Maximilian Salzmann.

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

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(4) In many cases these two layers cannot be kept apart in the section.
According to Grunert (79), this is the case when the eye has been under
the effect of eserin therefore, when the dilatator is relaxed. Then there
is only one layer of spindle cells visible between the iris stroma and the
pigment epithelium but no border lamella. Grunert, therefore, holds
the posterior border layer to be a contraction-appearance of the dilatator.
However, one sees this reputed contraction-appearance, i.e., the posterior
border lamella, in a perfectly typical way in most eyes when, moreover,
these have not been under the effect of atropin, and despite this the pupil
(as usual) is pretty small. According to de Lieto Vollaro (142), the
dilatator elements are not separated in the fresh state, but fused together
into a "myoid plate."

In this manner the dilatator pupillae extends along the posterior
surface of the vessel layer of the iris from the ciliary border of the sphincter
pupillae almost to the root of the iris^ in an absolutely uniform develop-
ment and with a strict maintenance of meridional fibrillation. The
course and development of its elements change only in the region of the
sphincter zone and in the neighborhood of the root of the iris itself.

On the pupil side the dilatator has no sharp border; its elements finally
go over into epithelial cells by means of incompletely formed fibers.
These transition forms are partly developed fibers (on one side, i.e.,
cells which carry a process of only one side), therefore, of a clubbed form

1 This description is rather confined to the middle portions of the iris.


(Herzog), or cells with a wholly irregular form and pigmented throughout
(PI. VIII, 10, Di). Some 0.2 to 0.3 mm in front of the pupil-border
the outer leaf of the optic vesicle again takes on a purely epithelial char-
acter; a double-layered pigment epithelium is, therefore, present in this
border zone. But the anterior layer of epithelium is not regular here, by
any means; some cells are larger, and I have found very much enlarged
multinucleated cells in this zone, structures which very much recall to
one giant cells. Occasionally attempts at the formation of epithelial
muscle cells are also found here.

Throughout the entire sphincter zone and its immediate neighborhood
the elements of the dilatator are united to those of the sphincter. The
former thereby loses its surface expansion : a bundle of pigmented fibers
is separated away from place to place, goes over into a bundle of ordinary
muscle-fibers, and in this way into the muscle framework of the sphincter.
Such radiations are found at the ciliary border of the sphincter, and on
its posterior surface.

The former lie at the pupillary ends of the structural furrows. On
account of the fact that the structural furrow reaches pretty deep into
the vessel layer the dilatator only needs to continue on from the end of the
furrow in its original direction to get to the ciliary border of the sphincter.
Such a bundle consists, peripherally, of pigmented dilatator cells, centrally
(in the neighborhood of the sphincter) of ordinary smooth muscle-fibers,
and, just as the peripheral portion- seems to be a branching of the dilatator,
so the central portion appears to be a derivative of the sphincter. On
surface-section these bundles (PL VII, 6, Sp) seem to branch off from
the sphincter like the spokes of a wheel from the axis, and for this reason
this bundle is called the spoke bundle. The name Michel's pigment
spur has been derived from its appearance in meridional section when the
pigmented dilatator elements are more prominent (PI. VIII, 3, Sp}.

As a rule, the above-described spoke bundle contains the only radially
directed smooth muscle-fibers in the iris. In many eyes, however, such
radial smooth muscle-fibers appear farther peripheric and then form bands
which strengthen the dilatator pupillae; these are placed on its anterior
surface, i.e., that turned toward the iris stroma. This variation has been
more accurately studied by Widmark (237) and Forsmark (59), who would
discredit some of the older descriptions of the dilatator (or of the spoke
bundle). Forsmark found such strengthening bands in a sixth of his

The unions of the dilatator pupillae to the posterior surface of the
sphincter are notably weaker, but more numerous than the spoke
bundles and consist usually of a single or a few fibers. On meridional


section one sees dilatator fibers from place to place ; they rise up from the
back surface and course through the firm connective tissue to the sphincter
in bows with the concavity directed forward (PL VIII, 3, e). Yet one
can seldom follow them this far because they go out of a meridional
direction. On transverse section one obtains a variety of pictures:
incompletely developed dilatator fibers, which go off in front, and sphincter
bundles coursing obliquely backward, also called Fuchs's pigment spur
on account of their incomplete pigmentation, are seen in the neighbor-
hood of the border of the pupil (PL VIII, 10). Farther away from the
pupillary border one sees cross-sections of the dilatator elements in the
connective tissue often lying in a circle about the vessels, after the manner
in which Fuchs (67) has drawn them.

