Ординатура / Офтальмология / Английские материалы / The Glaucomas Volume 1 Pediatric Glaucomas_Sampaolesi, Zarate_2009

Sometimes, the image observed may be very different from the one shown and be forked-shaped (two points), it is the corneal wedge (Fig. 11.4c), i.e., in the Schwalbe line there are three lines that come together, as shown in Fig. 11.4. This depends on the gonioscope used (Goldmann threeor one-mirror, Worst, etc.) and particularly on the angle formed by the optical observation axis (microscope) with the illumination axis (slit). If the angle is large the image will be like the one illustrated in Fig. 11.4a, whereas if it is smaller, it resembles Fig. 11.4b, and if it is too small, it will be fork-shaped, as in Fig. 11.4c. This is an easily under-

standable optical phenomenon of perspective and parallax. This fork shape is also more visible when the onemirror Goldmann lens is used (Fig. 11.5), since in this case the direction of the illumination axis is parallel to the posterior corneal surface.

When the anterior chamber is very shallow, the anterior position of the iris and pupil enables the equator of the crystalline lens, the ciliary processes, and the posterior zonular fibers (Fig. 11.6) to be seen with the three-mirror contact lens. It can also be seen in the deep chamber when the pupil is well dilated.

Fig. 11.4a–c Determination of the position of the Schwalbe line. The point of interruption of the anterior corneoscleral profile line, which signals the location of the Schwalbe line may be located either far away from the posterior corneoscleral profile line as in a, proximal to it as in b, or almost touching

it as in c. This depends on the angle formed by the observation axis (biomicroscope) and the illumination axis (illumination arm). In a, they are widely separated, in c, they are very close; b represents an intermediate position between a and c

Fig. 11.5 I direction of the rays in a gonioscope depending on whether a 62° one-mirror or a three-mirror round rim gonioscope with an inclination of 59° is used. These degrees are measured by the angle formed by the mirror with the anterior surface of the lens. When the one-mirror lens is used, the light bundle follows the posterior corneal surface and permits observation of the chamber angle fundus, as shown by II, i.e., the profile of the corneoscleral wall of the chamber angle and the front of the ciliary-iris part are seen. In contrast, when the round mirror of the three-mirror lens is used, the light bundle

Fig. 11.6 The chamber angle highly narrowed by the shifting of the iris-lens diaphragm to the front. The posterior corneoscleral profile line is not attached to the anterior one because the chamber angle is blocked. The anterior position of the iris-lens diaphragm provides a view of the posterior surface of the crystalline lens, the posterior zonular fibers, the Petit canal and, sometimes, the head of the ciliary processes

follows the anterior surface of the iris and then, as shown in III, the front of the corneoscleral surface of the chamber angle and the anterior end of the ciliary body band are seen. The iris surface is seen in profile and it obscures the recess of the chamber angle and the posterior part of the ciliary body band. This is the reason why using the 62° one-mirror lens, or a recently manufactured two-mirror lens, also with 62° in each mirror, is recommended. However, the three-mirror lens may be used in children up to 3 years of age since the recess of the chamber angle is absent at this age

Fig. 11.7a–d Clinical classification of the chamber angle according to gonioscopic visibility. Gonioscopic visibility of the chamber angle. a Open chamber angle with broad entry; the ciliary body band is complete and the iris root can be seen. b Chamber angle with narrow entry; the ciliary body band is visible only in its anterior part. c Very narrow chamber angle; the trabecular meshwork is barely visible at its anterior end, at

the level of the Schwalbe line. d The entry of the chamber angle is blocked, since not only is the trabecular meshwork not seen, but also the posterior corneal profile line is continued directly into the iris profile line with an absence of the parallax image represented by the illustration. At the bottom are the sagittal sections of the chamber angle corresponding to the four gonioscopic images at the top

Fig. 11.8a–c Influence of the shape of the chamber angle and of the depth of the anterior chamber on the visibility of the chamber angle. At the top, the illustrations represent the composition of the anterior chamber, and at the bottom of the drawing represents a section of the chamber angle that shows the composition of the chamber angle in each case. a Trapezoidal chamber angle and open chamber angle, which is very

easy to examine, even when the iris root is long. b Planoconvex anterior chamber. There is a direct relationship between the amplitude of the chamber angle and the length of the iris root. c Concave-convex anterior chamber; the circular last folds of the iris reduce the amplitude and make the chamber angle difficult to see (reproduced from [2])

The Shape of the Chamber Angle

There is a difference between chamber angle amplitude and its visibility. The amplitude (from the anatomical point of view) depends on the length of the ciliary band. This in turn depends on the iris root insertion into it. The closer to the spur the iris is inserted, the smaller the chamber angle is anatomically.

