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

stituting the lenticular capsule, is located in an external position. This happens around the 6th week, appearing at the same time as the vessels of the tunica vasculosa lentis (Fig. 8.7a), which arise from the hyaloid circulation and are located in the posterior part of the crystalline, and out of which come the vessels surrounding the equator and going to the pupillary membrane, constituting the anterior vascular capsule [5, 6].

At this stage (day 34–36), we can see the cornea in formation (two layers) and the recently separated crystalline vesicle, in which a central space can be distinguished between the anterior epithelium and the fibers being formed from the equator. To the sides and behind, the optic layer can be seen with its two layers; note that the outer layer corresponds to the pigmentary epithelium that has grains of melanin (Fig. 8.7b).

It should be remembered that by day 33–34 (around the 1st month) we have a cornea in formation, a crystalline vesicle separated from the ectoderm, and an optic layer (lateral projection of the prosencephalon) with a double cell layer: the outer one, the pigmentary epithelium, and the inner layer, the remaining layers of the retina. This real space dividing the two layers will later become virtual. However, in pathological states (retinal detachment), this space explains why the pigmentary epithelium generally remains attached to the choroids.

Then the different corneal layers are differentiated and the iris begins to develop, initially as a thin layer of

the pupillary membrane. At the same time, on the ectodermic side, the fundi of the sacs are already formed and both eyelids fused (Fig. 8.8a).

This stage, from day 60 onward, already shows us a formed anterior chamber with abundant endothelized mesenchyme; this can be seen in the image of a histological section of an ocular globe in its 3rd month of development, where we can recognize the cornea with all its layers, an anterior chamber with abundant mesenchyma tissue in the fetal chamber angle, the iris in the initial stages of formation, the lens surrounded by the tunica vasculosa lentis, vascularized primary vitreous, and in the posterior part, the internal layer of the developing retina separated by a real space from the external layer corresponding to the pigmentary epithelium (Fig. 8.8b).

Embryological development continues with some important details, summarized in Table 8.1, which mentions specifically the appearance of the Schlemm canal in the 4th month, the characterization of the fibrillocellular trabeculae in the 5th month coinciding with the functional start of the circulation of aqueous seen in the vacuoles present in the canal [7].

The 6th month is marked by the start of the formation of the aqueous humor and the posterior displacement of the ciliary muscle.

Is very interesting to consult the thesis of Dr. Francisco Contreras, titled Development and anomalies of the chamber angle [11].

Stratton, New York

2.Burian HM, Braley AE, Allen L (1956) A new concept of the development of the angle of the anterior chamber of the human eye. Arch Ophthalmol 55:439–442

3.Seefelder R, Wolfrum (1906) Zur Entwicklung der Vorderen Kammer und des Kammerwinkels beim Menschen nebts Bemerkungen uber ihre Entstehung bei Tieren. Grafes Arch Ophthl 63:430–451

4.Ehlers N, Matthiessen ME, Andersen H (1968) The prenatal growth of the human eye. Acta Ophthalmol 46:329–349

5.Barber AN (1955) Embryology of the human eye. Mosby, St Louis

6.Wilmer HA, Scammon RE (1950) Growth of the components of the human eyeball. Arch Ophthalmol 43:599–619

eye and its adnexa. In: Jakobiec FA (ed) Ocular anatomy embryology and teratology. Harper Row, Philadelphia,

pp11–96

9.Noden DM (1982) Perocular mesenchyme: neural crest and mesodermal interactions. In: Jakobiec FA (ed) Ocular anatomy embryology and teratology. Harper Row, Philadelphia,

pp97–119

10.Tripathi RC, Tripathi BJ (1982) Functional anatomy of the anterior chamber angle. In: Jakobiec FA (ed) Ocular anatomy embryology and teratology. Harper Row, Philadelphia,

pp197–248

11.Contreras Campos F (1972) Development and anomalies of the chamber angle in the eyes, Universidad Nacional Mayor de San Marcos, Lima, Peru

Anatomy of the Chamber Angle

The chamber angle is the outermost part of the anterior chamber, where the anterior or scleral wall converges with the posterior wall of the iris in a curved segment made up of the inner surface of the ciliary body.

