Maximilian Salzmann.

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

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fiber extensions, which show varying size upon cross-section, lie only
upon the outer surface of the lens capsule. On surface view they show a
meridional striation, which is not wholly uniform, i.e., it is made up of
larger and smaller elements ; this is due to the fact that the border fibers
extend beyond the limits of the insertion zone. In general, they extend
over a girdle 2.7 mm broad (measured along the surface). The borders
of this girdle are circles concentric with the equator (parallel circles);
this is especially plain on the anterior lens surface on account of the uni-
form length of the zonula fiber extensions (vZ). When, however, one
observes the actual points of insertion of the zonula fibers, and, therefore,
excludes the extensions coursing over the surface of the lens capsule, there
appears a girdle of measurable breadth and not mathematical lines, as
stated by Schoen (160), although marked individual variations are
shown ; if one takes into consideration only the fibers lying on the surface
of the whole fiber mass the insertions form very wavy lines, especially on
the posterior surface (hZ}. This alternating projection and retraction of
the most superficial fibers is probably the reason why the older anatomists
conceived of the zonula as a ruffled, folded membrane.

On the inner surface of the posterior capsule one not infrequently sees
a system of lines which inclose polygonal cell-like fields; these are the
impressions of the bases of the lens fibers in a thin layer of coagulated
fluid, which is secreted as a post-mortal appearance between the lens
substance and the lens capsule.



THE LENS 167

2. THE LENS EPITHELIUM

This extends beneath the lens capsule over the whole anterior surface
of the lens up to the equator (and sometimes a short distance beyond it).

This epithelium is disposed in two biologically different zones: the
one, covering over the anterior lens surface, has no relation to the forma-
tion of lens fibers and even under pathologic conditions is not capable of
forming such (its pathologic product is the capsular cataract) ; yet it plays
a significant part in the nutrition of the lens and its insult leads to a cloud-
ing of the lens substance. On the other hand, the narrow seam of the
epithe'ium, which lies at the equator of the lens, the epithelial border,
furnishes the lens fibers and thereby cares for the growth of the lens;
this growth continues throughout the whole of life, although, indeed, with
gradually decreasing intensity.

a) The Epithelium of the Anterior Lens Surface

In the neighborhood of the anterior pole these cells are n to 17 mu
broad and 5 to 8 mu high ; the nuclei are round in surface view and have a
diameter of 7 mu (PI. IX, 2); in cross-section they are ellipitical. The
arrangement of the cells is not a regular one and as a result the form of
the cells is not regular. In a fresh state the cell borders appear as fine
sharp lines whose position and course change with varying focus, i.e., the
lateral separating surfaces do not lie at right angles to the capsule but are
bowed. This comes out more cleanly when the epithelium is impregnated
with silver (Brabaschew, 15), and then one sees two systems of separating
lines which do not coincide. Spaces are not infrequently found between
the cells, and the portions connected are drawn out into bridges between
the cells, and the individual cells take on a more or less stellate form
(Hosch, 106). This latter appearance is apparently a result of the shrink-
ing of the cell, probably coming about through various influences; pos-
sibly, too, it occurs during life.

Farther toward the periphery the arrangement remains the same, but
the cells are notably smaller (8 to 12 mu in surface expanse) and higher
(9 to 15 mu), i.e., the cells approach the cylindrical form, and the nuclei
back up toward the inner end of the cell and become spherical (PI. IX,
3 the uppermost cells of the epithelium).

;3) The Epithelial Border and the Lens Vortex (Becker, 18) : the Formation of New Lens Fibers

At the epithelial border the heretofore irregularly arranged cells are
arranged in meridional rows. It is the service of Rabl (175) to have
recognized this linear arrangement as a typical appearance in the mam-
malian lens and to have brought out its fundamental significance for



1 68 ANATOMY AND HISTOLOGY OF THE HUMAN EYEBALL

the structure of the lens substance. In man, especially, in the adult,
these rows are very short and indistinct, probably because the cells grow
out so soon from the lens fibers.

