Maximilian Salzmann.

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

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anterior border layer of the vitreous, and often imbedded in canals in the
border layer; for this reason I have called them the innermost fibers
(posterior zonula bundle of Retzius, 180; central layer of Graf Spec,
210). They come from far back, have no fibers uniting them to the inner
surface of the ciliary body, and have nothing to do with the divisions of
the latter; they are the only fibers which even occasionally course along
the crests of the ciliary processes (PL VII, 2, iz); they end at the
posterior surface of the lens or in the border layer of the vitreous.

The rest of the zonula fibers vary away from the processes and course
into the valleys. The whole complex of zonula fibers entering into one
ciliary valley thus divides into two halves, which then course farther on
along the side surfaces of the processes and finally go over into the free
part of the zonula in meridional rows.



158 ANATOMY AND HISTOLOGY OF THE HUMAN EYEBALL

The outline of each row forms a triangle, the apex of which lies in the
posterior part of the corresponding ciliary valley and its base in the
equatorial zone of the lens capsule. The anterior surface of the triangle
is straight; the posterior surface describes a bow apposed to the wall
about the fossa patellaris.

The triangle is, however, by no means uniformly filled out with
zonula fibers, as O. Schultze (197) states, but the fibers are massed toward
the anterior and the posterior sides and a much smaller number of fibers
course in the middle portion. The anterior fibers are the largest and are
inserted in front of the equator of the lens; they form the main anterior
train of fibers (Topolanski, 222) and the totality of the main
anterior train of fibers, in all about 140 rows, forms the anterior
zonular leaf (PL I, vZ).

The posterior fibers are finer than the anterior; they unite or cross
over with the most anterior ones coming from the corona, and in this way
they form a double fan, or a figure similar to a row of tangents to a curve
or an evolute (Schoen, 192). These fibers, whose insertion is on the
posterior surface of the lens, i.e., lies behind the equator lentis, form
the main posterior train of fibers (Topolanski), and their totality forms the
posterior zonular leaf (PI. I, hZ).

The middle or equatorial fibers are inserted into the equator of the lens
or in the immediate neighborhood of it. They are the weakest of all and
least regularly developed (PL I, qZ}.

This description depicts the type or the principle of arrangement of
the zonula. It is fundamentally incorrect, however, to expect to find this
principle carried out with mathematical accuracy. To begin with, the
individual rows are, indeed, strictly meridional; the irregularity of the
ciliary processes makes the individual fibers go out of the row, and finally
the fibers diverge after their exit from the ciliary bodies in a frontal direc-
tion as well, or they branch in this direction.

When one looks at a very thick section one comprising several ciliary
valleys under weak magnification, it does, indeed, seem as if the zonula
fibers uniformly fill out the entire space which the older anatomists called
Petit's canal (O. Schultze, 197). But when one carries through a section
tangential to the equator, it is at once seen that the cross-sections of
zonula fibers are not uniformly distributed through this space, but are
at least thicker along the anterior and posterior sides. The study of the
insertion zone on the lens leads to the same result (cf. chap. xiii).

No description is able to give with absolute accuracy any intermediate concep-
tion between the regularity and irregularity of arrangement which characterizes the
organized structure. The one emphasizes the plan of the whole arrangement and



THE ZONULA CILIARIS 159

this description then naturally emphasizes the regularity; the other sees only the
variations from the rule and for this reason denies any law. The truth lies in the
mean between the two extremes.

All of the heretofore described elements of the zonula (and these
form by far the greater majority) possess a meridional direction or vary
only insignificantly from this direction. Moreover, the majority unite
the inner surface of the ciliary body to the equatorial zone of the lens.

Although then, we look upon these as the most important, function-
ally, and accordingly designate them as the typical zonula fibers, there
still remains a minority of fibers having another direction and united with
other structures; these we will call atypical zonula fibers for short,
from which, however, it is not to be understood that they are to be con-
sidered of no significance functionally.

To the atypical zonula fibers belong in the first place those coming
out of the vitreous and the backward-coursing zonula fibers, which we have
already discussed. Here, too, belong the inter- and intraciliary fibers
of Czermak (34), fine fibers uniting two ciliary processes with each other.
Furthermore, the short and thick fibers going out of the corona ciliaris
directed at right angles to the typical fibers and serving for the fixation of
these, described by Retzius (180), belong here. But in my opinion these
fibers do not unite with the typical fibers, but radiate into the border layer
of the vitreous or go over into circular fibers.