The dilatator, therefore, appears to go over into the sphincter every-
where or the two muscles together form a closed framework, probably
without free endings.

The ciliary border of the dilatator pupillae about corresponds to the
place where the posterior surface of the iris bends about onto the inner
surface of the ciliary body (at the posterior chamber angle), but only
approximately so, for the position of this border changes, indeed, from
section to section. At its ciliary border the dilatator no longer forms
one simple lamella, but there occurs a change in direction of the elements :
they become oblique and circular in part, and lie over one another. Only
a small portion maintains the meridional direction and from place to place
they ray out in the form of small bundles into the tissue of the iris root
and toward the anterior surface of the ciliary body; according to Ewing
(58), these radiations correspond to the ciliary valleys. The rest of the
fibers form arcades and in this way close off the dilatator lamella at the
periphery (PL VIII, 6). Whether a union with the ciliary muscle exists
here, as stated by some authors, is doubtful.

For the demonstration of the ciliary border of the dilatator one must not tear
the iris from the ciliary body; one must rather so remove the ciliary body that the
immediate environment of the posterior chamber angle remains still in connection
with the iris, and carefully brush off the pigment epithelium. If one will then lay the
preparation so obtained back surface up, the dilatator cells and their course can be
recognized by the peculiar hatched appearance of the pigmentation. The ciliary
border of the dilatator is often only incompletely retained on the torn iris. Surface-
sections give a no more satisfactory general view of the dilatator, although individual
details, e.g., the circular course of the margin, are visible in such sections.

On meridional section (PL I) the ciliary border of the dilatator
presents itself as a thickening, varying, however, with every section. The
arcades come out as cross-sections of the bundles of the spoke cells and


lie for the most part in front of the meridional coursing fibers when
the latter are present. The arcades are often widely removed from the
posterior surface and completely imbedded in the iris tissue or in the
tissife of the iris root. Its position, also, is subject to much variation.
As soon as the exclusively meridional direction of the dilatator element
ceases, the separation into the posterior border lamella and pigmented
spindle cells ceases. The fine unpigmented processes fail in the cells
of the border of the dilatator; its spindle-form body is more or less
pigmented throughout its entire extent.

It is fundamentally incorrect to think of the appearance of the dilatator as always
as typical as depicted. In the first place the structural furrows disturb things, and
one should, therefore, make it a rule to use sections for study in which the posterior
layers of the iris are cut strictly perpendicular to the surface expanse. Moreover,
aside from such hindrances to its recognition, it does not always show the same appear-
ance; the influence of the state of contraction (Grunert) was emphasized above.
Finally, it lies in the nature of the affair, in the incompleteness of the differentiation
process which the dilatator elements have gone through, so to speak, that one meets
different varieties. Remnants of undifferentiated epithelium such as described by
Grunert and Szili, and completely developed smooth muscle-fibers represent the
extremes of the variations.

It is only in this way that one can understand why the descriptions of the various
authors often vary so very much from one another; only in this way is it conceivable
that strife lasted so long as to whether there was a dilatator at all, although its exist-
ence was unconditionally demanded by physiology and pharmacology. This is not the
place to go into the abundant literature of the dilatator; the articles cited in the text
contain further references and are adequate to orient the reader concerning the varia-
tion of the views. The definition of the term muscle-fiber had a special influence upon
this mooted question. So long as only striped and smooth muscles were known oppo-
nents of the dilatator had to be, for as a matter of fact a dilatator made up exclusively
of such elements does not exist. It was only when the knowledge came that muscle-
fibers can develop out of epithelial cells that unanimity concerning the dilatator was
possible. Yet even today there are differences in the conceptions which have not
been worked out; for instance, Muench (161) endeavors to find the dilatator mainly
in the stroma-cell net of the vessel layer.

