Three-dimensional (3D) heads-up viewing systems have been utilized and explored in various anterior and posterior segment ophthalmic surgeries.1,2,3,4
Currently available or upcoming 3D visualization systems include the following:
- TrueVision 3D System (TrueVision Systems Inc., Santa Barbara, CA, USA)
- NGENUITY 3D Visualization System (Alcon, TX, USA)
- ARTEVO 800 Series Microscope (Zeiss, Oberkochen, Germany)
- Beyeonics One Exoscope (Beyeonics, Haifa, Israel)
- SeeLuma (Bausch + Lomb, NJ, USA; Heidelberg Engineering, Heidelberg, Germany).
Overview of 3D heads-up viewing systems
The use of the TrueVision3D system was studied by Eckhardt et al., who reported the vast majority of 20 volunteers preferred the digital viewing method in the completion of high dexterity tasks over the traditional method.3
The NGENUITY viewing system utilizes a high dynamic range digital video camera which replaces the microscope oculars, displaying the surgical field through a 55-inch OLED 3D 4K monitor. Passive 3D polarized glasses are worn by the surgeon and staff to provide stereopsis.
Advantages of the heads-up viewing system
There are various advantages of the heads-up viewing system compared to the traditional optical microscope. Improved ergonomics and reduction of cervical and lumbar strain have been reported. Given the deleterious effects of chronic neck pain prominent in ophthalmology, the heads-up viewing system may promote increased longevity of surgical careers.5
Benefits of the heads-up system:
- The large display also allows for surgical trainees and staff to simultaneously view the case and enhance the learning and teaching experience.
- The digital display obviates the need for image inverters, laser filters, and beam splitters required for the safe operation of the microscope.
- Finally, various studies have found that digital brightness enhancement allows for decreased intensity of endoillumination, thus potentially reducing phototoxicity to the patient.3
Disadvantage of the heads-up system
There are relatively few disadvantages to using heads-up viewing systems. Older iterations of image rendering software used in 3D visualization systems came with minor latency between surgeons’ actions and the display on the monitor. It was advised that slower, more cautious movements should be used due to this delay.
However, studies have shown non significant difference in operating time between those using the heads-up display versus the traditional microscope.4 In addition, newer iterations of rendering software have largely eliminated any substantial or noticeable display latency.
Other potential disadvantages of utilizing an alternative to the traditional binocular microscope include the initial learning curve and its start-up cost. Lastly, to date, there is no difference in insurance reimbursement for the physician or surgery center when this new high cost technology is used.
An overview of intraoperative OCT systems
The topic of intraoperative optical coherence tomography (iOCT) has been explored in a previous article. In brief, currently widely available systems include the Leica EnFocus (Bioptigen/Leica Microsystems, Wetzlar, Germany) and the Zeiss RESCAN 700 (Carl Zeiss Meditec, Inc., Oberkochen, Germany).
The Prospective Intraoperative and Perioperative Ophthalmic ImagiNg with Optical CoherEncE TomogRaphy (PIONEER) study and the Determination of Feasibility of Intraoperative Spectral Domain Microscope Combined/Integrated OCT VIsualization During En Face Retinal and Ophthalmic Surgery (DISCOVER) study were prospective studies evaluating outcomes of various anterior and posterior segment surgeries using iOCT and whether the use of such technology impacted surgical decision making.6,7
Advantages of iOCT
Several advantages and use cases for iOCT have been reported. For example, iOCT can provide dynamic live or frame-by-frame feedback, which may lead to intraoperative changes in surgical approach.
Previously reported uses for iOCT include:6,7,8
- Confirmation of hole closure following full-thickness macular hole (FTMH) repair.
- Assessment of foveomacular contour to determine sufficient release of vitreomacular traction in epiretinal membrane (ERM) peel.
- Monitoring foveal integrity following membrane peel, such as during ERM peel or tractional retinal detachment (TRD) or proliferative vitreoretinopathy (PVR) repair.
- Assessing the presence of subclinical subretinal fluid following retinal detachment repair, as well as adequate drainage following subretinal hemorrhage evacuation.
- Visualization of proper needle positioning and plane during biopsy of a chorioretinal lesion or during delivery of subretinal gene therapy.
- Visualization of proper depth of dissection of the corneal stroma in deep anterior lamellar keratoplasty.
- Assessment of the presence of gas or fluid between host and donor interface during Descemet stripping automated endothelial keratoplasty (DSAEK) or Descemet membrane endothelial keratoplasty (DMEK).
