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

Iris Zone

This is usually known as the iris root. It is a ring-shaped narrow band of the periphery of the iris implanted in the ciliary body (Fig. 9.6E, C). Its anterior surface forms part of the anterior chamber. Its posterior surface is in front of the heads of the ciliary processes, from which it is separated by a recess (recessus minimus of the posterior chamber).

The iris channel is the depression of the anterior chamber of the iris at the level of its root, produced by the disappearance in this zone of the superficial mesodermal layer. The limit is marked on the pupil side by the line of the last rolls of the iris, and on the ciliary body side by the insertion of the iris tissue into the trabeculoconjunctival layer (ciliary body band). This line of the last roll of the iris shows interindividual variation and varies in different zones of an individual’s chamber angle. In some individuals, the iris channel is so developed that there is a true recess of the chamber angle and this hampers gonioscopic examination.

The iris root is sometimes very short and almost absent. The insertion of the iris in the ciliary body rarely forms a neat line. The superficial mesodermal layer rises to partly cover the trabeculoconjunctival layer, becoming hook-shaped. This band of iris tissue covering part of the anterior surface of the ciliary muscle is known as the Busacca baseline layer of the iris processes.

The anterior edge of this layer is not definite and fine prongs of iris tissue expand from it and branch over the ciliary and scleral walls of the trabecular meshwork; these are the Busacca iris processes, remnants originating in the period of the chamber angle formation. They are Gomori-negative when stained and are normal mesodermal remnants.

Figure 9.11a shows a cross section of an angle of an human eye. Figure 9.11b shows a histological section of an normal chamber angle and in 9.11c the corresponding schema for locating the anatomical formation.

This section shows the iris root formed solely by its deep mesenchymal layer, the recess of the chamber angle, and the fibers of the ciliary muscle, which are adjacent to those of the trabecular meshwork (its tendon) and which have the shape of a perfect isosceles triangle. The external wall of the trabecular meshwork is bounded directly by the Schlemm canal from which it is separated by a denser tissue (juxtacanalicular tissue). One of its external collectors can be seen originating in the Schlemm canal.

Figure 9.12 is an original preparation that I made when I studied the surface electron microscopy of the chamber angle. The specimen was collected from a normal eye enucleated from a 45-year-old man who had died in an accident.

Summary

The chamber angle is an area of the anterior chamber that should be studied in depth, since the aqueous humor outflow pathways start here (conventional and nonconventional, or posterior pathways).

Its macroscopic structure can be studied by means of an anatomic dissection, but a correlation of this dissection with the gonioscopic image of an optical section (possible with magnification between 9 and 40) is more useful. In addition to this knowledge, histology enables the study of the structures that are visible gonioscopically, as well as those that are not, showing the complex architecture of this region where the five ocular functional systems and the three embryologic layers are involved.

The gonioscopic image should be correlated with the macroscopic anatomy and histology, both in nor-

mality and pathology. Only in this way will the semiology be truly useful.

The chamber angle has a fixed external wall and a mobile inner wall, which come together in a curve (the sinus or camerular gulf) at the spur. Knowledge of the ciliary muscle is very useful to clarify the concepts on the morphologic variations of the chamber angle under pathologic conditions and under the effect of drugs.

Reference

1.Rohen JW, Unger HH (1959) Zur Morphologie und Pathologie der Kammerbucht des Auges. Abhandlungen der Mainzer Akademie der Wissenschaften und Literatur Franz Steiner, Wiesbaden, pp 1–206

Gonioscopic Contact Lenses

To examine the chamber angle, we use one-, two-, or three-mirror Goldmann lenses (most commonly, the three-mirror lens), as well as the lens designed by Roussel and Fankhauser. The Goldmann lenses can be used with or without a scleral rim [1].

Sterilization of Gonioscopic Contact Lenses

Sterilization of the cone of gonioscopic contact lenses is recommended after using them, with sodium hypochlorite for 3 min on a Petri dish with a hole in its cap, so that only the edge that is in contact with the cornea can be sterilized with the solution. Then it is washed with water.

In this way, both HIV and adenoviruses are inactivated. The American Centers for Disease Control and Prevention (CDC) has reported that transmission of HIV through tears occurs at a rate of 0.04%. Other methods for inactivation are a fresh hydrogen peroxide solution, and ultraviolet light. The Draeger tonometer is sold with a sterilization device using ultraviolet light.

Placing the Lens

1.Anesthesia: one drop of Novesine 0.4% instilled deep in the lower conjunctival sac.

2.Preparation of the gonioscope: one drop of Methocel Dispersa (Dr. E. Baeschlin AG, Winterthur, Switzerland): Methylcellulose (Alcon Laboratories, Fort Worth, TX, USA) in its concave surface.

The liquid used for placement of the gonioscope is highly important. It should allow for a long examination, with neither corneal hazing nor discomfort to the patient.