When one studies an exactly meridional section of this region (PL
IX, 3), a broadening of those parts abutting upon the capsule is seen
to be the first change in the epithelial cells. The first of these cells
(cell 6 from above) takes on, thereby, the form of a trunkated pyramid
and the cells following become more and more oblique. The obliquity,
however, affects only the part of the cells turned toward the capsule at
first; the inner parts of the cells (in which the nuclei lie) retain their
form. These cells (n and 12 from above) also take on an oblique direc-
tion; the nucleus becomes larger and oval on cross-section. Farther
along the inner part of the cell elongates more and more, its obliquity
increases and soon exceeds that of the outer part, so that the whole cell
acquires a bowing (concavity forward and toward the capsule).

Under further elongation the cell, or rather the young lens fiber,
interposes its inner (now its anterior) end between the epithelium and
the older part of the lens substance, while the outer end is constantly
pushed backward by the subsequently growing cell. The nucleus thereby
becomes displaced farther forward, yet in a degree varying a great deal
among the different cells.

The nuclei of the epithelium, along with those of the young lens
fibers, form a very characteristic figure on meridional section, the pecu-
liarities of which are to be recognized even by moderate magnification;
the older authors called it the nuclear zone, Becker, the nuclear bow.
In the epithelium proper of the anterior lens capsule the nuclear row runs
parallel to the capsule; in the neighborhood of the epithelial border it is
somewhat removed from the capsule and at the very epithelial border
bows about to the front in a sharp curve or angle, but at the same time
the nuclei fall more and more into this order.

If one calls that end of an epithelial cell turned toward the surface the
free end (as does Rabl, 175), or the head of the cell (in analogy to the
basal cells of the corneal epithelium), the end turned toward the meso-
derm the basis on the other hand, and the line of union between the two
the main axis, these poles of the lens epithelium are oriented according
to the development as follows: the bases of the cells lie on the lens cap-
sule, the heads of the cells look toward the lens substance, and the main
axes are at right angles to the capsule.

In the transition into a lens fiber the epithelial cell grows in the
direction of the main axis, but at the same time this undergoes a rotation
of 90 with the inner end forward. The bases of all the lens fibers,



THE LENS 169

therefore, come to lie in the posterior part, the heads in the anterior part
of the lens.

By the rotation of the individual elements during development there
arises that peculiar figure seen at the epithelial border in a meridional
section called by Becker (18) the lens vortex.

The expression lens vortex was used by the earlier authors and by Rabl, too, to
indicate those figures which arise through the meeting of the fibers in the lens stars.
Schwalbe called this figure at the epithelial border the border vortex, for this reason.

The lens vortex forms an inward-projecting roll as a result of the
pressing together of the heads of the cells, and the youngest lens fibers,
therefore, acquire a concavity forward. Because now each fiber is thinner
over this roll than in front of or behind it, the concavity gradually flattens
out inward and finally goes over into a definite convexity (corresponding
to the curvature of the equatorial portions of the lens). In only one
place, at the nucleus, is the young fiber thicker. But these areas are not
superimposed and in this way they are smoothed out.

In a strictly meridional section there is a meridional row of epithelial
cells with lens fibers coming out of these, and when one follows the direc-
tion of the epithelial cells from before backward (the lens fibers in the
direction from without inward), one surveys at the same time a whole
row of different developmental stages of which the differences in respect
to age are nearly uniform. The temporal interval of the developmental
process thus corresponds to a juxtaposition in space, and this series has,
in general, the character of an arithmetical progression.

The more vigorous the growth of the lens, e.g., in children, the slighter
are the differences in age in this series; the more developmental stages,
one after another, one has before him, the more gradual is the transition
of the epithelium into the lens substance, the more round and long is
the nuclear bow. The more indolent the growth, e.g., in old people,
the greater are the differences in age in a series, the fewer the develop-
mental stages visible at one time, the sharper is the demarkation of the
epithelium from the lens substance, the shorter and more angular is the
nuclear bow.

That which proceeds from a meridional row of epithelial cells remains
constant in the meridian. The complete lens fibers form rows, there-
fore, even as do the epithelial cells, and because the individual elements
of these rows have significantly elongated in the direction of their main
axes, each such row has two dimensions : it becomes a meridional or radial
lamella (Rabl, 175), the most important textural element of the lens
structure.



i yo ANATOMY AND HISTOLOGY OF THE HUMAN EYEBALL

3. THE LENS SUBSTANCE

In middle life the outer layers of the lens substance are very soft and
without color (cortex), the deeper layers are appreciably harder and more
or less of a yellow color (lens nucleus). Corresponding to the consistence,
the index of refraction also changes; according to Halben (85), it varies
between 1.36 (cortex) and 1.4452 (nucleus). Heine (89) gives the
nucleus a maximum index of i .41.

