Relationship between ocular perfusion pressure and retrobulbar blood flow in patients with glaucoma with progressive damage: Author’s reply

Abstract

We would like to thank Dr. Ates and associates for the comments about our paper. They point to a study in which the issue of vascular alterations in glaucoma patients was investigated by means of color Doppler imaging. Many studies using color Doppler imaging have revealed-altered orbital hemodynamics in patients with glaucoma. Interestingly, retrobulbar hemodynamic alterations seem not to be present in patients with stable visual fields, whereas those with progressive visual field damage, especially patients with normal tension glaucoma, show altered retrobulbar hemodynamics. 1 Yamazaki Y. Drance S.M. The relationship between progression of visual field defects and retrobulbar circulation in patients with glaucoma. Am J Ophthalmol. 1997; 124 ([see comments]): 287-295 Abstract Full Text PDF Scopus (161) Google Scholar In addition, patients with asymmetric glaucomatous damage seem to have lower retrobulbar hemodynamics in the eye with the more advanced damage. 2 Nicolela M.T. Drance S.M. Rankin S.J. Buckley A.R. Walman B.E. Color Doppler imaging in patients with asymmetric glaucoma and unilateral visual field loss. Am J Ophthalmol. 1996; 121: 502-510 Abstract Full Text PDF Scopus (129) Google Scholar Finally, the eye with the more marked progression in damage has lower retrobulbar hemodynamics. 3 Schumann J. Orgül S. Gugleta K. Dubler B. Flammer J. Interocular difference in progression of glaucoma correlates with interocular differences in retrobulbar circulation. Am J Ophthalmol. 2000; 129: 728-733 Abstract Full Text Full Text PDF Scopus (70) Google Scholar These observations suggest that retrobulbar hemodynamic alterations may not just be secondary phenomena, but are primarily present in glaucoma patients. We welcome Dr. Ates and associates comments concerning additional literature available for the interested reader. However, our study does not exactly address the same issue. Based on the observation that studies assessing ocular blood flow show a marked overlap between glaucoma patients and normals, we hypothesized that instead of a continuous low-grade ischemia, vascular alterations in glaucoma patients may reside in some sort of dysregulation or lack of autoregulation, which would mean that ischemia, and possibly reperfusion damage, is only occurring periodically, and not continuously. Consequently, perfectly normal blood flow parameters may be measured in a glaucoma patient, but the same patient may react pathologically to some disturbance of the physiological homeostasis. Such a behavior of blood flow with undue variability may be more deleterious than low-grade ischemia. Interestingly, large variations in intraocular pressure represent an independent risk factor in glaucoma as well 4 Asrani S. Zeimer R. Wilensky J. et al. Large diurnal fluctuations in intraocular pressure are an independent risk factor in patients with glaucoma. J Glaucoma. 2000; 9: 134-142 Crossref Scopus (725) Google Scholar . In our study, in order to investigate whether some sort of vascular dysregulation can be seen in glaucoma patients, we sought to establish whether the relationship between blood flow parameters as they are determined by means of color Doppler imaging and ocular perfusion pressure is altered in glaucoma patients with progressive damage despite lowered intra ocular pressure.