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Retinal Physician

Article

Current Applications of Intraoperative Optical Coherence Tomography in Retinal Surgery

Recent advances could broaden its use.

By: KAREN MATAR, MD, Jacob T. Cox, MD, MPhil, Katherine E. Talcott, MD
Retinal Physician July 1, 2023 Vol 20, Issue July/August 2023 Page(s): 35-37

From the Archives

Optical coherence tomography (OCT) has revolutionized ophthalmic care. It is integral to the preoperative and postoperative evaluation of patients. Yet, intraoperatively, most surgeons are without this tool and are wholly reliant on the surgical microscope’s illuminated en face view for surgical maneuvers and decision making.

Intraoperative OCT (iOCT) serves to provide surgeons with the same cross-sectional and tomographic data that proves so critical in clinic.1 Since its advent in 2005, there have been notable advances in iOCT technology, ranging from early stand-alone time-domain systems to modern microscope-integrated systems equipped with heads-up diplays.2 The technology enables surgeons in real time to discern between retinal structures and evaluate for the presence or absence of subtle but key anatomic features, which can guide surgical decision-making. In fact, 2 large prospective clinical trials, PIONEER and DISCOVER, demonstrated that iOCT may alter intraoperative decision-making in a significant percentage of anterior-segment and posterior-segment surgeries.3,4 This article will discuss the evolution over time, various applications, and role in modern vitreoretinal surgery of iOCT.

HISTORY

The first use of iOCT was in 2005, when a time-domain OCT was used for real-time visualization of anterior-segment structures during lamellar keratoplasty and trabeculectomy.5 This initial experimental system worked by coupling a commercially available optical coherence tomograph to the front lens of a standard surgical microscope using a beam splitter.5

In 2007, the first portable OCT probe was developed for use intraoperatively using standard domain technology.6 These handheld systems allowed for high-quality 2-dimensional OCT imaging, but the handheld probes came with several limitations. Firstly, they were separate from the surgical microscope, and thus surgery had to be paused for image acquisition. Image reproducibility and optical aiming were limited. Motion artifact was common due to difficulty with imaging stabilization. Moreover, it was often difficult to maintain a sterile surgical field.

Thus, mounted systems were developed to provide improved stability. External mounts increased the system footprint and required additional operating room space. Microscope-mounted systems fastened the OCT probe directly to the microscope body. This not only improved stability but also allowed the foot pedal to control probe location and improve image reproducibility.4,7 However, all these systems required pausing surgery for image acquisition.4

The integration of OCT and microscope optics was the next major advancement in iOCT systems, providing real-time OCT-based visualization of instrument-tissue interaction and immediate imaging with surgeon feedback.8 Z-tracking and focus controls were incorporated into the device to improve the stability and quality of the captured images.2,9 There are currently 3 FDA-approved systems available: Haag-Streit iOCT, Zeiss Rescan 700, and Leica EnFocus, all of which employ spectral-domain OCT technology. Furthermore, newer systems are integrating swept-source technology and 3D heads-up display for improved functionality.

VITREORETINAL APPLICATIONS

Macular Surgery

The utility of iOCT has been extensively described in macular surgery. Intraoperative OCT can reveal residual membranes or completion of the membrane peel (Figure 1), potentially avoiding incomplete treatment or unnecessary surgical maneuvers.10 Studies have shown that iOCT can identify occult residual membranes in 12% of cases and are useful in confirming a completed membrane peel in 9% of cases.4 The DISCOVER trial showed a discrepancy between what surgeons perceived and what was actually present during the surgery. In 40% of cases where the surgeon believed there were residual membranes, iOCT showed complete removal of the membrane.3 Other studies have demonstrated that iOCT-assisted macular hole surgery achieved a single-surgery success rate of 97.6%, which was comparable to outcomes without iOCT.10-12

Figure 1. Intraoperative optical coherence tomography before (A) and after (B) a macular peel for a thick epiretinal membrane in the setting of proliferative vitreoretinopathy.
Figure 1. Intraoperative optical coherence tomography before (A) and after (B) a macular peel for a thick epiretinal membrane in the setting of proliferative vitreoretinopathy.

Furthermore, iOCT reduces reliance on intraocular dyes for peeling epiretinal membranes, potentially saving time, cost, and resources.13-15 According to 1 study, iOCT-guided membrane peeling was feasible in 40% of cases without the need for surgical staining agents.16 Intraoperative OCT has other benefits as well, such as determining the presence or absence of macular holes or evaluating for vitreous schisis.

