should review why this occurs. B. Why is it that lights rays can emerge anywhere from the anterior chamber except the angle? It is best to start with a simple unaltered light ray that emanates from the anterior chamber. A light ray parallel to the normal exits from the anterior chamber unchanged (not bent) when it exits the interface boundary. Obviously a light ray from the scleral spur is not able to escape parallel to a constructed normal. C. An incident light ray that approaches the normal (dotted white arrow) obliquely exits from the anterior chamber bent or refracted when it leaves the interface boundary. A substances index of refraction, n, defines how much it will bend light (n of aqueous = 1.38 and air n = 1.0). Aqueous bends light more than air. When a light ray passes from a medium of higher to lower index of refraction, the ray is bent away from the normal. Because the index of refraction of air is less then aqueous, the light rays are bent away from the normal and simultaneously away from the examiner. i = angle of incidence; r = angle of refraction. D. The amount the ray is bent is dependent on Snell's law. In this example it is determined an incident 30-degree ray of light is bent or refracted 44 degrees away from the normal as it emerges from the boundary of the cornea and air. The obvious problem is the more the incident angle is increased; the emergent ray is refracted away from the examiner. (Figure continues.)

Fig. 2b Continued. E. As the incident ray increases, at some point the refracted ray is bent 90 degrees and does not emerge, the critical angle, (yellow arrow). Solving for sine i reveals the critical angle is 46.5 degrees. Any incident ray of light that exceeds the critical angle (red arrow) will be reflected back into the eye. Beyond the critical angle, the cornea acts as a mirror and reflects, not refracts the light. N = normal. F. Light rays emanating from the chamber angle always exceed the critical angle and are reflected back into the eye; this is total internal reflection of light rays. This concept applies to light reflected down a fiber optic cable. G. The index of refraction of a Koeppe lens is approximately 1.4, almost exactly that of the cornea. According to Snell's law, the incident ray travels through the goniolens practically unaltered (dotted green line) because the index of refraction of the cornea and Koeppe are almost the same. The ray escapes because the angle of incidence at the new Koeppe air boundary is now less than the critical angle. When a new normal is constructed at the interface of the contact lens and air (yellow intersecting lines), the critical angle is no longer exceeded because the dome of the Koeppe is steeper than the cornea. Koeppe = 50 diopters. H. This is easier to visualize by simply studying the shape of the Koeppe lens. The curvature of the surface dome is greater than that of the cornea. The steeper dome of the Koeppe creates a new normal (N2) whose angle of incidence (2) is less than the critical angle and angle 1, thus the ray emerges (green arrow) into the air. (N1) normal where critical angle is exceeded. (Figure continues.)

Fig. 2c Continued. I. The escape of a light ray from the anterior chamber angle with a gonioprism is simpler than a goniolens (Koeppe). Note that table one divides the gonioscopic methods into refractive and reflective. A Goldmann or Zeiss equivalent gonioprism reflects light to the examiner; the goniolens refracts light towards the examiner. The problem of the critical angle is overcome with this system by allowing the light to reach a mirror with the proper inclination. The ray is simply reflected to the examiner. The majority of the mirrors are inclined at 59 degrees to 62 degrees for viewing the chamber angle.

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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).

Fig. 3 The normal angle. A. Can you identify structures 3, 4, 5, and 6? (correlate with B and C). B. This drawing identifies the six key structures to evaluate during gonioscopy: (1) pupil border; (2) peripheral iris; (3) ciliary body band; (4) scleral spur; (5) trabecular meshwork; and (6) Schwalbe's line. C. It is useful to correlate the goniophotograph with the histology of the angle. It is obvious the depth of the angle recess is partly dependent on where the iris inserts onto the ciliary body band. D. Ciliary body band width varies considerably. This goniophotograph is a developmental abnormality but is shown in this section because it is an excellent side-by-side example of variable width of the ciliary body band. The band is thinner at the green arrow and wider at the yellow arrow. The black arrow is scleral spur, red arrow is trabecular meshwork, and blue arrow is Schwalbe's line. E. Identification of the scleral spur is the critical step in sorting out angle anatomy. There are areas where the spur is easier to locate. The spur is harder to see at the yellow arrow and becomes obvious at the green arrow. Scan the angle to sort out the big picture. It may not be obvious through one mirror. Blue arrow = ciliary body band. F. Sometimes the scleral spur may be difficult to see. This is the normal angle of a child and as the angle matures, the spur is easier to define. The green arrow is where the spur should be located, the yellow arrow is an obvious ciliary body band and the black arrow is the trabecular meshwork.