The gonioscopic visibility (Fig. 11.7) of the chamber angle depends on the position of the inner iris wall relative to the fixed external scleral wall. The entry may be open, and it may be broad, narrow, or very narrow depending on the case. The entry of the chamber angle is broad if the ciliary body band is visible in at least half of the circumference (Fig. 11.7a). It is narrow if the ciliary body band is not visible (Fig. 11.7b) or is only visible at its anterior end. It is very narrow if the scleral trabecular meshwork is visible only in its anterior end or is not visible (Fig. 11.7c). The entry of the chamber angle is blocked when both walls are attached up to the Schwalbe line or even over it (Fig. 11.7d). In short, amplitude is an anatomical concept, while visibility is mostly physiological.

Amplitude and visibility are sometimes dependent on each other: if the iris root is short the chamber angle

is easily visible, even when it is anatomically reduced, with a very small ciliary band.

They are sometimes independent: if the iris root is long the chamber angle can only be seen at the site where the last rolls of the iris are short. If there is a place where the last rolls of the iris are tall, the chamber angle cannot be seen, even when it is anatomically broad.

Understanding these concepts becomes even more difficult when the anterior chamber depth is taken into consideration. The anterior chamber may be deep or shallow and this influences visibility.

The illustrations in Fig. 11.8 (modified from [2]) show the relationship between the chamber angle and the depth and shape of the anterior chamber. The depth of the chamber angle depends on the distance between the Schwalbe line and the farthest point in the ciliary profile line. The extension of the iris root is measured between the line of the last roll of the iris and the root insertion.

Chamber angle amplitude has two anatomic variations. Broad chamber angles correspond to a broad ciliary body band and a short iris root. Narrow chamber angles have a narrow ciliary body band and a long iris root.

The New Gonioscopic Lens of Roussel

and Fankhauser

In 1983, Fankhauser and Roussel [3] built a new contact lens, CGA1, with a mirror manufactured by HaagStreit Meridian, for irradiating pathological structures in the chamber angle with high power lasers (Figs. 11.9 and 11.10). Fankhauser explained to the mathematician Roussel the five problems of the three-mirror Goldmann contact lens and Roussel resolved the geometric problem presented by the optical aspects.

Since this lens has a spherical anterior surface, the movements made to focus precisely on the structures to photocoagulate have very little influence on the diameter of the beam and the focus and thus keep it constant. At the same time, the image is independent of any manipulation of the lens. This is why this lens is essential, for example, in laser microphotocoagulation in the trabecular meshwork after nonpenetrating deep sclerectomy (NPDS).

With its extraordinary quality, this lens enables very fine details to be recognized, and the resulting photographs and videos have a quality that is rarely seen. Its convex anterior surface is what gives great amplification and resolution to the image, and it is possible to recognize new structures in the chamber angle that could not previously be seen.

The lasers used for microsurgery today are much more powerful. Argon and krypton have a power of 3 W, while neodymium and others have a power of radiation of the order of 108 W, which can generate mechanical effects used for cutting or perforating the irradiated tissues. It is fundamental to have wide-angle beams, since otherwise the tissues behind or in front of those being treated would be damaged.

Today, even though it was designed for application with these new lasers, the great amplification and resolution it provides means that it is also used in all the diagnostic gonioscopies and for goniophotography.

Optical Properties

Its convex anterior surface enables the convergence of the rays without introducing aberrations, all the while providing high optical resolution. The mirror of this lens has an inclination of 58°, a magnification of 1.5, and its thickness is 17 mm. It reduces the focus of the laser on the structures by a factor of 1.5 in comparison with the Goldmann lens.

It has an antireflective layer. There are two types: CGA7 and CGA8, with a radius of curvature of 7.4 mm and 8.2 mm, respectively.

