Intraoperative OCT benefits anterior segment surgeries

With FDA clearance of three intraoperative OCT systems over the past 2 years, the technology is rapidly moving from potential to practice.

These microscope-integrated systems — the En-Focus intrasurgical OCT system (Bioptigen, a division of Leica Microsystems), the Rescan 700 (Carl Zeiss Meditec) and the iOCT (Haag-Streit) — allow for real-time, high-quality imaging that can influence surgical decision-making and potentially contribute to achieving better outcomes in anterior segment surgery.

“We are learning the advantages and disadvantages of each system. It is very much in the early period,” Justis P. Ehlers, MD, said. Ehlers is the Norman C. and Donna L. Harbert Endowed Chair for Ophthalmic Research at Cole Eye Institute and has used the EnFocus, Rescan 700 and two microscope-integrated systems built for research. The Rescan 700, in particular, “was designed as a complete integrated unit. Ergonomically, it is difficult to tell there is an OCT added to the microscope. The footprint is identical,” he said.

Image: Ehlers JP

In contrast, the EnFocus was initially built as a microscope add-on, allowing the user to fit it to a current microscope. But since last year when Bioptigen, a maker of OCT, was acquired by Leica, a maker of microscopes, “the technology has the potential to be integrated in an even more seamless way,” Ehlers said.

The iOCT system from Haag-Streit takes a different approach, according to Ehlers, in that it brings in the OCT through a camera port. “Thus, the overall change to the ergonomics is minimal,” he said. “But there are unique challenges with accessing the optical pathway through the side port.”

Usability and image quality

Although seamless integration with high value to patient outcomes is likely the ultimate goal of intraoperative OCT, two additional vital features from a systems standpoint are “usability and image quality,” Ehlers said. “A surgeon desires something that is fast and easy to direct to the area of interest for scanning. We also want to achieve high-quality images and high-quality feedback. The challenges around obtaining high-quality images in the operating room are so different than in clinic. You are dealing with factors such as blood and corneal edema that make the imaging environment suboptimal.”

The two areas of anterior segment surgery that hold the most promise for intraoperative OCT are lamellar keratoplasty and customizing IOL measurements, according to Ehlers. For deep anterior lamellar keratoplasty, “there is excitement about being able to visualize depth of dissection in real time and to identify the location of planes to create a successful big bubble,” he said. “Through enhancing the accuracy of big bubble creation and dissection, intraoperative OCT may also facilitate improved outcomes.”

Similarly, for Descemet’s membrane endothelial keratoplasty and Descemet’s stripping automated endothelial keratoplasty, “we have shown in some of our research that intraoperative OCT can be very helpful in identifying residual fluid between the graft and the host cornea,” Ehlers said. “This can have potential implications for interface haze and visual recovery time; intraoperative OCT may also play a role in dislocation rates of the grafts.”

OSN Cornea/External Disease Board Member Francis W. Price Jr., MD, believes the greatest application for intraoperative OCT to date has been with endothelial keratoplasty, either DSAEK or DMEK.

“It is helpful for DSAEK in that you can see if there is a separation between the donor and the recipient. That is kind of icing on the cake,” Price said. “With DMEK, you need to be extremely careful that you have the endothelial side turned toward the iris and the Descemet’s side toward the cornea. Intraoperative OCT allows you to see which way the graft is oriented, either without stain on the donor or if the cornea is cloudy and thick and hard to see through.”

Intraoperative OCT has also been helpful to Price with implantation of the Visian ICL (STAAR Surgical) because “intraoperatively we can check the vault,” Price said. “OCT provides us an idea if the vault is going to be appropriate or not for the lens implant.”

A third application of intraoperative OCT is for the positioning of a tube for glaucoma surgery. “The tube can be located though corneas that are slightly hazy in the periphery,” Price said. He has been using intraoperative OCT for more than 1 year, including a preapproval study for the Haag-Streit device.

Surgeon experiences

To date, Price has used the Zeiss and Haag-Streit systems, for which the learning curve for the surgeon is minimal. “It is like a point-and-click camera,” he said.

