PROBLEMS IN CORNEAL MORPHOGENESIS
87
Although the anterior epithelium of the cornea of those Amphibia and
mammals that have been studied possess a high regenerative capacity,
wounds of the chick embryonic cornea do not heal in vivo until the 10th
day of incubation (Weiss and Matoltsy, 1959).
The anterior corneal epithelium has complex functional relationships
with the rest of the cornea. When wounds extend into the stroma a
factor is proteolytically released from the anterior epithelium which
stimulates stromal fibroblasts to form connective tissue (Weimar, 1959a,
b ; Dunnington and Weimar, 1958). The fact that the adult anterior
epithelium is capable of activating the stromal fibroblasts in this
manner suggests a question of some importance. Is the anterior epithelium
of the cornea necessary during development to sustain the synthetic activity
of the stromal fibroblasts when they are actively constructing the stroma ? A
function which the anterior epithelium shares with the posterior
epithelium is the elimination of water from the stroma to maintain it
within those narrow limits of hydration that are compatible with its
transparency (Davson, 1955; Harris, 1957). Dehydration is initiated
during the development of the chick embryo by thyroxin (Coulombre
and Coulombre, 1959). One of the most significant functions of the developing anterior epithelium may be that of, laying down the postepithelial layer, a structure that will be discussed below. If, as present
evidence indicates, the epithelium is responsible for the synthesis of
this precursor of the stroma, then it may well dictate the geometry of
the collagenous matrix which subsequently develops in it. Ladijenski
seems to have clearly visualized this as early as 1915. Speaking of the
postepithelial layer Laguesse (1926) put the matter quite clearly: 'Cet
exemple montre que les epitheliums peuvent jouer le rôle principal dans
l'édification de certaines membranes basales ; et il est très vraisemblable
que partout ailleurs ils jouent au moins le rôle initial, les éléments
mésenchymateux venant s'y ajouter secondairement.'
IV. Stromal Architecture and Properties
A. Postepithelial Layer
Following the separation of the lens vesicle from the surface ectoderm, the space between the presumptive anterior corneal epithelium
and the lens vesicle contains an acellular deposit which has been given a
number of names (anhistic mass, Kessler, 1877; anterior vitreous body,
v. Lenhossék, 1911; mesostroma, Studnicka, 1911). O'Rahilly and
Meyer (1959) reviewed the descriptive studies of this material. Next, at
least in the chick embryo, a very thin acellular membrane that stains
with aniline blue appears behind the presumptive corneal epithelium
and parallel to it (Knape, 1909; Laguesse, 1923a, b ; Redslob, 1935;
87
Although the anterior epithelium of the cornea of those Amphibia and
mammals that have been studied possess a high regenerative capacity,
wounds of the chick embryonic cornea do not heal in vivo until the 10th
day of incubation (Weiss and Matoltsy, 1959).
The anterior corneal epithelium has complex functional relationships
with the rest of the cornea. When wounds extend into the stroma a
factor is proteolytically released from the anterior epithelium which
stimulates stromal fibroblasts to form connective tissue (Weimar, 1959a,
b ; Dunnington and Weimar, 1958). The fact that the adult anterior
epithelium is capable of activating the stromal fibroblasts in this
manner suggests a question of some importance. Is the anterior epithelium
of the cornea necessary during development to sustain the synthetic activity
of the stromal fibroblasts when they are actively constructing the stroma ? A
function which the anterior epithelium shares with the posterior
epithelium is the elimination of water from the stroma to maintain it
within those narrow limits of hydration that are compatible with its
transparency (Davson, 1955; Harris, 1957). Dehydration is initiated
during the development of the chick embryo by thyroxin (Coulombre
and Coulombre, 1959). One of the most significant functions of the developing anterior epithelium may be that of, laying down the postepithelial layer, a structure that will be discussed below. If, as present
evidence indicates, the epithelium is responsible for the synthesis of
this precursor of the stroma, then it may well dictate the geometry of
the collagenous matrix which subsequently develops in it. Ladijenski
seems to have clearly visualized this as early as 1915. Speaking of the
postepithelial layer Laguesse (1926) put the matter quite clearly: 'Cet
exemple montre que les epitheliums peuvent jouer le rôle principal dans
l'édification de certaines membranes basales ; et il est très vraisemblable
que partout ailleurs ils jouent au moins le rôle initial, les éléments
mésenchymateux venant s'y ajouter secondairement.'
IV. Stromal Architecture and Properties
A. Postepithelial Layer
Following the separation of the lens vesicle from the surface ectoderm, the space between the presumptive anterior corneal epithelium
and the lens vesicle contains an acellular deposit which has been given a
number of names (anhistic mass, Kessler, 1877; anterior vitreous body,
v. Lenhossék, 1911; mesostroma, Studnicka, 1911). O'Rahilly and
Meyer (1959) reviewed the descriptive studies of this material. Next, at
least in the chick embryo, a very thin acellular membrane that stains
with aniline blue appears behind the presumptive corneal epithelium
and parallel to it (Knape, 1909; Laguesse, 1923a, b ; Redslob, 1935;