As Halben has shown by his differential refractometer, the transition
of the cortex into the nucleus is completed to a certain depth pretty
suddenly, i.e., there is a rapid increase of the index of refraction. A
transition, indeed, does exist, but this is not as gradual as Matthiessen
(148) had earlier conceived it to be. The thickness of the transition zone
is so slight that the image reflected by it is quite plain, as Hess (97) and
his students have shown.

For example, when one studies the images of the lens with an intense
linear light, one perceives a dimmer and weaker picture, it is true, but
yet another, alongside of the two well-known Purkinje-Sanson images
of the anterior and posterior surfaces (which, according to Hess, should
rather be spoken of as the anterior and posterior cortex images); these
move in the same direction as the neighboring cortex images and are
directed the same as these. They are thrown by the anterior and pos-
terior nuclear borders and carry the names anterior and posterior nuclear
images. According to Freytag (60), the anterior becomes constant after
the twenty-fourth, the posterior after the thirty-first year of life. With
increasing age, these little images increase in luminosity, i.e., the difference
in the index of refraction becomes greater.

With the exception of the central portions, the whole lens substance
is made up of the characteristic radial lamellae of Rabl, described above
(PI. IX, 4). The number of the lamellae on the surface in the adult
can be considered as 2,100 to 2,300. With increasing depth the number
of lamellae decreases, partly because the individual lamellae sharpen out,
partly because neighboring lamellae fuse. In this way the lamellae
become more and more indistinct the nearer one approaches the center
(PI. IX, 5); in the center the arrangement of the sagittally coursing
fibers is irregular (Rabl's central fibers). The human lens is, in general,
characterized by slight regularity in the matter of formation of the
lamellae.

Since the formation of new lens fibers progresses about the whole cir-
cumference of the lens equator and a new fiber is started at about the same
time in each radial lamella, the lens substance acquires a stratification
conditioned by the difference in the age of the fibers. By maceration, e.g.,



THE LENS 171

cooking, these layers or lamellar-complexes can be separated from one
another: the lens can be split up into leaves parallel to its surface.

Within such a layer the fibers are arranged as follows : The fibers are
strictly meridional only in the neighborhood of the equator and only here
do they form a uniform layer. As soon as one comes upon the surfaces
of the lens in following out the fibers, one perceives a division into sectors,
and the lines of separation (sutures) of these sectors form a stellate
figure on each lens surface with the center at the pole (the so-called lens
star; PL II, i).

The lens star is indicated in a normal lens, even during life, on lateral
illumination, and often comes out much more plainly in incipient cata-
racts. In the anatomic preparation, too, the cadaverous appearances,
or the effect of fixation fluids, often brings out the lens stars; at other
times one can make them visible by a precipitation of silver along the
cement lines.

The lens star is not a regular figure. In the adult one can usually
count 9 to 12 rays, the intervals between which are unequal; moreover,
the points of union between neighboring rays and the pole do not
coincide exactly, so that at the pole itself a figure with fewer arms arises,
but I have never found the star figure as irregular as Fridenberg (62)
draws it.

In each sector the lens fibers first course parallel to the middle line,
then bow away from the radii of the star, and therefore meet at the star
ray in very blunt angles.

The two stars of the lens (the anterior and the posterior) are, as a rule,
so oriented that the rays of the one fall in the interspaces of the other, for
which reason the fibers reaching to the pole on the one side cease at the
end of a star ray on the other.

In the succeeding layers the figure of the lens star is repeated, yet
with increasing depth it becomes more and more simple, until finally it
is reduced to a three-rayed star, the anterior one of which has the form
of an inverted, and the posterior that of an erect Y. One sees exactly
these same relations in the lens star when one recurs to an earlier stage
in life. For it is a peculiarity of the lens that it always grows by a super-
imposition of newer layers upon the old. For this reason one finds all the
peculiarities which the lens shows in early childhood or in embryonal
life at corresponding depths of the adult lens.

