Maximilian Salzmann.

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

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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 24 of 27)
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reference to the original work. Most striking and, as it appears, pretty
constant is the relatively slight distance from the cornea at which the
m. rectus medialis is inserted.

The sclera has its greatest thickness at the posterior pole, its least in
the neighborhood of the cornea (E. von Hippel, 102). The thickness
of the cornea varies a great deal and is subject to the influence of the
fixation fluid perhaps in an even higher grade than in the adult.
Von Hippel found a maximum of 1.12 mm in fresh eyes. Still greater
thicknesses (2 mm, according to Hirschberg, 104) are possibly due
to swelling.

Bowman's membrane shows the same thickness as in the adult (17
to 21 mu, according to von Hippel). The stroma of the cornea, like the
sclera, is much richer in nuclei than in the adult eye. Descemet's mem-
brane, on the other hand, is still very delicate (2 mu).

According to von Hippel, the perichorioidal space is entirely absent;
according to Merkel and Orr it is absent in the posterior portion ; accord-
ing to Lange (135), however, it is as much or as little present in the
posterior segment as in the adult.

Pigment is absent in the stroma of the uveal tract (but not the cells
which will later bear it); at the most, pigmented chromatophores are
found in the neighborhood of the optic nerve. The iris also is almost
always gray, therefore, and, indeed, on account of the delicacy of the pars
uvealis, a pretty dark gray. In any case, the pigmentation of the anterior
border layer sometimes develops in the first days of life.

The stroma of the uveal tract, furthermore, shows a preponderance
of cells over collagenous intervening substance (Gutmann, 83), and, there-
fore, a greater richness in nuclei. The adventitia of the vessels is very
weakly developed and, therefore, the marking of the iris is more delicate
and uniform. The pupil is pretty narrow and, moreover, does not per-
mit of maximal dilatation.

The iris angle (chamber bay) is sharp and narrow, the uveal frame-
work (ligamentum pectinatum) still has its fetal character for the greater
part, i.e., it fills out the iris angle to a great extent.

The ciliary processes still reach far over onto the posterior surface of
the iris, they are thin and relatively smooth, i.e., the lateral folds and
bulgings, as well as the little warts in the valleys, are only suggested.
The ciliary muscle is already well developed and even the various types
can be recognized (Merkel and Orr, Lange). The inner surface of the
orbiculus ciliaris looks entirely smooth on cross-section (Taf. IX, n).

The pigment epithelium of the chorioidea shows a uniform develop-


ment; the much enlarged cells at the or a serrata fail. On the other hand,
according to Kuhnt (127), some larger cells, about which the smaller
ones group themselves as centers, appear at pretty regular intervals.
The pigmentation of the stratum pigmenti is very marked in comparison to
the pigmentation of the uveal stroma, indeed, in many places it is actually
more dense than in the adult. Such a place is the corona ciliaris; the
summits of the ciliary processes are just as dark a brown as the valleys;
the delicate radiating figure from which the corona ciliaris gets its name,
is, therefore, not visible in the newborn. Likewise the dilatator pupillae
appears much thicker and more densely pigmented.

The retina is, in general, well developed, to be sure, yet it still bears
more of a fetal character in two places, namely, the region of the fovea
and at the border.

The fovea centralis is shallow and the wall about it barely suggested.
According to von Hippel (102), all the layers are still present on the floor
of the fovea a simple layer of ganglion cells and an inner nuclear layer,
somewhat thinned and spaced up, to be sure, but yet always a plainly
distinguishable layer. On the other hand, the external nuclear layer
consists only of one layer of nuclei and the cones are short, thick, and few
in number (Wolfrum, 241).

The distance between the fovea and the papilla is as great as in the

According to von Hippel, the border of the retina shows plainly
formed teeth, although they are not as long as in the adult eye.