Methylcellulose 2% has a viscosity of 4,000 centipoises (a poise is a unit in the CGS system of dynamic viscosity: dyne per second per square centimeter). If methylcellulose is not available at this concentration, a gel can be used that is composed of carbomer 980 (polyacrylic acid) 200 mg, benzalkonium chloride 10 mg, sorbitol 400 mg, sodium hydroxide to adjust pH c.s., purified water c.s.p. 100 g.

The use of unsuitable liquids for gonioscopy is the reason why many ophthalmologists consider gonioscopy to be a complicated examination, since the corneal haze produced by many liquids prevents them from viewing the delicate structures of the chamber angle clearly.

3.The patient rests his chin and forehead on the slitlamp.

4.He is instructed to look up without moving his forehead from the slit-lamp support (Fig. 10.1a).

5.For the right eye, the gonioscope is placed with the left hand and the slit-lamp is moved toward the right. Conversely, for the left eye, the lens is placed with the right hand and the slit lamp is moved to the left.

6.With the free hand, and particularly with the fifth finger, the lower eyelid is pressed in order to rest the lower margin of the gonioscope in the deep lower conjunctival sac (Fig. 10.1b).

7.The gonioscope rests completely on the eye while the patient is directed to look to the front (Fig. 10.1c).

8.The patient is asked to look to the front and the lens is placed on the eye.

Fig. 10.1a–d Placement of the three-mirror contact lens. a The lens is held with the thumb and index finger. b With the ring finger or pinky, the lower eyelid is pressed and the patient is directed to look up. c Once a good palpebral opening has been

achieved, the lens is placed in contact with the eye with the eyelashes outside. d The patient is asked to look to the front and the lens is placed on the eye

Examination with the Slit-Lamp or Biomicroscope

The chamber angle should always be examined with a biomicroscope that allows for an optic cut and with a suitable contact lens.

However, in some departments where the Köppe lens is still used, the ophthalmologist performs the examination with a hand-held microscope while holding a small lamp, which is moved around the supine patient. This provides only a rough estimate of the chamber angle structures, with no details.

The examination starts with a broad slit and then proceeds with a narrow one. The examination with a fine slit enables a good optical cut of the visible structures of the chamber angle.

To obtain a good optical cut with a fine slit, one must be familiar with the necessary maneuvers, which vary

according to whether one wishes to observe the chamber angle at the vertical meridian at 6 or 12 o’ clock or at the horizontal meridian at 3 or 9 o’ clock (Fig. 10.2).

The elements that change their position depending on the structures to be observed are the direction in which the patient is looking, the anterior surface of the contact lens, and the direction of the light bundle of the slit-lamp.

If the purpose is to observe the chamber angle at 6 or 12 o’ clock, the patient should look laterally, as shown in Fig. 10.2, so that the light bundle of the slit falls normally (perpendicularly) on the anterior surface of the gonioscope (90° angle). The image thus obtained will be clear and useful for diagnosis.

In practice, if the slit lamp’s arm is on the right side of the observer, the patient should be asked to look slightly to his left, i.e., to the side where the light source is located.

For an observation of the chamber angle in the horizontal plane at 3 or 9 o’ clock with a fine slit, the follow-

-ing steps should be followed (Fig. 10.3): - Place the slit in a horizontal position. - Bend the illumination arm forward.

Dip the anterior plane of the gonioscope, while the patient is asked to look slightly downward (Fig. 10.3b).

This examination can only be done with a Haag-Streit 900 slit-lamp, the first one to enable the slit plane to be

inclined horizontally. Mr. Littman (Carl Zeiss, Meditec AG, Jena, Germany) designed a prism at our request so that the Zeiss slit-lamp could be inclined without bending the arm.

Figure 10.3 illustrates the reason for this maneuver, based on the geometric optical principles of light reflection on the mirrors.

The patient can be asked to fix the fellow eye on the small fixation lamp, instead of looking away, since some patients do this abruptly, causing air to come between the contact lens and the eye.

Fig. 10.2 Observation of the chamber angle with a fine slit. Optical cut at 6 and 12 o’ clock. The patient should be instructed to look to the side where the illumination arm of the lamp is located so that the light bundle of the slit falls normally on the anterior surface of the gonioscope: a 90° angle

Fig. 10.3a,b Observation of the chamber angle with a fine slit. Optical section at 3 and 9 o’ clock. The following steps should be followed for this observation. First, place the slit in a horizontal direction, as in a. Then, as shown in b, bend the light arm to the front; the patient is then asked to look down so that the anterior surface of the gonioscope forms a 90° angle with the luminous axis. As shown in b, when the light arm is bent, the angle of incidence of the mirror is lower than when the arm is in the vertical position. Since the angle of incidence to the mirror is lower than normal and the reflection angle is the same as that of incidence, the reflected ray that illuminates the gonioscope is deviated upward. This is why the patient should look down

