**1. Introduction**

The proliferation of smallsats and the small but highly capable scientific sensors on them have ushered in a new era of Earth remote sensing from space. Technology development lifecycles have been shortened, new and improved sensors can reach space more quickly, both launch vehicle and satellite costs have been reduced dramatically, and it is now both possible and affordable to consider flying large constellations of remote sensing instruments [1]. Notably, large constellations of smallsats in low Earth orbit have the potential to significantly improve upon the spatial and temporal sampling densities provided by a single traditional large satellite [2]. The improvement in sampling density with number of spacecraft is generally intuitive—more of them spread out around the globe will tend to sample more places at the same time and to sample the same place more frequently. We consider here the optimization problems of:

The optimization is performed with respect to specific orbit parameters of the constellation, namely the number and orientation of orbit planes and the number of satellites in each plane. When quantifying the notion of sampling density, it is helpful to consider a specific type and design of remote sensing instrument. Our optimization study is performed with respect to a Global Navigation Satellite System Reflectometry (GNSS-R) sensor. These sensors are the receiver half of a bistatic radar system in which the transmitters are the

**Citation:** Winkelried, J.; Ruf, C.; Gleason, S. Spatial and Temporal Sampling Properties of a Large GNSS-R Satellite Constellation. *Remote Sens.* **2023**, *15*, 333. https:// doi.org/10.3390/rs15020333

Academic Editor: Mehrez Zribi

Received: 21 November 2022 Revised: 22 December 2022 Accepted: 28 December 2022 Published: 5 January 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

existing constellation of navigation satellites, such as GPS and Galileo. Measurements of GNSS signals scattered back into space from the Earth surface contain information about a wide variety of scientifically valuable geophysical surface conditions [3–7]. The relevant instrument design parameters to be considered are the number of simultaneous GNSS surface reflections observed and the gain and field of view of the antenna through which the observations are made. The former design parameter affects the signal processing complexity and power requirement of the instrument, and the latter parameter affects the size and mass of the antenna. GNSS-R sensors are compatible with smallsats [8,9] and have been demonstrated to provide improved sampling density in small constellations [10], so are a natural type of measurement to consider for this study.

The satellite constellation design space being considered here is an extension of the point design used by the NASA CYGNSS mission [11]. Its constellation consists of 8 identical spacecraft spaced roughly equally around a single orbit plane at an altitude of ~525 km and an inclination angle of 35◦. Each CYGNSS spacecraft carries a GNSS-R sensor capable of measuring 4 simultaneous surface reflections.


Intraoperative Optical Coherence Tomography

*Samet Gulkas and Osman Cekic*

### **Abstract**

Recently, surgical instruments and imaging technology in ophthalmology have shown a great improvement. However, advances in the field of the operating microscope technology still remained unchanged with the various limitations for the surgeons. Invention of optical coherence tomography (OCT) led to a revolution in the diagnosis and monitoring of numerous anterior and posterior segment pathologies. Recently, OCT has been introduced into the operating room with an impact on the surgeons. In this chapter, we review the evolution of OCT for intraoperative use with its feasibility, surgical impacts, and limitations.

**Keywords:** intraoperative optical coherence tomography, microscope-integrated, anterior segment *i*OCT, posterior segment *i*OCT

### **1. Introduction**

Optical coherence tomography (OCT) is a rapid, noninvasive, noncontact, and cross-sectional imaging method that produces images of ocular tissues. OCT uses reflected light to obtain the images from the different layers on the ocular tissues that produce different backscattered lights [1]. After using of spectral-domain OCT (SD-OCT) instead of time-domain OCT (TD-OCT), the images produced by OCT have become with higher resolution; thus, OCT has begun to provide more detailed information on ophthalmologic diagnoses [2]. Recent developments in ocular imaging technology have made the OCT a vital diagnostic tool in patient care. More recently, the availability of OCT during surgery has begun to be discussed. The introduction of OCT into the operating room (OR) called as intraoperative OCT (*i*OCT) has provided new insights into the surgical management during ophthalmic surgeries.

### **2. Intraoperative OCT**

A number of researchers have examined the potential role of *i*OCT in various conditions and procedures, such as macular hole (MH), epiretinal membrane (ERM), retinal detachment surgery, and lamellar keratoplasty [3–6]. However, conventional clinical OCT devices are large and not portable; therefore, it would be difficult and impractical to transfer the conventional OCTs into OR. In addition, the supine position of the patient during a surgery and changes to surgical flow are other potential obstacles for image acquisition with good quality. All these hurdles forced researchers to produce a portable OCT device. Initial attempts with

intraoperative OCT indicated successful results in imaging of excised tumors, postmortem specimens, structural changes after laser surgery, and in vitro human arteries and nerves [7–10]. Early investigations with *i*OCT were based on timedomain technology. Nevertheless, these investigations resulted in suboptimal image quality due to lower sensitivity and speed than novel technologies of SD-OCT and swept-source OCT (SS-OCT). In recent years, to overcome suboptimal imaging during surgeries, researchers have discovered the microscope-integrated OCT devices (MIOCTs). So far, a short overview about the evolution of *i*OCT devices was introduced. The following section will discuss various *i*OCT systems and devices and their technologies.

### **2.1 Intraoperative OCT systems and devices**

*i*OCT devices can be classified into two main categories: portable OCT during surgical pauses and microscope-integrated OCT (MIOCT). Subsequently, portable OCTs have three subgroups: handheld, external-mounted, and microscopemounted. On the other hand, MIOCTs have two subgroups: live two-dimensional (2D) OCT imaging and live four-dimensional (4D) OCT imaging (**Tables 1** and **2**).

#### *2.1.1 Portable OCT devices*

Portable OCT devices were the beginning step for *i*OCT. There are two basic portable systems in the literature: the Bioptigen EnVisu (Bioptigen, Research Triangle Park, NC/Leica, Wetzlar, Germany) and the Optovue iVue (Optovue, Fremont, CA, USA) [6, 11–13]. These devices can be used with the systems, including handheld, external-mounted, and microscope-mounted for image acquisition.

Handheld imaging was the first examples of the portable OCTs [11, 14]. This system has a compact handheld imaging probe connected over flexible optical fiber to a portable device. In spite of restrictions on image reproducibility and optimal aiming with the device, handheld imaging can present a good image quality. Moreover, unlike clinic tabletop OCT devices, handheld OCT has no requirement upright and cooperative patient situation. Nevertheless, the need to protect the sterile surgical field and the occurrence of motion artifacts due to instability are examples of several handicaps of handheld OCT. More importantly, the main disadvantage of handheld OCT is that it is limited to surgical pauses because of the need to remove the microscope from the patient during imaging. Unfortunately, it is impossible to obtain images of the structural changes that ensued from live tissue-instrument interactions during surgery.

