Real-World Application of Microscope-Integrated 400 kHz Swept-Source Intraoperative OCT in Ophthalmic Surgery

1. Introduction

The introduction of optical coherence tomography (OCT) has profoundly transformed both the diagnosis and management of retinal diseases by providing non-invasive, high-resolution, cross-sectional images of retinal structures since 1991 [1]. The first microscope-integrated intraoperative OCT research system was demonstrated in 2010, by coupling a spectral-domain OCT (SD-OCT) device into the infinity space between the eyepiece and the objective of a commercial surgical microscope [2].

In 2013-2014, commercialized products such as the Leica Enfocus and Zeiss Rescan 700 was established, heralded the technology’s arrival as a mature feature for ophthalmic surgical microscopes. However, these systems all utilized SD-OCT which has limited imaging speed and depth. [3] Lu et. al. at 2018 demonstrated a 400 kHz SS-OCT intraoperative system employing post-objective injection of the OCT light, however this system lacked real time visualization [4].

Ophthalmic microsurgery is traditionally performed using stereomicroscopes and requires visualization and manipulation of sub-millimeter tissue structures with limited contrast. While there has been substantial progress in both research and commercialization efforts to bring OCT imaging into live surgery, its use is still somewhat limited due to factors such as low imaging speed, limited scan configurations, and suboptimal data visualization [5].

Recently implemented at our institution, a microscope-integrated 400 kHz swept-source intraoperative OCT (SS-iOCT) system enables real-time, high-resolution visualization of both anterior and posterior segment structures. We report its clinical utility by analyzing a series of 72 real-world surgical cases, detailing its application and discussing the specific intraoperative benefits it provides.

2. Materials and Methods

In this observational study, we analyzed surgical videos and data from 123 consecutive cases that underwent elective surgery with the assistance of this SS-iOCT system at Beijing Tongren Hospital between September 2, 2025, and February 10, 2026.

Surgical cases were included based on specific diagnoses for which the SS-iOCT was found to be demonstrably useful. A total of 72 cases met the inclusion criteria, comprising: 7 intraocular lens implantations with ciliary sulcus fixation, 19 macular holes, 3 cases of macular hole retinal detachment (MHRD), 4 cases of macular schisis with or without foveal detachment (MSRD), 12 cases of submacular hemorrhage, 20 cases of rhegmatogenous retinal detachment (RRD), and 7 intraocular mass lesions. Conversely, patients with a primary diagnosis of tractional retinal detachment (TRD), silicone oil removal, epiretinal membrane (ERM), or cataract were excluded from this analysis.

This study followed the tenets of the Declaration of Helsinki for research involving human subjects. Informed consent was obtained from all subjects to use the data for the study.

2.1. Images Selection and Evaluation

All surgeries were performed by a single expert surgeon (Wang ZY) using the TowardPi BO 4K ultra HD microscope integrated with a 400 kHz SS-iOCT system. The SS-iOCT operates at a wavelength of 1060 nm and provides an A-scan depth of 12 mm, an axial resolution of 7 µm (at 12 mm depth), and a scan length of 20 mm. The scanning modes include single-line scan, cross-line scan, five-line scan, radial scan, 3D scan, and 4D scan.

During surgery, intraoperative OCT provided the surgeon with clear visualization and guided surgical decision-making. For the fellow surgeons participating in the procedure, it additionally served a demonstrative and educational purpose. After the surgery, two physician (Zhang XF and Liu S) selected the clearest surgical video frames and OCT images from the recorded footage for presentation in the results section.

2.2. Statistical Analysis

The collected data encompassed patient demographics, surgical indications, procedure types, and specific intraoperative maneuvers performed. Statistical analysis was conducted using the Statistical Package for the Social Sciences (SPSS, version 27.0; IBM Corp., Chicago, IL, USA). Numerical variables are presented as mean ± standard deviation (SD), while categorical variables are expressed as frequencies and percentages. No advanced statistical analysis was performed. Additionally, the surgeon provided a qualitative assessment of the intraoperative images.

3. Results

Among 72 patients, 39 were male (54.2%) and 33 were female (45.8%), with a mean age of 55.8 years (range: 18–86 years).

3.1. Application in Anterior Segment Surgery

In anterior segment surgery, SS-iOCT provides “Mendez Ring” and reveals peripheral angle structures. In cases involving anterior segment anomalies, it clearly visualizes corneal, iris, and angle abnormalities, allowing immediate confirmation of surgical outcomes after peripheral synechialysis (Figure 1).

3.2. Application in Cataract Surgery

During phacovitrectomy surgery, SS-iOCT clearly delineates surgical steps, proving especially beneficial for teaching. This includes visualizing corneal incisions, hydrodissection and hydrodelineation, observing anterior and posterior capsule positions, and intraocular lens (IOL) implantation. Moreover, even when air bubbles in the anterior chamber obscure the IOL position to the naked eye following combined surgery with air-fluid exchange, SS-iOCT can accurately determine the IOL location (Figure 2).

