Intraoperative OCT and Vitreoretinal Surgery

COVER STORY Intraoperative OCT and Vitreoretinal Surgery

This technology has the potential to improve clinical outcomes and enhance understanding of the pathophysiology of a wide variety of surgical vitreoretinal diseases.

BY JUSTIS P. EHLERS, MD

ntraoperative optical coherence AB tomography (OCT) is an emerging diagnostic imaging modality with I significant potential to benefit surgeons and patients undergoing vitreoretinal surgery. The initial report of intraoperative SD-OCT came from cli- nicians at Duke University, led by Cynthia Toth, MD, who performed intraoperative imaging using a handheld spectral-domain OCT (SD-OCT) system (Bioptigen Spectral Domain Ophthalmic Imaging System; Bioptigen, Inc., Research Triangle Park, NC).1,2 Sunil Srivastava, MD, first reported utilizing a microscope-mounted handheld system Figure 1. Front microscope prototype SD-OCT mount allowing drape-free surgi- to enhance image acquisition through cal microscope operation (A). Prototype side-mount system for handheld SD-OCT improved stability and control of the system allowing complete draping of the entire surgical system (B). device.3 Currently, at the Cole Eye Institute, we use two different prototype microscope refine surgical techniques, and improve patient outcomes. mount systems (Figure 1). The first (Figure 1A) fixates the handheld system to the objective lens of the microscope IMPROVED UNDERSTANDING OF and allows the surgeon to use an undraped microscope. PATHOPHYSIOLOGY The second (Figure 1B) utilizes a modified plate to posi- Numerous gaps exist in our understanding of the tion the OCT probe to the side of the scope, allowing pathophysiology of many vitreoretinal diseases. For complete draping of the entire system. example, the source of fluid for optic pit-related maculopathy has been largely unknown. It is also unclear CROSS-SECTIONAL whether a connection exists across the optic pit between ANATOMIC INFORMATION the vitreous cavity and the intraretinal fluid. Multiple sur- The high-resolution cross-sectional anatomic informa- gical techniques have been suggested with varying levels tion obtained from SD-OCT is a perfect complement of success. Intraoperative OCT has allowed a new level of to the 3D aspects of vitreoretinal surgery. It provides understanding of the pathophysiology of optic pit-relat- detailed anatomic views from a cross-sectional perspec- ed maculopathy. During vitrectomy, an air-fluid exchange tive that are not possible intraoperatively through the was performed with prolonged aspiration over the area microscope. Utilizing this information, intraoperative of the optic pit. Intraoperative OCT during the vitrecto- OCT may further our understanding of vitreoretinal my showed significant collapse of the area of fluid adja- pathophysiology, assist in surgical decision-making, cent to the optic pit, strongly suggesting a connection

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A A

Figure 3. Intraoperative OCT of bullous macula-involving retinal detachment (red arrow; A). Intraoperative OCT during retinal detachment repair following perfluorocarbon liquid tamponade showing subclinical persistent subretinal fluid (blue arrow; B) and perfluorocarbon liquid interface (yellow Figure 2. Intraoperative OCT of full-thickness macular hole arrow; B). prior to internal limiting membrane peeling. Small area of subretinal hyporeflectivity (red arrows; A). Intraoperative OCT UNCOVERING NEW FINDINGS following internal limiting membrane removal with architec- Intraoperative OCT can also change our impression of tural alterations including increased height (white arrow) and the effects of our surgical maneuvers on the microarchi- increased width (blue arrow) of subretinal hyporeflectivity tecture of the retina and surrounding tissues. In epiretinal (B). Optimized postoperative day 1 OCT through gas bubble membrane (ERM) and macular hole surgery, increased showing closed macular hole (C). subretinal hyporeflectivity has been noted following surgical intervention using intraoperative OCT.3,5 Progressive between the vitreous cavity and the intraretinal space.4 increases in subretinal hyporeflectivity have been noted Twenty-four hours following surgery, the distribution of following peeling of successive layers (eg, ERM and inter- the intraretinal fluid had shifted to a new equilibrium. nal limiting membrane [ILM]). The significance of this Without intraoperative OCT, the direct effect of aspira- finding for visual outcomes is unclear. The possibility tion would not have been appreciated. exists that this may represent photoreceptor trauma, and

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A Intraoperative OCT can be particularly helpful in providing immediate feedback to surgeons following surgical manipulations.

width of subretinal hyporeflectivity. One day following surgery, OCT optimized through gas, shows that the macular hole has already closed.