For if one makes an anatomic preparation of the border layer of the
vitreous in the manner heretofore described and looks at the surface, one
sees a varying number of zonula fibers radiate into it (PI. VIII, 14).
One part of these fibers belongs to the innermost zonula fibers (see p.
157); the other part (&) consists of shorter or longer stumps, which
apparently come from the corona ciliaris, for the radiations into the
vitreous lie in this region. The individual fibers are thereby broadened
out into the form of a narrow triangle and then break up into a large
number of fine divergent processes. At times only a part of the fibers
radiate into the vitreous layer, and the remainder course on farther to the
lens, or one fiber-bundle takes root at two or three places in the vitreous
body in this way (m). The greater part of the fiber processes very soon
lose themselves in the border layer, the other part bends about in a sharp
curve into the circular course.

These circular zonula fibers (cZ) sometimes stretch over a great part
of the border layer, always following the corona ciliaris or rather the wall
which lies around the fossa patellaris. The border layer itself is always
pretty strongly folded in such places and for this reason one is not able
to follow the individual circular zonula fibers over wide stretches. When,



160 ANATOMY AND HISTOLOGY OF THE HUMAN EYEBALL

however, two radiations lie close to one another, a few fibers of union can
very easily be made out, and it is to be suspected that the most of the
circular fibers sooner or later go over again into typical ones, i.e., into
meridional-coursing zonula fibers.

The transition of meridional into circular fibers can only be plainly
seen in surface preparation of the anterior border layers; the circular fibers
themselves may, however, also be seen in meridional sections, for example,
when they are numerous and large, for the cross-section of the zonula
fibers stand out clearly on account of their size and characteristic appear-
ance in contrast with the-nner fibrillation of the border layer itself. They
lie in part, certainly, in the border layer and not simply upon it. A strong
folding of the border layer indicates the place where circular zonula fibers
are to be found (PL I, cZ). In transverse sections of this region the
circular fibers appear cut along their length, even on weak magnification,
and stand out thereby from the typical fibers, which are cut across,
throughout.

The circular zonula fibers have already been incidentally described by various
earlier authors, yet it is doubtful whether or not all these statements relate to
man. With the introduction of modern imbedding and section technique they have,
however, been forgotten, for it must be that the interciliary fibers of Czermak belong
in this category. I have again demonstrated their regular presence and have more
accurately described their situation and their course (184).

According to Graf Spee (210), two additional girdles of circular fibers are found,
one between the ora serrata and the corona ciliaris and one at the border of the patellar
fossa.

The zonula throughout consists of structureless, non-nucleated fibers,
clear as glass, which are stiff in comparison with other fibers, i.e., they
show no tendency to wavy undulation when they are relaxed, but
rather show angular nickings.

The finest fibers are encountered in the posterior border of the zonula
and everywhere along the inner surface of the ciliary body. They are
much too fine to be accurately measured ; they are, however, considerably
thicker than the vitreous fibrillae, and in sections are especially differen-
tiated by their taut, straight course. The largest zonula fibers have a
thickness of 30 to 40 mu; all possible transitions lie between.

The cross-section of a large fiber (PL VII, 5, Z) shows an irregular
form from elevations and constrictions, and these are to be noted as
fine longitudinal striae in the longitudinal view. This would show,
apparently, that we have in these larger fibers bundles of finer ones,
but the constituent parts of such a bundle are so thoroughly fused into
one another that neither the lines of separation nor the special cement



THE ZONULA CILIARIS 161

substance can be made out. A similar fusion is also found where the
zonula fibers cross. The compound nature of the large fibers is shown,
too, by the fact that it breaks up into fine fibers at the ends.

These branches are either brush-form, i.e., the fine fibers diverge in all
directions, or fan-like, i.e., the fibers diverge out into one plane from a
given point, or like a feather, i.e., the fine fibers gradually divide off
from the large one. The purest of the two first types are found at the
inner (axial) ends, i.e., at the insertion into the lens capsule and the
vitreous; the third type appears along the inner surface of the orbiculus
ciliaris.