Retinal Detachment

Intraoperative OCT during retinal detachment repair has proven to have many advantages, such as detecting residual subretinal fluid following perfluorocarbon liquid placement, identifying retinal breaks, and evaluating for proliferative vitreoretinopathy membranes. The DISCOVER trial revealed that, in RD repair, iOCT provided valuable feedback to surgeons in 36% of cases and altered surgical decision-making in 12% of cases.17 Intraoperative OCT provided valuable insight in complex redetachment cases compared to primary cases (50% vs 22%, P<.01).17

Proliferative Diabetic Retinopathy

Intraoperative OCT can be particularly insightful in cases with nonclearing vitreous hemorrhage where OCT cannot be used preoperatively (Figure 2).18,19 In these cases, media opacity can hinder preoperative surgical planning, but iOCT can identify surgical dissection planes intraoperatively.18 Intraoperative OCT has also been used to visualize cannula placement during viscodissection, to identify peripheral or macular holes/breaks, and to guide the selection of tamponade agents.18 A review of the DISCOVER study found that in surgery for proliferative diabetic retinopathy, surgeons considered iOCT to be valuable in 50.6% of cases and it influenced surgical decision-making in 26% of cases.18

Figure 2. Intraoperative optical coherence tomography showed subhyaloid macular hemorrhage during a proliferative diabetic retinopathy case.
Figure 2. Intraoperative optical coherence tomography showed subhyaloid macular hemorrhage during a proliferative diabetic retinopathy case.

Uveitis

In uveitis-related vitreoretinal surgery, iOCT serves several roles. It can provide valuable feedback during complex uveitic membrane peels.20 Intraoperative OCT can confirm the integrity of scleral wound closure during Retisert fluocinolone acetonide implant placement (Bausch + Lomb) in 84.6% of cases.20 Additionally, it is useful in 81.2% of chorioretinal biopsies by guiding biopsy site selection and ascertaining whether there is sufficient volume of subretinal material to enable a successful biopsy.20,21

Subretinal and Submacular Surgery

Subretinal gene therapy delivery risks complications such as hemorrhage, cannula tip obstruction, retinal pigment epithelium damage, or suprachoroidal delivery if the needle penetrates too deeply, and intraretinal hydration or retinoschisis if too shallowly.22 Several attempts to create a subretinal bleb can result in localized neurosensory retinal trauma and retinotomy enlargement. Intraoperative OCT can aid by evaluating for proper needle depth and guide bleb location by avoiding areas with high-risk features such as retinal atrophy or retinoschisis.22,23 Future iOCT systems may quantify bleb volume to more accurately dose subretinal therapies.24 Similarly, iOCT has also been used to administer subretinal injections of tissue plasminogen activator for submacular hemorrhage.25

LIMITATIONS AND CHALLENGES

Intraoperative OCT has shown promise in enhancing surgical outcomes in a range of vitreoretinal surgeries. However, there are several limitations to its use that warrant consideration. The light-scattering and shadowing effects of metal present a challenge for current iOCT systems when using metallic surgical instruments.1 Image acquisition can be affected by patient movement, eye movements, or instrument motion, leading to motion artifacts, image distortion, and reduced image quality. Current iOCT systems face difficulties in capturing images of the peripheral retina. Also, adoption is limited by cost, availability, and the fact that many ophthalmic surgeons simply do not perceive it as an essential tool for their routine clinical practice.26

FUTURE DIRECTIONS

As iOCT continues to gain traction, research and development efforts are focused on advancing its capabilities and expanding its applications. Ehlers et al in 2017 proposed the development of several OCT-compatible surgical instruments designed to facilitate real-time, image-guided surgeries and instrument stabilization.27

Recent advances include development of a 3D iOCT digital surgical system, which purports to improve surgical precision and enrich surgical education and training.28,29 Additionally, iOCT could be integrated into the Clarity visualization system developed by Beyeonics Surgical, whereby surgeons wear a head-mounted display that uses augmented reality to generate an image.29

Duke University has developed a prototype of iOCT technology that uses swept-source and 4-dimensional iOCT to provide real-time volumetric imaging. This latest technology allows for better visualization of tissue deformation and instrument motion, reducing the need for constant object tracking.30,31

Ongoing technological developments are investigating OCT-guided robotic systems.32 Cereda et al examined the utility of an instrument-integrated OCT-based distance sensor in vitreoretinal surgery, assessing its potential to improve accuracy and efficiency during surgical procedures.33

CONCLUSION

Over the past decade, the capabilities of iOCT have advanced significantly. There is mounting evidence that iOCT can guide surgical maneuvers and intraoperative decision making in various cases. It may reduce unnecessary surgical steps, shorten surgical time, and lead to improved and safer outcomes. While further research is needed to continue improving iOCT applications and analyzing its long-term impacts, ongoing advances in iOCT technology are likely to lead to more widespread acceptance and usage among vitreoretinal surgeons. RP

Karen Matar, MD, is a postdoctoral research fellow in ophthalmology at Cleveland Clinic in Cleveland, Ohio. She reports no relevant disclosures. Jacob T. Cox, MD, MPhil, is a vitreoretinal surgery fellow at Cole Eye Institute. He reports no relevant disclosures. Katherine E. Talcott, MD, FASRS, is an associate program director of the ophthalmology residency and an assistant professor of ophthalmology at Cleveland Clinic Lerner College of Medicine Cole Eye Institute of Cleveland Clinic. She reports consultancy to Alimera, Apellis, Bausch + Lomb, and EyePoint Pharmaceuticals; consultancy to and speaking for Genentech; speaking for Iveric Bio; and research for Regeneron, Regenxbio, and Zeiss. Reach Dr. Talcott at talcotk@ccf.org.

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