Ординатура / Офтальмология / Учебные материалы / Atlas of Glaucoma Second Edition Choplin Lundy 2007
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42 Atlas of glaucoma
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Figure 5.2 The natural inability to see the chamber angle. (a) Iris atrophy. Routine biomicroscopy reveals iris atrophy but nothing definitive about the chamber angle. Clearly, any patient with iris anomalies requires gonioscopy. This patient has mesodermal dysgenesis. (b) Light rays. No matter how hard one tries, it is impossible to see into the chamber angle due to the physical interaction of light rays as they cross the aqueous–cornea–air interface. The construct of a light ray is grounded on establishing a perpendicular line at the air–cornea–aqueous boundary, called the normal (white line).
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Gonioscopy 43 |
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GONIO DEVICE |
DIRECT |
ADVANTAGE |
DISADVANTAGE |
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Goniolens |
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Excellent anatomic view and convenient |
Patient must be in supine position, laborious |
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Koeppe |
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for examination under anesthesia. The |
examination, time consuming, examiner must |
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lens magnifies the view and there is no |
change position and hand-held slit lamp required. |
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angle distortion. Panoramic view of |
Not convenient for office use. |
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angle and lens comes in three sizes. |
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Barkan |
Surgical goniolens with blunted side |
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allows access for goniotomy, variable |
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sizes. |
May be difficult to stabilize on the globe during surgery.
GONIOPRISMS |
INDIRECT |
ADVANTAGE |
DISADVANTAGE |
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Goldmann |
Available in one, two or |
Best gonioprism for neophyte to learn |
Goniogel required for best view which |
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three mirror prism |
three mirrors. |
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angle anatomy, viscous bridge creates |
obscures patient’s vision and may compromise |
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suction effect stabilizing eye for |
further same-day diagnostic tests, corneal |
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examination and laser therapy. The |
abrasion in compromised cornea, part of angle |
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classic three-mirror prism allows a |
hidden in narrow angled eyes, time |
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simultaneous view of the angle and |
consuming when necessary to evaluate both |
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ciliary body 1, peripheral retina 2, the |
eyes. May distort angle when trying to view |
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trapezoidal mirror the mid-peripheral |
narrow-angled eyes. Time consuming on a |
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retina 3 and the center lens the fundus 4. busy clinic day. |
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4-mirror gonioprisms
Gaasterland
Zeiss
Volk
Rapid evaluation without goniogel, no corneal compromise with goniogel, further same day diagnostic tests not compromised, indentation or compression gonioscopy allows expert evaluation of narrow-angled eyes with hidden anatomy. Patient friendly with minimal movement to see 360 degrees.
Must first master Goldmann gonioprism, more hand–eye coordination necessary than for Goldmann gonioprism, handle required, easy to apply excessive force causing corneal folds with poor view of angle. The silver may peel off from the Zeiss, the Volk has a special coating and the Gaasterland requires no coating.
Figure 5.3 Advantages and disadvantages of direct and indirect gonioscopy. Direct and indirect gonioscopic techniques constitute the two major methods of overcoming total internal reflection of light rays and visualizing the angle. The comprehensive ophthalmologist must be proficient with both techniques in order to diagnose and treat glaucoma.