What Price likes about the Zeiss device is that it has a few modes and an x- and y-axis to better provide a cross section through the tissue.

“To determine which way a graft is curled or scrolled, you need to have that cross section perpendicular to the scrolled tissue to see how it is oriented,” he said. “If it is parallel, you will just see parallel lines of the tissue.” The Haag-Streit unit, in contrast, has a single line that can be rotated for different meridians, so it can be lined up perpendicular to a scroll no matter how it is oriented inside the eye.

Both the Haag-Streit and Zeiss devices have monitors, plus the images are embedded in an ocular of the microscope, “so the surgeon does not have to look away from the operating microscope to a monitor,” Price said. “As a result, the surgery goes much quicker and flows a lot better.” This is especially important in difficult cases.

However, as with any testing device that uses light, “it helps if you have the corneal surface moist. Sometimes, if the cornea dries out a lot, you may not get a clear image,” Price said. Employing the correct magnification and proper focus of the microscope are also important.

Anthony N. Kuo, MD, an assistant professor of ophthalmology in the Cornea and Refractive Surgery Service at Duke University School of Medicine, finds the microscope-integrated varieties of intraoperative OCT useful to easily obtain cross-sectional views of the area in which he is operating.

“Hand-held OCT probes in the past required stopping surgery, manually positioning the device or hanging it on the microscope, and having to switch to it,” Kuo said. “With microscope integration, I do not change my surgical routine and there is the added visualization of OCT where I am already operating.”

Kuo, who has been using intraoperative OCT for anterior segment surgery since 2012, initially employed spectral-domain microscope-integrated OCT, but more recently he is using swept-source 3-D microscope-integrated OCT in cataract surgery and lamellar keratoplasty.

“The cross sections are particularly useful for seeing depth-dependent instrument and tissue relationships,” he said. For instance, with DSAEK, microscope-integrated OCT “is fairly straightforward to determine whether or not there is any interface gap between the donor graft and host cornea. This is a lot more difficult with only the standard surgical microscope.”

Kuo was a co-author of a study on intraoperative OCT to improve visualization in DSAEK for advanced bullous keratopathy that appeared in Cornea in 2015.

“In this paper, we show how microscope-integrated OCT can be used to enable DSAEK in opaque corneas with poor visualization,” he said. “This allows these patients to have DSAEK, and with the associated less morbidity, instead of perhaps requiring a penetrating keratoplasty.”

Kuo also co-authored a preclinical evaluation and intraoperative human retinal imaging with a high-resolution microscope-integrated spectral-domain OCT device that appeared in Retina in 2013.

“This was one of the early papers from our Duke group showing the use of an OCT system integrated into the surgical microscope as an advance over previous hand-held OCT systems,” he said. “Microscope integration makes OCT a natural benefit rather than a separate process to achieve the additional visualization.”

One-year results of the Rescan 700 portion of the Cole Eye Institute’s DISCOVER study showed that surgeon decision-making was altered by intraoperative OCT guidance in a large portion of cases. The DISCOVER study has now enrolled more than 500 eyes. Investigators discovered that for anterior segment procedures, microscope-integrated intraoperative OCT provides significant information for lamellar keratoplasty procedures, such as guiding DALK dissection depth or optimally orienting DMEK grafts.

“Surgeons were able to successfully image with intraoperative OCT during both anterior and posterior surgery in the vast majority of cases,” according to Ehlers, the principal investigator of the DISCOVER study that involved 227 eyes at 1 year and lead author of the analysis that appeared in JAMA Ophthalmology in 2015.

Ehlers was also a co-author of a case series of eyes that underwent DMEK with the Rescan 700 from the DISCOVER study.

“Overall, intraoperative OCT was quite helpful in identifying graft orientation during surgery, which is critical for DMEK, as well as evaluating for apposition of the grafts to the host cornea,” Ehlers said of the study published in American Journal of Ophthalmology.

