At the earliest stage of clinical detection of open-angle glaucoma with visual field defect namely that of initial diagnosis prior to significant symptoms, one can already demonstrate a significant deviation of the distribution of C/D ratio from that of individuals with similar pressure readings who are free from glaucomatous visual field defect. This difference consists of a markedly reduced frequency of small C/D values in glaucomatous eyes and a great increase in large C/D values. In addition, one can demonstrate at this stage enlargement of the optic cup as evidenced by the increased frequency of a difference between the ratios of the two eyes which is > 0.2. In general, the C/D ratio was greater in the affected eye in monocular involvement and in the eye with greater field defect. It is hypothesized that the C/D ratio is one of the factors involved in determining the vulnerability of the visual field to higher ocular pressure in openangle glaucoma. This relationship results in a great increase in the relative frequency of involvement of the visual field by the glaucomatous process in eyes with large C/D ratios and a reduction of that frequency in eyes with small C/D ratios. It was also hypothesized that different sets of factors operate in the production of field defect in eyes with different C/D ratios. From the clinical standpoint, the findings emphasize the importance of ophthalmoscopic evaluation of the optic nerve in the early suspicion and detection of open-angle glaucoma. This evaluation should include a careful estimation, recording and monitoring in time the characteristics of the optic cup. © 1969 Dr. W. Junk N.V.
