Maximilian Salzmann.

The anatomy and histology of the human eyeball in the normal state, its development and senescence ; online

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of the nerve (see p. 101). As above reported, the cells lie at the periphery
of the individual bundles, in part, therefore, between the septa and the
nerve-fiber mass. For the most part, however, they lie in the prolongations
of the septa, which, accordingly, consist of cells and a reticulum of glial
fibers. The glial fibers also press into the interior of the nerve-fiber
bundles, and insinuate themselves between its fibers in a cross, oblique,
or, in part, longitudinal direction. They are thickest on the surface
of the nerve-fiber bundle. Inward they are less numerous, yet they per-
meate all the nerve-fiber bundles, so that one sees portions of glial fibers
(PL VI, 5, gl} everywhere between the cross-sections of the nerve-fibers.

The glial tissue is sharply separated from the connective tissue of the
septa; neither connective- tissue fibers nor vessels press down into the
nerve-fiber bundles, nor do glial fibers press into the septal system.
The nerve-fiber mass often shrinks a little in the hardening fluid, and then
cleft-like spaces form between the septa and the surface of the nerve-
fiber mass; the spaces are mostly bridged over by glial fibers, but often
appear quite empty. These spaces do not possess an endothelial lining;
they can, therefore, best be explained as artefacts. They are apparently
the same spaces as those produced by injections of the nerve trunk and
which have been looked upon as lymph spaces (PL VI, 3, Ly).

The nerve-fibers are of the same sort as those found in the white sub-
stance of the brain and spinal cord. They are fine fibers consisting only
of an axis cylinder and medullary sheath without a sheath of Schwann;


their thickness varies usually between 2 and 5 mu (PI. VI, 5, n). The
finer fibers have been looked upon as the actual visual fibers, the
thicker ones as pupillary fibers (von Gudden, Westphal, and others).
When hardened, these fibers show varicosities, i.e., nodular swellings.
The very great variation in the size of the cross-section of the fibers is
due to the fact that the section cuts many fibers through the nodes and
others through non-nodular portions.

The varicosities have been pretty generally looked upon as artificial products.
Bartels (17) has demonstrated a very large number of primitive fibrillae in the axis

At the periphery of the optic nerve a more or less well-marked, plain
layer of flattened and compressed bundles is found ; this consists only of
glial tissue (fibers and cells), and contains no nerve-fibers (Greeff's periph-
eral glial mantle, 74) (PL VI, 2, 6, glm). A structure analogous to
this is found in the brain and spinal cord; it is indicated even in the
newborn, but is not as plainly visible as later on account of the defect-
ive development of the medullary sheaths (Kiribuchi, 118; Greeff, 74).
These bundles are separated from the nerve-fiber bundles by stretches
of connective tissue septa, coursing parallel to the pial sheath (peripheral
septa of Fuchs, 66).

At the posterior end of the central connective-tissue strand the
peripheral glial mantle is turned in, like the pial sheath itself, and continues
along the central connective-tissue strand for a varying distance (PI.
VI, 2).

This place, usually spoken of as the entrance of the central vessels,
lies below and somewhat nasal, according to Deyl (38), almost straight
below, according to Strahl (214). Its significance lies mainly in the fact
that it corresponds to the posterior end of the fetal cleft (cf. chap, xvi),
and in the developed eye represents the only visible trace of this phase of
the embryologic development so important for the study of anomalies.

The main axis of the central connective-tissue strand consists of a
tubular continuation of the pial sheath (for a covering), and of the two
central vessels (arteria et -vena centralis retinae] as contents. The covering
consists of longitudinally fibrillated connective tissue and agrees in every
histologic particular with the septal system, into which it is directly con-
tinued. Between it and the central vessels, and, likewise, in the inter-
spaces between the two vessels, there is a loose connective tissue much
split up into longitudinal spaces (lined by epithelium?).

The central vessels give off only a few small branches in the trunk of
the optice nerve, and these are mostly veins. Therefore, they maintain
their caliber unchanged up to the lamina cribrosa. The arteria centralis


retinae does not, as a rule, show any evidence of contraction, but has a
wide-open lumen of some o. 13 mm diameter, a weakly developed intima,
a 0.02 mm thick muscularis, and an equally weak adventitia. The
vein wall consists solely of endothelial and connective tissue.

