On the Metachromatic Staining of the Corneal Tissue and Some Observations on Its Transparency

Abstract

o l m g r e v . + Historical review. Among the many very different kinds of 'collagen in the body, the corneal collagen is undoubtedly unique because it displays certain Characteristics which are lacking in the collagen of other parts of the body.The chief characteristics of the corneal collagen are the following.1. The almost perfect transparency. 2. Its capacity of swelling and of absorbing considerable quantities of water during which process it becomes opaque.3. Its pronounced metachromatic properties when stained with certain stains.The most evident of these properties is the transparency, which characteristic therefore for a long time has been investigated by many workers. Many explanations of this phenomenon have been advanced.Thus one has observed the regular stratification of the fibrils of the corneal stroma (Eider 1930, Kolmer and Lauber 1936) and some corneal opacities have been considered the result of a separation of the fibrils (see also Engelmann 1867). However, other investigators have considered this fact of no importance (Leber 1873, H. Virchow 1905). '1 Received march 18th 1952. 2Schweigger-Seidel ( 1869), u. Fleischl ( 1880), Ranvier ( 1898) and H . Virchow (1906) have all emphasized the importance of the optical homogeneity of the corneal stroma, i. e. that all its component parts have the same index of refraction. Renault (1889) also pointed out that this was necessary, when he said that the connective tissue fibrils must necessarily be surrounded by a substance of the same index of refraction as themselves.Sabatzky (1928) also points out that an optical homogeneity of the corneal stroma is necessary, and compares its structure with that of opaque corneal scars, which latter consist of a number of different tissues of different refractive indices (connective tissue strands, blood vessels, connective tissue cells etc.). Meyer (1948) has expressed similar views.It has long been known that the transparency of connective tissue organs is largely dependent on its water content. Already in 1821 Chevreuil pointed out that an opaque tissue such as a tendon, the sclera, or the ligamentum nuchae, became transparent when it dried. In 1886 Michel and Wagner observed the same phenomenon in the sclera of the swine. On the other hand it has been observed that the normally transparent cornea sweIls and becomes opaque when absorbing water. Ranvier (1898) explains the appearance of this opacity as follows: The refractive index of the corneal collagen decrcases when water is absorbed, whereas the refractive index of the connective tissue cells that do not absorb any water, remains unchanged. A s the cornea is thus rendered optically heterogenous, the transparency is lost. The most detailed study of these problems was made by F . P . Fischer (1926, 1931, 1932). He looks upon both the corneal and scleral tissues as a gel, and considers that the transparency is exclusively dependant on the dispersity of this gel. >>The sclera is opaque because it consists of another gel than does the cornea, i. e. it has a diff...

Corneal structure and transparency

“…The suggestion that collagen fibrils needed to have the same refractive index as their surroundings was stated specifically by Renault (1889) . These ideas persisted through the first half of the twentieth century, but measurements of the refractive index of the corneal collagen eventually indicated a significant difference between the collagen and the interstitial matrix ( Aurell and Holmgren, 1953 ). This lead researchers to look for other mechanisms and specifically to the ideas of interference between scattered light waves from ordered crystalline arrays of collagen fibrils ( Maurice, 1957 ).…”