The question of blood flow in glaucoma revisited

Glaucoma is one of the leading causes for blindness in industrialized countries. It is characterized by a progressive loss of retinal ganglion cells, morphological changes in the optic nerve head and a characteristic loss of visual field. Although increased intraocular pressure has been identified as the major risk factor for the development and the progression of the disease it has been speculated for a long time that impaired ocular blood flow may contribute to the pathogenesis of the disease. This concept has been supported by several epidemiological studies showing that low ocular perfusion pressure and small retinal vessel caliber are associated with the disease. Large-scale studies investigating the link between reduced blood flow and glaucoma are, however, lacking. This is to a large extent related to the technical difficulties of measuring blood flow in the human eye. We have recently introduced a new promising technique called bi-directional Fourier Domain Doppler Optical Coherence Tomography, which provides unprecedented validity and reproducibility. The proposed study uses this technique in patients with glaucoma to test the hypothesis that patients with glaucoma have reduced total retinal blood flow as compared to healthy subjects. In addition, information will be gained whether this technique can be used in large- scale longitudinal studies. An additional focus of our study will be directed towards blood flow autoregulation during an increase in ocular perfusion pressure. The experiments proposed in this grant proposal are an important step to clarify the degree of vascular involvement in glaucoma.

In the present project it was intended to re-evaluate the question of ocular blood flow in glaucoma. The focus was directed towards two questions. On the one hand changes in retinal blood flow and retinal oxygen extraction in glaucoma were evaluated. On the other hand autoregulation of optic nerve head blood flow was studies. The first study shows that retinal blood flow and retinal oxygen extraction are reduced in glaucoma. These changes correlate with both structural and functional damage. The second study shows that glaucoma patients show changes in autoregulation. The methods established within the framework of this grant can in the future be used in longitudinal studies.