PROBLEMS IN CORNEAL MORPHOGENESIS
95
C. The Fiber Matrix
There appear to be two fundamental types of fiber arrangement in
vertebrate stromas (Fig. 3). These arrangements cannot usually be
demonstrated by the use of axial sections alone but require either reconstruction in three dimensions from serial sections made parallel to a
plane tangent to the corneal midpoint, or layer by layer dissection of the
cornea. Polack (1961) has done a comparative study using silver
impregnated corneas from several vertebrate classes which reveals a
fundamental difference between the organization in the mammalian
stroma and that found in submammalian forms. In mammals the fibers
are arranged as broad ribbons which traverse the cornea from limbus
to limbus and which cross each other with no apparent order, but in
such a way that the stroma has an appropriate thickness at all points.
In submammalian forms, however, the fibers at any given depth in the
stroma are arranged in a parallel array to constitute a lamella which
touches the limbus at all points. The fibers in each lamella are disposed
roughly at right angles to those in the lamellae below and above them.
The genesis of this type of arrangement has been reconstructed in detail
in the developing chick embryo (Coulombre and Coulombre, 1961). The
deeper layers in the ply appear first and are clearly visible with the light
microscope on the 8th day of incubation. The co-ordinates of the internal
ply s are not precisely in register with those in more superficial layers.
As one views the stroma from the anterior epithelium in the chick
embryo, for example, there is a systematic angular shift of the mature
ply axes in a clockwise direction as one moves from the outer to the
inner surface of the stroma. The angular shift becomes progressively
smaller as the posterior epithelium is approached. It is a matter of some
interest that the direction of this shift is the same in both the right and
left eyes and is, therefore, asymmetric around the body midplane. This
rotation of fibre axis is depicted diagrammatically in Fig. 3 and can be
clearly seen in the transverse section of frog cornea in Fig. 4.
While we have little information concerning the details of genesis of
the mammalian fiber matrix, information is available concerning the
origin of the submammalian gridwork. The possibility that this threedimensional matrix is already laid down in the postepithelial layer
before the invasion of stromal fibroblasts has already been discussed.
If this conception of Ladijenski (1915) and Laguesse (1923a, b) is confirmed by future work (and preliminary work in my laboratory seems to
support it) the principal role of the fibroblasts is to enlarge this preexisting matrix by the synthesis of collagen which becomes polymerized
around the fine fibrils of the postepithelial layer. The fibroblasts invade
the posterior layers of the postepithelial layer first, and then progrès-
95
C. The Fiber Matrix
There appear to be two fundamental types of fiber arrangement in
vertebrate stromas (Fig. 3). These arrangements cannot usually be
demonstrated by the use of axial sections alone but require either reconstruction in three dimensions from serial sections made parallel to a
plane tangent to the corneal midpoint, or layer by layer dissection of the
cornea. Polack (1961) has done a comparative study using silver
impregnated corneas from several vertebrate classes which reveals a
fundamental difference between the organization in the mammalian
stroma and that found in submammalian forms. In mammals the fibers
are arranged as broad ribbons which traverse the cornea from limbus
to limbus and which cross each other with no apparent order, but in
such a way that the stroma has an appropriate thickness at all points.
In submammalian forms, however, the fibers at any given depth in the
stroma are arranged in a parallel array to constitute a lamella which
touches the limbus at all points. The fibers in each lamella are disposed
roughly at right angles to those in the lamellae below and above them.
The genesis of this type of arrangement has been reconstructed in detail
in the developing chick embryo (Coulombre and Coulombre, 1961). The
deeper layers in the ply appear first and are clearly visible with the light
microscope on the 8th day of incubation. The co-ordinates of the internal
ply s are not precisely in register with those in more superficial layers.
As one views the stroma from the anterior epithelium in the chick
embryo, for example, there is a systematic angular shift of the mature
ply axes in a clockwise direction as one moves from the outer to the
inner surface of the stroma. The angular shift becomes progressively
smaller as the posterior epithelium is approached. It is a matter of some
interest that the direction of this shift is the same in both the right and
left eyes and is, therefore, asymmetric around the body midplane. This
rotation of fibre axis is depicted diagrammatically in Fig. 3 and can be
clearly seen in the transverse section of frog cornea in Fig. 4.
While we have little information concerning the details of genesis of
the mammalian fiber matrix, information is available concerning the
origin of the submammalian gridwork. The possibility that this threedimensional matrix is already laid down in the postepithelial layer
before the invasion of stromal fibroblasts has already been discussed.
If this conception of Ladijenski (1915) and Laguesse (1923a, b) is confirmed by future work (and preliminary work in my laboratory seems to
support it) the principal role of the fibroblasts is to enlarge this preexisting matrix by the synthesis of collagen which becomes polymerized
around the fine fibrils of the postepithelial layer. The fibroblasts invade
the posterior layers of the postepithelial layer first, and then progrès-