In a retrospective case series of 40 eyes that underwent anterior or posterior segment surgery with the Rescan 700 published in Ophthalmic Surgery, Lasers and Imaging Retina, additional information was garnered “in 74.1% of the posterior and combined surgical cases, which resulted in altered decision-making in 41.9% of the cases,” Pfau and colleagues wrote.

Real-time decision-making

William J. Dupps Jr., MD, PhD, also of Cole Eye Institute, has experience using intraoperative OCT in a variety of settings: LASIK, intrastromal corneal rings such as Intacs (Addition Technology) that depend heavily on precise placement, cataract surgery and corneal transplant surgery.

“There is a definite benefit in improving graft adherence rates when you can visualize the attachment before leaving the operating room,” Dupps said. He has been using intraoperative OCT for more than 5 years, starting with the forerunner of EnFocus from Leica/Bioptigen, followed by the Zeiss device and a custom system developed at Cole Eye Institute.

Dupps is a co-investigator on several prospective intraoperative OCT studies, including the earlier prospective PIONEER study that evaluated intraoperative OCT in a variety of surgeries.

“The surgical setting of PIONEER was similar to the DISCOVER study, but without the benefit of an integrated system,” he said. In an 18-eye series of DALK procedures that was reported in Cornea in 2015, “we could easily visualize the depth of the first dissection, which is the most critical step of the procedure to achieve a successful result.”

Dupps said there is about a 50% conversion rate with DALK — in other words, accidentally breaking through the endothelial layer of the cornea, resulting in the need to remove it and convert to a full-thickness transplant.

“By sparing the recipient’s endothelium, you offer the patient a lower rejection rate,” he said. “Viewing directly through the surgical microscope, OCT images provide us with real-time depth feedback, which definitely adds efficiency to the process. Being able to make real-time decisions reduces the need for iteration and dependence on indirect surgical landmarks or signs.”

Performing a surgical maneuver and seeing how that affects the tissue in real time is very valuable. “You realize quickly which maneuvers are effective and which ones are not,” Dupps said. “The learning curve is also much faster when OCT is integrated into the scope because the barrier to capturing images is lower and users can be less selective about when to image. It is a fabulous teaching tool for residents and fellows.”

Dupps strongly favors microscope-integrated implementations of OCT technology.

Regarding imaging pearls, Dupps said, “Whenever you are trying to capture a high-quality image in the cornea or retina, make sure that the surface is moistened with balanced salt solution. This minimizes scattering at the surface, so more light gets into the eye to increase the signal-to-noise ratio and clarity of images.”

Three important criteria to consider when evaluating an intraoperative OCT system are one’s need for imaging depth, the quality of the images and the availability of desired software features, according to Dupps.

“I prefer to scan every lamellar corneal transplant surgery that I do, especially endothelial keratoplasty. It has become part and parcel to my approach to the surgery and has led to useful technique modifications,” he said.

Looking ahead

According to Ehlers, intraoperative OCT has the potential to refine IOL calculations during cataract surgery.

A 2015 review article of the progress of intraoperative OCT over the past several years, penned by Ehlers in Eye, noted that software analysis and OCT-compatible instrumentation are two areas that need further development to optimize the surgeon platform when using intraoperative OCT. Barriers to adoption were also highlighted.

“The cost of these systems is still fairly expensive,” Ehlers said in the review. “It seems that there is very good data to support that having intraoperative OCT changes surgeon decision-making in a fairly high percent of cases. However, the question remains: Does that change in decision-making ultimately translate to better outcomes? Research is ongoing to answer that question.”

A study published in PLOS ONE, for which Ehlers was the lead author, discussed several areas of intraoperative OCT needed to advance the field, including the integration of head-up display surgeon feedback. The lab-based study also mentioned the need for an electrically tunable lens as part of the microscope for increased flexibility during surgery. And for better visualization, the investigators assessed six semitransparent materials for instrument construction, selecting polycarbonate as a material substrate for prototype instrumentation.