Fine nerve branches enter with the central vessels, and form a
ganglion-cell-free plexus about the central artery; this can be followed
into the papilla (Krause, 122).

It is not rare to find the optic nerve changed in a peculiar way on cross-section;
one finds swollen or knotted areas in which the nerve-fibers are not cut across, as usual,
but longitudinally or obliquely; therefore they appear very indistinct, so that the
whole node, which, in general, is sharply set off from the normal tissue, is recognized
even by low magnification and, indeed, macroscopically in uncut tissues by another
color (PL VI, 6, c). These changes were described by Siegrist (207), and were con-
sidered to be areas of fatty degeneration. However, it came out in the discussion of
Siegrist's paper that these appearances are well known, and have usually been looked
upon as cadaverous appearances. Elschnig (53) finally demonstrated that the cause
of these changes is the bruising of the optic nerve by instruments in the preparation
of the orbital contents. The fleck-form degeneration of the optic nerve of Siegrist
is, according to this, listed as an artefact.


(PL I)

The ciliary body forms a girdle of about 5 to 6 mm in breadth,
narrower on the nasal side and above (4.6 to 5.2 mm) , broader on the
temporal side and below (5.6 to 6.3 mm). A meridian going obliquely
from temporal and above, nasal and downward, separates the narrower
from the broader part (PL II, i). The description of the outer surface
has been given above (pp. 12-13), likewise the characteristics of the two
zones on the inner surface: the orbiculus ciliaris and the corona ciliaris
(p. 10).

The orbiculus ciliaris is the broader of the two zones. Some 2 mm
throughout belongs to the corona ciliaris, the rest to the orbiculus ciliaris.
The significant difference in the breadth of the entire body depends,
therefore, upon the expanse of the latter. In general, the inner surface
of the orbiculus ciliaris is considerably darker than that of the chorioidea.
This depends, however, only upon the pigment epithelium. The following
details of its color can be recognized under certain circumstances.

Immediately in front of the ora serrata its color is often darker than
in the middle, or about a millimeter in front of the ora serrata one sees an
especially dark girdle, which reproduces the zig-zag form of the ora serrata
with absolute accuracy, although in a meridionally enlarged proportion,


therefore exaggerated to a certain extent. Corresponding to the teeth
of the ora serrata, there are narrow radial striae which open into the
corresponding valleys of the ciliary body (striae ciliares, O. Schultze).

The dark girdle is not always visible; often it is developed only in
the broader part of the orbiculus ciliaris and is entirely absent in many
eyes. But the striae ciliares (PL IV, 10, Si) are always to be seen except
in those cases in which the pigmentation is, in general, so intense that one
cannot make out any difference. The color is usually darker in front
toward the corona ciliaris.

Although one speaks of the orbiculus ciliaris as the flat portion of the
ciliary body, this is not to be taken absolutely literally. For example,
the dark girdle always shows a slight prominence when well developed.
Slight differences in level are also to be found over the orbiculus. The
same is true of the striae ciliares. In the most anterior portion of the
orbiculus, just behind the corona, one sees a system of little warts or folds
in many eyes ; these are very much smaller than the ciliary processes and
only visible when looked at with the loupe under strong focal light (sun-
light is best). These warts (PI. IV, 10, w) are elongated, sausage-like
structures with their long diameters meridional; they are often arranged
in chains and three or four such rows are found in a ciliary valley.

The corona ciliaris is much more uniformly developed throughout
its entire circumference than in the orbiculus ciliaris. The difference
between the nasal and temporal sides is slight and amounts to only a few
tenths of a millimeter at the most.

The meridional white striation, so striking even on macroscopic
examination, is due to the summits of the ciliary processes (processus
ciliares). These striae give the name to the zone and number about 70
in the entire circumference.

Each process (PI. I) presents a plate or ridge projecting axial (toward
the lens) and inward; it is about 2 mm long (in the meridional direction)
and o . 8 mm high (in a radial direction). The free border, or ridge, of the
process that turned toward the lens and the vitreous is less pigmented
than the side surface and the interspace and, therefore, appears clear upon
the neighboring dark background (PI. IV, 10, PC).

