Maximilian Salzmann.

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

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ciliary processes and the border of the lens, as a matter of fact, therefore,
only a linear dimension, which is, however, of great importance to physi-
ology; yet its constant presence in all ages 1 and in all states of contraction
of the ciliary muscle proves it only acts by the mediation of the zonula
and in any case possibly of the vitreous (Tscherning, 228).

Considered as an actual space, its borders are: outward, the crests
of the ciliary processes; inward, the equatorial portions of the lens;
behind, the border layer of the vitreous. In front it really has no border;
for the sake of nomenclature alone, one can think of the most anterior
zonula fibers as forming this border. Its form is angular. Frontally
it measures scarcely 0.5 mm; its expanse in the sagittal direction depends
upon the form of the lens border. It is somewhat narrower on the nasal
side than upon the temporal.

The fourth division is the prezonular space (Czermak, 34), or the
posterior chamber in the stricter sense. This space lies between the
posterior surface of the iris, on the one hand, the anterior surface of
the lens, the most anterior zonula fibers and the anterior declivities of the
ciliary processes, on the other hand. It opens into the circumlental space
behind through' the spaces between the zonula fibers, at the periphery
into the ciliary valleys, axialward through the pupil into the anterior
chamber.

The prezonular space has its greatest depth over the crests of the ciliary
processes (0.4 to 0.6 mm), from thereon very gradually narrows toward
the pupil and disappears a short distance before the pupil-border of the
iris is reached. Toward the periphery it narrows rapidly and at the same
time forms there a narrow angle. Since, however, the ciliary processes
reach a little over onto the posterior surface of the iris, the periphery of
the prezonular space has a wavy or cogged form.

The prezonular space is the only division of the posterior chamber
which has no zonula fibers and contains only aqueous.

The older anatomists conceived of the zonula as a folded membrane running from
the ciliary processes to the lens. Their posterior chamber, therefore did not reach
farther than the zonula and corresponded to our prezonular space. The space between
the zonula and the vitreous was called Petit's canal. The Petit's canal about coincides
with the circumlental space, yet it appears that after certain methods of preparation,
e.g., after insufflation of air, sections of the posterior chamber lying still farther back-
ward become drawn into connection with it.

One can inflate the so-called Petit's canal with air because of the surface tension
of the surrounding fluid; air is imprisoned, just as one can occasionally observe to his

1 Exceptionally it disappears in senility (chap. xix).



176 ANATOMY AND HISTOLOGY OF THE HUMAN EYEBALL

discomfort in celloidin imbedding, between or beneath the zonula fibers in such a
way that one cannot bring it out by mechanical means. Yet as soon as one attempts
to inject the postulated canal with a colored aqueous solution, this at once goes over
into the prezonular space.

b) The Anterior Chamber

Of much simpler form than the posterior chamber, the anterior
chamber is bordered in front by the cornea, by the trabeculum of the
iris angle at the periphery, and behind by the anterior surface of the iris
and that portion of the anterior surface of the lens which at the time is
exposed in the pupil.

The frontal diameter of the anterior chamber amounts to 11.3 to
12.4 mm, and is, therefore, about equal to the horizontal diameter or
the anterior surface of the cornea; the vertical diameter is as great as
the horizontal. The greatest depth of the anterior chamber is found
in the middle and corresponds to the pupil (some 2 .8 mm).

That which one designates as the chamber depth in the dioptric system of the eye
is not, however, this value, but the distance of the anterior surface of the cornea from
the anterior surface of the lens, because one can ignore the refraction of the posterior
surface of the cornea for optical purposes. The optical chamber depth amounts to
about 3 .6 mm.

The individual variations of the chamber depth are considerable. Tscherning (228)
added together 64 measurements of various authors (the most of them from
Maklakoff) ; the chamber depths, measured ophthalmometrically, vary between 2 . 2
and 5 . i mm; most frequently these values lie between 3 .4 and 4 . i mm.