*a Speed is listed in terms of A-scans/second; resolution refers to axial resolution; wavelength refers to the central wavelength of the source.*

† *Not specified in publications. Range provided by manufacturer.*

#### **Table 1.**

*System specifications and features of commercial HHOCT systems used in human retinal surgery to date.a With the permission of Carrasco-Zevallos OM et al. under the license of CC licensing [23].*

**21**

image repeatability [4].

*2.1.2 Microscope-integrated OCT devices*

*Intraoperative Optical Coherence Tomography DOI: http://dx.doi.org/10.5772/intechopen.81515*

**technology**

Spectral domain

Spectral domain

Spectral domain

**Speed, resolution, wavelength**

10k, 10 lm, 840 nm

27k, 5.5 lm, 840 nm

32k, 4 lm, 860 nm

**System OCT**

Haag-Streit surgical *i*OCT

Zeiss Rescan 700

Bioptigen EnFocus

*wavelength of the source.*

*a*

**Table 2.**

Mounting systems for the portable OCT systems were developed to address most of the handheld imaging. These external mounts contribute more stability, yet these systems require a supplementary footprint and place in the operating room [4, 6]. The microscope holders allow the surgeon to attach the portable probe directly to the microscope body, thus providing more stability than handheld imaging. Microscope foot pedal controls make it possible to control the probe position with X-Y-Z foot pedals. This foot pedal control makes easier imaging with improved

*Speed is listed in terms of A-scans/second; resolution refers to axial resolution; wavelength refers to the central*

*System specifications and features of all commercial MIOCT systems used in human retinal surgery to date.a*

*With the permission of Carrasco-Zevallos OM et al. under the license of CC licensing [23].*

**Primary visualization modes**

Live B-scans on binocular, monoscopic HUD

Live B-scans on monocular, monoscopic HUD

Live B-scans, static en face on external monitor

**OCT acquisition and features**

OCT operator control, surgeon control of OCT display via foot pedal, optical zoom

OCT operator control with tracking, surgeon control of OCT scan location via foot pedal

OCT operator control, surgeon control via foot pedal

**Commercial status**

FDA approved

FDA approved

FDA approved

Unfortunately, the main disadvantage of portable OCTs is that it is limited to surgical pauses because of the need to remove the microscope from the patient during imaging. In other words, it is impossible to obtain images of the structural changes that ensued from live tissue-instrument interactions during surgery.

A step-by-step initiative in the *i*OCT has been the integration of OCT into microscope optics called MIOCT. Leica (Leica, Wetzlar, Germany) and Zeiss (Carl Zeiss Meditec, Oberkochen, Germany) were the first examples of these systems. In the Zeiss adaptation, a modified Cirrus (Carl Zeiss Meditec) and a modified Visante (Carl Zeiss Meditec) OCT system integrated into Zeiss microscope optical path for the posterior and anterior segment imaging, respectively, were used [3, 15, 16]. These two systems allow surgeons for real-time imaging by visualizing the instrument-tissue interaction. On the other hand, these two systems bring with it new software requirements, the need for heads-up image acquisition, and the compatibility of OCT with the surgical instrument used during imaging. Additionally, surgical maneuvers during the surgery also require Z-axis stabilization and automated tracking system to improve image quality. After the investigation of first MIOCT systems, three commercial systems were identified. Zeiss Rescan 700 was defined as the first FDA-approved MIOCT system. This system is integrated into the Zeiss Lumera 700

*Intraoperative Optical Coherence Tomography DOI: http://dx.doi.org/10.5772/intechopen.81515*

*a Speed is listed in terms of A-scans/second; resolution refers to axial resolution; wavelength refers to the central wavelength of the source.*

#### **Table 2.**

*Novel Diagnostic Methods in Ophthalmology*

**2.1 Intraoperative OCT systems and devices**

and their technologies.

*2.1.1 Portable OCT devices*

**System OCT**

Optovue iVue

Bioptigen Envisu

*wavelength of the source.*

**technology**

Spectral domain

Spectral domain

*Not specified in publications. Range provided by manufacturer.*

intraoperative OCT indicated successful results in imaging of excised tumors, postmortem specimens, structural changes after laser surgery, and in vitro human arteries and nerves [7–10]. Early investigations with *i*OCT were based on timedomain technology. Nevertheless, these investigations resulted in suboptimal image quality due to lower sensitivity and speed than novel technologies of SD-OCT and swept-source OCT (SS-OCT). In recent years, to overcome suboptimal imaging during surgeries, researchers have discovered the microscope-integrated OCT devices (MIOCTs). So far, a short overview about the evolution of *i*OCT devices was introduced. The following section will discuss various *i*OCT systems and devices

*i*OCT devices can be classified into two main categories: portable OCT during surgical pauses and microscope-integrated OCT (MIOCT). Subsequently, portable

Portable OCT devices were the beginning step for *i*OCT. There are two basic portable systems in the literature: the Bioptigen EnVisu (Bioptigen, Research Triangle Park, NC/Leica, Wetzlar, Germany) and the Optovue iVue (Optovue, Fremont, CA, USA) [6, 11–13]. These devices can be used with the systems, including handheld,

Handheld imaging was the first examples of the portable OCTs [11, 14]. This system has a compact handheld imaging probe connected over flexible optical fiber to a portable device. In spite of restrictions on image reproducibility and optimal aiming with the device, handheld imaging can present a good image quality. Moreover, unlike clinic tabletop OCT devices, handheld OCT has no requirement upright and cooperative patient situation. Nevertheless, the need to protect the sterile surgical field and the occurrence of motion artifacts due to instability are examples of several handicaps of handheld OCT. More importantly, the main disadvantage of handheld OCT is that it is limited to surgical pauses because of the need to remove the microscope from the patient during imaging. Unfortunately, it is impossible to obtain images of the structural changes that ensued from live tissue-instrument interactions during surgery.

> **Primary visualization modes**

B-scans, volumes, en face on external monitor

B-scans, en face on external monitor

*Speed is listed in terms of A-scans/second; resolution refers to axial resolution; wavelength refers to the central*

*System specifications and features of commercial HHOCT systems used in human retinal surgery to date.a*

**Modes of operation**

Mounted onto stabilizing arm

Handheld, mounted onto microscope

**Commercial status**

FDA approved

FDA approved

 *With*

OCTs have three subgroups: handheld, external-mounted, and microscopemounted. On the other hand, MIOCTs have two subgroups: live two-dimensional (2D) OCT imaging and live four-dimensional (4D) OCT imaging (**Tables 1** and **2**).

external-mounted, and microscope-mounted for image acquisition.