With several companies in the intraoperative OCT space, “there is going to be pressure to improve the technology and achieve better resolution,” Price said. “I think things will only get better. It will be tremendously helpful for endothelial keratoplasty, in particular DMEK. Intraoperative OCT will become the procedure of choice for ensuring that the graft is in the right position.”

Dupps expects to see a shift toward real-time quantification of key tissue dimensions and depths during intraoperative OCT, as well as further expansion to cataract and refractive surgery. He also feels that barriers to adoption of intraoperative OCT are decreasing with system integration. “Integration saves time. Everything is right there in your scope,” Dupps said. “Plus, the value proposition is easy to see for anterior segment applications.”

“While hand-held probes work, I think microscope integration is going to be the form that is most natural for surgeons to use,” Kuo said. Moreover, “both faster scan speeds enabling live 3-D imaging and automated tool tracking make intrasurgical OCT more useable. Live 3-D imaging enables the surgeon to see the entire surgical field instead of a single 2-D slice. With the entire surgical field in view, you could imagine being able to operate with only the OCT visualization. For tracking, chasing an active surgical instrument with only a 2-D scan is not easy; 3-D helps because the desired scan is in the volume somewhere, but tracking to keep the scan where you want it will make OCT easier to use intraoperatively.”

At Duke, researchers have developed ways to show the volumetric OCT information to the surgeon in 3-D.

“We have accomplished this by projecting slightly rotated OCT images to the left and right surgical eyepieces, which allows the surgeon to perceive the OCT information in 3-D,” Kuo said. “We have also projected the 3-D OCT scans to the surgeon using a 3-D TV and 3-D glasses.”

Most notably, though, the researchers have used virtual reality, including head-mounted displays such as the Oculus Rift, to immerse the surgeon in the 3-D OCT scan.

“Because the 3-D scan is live and interactive, the surgeon can operate in the real world using only the 3-D visualization he or she sees on the immersive [virtual reality] displays,” Kuo said. – by Bob Kronemyer

• References:
• Au J, et al. Cornea. 2015;doi:10.1097/ICO.0000000000000508.
• Cost B, et al. Am J Ophthalmol. 2015;doi:10.1016/j.ajo.2015.05.020.
• Ehlers JP. Eye (Lond). 2015;doi:10.1038/eye.2015.255.
• Ehlers JP, et al. JAMA Ophthalmol. 2015;doi:10.1001/jamaophthalmol.2015.2376.
• Ehlers JP, et al. PLoS One. 2014;doi:10.1371/journal.pone.0105224.
• Hahn P, et al. Retina. 2013;doi:10.1097/IAE.0b013e3182831293.
• Pasricha ND, et al. Cornea. 2015;doi:10.1097/ICO.0000000000000661.
• Pfau M, et al. Ophthalmic Surg Lasers Imaging Retina. 2015;doi:10.3928/23258160-20151027-03.

• For more information:
• William J. Dupps Jr., MD, PhD, can be reached at Cole Eye Institute, 9500 Euclid Ave., i32, Cleveland, OH 44195; email: bjdupps@sbcglobal.net.
• Justis P. Ehlers, MD, can be reached at Cole Eye Institute, 9500 Euclid Ave., i32, Cleveland, OH 44195; email: ehlersj@ccf.org.
• Anthony N. Kuo, MD, can be reached at Duke Eye Center, DUMC Box 3802, Durham, NC 27710; email: anthony.kuo@duke.edu.
• Francis W. Price, MD, can be reached at Price Vision Group, 9002 N. Meridian St., Suite 100, Indianapolis, IN; email: fprice@pricevisiongroup.net.

Disclosures: Dupps reports he and his group have had non-OCT research be sponsored by Carl Zeiss Meditec. Ehlers reports he is a consultant to Carl Zeiss Meditec, Leica, Bioptigen, ThromboGenics, Allergan and Alcon and has licensed intellectual property to Bioptigen and Synergetics USA. Kuo reports he is a co-author of a patent on OCT image analysis, unrelated to surgical OCT, licensed to Bioptigen. Price reports no relevant financial disclosures.