Toward the periphery the depth of the anterior chamber gradually
decreases; yet its minimum does not always lie at the border, but fre-
quently somewhat farther axialward, somewhere between the border zone
of the iris and the border of Descemet's membrane. Only in cases in which
the iris thins out very gradually toward the ciliary border, is the periphery
of the anterior chamber formed by an angle somewhat rounded off at
its apex. When, however, as is usually the case, the thickness of the iris
is not essentially changed in the region of the ciliary zone, the anterior
surface of the iris descends abruptly toward the ciliary body, and then the
outermost zone of the anterior chamber or the portion adjacent to the
trabeculum (the iris angle, or the chamber bay) is wider than its entrance
from the anterior chamber proper. The shallower the anterior chamber,
in and of itself, the more noticeable is this difference, the more plainly does
the chamber bay appear bowed backward.

Czermak (36) called attention to the significance of this configuration for the
pathology of the eye and in this way established, as it appears to me, the only plausible
explanation of the origin of peripheral synechia.



CHAMBERS OF EYEBALL AND TOPOGRAPHY OF THIS REGION 177

The trabeculum of the iris angle does not form a continuous wall;
the numerous spaces in it stand in free communication with the iris angle
itself, so that the aqueous can bathe the wall of the Schlemm's canal.
This system of spaces is often called Fontana's spaces, because it was held
to be an analogue of the canalis fontanae.

The reasons which speak against the use of this name have been brought out in
extenso by Rochon-Duvigneaud (182), and especially by H. Virchow (234). Fontana's
canal is bound up in the existence of a genuine "ligamentum pectinatum," i.e., in the
presence of arrow-like iris processes. These, however, do not occur at all in man;
when iris processes are present, they course in the plane with the anterior surface of
the iris to the trabeculum. But even these are not present in all eyes, and when they
do occur, are so sparse that they cannot be made use of as a limitation of a space.
According to Rochon-Duvigneaud the whole iris angle is much more analogous to
Fontana's canal.

The anterior chamber possesses an endothelial lining which is con-
tinuous over the cornea and through the trabeculum, incomplete, however,
over the iris (spaces at the crypts), and in the territory of the pupil
it is entirely absent.

e) Content of the Chambers

Both chambers contain aqueous, i.e., a completely clear, colorless,
odorless, watery fluid of alkaline reaction. According to Leber (138),
the specific gravity in man is 1.0034 to 1.0036, the content in solid
substance is 0.82 per cent, including albuminous bodies, yet this is so
slight a mass that the aqueous gives no notable coagulum on hardening.
In the microscopical preparation, therefore, the chamber appears to be
filled out only by the imbedding mass ("empty"). Any other content
is, therefore, patho ogic.

The index of refraction of the aqueous is i .33366 to i .33485, accord-
ing to Freytag (61), and is, therefore, so very little different from the
index of the vitreous that for the purpose of the diopteric system one is
accustomed to think of a uniform medium in front of and behind the lens.

d} Topography of the Anterior Segment

The watery content of the chambers and the physical processes to which this is
subjected in the dead eye, as well as the relative slight fixation of many of the parts
which border the chambers, brings it about that the norma'l relations in position are
easily disturbed. Therefore we should not look upon the relations found in the com-
pleted sections-preparation as corresponding necessarily to those present in life.

The depth of the anterior chamber is most easily extensively changed. Moreover,
fluid still niters into Schlemm's canal after death, the eye becomes soft, and the anterior
chamber shallow. The diffusion process between the almost pure water of the chamber
and the relatively concentrated fixation fluid can also lessen the volume of the anterior



1 78 ANATOMY AND HISTOLOGY OF THE HUMAN EYEBALL

chamber in the eye, enucleated during life, wholly aside from shrinkage processes in the
tissues of the eye, so it comes about that we have before us ordinarily an abnormally
shallow anterior chamber in the completed preparation.

The decrease of chamber depth expresses itself in a throwing forward of the lens,
and this, again, as long as the lens is plastic enough, is combined with a greater vaulting
of its anterior surface. The iris thereby approaches the cornea and its conical form is
increased.

Still more striking is the influence of the dislocation of the lens upon the form of the
circumlental space. The border of the lens is shifted forward almost as much as the
anterior lens pole; the ciliary body, on the other hand, remains pretty much in place.
The narrower the circumlental space is, the more must it be distorted, the more must the
direction of the zonula fibers which pass through it be changed.