**Speed, resolution, wavelength**

26k, 5 lm, 840 nm

17–32k†, 3–5† lm, 870 nm

*the permission of Carrasco-Zevallos OM et al. under the license of CC licensing [23].*

**20**

*a*

†

**Table 1.**

*System specifications and features of all commercial MIOCT systems used in human retinal surgery to date.a With the permission of Carrasco-Zevallos OM et al. under the license of CC licensing [23].*

Mounting systems for the portable OCT systems were developed to address most of the handheld imaging. These external mounts contribute more stability, yet these systems require a supplementary footprint and place in the operating room [4, 6]. The microscope holders allow the surgeon to attach the portable probe directly to the microscope body, thus providing more stability than handheld imaging. Microscope foot pedal controls make it possible to control the probe position with X-Y-Z foot pedals. This foot pedal control makes easier imaging with improved image repeatability [4].

Unfortunately, the main disadvantage of portable OCTs is that it is limited to surgical pauses because of the need to remove the microscope from the patient during imaging. In other words, it is impossible to obtain images of the structural changes that ensued from live tissue-instrument interactions during surgery.

#### *2.1.2 Microscope-integrated OCT devices*

A step-by-step initiative in the *i*OCT has been the integration of OCT into microscope optics called MIOCT. Leica (Leica, Wetzlar, Germany) and Zeiss (Carl Zeiss Meditec, Oberkochen, Germany) were the first examples of these systems. In the Zeiss adaptation, a modified Cirrus (Carl Zeiss Meditec) and a modified Visante (Carl Zeiss Meditec) OCT system integrated into Zeiss microscope optical path for the posterior and anterior segment imaging, respectively, were used [3, 15, 16]. These two systems allow surgeons for real-time imaging by visualizing the instrument-tissue interaction. On the other hand, these two systems bring with it new software requirements, the need for heads-up image acquisition, and the compatibility of OCT with the surgical instrument used during imaging. Additionally, surgical maneuvers during the surgery also require Z-axis stabilization and automated tracking system to improve image quality. After the investigation of first MIOCT systems, three commercial systems were identified. Zeiss Rescan 700 was defined as the first FDA-approved MIOCT system. This system is integrated into the Zeiss Lumera 700

microscope platform. Zeiss Rescan 700 was also integrated into the microscope foot pedal system to provide surgeon targeting, orientation control. More importantly, Zeiss Rescan 700 has the first MIOCT having Z-tracking system [17, 18]. The second FDA-approved MIOCT system was the Haag-Streit MIOCT system (Haag-Streit, Koeniz, Switzerland). This system consists of a side port using OPMedT (OPMedT, Lübeck, Germany) OCT system. This system has not only a microscope-mounted viewing but also a heads-up screen too [19]. Unlike Zeiss Rescan, the Haag-Streit Surgical *i*OCT has no control system with Z-tracking; differently, this system has an optical zoom. The third commercially available and FDA-approved MIOCT system was Bioptigen EnFocus iOCT system. This system can be adapted to both Leica and Zeiss microscopes. The system has a 4-μm resolution and a different static en face on external monitor as a visualization mode. Dissimilarly, Bioptigen EnFocus system has an essential long-fiber that provides more flexibility to insert the OCT device and its computer inside the operating room (**Figure 1**) [20].

With regard to limitations of the MIOCT devices, while a volumetric data could be obtained, acquisition of the volume is slow, and volume analysis as well as visualization has necessitated comprehensive postprocessing. Another important limitation of MIOCT devices is an inefficient display of continuous instrument movement due to intraoperative real-time visualization limited by B-scans. In other words, intraocular instruments used during live surgery generally give rise to shadows on the underlying tissue in B-scan mode. This issue requires alignment of the surgical maneuvers with the B-scan to eliminate instrumental ghosting during surgery. Ehlers et al. [21] described and characterized this shadowing effect with ex vivo porcine eye surgeries. Regarding surgical instrument shading, some authors have suggested the idea of an automated instrument tracking system using a stereo camera pair [22].

#### **Figure 1.**

*Live 2D MIOCT imaging of human retinal surgery with the commercially available Rescan 700 and a Cirrus HD-OCT system adapted to an operating microscope. (A) Frame captured with the camera that records the surgeon's view through the operating microscope. The orthogonal arrows correspond to the B-scan locations. (B) Horizontal (B1) and vertical (B2) B-scans acquired with the Rescan 700 during inner limiting membrane (ILM) peeling. The membrane edge (white arrowheads) is clearly visible in the B-scans along with "shadowing" (yellow arrowheads) from the intraocular forceps. With the permission of Carrasco-Zevallos OM et al. under the license of CC licensing [23].*

**23**

*Intraoperative Optical Coherence Tomography DOI: http://dx.doi.org/10.5772/intechopen.81515*

ing via a foot pedal joystick.

*2.2.1 Anterior segment*

procedures [4, 15, 16, 19, 22].

**2.2 Clinical applications of intraoperative OCT**

All real-time MIOCTs described above were limited to B-scan due to involvement of SD-OCT system having slower A-scan rate. Carrasco-Zevallos et al. [23] were the first authors who described the volumetric *i*OCT imaging of live model eye surgery. They presented a custom ultrafast SS-OCT system operating at 100 kHz of A-scan rate. This speed was three to five times faster than previous MIOCT devices. A software called a special graphics-processing unit was simultaneously used to get, process, and render volumes. Later, the same authors developed a custom microscope-integrated heads-up display (HUD) unit for stereoscopic imaging of MIOCT volumes [24, 25]. SS-MIOCT and stereoscopic HUD together were called as 4D MIOCT. In 2015, 4D MIOCT was first demonstrated by Carrasco-Zevallos et al. [23] for imaging of human retinal surgery. The volumetric frame rate varied 3.3–10 volumes per second during the surgery. Through a special mode "stream saving," OCT volumes were saved, and thus continuous volumetric recording could be acquired in the surgery. Visualization of the stereoscopic volumes by the HUD was enabled, and the surgeon could control the volume render-

Although 4D MIOCT devices have faster scan rate than 2D MIOCT due to faster A-scan rate, it requires faster A-scan rate as well as human flicker fusion rate (16 Hz) to attain optimal lateral resolution. In addition to that, instrumental shading effect is

still one of the major limitations in 4D MIOCT as well in 2D MIOCT devices.

