A comparative analysis of the collagen type and distribution in the trabecular meshwork, sclera, lamina cribrosa and the optic nerve in the human eye

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Abstract
A theory has been advanced (Tengroth et al 1984) that one common factor might be involved in the pathogenesis of chronic open angle glaucoma. The mechanical properties of the collagen could be one such factor. To characterize the collagen composition of the critical structures in cases with chronic open angle glaucoma i.e. the trabecular meshwork and the lamina cribrosa in the human eye, the following investigations were performed. Using immunperoxidase technique and type specific antibodies to the genetically distinct collagen types I, III, IV and procollagen I along with the major non collagen proteins in the extracellular matrix laminin and fibronectin a light microscopic study was undertaken on the trabecular meshwork, cornea, sclera, lamina cribrosa and the optic nerve of the human eye. Furthermore biochemical analysis was performed on the collagen associated aminoacids hydroxyproline (Hyp), hydroxylysine (Hyl) and prolin (Pro) from microdissected samples of trabecular meshwork, sclera, lamina cribrosa and optic nerve. Both the immunohistological and the biochemical findings suggested similarities in the collagen composition between the trabecular meshwork and the lamina cribrosa. The immunohistochemical findings showed stronger staining of type III and IV in the trabecular meshwork and lamina cribrosa as compared to sclera or cornea while the opposite was true for type I and procollagen I. Fibronectin and laminin were present in both the trabecular meshwork and lamina cribrosa. These findings were in agreement with the amino acid analysis when the Hyp/Hyl ratio was calculated for each sample. The trabecular meshwork and lamina cribrosa had almost identical ratios which were lower than in the sclera and the optic nerve retrolaminary, indicating a higher proportion of type IV in the former structures. The biochemical and immunohistochemical findings suggest a similar collagen composition in the trabecular meshwork and lamina cribrosa as opposed to the cornea, sclera and optic nerve proper. A common embryological background of the critical tissues is discussed.