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.

Pupil Border

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.

Peripheral Iris

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.

Scleral Spur

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.

Trabecular Meshwork

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

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.

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Angle Vessels

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

Fig. 4 Normal angle vessels. Blood vessels may normally be visible in the angle. It is imperative to differentiate normal from abnormal angle vessels. The normal angle has three types of vessels: (1) circular ciliary body band vessels; (2) radial iris vessels; and (3) radial ciliary body band vessels. This is an example of a circular ciliary body band vessel. It is completely normal and the most common of the three types. If angle vessel that bridges the scleral spur is seen, it is probably abnormal.

Iris Processes

Iris processes (Fig. 5) may be confused with peripheral anterior synechiae. Iris processes are most common nasally and gradually diminish with increasing age.9

Fig. 5 Iris processes. Iris processes are present in approximately 35% of normal eyes. They are pigmented in brown eyes and grey in blue eyes. Broad iris processes may obscure the scleral spur as seen in this goniophotograph. Iris processes are typically finer than peripheral anterior synechiae (PAS), most common nasally and allow some view of posterior angle structures.

Schlemm's Canal

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.

Fig. 6 Blood in Schlemm's canal. Blood may normally reflux in to Schlemm's canal and this may be seen during routine gonioscopy. Blood in the canal is more common under conditions of elevated episcleral venous pressure. This should always be correlated with dilated episcleral vessels. Hypotony may also cause blood to reflux in to the canal.

Angle Pigmentation

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.

Fig. 7 Angle pigment. Excessive angle pigment always demands an explanation. It is common to see some pigment dusting the inferior portion of the angle, especially in individuals over age 50. Figure 3A reveals moderate trabecular pigment. Excessive trabecular pigment at the 12 o'clock position occurs in only 2.5% of individuals and is usually pathologic. This goniophotograph shows excessive trabecular pigment representing pigmentary dispersion syndrome.

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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.
  1. Genetics
  2. Refractive error
  3. Age
  4. Gender
  5. Size of the lens
  6. Diurnal variability

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

Fig. 8 Anterior chamber depth. Ethnicity creates gonioscopic expectations. The insertion of the iris into the ciliary body band is partly genetically determined. This fact is useful in the early diagnosis of angle closure glaucoma and recognizing angle recession. A. The iris inserts just below the scleral spur in this goniophotograph from an Asian patient. This is a common angle configuration for Asians and may predispose to chronic angle closure disease. B. The iris inserts much deeper into the ciliary body band (green arrow). This is the most common angle configuration for a Caucasian. The patient's ethnicity prompts the examiner to be on the alert for angle closure disease.


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.

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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).

TABLE 2. van Herick and Shaffer grading systems

van Herick Grade ACD   CT Shaffer Grade Degrees Interpretation Population: White Population: Japanese
4 ACD = or > CT
4 wide open 40 degrees Closure improbable 38.6%  
3 ACD = 1/4 to 1/2 CT 3 open 30 degrees Closure improbable 60% 92% (G 3,4)
2 ACD = 1/4 CT
2 moderately narrow angle 20 degrees Closure possible 1% 5.1%8 {Au: Please Clarify}
1 ACD < 1/4 CT 1 extremely narrow angle 10 degrees Closure probable 0.64% 2.6%
Slit ACD = Slit Slit <10 degrees Areas appear closed 0% 0.3%

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.


