March 2020

IN FOCUS

Illuminating intraoperative technologies
Intraoperative OCT in practice


by Chiles Samaniego Contributing Writer


Intraoperative swept-source OCT of the anterior
segment depicting the empty capsule bag after
I/A and the anterior hyaloid interface
Source: Oliver Findl, MD




Image from the RESCAN (Carl Zeiss Meditec) of a difficult cataract case in a patient with Stevens-Johnson syndrome and a large corneal scar. OCT was helpful in visualizing the capsulorhexis through the dense scar.
Source: Julie Schallhorn, MD

“I expect that it will eventually become routine to use OCT during most types of surgery.”

—Julie Schallhorn, MD

Intraoperative OCT expands the amount of visual information surgeons have at their disposal during any given ophthalmic surgical procedure, well beyond that provided by the standard binocular surgical microscope.
“OCT is helpful to really see the third dimension,” said Oliver Findl, MD. While the binocular microscope provides a “3D impression,” Dr. Findl said, “at the end of the day we don’t have a detailed depth resolution.” The OCT provides detailed optical slices for the surgeon to examine in real time.
Just how useful is this information, and what is the technology’s role in practice? That’s what EyeWorld discussed with Dr. Findl, Julie Schallhorn, MD, and Marie-Jose Tassignon, MD.

Cataract surgery

Dr. Schallhorn thinks intraoperative OCT is useful in phaco cases when there are corneal scars or otherwise poor visibility. “[A]nytime I am having difficulty with visualization, I turn on the OCT,” she said. “The OCT wavelength is longer than visible light and can penetrate scars better. I have used it to check for capsular integrity and to help my capsulorhexis when I am having difficulty seeing the flap. If you are a divide-and-conquer surgeon, you can also use OCT to check the thickness of the remaining lens.”
Dr. Tassignon also thinks intraoperative OCT is “of great help” in cataract surgery, for which it is her “main indication.” “In adult cataract, it helps to understand the relationship between the posterior capsule and the anterior hyaloid and explains the ‘floppy capsule,’ a condition due to the detachment of the anterior hyaloid from the posterior capsule, also called AVD [anterior vitreous detachment],” she said. “It is probably the most important cause of posterior capsule tear. In pediatric cataract it allowed me to describe a new type of congenital cataract based on a dysgenesis of the anterior interface.”1,2
Though primarily a vitreoretinal surgeon, Dr. Findl has had a prototype OCT system as far back as 2011 and has conducted various trials demonstrating the technology’s potential for use in cataract and corneal surgery. For instance, he has used intraoperative OCT to study the movements of nuclear fragments during emulsification. They observed tiny fragments making pinpoint contact with the central endothelium, resulting in endothelial cell loss, even when the view through the microscope showed an apparently perfect surgery.
Dr. Findl has also been studying the technology’s potential to improve refractive outcomes by refining IOL power calculations. As he described in his 2018 ASCRS Binkhorst Lecture, “The Challenge of Choosing the Right IOL Power,” intraoperative OCT can be used to measure the post-cataract removal position of the capsule relative to the corneal apex, which is a good predictor of the IOL position after surgery. This, he said, would be useful for unusually short or long eyes, which can result in refractive surprises.
This application, however, requires a prototype swept-source OCT not yet ready for commercial use, Dr. Findl said.

Implications for bag-in-the-lens technique

The information on the anterior interface that intraoperative OCT provides has had a particular impact on Dr. Tassignon’s practice. Having intellectual and proprietary interests in the bag-in-the-lens (BIL) technique, Dr. Tassignon has routinely used this method to implant IOLs since 2004.
“This technique requires performing a primary posterior circular, continuous capsulorhexis (PPCCC),” she said. While considered standard in pediatric cases, PPCCC had been “enigmatic” for most cataract surgeons because no one knew the precise anatomy of the anterior interface. “With the advent of the intraoperative OCT, our group was able to describe the fascinating variations of the anterior interface from birth till adulthood and to evaluate its aging process,” she said. “It became evident that this anterior interface changes over time and becomes bigger and bigger until it detaches from the posterior capsule. This process was called anterior vitreous detachment, which is the equivalent of the posterior vitreous detachment (PVD).”3

Corneal surgery

Dr. Schallhorn uses intraoperative OCT in all of her lamellar corneal cases, including DSAEK, DALK, and DMEK. “It is great to see if there is any fluid in the interface in DSAEK cases and to check if there are any peripheral Descemet’s remnants that are preventing the DMEK graft from adhering 100%,” she said. “It is invaluable in DALK cases to check the depth of your cannula before the big bubble and to ensure that all the stroma has been removed prior to placing the graft.”
“Intraoperative OCT is helpful in all conditions of corneal surgery,” Dr. Tassignon agreed. For any residual interface fluid in DSAEK, she and Dr. Findl described performing a corneal massage or creating venting incisions under OCT control. “You can be sure that at the end of surgery you don’t have fluid interface between the transplant and recipient cornea,” Dr. Findl said.
The technology is also useful for orienting the rolled donor tissue during DMEK. “Once you’re unfolding that, you can see quite well whether it’s the right way up or upside down,” Dr. Findl said.