NORMAL ANGLE VARIABILITY
Routine gonioscopy reveals wide variations in chamber depth, iris processes, ciliary body band width, angular approach, trabecular pigment and vessels (Figure 5.5). An appreciation of this immense variability facilitates early identification of angle pathology. This variability is rarely seen, because gonioscopy is not routinely performed unless ocular
pathology, such as rubeosis iridis, prompts the examiner to look further. The depth and peripheral configuration of the anterior chamber are the most important factors that lead to visual disability. 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. The depth of the anterior chamber is highly variable
Light rays emerging from the iris either are bent (refracted), exit parallel (unbent) to the normal of the cornea, follow the critical angle or reflect internally. The dotted white arrow represents a light ray emerging unbent from the cornea because it emerges parallel to the normal. When an incident light ray (green arrow) approaches the normal obliquely, then the ray will emerge bent according to Snell’s Law. (n1 * sine i n2 * sine r) with n1 index of refraction of medium (aqueous), sine i the sine of the angle of incidence, n2 index of refraction of medium (air), sine r the sine of the angle of refraction. The ray is bent away from the normal as it emerges because the index of refraction of the aqueous humor is greater than that of air. Similarly, when you try to look into the angle, light rays are bent away from the angle towards the pupil because the index of refraction of aqueous is greater than that of air (1.38 vs. 1.0). Light emanating from the peripheral iris creates an even larger oblique incident ray and, according to Snell’s Law, a critical angle occurs when the ray is bent 90 from the normal (yellow arrow). The critical angle does not emerge from the cornea and is unseen by the examiner. The critical angle is 46.5 for the anterior chamber. Any ray of light that exceeds 46.5 will be reflected back into the anterior chamber (red arrow). This represents total internal reflection of light and is the reason the angle cannot be visualized without a gonioprism. (c) Direct gonioscopy with a Koeppe lens. The Koeppe lens eliminates total internal reflection of light rays by two methods. First, the index of refraction of the lens is 1.4, very close to that of aqueous. This practically eliminates any significant bending of light at the cornea–air interface and the light passes through. The curvature of the Koeppe is steeper than the cornea, further allowing the light ray to pass to the examiner. Indirect gonioscopy with a gonioprism, lateral view (d) and frontal view (e). This gonioprism also eliminates the problem of total internal reflection of light rays through an indirect view of the angle. The Gaasterland lens (Ocular Instruments) is constructed of glass. The index of refraction of glass approximates that of the aqueous, thereby allowing light to pass through the cornea into the lens (white dotted line). Either a mirror or in this case the high index refraction of the glass acts as a mirror and reflects the light to the observer (green arrow).
44 Atlas of glaucoma
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Figure 5.4 Six key anatomic landmarks of the normal chamber angle. The typical 140 panoramic view of the angle as seen through a gonioprism can be overwhelming unless the observer purposely seeks to find the six key structures in every patient. The scleral spur (4) is the most reliable gonioscopic landmark. This circular white roll bar is the scleral anchor for the ciliary body, which separates trabecular from uveoscleral outflow. It consistently is the least variable of the angle structures. View the diagram, identify the six key structures and refer to the six-point gonioscopy checklist. Correlate the drawing with the slit beam and the overview goniophotographs.
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and dependent on multiple factors including genetics, refractive error, age, sex, size of the lens and even diurnal factors.
Gonioscopy is important for family members of angle closure glaucoma patients, for they 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. The iris is more likely to insert anteriorly in Eskimos–Inuit Asians Blacks Whites. An understanding of the ethnic traits of the iridocorneal angle facilitates the early diagnosis of glaucoma.
Figure 5.5 Normal variability of the chamber angle. (a) Serpentine angle vessel. Blood vessels are normally visible in the angle in 62% of individuals with blue eyes and 9% with brown eyes. These circular vessels are nestled in the face of the ciliary body and do not cross the scleral spur. As seen during gonioscopy, any vessel that crosses the scleral spur (green arrow) is considered abnormal. (b) Blood in Schlemm’s canal. Blood may reflux into Schlemm’s canal during gonioscopy and appear as a red band. It is not unusual to have a segmental appearance as the canal has many branches. Blood is more likely to reflux into the canal associated with hypotony or elevated episcleral venous pressure. (c) Iris processes. Iris processes are present in approximately 35% of normal eyes. They are pigmented in brown eyes and gray in blue eyes. Iris processes (green arrow) are typically finer than PAS, most common nasally and allow some view of posterior angle structures. The white arrow points to the scleral spur. (d) Absence of trabecular pigment. Lack of trabecular pigment further blurs outflow boundaries as seen gonioscopically. This juvenile angle reveals the ciliary body band (green arrow) but the scleral spur is not distinct (white arrow), and there is no pigment in the trabecular meshwork (red arrow). (e) Mild trabecular pigment. This goniophotograph of a 5-diopter myope reveals a variable insertion of the iris onto the ciliary body band (green arrows). The scleral spur is seen (white arrow), and trabecular pigment (red arrow) is minimal. It is common to see some pigment dusting the angle, especially in individuals over age 50. Excessive trabecular pigment at the 12 o’clock position occurs in only 2.5% of individuals and is usually pathological. (f) Deep anterior chamber. The insertion of the iris into the ciliary body band along with its curvature is partly genetically determined. This goniophotograph of a deep anterior chamber makes it easy to see the scleral spur and trabecular meshwork. (g) Shallow anterior chamber. A shallow anterior chamber greatly increases the likelihood of angle closure disease. The best method to detect a shallow chamber is with gonioscopy, because the chamber depth may appear deep at the slit lamp, but the angle may already demonstrate peripheral anterior synechiae.