As already repeatedly stated, an intergrowth of the mesoderm and the ectodermal
elements takes place in the development of the iris. Forsmark has set up the view that
the degree of differentiation of these ectodermal elements into muscle-fibers depends
upon the position into which it has been thrown by development; elements entirely
separated from the native soil and wholly imbedded in the iris stroma grow out fully
into smooth muscle-fibers (the sphincter and the strengthening band of the dilatator) ;
such as remain in situ, on the other hand, i.e., on the surface of the mesoderm, only
undergo this differentiation in the basal portion (typical dilatator cells). But, original
as this conception is, it can have no general value, for the clump cells are ectodermal
elements which have been completely separated from the native soil and have
maintained their epithelial structure throughout.



This layer has an epithelial character throughout. Its cells are so
densely filled with dark-brown, round, gross pigment granules that
neither cell borders nor nuclei are visible. It is unconditionally neces-
sary that one study bleached preparations in order to come into a clear
visualization of the composition of this layer. One then very easily
recognizes the individual cells as elements having a height of 36 to 55 mu,
a breadth of 1 6 to 25 mu; they are prismatic or more pyramidal elements
with round nuclei no larger than in other epithelial cells (7 mu), and only
seem strikingly small in comparison with the size of the cells; they contain
one or two nucleoli lying close to the nuclear membrane.

The pigment epithelium seems most regular in a transverse section
through the ciliary zone (PL VIII, 9, P) a simple layer of uniformly
high cells. Meridional sections through this zone show a slight irregular-
ity, because they run at right angles to the circular furrow system (PI.
VIII, 8, P). The furrows appear as sharp incisions, the rolls between
them as rounded caps ; in the neighborhood of the root of the iris the rolls
are higher and often project forward a great deal. The cells on the
floor of the furrows are low (35 mu) and often wedge-form (triangular);
in the flatter rolls the cells are simply higher and somewhat pyramidal,
i.e., the lateral cell borders diverge toward the inner surface. Indeed, the
higher the rolls become, the more marked duplication of the epithelium
there is; the highest rolls are outspoken folds of epithelium. The dilata-
tor, however, courses smoothly over all these folds and furrows; the
circular furrows of the ciliary zone, therefore, lie only in the pigment

The same is true for parts of the radial furrows in the sphincter zone,
namely, for those in the immediate neighborhood of the pupil-border
(PL VIII, 10, P). Farther away from the pupil-border the radial fur-
rows also go down into the vessel layer of the iris and the structural
furrows of the ciliary zone do the same. In all these furrows the pigment
epithelium and the dilatator sink down in to an equal extent.

The pupil-border of the pigment epithelium is the limit of the optic
vesicle, the place where the outer leaf of the vesicle turns about into the
inner one, or the transition point. As a rule, this projects a little over
the pupillary limit of the pars uvealis and bends about this border a
bit toward the front (physiologic ectropium of the pigment epithelium;
PL VIII, 3, Ps). For this reason the transition area is visible from in
front as a pigment seam (PL VIII, i, Ps). Since the outer leaf has a
purely epithelial structure in the neighborhood of the transition, the iris


possesses a doubled pigment epithelium in the neighborhood of the pupil-

In bleached sections the place of transition itself has the appearance
of the apex of an epithelial fold and the cells in question are of wedge shape.
As already noted, it is almost in contact with the pupil-border of the
sphincter, a permanent indication that the sphincter pupillae develops
out of the border of the optic vesicle.

Many authors add a membrana limitans interna to the description of
the pigment epithelium of the iris, similar to that which the ciliary epi-
thelium possesses-. I have, indeed, seen an extremely thin colorless mem-
brane on the free surface of the pigment epithelium in many preparations,
but it is unusually delicate and cannot be isolated over any considerable

c) Variations in the Appearance of the Iris
(Influence of the width of the pupil and individual variations}

In an organ possessing such great mobility as the iris, the appearance
must vary according to the state of contraction of its muscle.