The border of the retina shows an especially characteristic picture on
meridional section (Taf. IX, n), because it varies much from that of
the later state. In particular, the retina (R) goes over into the ciliary
epithelium more gradually. At the place where the inner plexiform layer
ceases, or even somewhat farther posterior, the two nuclear layers fuse
into one, and out of these fused nuclear layers there comes a tissue which
strikingly recalls the first stages of the development of the retina in the
embryo. This zone contains numerous uniform oval superimposed nuclei
and to the inside a very narrow "border film." It thins very gradually
into the ciliary epithelium (CE), which appears very much more uniform
and lower than in the adult eye.

The border portion of the retina and this transition zone elevate them-
selves very readily from the pigment epithelium and then form a fairly high
and sharp circular fold (F), which springs inward toward the vitreous and
somewhat forward; this has often been called Lange's fold because this
author (134) has made remark upon its regular occurrence. Yet it is to
be looked upon as an artificial product, as Lange himself concedes (135).


The border of the retina always lies still farther forward, about at the
posterior end of the ciliary muscle; the orbiculus ciliaris is, therefore,
strikingly short (1.4 mm).

The pigment epithelium of the iris shows a relatively slight pigmenta-
tion, especially toward the ciliary border; its cells are small and the
circular furrow system is absent. The sphincter pupillae is as broad as
in the adult, but thinner.

The intraocular end of the optic nerve often shows a plain excavation
not simply a vessel funnel but an excavation with a lateral (elbow-
formed) transposition of the nerve-fiber bundles. Remnants of the glial
mantle of the arteria hyaloidea are at times still present. The diameter of
the chorioidal foramen (the ophthalmoscopic papilla) measures about imm.
The optic-nerve fibers behind the lamina cribrosa are still unmedullated.

The vitreous is of a more uniform consistence; the border layers are
only weakly developed.

The zonula consists of numerous fine fibers; moreover, zonula fibers
are given off even from the posterior chamber angle, indeed, even from
the posterior surface of the iris, as far as the ciliary processes reach. Yet
there fail any of the divisions characteristic of later periods of life; the
fibers are uniformly distributed and of uniform size.

The statements concerning the form and the diameter of the lens read
very differently. In the text and drawing (Text Fig. 5) I hold myself to
the photograph of von Pflugk (172), since the method of this author offers
the assurance that the relations of fresh cadaver-eyes are best conserved.

According to von Pflugk, the form of the lens in the newborn is not
so fundamentally different from that of the adult as given by the older
statements. The equatorial diameter amounts to 6.6 to 7 mm, the
thickness to 3.4 to 4 mm. The radius of curvature of the anterior
surface is 5 mm, that of the posterior 4 mm. The anterior surface
flattens somewhat toward the equator, the posterior surface shows a
slight concavity in the neighborhood of the equator; the equator itself
is pretty sharp. The border of the lens is smooth and without crenations.

The lens capsule is delicate; only the thickening at the periphery
of the posterior capsule, which even Becker (18) observed, is strongly
marked (cf. the table on p. 165) and is especially striking on account of
the delicacy of the remaining portion of the lens capsule. The nuclear
bow of the lens is still long and rounded, the nuclei reach to a depth of
at least o . 4 mm. The central portions of the lens, already characterized
by a somewhat greater density, are without nuclei.

On account of the strong vaulting of the lens the anterior chamber
is pretty shallow (2.3 to 2.7 mm, according to von Pflugk).



According to the curve drawn by Weiss (235), the eyeball grows most
rapidly in the first years of life, then more slowly. From the fourteenth
year of life on there is again a somewhat greater growth up into the twenties.
The growth of the eye keeps pace with the growth of the brain; in its
whole period of growth the eye grows 3.25 times, the brain 3 . 76 times
the body, on the other hand, 21 .36 times.

The rapid growth at the beginning mainly concerns the formation
of the anterior segment. Von Reuss (181) has shown that the average
diameter of the cornea in children between the first and sixth years is
not much less than the average in the adult. This would therefore indicate
that the cornea has attained almost its complete size in the course of the
first year of life. According to the table published by Grod (77), it
attains this in the second year of life.

While the cornea thereby grows 1.25 times, the neighboring scleral
zone, i.e., the zone between the lines of the insertion of the recti muscles
and the border of the cornea, broadens, in general, i .358 to i .374 times
(on the average), according to Weiss, and the completed size of this
segment is at times attained even in early childhood.

