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Optometric Management

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Know the Many Functions of OCT-A

A review of this latest modality, and what it can offer both patients and practices.

By: JENNA PYLE, OD, SCOT MORRIS, O.D., F.A.A.O.
Optometric Management June 1, 2022 Vol 57, Issue June 2022 Page(s): 28, 30, 32, 33

Optical Coherence Tomography (OCT) has a wide variety of functions and modalities which can be better utilized in the optometric practice. One of the modalities introduced more recently, OCT-Angiography (OCT-A) offers many benefits in terms of detecting disease and monitoring disease progression.

In the article below, we review how to best use this new modality in your clinic.

WHAT IS OCT-A?

OCT-Angiography (OCT-A) is a newer, non-invasive technology which can be very beneficial in detecting early stages of neovascularization, ischemia, diabetic retinopathy (DR) throughout the posterior pole, and many vitreoretinal interface disorders including the various stages of macular holes, lamellar holes, epiretinal membranes, and more.

OCT-A functions by imaging movement of fluid in the vasculature within the three capillary areas in the eye: the superficial capillary plexus between the nerve fiber layer and ganglion cell layer, the middle capillary plexus between the inner plexiform layer and inner nuclear layer, and the deep capillary plexus (DCP) between the inner nuclear layer and outer plexiform layer.1

One of the more important areas imaged by OCT-A is the foveal avascular zone (FAZ). The FAZ is the area of the fovea that lacks retinal vessels and has the highest concentration of cone photoreceptors, which produce central vision.2 A study by Morales et al retrospectively reviewed the FAZ of healthy patients of a variety of ages and determined that the FAZ measurements by OCT-A are reproducible between observers and increases with age, meaning the FAZ is an accurate measurement tool to be used to monitor various ocular conditions.2 The larger the FAZ, the larger the central vision loss.3

While OCT-A does not replace fluorescein angiography (FA), it is a fast and easy alternative without the risks of injecting dye into the patients. OCT-A can acquire images in seconds, whereas it can take 10-30 minutes to perform FA.1 According to a study by Hirano et al, OCT-A was 79% sensitive and 96% specific compared to FA in detecting non-perfusion areas or retinal neovascularization.4 Another study by Sawada et al showed that wide-angle OCT-A was 100% sensitive and 97% specific compared to ultra-wide field FA for detecting retinal neovascularization.5 These results indicate there is a strong indication to use OCT-A in the optometric practice when FA is not possible.

 

These images, from a review by Moir et al, show the decreasing vascular density measurements in patients who have diabetes sans retinopathy, and patients with increasing severity of DR seen on OCT-A.Image attribution: Moir, J., Khanna, S., & Skondra, D. (2021). Review of OCT angiography findings in diabetic retinopathy: Insights and perspectives. International Journal of Translational Medicine, 1(3), 286–305. https://doi.org/10.3390/ijtm1030017. Image used via open access under the Creative Commons Attribution License.
These images, from a review by Moir et al, show the decreasing vascular density measurements in patients who have diabetes sans retinopathy, and patients with increasing severity of DR seen on OCT-A.Image attribution: Moir, J., Khanna, S., & Skondra, D. (2021). Review of OCT angiography findings in diabetic retinopathy: Insights and perspectives. International Journal of Translational Medicine, 1(3), 286–305. https://doi.org/10.3390/ijtm1030017. Image used via open access under the Creative Commons Attribution License.

 

HOW IT CAN BE USED

Monitoring Diabetic Retinopathy

DR is considered one of the more common ocular conditions managed by optometrists. Diabetes affects the vasculature of the eye and can cause hemorrhaging and areas of exudates and ischemia, depending on the severity. The Early Treatment Diabetic Retinopathy Study (ETDRS) is the more common reference used to grade the severity of the diabetic retinopathy and is used in conjunction with macular OCTs in order to confirm the presence or absence of clinically significant macular edema (CSME).

A study by Schaal et all determined that using OCT-A allows earlier detection of DR, even before it is seen clinically on dilated exams or with fundus photography. The study shows that when the diabetic patient has an enlarged FAZ, this is associated with the beginnings of DR and the worsening of visual acuity.3,6 Using OCT-A can help clinicians guide the patients to seek care from their primary care doctor earlier, to better manage their diabetes.