The pupil width may vary between i . 3 and 9 mm during life ; the
average width is 4 mm. These figures are, however, not taken from the
actual pupil, but from the enlarged image which the cornea gives of it.
This image is one-eighth larger than the actual pupil in a normally deep
chamber of 3^ mm and the actual pupil lies about o . 54 mm farther for-
ward. The above-given limits, therefore, correspond to an actual pupil
width of i . i to 8 mm.

According to Albrand and Schroeder (7), the pupil becomes very
much widened (8 mm) just before death; then, however, slowly narrows
from day to day. Therefore, an average pupil width is usually found in
the cadaver. Fixation fluids bring about a slight narrowing of the pupil
as a rule; therefore, it comes about that in the hardened cadaver-eye the
pupil width is usually only 2 to 3 mm.

It is not possible to fix the pupil at the extreme widths caused by
atropin and eserin during life for anatomic study. The effect of these
poisons upon the pupil passes off after death or after the enucleation of
the eyeball, and the limits between which the pupil can vary in anatomic
preparations are 2 and 5 . 5 mm. The width of the iris (the radius of the
iris, i.e., the distance of the ciliary border from the pupillary border)
varies between 5 and 3 mm (PL VIII, 12, 13).

From this general survey it is evident to what extent we can accurately
study the influence of the width of the pupil upon the appearance of the


iris; we can study the changes of the anterior iris surface throughout the
full extent of the movement of the pupil, since these observations can be
made in the living; in respect to the posterior iris surface and the inner
make-up we are dependent upon anatomic preparations.

Yet the posterior iris surface can be studied in the living eye by the
method of Hess (100); for the most part, however, we are thrown back
upon anatomic preparations for this, and with respect to its inner make-up,
therefore, must be satisfied with a lesser play in the width of the pupil.

According to Fuchs (67), the following changes in the anterior surface
come into play in the narrowing of the pupil: the pigment seam of the
border of the pupil becomes broader and its crenation more plain; the
pupillary zone is broader, its ridges take on a meridional course, the crypts
stretch out into meridional spaces, the angular line becomes more angular.
When the sphincter is visible, its width remains the same or increases
somewhat; yet the broadening of the sphincter is relatively less than
that of the pupil zone, and the angular line, therefore, moves away from
the ciliary border of the sphincter. The vessels in the ciliary zone stretch
out, the contraction furrows are smoothed out and the border zone comes
out partially from behind the corneoscleral border.

On the posterior surface of the iris one notes an appreciable increase
of the radial folding at the pupil-border (Hess, 139), while the circular
furrow system is almost obliterated as far as to the most peripheral furrows
in the neighborhood of the ciliary border.

On cross-section (PL VIII, 13) the sphincter is shown to be broader
and probably also thicker, and lies more nearly parallel to the posterior
surface. The whole pupillary border is more bowed about toward the
front; the border of the pigment epithelium covers the pupil-border of
the sphincter (ectropium of the pigment epithelium becomes more marked).

In the widening of the pupil the pigment seam of the pupillary border
becomes narrower or disappears entirely, the pupil zone narrows a great
deal, and the anterior or surface of the iris falls abruptly away from the
now more prominent angular line toward the pupil-border. The angular
line is stretched out and has almost entirely lost its angular form; like-
wise the crypts are drawn out to oblique clefts. The sphincter has become
narrower but not to the same extent as the pupillary zone, for the angular
line has mounted up over the sphincter. The vessels in the ciliary zone
are more tortuous, the contraction furrows are deeply incised, the border
zone has become invisible. The radial foldings on the posterior surface
are less marked, the circular ones more marked.

On cross-section the iris seems to be blunt (PL VIII, 12), the
sphincter appears shorter, narrower, and more obliquely placed, i.e.,


its ciliary border is farther removed from the posterior surface than is
the pupillary border. The pigment epithelium has retracted, and does not
any longer cover the pupil-border of the sphincter (the ectropium has
disappeared) .

The dilatator lamella, however, remains straight in all widths of the
pupil, it never shows foldings or bowings except where the iris as a whole
is bowed or folded, and on this ground alone it is evident that the pupil-
dilating principle must lie in this layer. The mesodermal layers of the
iris remain behind, decidedly, in the widening of the
pupil, and, therefore, apparently only passively follow
the pull of the dilatator lamella.