Only the nasal portion of this zone, i.e., the interval between the
insertion of m. rect. medialis and the border of the cornea shows a much
greater growth, for this distance is on the average i .629 times greater in
the adult. It appears that this greater growth sets in first in later child-
hood, yet the number of the cases is still much too small to cover the
great individual differences, despite the comprehensive investigations of
Weiss concerning this circumstance.

It has already been emphasized that the distance between the fovea
centralis and the papilla is as great in the newborn (and even in the last
months of fetal life) as in the adult. This portion of the wall of the bulb,
at least that which concerns the retina and the pigment epithelium and
probably the chorioidea also, does not grow any more, therefore.

The last increase of growth from the fourteenth year of life on appears
mainly concerned with the enlargement of the posterior segment.

As we now turn to the finer anatomic and histologic developmental
processes and attempt to arrange these chronologically, the development
of the medullary sheaths in the optic nerve must be considered first. At
the very latest this is completed in three weeks (Bernheimer, 22). On
this account alone this process must receive special attention, because


it shows how the conditions of life as changed by birth affect develop-
ment: it is the light which favors the development of the medullary
sheaths. Prematurely born babes who have lived some time extra-
uterine show farther advanced sheath development than fetuses of the
same age which have remained in utero, for example.

The development of the fovea centralis requires a somewhat longer
time. After four weeks a plain, steep-sided depression has formed (von
Hippel, 102), and the cerebral layer is so far reduced in the center that one
can no longer recognize a stratification. But the outer nuclear layer is
always still poor in nuclei and the cones are short. The fovea first
attains its full development months after birth (Wolfrum, 241).

The perichorioidal space must open up very soon after birth. At
least Elschnig (54) has shown that a strong contraction of the ciliary
muscle occurs even in the newborn, although it is still without plan, and
this is probably not conceivable without an opening of at least the anterior
part of the perichorioidal space.

As already stated, the cornea concludes the greater part of its growth
in the course of the second year of life. The diameter of the cornea
does not essentially change; later the radius of curvature alone is
somewhat increased. According to von Reuss (181), in a 5- to 6-year-
old child this is 7.36 mm on the average, increases by the twelfth year
to 7.45 mm, and at the time of puberty nearly attains the average size
for the adult.

With the increase in size of the cornea, the fibrillar intermediary
substance develops more and more, so that the nuclear richness decreases.
No further changes appear in Bowman's membrane. Descemet's mem-
brane soon attains the thickness of 5 mu, and maintains this throughout
the whole of childhood. Its periphery is still smooth at first. I have
seen the earliest suggestion of warts in the ninth year of life.

The iris, too, undergoes further development during this period. The
difference between the ciliary and the pupillary zone, which is pretty
indistinct in the newborn, comes plainly in the course of the first
half-year of the extrauterine life. The definitive iris color, however, needs
a longer time for its complete development. In 2-year-old children one
sees even a well-developed adventitia in the vessels of the iris, large crypts,
and a very loose make-up in the interior. The connective tissue behind
the sphincter thickens in the fourth year of life. The system of circular
furrows in the pigment epithelium I have first seen completely developed
in a 7-year-old, however.

Yet I would not attach too much weight to this and many other state-
ments relating to age. They are not the result of thorough studies, but


of occasional observations, and it is conceivable that a great variability
rules in this respect.

The development of the definitive form of the ciliary body also falls in
this period. This depends upon the further carrying out of processes
which have already begun in the latter period of fetal life: the border of
the retina moves farther backward, or, more correctly stated, the meso-
dermal layers of the walls of the eye grow farther over the border of the
retina. The material for the covering of the ever-broadening orbiculus
appears to be that in the transition zone between the retina and the
ciliary epithelium resembling the embryonal retina that which is so
characteristic of the eye of the newborn. In a 2-year-old child, for
example, the demarkation of the retina from the ciliary epithelium is
sharp, still the border is somewhat rounded; the tendency to the forma-
tion of the fold of Lange is still present. In the 7-year-old child, I find
the same relations on the nasal side as in the adult, i.e., a marked pro-
jection of the retina over the ciliary epithelium.