Despite its simple definition, the anatomy and histology of this area reveal its great complexity. Figure 9.1, schematic representations made by Benninghoff and reproduced and quoted for the first time by Rohen and Unger in 1959 [1], show the variety of systems converging in the area of the chamber angle.

Fig. 9.1 a Benninghoff ’s schematic representation of the five ocular functional systems. The main system (yellow): the retina and optic nerve 1; accommodation system 2 (light blue); crystalline lens, zonule, ciliary body with muscle and elastic choroid: diaphragm-iris system 3 (red); transparency and protection system 4 (green and striped area): eyelids, lacrimal system,

conjunctiva and cornea; motility system 5 (gray): sclera and extrinsic muscles. b Magnification of the area within the rectangle in a. The black dot marks the place where all five systems described in a come together: the chamber angle. This is why this zone is so complicated

These systems are:

1.Main system: retina-optic nerve;

2.Accommodation apparatus (lens, zonule, ciliary body with ciliary muscle and choroid);

3.Diaphragm-iris;

4.Motility apparatus (sclera and extrinsic muscles);

5.Eyelids, lacrimal system, conjunctiva, and cornea.

The complexity of the chamber angle is evident in these schematic representations (Fig. 9.1a,b), since there are tissues of different origins and five systems with different functions involved. This complex anatomy has a correspondingly complicated physiology.

The eyeball has a spherical shape and lodges the optical apparatus for transmission, consisting of three parts: the transparency system (4), the accommodation system (2), and the diaphragm system (3). This apparatus produces inverted images that are smaller in size than in the outer world.

The images are formed on a layer of nerve cells embryologically derived from the brain tissue in an anterior prolongation, and which are differentiated into photoreceptors: the retina-optic nerve system (1), which is the receptive sensory part of the optical system.

The role of physiological ocular pressure is to keep the dimensions of this optical system constant, a vital prerequisite for adequate image formation.

The explanation will be simplified as much as possible without sacrificing accuracy.

In its anterior edge, the sclera (yellow in Fig. 9.2) has three finger-like prongs, two of which are longer – the limbus and scleral septum – and the third, which is shorter – the spur.

Two channels are formed between these three prongs: an anterior angle that lodges the optical element – the cornea (Fig. 9.3) – and a posterior one, the scleral channel, lodging the filtration system (Fig. 9.4) – the Schlemm canal and the trabecular meshwork.

The scleral septum and spur form the posterior channel of the anterior end of the sclera. This is the filtration channel, which lodges the Schlemm canal and the trabecular meshwork (blue and green, respectively).

The ciliary muscle (red, Fig. 9.5) is located between the sclera and the iris.

The root of the iris is always inserted in the internal face of the ciliary body, in the middle in emmetropic eyes, in the anterior part in hyperopic eyes, and in the posterior part in myopic eyes. The iris can be seen in brown with the posterior layer of the iris with the pigmentary epithelium in light brown, and in dark brown, the superficial mesenchymal layer of the iris with the circular folds. The root of the iris is formed only by the deep layer (Fig. 9.5).

The intermediate wall of the chamber angle is formed by the anterior part of the inner surface of the ciliary muscle (red) and the inner wall of the chamber angle is formed by the iris and its root.

The anterior boundary is a circular white line which is more or less visible depending on each individual case, and the line known as the Schwalbe line (the Schwalbe ring; S, Fig. 9.6). The posterior, or iris, limit is located over the line of the last roll of the iris (C, Fig. 9.6), which is the highest part of the outermost circular fold of the iris.

The chamber angle has the following components: the anterior edge of the sclerotic coat, the inner surface of the ciliary body, and the iris root (Fig. 9.7).