The elements of which the lamellae, as well as the layers, are made
up are the lens fibers. These are flatly compressed, prismatic, almost
band-like cells of considerable length. If there were a complete regularity
in arrangement each fiber would be somewhat longer than one-fourth of



172 ANATOMY AND HISTOLOGY OF THE HUMAN EYEBALL

a lens meridian; as a result of the alteration of the lens-star, according
to Becker, the length actually varies between 7 and 10 mm.

The breadth of the lens fiber, i.e., the dimension at right angles to the
length and parallel to the surface, amounts to 8 to 12, an average of 10 mu
in the region of the equator. Near the end of the star ray the fiber
gradually broadens out to double this size, and at the same time takes
on a bowing. Only those fibers reaching to the pole or to the division-
places of the star rays, or their ends, escape this bowing and the broadening
of the ends.

The thickness of the fiber, i.e., the dimensions at right angles to the
surface, scarcely amounts to 2 mu; only at the point where the nucleus
lies does it reach 5 mu.

The cross-section of a lens fiber has the form of an elongated six-
sided figure with two long and four short sides; the long sides are parallel
to the surface, and the fibers lie upon one another with these sides apposed
(PI. IX, 4). But all these measurements and the form on cross-section
only hold true for the young fibers, those arranged regularly in lamellae.
The relations of breadth and thickness and the form on cross-sections
changes in the depth of the lens substance where the arrangement
becomes irregular (PL IX, 5).

The young fibers, those lying near the surface, have smooth borders,
a well-staining oval nucleus of about 1 2 mu in length, 7 mu in breadth and
4 . 6 mu in thickness, and a transparent body in which one can differentiate
a firmer covering and tenacious fluid content.

With increasing age, i.e., at a depth of 0.15 mm, the cell-nucleus
disappears. It first takes on an almost spherical form, then shrinks to a
small, very intensely-staining fragment lying in a cavity of the size of
the original nucleus. Finally, these last traces also disappear. In such
an old lens fiber a fine serration appears along the edge, the content of the
fiber thickens, and the fiber becomes homogeneous.

The union between the lens fibers is effected by a cement substance,
more developed on the narrow sides of the fibers than it is on the broad
sides; as usual, this can be brought out by silver nitrate. This same
substance also appears in the neighborhood of the lens fibers, i.e., in the
rays of the lens star, yet a more marked aggregation of homogeneous or
drop-like coagulated substance signifies a cadaverous appearance or an
artefact in these and in other places.

According to the above statements, the picture of the lens substance has a form
differing a great deal according to the method of preparation.

The surface view of the lens substance can only be obtained by a splitting up of
several layers. It shows the lens fibers as broad bands, the bowing toward the star rays,
the broadening into these, etc.



CHAMBERS OF EYEBALL AND TOPOGRAPHY OF THIS REGION 173

A section through the lens in the plane of the equator cuts all the lens fibers cross-
wise. This is the direction of section which best explains the texture of the lens sub-
stance. In PL IX, 4, 5 I have depicted a part of such an equatorial section through
the lens of a two- weeks-old child; at this age the structure of the lens is still regular and,
moreover, the central parts show the fibers well.

In the superficial layers (PL IX, 4) one sees the regularly developed Rabl lamellae;
they appear as bands directed at right angles to the surface with borders formed by
fine zig-zag lines. The cross-sections of the fiber out of which the bands are put
together, are exactly superimposed, but they are not all of the same breadth, and often
not of the same thickness. The fibers in one lamella are displaced half of the thick-
ness of the fiber in the neighboring lamella, whereby the six-sided form of the cross-
section arises. But even in the youngest portions of the lens, irregularities are seen
here and there (lower part of the figure). Indeed, the farther one goes from the capsule,
the greater become the irregularities, and at a depth of i .3 mm (from the equator)
(PL IX, 5) scarcely any indication of the lamellae remains; the form of the cross-
section of the lens fiber is, therefore, very irregular.