Case Sample: Macula-involving Retinal Detachment During RD repair, intraoperative OCT reveals the bul- B lous nature of the RD (Figure 3). Following perfluorcar- bon liquid tamponade, significant persistent subclinical subretinal fluid is noted.

INTRAOPERATIVE FEEDBACK FOLLOWING SURGICAL MANUEVERS Intraoperative OCT can be particularly helpful in providing immediate feedback to surgeons following surgical manipulations. In complex cases, such as tractional retinal detachments and proliferative diabetic retinopathy, it can be difficult to determine whether complete mem- Figure 4. Pre-incision OCT revealing inner retinal irregularity brane removal has been achieved. Following ERM surgery, with a prominent epiretinal membrane (red arrow; A).The intraoperative OCT can provide high-resolution visualiza- posterior hyaloid is seen above the retinal surface (yellow tion of any residual membranes and help to identify arrow; A). Intraoperative OCT following core vitrectomy and whether the traction has been relieved. This immediate epiretinal membrane/internal limiting membrane peeling (B). feedback can help to minimize unnecessary surgical Posterior hyaloid is no longer visible (B). Inner retinal surface maneuvers if total removal has been accomplished, shows Successful removal of epiretinal membrane (blue improving surgical feedback. Additionally, if subclinical arrow; B). Minimal extrafoveal remaining membrane is visual- residual membranes are present, intraoperative OCT may ized (orange arrow; B). reduce the need for additional surgery by allowing additional removal during the initial procedure. refinement of surgical techniques to minimize this disrup- tion may improve visual outcomes. Case Sample: ERM Removal Visual recovery following macula-involving retinal Intraoperative OCT during vitrectomy for ERM detachments (RD) is difficult to predict. Intraoperative removal identifies inner retinal striae with a prominent OCT during RD repair has shown numerous novel find- ERM (Figure 4).The posterior hyaloid can be seen above ings, including persistent subclinical subretinal fluid and the retinal surface. After core vitrectomy and combined significant alterations to the foveal architecture.6 Intra- ERM/ILM) peeling, intraoperative OCT confirms com- operative OCT findings such as height of residual fluid plete membrane removal except for a minimal following drainage and repair may prove useful in prog- extrafoveal membrane noted nasally. nosticating visual recovery. Case Sample: Proliferative Diabetic Retinopathy with Case Sample: Full-thickness Macular Hole Posterior Hyaloidal Traction Figure 2 documents intraoperative OCT findings dur- Membrane removal and hyaloid elevation can be ing macular hole surgery. A small area of subretinal complex in proliferative diabetic retinopathy. In this hyporeflectivity is noted prior to peeling the ILM. After case, preoperatively there appeared to be posterior ILM removal, intraoperative OCT reveals architectural hyaloidal traction with an underlying ERM (Figure 5). alterations including increased height and increased During the surgical procedure, as the hyaloid was

