Intraoperative optical coherence tomography (iOCT) represents one of the most significant technological advancements in retinal surgery in recent years.
This innovation directly integrates real-time, high-resolution, cross-sectional imaging into the surgical environment, enhancing the surgeon's ability to visualize tissue planes and anatomical structures during procedures.
Overview of optical coherence tomography (OCT)
Optical coherence tomography functions on principles similar to ultrasound but utilizes light waves rather than sound waves to generate detailed cross-sectional images of tissue layers.
The technology has been used regularly in clinical ophthalmology, providing diagnostic information for numerous retinal pathologies, including:
- Macular degeneration
- Diabetic retinopathy
- Retinal vein occlusion
- Epiretinal membranes
- Macular holes
Integrating this technology into the operating room environment allows surgeons to access high-resolution imaging in real-time during surgical procedures, potentially improving decision-making and surgical outcomes.
Landmark studies of iOCT
The clinical utility of iOCT has been systematically evaluated through several landmark studies. The PIONEER (Prospective Intraoperative and Perioperative Ophthalmic Imaging with Optical Coherence Tomography) trial was the first investigation into the feasibility, safety, and clinical utility of iOCT technology.1
This study demonstrated that iOCT imaging was feasible across a wide range of anterior and posterior segment surgical procedures, establishing the foundation for subsequent research in this field. One subset of the PIONEER trial examined the application of iOCT during pars plana vitrectomy with subretinal tissue plasminogen activator (tPA) injection to treat subretinal hemorrhage.
In all four eyes evaluated, iOCT imaging was successfully performed, and valuable surgical feedback was provided. The technology confirmed increased subretinal fluid in all cases and verified appropriate localization of tPA injection, providing surgeons with real-time confirmation of therapeutic delivery.1
Building on these initial findings, the DISCOVER (Determination of Feasibility of Intraoperative Spectral-Domain Microscope Combined/Integrated OCT Visualization During En Face Retinal and Ophthalmic Surgery) trial further expanded the investigation of iOCT technology.2 This study included 837 eyes, with 244 anterior segment and 593 posterior segment surgical procedures.
The DISCOVER trial demonstrated the feasibility of iOCT, with successful image acquisition in 820 eyes (98%). More significantly, in 352 posterior segment procedures, iOCT was reported to provide valuable information about surgical anatomy or procedural details that enhanced the surgeon's understanding of the operative field.2
One of the most significant results from the study showed that iOCT altered their intra-operative decision-making in 173 cases (29.2%), suggesting that this technology could impact surgical approach and technique meaningfully.1 This high rate of clinical impact across a diverse range of procedures demonstrates the potential value of incorporating iOCT into routine vitreoretinal surgical practice.
Macular surgery and membrane peeling
The DISCOVER trial revealed several specific scenarios where iOCT provided valuable feedback. Following posterior hyaloid elevation, iOCT imaging was performed in 95 cases.
In 15 of these cases, iOCT identified previously undetected full-thickness macular holes or other retinal breaks that significantly altered surgical management, including decisions regarding additional internal limiting membrane (ILM) peeling or selection of gas tamponade.1
In membrane peeling procedures, iOCT demonstrated utility in confirming the completeness of tissue removal. In 35 of 177 cases where surgeons believed membranes had been wholly removed, iOCT identified residual membrane tissue requiring additional intervention.
Conversely, in 38 of 95 cases where surgeons suspected residual membranes remained, iOCT confirmed complete membrane removal, allowing surgeons to avoid unnecessary additional maneuvers.1
Interestingly, despite the availability of real-time imaging capabilities, surgeons preferred static iOCT image capture over real-time acquisition in 86% of membrane peeling cases.1 This preference likely reflects the value of high-quality, static images for carefully assessing subtle tissue planes during these delicate procedures.
Retinal detachment surgery
In managing retinal detachment, iOCT provided insight in 65 of 120 cases by identifying significant persistent subretinal fluid that might have been overlooked using conventional visualization techniques.1 In 21 eyes with retinal detachments, the iOCT findings directly resulted in modifications to the surgical approach.
These modifications included improved localization of occult membranes and retinal breaks, as well as identification of residual perfluorocarbon liquid (PFCL) that might otherwise have remained undetected.1
A specific application in this domain was evaluated for removing subretinal perfluoro-n-octane during posterior segment procedures.3 Results demonstrated that iOCT provided real-time feedback that effectively guided surgical maneuvers to facilitate the complete removal of this material.
This application highlights the technology's utility in addressing challenging complications that may be difficult to visualize with conventional microscopy.