Differentiating Between Ischemic or Non-Ischemic Central Retinal Vein Occlusions (CRVOs):

When a patient has been diagnosed with having a CRVO, it is important to differentiate between ischemic or non-ischemic CRVOs in order to finalize the treatment plan and schedule follow-up visits. Of patients with ischemic CRVOs, 60% will develop anterior neovascularization, which can lead to neovascular glaucoma; however there is very little risk for non-ischemic CRVOs to develop any neovascularization.7 Specifically, patients with 30-75 disc diameter areas of capillary non-perfusion are at high risk of developing neovascularization.7 OCT-As can show areas of severe capillary non-perfusion in the DCP, which is consistent with a diagnosis of an ischemic CRVO. This can aid clinicians to watch these patients more carefully than those with non-ischemic CRVOs.1,7

Diagnosing Early Choroidal Neovascularization (CNVMs):

Age-related macular degeneration is one of the main causes of patients developing CNVMs, however there are other possible causes such as presumed ocular histoplasmosis (POHS), angioid streaks, and more. CNVMs can be sight-threatening and cause significant ocular complications, including hemorrhaging and tractional retinal detachments.1 OCT-A can detect early neovascularization not easily clinically detected on dilated exams or with fundus photography. Active CNVMs on OCT-A will have lacy or sea-fan looking vessels, with possible branches between capillaries, and a hypo-intense halo surrounding the lesion.1 These findings can allow the clinician to help the patient seek care from a retinal specialist for treatment sooner rather than later.1

Looking for Further Reading on OCT-A?

TRY THESE OTHER RESOURCES FROM
Optometric Management:

OM publishes a regular newsletter on OCT called OCT Insights. Find the latest issue and the archives at https://www.optometricmanagement.com/newsletters/oct-insights .

Our glaucoma columnist, Austin Lifferth, OD, FAAO, recently wrote about how OCT-A can provide complementary and supportive information for glaucoma patients. Read his “Utilize OCT-A” column at bit.ly/OM0621Lifferth .

In “A Guide to OCT Angiography,” by contributing editor Karen Blum, several ODs discuss how OCT-A has benefited their practices, such as the OCT-A devices’ ease of use and image quality. Read this article at bit.ly/OMOCTAblum .

Determining Early Progression in Glaucoma:

While glaucoma can be detected on clinical exams and damage can be monitored with visual field tests and optic nerve OCTs, several studies have determined that OCT-A allows clinicians to see early changes indicating progression prior to any functional changes.8,9 One study showed the average rate of decline in macular vessel density over the course of 1 year was significantly higher in glaucomatous eyes than healthy eyes or eyes with suspected glaucoma.9 Specifically, there was a reduction in blood flow, capillary diameter, and vascular density in the glaucomatous eyes.8,9 Using OCT-A in the setting of glaucoma could allow clinicians to initiate treatment earlier in order to decrease the likelihood of any functional loss of vision by the patient.8,9

Monitoring Outcomes of Vitreoretinal Conditions:

Most vitreoretinal conditions can be detected with a clinical exam and with macular OCTs, including epiretinal membranes, the various stages of macular holes and lamellar holes, as well as vitreomacular traction and adhesion. In surgical cases, the visual outcome of primary pars plana vitrectomy and internal limiting membrane peel is not certain.10 It has been shown that OCT-A can allow clinicians to see if there is a reduction in the size of the FAZ after surgery, indicating a possible improvement in visual disruption from the retinal condition.10

UNDERSTANDING POTENTIAL DRAWBACKS

As when using any diagnostic technology, it is important to consider any limitations and improvements to be made. Because it is motion sensitive, OCT-A is dependent on the patient remaining very still — artifacts can develop with blinks, head movement, and saccadic eye movements.1 The OCT-A exam may be difficult for visually-impaired patients to complete, as the device requires patients to be able to reasonably fixate. Additionally, as this is not FA, the OCT-A has a more difficult time imaging the choriocapillaris than FA. Finally, as a newer technology, the OCT-A is still developing its database in regard to normative values for different sexes and ages.1 Despite these drawbacks, OCT-A is a great addition to any optometric practice and can aid in the diagnosis and treatment of many different ocular conditions

CONCLUSIONS

The options provided by OCT-A give practices many resources for diagnosing patients. The benefits OCT-A provides allows practices to diagnose ocular conditions early, allowing better preventative care and ocular disease maintenance. When it comes to eye health, it’s best not to leave any option on the table. OM