The complete widening out of the angle of the iris appears to coincide
with the backward displacement of the ciliary processes and occurs in
the period between the second and fourth years of life.

In general, the ciliary processes maintain the appearance and the
dark pigmentation which we have found in the newborn until an age
of later childhood.

According to Kerschbaumer (117), the reticulum of H. Mueller is
demonstrable in a child of i|- years; still it is then very delicate in any
case. In sections it is scarcely apparent at this age. It (as well as the
interlamellar connective tissue) first appears in later childhood, or at the
time of puberty, when it attains its complete development.

Unlike these processes which mostly come to an end in the first
part of childhood, the lens grows throughout the whole of life; of course,
the greatest changes in it are found in the first year of life. According to
Dub (47), the equatorial diameter is 7 . 46 mm at the age of 10 to 1 1 months
and the thickness of the lens 2 . 46 mm. The lens, therefore, has increased
in the equatorial direction by this period, and has also become thinner.
The explanation of this lies in the enlargement of the anterior segment,
in particular of the ciliary ring, whereby the still soft and plastic lens is
displaced in the frontal direction through greater tension.

Both diameters increase in further growth, the equatorial to a greater
extent than the sagittal; in a 3- to 3 ^-year-old child the lens mass is
8 . 46X 2 . 83 mm, according to Dub. This further change of the lens-form
apparently has its ground in the fact that the new-built fiber layers are
thicker in the equatorial zone than at the poles, for this fact can be easily


established anatomically. For example, in a child of (probably) 1 2 years
I measured the thickness of the less-stained cortex layers at the equator as
0.34 mm, at the anterior pole, however, as 0.14 mm. This difference
gradually decreases with increasing age, and the thickness of the new-
formed layers becomes more uniform.

An estimate of the growth of the lens is rendered difficult by the fact that the
various figures have not been obtained by the same methods. The figures of von
Pflugk (172), which were made on the basis of an eye of a newborn, were obtained in
cross-section, after freezing, the figures for the adult, by ophthalmometric means;
Dub (47), on the other hand, has measured isolated lenses and estimated their thick-
ness on a hard base. At the same time the material studied is much too small to rule
out disturbance by individual differences.

Now we know, however, that the severing of the zonula markedly changes the
forms of the lens, and this change is still greater in young lenses than in old; indeed,
in general, very slight forces are adequate to effect a notable change in the form of the
lens (Heine, 89). According to this, the measurements contributed are not comparable,

This much is certain, that, aside from the appositional growth, i.e., aside from the
formation of new lens layers on the surface, still other factors affect the form of the
lens. Such a factor is the enlargement of the ciliary ring; a second in all probability
is the still-to-be-discussed sclerosis of the lens.

The inner part of the lens possesses a greater density, even in child-
hood; this is apparent from the way in which the lens substance absorbs
after discission. This thickening (sclerosis) of the lens substance is, there-
fore, a process which has possibly set in in fetal life and has attained such
a height somewhere in the thirties that spontaneous absorption is impos-
sible and, therefore, the extraction must replace the discission.

It is highly probable that this thickening depends upon a loss of water,
and that this goes on with a loss of volume. That such a shrinking
must in part compensate for the increase in volume as a result of the
appositional growth is easily understood. Yet we are without means of
stating anything accurately concerning the degree of this shrinking.

The older the person is, the more the appositional growth of the lens
decreases, i.e., the fewer the epithelial cells concerned in growth at any one
given time. The influence which this has upon the appearance of the lens
vortex has already been spoken of (p. 169). According to Becker (18), 25
cells form the nuclear bow of the lens in the newborn, only 8 in the
4-year-old child, and but 2 to 3 cells in the older person.