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AB Significant advances are needed in multiple areas to bring OCT into main- stream use in the OR. Surgical instrumen- tation will need refinements to achieve OCT compatibility. Metallic instruments result in severe shadowing and limited visualization during intraoperative maneuvers.3 We are currently testing numerous materials to identify those compatible with OCT visualization. Simultaneous display of OCT imaging CDand the surgical field are necessary for successful integration. Rapid aiming mechanisms to guide the OCT to the area of interest will be needed to opti- mize efficiency during intraoperative use. Advances in software analysis packages are needed to provide real-time analysis of OCT data to give key data to the surgeon without information overload. In the past few years, significant Figure 5. Intraoperative OCT of posterior hyaloidal traction with appearance progress has been made in the field of of partially separated posterior hyaloid (blue arrow) and underlying epiretinal intraoperative OCT. Although numerous membrane (red arrow; A and B). Intraoperative OCT following posterior hurdles remain, the future is promising hyaloid elevation without membrane peeling (C and D). Intraoperative OCT for true integration of OCT into the art of identifies complete removal of membranes (yellow arrow; C and D) following vitreoretinal surgery. In clinical practice, hyaloid elevation confirming vitreoschisis and limiting unnecessary additional OCT has revealed things we never membrane peeling procedures. expected and has allowed us to be better physicians. With the anatomic informa- elevated there appeared to be significant vitreoschisis. tion OCT provides, this technology is a natural comple- Following elevation of the hyaloid, intraoperative ment to the OR and will hopefully allow us to become OCT confirmed complete removal of all membranes better surgeons as well. ■ confirming vitreoschisis without an underlying ERM. Utilizing intraoperative OCT, additional membrane Justis P. Ehlers, MD, is a Staff Physician with the peeling was minimized by confirming complete Vitreoretinal Service of the Cole Eye Institute in the removal prior to additional maneuvers. Department of Ophthalmology at Cleveland Clinic.

1. Dayani PN, Maldonado R, Farsiu S, Toth CA. Intraoperative use of hand- TIME WILL TELL held spectral domain optical coherence tomography imaging in macular surgery. Retina. Intraoperative OCT is still in its infancy, and current 2009;29(10):1457-1468. 2. Srivastava SK, Ray R, Hubbard B, et al. Intraoperative optical coherence tomography. Paper systems have significant limitations. Handheld or modi- presented at: the American Society of Retina Specialists Annual Meeting. August 20-24, fied tabletop units require the surgical procedure to be 2011; Boston. 3. Srivastava SK. Intraoperative diagnostic techniques. Paper presented at: the American stopped, resulting in time delays. Additionally, this pre- Academy of Ophthalmology Retina Subspecialty Day. October 15-16, 2010; Chicago. vents true real-time evaluation of surgical maneuvers. 4. Ehlers JP, Kernstine K, Sarin N, Maldonado R, and Toth CA. Real-time analysis of pars plana vitrectomy for optic pit-related maculopathy. Arch Ophthalmol. 2011; In press. True microscope integration of the OCT device is 5. Ray R, Baranano D, Fortun J, et al. Intraoperative microscope mounted spectral domain needed to provide a seamless system for real-time intra- optical coherence tomography for evaluation of retinal anatomy during macular surgery. Ophthalmology. 2011; In press. operative OCT. At Duke University, Dr. Toth has devel- 6. Lee LB, Srivastava SK. Intraoperative spectral-domain optical coherence tomography dur- 7,8 oped a microscope-integrated prototype. This system ing complex retinal detachment repair [published online ahead of print August 11, 2011]. Ophthalmic Surg Lasers Imaging. doi:10.3928/15428877-20110804-05. allows simultaneous surgical maneuvers and OCT scan- 7. Tao YK, Ehlers JP, Toth CA, Izatt JA. Intraoperative spectral domain optical coherence 8 ning. Additionally, Susanne Binder, MD, along with col- tomography for vitreoretinal surgery. Opt Lett. 2010;35(20):3315-3317. 8. Ehlers JP, Tao YK, Farsiu S, Maldonado R, Izatt JA, Toth CA. Integration of a spectral leagues in Vienna, has described a microscope-integrated domain optical coherence tomography system into a surgical microscope for intraoperative Cirrus OCT (Carl Zeiss Meditec, Germany) prototype for imaging. Invest Ophthalmol Vis Sci. 2011;52(6):3153-3159. Print 2011 May. 9 9. Binder S, Falkner-Radler CI, Hauger C, Matz H, Glittenberg C. Feasibility of intrasurgical intraoperative use. spectral-domain optical coherence tomography. Retina. 2011;31(7):1332-1336.

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