The role of ocular blood flow in the glaucoma disease process has been an area of interest for quite some time. What is the significance of vascular abnormality in the optic nerve head or elsewhere in the development or progression of glaucoma? Is it a cause, an effect, or correlated in some other way? Does dysfunctional ocular blood flow or lack of perfusion in ocular structures and tissue increase sensitivity to IOP? Is the mechanical aspect of the disease, i.e., IOP, completely separate from or closely related to a vascular element? With the emergence of OCT angiography (OCTA) and its improved ability to measure retinal blood flow and vessel density, we have an exciting new way to explore answers to these and other important questions.
Huang and colleagues were the first to report on the use of OCTA in glaucoma,1 and other groups have been investigating relationships between structural and vascular findings in the optic nerve head and peripapillary and macular regions, as well as their relationship to visual function, along the disease continuum.2-6 The superficial vascular supply is currently the focus of most OCTA glaucoma studies, but the technology is capable of providing unprecedented visualization and measurement of the microvasculature in deeper layers of the retina as well.
As more longitudinal data is obtained, the hope is that we’ll be able to use OCTA parameters in conjunction with visual field testing and the current parameters derived from standard structural OCT to more accurately detect, monitor, and manage glaucoma. Should OCTA prove to be capable of earlier diagnosis, it would be an especially useful advance. OCTA may also provide quantifiable endpoints beyond IOP for clinical trials, which could facilitate the development and use of more precisely targeted therapies. Furthermore, the dyeless, noninvasive, efficient nature of OCT makes it very well-suited for use in daily clinical practice should that prove to be advantageous for glaucoma patients.
I’m currently enrolling patients with mild or moderate open-angle glaucoma into a study in which I’ll examine correlations between changes on structural OCT and changes on OCTA over time. I look forward to analyzing the results and adding what is learned to the growing body of knowledge surrounding OCTA in glaucoma.
Structural OCT imaging and OCT angiography in an eye with moderate glaucoma. The red circle indicates an area of reduced vascularity that is associated with an area of nerve fiber dropout.
1. Jia Y, Morrison JC, Tokayer J, et al. Quantitative OCT angiography of optic nerve head blood flow. Biomed Opt Express. 2012;3(12):3127-3137.
2. Yarmohammadi A, Zangwill LM, Diniz-Filho A, et al. Optical coherence tomography angiography vessel density in healthy, glaucoma suspect, and glaucoma eyes. Invest Ophthalmol Vis Sci. 2016;57(9):OCT451-459.
3. Yarmohammadi A, Zangwill LM, Diniz-Filho A, et al. Peripapillary and macular vessel density in patients with glaucoma and single-hemifield visual field defect. Ophthalmology. 2017;124(5):709-719.
4. Yarmohammadi A, Zangwill LM, Diniz-Filho A, et al. Relationship between optical coherence tomography angiography vessel density and severity of visual field loss in glaucoma. Ophthalmology. 2016;123(12):2498-2508.
5. Rao HL, Pradhan ZS, Weinreb RN, et al. Regional comparisons of optical coherence tomography angiography vessel density in primary open-angle glaucoma. Am J Ophthalmol. 2016;171:75-83.
6. Rao HL, Pradhan ZS, Weinreb RN, et al. Vessel density and structural measurements of optical coherence tomography in primary angle closure and primary angle closure glaucoma. Am J Ophthalmol. 2017;177:106-115.
Dr. Bacharach, who specializes in medical and surgical glaucoma care, is the founder of North Bay Eye Associates, which serves patients throughout Sonoma County, Calif.