In this part of the chapter, we will provide information on the clinical use of *i*OCT. In terms of both anterior and posterior segments, there are numerous of clinical studies related to feasibility and real-time assessment of the surgical feedback during the anterior and posterior surgeries [4–6, 11, 13, 14, 16–18, 20]. The two most important prospective clinical studies are the PIONNER study and the DISCOVER study [4, 20]. In these studies, the portable microscope-mounted *i*OCT in the PIONNER study (n = 531) and the microscope-integrated *i*OCT in the DISCOVER study (n = 227) were evaluated. There are not only large-scale prospective but also numerous smaller clinical studies in the literature. In the section that follows, feasibility and efficacy of *i*OCT for the anterior segment applications will be argued.

Intraoperative OCT has been used for various anterior segment surgeries involving penetrating and lamellar keratoplasty, cataract surgeries, and excisional biopsy

*i*OCT has been used for full-thickness and lamellar keratoplasty surgeries for decision-making. Particularly, *i*OCT can be very useful to evaluate in cases with extensive synechiae or iridocorneal scars. It may help to protect iris tissue from traumas during initial trephination [26]. Furthermore, the graft-host position can be estimated during surgery; thereby, it can help to construct proper graft-host relationship. In anterior lamellar keratoplasty, the presence of residual corneal opacities following microkeratome-assisted removal of anterior stromal layers can be detected, and their extensions may be easily confirmed by *i*OCT. Again, the thickness of residual stromal bed can be assessed, thus increasing the safety of operation [27]. As is known, it is very important to maintain an intact descemet membrane (DM) during deep anterior lamellar keratoplasty (DALK), and large bubble technique is widely used for this purpose. The *i*OCT helps to confirm the presence of large bubbles, detect subclinical large bubbles, and conduct additional dissections. In addition to these, the presence of any interface fluid can be determined with

#### *Intraoperative Optical Coherence Tomography DOI: http://dx.doi.org/10.5772/intechopen.81515*

*Novel Diagnostic Methods in Ophthalmology*

microscope platform. Zeiss Rescan 700 was also integrated into the microscope foot pedal system to provide surgeon targeting, orientation control. More importantly, Zeiss Rescan 700 has the first MIOCT having Z-tracking system [17, 18]. The second FDA-approved MIOCT system was the Haag-Streit MIOCT system (Haag-Streit, Koeniz, Switzerland). This system consists of a side port using OPMedT (OPMedT, Lübeck, Germany) OCT system. This system has not only a microscope-mounted viewing but also a heads-up screen too [19]. Unlike Zeiss Rescan, the Haag-Streit Surgical *i*OCT has no control system with Z-tracking; differently, this system has an optical zoom. The third commercially available and FDA-approved MIOCT system was Bioptigen EnFocus iOCT system. This system can be adapted to both Leica and Zeiss microscopes. The system has a 4-μm resolution and a different static en face on external monitor as a visualization mode. Dissimilarly, Bioptigen EnFocus system has an essential long-fiber that provides more flexibility to insert the OCT device

With regard to limitations of the MIOCT devices, while a volumetric data could be obtained, acquisition of the volume is slow, and volume analysis as well as visualization has necessitated comprehensive postprocessing. Another important limitation of MIOCT devices is an inefficient display of continuous instrument movement due to intraoperative real-time visualization limited by B-scans. In other words, intraocular instruments used during live surgery generally give rise to shadows on the underlying tissue in B-scan mode. This issue requires alignment of the surgical maneuvers with the B-scan to eliminate instrumental ghosting during surgery. Ehlers et al. [21] described and characterized this shadowing effect with ex vivo porcine eye surgeries. Regarding surgical instrument shading, some authors have suggested the idea of an automated instrument tracking system using a stereo camera pair [22].

*Live 2D MIOCT imaging of human retinal surgery with the commercially available Rescan 700 and a Cirrus HD-OCT system adapted to an operating microscope. (A) Frame captured with the camera that records the surgeon's view through the operating microscope. The orthogonal arrows correspond to the B-scan locations. (B) Horizontal (B1) and vertical (B2) B-scans acquired with the Rescan 700 during inner limiting membrane (ILM) peeling. The membrane edge (white arrowheads) is clearly visible in the B-scans along with "shadowing" (yellow arrowheads) from the intraocular forceps. With the permission of Carrasco-Zevallos OM*

and its computer inside the operating room (**Figure 1**) [20].

**22**

**Figure 1.**

*et al. under the license of CC licensing [23].*

All real-time MIOCTs described above were limited to B-scan due to involvement of SD-OCT system having slower A-scan rate. Carrasco-Zevallos et al. [23] were the first authors who described the volumetric *i*OCT imaging of live model eye surgery. They presented a custom ultrafast SS-OCT system operating at 100 kHz of A-scan rate. This speed was three to five times faster than previous MIOCT devices. A software called a special graphics-processing unit was simultaneously used to get, process, and render volumes. Later, the same authors developed a custom microscope-integrated heads-up display (HUD) unit for stereoscopic imaging of MIOCT volumes [24, 25]. SS-MIOCT and stereoscopic HUD together were called as 4D MIOCT. In 2015, 4D MIOCT was first demonstrated by Carrasco-Zevallos et al. [23] for imaging of human retinal surgery. The volumetric frame rate varied 3.3–10 volumes per second during the surgery. Through a special mode "stream saving," OCT volumes were saved, and thus continuous volumetric recording could be acquired in the surgery. Visualization of the stereoscopic volumes by the HUD was enabled, and the surgeon could control the volume rendering via a foot pedal joystick.

Although 4D MIOCT devices have faster scan rate than 2D MIOCT due to faster A-scan rate, it requires faster A-scan rate as well as human flicker fusion rate (16 Hz) to attain optimal lateral resolution. In addition to that, instrumental shading effect is still one of the major limitations in 4D MIOCT as well in 2D MIOCT devices.

### **2.2 Clinical applications of intraoperative OCT**

In this part of the chapter, we will provide information on the clinical use of *i*OCT. In terms of both anterior and posterior segments, there are numerous of clinical studies related to feasibility and real-time assessment of the surgical feedback during the anterior and posterior surgeries [4–6, 11, 13, 14, 16–18, 20]. The two most important prospective clinical studies are the PIONNER study and the DISCOVER study [4, 20]. In these studies, the portable microscope-mounted *i*OCT in the PIONNER study (n = 531) and the microscope-integrated *i*OCT in the DISCOVER study (n = 227) were evaluated. There are not only large-scale prospective but also numerous smaller clinical studies in the literature. In the section that follows, feasibility and efficacy of *i*OCT for the anterior segment applications will be argued.