A second process which disturbs the topography is the shrinking of the tissue.
The changes which the whole process of fixation and hardening bring about in the lens
have already been emphasized (p. 163). The shortening of the equatorial diameter of
the lens widens the circumlental space and, indeed, to about double its natural size.
The zonula fibers become tensely spanned, and this pull must, on its part, be again
expressed at the ciliary body. Microscopic distortions at the insertion point of the zonula
fibers are the result of hardening, but in no case the result of strained accommodation.

In connection with the shrinkage of the vitreous this pull also leads to the detach-
ment of the ciliary body from the sclera, Since, however, the ciliary body is firmly
fastened in front so that the detachment effects a rotation of the whole ciliary body
about its punctum fixum, the anterior surface must approach more the frontal, the
inner surface more the sagittal direction. The chorioidea naturally follows this detach-
ment, at least the anterior portions and the whole perichorioidal space appears unnatu-
rally wide.

But even when one succeeds in preventing all this, the shrinking of the imbedding
mass can still change the topographic relations. The only way to get around these
artefacts is to make use of fresh material, which one freezes before cutting. But only
the grosser anatomic relations can be studied and measured in this way; finer details
must be added afterward to the survey picture obtained. Some dimensions can be
established during life, e.g., the ophthalmometer is a very desirable and useful means
of testing the correctness of topographic relations and especially for adjudicating them.

How great the difference in the position of the parts can be is seen best by a com-
parison of Text Fig. i (p. 3) and PL I; Text Fig. i shows the normal topographic
relations from the above-presented points of view, corrected as necessary; PI. I, on the
other hand, shows the relations of a cadaver-eye, which, in general, has been very well
conserved.

Topographic relations can be much more easily reproduced by draw-
ing than by description. It is, therefore, only necessary really to refer
to Text Fig. i; still I" would emphasize here certain particularities, partly
because of their clinical, partly because of their physiologic importance.

Since the frontal diameter of the anterior chamber is about equal to
that of the horizontal diameter of the cornea, the root of the iris lies pretty
nearly behind the outer border of the cornea in the horizontal meridian,
and the removal of it from this (in the sagittal direction) is i . 6 to i . 8 mm



CHAMBERS OF EYEBALL AND TOPOGRAPHY OF THIS REGION 179

Above and below, however, the iris root lies considerably farther equatorial.
When, therefore, one plunges a knife into the cornea i mm from its border,
and presses the blade forward parallel to the base of the cornea, the inner
wound falls far inside (axial to) the border of Descemet's membrane.

The height of the cornea is 2 . 6 mm. The plane of the iris root,
therefore, lies at least 4 . 2 mm behind the vertex of the cornea. Since the
distance of the lens from the vertex of the cornea is 3 . 6 mm, the anterior
lens pole thus projects at least o . 6 mm in front of the plane of the iris root.
The iris, therefore, forms a flat cone, especially in a narrow pupil.

It is a necessary result of this conical form of the iris that the sphincter
is pressed against the lens with a certain component. This component
is, however, only a small fraction of the whole force of the sphincter, for
it is proportional to the sinus of that angle which the meridian of the
iris forms with the frontal plane. The steeper the iris is inclined (the
narrower the anterior chamber) the greater is this component.

Now, according to the observation of Ulbrich (229), it appears that
this component is great enough to prevent for a time the passage of
fluid out of the posterior into the anterior chamber. Only in this very
limited sense can one speak of a physiologic seclusion of the pupil, never,
however, in the strict sense in which Hamburger (86) uses this phrase.

The lateral portions of the anterior lens surface (lying behind the iris),
the most anterior zonula fibers and the inner surface of the ciliary body
(considered as a whole with the- exception of the processes) lie almost
exactly in one plane, and together form likewise almost a single conical
mantle. This conical mantle under certain circumstances, especially in a
shallow anterior chamber, may take on a certain concavity from the sims
of the ciliary body. Attention was first directed to this concavity by
Schoen (192), as an important support for his theory of accommodation,
yet he has probably emphasized it unduly, and the preparations depicted by
him as conclusive are not free from disturbances of topographic relations.

The apices of the ciliary processes, i.e., the points farthest axialward,
lie distinctly in front of the lens equator and the. wall about the petellar
fossa of the vitreous lies on the posterior halves of the corona ciliaris.