The meridional section (PL IX, 3) shows the longitudinal section picture of the
lens, fibers, i.e., narrow, smooth-bordered fibers, which are only a little thicker at the
nucleus. It shows, furthermore, the lamella tion (stratification) of the lens structure;
each layer is thicker in the region of the equator than at the poles; as a result, the radius
of curvature of the layers decreases with the depth to a marked extent and corresponds
to the depth. The border of the lens stains less intensely, and the fiber contours arej
therefore, plainer, the nucleus characterized by a greater affinity for coloring substances,
and an indistinct fibrillation. On meridional section, too, one can at times see the
cross-section picture of the lens substance, and, indeed, in the neighborhood of the pole;
as soon as the section is other than exactly meridional, it may cut across the tapering
end of a sector of lens fibers.

Under the influence of hardening fluids, artefacts very easily arise in the lens sub-
stance, i.e., spaces filled with a homogeneous fluid, or spheres of coagulated fluid, or a
layer of fluid develops between the capsule and the lens substance.



CHAPTER XIV. THE CHAMBERS OF THE EYEBALL AND
THE TOPOGRAPHY OF THIS REGION

a) The Posterior Chamber

The posterior chamber is bounded on the one side by the tunica interna,
and, indeed, by the ciliary epithelium and the pigment epithelium of the
iris, on the other side by the anterior border layer of the vitreous up to
the ligamentum hyaloideo-capsulare and from there on by the surface of the
lens. Since the pupil-border of the iris lies upon the lens, the posterior
chamber has a limitation which is neither absolute nor fixed on this side.
It is not the former, because the pupil-border of the iris is not grown to
the lens. Yet it appears from the observations of Ulbrich (229) that no
continuous stream of fluid flows from the posterior into the anterior
chamber the difference in pressure is only equalized from time to time,



i 7 4 ANATOMY AND HISTOLOGY OF THE HUMAN EYEBALL

usually after a change in the width of the pupils. The position of this
border also changes as a result of the pupil play.

In this wider sense, the posterior chamber is a space of very compli-
cated form, and for the purposes of description, it is, therefore, advisable
to subdivide it into smaller portions.

The most posterior (peripheric) portion of the posterior chamber is
that narrow cleft-form space which lies between the inner surface of the
orbiculus ciliaris and the corresponding portion of the anterior border
layer of the vitreous. I (184) have called this space the orbicular space,
taking this name from Gamier (72), although it is not used by this author
in exactly the same sense (PL I).

Behind, the orbicular space has no sharp border; its most posterior
portion is extensively bridged over by the vitreous fibrillae and very
gradually passes over into the body of the vitreous through the zonular
cleft (see p. 153). The depth of the orbicular space is very slight at the
posterior end, not greater than the thickness of the layer of zonula fibers,
i.e., some o.oi mm. Here the space is in reality wholly filled out by the
zonula fibers. In the anterior part, however, the border layer of the
vitreous is pressed away by the various projections of the ciliary body,
the largest zonula fibers are displaced to the inner smooth wall of the space,
and outwardly there remains a relatively free space, traversed only by the
fine, straight, and backward-coursing fibers. The space is only present
where depressions have arisen between adjacent projections of the ciliary
body. In such places the depth of the orbicular space may amount to
o . i mm.

In front, the orbicular space goes over into the second portion, the
system of ciliary valleys (PL VII, 2). Since the anterior border layer
of the vitreous is closely apposed to the posterior halves of the ciliary pro-
cesses, the corresponding portions of the ciliary bodies are closed off into
short canals which only communicate with one another in so far as the
vitreous is not grown to the ciliary processes; it only lies close to them.

In the meridional direction these canals measure some o . 8 to i . o mm,
in the equatorial direction some o . 3 at the posterior end, in front o . 2 mm,
while their depth (in a radial direction) increases from behind forward up
to something like o . 5 mm. In the middle of the corona ciliaris the sur-
face of the vitreous bows away toward the lens, and the anterior halves of
the ciliary valleys are thereby transformed into furrows, which in their
course open up into the succeeding division of the posterior chamber.
The arrangement of the zonula fibers in the ciliary valleys has been
described on pp. 157-158. Aside from these, there still remains abundant
space for the aqueous.



CHAMBERS OF EYEBALL AND TOPOGRAPHY OF THIS REGION 175

The third division of the posterior chamber is the circumlental space.
By this usually one understands only the space between the crests of the


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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 20 of 27)