Fig. 9.7 Schematic representation of the chamber angle. The image on the left is a section of the chamber angle, combined with the gonioscopic image on the right. The following elements can be seen in the section: 7 sclera, 5 ciliary muscle, 6 ciliary body, 8 anterior prong of the sclera:limbus, 9 scleral septum, 10 Schwalbe line, 11 iris, 12 cornea, 13 Schlemm canal, 14 crystalline lens. The gonioscopic image shows the following elements: S spur, Tr trabecular meshwork, Tr. Schl trabecular meshwork lining the Schlemm canal, L. Schw Schwalbe line, BCC ciliary body band, UPC iris, last circular fold of the

Anatomic Components of the Chamber Angle

iris, 4 iris processes. In addition, the optical section shows the following elements: 1 posterior corneal profile line, 2 anterior corneal profile line, which is no longer visible at the level of the Schwalbe line, 3 iris profile line, 10 trabecular meshwork above the Schlemm canal. There are three dotted lines in the figure: the anterior one bends forward until it joins the anterior iris line; this is the uveal trabecular meshwork. Below it, the second dotted line represents the tendon where the ciliary muscle is inserted. The third one represents the trabecular meshwork fibers that run from the septum to the spur

Schwalbe Line

The chamber angle is divided into the following anatomic elements (Fig. 9.6): the scleral area (black line in the figure) running from the Schwalbe line (S) to the spur (E), a uveal area (red line) running from the spur to the line of the last roll of the iris (C). The former is fixed and the latter is variable.

Scleral Area

The scleral area of the chamber angle extends from Schwalbe’s ring to the spur line. This is the fixed part of the chamber angle.

The scleral channel, which contains the Schlemm canal and the trabecular meshwork (Fig. 9.5, the former in blue and the latter in green), is located between the limits mentioned above.

The Schwalbe line is a narrow band of an apparent thickness of 1 mm, located at the dividing line between the wall of the chamber angle and the Descemet membrane. In some pathological conditions, some parts are thickened or sometimes it extends into the anterior chamber.

Most authors believe it to be the anterior end of the trabecular meshwork. Busacca, based on its gonioscopic appearance, considered it to be the distal end of the scleral prong viewed between the corneal tissue and the scleral trabecular meshwork. He named it scleral septum.

Some authors describe the Schwalbe line as a protrusion into the anterior chamber, but this is not the case and there is no evidence for this in histologic sections. The appearance of an uneven surface stems from the contrast produced when there is an opaque tissue (scleral septum) between two transparent tissues (cornea and scleral trabecular meshwork).

Scleral Channel

In the inner surface of the sclerotic, in the area in which it passes into the corneal tissue, there is a posteriorly concave channel known as the scleral channel. This channel has two walls: an external (or anterior) wall formed by the scleral septum: a prong prolonging the sclera forward like a finger, and an inner (or posterior) wall formed by another smaller scleral protrusion, known as the scleral spur.

Scleral Spur

This is a protrusion of the scleral tissue viewed between the tendon of the ciliary muscle and the Schlemm canal. It is the point of insertion of the longitudinal part of the ciliary muscle and the trabecular meshwork fibers.

Its development varies depending on the individual, and it may be strong and thick, or long and thin. It is made up of a set of scleral fibers that are circular in shape, the same as those forming the scleral septum, and reaching posteriorly as far as the pars plana (orbiculus ciliaris) of the ciliary body (formation of the spur).

The same happens as with the Schwalbe line: it looks as if it goes into the anterior chamber, because it is an opaque tissue adjacent to a transparent one. When there is pigment present on the trabecular meshwork, it is clear that the spur is behind it.

Schlemm Canal

This is located in the scleral channel and its walls are formed by endothelial cells. In its external wall, it lies directly on the scleral fascicles and is in contact with the intrascleral veins. The inner wall is bounded by the juxtacanalicular tissue. The external wall is smooth and the inner wall is irregular.

Scleral Trabecular Meshwork

The scleral trabecular meshwork (Fig. 9.8) is a triangular system made up of small lamellae known as trabeculae. It has the shape of an isosceles triangle with its upper vertex seen under the Descemet membrane at the level of the Schwalbe line. Its three sides have three surfaces:

1.The inner surface (Fig. 9.8, AC) is adjacent to the anterior chamber at this site and opens into it through several small spaces between the trabeculae (intertrabecular spaces).

2.The outer surface (Fig. 9.8, SS and SchC) is in direct contact with the scleral septum (SS) at its anterior part and is part of the inner wall of the Schlemm canal (SchC) at its posterior part.