If, indeed, the large zonula fibers do not with certainty form a histo-
logic unit it is certainly not possible to distinguish between elementary
fibrillae and compound fibers in an unexceptionable way; one does not
know where to draw the line among the multitudinous transitions in
size and form on a cross-section.

With respect to the tinctorial relations the zonula fibers agree with the
glass membranes (cuticular formations) . It follows that a certain affinity
for orcein is present. It is a striking fact that they take the Weigart
neuroglia stain (Agababow, 5). Yet it is going too far to deduce from this
a relationship to neuroglia, for, in my preparations at least, other elements,
which have not the least relationship to neuroglia, take this stain as well.

The typical zonula fibers unite with cuticular structures at both ends,
in my opinion, with the lens capsule on the one side (cf. chap, xiii), and
with the limitans interna ciliaris on the other side.

With respect to the first point, i.e., the union with the lens, not the slightest differ-
ence of opinion exists. So far as the second point is concerned, i.e., the union with
the limitans interna ciliaris, there are a number of authors who differ in their views.

Schoen (192) thinks one zonula fibrilla proceeds out of each ciliary epithelial cell.
According to Terrien (221), they come out between these cells and take their origin
from the glass membrane of the ciliary body (our cuticular lamella, p. 117). Wolf rum
(242), finally, claims to have followed the finest extensions of the zonula fibrillae through
the protoplasm of the epithelial cells up to the cement ridge between the ciliary epithe-
lium and the pigment epithelium.

It is conceivable that all of the authors who consider that the zonula fibers are
given off from the ciliary epithelium do not admit the existence of a limitans interna
ciliaris, at least in those places where the zonula fibers are given off.

Special relations exist between the ridges which the limitans interna
ciliaris forms in the anterior part of the orbiculus and the straight- and
backward-coursing zonula fibers. On transverse section (PI. VII, 5),
one sees the cross-sections of new fine zonula fibers here and there between
the closely apposed leaves of such a ridge, and in other places small rows
of zonula fibers lie just over the ridges, out of which they apparently



162 ANATOMY AND HISTOLOGY OF THE HUMAN EYEBALL

come, as shown by their oblique course. In these places the zonula fibers
certainly do not press into the protoplasm of the ciliary epithelium.
They remain keyed in between the leaves of the ridge which incloses them
in a fold.

It appears to me highly probable, although I cannot yet prove it,
that these fibers pass over the ridges, but do not end in them, i.e., that
they are fibers which come from behind and appear on the ridges, describe
a flat bow, and come out in front again as straight-coursing fibers.

Nothing can be accurately stated concerning the union of the zonula
fibers with the tissue of the vitreous. One can follow such a zonula fiber
only a short distance into the tissue of the vitreous, then it disappears;
whether or not it goes over into vitreous fibrillae remains unsettled.

The cells occasionally seen upon the zonula fibers have been subjected
to very different interpretations. According to my observations, one
finds the same cells on the outer surface of the vitreous base as along the
posterior border layer. Occasionally such cells are displaced still farther
forward onto the zonula fibers. They are all wandering cells. The folds
and rolls of the ciliary epithelium may give rise to confusion, as for
instance, when, as in older people, the membrana limitans interna ciliaris
projects forward between the ridges and the meridional section cuts them
longitudinally. Perhaps the cell-layer between the ciliary epithelium and
the zonula described by Graf Spee (210) belongs in this category. No
cells not even wandering cells are found in the free part of the zonula.

I have not been able to convince myself of a direct connection between
the zonula fibers and the border of the retina or the supporting tissue of
the retina, as contended for by Schoen (192).

CHAPTER XIII. THE LENS (LENS CRYSTALLINA)

The lens has the form of a biconcWe?, lens with unequal sides and
rounded border; accordingly, one differentiates an anterior and a posterior
lens surface, and a lens border ,or equator lentis. The center of the
anterior surface is designated as the anterior lens pole, that of the pos-
terior surface as the posterior lens pole, and the line of union between
the two, the axis of the lens.

Looked at from in front or behind, the lens has a circular form and a
diameter of about 9 mm 1 (PI. II, i). This dimension is the frontal or
equatorial diameter. The lens border is not entirely smooth, but pro-



1 All of the measurements and statements, where not expressly otherwise stated, relate to a middle
age of life and with the lens focused for distance. Concerning the influence of the age of life upon the
lens, see chap, xviii.