Goldmann’s threeand one-mirror lenses are probably the most useful ones for this examination. In addition, it is vital to use a good contact liquid (Methocel Dispersa). Knowledge of the application technique, and especially of the optical pathway of the slit-lamp and gonioscopic lens rays, is also important. The entire circumference of the chamber angle can thereby be observed in an optical section. From a practical point of view, to obtain good optical sections, the light bundle should fall perpendicular to the contact lens. When the areas at 6 and 12 o’ clock are examined, the patient should look toward the light source, whereas when the chamber angle is examined at 3 and 9 o’ clock, the slit, which has been previously shifted horizontally, should be inclined, and the patient should look slightly down so that the light rays fall perpendicular to the lens, which is moved in this direction by the ophthalmologist.

To examine the chamber angle in children, there are two new models of Goldmann lenses available, manufactured by Haag Streit, one with a 10-mm diameter and the other an 11-mm diameter. The Roussell Fankhauser goniolens with its high resolution is very useful.

1.Sampaolesi R (1994) Glaucoma. 2nd edn. Panamericana, Buenos Aires, Argentina

Lenses for Gonioscopy

Figure 11.1a (upper and lower parts) illustrates the onemirror Goldmann lens and the two-mirror Goldmann lens, respectively; Figure 11.1b, upper and lower parts, illustrate the three-mirror-Goldmann lens; and Figure 11.1c, upper and lower parts, the Goldmann lens with three 10and 11-mm-diameter mirrors, respectively, for studying the chamber angle in children.

Looking through the center of the three-mirror Goldmann lens, the posterior pole can be seen from the papilla to the macula. With mirrors two and three, the retina can be seen in the periphery. With mirror four, the chamber angle can be seen (Fig. 11.2).

In order to obtain a comprehensive image, the examination should start with a biomicroscope with a × 10 magnification. The medical practitioner, if still untrained in the observation of the chamber angle, should take the following landmarks into account:

1.The corneoscleral wall (light) can be distinguished easily from the iris wall (dark) by their different colors.

2.In the corneoscleral wall, the Schwalbe line should be found. This landmark will help assess the visibility, or amplitude, of the chamber angle. With a broad slit, it is sometimes very easy to find, since it is clearly visible in the following cases:

–A nacreous Schwalbe line;

–The Schwalbe line with pigment deposited on the upper end of the trabecular meshwork;

–A prominent Schwalbe line at the anterior chamber (pathological), etc.

Usually there are no landmarks in the external wall to make it evident. In these cases, illumination with a fine slit, using the technique already described (see Chap. 10), is required so that the image obtained is clear. At this time, the image resembles Fig. 11.3.

Since the cornea is inserted in a wedge shape (like a watch glass) into the sclera (c) where the anterior channel is located, both lines tend to converge (Fig. 11.3, I).

However, though both lines come together, as shown in Fig. 11.3, I, the consequent image is that shown in Fig.11.3, II, since the anterior profile line (b) is only visible up to the Schwalbe line, because from here downward, the scleral septum (dotted line, c), which is an opaque tissue, obscures it (Fig. 11.3, II). In brief, the position of the Schwalbe line derives from the discontinuation of the anterior profile line (b). This detail is what the ophthalmologist should look for (Fig. 11.3, III). In other words, there are two profile lines above the Schwalbe line (a and b) but only one below it. This is a valuable and meaningful landmark for finding the Schwalbe line in the corneoscleral wall.

Fig. 11.3 Optical section with a narrow slit in the biomicroscopic examination of the chamber angle. a Posterior corneoscleral profile line which runs through the whole chamber angle up to the iris wall. b anterior corneoscleral profile line. c Optical channel in which the cornea is lodged between two scleral prongs: the limbal prong and the septum. Schw Schwalbe line, Sp scleral spur

I.The limbal prolongation of the sclera and the scleral septum, which form the optical channel where the cornea (c) is lodged, is represented by a dotted line. The posterior corneoscleral profile line is completely visible (a). The anterior corneoscleral profile line (b) is completely visible up to the Schwalbe line. The small dots continue the invisible part of this line.

II.Image seen through the microscope. The outline representing the sclera in I have been removed. This site where the anterior corneoscleral line becomes invisible represents the

Schwalbe line location.

III.When there is neither blood nor pigment in the Schlemm canal, the spur is barely visible, and the ciliary body band is obscured. The point at which the anterior corneoscleral line is discontinued (b) shows the position at which the Schwalbe line is placed, located at schw in the image. This observation is vital since it is indicative of the fact that the filtrating trabecular meshwork is located between this line and the iris root with no obstacles hindering aqueous humor inflow. a Posterior corneoscleral profile line (posterior corneal surface); b anterior corneoscleral profile line (anterior corneal surface)