3.The base or posterior surface (Fig. 9.8, SSp) is adjacent to the spur, and depending on its developmental stage, there may be more or fewer trabecular fibers inserted into it.

There are three types of trabecular fibers (Fig. 9.9):

1.Fibers inserted into the spur (light blue);

2.Fibers coming from the longitudinal ciliary muscle (ciliary muscle tendon) (red);

3.Fibers extending over the ciliary trabecular meshwork (brown).

The fibers (light blue) extending from one sclera to the other, from the spur to the scleral septum near its end at the Schwalbe line, form an arched bundle surrounding the Schlemm canal and separated from it by the porous tissue. In red, trabecular meshwork fibers represent the tendon where the ciliary muscle is inserted. They bridge the spur and insert themselves into the Schwalbe line and are the tendinous continuation of muscular bundles of the ciliary muscle. In brown, one can see the fibers originating at different levels between the Schwalbe line and the spur and also ending at different levels from the insertion of the iris root to the last rolls of the iris. These form the ciliary trabecular meshwork and are actually normal mesodermal remnants, also known as mesoderm of the chamber angle or iris processes.

The innermost fiber layer of the trabecular meshwork (Fig. 9.9, light blue) is made up of conjunctival fibers that will form the Busacca conjunctivo-trabecular layer, which will be described in the next section on the uvea. These fibers extend over the interfascicular conjunctival tissue that separates the muscle fascicles from the ciliary muscle.

Trabeculae are made up of a central core of fibers surrounded by a homogeneous substance. This, in turn, is surrounded by a thick transparent layer known as vitreous membrane. Finally, all these constituents are covered with endothelial cells with their nuclei, continued in the cells of the Schlemm canal to the outside and leaving an open space toward the anterior chamber to the inside.

Fig. 9.8 Scleral trabecular meshwork. In the drawing, the scleral trabecular meshwork is represented as a black isosceles triangle. The inner surface (AC) is the boundary of the anterior chamber at that site, opening up to it through numerous small spaces and coming into contact with the aqueous humor. The outer wall of the triangle is in contact with the scleral septum (SS) in the half proximal to the center of the cornea, while in the distal part it forms the inner surface of the Schlemm canal (SchC) through porous tissue. The base or posterior surface is bounded by the scleral spur (SSp). Schw L marks the Schwalbe line

Fig. 9.9 Trabecular fibers. The fibers (light blue) extending from one sclera to the other, from the spur to the scleral septum near its end at the Schwalbe line, form an arched bundle surrounding the Schlemm canal and separated from it by the porous tissue. In red, trabecular meshwork fibers represent the tendon where the ciliary muscle is inserted. They bridge the spur and insert themselves into the Schwalbe line and are the tendinous continuation of muscular bundles of the ciliary muscle. In brown, one can see the fibers originating at different levels between the Schwalbe line and the spur and also ending at different levels from the insertion of the iris root to the last rolls of the iris. These form the ciliary trabecular meshwork and are actually normal mesodermal remnants, also known as mesoderm of the chamber angle or iris processes.

Uveal Area

The uveal area is defined as the variable part of the chamber angle. Its length depends on:

1.The thickness of the ciliary muscle (greater in hyperopic eyes and smaller in myopic ones);

2.The apparent insertion of the iris root.

Boundaries

The uveal area extends from the spur line to the line of the last rolls of the iris.

Constituents

The uveal area has a ciliary part and an iris part.

Ciliary Body

The ciliary body (circular portion of the muscle) is part of the chamber angle at this site between the spur and the insertion of the iris root. The inner surface of the muscle mass forms this segment of the chamber angle. In gonioscopic terminology, it is known as the ciliary body band (CBB).

At the side adjacent to the anterior chamber, it is covered by a conjunctival tissue layer that contains the ciliary trabecular meshwork in its thickness. This is the Busacca trabecular conjunctival layer (or the Rohen iridoscleral membrane). This layer is posteriorly adjacent to the tissue of the iris root and to the ciliary body and has extensions between the fascicles of the ciliary muscle at a deeper level. The peripheral end of the pupillary dilating muscle ends here. This layer is the tissue that separates the anterior chamber from the ciliary muscle (Fig. 9.10).