#### *2.2.1 Anterior segment*

Intraoperative OCT has been used for various anterior segment surgeries involving penetrating and lamellar keratoplasty, cataract surgeries, and excisional biopsy procedures [4, 15, 16, 19, 22].

*i*OCT has been used for full-thickness and lamellar keratoplasty surgeries for decision-making. Particularly, *i*OCT can be very useful to evaluate in cases with extensive synechiae or iridocorneal scars. It may help to protect iris tissue from traumas during initial trephination [26]. Furthermore, the graft-host position can be estimated during surgery; thereby, it can help to construct proper graft-host relationship. In anterior lamellar keratoplasty, the presence of residual corneal opacities following microkeratome-assisted removal of anterior stromal layers can be detected, and their extensions may be easily confirmed by *i*OCT. Again, the thickness of residual stromal bed can be assessed, thus increasing the safety of operation [27]. As is known, it is very important to maintain an intact descemet membrane (DM) during deep anterior lamellar keratoplasty (DALK), and large bubble technique is widely used for this purpose. The *i*OCT helps to confirm the presence of large bubbles, detect subclinical large bubbles, and conduct additional dissections. In addition to these, the presence of any interface fluid can be determined with

the help of the *i*OCT, thus helping to determine the extra maneuvers that need to be done to ensure proper position of tissues to the end of the surgery. However, the instrumental shadowing effect may hinder the visualization of the underlying structures, thereby limiting the effective use of *i*OCT during intrastromal insertion of the needle. Therefore, surgical pause is necessary to evaluate the underlying tissues [17, 28, 29]. *i*OCT is a helpful intraoperative imaging method not only in full-thickness and lamellar but also in endothelial keratoplasty applications, e.g., descemet stripping automated endothelial keratoplasty (DSAEK) and descemet membrane endothelial keratoplasty (DMEK). Especially, in double-pass technique in DSAEK, the residual donor thickness following the first microkeratome passing can be easily determined with guiding *i*OCT to select of ideal blade size for the next microkeratome passing. This will minimize the chance of perforation of donor tissue by obtaining very thin donor lenticules [30]. Additionally, *i*OCT provides an advantage to identify and remove the descemet membrane in case of extreme edematous corneas. Furthermore, *i*OCT allows a continuous monitoring during the graft insertion and unfolding process. In DMEK, *i*OCT is a very convenient tool to provide faster graft orientation and position, especially in cases with edematous cornea [31]. In the DISCOVER study, it was reported that the surgeons required additional surgical maneuvers in 41% of the cases having DSAEK [18]. Similarly, in the PIONNER study, results showed that 19% of the cases in which surgeons believed the graft was completely apposed had still persistent fluid detected in the *i*OCT; hence, it would require more maneuvers and vice versa; in 47% of cases where the surgeon believed the graft to be partially apposed, there was complete apposition in *i*OCT imaging [4]. These two studies have also revealed that *i*OCT aids changes in dissection depth in 38–56% of cases [4, 20]. Briefly, it can be concluded that *i*OCT in keratoplasty procedures can minimize unnecessary manipulations and surgical time.

Recently, *i*OCT has been used in various stages of a cataract surgery. The wound structure, status of posterior capsule, and position of intraocular lens (IOL) can be easily assessed via *i*OCT during a cataract surgery [32]. In a case report, it was reported that MIOCT was a very feasible tool to evaluate the wound architecture, integrity of the posterior capsule, IOL position, and efficacy of stromal hydration. The authors suggested that *i*OCT could be helpful in real-time early detection of various complications of cataract surgery, thus allowing the surgeon to manage the complication immediately [33].

More recently, in taking biopsy and excisional procedures, such as retrocorneal fibrosis and pterygium excision, and evaluating intraoperative changes in corneal structure during excimer laser phototherapeutic keratectomy, feasibility of *i*OCT was assessed, and the results were promising [34, 35].

#### *2.2.2 Posterior segment*

Similar to the use of *i*OCT for anterior segment surgery, *i*OCT has a wide range of potentials for posterior segment surgery. Numerous vitreoretinal pathologies were described with *i*OCT, such as retinopathy of premature (ROP), proliferative diabetic retinopathy, macular hole, epiretinal membrane (ERM), retinal detachment, and myopic foveoschisis [4, 5, 20, 36–39]. The *i*OCT has provided new insights into the underlying pathophysiology for some of these conditions. PIONEER and DISCOVER studies provided valuable information about *i*OCT for posterior segment surgeons [4, 20]. We will discuss the results of these studies at the end of this section.

Chavala et al. [11] reported that they identified preretinal structures and retinoschisis with *i*OCT in case of ROP. They suggested that these new findings might

**25**

**Figure 2.**

*Intraoperative Optical Coherence Tomography DOI: http://dx.doi.org/10.5772/intechopen.81515*

fronds during the surgery.

fiber layer.

retina.

markedly affect the surgeons to make a decision resulting in various alterations during the operation. It is thought that *i*OCT may allow the surgeons to assess the extents of both horizontal and anteroposterior tractional structures in ROP cases; thus, the surgeons could carefully dissect or peel while sparing the other retinal structures. Additionally, *i*OCT is very useful detecting the flat neovascular fronds in ROP cases as well as other vascular retinopathies; thereby, this could prevent iatrogenic hemorrhages by determining the extent and location of the neovascular

The *i*OCT helps the surgeon to determine the firmness of vitreomacular tractions; therefore, in case of foveal cyst, de-roofing risk would diminish, and inadvertent macular hole could be eliminated. Similarly, during an ERM and internal limiting membrane (ILM) peeling, the *i*OCT decreases the risk of inadvertent

One of the retinopathies in which the *i*OCT is used is myopic foveoschisis. As known, there are multiple layers of schisis in this retinopathy, and this involves vital dye staining to make certain that the whole cortical vitreous has been removed. However, the cases with myopic foveoschisis have a longer axial length, thus giving rise to poor dying. The *i*OCT can allow not only to better evaluate the ILM but also to prevent iatrogenic breaks by improving visualization in a myopic

*i*OCT enables to provide more information in retinal detachment cases. In recent various studies, the *i*OCT revealed the presence of subclinical persistent subretinal fluid under perfluorocarbon tamponade in most of the cases undergoing retinal