Gonioscopy 45
Scleral spur
ciliary body
normal angle vessel
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46 Atlas of glaucoma
This marked variability of the configuration of the |
to classification systems, additional findings such |
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angle has stimulated an evolution of classification |
as pigmentation, synechiae, iris processes, clefts, |
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systems. |
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recession, vessels, precipitates, cysts, etc. are noted |
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with their clock hour location. The Schaefer and |
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ANGLE CLASSIFICATION SYSTEMS |
Scheie systems are well known and have signifi- |
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cantly improved angle grading. However, in the 21st |
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century, thorough descriptions of angle anatomy |
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One of the stumbling blocks related to gonioscopy |
are now driven by age, gender, and population. |
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is the concise documentation of angle findings. |
The Spaeth Gonioscopy System evaluates |
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A reliable system is crucial to document and under- |
three angle variables and continues to gain global |
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stand how the chamber angle changes (Figure 5.6). |
momentum. The reason is that it enhances the |
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Chart documentation should accurately reflect |
description of the angle because the iris may insert |
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angle findings. The chamber angle is a very com- |
onto the inner wall of the eye differently in an Asian |
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plex structure. For example, during a new patient |
compared to a Caucasian and this is easy to com- |
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examination it is not enough to say the angle is |
municate with the system. It adds validity to any |
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‘open’ or ‘narrow.’ This is tantamount to saying the |
examiner’s description of the angle by forcing them |
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optic nerve is ‘normal.’ Even if the nerve looks nor- |
to describe in alphanumeric form what they see. |
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mal, its appearance is documented with a picture, |
The mandatory decisiveness of the system is its |
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drawing, or description in order to establish a base- |
key to success. After learning the system, a three- |
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line for future reference. The chamber angle is no |
dimensional view of the angle is communicated in |
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different – it can change yearly, or daily, especially |
alphanumeric form (Figure 5.7) compared to a |
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if pharmacologically provoked. The standard of |
simple ‘angle is open’. |
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care is to document findings according to one of |
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the angle classification systems or to completely |
INDENTATION GONIOSCOPY AND THE |
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annotate descriptive initial findings. Future refer- |
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ence may indicate that the angle has not changed |
NARROW-ANGLED EYE |
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and is ‘open’, but initially a full angle description is |
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required. For example, a more appropriate angle |
Additional skills are required to view the crowded |
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description is ‘wide open for 360 , ciliary body |
or narrow-angled eye (Figure 5.8). To diagnose and |
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band easily seen and moderate trabecular pigmen- |
treat the narrow angle adequately, the gonioscopist |
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tation.’ This angle can be dilated safely. In addition |
must understand the relationship between the |
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SYSTEM |
SYSTEM |
ANGLE STRUCTURES |
CLASSIFICATION |
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BASIS |
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Scheie |
Extent of angle |
all structures seen |
Wide open |
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1957 |
structures |
iris root not seen |
Grade I narrow |
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visualized |
ciliary body band not seen |
Grade II narrow |
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posterior trabeculum obscured |
Grade III narrow |
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only Schwalbe’s line visible |
Grade IV narrow |
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Shaffer |
Angular width of |
wide open (30°–45°) |
Grade 3–4, closure improbable |
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1960 |
the recess |
moderately narrow (20°) |
Grade 2 closure possible |
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extremely narrow (10°) |
Grade 1 closure probable |
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partly or totally closed |
Grade 0 closure present |
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Spaeth Three variables: 1971 1. Angular
approach to the recess
2. Configuration of peripheral iris 3. Insertion of iris root
1. Level of iris insertion
Anterior to Schwalbe’s line
Behind (posterior) to Schwalbe’s
sCleral spur
Deep into ciliary body band
Extremely deep
2.Angular approach to recess
3.Peripheral iris configuration
flat approach
bowing (forward bow, 1 to 4 plus)
concave (post. bow, 1 to 4 plus)
p = plateau
A
B
C
D
E
0°–40°
f
b
c p
Figure 5.6 Angle classification systems. Classification systems of the angle vary widely. These systems continue to evolve. The author uses the Spaeth system, which forces the examiner to grade three critical areas of the outflow system.
Gonioscopy 47
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Figure 5.7 Gonioscopic classification systems. 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. The Spaeth 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 and is explained in the next section.