It is only because of the magnification produced by the cornea that
one cannot see the iris throughout its entire extent during life. For the
same reason in a given case, e.g., in iridodialysis, one can see only the
apices of the ciliary processes, and when viewed from in front the border
of the lens almost coincides with the border of the cornea, although the
frontal diameter of the lens is 2 to 3 mm smaller than the horizontal diame-
ter of the cornea. The magnification occasioned by the cornea increases,
indeed, with the depth; thus the iris appears magnified one-ninth, the



i8o ANATOMY AND HISTOLOGY OF THE HUMAN EYEBALL

lens on the other hand, one-fifth, if one conceives of the plane of the lens
equator as 5 mm removed from the vertex of the cornea. A structure
lying in the focal point of the cornea, e.g., a posterior polar cataract,
must appear magnified one-third.

The refraction of the cornea furthermore emphasizes the iris, therefore
makes the anterior chamber appear shallower than it actually is. This
principle holds true for everything which lies between the anterior sur-
face of the cornea and the focal point of it (more accurately the nodal
point of the whole eye).

Of course, the figures "given apply only to an average (schematic eye).

CHAPTER XV. THE VESSELS AND NERVES OF THE EYEBALL

So far as these are constituent parts of the tissue, they have already
been mentioned in connection with it. Only a few details concerning the
supply of the eyeball with blood-vessels and nerves are added here and
the relations of the individual circulatory and innervation districts dis-
cussed.

a) Blood-Vessels of the Eyeball

All of the arteries of the eyeball are branches of the arteria ophthalmica
in the last instance. These course in part directly to the posterior parts
of the eyeball and optic nerve, in part to the anterior segment by means of
a roundabout way along the eye muscles. The veins empty their blood
into the orbital veins, and by means of this partly direct into the sinus
cavernosus, although anastomoses of the orbital veins with those of the
face also occur.

But in the eyeball itself, there can be differentiated two vessel dis-
tricts, according to Leber (138), whose classical presentation I follow in
the main the retinal or inner, and the ciliary or outer vessel system.

I. THE RETINAL SYSTEM

In the adult eye this is represented by the arteria and vena centralis
retinae. Its territory is, especially, the retina, a minor portion of the
optic nerve and its sheaths.

The arteria centralis retinae enters the optic nerve 7 to 12 mm behind
and below the bulb. It first supplies the neighboring portions of the
sheaths, then its immediate neighborhood in the optic nerve, in the axis
of which it courses farther on to the bulb. Its part in the supply of the
optic nerve is, therefore, a minor one; only at the lamina cribrosa does it
give off a larger number of fine branches. Here and in the intrachorioidal



THE VESSELS AND NERVES OF THE EYEBALL 181

section of the optic nerve the last capillary anastomoses between the
retinal and the ciliary vessel systems are found, but from the inner end
of the optic nerve canal on, the retinal is completely separated from the
ciliary system, as a rule. This portion of the arteria centralis retinae
is an end artery in the sense of Cohnheim, and, furthermore, all of the
blood carried by the arteria centralis retinae is carried away by the vena
centralis retinae.

The arteria centralis retinae divides into an upper and lower main
branch (arteriae papillaris superior et inferiores) on the inner surface of the
papilla and these, again, into a nasal and temporal branch (arteriae
nasales super, et inf., arteriae temporales super, et inf.} (PI. VII, i). Yet
even in respect to the branches of the second order there rules a signifi-
cantly lessened regularity. Under further gable-like divisions the arteries
broaden out into the retina mostly in a radial direction; the temporal
branches alone course in wide bows above and below the fovea and,
converging, send fine branches to the fovea. Finally, as a rule, a few
fine branches go directly over the temporal border of the papilla to the
fovea.

Concerning the capillary system the reader is referred to p. 82. The
last extensions in the neighborhood of the ora serrata bow about in loops
into the veins. These communications are, indeed, somewhat larger
than the capillaries, but they only go back into the same vessel system,
and cannot, therefore, functionate^as collateral paths.

The distribution of the veins fully corresponds for the most part to
that of the arteries; the vena centralis retinae accompanies the artery of
the same name and, along with it, is united to the central connective-
tissue strand (pp. 91, 106) by an extension of the pial sheath; it usually
empties directly into the sinus cavernosus.

