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CORRESPONDING AUTHOR Dr hab. n. med. Joanna Wierzbowska, prof. WIM, Department of Ophthalmology, Military Institute of Medicine, 128 Szaserów St., 04-141 Warsaw, Poland, e-mail: jwierzbowska@wim.mil.pl INTRODUCTION Based on the current state of knowledge, glaucomatous optic neuropathy is a neurodegenerative disease involving pathological changes in the biomechanics of the optic disc, genetic factors, vascular disorders, and immunological factors. The mechanical and vascular hypotheses explaining the pathomechanism of glaucoma which prevailed in the 20th century were replaced at the turn of the millennium by a new, biomechanical concept of glaucomatous damage which takes into account the dynamic interaction between intraocular pressure (IOP), biomechanical properties of ocular tissues, dynamics of aqueous humor, and ocular blood flow [1]. Ocular hemodynamics in glaucoma can be altered both by local factors, related primarily to vascular endothelial dysfunction, impaired flow autoregulation mechanism or abnormal translaminar pressure [2, 3], and general factors, including an increased activity of the sympathetic component of the autonomic nervous system or altered rheological properties of blood [4, 5]. The factors listed above are believed to have critical pathogenetic implications in patients with normal-tension glaucoma, in whom moderate and short-term but repeated changes in perfusion pressure “sensitize” the optic nerve to damage even under conditions of statistically insignificantly elevated IOP. Blood supply to the eye comes from the ophthalmic artery (OA), which is the first branch of the internal carotid artery. The choroidal circulation, which accounts for 85% of the total blood flow in the eye, is supplied by the anterior and posterior ciliary arteries, while the retinal circulation is supplied by the central retinal artery (CRA). The retinal vasculature feeds the inner layers of the retina up to the inner nuclear layer, and the choroidal circulation supplies the outer retinal layers. The main sources of vascularization of the optic disc are the nasal and temporal short posterior ciliary arteries (NSPCA, TSPCA), which in most people are connected by anastomoses, forming the arterial circle of Zinn-Haller. They supply the deeper layers of the prelaminar region of the optic disc, and its laminar and anterior retrolaminar parts. The vascular network of the central retinal artery supplies the superficial layers of the prelaminar part of the optic disc and the central area of the posterior retrolaminar region [6]. The small branches of the central retinal artery are both anatomically and functionally terminal vessels; the characteristic features of retinal capillaries include the absence of innervation and the presence of tight junctions between endothelial cells. As a consequence, the regulation of retinal circulation involves mainly endothelial cells, which release a number of vasoactive factors including nitric oxide or endothelin 1 (the most potent ABSTRACT Patients with glaucoma demonstrate disturbed ocular blood flow that is induced by oxidative stress, endothelial dysfunction and impaired autonomic nervous system activity. It has not yet been clarified whether the reduced blood flow in glaucoma is secondary (to tissue loss or a decrease in perfusion pressure with disturbed autoregulation) or is itself the primary cause of optic neuropathy. Due to the complex system of blood supply to the optic disc and retina there is no single diagnostic method that allows the measurement of all vascular beds in the eye important for glaucoma. The article, based on a review of the literature, discusses current and previous techniques for assessing retinal, choroidal and retrobulbar circulation in glaucoma, with particular attention to color Doppler ultrasonography and optical coherence tomography angiography. Advantages and limitations of each technology are presented and the results of the most important research with their use are listed. In the light of the latest research, optical coherence tomography angiography is an imaging modality that has great scientific and clinical potential to enhance the knowledge of glaucoma pathogenesis and to improve the ability to detect glaucomatous damage.

Evaluation of ocular blood flow in glaucoma – possibilities and barriers