*B-scan (C1) and volume (C2) acquired intraoperatively before epiretinal membrane (ERM) peeling with the reconfigured Cirrus HD-OCT system. B-scan (D1) and volume (D2) acquired after ERM peeling. The volumes required intensive postprocessing to render and were visualized postoperatively. The prepeeling volumes depict ERM and puckering of the retina, while the post-peeling volumes show a small residual part of ERM*  (*Figure 1*). *With the permission of Carrasco-Zevallos OM et al. under the license of CC licensing [23].*

grasping of the retina while completing ERM/ILM peeling (**Figure 2**). In a recent study, it was reported that a membrane peeling with the guidance of *i*OCT was enabled without the use of adjuvant dyes to identify of membrane edges [36]. Especially in a macular hole surgery, this advantage of *i*OCT allows visualization of the alterations in the macular hole architecture as well as in the outer retina [37, 40]. In addition, during a macular hole surgery, the surgeon may worry about inadvertent touching or tearing on nerve fiber layer. In such situation, the *i*OCT with real-time feedback can prevent inadvertent damage on nerve

#### *Intraoperative Optical Coherence Tomography DOI: http://dx.doi.org/10.5772/intechopen.81515*

*Novel Diagnostic Methods in Ophthalmology*

the help of the *i*OCT, thus helping to determine the extra maneuvers that need to be done to ensure proper position of tissues to the end of the surgery. However, the instrumental shadowing effect may hinder the visualization of the underlying structures, thereby limiting the effective use of *i*OCT during intrastromal insertion of the needle. Therefore, surgical pause is necessary to evaluate the underlying tissues [17, 28, 29]. *i*OCT is a helpful intraoperative imaging method not only in full-thickness and lamellar but also in endothelial keratoplasty applications, e.g., descemet stripping automated endothelial keratoplasty (DSAEK) and descemet membrane endothelial keratoplasty (DMEK). Especially, in double-pass technique in DSAEK, the residual donor thickness following the first microkeratome passing can be easily determined with guiding *i*OCT to select of ideal blade size for the next microkeratome passing. This will minimize the chance of perforation of donor tissue by obtaining very thin donor lenticules [30]. Additionally, *i*OCT provides an advantage to identify and remove the descemet membrane in case of extreme edematous corneas. Furthermore, *i*OCT allows a continuous monitoring during the graft insertion and unfolding process. In DMEK, *i*OCT is a very convenient tool to provide faster graft orientation and position, especially in cases with edematous cornea [31]. In the DISCOVER study, it was reported that the surgeons required additional surgical maneuvers in 41% of the cases having DSAEK [18]. Similarly, in the PIONNER study, results showed that 19% of the cases in which surgeons believed the graft was completely apposed had still persistent fluid detected in the *i*OCT; hence, it would require more maneuvers and vice versa; in 47% of cases where the surgeon believed the graft to be partially apposed, there was complete apposition in *i*OCT imaging [4]. These two studies have also revealed that *i*OCT aids changes in dissection depth in 38–56% of cases [4, 20]. Briefly, it can be concluded that *i*OCT in keratoplasty procedures can minimize unnecessary manipulations and

Recently, *i*OCT has been used in various stages of a cataract surgery. The wound structure, status of posterior capsule, and position of intraocular lens (IOL) can be easily assessed via *i*OCT during a cataract surgery [32]. In a case report, it was reported that MIOCT was a very feasible tool to evaluate the wound architecture, integrity of the posterior capsule, IOL position, and efficacy of stromal hydration. The authors suggested that *i*OCT could be helpful in real-time early detection of various complications of cataract surgery, thus allowing the surgeon to manage the

More recently, in taking biopsy and excisional procedures, such as retrocorneal fibrosis and pterygium excision, and evaluating intraoperative changes in corneal structure during excimer laser phototherapeutic keratectomy, feasibility of *i*OCT

Similar to the use of *i*OCT for anterior segment surgery, *i*OCT has a wide range of potentials for posterior segment surgery. Numerous vitreoretinal pathologies were described with *i*OCT, such as retinopathy of premature (ROP), proliferative diabetic retinopathy, macular hole, epiretinal membrane (ERM), retinal detachment, and myopic foveoschisis [4, 5, 20, 36–39]. The *i*OCT has provided new insights into the underlying pathophysiology for some of these conditions. PIONEER and DISCOVER studies provided valuable information about *i*OCT for posterior segment surgeons [4, 20]. We will discuss the results of these studies at

Chavala et al. [11] reported that they identified preretinal structures and retinoschisis with *i*OCT in case of ROP. They suggested that these new findings might

**24**

surgical time.

complication immediately [33].

*2.2.2 Posterior segment*

the end of this section.

was assessed, and the results were promising [34, 35].

markedly affect the surgeons to make a decision resulting in various alterations during the operation. It is thought that *i*OCT may allow the surgeons to assess the extents of both horizontal and anteroposterior tractional structures in ROP cases; thus, the surgeons could carefully dissect or peel while sparing the other retinal structures. Additionally, *i*OCT is very useful detecting the flat neovascular fronds in ROP cases as well as other vascular retinopathies; thereby, this could prevent iatrogenic hemorrhages by determining the extent and location of the neovascular fronds during the surgery.

The *i*OCT helps the surgeon to determine the firmness of vitreomacular tractions; therefore, in case of foveal cyst, de-roofing risk would diminish, and inadvertent macular hole could be eliminated. Similarly, during an ERM and internal limiting membrane (ILM) peeling, the *i*OCT decreases the risk of inadvertent grasping of the retina while completing ERM/ILM peeling (**Figure 2**). In a recent study, it was reported that a membrane peeling with the guidance of *i*OCT was enabled without the use of adjuvant dyes to identify of membrane edges [36]. Especially in a macular hole surgery, this advantage of *i*OCT allows visualization of the alterations in the macular hole architecture as well as in the outer retina [37, 40]. In addition, during a macular hole surgery, the surgeon may worry about inadvertent touching or tearing on nerve fiber layer. In such situation, the *i*OCT with real-time feedback can prevent inadvertent damage on nerve fiber layer.

One of the retinopathies in which the *i*OCT is used is myopic foveoschisis. As known, there are multiple layers of schisis in this retinopathy, and this involves vital dye staining to make certain that the whole cortical vitreous has been removed. However, the cases with myopic foveoschisis have a longer axial length, thus giving rise to poor dying. The *i*OCT can allow not only to better evaluate the ILM but also to prevent iatrogenic breaks by improving visualization in a myopic retina.