2. THE CILIARY SYSTEM

This supplies the rest of the coats of the eyeball, the neighboring por-
tions of the optic nerve and its sheaths, as well as the conjunctiva. The
arterial radical of this system divides into the posterior and anterior
ciliary arteries; the venous radical is made up of the vortex veins and the
anterior ciliary veins. Arteries and veins do not correspond to each
other in this system, either their course or yet in circulatory areas, so that
the arteries come out more strongly in one place, the veins in another
place, especially in the uveal tract.

The number of the posterior ciliary arteries (art. ciliares posteriores}
amounts to about twenty. They surround the optic nerve and enter the
eyeball in its neighborhood and in the region of its posterior pole. At



1 82 ANATOMY AND HISTOLOGY OF THE HUMAN EYEBALL

first they are distributed to the episcleral vessel net (as far as the in-
sertions of the recti muscles), then they pass into the sclera (emissaria;
cf. p. 1 8).

Most of them pass directly out of the sclera into the chorioidea, and
become known as the short posterior ciliary arteries (art. cil. post, breves').
The course of these vessels shows great variation; some press into the
dural sheath directly at the root and turn toward the optic nerve, others
enter at a greater distance; sometimes, too, a short posterior ciliary artery
branches off from a long one or, united with it, enters an emissarium.

The short posterior ciliary arteries supply the back half of the uveal
tract and the optic nerve ; those entering in the neighborhood of the dural
sheath form a circle of anastomoses about the optic nerve by means of a
few branches the circulus arteriosus nervi optici (p. 25). The neighbor-
ing portions of the pial sheath, especially the very rich vessel net of the
lamina cribrosa, are supplied by this.

Elschnig (52) has called attention to a special variation in the terri-
tory of the posterior ciliary arteries. A relatively large artery enters
the dural sheath behind the bulb some 3 mm from the end of the inter-
vaginal space and, splitting the dural sheath into two leaves, courses in
this to the sclera, then goes along the insertion of the dural sheath over
into a circular course, and extends about halfway around the circumfer-
ence of the optic nerve, dividing up into finer branches.

According to Elschnig, the circulus arteriosus nervi optici is absent in
such eyes; according to my observations (185), however, it is not
always, but the branches of the abnormal artery enter the circulus or go
directly into the chorioidea. At times, too, there is a larger recurrent
branch for the pial sheath and the medullary section of the optic nerve.
This variation occurs in about half the eyes; it very easily escapes
observation, however, because the vessel does not lie in the horizontal
meridian of the papilla.

As already noted, only a capillary connection exists between the retinal
and ciliary systems, and this does not reach beyond the level of the chorio-
capillaris. This rule, however, is subject to many exceptions.

Anastomoses of larger caliber, visible ophthalmoscopically, are rare
and occur most frequently between the veins. A very large, band-like,
flattened vein sometimes branches off from the central vein or 'one of its
main branches, courses across through the tissue of the papilla, and dis-
appears beneath the margin of the papilla (optico-ciliary vein, Elschnig,
49). Oeller (167) depicts an analogous artery.

The anatomic proof of such an anastomosis was first brought by Kuhnt
(131); however, the vessel observed by him could not have been visible



THE VESSELS AND NERVES OF THE EYEBALL 183

ophthalmoscopically on account of its position behind the lamina cribrosa.
Elschnig (51) then demonstrated a typical optico-ciliary vein in an eye
affected with a neuritic optic-nerve atrophy. It went off from the central
vein immediately in front of the lamina cribrosa and emptied into the
vessel system of the chorioidea. In choked disk and other similar con-
ditions such venous unions have been shown to exist heretofore, yet it
is questionable whether these were not pathologic distentions of originally
capillary unions.

Much more frequently it happens that a smaller or larger territory
of the retina is not supplied by the central artery but by branches of the
ciliary vessel system, or that it does not empty its blood into the central
vein. Such abnormal vessels are called cilio-retinal.

According to Elschnig (50), the cilio-retinal arteries are throughout
derivatives of the circulus arteriosus nervi optici, which either go directly
from this through the sclera and the border tissue in an oblique direction
into the non-medullated section of the optic nerve, or take the roundabout
course through the chorioidea and, therefore, appear as branches of the
chorioidal arteries. In both cases they attain the intrachorioidal section
of the optic nerve and bend about the border of the chorioidal foramen inio
the retina, where they are distributed like typical retinal vessels. This


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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 21 of 27)