Figure 11.11 (C) provides a virtual image of the angle corresponding to the center of curvature of the lens. L is the ray of light and R the reflection of the image.

In Fig. 11.12, the vertical axis represents the larger dimension of the laser focus with aberration occurring almost at the level of the vertex of the anterior chamber angle (ordinate). The abscissa represents the angular position of the contact lens on the cornea. For example, if the position of the lens on the cornea has a 4° tilt, the size of the laser focus is around 20 µm, while with the Goldmann lens it would be more than 60 µm. If it were 8°, with the Fankhauser lens it would be 25 µm, while with the Goldmann lens it would be 130 µm.

The aberration of the CGA lens is lower than that of the Goldmann lens when tilting the lens and increasing the rotation angle.

Fig. 11.9 Fankhauser and Roussel gonioscopic lens, lateral view

Fig. 11.10 Front view and spatial configuration of the Fankhauser and Roussel gonioscopic lens

Goniophotographs Taken

with the Roussel and Fankhauser Lens

The goniophotographs in Fig. 11.13 enable the normal elements of the angle as well as the angle in open-, narrow-, and blocked-angle glaucoma to be individualized, and the normal angle from cases of goniodysgenesis can be differentiated. To make these goniophotographs, the Roussel and Fankhauser lens described above was used.

Figure 11.13 is a goniophotograph made with a narrow slit and the maximum of light, to obtain the image

in the fork that enables the Schwalbe line to be perfectly located. Figure 11.13a illustrates the corresponding sketch, Fig. 11.13b, the goniophotograph.

Figure 11.14 shows different goniophotographs of the image in fork. In the last goniophotograph, it can be seen that the pigment at the level of the Schwalbe line has two lines, since this is an exfoliative syndrome that presents, above the Schwalbe line, the characteristic waves in the pigment in the posterior face of the cornea.

Iris Process

Figure 11.15b shows an iris process, which is a normal mesodermal remnant that is very commonly seen in normal eyes. Figure 11.15b is an illustration of the corresponding histology, and in Fig. 11.15a, the explanatory diagram.

The corneoscleral trabecular network is formed of fibers that run from sclera to sclera (1), by fibers that come from the ciliary muscle, pass by the spur, and reach the Schwalbe line, and then form the ciliary muscle tendon. Fiber 3 represents the iris process.

Fig. 11.15 Iris process. a Diagram; b histology, iris process (C cornea, Schl Schlemm canal, S scleral septum ending in the Schwalbe line, SP scleral spur), 1 cornea, corneal trabecular meshwork, 2 tendon of the ciliary muscle between scleral spur and the Schwalbe line, 1–3 uveal

In Fig. 11.16 illustrates the iris processes that do not normally pass the spur, with the corresponding diagram.

It is important to distinguish these iris processes, normal mesodermal remnants, common in open angles, from goniodysgenesis, as illustrated in Fig. 11.17a, iris processes, and Fig. 11.17b, goniodysgenesis. In cases of goniodysgenesis, there is pathologic mesodermal tissue and similar tree-like extensions that cover the entire trabecular network and reach the Schwalbe line (see goniographs in Fig. 11.17b in Fig. 11.17c).

When the gonioscope is moved backward, suction is produced, and in general, the Schlemm canal fills with blood. Other times it fills with blood spontaneously (Fig. 11.18).

Narrow Angle Glaucoma

Figure 11.19 shows a narrow angle glaucoma: the flat chamber (Fig. 11.19a), goniophotograph (Fig. 11.19b), corresponding diagram (Fig. 11.19c), and the histological section (Fig. 11.19d).

Figure 11.20 belongs to Goldmann [4] and shows how in a blocked angle, the posterior profile line of the cornea and the anterior profile line of the iris continue directly one from the other (Fig. 11.20a). However, when the angle is narrow and not blocked

(Fig. 11.20b), the posterior profile line of the cornea does not continue the anterior profile line of the iris, which is displaced to one side by the parallax.

Figure 11.21a is a steel sheet with three curved, parallel perforations that permit an angle to be drawn easily, an idea from Busacca. Figure 11.21b shows a sketch of the three lines described, traced by the plate, and how they are used to draw an angle. It is a good idea for the ophthalmologist to make these drawings on the patients’ clinical histories as well as photographs.