The interspaces (ciliary valleys) between the processes carry numerous
similar projections; posteriorly these go over into the above-mentioned
warts ; in front they become larger and here and there they grow to espe-
cially large prominences (plicae ciliares) in the neighborhood of the iris
root, but they always remain much smaller than the ciliary processes.
These plicae are as darkly pigmented as the floor of the ciliary valley and,
therefore, are not plainly visible in macroscopic examination. Finally,


the whole system of elevations and projections is succeeded in front by
a circular ridge which juts forth about opposite the border of the lens
(sims of H. Virchow, 232).

Smaller irregularities in the development of the corona ciliaris fre-
quently appear without particular reference to location; thus here and
there the ciliary valleys are wider or the individual processes are notably
lower than their neighbors (PL II, i). The marked individual variations
in this region have recently been elucidated through the excellent draw-
ings by Hess (101).

At its posterior border, the ciliary body is not any thicker than the
peripheral parts of the chorioidea; where the ciliary muscle begins, how-
ever, some 3 mm behind the anterior border, the thickness of the ciliary
body gradually increases and attains a maximum of 0.8 mm at its very
anterior border. With this maximal thickness the ciliary body ceases as
such, as a rule, and thereby acquires a three-sided prismatic form; an
outer surface is turned toward the sclera, an inner toward the vitreous,
and a narrow anterior surface is turned toward the center of the cornea
or the pupil.

The ledge formed by the outer and anterior surfaces borders on the
scleral roll (PL III, i, Sw); here one finds the insertion of the ciliary
body into the sclera, as well as the anterior insertion of the uveal tract,
in general. The inner and the anterior surfaces unite in a rounded ridge
projecting in the direction of the border of the lens ; this will be spoken of
as the inner ledge ; it is crowned by the sims.

The insertion of the iris root into the anterior surface lies in the
neighborhood of this ledge, whereas the meshwork of the iris angle, in so
far as it does not go over into the scleral roll, unites with the peripheral
parts of the anterior surface of the ciliary body. There remains a narrow
strip of the anterior surface between the two in many eyes ; this is covered
only by the innermost lamellae of the trabeculum (the uveal meshwork)
and so takes part in the limitation of the anterior chamber. In other
cases the anterior layers of the iris extend to the scleral meshwork as a
much-broken layer and so cover over this remnant of the anterior surface.

The direction of the anterior surface varies even under normal
conditions, and even more so when one takes into account eyes with an
abnormally long axis; and, indeed, as follows:

i. The direction of the anterior surface is more nearly sagittal; if
one erect a line perpendicular to the inner surface of the sclera at the
inner ledge, the foot of this line falls behind the scleral roll; the ciliary
muscle is, in general, longer the myopic type, so called because it is
found in pronounced form in eyes with axial myopia.



2. The anterior surface is more frontally placed; the perpendicular
line drawn from the inner ledge to the inner surface of the tunica fibrosa
falls in front of the insertion of the ciliary muscle; the muscle is, in
general, shorter hypermetropic type, because it is found mainly in eyes
of lessened axial length.

Aside from these individual differences one notes differences as well
between the nasal and temporal sides in many eyes, such as the ciliary
body approaching the type of hypermetropia on the nasal side, and that
of myopia on the temporal side.

The greater part of each ciliary process sets upon the inner surface, a
smaller part extends over the inner ledge to the iris root, and even reaches
a short way over onto the back surface of the iris. In a side view the
ciliary process appears uniformly rounder, aside from small indentations,
similar to the circumference of the pinna of the ear. But one only obtains
this view in the meridionally bisected eyeball or in very thick meridional
sections. The microscopic preparation also shows interruptions and
defects in the ciliary processes, even when' the direction of section is most
carefully thought of (PL I); these are not actual interruptions but only
uncapped depressions of the side surfaces. One recognizes these relations
much better in transverse sections of the corona ciliaris (PL VII, 2) ; here,
where one has a whole series of ciliary processes in cross-section before him,
one is convinced that the continuity of the tissue is nowhere broken, but
that the side surface is only wrinkled and the ridges somewhat rounded off.