THE LENS 163

vided with rounded or dentate prominences corresponding to the ciliary
valleys and apparently arising from the pull of the zonula fibers. It is
not a form of hardening effect, for it can be seen in the living lens as
well (Magnus, 146; Topolanski, 223). According to Hess (96), they are
more marked in atropinized eyes than in eserinized eyes.

The form of the anterior surface varies only a little from that of the
surface of a sphere. At its vertex the radius of curvature is 8.4 to
13 .8 mm an average of 10.64 mm according to the numerous measure-
ments of Tscherning's (228) students, Auerbach, Saunte, Maklakoff,
and others; and, according to the latest, measurements of Zeeman (244),
the average in emmetropes is 11.05 mm -

The form of the posterior surface is that of a paraboloid with a vertex
curvature of 4.6 to 7.5 mm, an average of 5 . 98 mm. A flat circular
furrow (concavity forward) has been found by several authors in the
peripheral zone of the posterior surface; Zeeman (243) has found it in
the living by the doubling of the image reflected by the posterior lens
surface at a distance of 3 . 5 mm from the optic axis, and von Pflugk (172)
in the newborn after fixation of the form of the lens by his freezing method.

From ophthalmometric measurements, the thickness or sagittal
diameter of the lens is 2 . 9 to 5 . i mm, an average of 3 . 7 mm (Tscherning) ,
an average of 3.76 mm in emmetropes, according to Zeeman. In ana-
tomic study, however, the thickness of the lens will be found greater,
and according to the old measurements of Pourfour du Petit, contributed
by Tscherning, an average of 4 . 7 mm according to Krause, 4 . 9 mm.

Meridional asymmetry has not heretofore been certainly proven for
the lens, yet many things speak for this and, too, for the fact, that the lens
possesses a slight degree of meridional asymmetry or in any case acquires
it, in later life.

A correct conception of the form and size of the lens can only be obtained by a study
of fresh material. All of the fixation and hardening means lead to a considerable
shrinking and change of form in the lens. The equatorial diameter shortens about
i mm, and the anterior surface takes on a stronger curvature.

But the fresh lens also changes its form markedly, and the curvature of the surfaces
is lost as soon as it is separated from its connections. The task of fixing the natural
form of the lens, i.e., that present in life, is an especially difficult one; von Pflugk
thought he had solved this with his freezing method; according to Hess (99), this suc-
ceeds only after previous fixation with formalin.

The lens is completely clear and transparent in the fresh state, but,
according to Hess (97), it is never entirely without color, and even in youth
has a tinge of yellow which always becomes more marked with age.

The union of the lens with its environment is effected by means of
two structures: the zonula ciliaris unites it with the ciliary body, the



1 64 ANATOMY AND HISTOLOGY OF THE HUMAN EYEBALL

ligamentum hyaloideo-capsulare with the vitreous body. The first union
is by far the more important one, for even in complete relaxation of the
zonula (and still more after it is separated) the lens loses its fixed position
and sinks from gravity. Complete dislocation (luxation) of the lens is
only possible, however, when the ligamentum hyaloideo-capsulare has also
been torn.



In histologic respects, three different constituent parts of the lens
can be demonstrated. From without inward, they are: the lens capsule,
the lens epithelium, and, the lens substance. The latter is a product of
the epithelium, and, thanks to the never completed growth of the lens,
one finds the lens substance in process of formation at every age of life.
The histologic peculiarities of this will be described under the heading
of "epithelial border."

I. THE LENS CAPSULE
(PL IX, 3 , 4 , K)

This is a typical g'ass membrane, i.e., a structureless, highly refracting,
very firm elastic membrane, highly resistant to chemical and pathologic
influence, whose wound borders have a marked tendency to roll outward.
A lamellar composition is not ordinarily seen, yet a thin superficial lamella
often appears in the region of the lens equator; it carries the last exten-
sions of the zonula fibers and has been called the zonular lamella by
Berger (20), the pericapsular membrane by Retzius (180).

The lens capsule forms a closed hull about the lens. Solely upon
practical grounds, such as those of operative technique, one differentiates
an anterior capsule, i.e., that part drawn over the anterior surface, and a
posterior capsule, the covering of the posterior surface.

