PROBLEMS IN CORNEAL MORPHOGENESIS
83
avascularity, tensile strength, deturgesence, a tissue specific population
of inorganic and organic ions, an ability to regenerate its parts, a
characteristic interference pattern seen between crossed polarizers,
refracting power (refractive index and curvature), and transparency.
The developing cornea must make each of the cell types and each of the
extracellular constituents do multiple duty in satisfying the diverse
functional requirements represented by these properties. Furthermore,
the successive solution of each of these functional problems during
development progressively limits the number of alternative ways in
which the materials in the cornea can be used if all the functional problems are to find compatible solutions.
The first objective of the review is to reflect current knowledge of the
components from which the cornea is built, the manner in which they
are produced, and how they are brought together in space and time to
form a structure with the properties listed above. While this has
involved a relatively complete coverage of the pertinent literature, it is
not intended to be exhaustive. Phylogenetic differences have not been
emphasized in the interest of abstracting those features which are
common to most vertebrates. The extensive literature relating to the
adult cornea in health and disease has been used only where it is relevant
to developmental phenomena. General works which also deal with
corneal development or with related topics are: Coulombre (1961);
Dejean et al (1958); Lopashov and Stroeva (1961, 1963); Mann (1950,
1957); Polyak (1957); Rochon-Duvigneaud (1943); Thomas (1955);
Twitty (1955); Wolff (1958); Walls (1963). Reviews which are more
specifically focused on corneal development are: Mangold (1931); Mann
(1931); Meyer and O'Rahilly (1959); O'Rahilly and Meyer (1959, 1960);
Redslob (1935). The chemistry of the eye, including the cornea, is
treated by Pirie and van Heyningen (1956).
A flow-sheet of events in the development of the cornea (Fig. 1) summarizes the complex interactions that are discussed in the text. Despite
the absence of pertinent detail from this scheme, and the inevitability
that future work will force its modification, it is offered as an aid in
following the presentation and as an abbreviated summary of our present
knowledge of corneal development. The second objective of this summary is to indicate some of the unsolved problems in corneal development. Attention will be directed to these by the use of italics.
II. Induction of the Cornea
Mangold (1931) and Lopashov and Stroeva (1961, 1963) give excellent
reviews of corneal induction. The first corneal rudiment, the presumptive corneal epithelium, appears over the lens and the opening in the
83
avascularity, tensile strength, deturgesence, a tissue specific population
of inorganic and organic ions, an ability to regenerate its parts, a
characteristic interference pattern seen between crossed polarizers,
refracting power (refractive index and curvature), and transparency.
The developing cornea must make each of the cell types and each of the
extracellular constituents do multiple duty in satisfying the diverse
functional requirements represented by these properties. Furthermore,
the successive solution of each of these functional problems during
development progressively limits the number of alternative ways in
which the materials in the cornea can be used if all the functional problems are to find compatible solutions.
The first objective of the review is to reflect current knowledge of the
components from which the cornea is built, the manner in which they
are produced, and how they are brought together in space and time to
form a structure with the properties listed above. While this has
involved a relatively complete coverage of the pertinent literature, it is
not intended to be exhaustive. Phylogenetic differences have not been
emphasized in the interest of abstracting those features which are
common to most vertebrates. The extensive literature relating to the
adult cornea in health and disease has been used only where it is relevant
to developmental phenomena. General works which also deal with
corneal development or with related topics are: Coulombre (1961);
Dejean et al (1958); Lopashov and Stroeva (1961, 1963); Mann (1950,
1957); Polyak (1957); Rochon-Duvigneaud (1943); Thomas (1955);
Twitty (1955); Wolff (1958); Walls (1963). Reviews which are more
specifically focused on corneal development are: Mangold (1931); Mann
(1931); Meyer and O'Rahilly (1959); O'Rahilly and Meyer (1959, 1960);
Redslob (1935). The chemistry of the eye, including the cornea, is
treated by Pirie and van Heyningen (1956).
A flow-sheet of events in the development of the cornea (Fig. 1) summarizes the complex interactions that are discussed in the text. Despite
the absence of pertinent detail from this scheme, and the inevitability
that future work will force its modification, it is offered as an aid in
following the presentation and as an abbreviated summary of our present
knowledge of corneal development. The second objective of this summary is to indicate some of the unsolved problems in corneal development. Attention will be directed to these by the use of italics.
II. Induction of the Cornea
Mangold (1931) and Lopashov and Stroeva (1961, 1963) give excellent
reviews of corneal induction. The first corneal rudiment, the presumptive corneal epithelium, appears over the lens and the opening in the