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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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).

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.

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.