In the study of meridional sections the error is not infrequently made of holding the
sims or an incomplete cut through the process to be the entire process. One can protect
himself against this error if one give heed to the pigmentation of the epithelium; the
pigmentation of the epithelium is very much less upon the very height of the projec-
tion, and then only does the section actually go through the ridge of the ciliary process.

The histologic peculiarities of the ciliary body are easiest made clear
by a comparison with the posterior zone of the bulb :

Middle Zone

Musculus ciliaris and suprachorioidea
Vessel layer of the ciliary body

Elastic lamella

Intermediary connective tissue

Cuticular lamella

Posterior Zone
Vessel layer of the chorioidea

Elastic lamella

Cuticular lamella




Pigment epithelium of the ciliary body

Ciliary epithelium

Membrana limitans interna ciliaris

Pigment epithelium of the chorioidea
( Layers i to 8


( Membrana limitans interna


a) The Uveal Portion of the Ciliary Body


If one follows the suprachorioidea from behind forward new structural
elements smooth muscle-fibers appear even in the equatorial region
or, at times, still farther posterior, therefore in the territory of the
chorioidea. They are grouped in bundles singly or for the most part
branched and then forming three or more rayed stellate little figures
(muscle-stars, PL IV, 8).

The muscle-stars are flattened, in keeping with the lamellar structure
of the whole layer, and, therefore, appear only as very slender spindles on
meridional section. Their true form and their distribution in the plane
of the surface can only be studied in teased preparations of the chorioidea.
They are disposed over both surfaces of the suprachorioidal lamella,
and their fibers go out in tufts of elastic fibers radiating into the elastic
plexus of the neighboring lamellae (/).

Sparse and separated by wide interspaces to begin with, the muscle-
stars become more numerous and more distinct as one approaches the
posterior border of the ciliary muscle; finally, they run together into
polyhedral meshes (PL IV, 9, si). The ciliary nerves bifurcate in the
same zone and form a wide-meshed plexus by means of their larger and
smaller branches.

The ciliary muscle proper (M) begins with these meshes of muscle-
bundles. A closed framework soon develops out of this, i.e., the bundles
disposed in various planes unite with one another and the muscle mass
becomes thicker and thicker through further branching. This structural
framework is maintained throughout the entire ciliary muscle, only the
prevailing direction changes gradually, so that the ciliary muscle falls
into various portions.

In the outer layers of the muscle the bundles have an almost pure
meridional direction, i.e., the meshes of the framework are narrow and
drawn out in the meridional direction; therefore, one sees almost no
intermediary tissue. The respective layers of muscle-bundles, indeed,
show many unions in the direction parallel to the surface, but among them-
selves these bundles are only sparsely united with one another; the
suprachorioidal lamellae go deeply in between these layers and their
denser pigmentation can be followed for a long distance into the muscle.
This portion of the muscle itself, therefore, appears to be lamellated
and on meridional section to be composed of many longitudinally dis-
posed bundles. It is called the meridional portion, from the direction
of the bundles.


Forward the thickness of this portion gradually increases up to one-
third of the maximum of the entire muscle. At the very fore part it
again thins and ends at the scleral roll: the muscle-fiber bundles go
over into finely fibrillated connective tissue, likewise of a meridional
course ; this tissue presses in between the circular bundles of the scleral roll
and probably continues farther into the lamella of the scleral trabeculum.
Occasionally individual cross-sections of bundles are seen at the anterior
end of the meridional portion.

The suprachorioidea is at length completely lost in the meridional
portion of the ciliary muscle; the majority of the lamellae enter the
posterior border of the ciliary muscle along with the muscle-stars, and
the few lamellae which lie outside this gradually go over into the muscle-
bundles from the outer surface. So it comes about that the most anterior
part of the perichorioidal space is entirely free of suprachorioidal lamellae.
Not infrequently one sees a short muscle-bundle inserted into the lamina
fusca sclerae at the very front, and, therefore, not taking part in the
general detachment of the ciliary body (Sattler, 188).