The thickness of the lens capsule shows wide variation among indi-
viduals and at different ages, for it increases appreciably in thickness
with age. But the thickness of the capsule also varies in different zones
in the same lens. The table on p. 165 gives a survey of the measurements
of this variation.

In general, the anterior capsule and the region of the equator is thicker
than the posterior capsule. The minimum thickness lies at the posterior
pole under all circumstances.

Since this is constant and easy to be made out, it can be made use of for the orienta-
tion of the surfaces of the lens, e.g., anomalies in the position or situation of the lens

The thickest portions of the capsule form two zones concentric with
the equator, one on the anterior, one on the posterior surface. The zone
of maximum thickness of the anterior surface lies about 3 mm from the



THE LENS



165



anterior pole or i mm inside (axial to) the insertion girdle of the anterior
zonula fibers. The zone of the maximum thickness of the posterior fibers
lies still farther peripheralward, somewhat inward from the posterior
zonular insertions and the ligamentum hyaloideo-capsulare. Not infre-
quently this maximum exceeds that of the anterior, as for instance, in
the child's eye (see No. i of the table).

The thickness of the equatorial zone varies much; the measurement
given in the table is taken from immediately behind the epithelial border,
where a relative minimum lies. In front of and behind this place the
capsule is somewhat thicker.



No.


AGE


THICKNESS OF THE LENS CAPSULE IN M u


Anterior Pole


Maximum of
the Anterior
Surface


Equator


Maximum of
the Posterior
Surface


Posterior Pole


I


14 days
2 . 5 years
7
9
15
19
23
26

32
35
36
40

4i
48

53
56
7i


6
8
8
8
9

12
II
10
12
14
9

16

ii
ii

14
18

14


8
12
13
15
14
23

18
18
16

21

21
22

18

22
25
23
21


3
7
9
8

14
17
14
10
16

17
16
16
18

15
16

14
9


18
18
17

22

23
26
21

17
21

23
22

18

23
28

23

16
9


2-5
2
2
2
3
3

3
3
2-3
4
3-4
3
3
3-4
3
3
2-3


2


2


4.


e


6


7


8


o . .


10


ii . . .


12


12


14


I c


16


17





The greatest interest attaches to the zones of the maxima. The
anterior maximum corresponds to that place in which Tscherning (227)
found a flattening of the anterior lens surface in accommodation; the
posterior maximum corresponds to that place in which Zeeman (243) and
von Pflugk (172) have seen concavities. Both maxima lie somewhat
axial to the insertions of the zonula fibers, but they are not brought
about by these, for at the very places of insertion the thickness of the
capsule is less.

The insertion of the zonula fibers follows a zone concentric with the
equator and inclosing it. The anterior zonula fibers reach much farther
over onto the anterior than do the posterior zonula fibers onto the posterior
surface. As a result, the equator does not lie in the center of this zone
but it divides it somewhat in the relation of 3 to 2 (PL I). Measured
along the surface, the whole insertion zone is about 2 mm broad; measured
along a chord, 1.3 to 1.9 mm. depending upon the degree of rounding of



1 66 ANATOMY AND HISTOLOGY OF THE HUMAN EYEBALL

the lens border; its posterior border coincides almost exactly with the
insertion of the ligamentum hyaloideo-capsulare into the lens capsule.

The angle at which the zonula fibers are inserted into the lens capsule
varies between o and 90, for the most anterior and posterior fibers
approach the lens capsule in a tangential direction, the middle ones at
right angles ; the fibers lying in between show an angle of insertion increas-
ing as they approach the equator. The zonula fibers are broken up first
upon the lens capsule into the last finest extensions (in so far as this has
not already occurred in the free portion), and then continue a stretch
farther on over the capsule in a meridional direction (PI. IX, i). Espe-
cially is this true of the tangentially inserted fibers, i.e., those lying at
the borders of the insertion territory (they are inserted with band-like
expansions) ; their expanse reaches about o . 4 mm farther forward beyond
the margins of the insertion zone.

The middle zonula fibers (qZ) divide previously into brushes of finest
fibers, which course without further subdivision to the surface of the
capsule and then go partly forward, partly backward.

The extensions of the zonula fibers remain on the surface of the lens
capsule throughout, as can best be seen in equatorial sections; zonula


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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 19 of 27)