REFERENCES

  1. Onishi, Alex C., and Amani A. Fawzi. “An Overview of Optical Coherence Tomography Angiography and the Posterior Pole.” Therapeutic Advances in Ophthalmology, vol. 11, Jan. 2019, p. 251584141984024. DOI.org (Crossref), https://doi.org/10.1177/2515841419840249 .
  2. Morales, David, et al. “The Foveal Avascular Zone Area in Healthy Eyes Measured by Ocular Coherence Tomography Angiography Using a Full Spectrum Probabilistic Algorithm.” International Ophthalmology, vol. 41, no. 6, June 2021, pp. 2187–96. DOI.org (Crossref), https://doi.org/10.1007/s10792-021-01776-3 .
  3. Samara, Wasim A., et al. “Quantification of Diabetic Macular Ischemia Using Optical Coherence Tomography Angiography and Its Relationship with Visual Acuity.” Ophthalmology, vol. 124, no. 2, Feb. 2017, pp. 235–44. DOI.org (Crossref), https://doi.org/10.1016/j.ophtha.2016.10.008 .
  4. Hirano, Takao, et al. “Wide-Field En Face Swept-Source Optical Coherence Tomography Angiography Using Extended Field Imaging in Diabetic Retinopathy.” British Journal of Ophthalmology, vol. 102, no. 9, Sept. 2018, pp. 1199–203. DOI.org (Crossref), https://doi.org/10.1136/bjophthalmol-2017-311358 .
  5. Sawada, Osamu, et al. “Comparison between Wide-Angle OCT Angiography and Ultra-Wide Field Fluorescein Angiography for Detecting Non-Perfusion Areas and Retinal Neovascularization in Eyes with Diabetic Retinopathy.” Graefe’s Archive for Clinical and Experimental Ophthalmology, vol. 256, no. 7, July 2018, pp. 1275–80. DOI.org (Crossref), https://doi.org/10.1007/s00417-018-3992-y .
  6. Schaal, Karen B., et al. “VASCULAR ABNORMALITIES IN DIABETIC RETINOPATHY ASSESSED WITH SWEPT-SOURCE OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY WIDEFIELD IMAGING.” Retina, vol. 39, no. 1, Jan. 2019, pp. 79–87. DOI.org (Crossref), https://doi.org/10.1097/IAE.0000000000001938 .
  7. Senthil, Sirisha, et al. “Neovascular Glaucoma - A Review.” Indian Journal of Ophthalmology, vol. 69, no. 3, 2021, p. 525. DOI.org (Crossref), https://doi.org/10.4103/ijo.IJO_1591_20
  8. Daneshvar, Ramin, and Kouros Nouri-Mahdavi. “Optical Coherence Tomography Angiography: A New Tool in Glaucoma Diagnostics and Research.” Journal of Ophthalmic and Vision Research, vol. 12, no. 3, 2017, p. 325. DOI.org (Crossref), https://doi.org/10.4103/jovr.jovr_36_17 .
  9. Li, Fei, et al. “Association of Foveal Avascular Zone Area With Structural and Functional Progression in Glaucoma Patients.” British Journal of Ophthalmology, Apr. 2021, p. bjophthalmol-2020-318065. DOI.org (Crossref), https://doi.org/10.1136/bjophthalmol-2020-318065 .
  10. Bacherini, Daniela, et al. “OCT-A in the Management of Vitreoretinal Diseases and Surgery.” Asia-Pacific Journal of Ophthalmology, vol. 10, no. 1, Jan. 2021, pp. 12–19. DOI.org (Crossref), https://doi.org/10.1097/APO.0000000000000373 .
DR. PYLE is a recent graduate from the New England of Optometry and is currently completing her optometric residency at Georgia Eye Partners, specializing in ocular disease, refractive surgery, and specialty contact lens fits.

DR. PYLE is a recent graduate from the New England of Optometry and is currently completing her optometric residency at Georgia Eye Partners, specializing in ocular disease, refractive surgery, and specialty contact lens fits.

DR. MORRIS is the former chief optometric editor of Optometric Management magazine, an international speaker, educator, author and management consultant, who practices at Eye Consultants of Colorado, LLC, in Conifer, Colo.

DR. MORRIS is the former chief optometric editor of Optometric Management magazine, an international speaker, educator, author and management consultant, who practices at Eye Consultants of Colorado, LLC, in Conifer, Colo.

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