*i*OCT enables to provide more information in retinal detachment cases. In recent various studies, the *i*OCT revealed the presence of subclinical persistent subretinal fluid under perfluorocarbon tamponade in most of the cases undergoing retinal

#### **Figure 2.**

*B-scan (C1) and volume (C2) acquired intraoperatively before epiretinal membrane (ERM) peeling with the reconfigured Cirrus HD-OCT system. B-scan (D1) and volume (D2) acquired after ERM peeling. The volumes required intensive postprocessing to render and were visualized postoperatively. The prepeeling volumes depict ERM and puckering of the retina, while the post-peeling volumes show a small residual part of ERM*  (*Figure 1*). *With the permission of Carrasco-Zevallos OM et al. under the license of CC licensing [23].*

detachment operation [4, 5, 20]. Furthermore, *i*OCT can help to detect proliferative vitreoretinopathy changes and border architecture of retinal tears.

In proliferative diabetic retinopathy, *i*OCT provides an enhanced imaging during delamination of membranes. For this reason, the *i*OCT facilitates the identification of the surgical plane, which permits membrane peeling in a safe manner. In addition to that, in the cases of dense vitreous hemorrhage, *i*OCT can help to assess intraoperatively the underlying macular pathology, such as intraretinal fluid, macular edema, or presence of a membrane, which may impact the surgeon in changing operation plan [38, 39].

Recently, in the 3-year outcome reports of the DISCOVER study, the use of *i*OCT for image-guided retinal biopsy and placement of Argus II implant was reported. It was demonstrated that *i*OCT facilitates insertion of the biopsy site and enabled confirming placement of the implant in optimal location [41, 42]. More recently, a few studies reported the use of *i*OCT verifying subretinal location of gene therapy and stem cells during the operation [43, 44].

Finally, the outcomes in posterior segment surgery in the PIONNER and DISCOVER studies showed that *i*OCT identified residual membranes in 13–22% of the cases whom the surgeon believed that membrane peeling was completed; conversely, in 15–40% of the cases, the surgeon still thought the presence of residual membrane, yet *i*OCT indicated that complete removal of the membrane had been performed [4, 20]. Additionally, *i*OCT provided addition of useful data concerning surgical anatomic features in 59.4% of the cases, and the information obtaining with *i*OCT impacted the surgery in 29.2% of the cases [20].

### **3. Conclusion**

As known, in a very short time, conventional tabletop OCT has acquired its place in practice; subsequently, real-time intraoperative feedback with the *i*OCT appears to be a revolution in the OCT technology. Up to now, overall study reports related to *i*OCT, especially the PIONNER and DISCOVER study, have enhanced our understanding of *i*OCT technology and its unique advantages in surgical efficiency. *i*OCT may lead to refine and replace conventional surgical procedures with novel procedures, so that, with this technology, improved individual surgical management and patient care can be achieved. However, this technology has still a few limitations. The overall outcomes related to feasibility of *i*OCT need to be validated with additional prospective randomized trials.

**27**

**Author details**

Samet Gulkas1

provided the original work is properly cited.

\* and Osman Cekic2

1 Sanliurfa Training and Research Hospital, Sanliurfa, Turkey

2 University of Marmara, School of Medicine, Istanbul, Turkey

\*Address all correspondence to<EMAIL_ADDRESS>
*Intraoperative Optical Coherence Tomography DOI: http://dx.doi.org/10.5772/intechopen.81515*

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

#### **Conflict of interest**

There are no conflicts of interest.

*Intraoperative Optical Coherence Tomography DOI: http://dx.doi.org/10.5772/intechopen.81515*

*Novel Diagnostic Methods in Ophthalmology*

and stem cells during the operation [43, 44].

with additional prospective randomized trials.

There are no conflicts of interest.

with *i*OCT impacted the surgery in 29.2% of the cases [20].

operation plan [38, 39].

**3. Conclusion**

**Conflict of interest**

detachment operation [4, 5, 20]. Furthermore, *i*OCT can help to detect proliferative

In proliferative diabetic retinopathy, *i*OCT provides an enhanced imaging during delamination of membranes. For this reason, the *i*OCT facilitates the identification of the surgical plane, which permits membrane peeling in a safe manner. In addition to that, in the cases of dense vitreous hemorrhage, *i*OCT can help to assess intraoperatively the underlying macular pathology, such as intraretinal fluid, macular edema, or presence of a membrane, which may impact the surgeon in changing

Recently, in the 3-year outcome reports of the DISCOVER study, the use of *i*OCT for image-guided retinal biopsy and placement of Argus II implant was reported. It was demonstrated that *i*OCT facilitates insertion of the biopsy site and enabled confirming placement of the implant in optimal location [41, 42]. More recently, a few studies reported the use of *i*OCT verifying subretinal location of gene therapy

Finally, the outcomes in posterior segment surgery in the PIONNER and DISCOVER studies showed that *i*OCT identified residual membranes in 13–22% of the cases whom the surgeon believed that membrane peeling was completed; conversely, in 15–40% of the cases, the surgeon still thought the presence of residual membrane, yet *i*OCT indicated that complete removal of the membrane had been performed [4, 20]. Additionally, *i*OCT provided addition of useful data concerning surgical anatomic features in 59.4% of the cases, and the information obtaining

As known, in a very short time, conventional tabletop OCT has acquired its place in practice; subsequently, real-time intraoperative feedback with the *i*OCT appears to be a revolution in the OCT technology. Up to now, overall study reports related to *i*OCT, especially the PIONNER and DISCOVER study, have enhanced our understanding of *i*OCT technology and its unique advantages in surgical efficiency. *i*OCT may lead to refine and replace conventional surgical procedures with novel procedures, so that, with this technology, improved individual surgical management and patient care can be achieved. However, this technology has still a few limitations. The overall outcomes related to feasibility of *i*OCT need to be validated

vitreoretinopathy changes and border architecture of retinal tears.