When the whole extrauterine development of the eyeball is surveyed, one sees
at once that a few processes which in the course of the fetal development have not
been completely brought to closure, e.g., the development of the fovea, are carried on

How much the use of the eye as a sense organ has an influence upon its develop-


ment still remains to be more accurately studied. The influence of light upon the
development of the medullary sheaths in the optic nerve appears to be conclusively
established. Furthermore, Grod (77) has established that the cornea lags behind
0.8 mm on the average in its growth when the lens is removed early (at the age of
i to 9 years). Thereby a process discovered by Wesseley (236) in the course of
animal experiments is also proven true for man, although in a lesser degree. Of course,
the question still remains open, whether the factor which causes the cornea to remain
smaller is a functional insult or another, possibly a mechanical one.

The growth of the eye without doubt makes greater demands upon the power
of resistance of the tunics of the bulb. .We see a tendency to the increase and thickening
of the fibrillar intervening substance of the connective tissue, at first of the collagenous,
and later also of the elastic fibers. According to Fuss (71), the latter attain their full
development at the age of 10 to 1 1 years and increase somewhat in number from there
on up to the thirties. The thickening of the cuticular membranes is probably to
be ascribed to the same cause.

Finally, it is to be remembered that the optical relations also change decidedly with
the growth of the eye. The hypermetropia of the newborn eye is not sufficient to
compensate for the later addition to the axial length; an enlargement of the main
focalizing limits of the optical system must occur, therefore, and this is affected for the
most part by the flattening of the lens.


There are changes in the eyeball which gradually develop during the
whole of life and which, therefore-, have attained a higher grade in old
people than in young. To these, among others, belong the sclerosis of the
lens and its physiologic equivalent, the decrease of the accommodation,
and the thickening of the glass membranes. Other changes occur first
in the adult eye, but during the period of complete strength and vigor,
and increase with age, like the cystoid degeneration of the retina. None
of these conditions can properly be characterized as senile; to a certain
extent they form an index of the individual, but they are not characteristic
for the age of senility.

Among other things, the arcus senilis of the cornea, the clouding of the
lens, the so-called verruca of the chorioidea, actually do set in in senility
or a few years earlier. Therefore, these are actual senile appearances.
Many of these can, however, also appear in younger individuals as
pathologic processes, and possibly they are often such in -senility. In
general, therefore, one sees how uncertain the matter is, and, in particular,
how wide the play for subjective conception.

According to Priestley-Smith (174), the diameter of the cornea
decreases in great age ; the average from 40 to 60 years is 1 1 . 48 mm,
for persons over 60 years, 11.46 mm, and is 0.24 mm smaller than the


average from 20 to 30 years. Priestley-Smith seems to think of a true
decrease of the cornea; it is also possible, however, that the limbus
becomes more clouded and so limits the transparent area.

According to Steiger, the cornea in general flattens in age. More
striking, however, is the frequency of perverse astigmatism. This in-
creases gradually to the seventieth year of life, and from there on rapidly ;
the vertical meridian of the cornea flattens more than the horizontal.

In general, the sclera increases in thickness and becomes more
rigid and less distensible, yet this thickening does not go so far that a
notable limitation of the interior of the eyeball arises.

Throughout the whole tunica fibrosa a certain degree of fatty degenera-
tion manifests itself in age. The sclera thereby loses its porcelain-
white color and becomes more yellowish; in the cornea the degeneration
makes itself manifest by clouding. Yet this clouding remains confined
to the marginal portions of the cornea proper (exclusive of the limbus)
and is, therefore, called arcus senilis, gerontoxon.

According to Takayasu (218), the fat lies in the intervening sub-
stance in finest round or elongated drops; the degeneration affects first
the superficial layers of the corneal stroma and extends along the surface
and into the depth. Little fat drops also appear in Bowman's membrane,
yet these are finer than in the corneal stroma. Toward the periphery the
degeneration is superficially limited by the border of Bowman's mem-
brane; in the depths, however, it progresses farther toward the sclera, so
that the peripheral border has a terraced appearance on cross-section.

In the uveal tract a greater development of the collagenous inter-
mediary substance, or a thickening of this, makes itself manifest before
anything else. One place in which especially dense sclerotic connective

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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 24 of 27)