3.3. Application in IOL Ciliary Sulcus Fixation

SS-iOCT was used to assist intraoperative surgical guidance in 7 patients (9.7%) undergoing IOL ciliary sulcus fixation. Among them, 3 were male and 4 were female. The mean age was 61.3 years (range: 42–73 years), and the mean axial length was 29.14 mm (range: 28.14–32.95 mm). SS-iOCT enabled real-time monitoring of manipulations within the anterior chamber, helping to prevent inadvertent contact between surgical instruments or a dislocated IOL and the corneal endothelium, thereby reducing the risk of corneal endothelial damage. During IOL fixation, adjustments were made based on the IOL position along two perpendicular meridians to ensure optimal IOL placement and minimize postoperative astigmatism (Figure 3).

3.4. Application in Rhegmatogenous Retinal Detachment (RRD)

Twenty (27.8%) eyes diagnosed with rhegmatogenous retinal detachment (RRD) were treated. Among them, 14 were male and 6 were female, with a mean age of 44.9 years (range: 18–66 years) and a mean axial length of 27.6 mm (range: 23.14–33.17 mm).

In one patient undergoing scleral buckling with a 25G endoilluminator, intraoperative OCT revealed shallow retinal detachment in the inferior degenerative area outside the primary detachment zone, guiding intraoperative adjustment of the buckling extent and contributing to improved primary success rate.

In RRD surgeries associated with pathological myopia, intraoperative OCT assisted in evaluating macular structure against a background of diffuse posterior pole atrophy, determining the presence of a macular hole and the status of the macula, thereby guiding the decision to perform either internal limiting membrane (ILM) peeling or fovea-sparing ILM peeling.

In RRD associated with chorioretinal coloboma, retinal structures within the colobomatous area—including critical landmarks such as the optic disc, macula, and retinal breaks—were frequently indistinguishable. iOCT provided real-time imaging, allowing detailed scanning and observation of targeted regions beyond the capabilities of preoperative conventional OCT. However, structural identification in colobomatous eyes remains challenging and warrants further investigation (Figure 4).

3.5. Application in Primary or Recurrent Macular Hole (MH)

Nineteen eyes (26.4%) diagnosed with primary or recurrent macular hole (MH) were treated. Among them, 7 were male and 12 were female, with a mean age of 64.9 years (range: 48–77 years), a mean axial length of 25.3 mm (range: 22.32–34.29 mm), and a mean MH diameter of 533.5 µm (range: 128–2227 µm). Postoperatively, one MH failed to close, yielding a primary closure rate of 95%.

In primary MH, the value of intraoperative OCT (iOCT) was primarily educational. However, in refractory or recurrent MH, iOCT provided critical intraoperative guidance for determining the precise positioning of the internal limiting membrane (ILM) insertion, with adequate ILM insertion contributing to improved hole closure rates.

In lamellar macular hole, iOCT offered surgeons additional anatomical information, facilitating assessment of macular configuration and serving as a valuable teaching tool (Figure 5).

In the surgical management of a giant recurrent macular hole (2227 µm) with amniotic membrane insertion technique, iOCT clearly demonstrated the insertion process, and macular architecture remained well visualized following gas-fluid exchange (Figure 6).

3.6. Application in Myopic Traction Maculopathy (MTM)

Seven eyes (9.7%) with myopic traction maculopathy (MTM) were treated, including 3 eyes diagnosed with macular schisis, 3 eyes with macular hole retinal detachment (MHRD), and 1 eye with foveal detachment (MSRD). Among them, 2 were male and 5 were female, with a mean age of 51.9 years (range: 36–73 years) and a mean axial length of 29.4 mm (range: 25.84–32.48 mm). The challenge of performing macular surgery in highly myopic eyes lies in clearly identifying macular structures. Therefore, SS-iOCT proved extremely helpful in MTM surgeries. Moreover, SS-iOCT maintained clear imaging under various conditions, such as in the presence of ICG (Indocyanine green) dye, absence of endoillumination, or even when the microscope illumination was turned off (Figure 7).

3.7. Application in Subretinal t-PA Injection

Among the 12 cases (16.7%) of submacular hemorrhage (SMH) treated with PPV + ILM peeling + subretinal t-PA (tissue-type plasminogen activator) injection, there were 8 cases of polypoid choroidal vasculopathy (PCV), 1 case of retinal macroaneurysm, and 1 case of secondary macular hemorrhage due to laser injury. The cohort included 8 males and 2 females, with a mean age of 59.75 years (range: 19–86 years).

In one patient with subretinal hemorrhage complicated by vitreous hemorrhage, SS-iOCT) clearly demonstrated the anterior hyaloid membrane and sand-like opacities within the anterior vitreous. The turbid anterior vitreous obscured the fundus view; during anterior hyaloid membrane dissection, SS-iOCT assisted in anatomical identification, thereby preventing posterior capsular injury. During subretinal t-PA injection, intraoperative OCT enabled real-time tracking of the 41G needle tip, confirmed that the medication was delivered into the subretinal space, and guided the injection volume (Figure 8).