Fig. 9 Peripheral anterior chamber depth: anatomic correlates and why estimates of limbal chamber depth (van Herick) are not a substitute for gonioscopy. A. The loss of transparency at the corneoscleral limbus prevents a direct view of the underlying chamber angle. The projected surface locations of the outflow structures are noted to demonstrate how the limbus normally conceals the angle structures. A thorough understanding of this area is crucial especially during angle surgery and in classifying the glaucomas. The projected structures in order from anterior to posterior include: red, corneal limbus, conjunctival epithelium ends at periphery of Bowman's layer of the cornea; dotted black line, approximate end of Descemet's membrane and beginning of outflow system typically seen during gonioscopy as Schwalbes' line; green zone, anterior trabecular outflow; blue zone, posterior trabecular outflow; white, approximate location of scleral spur, posterior limit of limbus and trabecular outflow system; and yellow zone, ciliary body band and beginning of uveoscleral outflow. B. Because of the transition of orderly collagen fibers into coarse scleral fibers at the corneoscleral junction, there is a loss of transparency at the limbus and the location of angle structures is unknown. Guess the location of the scleral spur in this intraoperative photograph. You would probably guess the black arrow, but it is actually the white arrow. This is proved by the layer-by-layer dissection that is required during a nonpenetrating procedure. During a deep sclerectomy procedure where the deep scleral flap is retracted, the underlying angle structures become visible. The scleral spur, white arrow, is seen well posterior to the corneal limbus, black arrow. Most ophthalmologists do not realize how far posterior the canal and meshwork may be located. The opposite may hold true with the spur situated very close to the corneal limbus. During this deep sclerectomy, the dissection of the deep flap reveals the scleral spur, floor of Schlemm's canal, and underlying posterior trabecular meshwork. It is rare for ophthalmologist to see this layer-by-layer dissection of the limbus and note how it correlates with what they see at the slit lamp. The point of the discussion is that the location of the scleral spur is highly variable and the van Herick test is unable to compensate for this, thus the reason gonioscopy is essential. (Figure continues.)

Fig. 9 Continued. C. The van Herick test is an estimate of angle width. The slit lamp beam is aligned at the limbus and peripheral iris at approximately 60 degrees. The corneal thickness (CT), is compared to the anterior chamber depth (ACD). The scale and corollary to the Shaffer system is shown in Table 2 In this example, a van Herick grade 4 is noted. D. This is the goniophotograph of the actual angle from the grade 4 van Herick in (C). The exact location of the spur, the amount of pigment in the meshwork, where the iris inserts into the angle are now known. The van Herick estimate was popular during the reign of office based Koeppe gonioscopy, which was burdensome. Modern-day indirect gonioscopy allows a rapid assessment of the angle while the van Herick remains an estimate. E. Another example with peripheral iris closer to limbal cornea. This is a van Herick grade 2. F. In this case the iris appears close to the cornea not because of pupil block and iris bowing, but because of a high insertion of the iris into the ciliary body band. The clinical point is when the van Herick is narrow; it is impossible to know if it is due to forward bowing of the iris as in pupil block or a high insertion of the iris as in this case.

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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


TABLE 3. Angle Classification Systems

SystemSystem BasisAngle StructuresClassification
Scheie 1957Extent of angle structures visualizedAll structures seenWide openopen
  Iris root not seenGrade I
  Ciliary body band not seen, posterior trabeculum obscured, only Schwalbe's line visibleGrade II 
   Grade III 
   Grade IVclosed
Shaffer 1960Angular width of the recessWide open (30 degrees to 45 degrees)Grade 3–4, closure improbableopen
  Moderately narrow (20 degrees)Grade 2 closure possible
  Extremely narrow (10 degrees)Grade 1 closure probable 
  Partly or totally closedGrade 0 closure presentclosed
Spaeth 19711. Insertion of iris rootIris insertion  
 2. Angular width of the recess Anterior to Schwalbe's lineThis system requires a combination of all three descriptors before deciding on classification.
 3. Configuration of peripheral iris Behind Schwalbe'sExamples:
 4. Apparent and actual insertion of iris sCleral spur 1. A40f = complete closure
   Deep into ciliary body band 2. D40f = open angle, normal for Caucasian
   Extremely deep 3. C40f = open angle, normal for Asian
  Angular approach to recess 0 degrees to 45 degrees 4. C25p = plateau iris, requires therapy
  Peripheral iris configuration 5. E40f = angle recession in Black patient
   f = flat approach 6. E40c = reverse pupil block,
   c = concave, (post. bowing) 7. C15b3+ = worrisome narrow angle
   b = bow 1 to 4 plus 8. (B)D10b3+ = optical closure, indents open
   p = plateau 9. B20b2+ = angle closure


