The pressure theory is still predominant in explaining the pathophysiology of the chronic open angle glaucoma. An insufficient drainage system resulting in an increased intraocular pressure is the basis for this theory. The pressure will exert an effect upon the optic disc which either directly on the nerve fibres or indirectly via the vascular system will result in a characteristic optic atrophy. The collagen fibres, both in the trabecular meshwork of the anterior chamber and in the lamina cribrosa of the optic disc, form a mesh through which the aqueous humour and the nerve fibres, respectively, pass through the wall of the eye. A hypothesis explaining the pathophysiology of this disease, and based on the assumption that there is a primary change in the collagen molecules, resulting in a weaker structure than normal both in the trabeculae and in the laminae, is forwarded. The structures analysed for the content of hydroxyproline, hydroxylysine and proline were the trabecular meshwork, the sclera and the lamina cribrosa. Three categories of autopsy eyes were studied, i.e. normal eyes, glaucomatous eyes, and eyes under a suspicion of glaucoma. In the normal eyes, the collagen composition in the trabecular meshwork was different from that in the sclera and the lamina cribrosa. There is also a difference in the composition between the sclera and the lamina cribrosa. In glaucoma, the content and/or the composition of the collagen molecules in the lamina were significantly changed. In the eyes under suspicion of glaucoma the same changes as in the glaucomatous eyes could be demonstrated. However, 5 of the 7 eyes in this category had no demonstrable nerve atrophy. The findings suggest that the change in collagen pattern is primary. This study has not demonstrated which types of collagen are present or the physical properties of this collagen. Further tests to demonstrate the different types of collagen and their rigidity are planned.