3.8. Application in Intraocular Mass

Seven eyes (9.7%) diagnosed with intraocular mass were treated. Among them, 5 were male and 2 were female, with a mean age of 54.7 years (range: 18–83 years). The use of intraoperative OCT enabled the real-time visualization and documentation of findings unseen on preoperative exams, capturing valuable data including tumor-associated retinal pigmentation (TARP) and the tumor’s relationship with surrounding tissues. (Figure 9 and Figure 10).

4. Discussion

In this study, we descriptively report the advantages and feasibility of microscope-integrated 400 kHz SS-iOCT in managing various ophthalmic diseases in a real-world setting. From its role in surgical teaching using routine cases to its application in complex surgical scenarios, we have accumulated experience across a wide spectrum of anterior and posterior segment diseases. Additionally, we provide the first report on the application of SS-iOCT in intraocular tumors.

Intraoperative OCT is utilized in a wide range of retinal procedures, including retinal detachments [6,7,8], epiretinal membrane (ERM) peeling [9,10] macular hole surgery (e.g., human amniotic membrane grafting, [11] VMT [12], optic disc pit maculopathy [13],subretinal gene therapy delivery, pediatric retinal surgeries, high myopia [14] and IOL positioning [15,16]. It provides surgeons with immediate feedback on tissue architecture, instrument-tissue interactions, and the completeness of surgical maneuvers, thereby directly influencing surgical decisions, especially in complex cases. [6,14,17].

In our experience, intraoperative OCT is valuable for surgical demonstration and teaching in routine procedures. In anterior segment surgeries, it helps visualize pathologies such as anterior synechiae, posterior synechiae, and the success of goniosynechialysis. In cataract surgery, it clearly demonstrates surgical steps including corneal incision, hydrodissection and hydrodelineation, and IOL positioning. In vitrectomy, it enables visualization of posterior vitreous detachment (PVD) and the covering or plugging of ILM flaps.

In complex cases, intraoperative OCT assists surgeons in intraoperative decision-making, contributing to improved surgical success rates. For instance, during IOL ciliary sulcus fixation, it confirms optimal IOL positioning, helping to reduce postoperative astigmatism and enhance visual outcomes. In macular hole surgery, it verifies successful ILM or amniotic membrane insertion, with adequate ILM insertion contributing to improved hole closure rates [18,19]. In pathological myopia, structures difficult to assess intraoperatively—such as macular architecture in the setting of diffuse posterior pole atrophy—can be clearly visualized with OCT, including in eyes with axial lengths up to 34mm. In choroidal coloboma, the absence of typical choroidal architecture complicates retinal break localization, making surgery more challenging. Intraoperative OCT helps by aiding in the identification of retinal structures [20].

Furthermore, intraoperative OCT captures images not typically obtained during routine preoperative scans. For example, it provides detailed imaging of the lens–anterior vitreous interface—an area often overlooked between routine anterior segment and macular OCT examinations. In PCV cases, intraoperative OCT offers clear visualization during anterior hyaloid removal, helping to avoid inadvertent damage to the posterior capsule. In eyes with intraocular tumors, it provides valuable imaging data, documenting retinal changes not typically captured on routine OCT, and enables real-time observation and documentation of intraoperative findings.

We report, for the first time using intraoperative OCT, the detection of subretinal pigmentary alterations secondary to retinal detachment associated with uveal melanoma (UM), which are referred to as tumor-associated retinal pigmentation (TARP). These alterations resemble those previously described in the literature, and electron microscopy has identified them as RPE cells containing melanolipofuscin granules. [21,22,23,24]。

Swept-source optical coherence tomography (SS-OCT), including systems like TowardPi, is transforming intraoperative imaging during vitrectomy by providing high-speed, high-resolution, and deep-penetration visualization of anterior segment and vitreoretinal structures. TowardPi system allow real-time overlay of OCT data on surgical fields, improving ergonomics and efficiency [25,26]. The OCT image quality is minimally affected by potential intraoperative interferences, such as the presence of ICG dye, absence of illumination, or the presence of vitreous or anterior chamber gas bubbles. Additional functional features, such as the “Mendez Ring”, enable more precise refractive surgeries, including considerations for toric IOL implantation and ICL procedures.

This study has limitations inherent to its observational design based on a consecutive case series. Moving forward, we aim to accumulate additional cases and clinical experience to further explore valuable applications of SS-iOCT. Alternatively, future studies may incorporate control groups to quantitatively assess the impact of SS-iOCT on improving surgical success rates. This report reflects the real-world clinical implementation of an emerging technology, and as its use expands, additional clinically relevant signs and applications are likely to be identified.

5. Conclusions

In conclusion, this real-world study demonstrates the broad utility and feasibility of intraoperative SS-iOCT across a diverse spectrum of ophthalmic surgeries. While this observational study highlights the real-world clinical value of an emerging technology, future research will further expand its impact on surgical outcomes and uncover additional applications.