Fig. 10 Gonioscopic classification systems. A. Scheie system. The basis for this system is posterior angle structures visualized. A grade IV angle is completely closed and a grade I is slightly narrow. No comment is made on the approach of the iris or its peripheral configuration. B. Schaffer system. The basis for this system is width of the angular recess. A grade I Shaffer angle is worrisome for closure and a grade IV approach typically implies the angle is open. An open angle however does not always imply an unobstructed trabecular meshwork. A deep angle does not always imply trabecular protection or the lack of pupil block, as is seen with reverse pupil block in pigmentary glaucoma. C. Spaeth system (see Table 3). The basis for this system is threefold. The alphanumeric designation permits a three-dimensional reconstruction of the chamber angle. The gonioprism of choice for this system is a Zeiss-type lens that facilitates indentation gonioscopy. 1. Site of insertion of iris onto the inner wall of eye in (D). 2. Angular approach in degrees (E). 3. peripheral configuration of iris (F).

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).

Fig. 11 Grade the angle. A. The intraocular pressure (IOP) is 28 mm Hg and routine gonioscopy revealed this angle. Gonioscopy in the fellow eye reveals a C40f configuration. At first glance the angle is graded in the following manner: Grading at position of yellow arrow reveals: Scheie grade wide open 4+ pigment; Shaffer grade, 4, 4+ pigment 40 degrees closure impossible; Spaeth, E40f. Grading at position of red arrow reveals: Scheie grade, wide open 4+ pigment; Shaffer grade 4, 4+ pigment, 40 degrees closure impossible; Spaeth C40f. The Spaeth system allows a differentiation of the “open” angle where recession is noted at the E40f area and normal angle designated by C40f. This is classic angle recession. A system that forces the examiner to look at specific points will help differentiate normal from abnormal. B. Grade the angle. Scheie grade wide open trace pigment; Shaffer grade 4 trace pigment 40 degrees, closure impossible; Spaeth D40f trace pigment. The iris inserts into ciliary body band, which is a pale gray, angular approach is 40 degrees, and the peripheral configuration of the iris is flat. The scleral spur can barely be appreciated. C. Grade the angle Scheie grade wide open, PAS trace pigment; Shaffer grade 4 trace pigment, peripheral anterior synechiae (PAS) 40 degrees, closure impossible; Spaeth C40f trace pigment, PAS. The iris inserts high onto the inner wall of the eye, directly into scleral spur increasing the likelihood of chronic angle closure glaucoma. The angular approach is wide open and the peripheral configuration is flat. The point is according to the Shaffer system the angle would not be capable of closure, but there are PAS and the eye required a peripheral iridectomy. Thus the angular approach does not have to be steep to have angle closure disease. Clearly, more than one descriptor is necessary for many angles.

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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:
  1. History of symptoms of angle-closure disease;
  2. Any sign of angle-closure disease (glaucomflecken, iritis, iris atrophy);
  3. Family member with angle-closure disease
  4. Positive van Herick;
  5. High-risk angle-closure background (Asian, Alaskan, Indian heritage);
  6. History of any type of glaucoma, field loss, or disc damage;
  7. Elevated IOP, especially a significant change from baseline;
  8. Anticipated trabeculoplasty;
  9. Hyperopia;
  10. History of nanophthalmos;
  11. Pigment dispersion syndrome;
  12. Ocular blunt trauma or history of foreign body;
  13. Pseudoexfoliation syndrome;
  14. History of proliferative retinopathy;
  15. Hyphema;
  16. Preoperative cataract surgery to look for PAS;
  17. Retinal vascular occlusion;
  18. Following laser peripheral iridotomy;
  19. After use of pilocarpine;
  20. History of ocular tumor;
  21. Any suspicious iris lesion or cyst should prompt an angle examination;
  22. Posterior embryotoxon (prominent Schwalbe's line); and
  23. Unexplained hypotony to look for a cyclodialysis cleft

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.