 

Is there value in incorporating intraoperative OCT in glaucoma surgery?

Value of intraoperative OCT will parallel MIGS devices

The introduction of OCT in ophthalmology changed the practice of patient care in many areas, including glaucoma. As the evolution of OCT and its capabilities continues, the use of this technology also progresses. The application of OCT has now expanded from uses in the office for diagnosing disease to the operating room where results of surgery can be assessed. This is seen in other subspecialties such as retina for retinal detachment repair and the anterior segment for corneal graft procedures. In glaucoma surgery, OCT has been used to evaluate trabeculectomy blebs when the patient is seen in the office postop at the slit lamp and now even intraoperatively for trabeculotomy.

The use of intraoperative OCT in glaucoma surgery can be expected to increase in the future as MIGS continues to evolve. The benefit of OCT is the visualization of structures that are difficult for providers to see with a microscope. The MIGS products in the pipeline or those available now work in spaces not easily seen. These sites include Schlemm’s canal for the iStent (Glaukos) and Hydrus (Ivantis); suprachoroidal space for the iStent Supra (Glaukos) and CyPass (Transcend Medical); and subconjunctival space for the Xen gel stent (AqueSys/Allergan). The ability to verify proper placement of these products intraoperatively will aid in their success. One important factor is whether the technology will allow for rapid and adequate visualization of these landmarks during surgery.

Three important results will occur with the use of intraoperative OCT in glaucoma surgery. First, it will provide the surgeon with real-time feedback about the correct orientation and placement of these MIGS products. Second, it will allow the evaluation of these procedures in patients to see if they were successful, thus removing the uncertainty of whether the products are in the right position. Third, the resulting data will supply additional information regarding how to improve MIGS procedures in the future.

The value of intraoperative OCT will parallel the development and utilization of MIGS in the treatment of glaucoma. Given what is in the MIGS pipeline, this value should be expected to increase moving forward.

Savak “Sev” Teymoorian, MD, MBA, is an OSN Glaucoma Board Member. Disclosure: Teymoorian reports he is a paid consultant to Glaukos and Allergan.

• References:
• Heindl LM, et al. Curr Eye Res. 2015;doi:10.3109/02713683.2014.995311.
• Singh M, et al. Ophthalmology. 2007;doi:10.1016/j.ophtha.2006.05.078.
• Toygar O, et al. Eye (Lond). 2016;doi:10.1038/eye.2015.230.

Integrated microscope adds ‘tremendous’ potential

I think that OCT integrated into microscopy, specifically an operating microscope, has tremendous potential in glaucoma, especially for the minimally invasive glaucoma surgeries, whether it is from the outside in or the inside out.

For the ab externo approach to Schlemm’s canal, intraoperative OCT can afford a rapid visualization of Schlemm’s canal, as the tissue is thinned over the canal. Conversely, for the ab interno approach, the technology can identify Schlemm’s canal intraoperatively for various surgical maneuvers.

Identifying collector channels for use with implants in Schlemm’s canal or removal of trabecular meshwork in the inner wall of the canal is one area we feel intraoperative OCT could be very helpful. There is more bang for the buck if you provide the fluid easier access right where the collector ostia reside, as opposed to in-between ostia. We and other groups have shown in the clinic and the lab that these ostia can be identified. The ability to actually structurally see the ostia in vivo would make the procedure easier for the surgeon to perform more quickly and achieve better long-term results.

The potential to identify collector channel ostia and operate just in the areas where the ostia are would make minimally invasive glaucoma surgery even more minimally invasive and at the same time allow for better outcomes. You would also expect the procedure to be safer because you would know where the structures are that you are trying to approach. However, the utility at this point of OCT integrated into an operating microscope is still not realized. We need better algorithms and a more optimized system for use in glaucoma surgery. But the potential is certainly there.

Joel S. Schuman, MD, FACS, is an OSN Glaucoma Board Member. Disclosure: Schuman reports he receives royalties for intellectual property related to OCT that is licensed by MIT and Massachusetts Eye and Ear to Zeiss.