(a) Deep angle goniophotograph. This is an obviously deep angled goniophotograph. Classify the angle according to the three systems. Scheie wide open; Shaffer 4; Spaeth D40f. Note the wide ciliary body band (3) and the scleral spur (4). (b) Spaeth D40f. The Spaeth system requires identifying where the iris inserts onto the inner wall of the eye, the peripheral shape of the iris, and the angular approach. This is a common angle configuration for individuals of European ancestry. This is the Spaeth classification of the goniophotograph from (a). (c) Deep angle goniophotograph. This is another deep angled goniophotograph; however, note the difference in classification systems and to what they relate. Scheie grade I, Shaffer 4; Spaeth C40f. (d) Spaeth C40f. Even though the angle is ‘wide open’, creeping angle closure is more likely in this individual of African-American descent, because the iris inserts much higher onto the inner wall of the eye, closer to the meshwork. The Spaeth system denotes this through the C nomenclature; the other classification systems do not differentiate this insertion point. The green arrow points to the variable high insertion; this is not a peripheral anterior synechia. (e) Narrow angle goniophotograph. This angle is clearly narrow (Scheie III, Shaffer Grade 2 and Spaeth ?A25b3 ); however, there is more to the Spaeth grading as divulged in the next section. (f) Spaeth ?A25b3 . This system dictates that the iris appears to insert high, but is it possible the iris inserts further into the angle and the true insertion site is hidden by the iris? The angular approach is worrisome and designated by 3 .
48 Atlas of glaucoma
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Figure 5.8 Additional methods of viewing the narrow-angled eye. (a) Angle–mirror alignment. In the narrow-angled eye, the last roll of the iris may block the view of the peripheral angle. In this drawing, it is difficult to see far into the angle recess. (b) Angle–mirror alignment improved with gaze. Instruct the patient to look towards the mirror of regard. This will further rotate angle structures into the plane of the mirror, allowing visualization of the angle.
(c) View through Zeiss gonioprism without indentation. The iris hides the outflow structures. (d) View through Zeiss gonioprism with indentation, appositional closure. Compression gonioscopy forces the iris backwards, opening the angle. The scleral spur is seen along with the trabecular meshwork. This angle is optically or appositionally closed. (e) View through Zeiss gonioprism with indentation, synechial closure. With indentation, there are broad PAS. This angle is severely compromised by angle closure disease.
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Gonioscopy 49 |
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anterior chamber angle, the viewing mirror, and |
Any patient with a pigmented iris lesion |
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dynamic or indentation gonioscopy. Gonioprisms |
deserves gonioscopy (Figure 5.13). This patient har- |
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with a large cornea-contact area are not well suited |
bored significant angle pathology and, when dis- |
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for dynamic gonioscopy because they distort the |
covered, required complex iridocyclectomy to |
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iridocorneal angle. Indentation or dynamic gonio- |
remove a malignant melanoma of the ciliary body. |
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scopy facilitates the differentiation between appo- |
The patient had no visual complaints. |
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sitional and synechial angle closure. Indentation |
Ocular trauma causes a myriad of anterior |
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gonioscopy is best performed with a small contact |
segment findings. One of the most difficult to appre- |
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surface diameter of 9 mm, as seen with a Zeiss-type |
ciate is a cyclodialysis cleft, especially if small. All |
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gonioprism. Dynamic or indentation gonioscopy |
patients with a significant cleft demonstrate hypotony |
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consists of a firm forward motion of the gonioprism |
with poor vision (Figure 5.14). Another conse- |
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against the central portion of the cornea. This forces |
quence of trauma is angle recession (Figure 5.15). |
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the aqueous posteriorly, pushing the iris back- |
The discovery of angle recession may help prompt |
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wards, opening the peripheral angle to reveal either |
the patient to remember a traumatic ocular event |
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appositional or synechial closure (Figure 5.9). |
that occurred decades earlier. These patients |
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should be followed for life for the development of |
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ANGLE PATHOLOGY |
secondary glaucoma. |
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A gonioprism is also useful to magnify struc- |
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tures in the posterior chamber and lens area in |
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Angle pathology may be subtle, especially during |
children during an examination under anesthesia. |
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the nascent stage of a disease, or the presentation |
The Koeppe lens facilitates evaluation of the anterior |
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may be dramatic depending on a congenital or trau- |
segment by revealing dragged ciliary body processes |
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matic structural abnormality. Gonioscopy may help |
on the posterior lens capsule (Figure 5.16). This was |
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clinch the diagnosis in many cases – a simple ele- |