Fig. 12 Gonioscopy techniques. A. Koeppe gonioscopy requires a hand-held slit lamp to view the angle, a lid speculum to assist in inserting the device, an appropriately sized Koeppe lens, and a saline bridge. The slit lamp is held in the examiner's dominant hand. Simultaneously the nondominant hand acts as a proprioceptive bridge to steady the slit lamp and keep the correct distance to the eye. B. Angle view through medium-sized Koeppe lens. The oniophotograph reveals intermittent PAS secondary to chronic trabeculitis. C. The Goldmann lens comes in various sizes in order to fit into the palpebral fissure area. Store the methycellulose viscous material inverted to avoid the instillation of air bubbles onto the contact lens. D. Apply the goniogel to the lens in a bubble-free fashion. E. Tell the patient that a contact lens will be placed on their eye in order to view the drainage area. The patient should be seated the at the slit lamp so that the eye is level with the positioning marks on the headrest. The upper lid is grasped and the patient instructed to look up slightly. The contact lens portion of the prism is tilted up to ease the insertion of the lower pole of the Goldmann lens into the lower fornix and onto the globe. F. As the lens is rotated into position, the patient is asked to look forward to bring the cornea into contact with the Goldmann and the upper lid is simultaneously released. There are variations of this technique; the examiner must find what works best for him. (Figure continues.)

Fig. 12 Continued. G. Both the examiner and patient are comfortable. The examiner rests his or her elbow on the slit-lamp base for stability while holding on to the gonioprism. The patient is comfortable at the slit lamp with their eye lined up perfectly for indirect gonioscopic evaluation. H. Difference in contact size between Goldmann and Zeiss lenses. The smaller contact area of the Zeiss lens causes less angle distortion especially when trying to view a narrow angle. The smaller area negates the need for a viscous bridge. I. The Zeiss lens inserted with the diamond orientation causes excessive contact with the lids and increases pain. Some examiners prefer this configuration. This is related to the variable handle designs and holding patterns adopted around the world. J. The square orientation is preferred. The lens causes less pain in this position and all four mirrors are then evaluated. K. This incomplete capillary bridge (black arrow) is easily seen in this picture. When learning Zeiss gonioscopy, it is imperative to evenly distribute the tear film, which implies the pressure across the cornea is roughly equal. When learning Zeiss gonioscopy, the examiner should rest their fourth and fifth digits on the patient's cheek for stabilization and orientation, look directly at the patient's eye when starting to insert the prism, and after globe contact, look through the biomicroscope. L. Excessive or uneven pressure on the cornea will cause corneal striae. Initially this is common and the examiner must anticipate this and adjust the force on the cornea. (Figure continues.)

Fig. 12 Continued. M. Which mirror has the proper orientation? Objects seen in the mirror are simply 180 degrees away, not crossed over. Angle orientation is simple and straight across. Mirror A is the correct answer. Mirror B is crossed over and is incorrect. N. Both mirrors now show the proper orientation. O. Diagram your findings. This goniophotograph is a view of the superior mirror revealing the inferior angle from an area that is recessed at the 4 o'clock posisiton to a broad area of PAS at approximately the 7:30 position. One method is to make a circle and use your favorite alphanumeric system to describe the angle at the appropriate clock hours. P. Refinishing a Zeiss mirrored lens is difficult. The silver mirror coating eventually has to be replaced. A higher grade of glass with greater reflectivity is an engineering marvel and acts as a mirror and reflects the light to the examiner. Therefore a mirror coating is not necessary. These lenses are new and are just starting to be evaluated in the field at the time of this writing (Gaasterland lens, Ocular Instruments, Bellevue, WA).

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.

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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.