Diabetic vitreoretinopathy
Applying iOCT in proliferative diabetic retinopathy (PDR) cases has shown particular promise. In a study of 81 eyes with PDR, successful iOCT imaging was achieved in 80 cases (98.8%).4
In 41 cases, surgeons reported that iOCT provided valuable information that enhanced their understanding of the surgical field, including improved identification of dissection planes and detection of retinal holes that might have been missed.
Beyond enhancing visualization, iOCT directly altered surgical decision-making in 21 PDR cases, influencing determinations of membrane peel completion and selecting appropriate tamponade agents.1
The technology also helped differentiate fibrovascular proliferations from underlying retinal detachments—a distinction that can be challenging with conventional visualization techniques. Significantly, no adverse events were attributed to the iOCT system across this series, supporting its safety profile.
Chorioretinal biopsy
The DISCOVER trial also evaluated the utility of iOCT during chorioretinal biopsy procedures. Surgeons used the technology to assess retinal and choroidal lesions before incision, providing valuable information about lesion characteristics and optimal biopsy approach.5
During the biopsy procedure, iOCT facilitated proper positioning and depth assessment, potentially improving the diagnostic yield of the specimen while minimizing tissue trauma. In two cases where pre-operative OCT could not adequately evaluate retinal lesions, intra-operative OCT successfully provided the necessary visualization immediately before biopsy.5
Following the procedure, iOCT was also employed to assess retinal attachment and wound margin integrity, immediately confirming surgical success and potentially identifying complications requiring further intervention.1
Advanced applications of iOCT
The versatility of iOCT extends to highly specialized procedures. A 2015 case review investigated using iOCT to ensure proper positioning of Argus II Retinal Prosthesis implantation.6
Optimal placement of the device over the macula is essential in obtaining the best patient visual outcomes. Specifically, the technology assisted the surgeons with determining the distance between the implant and the retina, which was difficult with the microscope alone.
Integration of iOCT with other visualization technologies
The DISCOVER trial also explored the potential of combining iOCT with other visualization technologies. A subset of seven eyes with various pathologies—including epiretinal membranes (n = 3), macular holes (n = 2), and symptomatic vitreous opacity (n = 1)—underwent procedures utilizing both iOCT and 3D HUD technology.
In all cases, OCT images were successfully acquired and displayed on a 4K screen.7 Surgeons reported that the 4K screen provided enhanced visualization of OCT data compared to the semi-transparent ocular view available in some systems.
This integrated approach allowed all surgical personnel to simultaneously view both the OCT images and the surgical field—a significant advantage for educational purposes and team coordination.
The system facilitated the identification of subtle retinal alterations that might have been missed with conventional visualization. All procedures were completed successfully without complications, and no cases required reverting to traditional microscopy.6
The evolution of iOCT technology has focused on seamless integration into the surgical workflow. Early systems required pausing surgery and moving external devices into position to capture images—a cumbersome process that limited practical utility.
iOCT with the RESCAN 700 and EnFocus systems
More recent developments have integrated OCT systems directly into the microscope optical pathway, allowing for more efficient image acquisition without disrupting surgical flow. Systems such as the RESCAN 700 (ZEISS) and EnFocus (Leica Microsystems) represent this new generation of integrated technologies.
In evaluating the EnFocus system within the DISCOVER trial, successful images were obtained in 46 of 50 eyes (92%).1 In eight of these cases, surgical management was modified based on iOCT findings, further supporting the clinical impact of this technology.
Interestingly, despite advances in heads-up display technology, 68.6% of surgeons in the DISCOVER trial preferred viewing OCT images on an external screen rather than using a heads-up display within the oculars.1 In some circumstances, this preference may reflect the importance of image quality and the cognitive benefit of separating OCT data from the primary surgical view.
Conclusion
iOCT has unequivocally transitioned from a novel concept to an indispensable tool in the armamentarium of the modern retinal surgeon.
Its ability to provide real-time, high-resolution, cross-sectional imaging has fundamentally enhanced surgical visualization, refined intraoperative decision-making, and contributed to improved anatomical outcomes across a diverse range of vitreoretinal procedures, from macular surgery and membrane peeling to the management of retinal detachments and diabetic retinopathy.8
As this technology continues to evolve with more seamless integration into surgical workflows and advanced capabilities, its role is expanding into increasingly sophisticated applications. These include guiding the precise placement of retinal prostheses, enhancing the safety and efficiency of subretinal gene therapy delivery, and improving the accuracy of interventions in the peripheral retina.8
Ultimately, iOCT stands as a testament to the power of innovative imaging in advancing the frontiers of ophthalmic surgery, promising continued improvements in patient care and surgical excellence.
