PROBLEMS IN CORNEAL MORPHOGENESIS
97
zone of contact from fibers in one level to orthogonally disposed fibers
in the next layer, there is no interweaving of fibers and, as a consequence,
the individual lamellae remain distinct as they grow in thickness. The
orientation of the gridwork in the deepest lamellae of the stroma, and
consequently of all more superficial layers, has a fixed orientation with
respect to the eye at all stages. The fiber matrices of right and left eyes
are asymmetrical with respect to the body midplane. Coulombre and
Coulombre (1961) demonstrated this by referring the orientation of the
fiber grid in tangential sections of the cornea of the chick embryonic eye
to the position of the choroid fissure.
As a result of the steady accretion of fibrils, individual lamellae become coarser and readily visible in the light microscope. In the chick
embryo Neüschuler (1931) did not observe these coarse lamellae until
the 11th day of incubation. Snesarev (1939), Meyer and O'Rahilly (1959)
and Coulombre and Coulombre (1961) agree that the first coarse gridworks can be seen on the 7th or 8th days of incubation. The first
lamellae to coarsen are posteriorly situated and the posterior regions of
the stroma are always the more advanced in differentiation during
development (Smelser and Ozanics, 1957; Coulombre and Coulombre,
1961).
The pattern of disposition of collagen fibers in the stromal space in
both mammals and submammalian forms has a bearing on some of the
properties of the cornea. The form birefringence of the cornea is based
on the parallel array of fibrils within the fibers. Kikkawa (1955, 1956,
1959), Naylor (1953a, b), Stanworth (1950), and Stanworth and Naylor
(1953a, b) have pointed out that the complex interference pattern which
is seen when the cornea is placed between crossed polarizers and viewed
axially must ultimately rest upon coarser matrix formed by the fibers.
When the axis of one of the polarizers is in register with the corneal
diameter passing through the choroid fissure, the interference pattern
takes the form of dark hyperboloids in the anterior superior and inferior posterior quadrants of the cornea (Coulombre and Coulombre,
1961) (Fig. 5). As the cornea is rotated 45° between the polarizers the
pattern shifts so that the dark lines form a cross whose intersection lies at
the center of the cornea.
The two patterns alternate with one another as the rotation continues, the cycle being 90° of rotation (Fig. 5). Unlike the fiber matrix,
the interference pattern is symmetrical around the body midline.
Essentially the same pattern appears in submammalian forms and in
mammals despite the difference in detail öf the manner in which the
fibers are disposed in the stroma. In addition the quadrants in which
the hyperboloids appear can be altered simply by altering the shape of
the cornea mechanically. Thus, while the interference pattern of the
97
zone of contact from fibers in one level to orthogonally disposed fibers
in the next layer, there is no interweaving of fibers and, as a consequence,
the individual lamellae remain distinct as they grow in thickness. The
orientation of the gridwork in the deepest lamellae of the stroma, and
consequently of all more superficial layers, has a fixed orientation with
respect to the eye at all stages. The fiber matrices of right and left eyes
are asymmetrical with respect to the body midplane. Coulombre and
Coulombre (1961) demonstrated this by referring the orientation of the
fiber grid in tangential sections of the cornea of the chick embryonic eye
to the position of the choroid fissure.
As a result of the steady accretion of fibrils, individual lamellae become coarser and readily visible in the light microscope. In the chick
embryo Neüschuler (1931) did not observe these coarse lamellae until
the 11th day of incubation. Snesarev (1939), Meyer and O'Rahilly (1959)
and Coulombre and Coulombre (1961) agree that the first coarse gridworks can be seen on the 7th or 8th days of incubation. The first
lamellae to coarsen are posteriorly situated and the posterior regions of
the stroma are always the more advanced in differentiation during
development (Smelser and Ozanics, 1957; Coulombre and Coulombre,
1961).
The pattern of disposition of collagen fibers in the stromal space in
both mammals and submammalian forms has a bearing on some of the
properties of the cornea. The form birefringence of the cornea is based
on the parallel array of fibrils within the fibers. Kikkawa (1955, 1956,
1959), Naylor (1953a, b), Stanworth (1950), and Stanworth and Naylor
(1953a, b) have pointed out that the complex interference pattern which
is seen when the cornea is placed between crossed polarizers and viewed
axially must ultimately rest upon coarser matrix formed by the fibers.
When the axis of one of the polarizers is in register with the corneal
diameter passing through the choroid fissure, the interference pattern
takes the form of dark hyperboloids in the anterior superior and inferior posterior quadrants of the cornea (Coulombre and Coulombre,
1961) (Fig. 5). As the cornea is rotated 45° between the polarizers the
pattern shifts so that the dark lines form a cross whose intersection lies at
the center of the cornea.
The two patterns alternate with one another as the rotation continues, the cycle being 90° of rotation (Fig. 5). Unlike the fiber matrix,
the interference pattern is symmetrical around the body midline.
Essentially the same pattern appears in submammalian forms and in
mammals despite the difference in detail öf the manner in which the
fibers are disposed in the stroma. In addition the quadrants in which
the hyperboloids appear can be altered simply by altering the shape of
the cornea mechanically. Thus, while the interference pattern of the