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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

Fig. 13 Gonioscopic techniques for the narrow-angled eye. A. The small contact area of the Zeiss lens facilitates evaluation of the narrow angled eye. When the last roll of the iris obstructs the view into the recess, have the patient look into the mirror of regard. This helps to bring the angle recess into view. In this figure the examiner is evaluating the superior angle through the inferior mirror. In order to see further into the recess, the patient is instructed to look down, into the mirror of regard. B. The Goldmann lens has a much larger contact area and the edge of the lens compresses the limbus. C. When the patient looks down, the superior flange of the lens compresses the superior limbal area, distorting the peripheral angle. This will artificially narrow the angle and the view is compromised due to striae in the cornea. D. Indentation gonioscopy is an excellent technique to differentiate PAS from optical closure. Indentation gonioscopy is best performed with a Zeiss-type lens. When the examiner is unable to see into the angle recess because of bowing of the iris, compression gonioscopy is essential. With constant pressure, the examiner indents the cornea with enough force to displace aqueous posteriorly into the iris. In areas where the iris is unsupported, the iris separates from the cornea and the angle opens and the recess is seen. If the displaced iris opens all the way in to the recess, it is optical closure and the angle is still likely functional. If the angle opens up only into the meshwork, peripheral anterior synechiae (PAS) are present. In this example, the superior angle is optically closed and the inferior angle is permanently closed. (Figure continues.)

Fig. 13 Continued. E–1. View into the chamber recess in a narrow angled eye. Figure e–1 is the preindentation appearance. Only a small amount of pigment is seen and landmarks are lost. E–2. The angle structures are easy to see with indentation. As the iris is temporarily pushed back, the heavy pigmentation of the meshwork is seen and the irregular insertion of the iris onto the ciliary body is noted. This is angle closure at an early stage. The PAS are starting to develop deep in the recess. Indentation gonioscopy permitted the correct diagnosis at an early stage and this patient did well with a peripheral iridotomy. F. View of narrow angle as seen through a Goldmann lens. No angle structures are visualized. How would you grade this angle? Shaffer grade 2 to 3, obviously narrow. The Spaeth system requires a grade of the apparent insertion of the iris before and after indentation. The apparent insertion is designated by parentheses. Preliminary Spaeth = (A)20b3+. G. View of narrow angle as seen through Goldmann lens with patient looking in direction of mirror. Sometimes this maneuver will bring the recess into view. The angle is so narrow in this case that it does not help. (Figure continues.)

Fig. 13c Continued. H. View of same angle through a Zeiss lens. The angle recess is still hidden from view by the iris. I. View of same angle with indentation gonioscopy. There is a dramatic deepening of the chamber angle by a temporary posterior displacement of aqueous. The iris moves posteriorly opening the angle. In this case, the scleral spur is seen, green arrow. This angle is optically closed in this region. The knowledge the angle is optically closed instead of covered by PAS is important in predicting the outcome of laser iridotomy. The Spaeth grading of this angle is (A)C20b3+. A review of the Spaeth system implies the actual insertion of the iris is just below the scleral spur, the apparent insertion is Schwalbe's line, and the iris bows significantly. J. Appearance of angle post laser iridotomy. Pigment is dispersed postiridotomy and seen covering part of the inferior angle. The grading of this angle is now a C40f1+ptm. Thus the angle changes from a (A)C20b3+ to a C40f. This type of chart documentation reveals a great deal about the change in angle anatomy post iridotomy.

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.

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  1. Axenfeld's syndrome
  2. Squamous cell carcinoma at the limbus
  3. Squamous cell carcinoma invading the angle
  4. Posterior polymorphous dystrophy (PPD)

      PPD has a highly variable clinical presentation, but in many cases appears similar to an iridocorneal endothelial syndromes (ICE) syndrome but is bilateral. When it appears to be a bilateral ICE, think of PPD.