Disadvantages of iOCT
The main disadvantage of iOCT is the limited size and resolution of the OCT image when viewed through the microscope oculars. Thus, many surgeons in the DISCOVER study preferred to utilize the external display to review the OCT, necessitating them to look away from the surgical field and limiting the ability of the surgeon to correlate “real-time” images with surgical maneuvering and planning.7
Similar to the 3D visualization systems mentioned above, there is no difference in insurance reimbursement for the physician or surgery center when this new high-cost technology is used.
Combining 3D visualization systems with iOCT
Combining 3D viewing systems and iOCT systems, in which the retinal anatomy is overlaid on top of the surgical field, is a novel technique that may enhance the value of iOCT. The main advantage of viewing iOCT with a heads-up display is improved resolution of the retinal anatomy compared with iOCT displayed through the microscope oculars, while also reducing the need for the surgeon to turn their gazes away from the operative field.
At the time of this review, few publications have reported outcomes of vitreoretinal surgeries using the integration of heads-up 3D viewing systems with iOCT. Ehlers et al. published the largest cohort of patients who underwent vitreoretinal surgery using this combination technique.9 This study coupled the Rescan 700 iOCT with the NGENUITY viewing system in seven patients undergoing vitreoretinal surgery. The cases involved three ERM peels, two FTMH repairs, one symptomatic vitreous opacity evacuation, and one traumatic retinal detachment (RD) with severe PVR.
The Rescan 700 was chosen for its ability to inject OCT datastream to the NGENUITY display system, showing scans at a resolution of 5.5μm through one of the observer’s eyes using the passive 3D polarized glasses. The retinal scans were displayed semi-transparently over the surgical field when a wider field of view was employed using the noncontact lens, while the scans were displayed over a black screen adjacent to the surgical field when a narrower field of view was employed using the high magnification contact lens.
Evaluating 3D visualization systems with iOCT
Surgeons found the OCT displayed over a black background easier to view. In this study, 100% of cases were performed with successful display of the iOCT images on the 4K display without the need to convert to the conventional microscope. Surgeons reported good contrast and image visualization while also reporting sufficient OCT resolution displayed onto the monitor without the need to look toward the external OCT display.9
Various advantages of iOCT were documented, including the confirmation of foveal integrity, identification of residual ERM, pre-operative evaluation of macular hole anatomy, and visualization of subclinical subretinal fluid after perfluorocarbon liquid infusion during PVR repair. There was no significant increase in operative time and no intraoperative adverse effects directly attributable to the visualization system.9 They also found that turning the iOCT on or off did not affect display latency.
Palacios also reported favorable outcomes following myopic schisis repair utilizing a similar combination viewing system with the NGENUITY.10 In this case, pre-operative OCT showed macular schisis with increased subfoveal macular thickness to 706μm, corresponding clinically to a visual acuity of 20/200.
Using the heads-up display and iOCT, pars plana vitrectomy and internal limiting membrane (ILM) peeling was successfully undertaken with post-operative OCT, showing improvement in subfoveal macular thickness and improvement in visual acuity to 20/40 at the 7-month follow-up. The author noted iOCT was useful for assessing ILM anatomy and visualization of resolution of vitreoretinal traction following surgery.10
At the time of writing of this article, no studies have directly compared iOCT paired with conventional optical microscope vs. 3D digital viewing systems.
Limitations of 3D viewing systems and intraoperative OCT
The main limitation of the widespread utilization of heads-up 3D visualization systems, iOCT, and their combination is the high cost of startup in terms of capital and manpower. At the time of this article, the NGENUITY system costs between $50,000 and $75,000, while the Zeiss Rescan 700 iOCT integrated surgical microscope costs between $31,000 and $52,000.
There is also the complexity of setup, the difficulty of training surgical staff in familiarization with the technology, and the increased number of hardware potentially consuming space in the operating room. This high initial cost may make it difficult for community practices to justify its purchase.
Conclusion
In this article, the current state of 3D visualization systems integrated with iOCT in vitreoretinal surgery was explored. Simultaneous semi-transparent or adjacent display of high-resolution live retinal scans onto a single large 3D display enhances the utility of iOCT while also providing ergonomic benefits.
While its widespread use is currently limited by high startup cost, this combination system may provide vitreoretinal surgeons with valuable real-time data that may critically alter intraoperative maneuvering and planning.
