Using microscope-integrated intraoperative OCT in VR surgery

By Michelle Dalton, ELS; Reviewed by Justis Ehlers, MD

Cleveland-Intraoperative optical coherence tomography (OCT) that works in real-time can be an invaluable resource for surgeons, said Justis Ehlers, MD.

However, the optimal platform for OCT integration into ophthalmic surgery remains unknown, said Dr. Ehlers, a staff physician on the vitreoretinal service of the Cole Eye Institute, Department of Ophthalmology, Cleveland Clinic.

Discover study

Dr. Ehlers and colleagues are conducting a prospective, multisurgeon, single-center study-the DISCOVER Study-examining the use of multiple microscope-integrated prototypes with real-time surgeon feedback through a heads-up display system, including the Rescan 700 (which is built into the Lumera 700 platform, Carl Zeiss Meditec) and a Cole Eye Institute iOCT System. The DISCOVER Study evaluated both anterior and posterior segment surgery.

“The Rescan 700 is a prototype microscope-integrated iOCT system that is based on the Lumera 700 platform that includes heads-up display of the OCT data stream for the surgeon,” said Dr. Ehlers, who discussed the vitreoretinal surgery component.

The interim 4-month analysis included 114 eyes (78 of which presented with vitreoretinal surgery needs). Average age was 61 years, and 47% of the patients were male.

Intraoperative OCT image acquisition was achieved in 77/78 eyes that underwent vitreoretinal surgery (99%). Surgical indications included epiretinal membranes, macular holes, vitreomacular traction, retinal detachment, and IOL subluxation. Of those eyes, 45 (58%) were phakic, 29 (37%) were pseudophakic, and four (5%) were aphakic.

Retinal detachment and epiretinal membrane were the most frequent diagnoses (23% and 31%, respectively). Vitreoretinal imaging was accomplished with both non-contact wide-angle and a contact lens viewing system.

Heads-up display system

“Initially, surgeons may have challenges adapting to the heads-up display system while performing particularly delicate manueuvers,” Dr. Ehlers said, but he believes this is primarily attributed to the typical learning curve rather than a true deterrent to the system.

Additionally, at any time the heads-up display and OCT imaging system can be turned off during surgery with foot-pedal surgeon control, he said.

“Generally, there was rapid adaption,” he said. “Surgeons using this system included a wide range of surgical experience from 20 years-plus to first-year retina fellows.”

The heads-up display system provided real-time feedback to the surgeon regarding anatomic configurations during surgery and allowed for visualization of instrument-tissue interactions. The overwhelming number of surgeons preferred the heads-up display and real-time data acquisition.

However, in 5% of cases, the device was judged to interfere with the case, Dr. Ehlers said.

Several adverse events occurred during the surgical procedures, such as elevated IOP and epithelial defects. However, no adverse events were directly attributed to the iOCT system.

“In addition to cost, the only real disadvantage to the system is the potential for increased time of surgery,” Dr. Ehlers said. “On the other hand, there are certain cases where the system speeds up the surgery because it confirms the surgeon has done everything he or she needed to do before the surgeon necessarily knew it. You’re potentially able to end surgery more quickly.”

Changing surgical strategies

Residual membranes, occult formation of full-thickness macular holes, and confirmation of optimal IOL position were identified with the iOCT system resulting in alterations to the surgical decision-making process. (See Images A, B, and C on Page 24 for examples of the images obtained intraoperatively.)

The iOCT showed residual membrane requiring additional peeling in 14% of cases (5/36) where the surgeon believed peeling was complete. There was complete membrane peel in 11% of cases (4/36) where the surgeon thought additional peeling was necessary.

The real questions that we want to answer, suggested Dr. Ehlers, are: How does iOCT impact long-term patient outcome, and what outcomes would these patients have had without the iOCT?

Until there are “masked, randomized trials, we’re not going to know the definitive answer,” he said, adding the Cole Eye Institute group is in the planning stages for those studies.

Coincidence?

“Re-proliferation or recurrence of epiretinal membrane is typically thought to occur in the 5% to 15% range,” he said. “What if, in fact, surgeons aren’t getting OCTs until the postoperative 3-month time frame, and they come to the conclusion that there was re-proliferation? But what if they just didn’t get it all during the original surgery? Our preliminary data seems to support that in around 10% of cases, surgeons are not realizing that residual membranes are present without iOCT.”

While acknowledging it’s still too soon to make a definitive statement, the DISCOVER study comprised surgeons with all levels of experience yet still found 14% of peels were incomplete based on iOCT data.

“This is a number that keeps popping up,” he said. “Our PIONEER study that was recently published (2-year results with more than 500 patients) used an external microscope-mounted intraoperative OCT and we found similar numbers there, too-in about 15% of epiretinal membrane cases, the OCT revealed membranes the surgeon thought had been removed.”

Through the use of iOCT, “we are learning that we don’t understand what all is going on in the eye when we’re manipulating it with surgery,” Dr. Ehlers said. “We have a lot of things to learn about what our surgical manipulations do to the architecture of the eye and how those subtle architectural alternations may have implications for outcomes.

“The technology may be in a similar stage to when OCT was first introduced in the clinic,” he said. “Many people didn’t believe that it would pay a significant role in the clinical care of vitreoretinal patients, and now we’re using it on 70% of our patients who come through our clinics. We still have a lot to learn about the benefits of this technology.”