  5. Traumatic cyclodialysis cleft.

      Red arrow—Angle recession
      Yellow arrow— This area demonstrates disinsertion of the iris and ciliary body from the scleral spur. Iridodialysis implies the root of the iris is torn away from its attachment. In thisexample, the root of the iris is still attached to the ciliary body. The light tan area is the ciliary body and uveal tract separated from the scleral wall and this tan area represent the beginning of the cyclodialysis cleft.
      Black arrow—This dark oval-shaped area is a severe cyclodialysis cleft that extends far into the potential suprachoroidal space. This is the cause of the severe hypotony.

  6. Brushfield spots are most commonly seen in Down's syndrome (80%), but not exclusively (20% of normal subjects). The white spots run in a circle around the periphery of the iris and are caused by a localized area of increased density of the anterior layer of the stroma.
  7. Goniophotograph of patient from Figure 14F. The angle landmarks are poorly identified and the iris inserts high into the angle. This 6-month-old infant has congenital glaucoma with corneal edema and classic trabeculodysgenesis. A clear appreciation of normal facilitates recognition of developmental angle anomalies such as trabeculodysgenesis, which may present clinically at any age. Obviously when the defects are severe, the presentation is at birth or soon after. Less severe defects may present as juvenile glaucoma. A very high insertion of the iris onto the inner wall of the eye is classic for trabeculodysgenesis. This is typically associated with a lack of definition of iridocorneal structures. Haab striae are usually seen in congenital glaucoma as well as other iris defects. Note the Brushfield spots on the iris.
  8. Appearance of the angle 6 months post–360 degree trabeculotomy. The angle recess is much wider and the tan ciliary body band can be seen (white arrow), scleral spur (red arrow) and trabecular meshwork (green arrow). Vision improved 2 weeks after surgery because of IOP reduction and corneal clearing. Two weeks later, the infant started smiling at his parents for the first time.

Fig. 14 Mystery angles (answers in body of text in last paragraph). A. Goniophotograph captured through a Koeppe lens during an examination under anesthesia (EUA) of a 4-year-old with suspicious optic discs and borderline intraocular pressures (IOPs). The iris sweeps from the recess all the way up to a prominent Schwalbe's line. The appearance of the iris is almost transparent or diaphanous; it is not opaque because the majority of the underlying angle structures are visualized. The black arrow indicates iris processes that sweep up into the angle; these are not peripheral anterior synechiae. The red arrow points to the ciliary body band, the scleral spur is poorly seen. The yellow arrow indicates a prominent Schwalbe's line. The fellow eye has the same appearance. What is your diagnosis? B. Slit-lamp photograph of a limbal lesion. The lesion appears confined to the cornea and the IOP is normal. Treatment included aggressive cryotherapy of the area. C. The goniophotograph of (B) reveals the lesion has invaded the chamber angle. A white mass is seen in the angle. What is your diagnosis? D. Goniophotograph obtained through a Koeppe lens immediately prior to trabeculectomy for uncontrolled glaucoma. The angle process is bilateral. The patient is 54-year-old female with a 30-year history of initially open-angle glaucoma. The angle originally appeared open; however, over the past 10 years has developed the captured appearance. Note the difference in the characteristics of the iris. No angle structures are seen underneath the iris. It is totally opaque, not diaphanous as in figure a. These peripheral anterior synechiae (PAS) bridge the angle far onto the cornea, a highly abnormal position for the iris except for a few conditions. What is your differential and diagnosis? If a unilateral process, iridocorneal endothelial syndromes (ICE) would be first. This process is bilateral. The corneal endothelium demonstrates various areas of endothelial plaques, vesicles, and striae. (Figure continues.)

Fig. 14 Continued. E. This child suffered blunt trauma to the globe with subsequent severe hypotony. The red arrow indicates an area of angle recession where the face of the ciliary body appears sheared compared to other areas. What do the yellow and black arrows reveal? F. Six month-old infant with inability to follow and no fixation found to have significant cupping of the optic nerves. The abnormalities were bilateral. Peculiar white iris spots were identified. Identify these spots. G. Goniophotograph of angle through a Koeppe lens of same infant with peculiar iris lesions. Describe the angle and what is the most likely diagnosis? H. Goniophotograph of angle after surgical procedure. Describe the angle and identify the most likely type of angle surgery performed.