Retina

Intraoperative OCT plays a major role in Dr. Findl’s retina cases. The technology allows him to identify the presence of a thickened macula, epiretinal membrane, thickened and/or adherent internal limiting membrane (ILM), or cystoid macular edema. During peeling, it allows him to see the tension he’s putting on the retina, allowing him to adjust his technique.
“Last but not least, I like to use it for macular hole surgery because we like to do the ILM flap technique, where we put a part of the ILM flap on top of the macular hole, especially for large macular holes,” he said. “For that it’s quite nice because you can actually see the flap, and when you’re introducing air into the eye, you can see and control the position of the flap until the very end when you have a complete air fill.”

Training, general applications

For training purposes, Dr. Findl and Dr. Schallhorn both said their residents learn to operate using standard surgical microscopes, without intraoperative OCT. However, intraoperative OCT is useful for evaluating their performance.
The technology, however, is “100% useful for experienced surgeons,” Dr. Schallhorn said. “I find it most useful in my corneal cases and have been surprised at times by how much fluid is left in the graft interface when it looks perfectly attached to me.”
An additional use for intraoperative OCT in Dr. Findl’s hands would be for OVD removal. “The problem with OVDs is they are very similar to water—the refractive index of OVD and water is quite similar—so in my hands I don’t see the interface well,” he said.
Finally, Dr. Tassignon reiterated the technology’s utility in observing the anterior interface. “It predicts the degree of surgical difficulty in cases of pediatric cataract with anterior interface dysgenesis since in these cases there is an abnormality in the development of the anterior hyaloid and the posterior capsule,” she said. “The repair mechanism to compensate for this dysgenesis resulted in a posterior cataract, which has been recognized as a separate pediatric cataract entity.”

Looking forward

Intraoperative OCT, Dr. Tassignon said, will hopefully answer remaining questions such as the size of the anterior interface and the role of an AVD on post-cataract cystoid macular edema or retinal detachment. Meanwhile, Dr. Findl hopes for further technological developments, such as an entire eye OCT, perhaps some robotic automation, and plastic instruments that do not cast shadows on OCT images.
Something concrete to look forward to is an intraoperative OCT course that Dr. Schallhorn, Charles Lin, MD, and Matthew Feng, MD, are designing for the 2020 ASCRS Annual Meeting. The course will cover the basic design and use of the various commercially available intraoperative OCT microscopes and will include a wet lab for OCT use in lamellar corneal surgery. This will be a great opportunity to learn about a technology that Dr. Schallhorn expects will have an expanding role in practice. “Because of the unique advantages of OCT over direct visualization (cross-sectional image, longer light wavelength), it adds to the surgeon’s understanding of what is happening during an operation,” she said. “I expect that it will eventually become routine to use OCT during most types of surgery.”

At a glance

• Intraoperative OCT is helpful in cataract surgery cases that have poor visibility, and it provides useful information on the relationship between the posterior capsule and anterior hyaloid.
• It is useful in all forms of corneal surgery, elucidating the layers of the cornea, identifying any residual fluid in the donor-recipient interface, and helping orient donor tissue.
• Retina cases benefit from intraoperative OCT’s delineation of the layers of the retina, the identification of pathologies such as epiretinal membranes and cystoid macular edema, and real-time assessment of traction during maneuvers such as membrane peeling.

About the doctors

Oliver Findl, MD
Chair and associate professor of ophthalmology
Hanusch Hospital
Vienna, Austria

Julie Schallhorn, MD
Assistant professor of ophthalmology
University of California,
San Francisco
San Francisco, California

Marie-Jose Tassignon, MD
Chair
Department of Ophthalmology
Antwerp University Hospital
Antwerp, Belgium

References

1. Tassignon MJ. The history of the anterior interface. Innovative Implantation Technique: Bag-in-the-Lens Cataract Surgery. Springer Nature. 2019:25–32.
2. Tassignon MJ. Clinical variations of the vitreo-lenticular interface. Innovative Implantation Technique: Bag-in-the-Lens Cataract Surgery. Springer Nature. 2019:33–44.
3. Tassignon MJ, Ni Dhubhghaill S. Real-time intraoperative optical coherence tomography imaging confirms older concepts about the Berger space. Ophthalmic Res. 2016;56:222–226.

Relevant disclosures

Findl
: Alcon, Johnson & Johnson Vision, Carl Zeiss Meditec
Schallhorn: Carl Zeiss Meditec Tassignon: Intellectual and proprietary interests in the bag-in-the-lens technique

Contact

Findl
: oliver@findl.at
Schallhorn: jschallhorn@gmail.com
Tassignon: marie-jose.tassignon@uza.be

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