The radial portion succeeds the meridional portion inward. In
this the structure of the framework is most pronounced and the section,
therefore, shows an irregular net-form marking. Many of the bundles
appear to end blind; these are the obliquely coursing bundles whose
continuation falls in the next section. The interstices of the framework
are filled out by a pretty dense connective tissue, which carries the blood-
vessels and the especially numerous nerve branches, and in heavily
pigmented eyes also contains a few scattered chromatophores. This por-
tion received its named from the fact that a fan-like radiation of the surface
was read out of a divergence of the bundles. Yet one is at great pains to
find such an arrangement of the musculature, and I would prefer to call
it the reticulated portion.

The radial portion attains its greatest thickness in the neighborhood of
the inner ledge of the ciliary body. A special ending is not to be ascribed
to this portion, for the framework turns back into itself. For example,
this closure of the framework by means of many circular coursing muscle-
bundles is to be seen in the form of a net along the inner surface of the
muscle (F. E. Schultze, 196).

The union with adjacent structures, especially the surface union with
the vessel layer of the ciliary body, is only mediated by the interstitial
connective tissue of the muscle, which goes directly over into the con-
nective tissue of the vessel layer. In a similar way the anterior end of the
radial portion unites with that portion of the scleral framework which
does not enter the scleral roll: the connective tissue substratum of the


trabeculum of the iris angle goes over into the interstitial connective
tissue of the muscle.

On the side of the anterior chamber, in the delimitation of which just
this portion of the muscle takes some part, the muscle framework is bor-
dered by a thin layer of connective tissue united with the meshwork of
the iris angle, on the one hand, and with the iris stroma on the other hand.
This layer, as well as the most anterior portions of the interstitial tissue,
is especially rich in fine, wavy, elastic fibers; these are pressed together at
the inner border of the scleral roll, for instance, and radiate out from here
toward the root of the iris and into the muscle. Chamberward the
trabeculae of the uveal meshwork course to the root of the iris covered by
and snugly inclosed in this layer. In general, this layer varies greatly
in its density and composition in various individuals.

At the inner ledge of the ciliary body lies the circular portion of the
ciliary muscle, the so-called Mueller's muscle, named after its discoverer,
Heinrich Mueller (157). As its name indicates, it is characterized by the
circular course of the bundles and, therefore, appears as a group of cross-
sections in the meridional section. The intermediary tissue is looser than
in the radial portion; it has more of the appearance of the stroma of the
iris, whose root lies just in front of this portion.

But the circular portion likewise forms only a part of the muscle
framework; the meshes are much drawn out in a circular direction, and
do not form a separate part independent from radial portion. Unions
and transitions. between the two portions occur, so that in most sections
one cannot state exactly how far the circular portion extends. In any
case the drawings of Iwanoff (114) do not correspond to the actual
conditions in this respect.

The form of the ciliary muscle, especially, and thereby that of the
entire ciliary body, depends upon the grade of development of the circular
portion. In the myopic type the circular portion is very weakly developed
or fails entirely; in the hypermetropic type it is very strongly developed,
on the other hand, and, therefore, causes the inner ledge to project forward
and inward.

It at once comes to mind that these various types of the ciliary muscle are nothing
more than the expression of the particular requirements of accommodation for the
refraction concerned. For the hyperope, who must accommodate for distant vision,
certainly uses much more accommodation in his whole life than does the myope, who
can work even at near objects without any particular accommodation. But this
relationship must not be so conceived of that the ciliary muscle of the hyperope is
thought of as hypertrophic, and that of the myope as atropic, because the whole mass
of the muscle in the myopic type may be even greater than in the hyperope.

Now Heine (90) has shown that the eserinized (contracted) muscle approaches the


hyperopic type, the atropinized (relaxed) muscle the myopic type. It is, therefore,
conceivable that the different types are nothing more than different states of contraction
of the muscle. Against this it is to be argued that, as a rule, there is no occasion for the
hyperope to accommodate just before the eye comes to anatomic study, as for example
in the last hours of life if the eye is removed from the cadaver, nor during the anaesthesia
if it is enucleated during life. Finally, the same variations are found even in the new-

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Online LibraryMaximilian SalzmannThe anatomy and histology of the human eyeball in the normal state, its development and senescence ; → online text (page 13 of 27)