easily seen with a hand-held slit lamp with the |
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gant method of augmenting one’s diagnostic skills. |
Koeppe lens. |
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One area of confusion centers on the differential |
Peripheral anterior synechiae may be subtle or |
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between mesodermal dysgenesis, iridocorneal endo- |
dramatic and may be confused with iris processes. |
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thelial syndrome (ICE), and posterior polymorphous |
Review the differences between PAS and iris |
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dystrophy (Figure 5.10). |
processes (Figure 5.17). In early neovascularization |
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The angle in aniridia is another very confusing |
of the angle, vessels grow over the scleral spur into |
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picture (Figure 5.11). There may be a small stump of |
the trabecular meshwork area and then arborize |
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iris remaining, and outflow structures are obscured. |
laterally; compare to normal vessels (Figure 5.5a). |
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It is imperative to differentiate between sporadic |
The angle is laced with vessels and, when the asso- |
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and autosomal dominant forms of aniridia in order to |
ciated fibrovascular membrane contracts, it closes |
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determine the risk for Wilms’ tumor. Angle surgery |
the angle (Figure 5.17d). |
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in aniridia may be impossible due to the lack of |
Gonioscopy is an immensely useful adjunctive |
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development of Schlemm’s canal. |
tool to diagnose and treat eye disease. A thorough |
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Angle findings post-intraocular surgery may |
understanding of normal is a prerequisite to appre- |
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enhance diagnosis or at least help explain visual |
ciate early angle pathology. The ability to scan the |
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symptoms (Figure 5.12). Any surgeon who performs |
angle rapidly, indent when necessary, record find- |
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intraocular surgery should be aware of epithelial |
ings and compare this to future and past examina- |
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implantation cysts, which may become apparent |
tions will reduce blindness due to a number of eye |
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years after surgery. Many patients respond to alcohol |
diseases. There are a plethora of books and chapters |
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injection into the cyst. This patient has undergone |
on gonioscopy and the reader is encouraged to |
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penetrating keratoplasty. |
review these valuable sources. |
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50 Atlas of glaucoma
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(d) |
Figure 5.9 Indentation gonioscopy. The goniophotograph of the narrow angle in Figure 5.7f demands further evaluation. The observer does not know whether the closure is appositional (optical) or synechial (PAS) in nature. (a) Goldmann view of narrow angle. Indentation gonioscopy is not possible with this size lens; it is impossible to see any angle detail without distorting the angle. (b) Goldmann view of narrow angle with gaze shifted into the mirror. Even when the patient shifts their gaze further into the mirror, the details of the angle are not evident. (c) Zeiss view without indentation. It is still impossible to see any angle detail with the Zeiss prism Spaeth A25b3 . (d) Zeiss view with indentation. Finally, with compression or indentation gonioscopy, the iris is easily displaced posteriorly, demonstrating the scleral spur and trabecular meshwork. This angle is appositionally or optically closed. The angle as seen prior to indentation is noted in parenthesis. Following indentation, the insertion site is recorded as seen: (A)C25 b3plus,1 PTM, no PAS. (e) Zeiss view post-iridotomy. The angle deepens considerably following laser iridotomy. Pigment dusts the angle liberated from the iridotomy. Spaeth C40f. The classification system facilitates the recording of how the angle changes following intervention. (f) Zeiss view of narrow-angled eye. It is impossible to see into the peripheral angle. This is an apparent A insertion with a 30 approach and marked bowing of the iris, A30b3 . (g) Zeiss view with indentation of (f) . Indentation gonioscopy reveals significant angle pathology. The dark area that the iris inserts into is actually the pigmented trabecular meshwork, not the ciliary body. The white area above that is the anterior trabecular meshwork and the pigment above that is dusting Schwalbe’s line. (A)B30b3 . This alphanumeric explanation of the angle informs the examiner that the iris appears to insert into the cornea, but with compression inserts into the trabecular meshwork and the angle bows significantly. Clearly, this patient needs a peripheral iridotomy. Without indentation gonioscopy, it is impossible to see into the depths of the angles in this narrow-angled eye. This amount of detail would be impossible to obtain accurately with a standard Goldmann-type gonioprism.
Gonioscopy 51
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Figure 5.9 Continued.
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Figure 5.10 Angle pathology. Differentiating mesodermal dysgenesis from iridocorneal endothelial syndromes (ICE). (a) and
(b) Iris atrophy with ICE syndrome. Note the iris atrophy (green arrow). Iris anomalies should always prompt an angle examination. The iris is dragged far onto the cornea. The goniophotograph (b) reveals very high PAS. Only a few diseases cause very high anterior PAS, such as ICE, posterior polymorphous dystrophy, rubeosis iridis, and mesodermal dysgenesis.