Although the iris has doubled its width in the
narrowing of the pupil, its thickness only increases
one-third at the most, according to Fuchs. This
striking lack of relationship seems an anomaly upon p IG . 4 ._ ins surface
first thought, but is very easily explained by the fact and P U P [I widths; mag-
that the thickness of the iris does not depend upon the the text
breadth of the iris, but only upon the extent of the
surface expanse. This, however, does not increase in the same ratio as
the breadth of the iris.

In Fig. 4 the outer circle represents the fixed periphery of the iris
(the ciliary border); its radius may be looked upon as 6 mm. The
middle circle has a radius of 3 mm and would signify the maximal width
of the pupil in anatomic preparation. In this pupil width of 6 mm the
surface of the iris is

6V 3 2 T = (36 Q)TT = 27T.

When the pupil is narrowed to 2 mm (inner circle) the surface of the
iris amounts to

In this the breadth of the iris has increased from 3 to 5 mm, i.e.,
two- thirds; the surface of the iris, however, not quite one-third. The
average thickness of the iris must, therefore, increase to this extent, and
this corresponds exactly to the observations.

Of course the iris of the normal eye is not completely broadened out
into a plane, but this has no essential influence on the relation of the iris
surfaces in a narrow and wider pupil.

Finally, in no other part of the eye is individual variability so great
as in the iris. It is widely known how much the color of the iris varies,
the same holds true of the thickness of the iris, of the relief, of the internal
structure. A thorough description of these varieties is impossible, it


would eventuate in an individual description. Moreover, the most
important variations have already been reported in the proper place.

As a curiosity only, it should be reported that the variation in color and marking
of the iris called forth remark even in antiquity, and finally has been worked out to a
system of "eye diagnosis," the rankest nonsense which uncritical and unscientific
nature-study in connection with mysticism and speculation could bring forth in the
hands of credulous laymen and unscrupulous impostors (206).


The vitreous as a whole has the form of a sphere flattened sagittally
and marked in front by a round della. The posterior half and the lateral
part of the surfaces show the mould of the shell of the retina; the della,
patellar fossa (fossa patellaris), is the negative of the posterior surface of
the lens, to which it is opposed. The transition from the fossa patel-
laris over into the outer convex surface of the vitreous presents a low
wall, on the back of which the posterior half of the corona ciliaris lies in
undisturbed topographic relations and receives the shallow radial impres-
sions of the ciliary processes.

The vitreous is fixed to the papilla and, less firmly, to the inner surface
of the retina, most firmly, however, at the ora serrata and to the ciliary
epithelium in a zone some i . 5 mm broad immediately adjacent to the
ora serrata. When the vitreous draws together under the influence of
fixation and hardening fluids, when under pathologic relations it is
shrunken down to a minimum it clings at this point. Even severe
injuries do not tear away the living vitreous in this situation, and when
it is torn from it part of the ciliary epithelium goes with it, and the end of
the retina loses its attachment.

Since, furthermore, this zone is of significance in respects other than
purely anatomic, it may be justifiable to give it a special name, and I
would call it the base of the vitreous (PL I, GV). (Wolfrum, 242, calls this
the zone of origin of the vitreous.)

In front of the base the vitreous borders upon a free space (the pos-
terior chamber) ; in this region its fixation is less firm, for it is united to
the bulb wall (the ciliary body) directly only here and there by delicate
processes and mediately by zonula fibers.

Where the vitreous adjoins the lens, a more firm union is again present
in the form of a ring of 8 or 9 mm diameter concentric with the lens border;
here lies the ligamentum hyaloideo-capsulare (PL I, Lhc] described by
Wieger (238).


The portion of the anterior surface of the vitreous lying inside this
ring is not grown to the lens but can easily be drawn away as soon as the
resistance of the ligamentum hyaloideo-capsulare has been overcome. A
capillary space lies between it and the lens, the post-lenticular space of
Berger (21).

Nasal, close to the axis of the vitreous, courses a canal (central canal

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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 17 of 27)