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.

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2. Foster PJ, Oen FT, Machin D, et al: The prevalence of glaucoma in Chinese residents of Singapore: a cross sectional population survey of the Tanjong Pagar district. Arch Ophthalmol 118:1105, 2000

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

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

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6. Quigley HA, Friedman DS, Congdon NG: Possible mechanisms of primary angle-closure glaucoma and malignant glaucoma. J Glaucoma 12:167, 2003

7. Coster DJ, ed. Physics for Ophthalmologists. Edinburgh: Churchill Livingstone, 1994:38–40

8. Henkind P: Angle vessels in normal eyes. A gonioscopic evaluation in anatomic correlation. Br J Ophthalmol 48:551, 1964

9. Lichter PR: Iris processes in 340 eyes. Am J Ophthalmol 68:872, 1969

10. Devereux JG, Foster PJ, Baasanhy J, et al: Anterior chamber depth measurement as a screening tool for primary angle-closure glaucoma in an east Asian population. Arch Ophthalmol 118:257, 2000

11. Spaeth GL: Gonioscopy: uses old and new. The inheritance of occludable angles. Ophthalmology 85:222, 1978

12. Wojciechowski R, Congdon N, Anninger W, et al: Age, gender, biometry, refractive error, and the anterior chamber angle among Alaskan Eskimos. Ophthalmology 110:365, 2003

13. Foster PJ, Johnson GJ: Glaucoma in China. How big is the problem? Br J Ophthalmol 85:1277, 2001

14. Siom DH, Goh LG: Screening for glaucoma in the Chinese elderly population in Singapore. Singapore Med J 40:644, 1999

15. Mapstone R, Clark CV: Diurnal variation on the dimensions of the anterior chamber. Arch Ophthalmol 103:1485, 1985

16. George R, Paul PG, Baskaran M, et al. Ocular biometry in occludable angles and angle closure glaucoma: a population based survey. Br J Ophthalmol 87:399, 2003

17. van Herick W, Shaffer RN, Schwartz A: Estimation of width of angle of anterior chamber: incidence and significance of the narrow angle. Am J Ophthalmol 68:626, 1969

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

19. Congdon NG, Spaeth GL, Augsburger J, et al: A proposed simple method for measurement in the anterior chamber angle: biometric gonioscopy. Ophthalmology 106:2161, 1999

20. Scheie H: Width and pigmentation of the angle of the anterior chamber. A system of grading by gonioscopy. Arch Ophthalmol 58:510, 1957

21. Shaffer RN: Gonioscopy, ophthalmoscopy, and perimetry. Trans Am Acad Ophthalmol Otolaryngol 64:112, 1960

22. Spaeth GL: The normal development of the human chamber angle: a new system of descriptive grading. Trans Ophthalmol Soc UK 91:709, 1971

23. Forbes M: Gonioscopy with corneal indentation: a method for distinguishing between appositional and synechial closure, Arch Ophthalmol 76:488, 1966

24. Alward W: Color Atlas of Gonioscopy. Barelona: Mosby-Wolfe, 1994

25. Palmberg P: Gonioscopy. In Ritch R, Shields MB, Krupin R, eds: The Glaucomas. St Louis: Mosby, 1996

26. Becker S: Clinical Gonioscopy—A Test and Stereoscopic Atlas. St Louis: CV Mosby, 1972

27. Shields MB: Textbook of glaucoma, fourth edition, 1998, Williams and Wilkins,

28. Stamper RL, Leiberman MF, Drake MV: Methods of Gonioscopy, Becker-Shaffer's Diagnosis and Therapy of the Glaucomas, 7th ed. St Louis: Mosby, 1999

29. Fellman RL: Gonioscopy. In Choplin NT, Lundy DC. eds. Atlas of Glaucoma. London: Martin Dunitz, 1998:39–55:

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

31. Henkind P, Starita RJ: Atlas of Glaucoma. Clinical Signs in Ophthalmology. Clinical Signs series, Alcon Laboratories, Fort Worth,1986

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