OCTA allows clinicians to identify patients with vascular compromise
Glaucoma is traditionally characterized by progressive loss of the retinal ganglion cell layer, leading to visual field defects, advancing to central islands and, finally, total blindness. However, that may change in the future.
The role of vascular contribution to ganglion cell loss is a current topic of research around the world. Compromised vascular function has been linked to open angle glaucoma (Leighton et al.), and systemic diseases that indicate defective vasoregulation, such as Raynaud’s phenomenon and migraines, have been correlated to normal tension glaucoma (Mallick et al.). In addition, several studies within the last 5 to 10 years have demonstrated peripapillary vessel density changes prior to any ganglion cell loss or visual field changes (Jia et al., Yarmohammadi et al.). With all of this emerging data, it makes sense for clinicians to include investigation of retinal vascular function in their glaucoma patients and suspects.
OCT angiography (OCTA) is an additional modality on an OCT device that builds upon the information previously acquired via dye-based procedures. OCTA produces ultra-high resolution, three-dimensional images that permit the analysis of tissue perfusion. It uses the motion of blood cells to produce high-resolution images of microvascular networks in the retina, optic discs and choroid.
In addition to qualitative pictures of the capillary beds, the latest technology added to the AngioVue OCTA system (Optovue) is a quantitative software system called AngioAnalytics. This software measures vessel density in the radial peripapillary plexus (RPC) and the superficial vascular complex, in addition to detecting areas of abnormal flow in the outer retina and choroid. It then exports numerical values in four quadrants of the optic nerve, enabling assessment of visit-to-visit change and trend reports that can predict change over time.
As this quantitative data is accumulated, it will likely allow for the future development of a reference database that will be able to establish normative values of patients of different ages. In the future, we will be able to examine a patient and know if their retinal vascular function is appropriate for their age. This opens the door to the exciting possibility of improving vascular function prior to significant optic nerve damage.
Understanding the role of blood flow in glaucoma also leads to the issue of targeted treatments. While no causal relationship has been established, there is a known correlation between adequate nutrient delivery and the health of retinal ganglion cells. A rigorous study of the effect of the dietary supplement Optic Nerve Formula (ONF, ScienceBased Health) on retinal and retrobulbar blood flow in patients with confirmed open angle glaucoma showed significant improvements in several measurements in patients given the supplement over the control group (Harris et al., 2018). Improvements were seen in peak systolic and/or end diastolic blood flow velocities in all retrobulbar blood vessels and vascular resistance in the central retinal and nasal short posterior ciliary arteries, while increased superior and inferior temporal retinal capillary mean blood flow and perfusion (ratio of active to nonactive retinal capillaries) was demonstrated in the peripapillary area.
In our clinic, we have been using ONF for approximately 6 to 12 months with patients who meet the criteria for earlier vascular compromise as seen with OCTA, which is primarily our normal tension and low-tension glaucoma patients. However, this supplement is indicated in any patient with vascular compromise, as risks and side effects are minimal. While we do not yet have data over the long term, this treatment, along with other traditional glaucoma treatments, are likely giving our patients the most potential for altering the course of their disease.
A study by Harweth and Quigley found that 40% of ganglion cell death occurs before visual field defects manifest. This is just one more demonstration of the importance of technology that will warn of glaucoma much earlier. We have been using OCTA for more than 3 years, and it provides an important, additional piece of information that gives us the best chance of protecting our patients’ optic nerves from compromise. The more information and methods of detection we use with our patients, the better-informed decisions we can make, and the better care we can provide. – by Nate Lighthizer, OD
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Arthur B. Epstein, OD, FAAO, is head of the Dry Eye – Ocular Surface Disease Center and director of clinical research at Phoenix Eye Care – the Dry Eye Center of Arizona in Phoenix. He can be reached at: email@example.com.
Disclosure:Epstein reports he is a consultant for Alcon, Johnson & Johnson Vision, Lumenis and Sight Sciences.