OCT Angiography in Glaucoma

In this episode of Interventional Mindset, Grace Richter, MD, a glaucoma specialist at Kaiser Permanente Los Angeles Medical Center, discusses optical coherence tomography angiography (OCTA) and its benefits in glaucoma diagnosis and management.

Benefits of OCT angiography in glaucoma

As a chronic disease and leading cause of blindness, glaucoma is one of the most demanding aspects of an ophthalmologist’s practice. However, even when patients are getting routine visual field testing and traditional OCT scans, there are cases where evidence of glaucoma or signs of progression are not definitive.

OCTA is a non-invasive imaging technique that uses motion detection to produce depth-resolved imaging of the retinal tissue and surrounding vasculature.¹ Rather than relying on contrast dyes, OCT angiography uses the movement of red blood cells to map the microvasculature of the retina in various layers. This allows for greater depth of data, including the vasculature structure and function in addition to the anatomical structure that traditional OCT offers.²

Dr. Richter says that OCT angiography works well to complement OCT to better understand a patient’s glaucoma status by providing insight into the metabolic health and perfusion of the tissue. In her practice, qualitative evaluation of OCTA has been helpful in the early detection of glaucoma as well as to confer progression in specific situations.

Figure 1: OCTA image of healthy peripapillary vessel density.

^{Figure 1: Courtesy of Grace Richter, MD.}

Figure 2: Representative images of the radial peripapillaries at the optic nerve head of glaucomatous eyes on spectral-domain OCTA.

^{Figure 2: Courtesy of Burkemper et al.}

She refers to two main categories of peripapillary OCT-A findings in glaucoma patients as seen in Figure 2 from a study her team published in 2022:³

Wedge defects: In the top row, focal wedge-shaped defects as they appear in mild, moderate, and severe glaucoma (A-C)
Generalized reduced perfusion: In the bottom row, nonspecific microvascular loss is marked by an asterisk in mild, moderate, and severe glaucoma (D-F)

The study showed that focal defects were present in 45% of glaucoma patients, and were more likely in patients with a history of disc hemorrhage, paracentral visual field loss, a larger cup disk ratio, and retinal nerve fiber layer (RNFL) thinning.³

Case studies in identifying glaucoma with OCTA

The following case studies show OCTA findings which were clinically relevant for Dr. Richter’s management of glaucoma patients. They demonstrate how OCTA complements OCT and visual field testing, and can help identify cases of glaucoma or progression where these other modalities are limited.

Case 1: Detecting very early POAG

Here we see OCT and disc photos in a patient whose visual field was normal. However, the OCTA revealed a superotemporal Y-shaped defect in the right eye, signaling glaucoma damage. These data suggested pre-perimetric glaucoma, or very early primary open-angle glaucoma (POAG), in this patient.

Figures 3, 4, and 5: Fundus photography, OCT, and OCTA imaging of the patient.

^{Figure 3: Courtesy of Grace Richter, MD.}

^{Figure 4: Courtesy of Grace Richter, MD.}

^{Figure 5: Courtesy of Grace Richter, MD.}

Case 2: Detecting early POAG

This patient has a strong family history of glaucoma, normal visual field, and OCT with some non-specific areas of thinning. Upon examination, there was a disc hemorrhage as shown on the fundus photo supertemporally in the left eye. The OCTA showed a focal wedge defect in that supertemporal location, supporting a mild preperimetric POAG diagnosis.

Figures 6, 7, and 8: Fundus photographs of the patient OD and OS as well as a comparison of the visual field testing and OCTA imaging.

^{Figure 6: Courtesy of Grace Richter, MD.}

^{Figure 7: Courtesy of Grace Richter, MD.}

^{Figure 8: Courtesy of Grace Richter, MD.}

Case 3: Finding structure function correlation

The visual field for this patient showed an inferior nasal step, however the OCT vaguely showed some inferior thinning. Unexpectedly, there was no superior nerve thinning that is expected with an inferior visual field defect.

The OCTA revealed a pathognomonic supertemporal wedge defect that correlates with the inferior nasal step on the visual field exam. The disc photo also showed a supertemporal wedge defect to help explain the loss of microvasculature in that area. This ultimately led to a diagnosis of moderate POAG in the left eye.

Figures 9, 10, 11, and 12: OCT imaging, visual field testing (OS and OD, respectively), OCTA, and fundus imaging of the patient.

^{Figure 9: Courtesy of Grace Richter, MD.}

^{Figure 10: Courtesy of Grace Richter, MD.}

^{Figure 11: Courtesy of Grace Richter, MD.}

^{Figure 12: Courtesy of Grace Richter, MD.}

^{Figure 13: Courtesy of Grace Richter, MD.}

Case 4: Identifying progressing in NTG

Here is a patient with normal-tension glaucoma (NTG). The left eye is more advanced with a large inferior focal wedge defect. The OCTA showed the progression in the right eye over 1.5 years. While the OCT showed modest thinning, the OCT-A demonstrated the narrow but very deep microvasculature defect that worsened over time. Since all other treatment measures had failed, they proceeded with a trabeculectomy.

Figures 12, 13, 14, and 15: OCT imaging OD and OS, respectively, and visual field testing and OCTA imaging from March 2019 to November 2020.

^{Figure 12: Courtesy of Grace Richter, MD.}

^{Figure 13: Courtesy of Grace Richter, MD.}

^{Figure 14: Courtesy of Grace Richter, MD.}

Limitations and future directions

Dr. Richter says a major limitation is that artifacts appear in OCTA images.^4,5 This is often a motion artifact, since patients must remain very still for much longer than with OCT. Additionally, OCTA is very sensitive to floaters blocking the signal. This causes focal areas with a falsely low signal.

Typically with glaucoma, segmentation affects the superficial microvasculature supplying the RNFL. So just as OCT scans are subject to segmentation error—for example, in patients with peripapillary atrophy—the same limitation can occur with OCTA.

In myopic glaucoma patients, OCT shows diffuse RNFL-thinning specific microvascular dropout. However, OCT is often limited by the measurement floor, where the measurements are no longer thinning but there is continued glaucoma progression. Studies demonstrate that OCTA may be helpful in these advanced cases.^6,7

There are also promising studies demonstrating how OCTA is also useful in studying vascular pathophysiology in different phenotypes of glaucoma.^8,9

Conclusion

Despite the limitations, good quality OCTA images have given Dr. Richter a better understanding of her patient’s glaucoma status and help to guide her management. While not a replacement for structural OCT imaging, OCTA is a fantastic complimentary tool to incorporate into your practice.

This article was written by Mariel Mohns, MS, based on the recorded video from Dr. Richter.