**26**

### **Author details**

Samet Gulkas1 \* and Osman Cekic2

1 Sanliurfa Training and Research Hospital, Sanliurfa, Turkey

2 University of Marmara, School of Medicine, Istanbul, Turkey

\*Address all correspondence to<EMAIL_ADDRESS>
© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **References**

[1] Huang D, Swanson EA, Lin CP, et al. Optical coherence tomography. Science. 1991;**254**:1178-1181

[2] Choma M, Sarunic M, Yang C, et al. Sensitivity advantage of swept source and Fourier domain optical coherence tomography. Optics Express. 2003;**11**:2183-2189

[3] Binder S, Falkner-Radler CI, Hauger C, et al. Feasibility of intrasurgical spectral-domain optical coherence tomography. Retina. 2011;**31**:1332-1336

[4] Ehlers JP, Dupps WJ, Kaiser PK, et al. The prospective intraoperative and perioperative ophthalmic ImagiNg with optical coherence tomography (PIONEER) study: 2-year results. American Journal of Ophthalmology. 2014;**158**:999-1007

[5] Ehlers JP, Ohr MP, Kaiser PK, et al. Novel microarchitectural dynamics in rhegmatogenous retinal detachments identified with intraoperative optical coherence tomography. Retina. 2013;**33**:1428-1434

[6] Ray R, Baranano DE, Fortun JA, et al. Intraoperative microscopemounted spectral domain optical coherence tomography for evaluation of retinal anatomy during macular surgery. Ophthalmology. 2011;**118**:2212-2217

[7] Boppart SA, Bouma BE, Pitris C, et al. Intraoperative assessment of microsurgery with three-dimensional optical coherence tomography. Radiology. 1998;**208**:81-86

[8] Boppart SA, Herrmann JM, Pitris C, et al. Real-time optical coherence tomography for minimally invasive imaging of prostate ablation. Computer Aided Surgery. 2001;**6**:94-103

[9] Brezinski ME, Tearney GJ, Bouma B, et al. Optical biopsy with optical

coherence tomography. Annals of the New York Academy of Sciences. 1998;**838**:68-74

[10] Shakhov AV, Terentjeva AB, Kamensky VA, et al. Optical coherence tomography monitoring for laser surgery of laryngeal carcinoma. Journal of Surgical Oncology. 2001;**77**:253-258

[11] Chavala SH, Farsiu S, Maldonado R, et al. Insights into advanced retinopathy of prematurity using handheld spectral domain optical coherence tomography imaging. Ophthalmology. 2009;**116**:2448-2456

[12] Dayani PN, Maldonado R, Farsiu S, et al. Intraoperative use of handheld spectral domain optical coherence tomography imaging in macular surgery. Retina. 2009;**29**:1457-1468

[13] Pichi F, Alkabes M, Nucci P, et al. Intraoperative SD-OCT in macular surgery. Ophthalmic Surgery, Lasers & Imaging. 2012;**43**:S54-S60

[14] Scott AW, Farsiu S, Enyedi LB, et al. Imaging the infant retina with a handheld spectral-domain optical coherence tomography device. American Journal of Ophthalmology. 2009;**147**:364-373

[15] Hirnschall N, Amir-Asgari S, Maedel S, et al. Predicting the postoperative intraocular lens position using continuous intraoperative optical coherence tomography measurements. Investigative Ophthalmology & Visual Science. 2013;**54**:5196-5203

[16] Hirnschall N, Norrby S, Weber M, et al. Using continuous intraoperative optical coherence tomography measurements of the aphakic eye for intraocular lens power calculation. The British Journal of Ophthalmology. 2015;**99**:7-10

[17] Ehlers JP, Goshe J, Dupps WJ, et al. Determination of feasibility

**29**

*Intraoperative Optical Coherence Tomography DOI: http://dx.doi.org/10.5772/intechopen.81515*

and utility of microscope-integrated optical coherence tomography during ophthalmic surgery: The DISCOVER study RESCAN results. JAMA Ophthalmology. 2015;**133**:1124-1132

tomography. Biomedical Optics Express.

[25] Tao YK, Ehlers JP, Toth CA, et al. Intraoperative spectral domain optical coherence tomography for vitreoretinal surgery. Optics Letters.

[26] Eguchi H, Kusaka S, Arimura-Koike E, et al. Intraoperative optical coherence tomography (RESCAN((R)) 700) for detecting iris incarceration and iridocorneal adhesion during keratoplasty. International Ophthalmology. 2017;**37**:761-765

[27] Titiyal JS, Kaur M, Falera R. Intraoperative optical coherence tomography in anterior segment surgeries. Indian Journal of Ophthalmology. 2017;**65**:116-121

Cornea. 2015;**34**:1039-1043

[28] Au J, Goshe J, Dupps WJ Jr, et al. Intraoperative optical coherence tomography for enhanced depth visualization in deep anterior lamellar keratoplasty from the PIONEER study.

[29] Steven P, Le Blanc C, Lankenau E, et al. Optimising deep anterior lamellar keratoplasty (DALK) using intraoperative online optical coherence tomography (iOCT). The British Journal of Ophthalmology. 2014;**98**:900-904

[30] Kobayashi A, Yokogawa H, Mori N, et al. Visualization of precut DSAEK and pre-stripped DMEK donor corneas by intraoperative optical coherence tomography using the RESCAN 700. BMC Ophthalmology. 2016;**16**:135

[31] Saad A, Guilbert E, Grise-Dulac A, et al. Intraoperative OCT-assisted DMEK: 14 consecutive cases. Cornea.

[32] Das S, Kummelil MK, Kharbanda V, et al. Microscope integrated

intraoperative spectral domain optical coherence tomography for cataract

2015;**34**:802-807

2016;**7**:1711-1726

2010;**35**:3315-3317

[18] Ehlers JP, Kaiser PK, Srivastava SK. Intraoperative optical coherence tomography using the RESCAN 700: Preliminary results from the DISCOVER study. The British Journal of Ophthalmology. 2014;**98**:1329-1332

[19] Steven P, Le Blanc C, Velten K, et al. Optimizing descemet membrane

[20] Ehlers JP, Modi YS, Pecen PE, et al. The DISCOVER study 3-year results: Feasibility and usefulness of microscope-integrated intraoperative OCT during ophthalmic surgery. Ophthalmology. 2018;**125**:1014-1027

[21] Ehlers JP, Tao YK, Farsiu S, et al. Integration of a spectral domain optical coherence tomography system into a surgical microscope for intraoperative imaging. Investigative Ophthalmology & Visual Science. 2011;**52**:3153-3159

[22] El-Haddad MT, Tao YK. Automated stereo vision instrument tracking for intraoperative OCT guided anterior segment ophthalmic surgical maneuvers. Biomedical Optics Express.

[23] Carrasco-Zevallos OM, Keller B, Viehland C, et al. Optical coherence tomography for retinal surgery:

Perioperative analysis to real-time fourdimensional image-guided surgery. Investigative Ophthalmology & Visual Science. 2016;**57**:OCT37-OCT50

integrated stereoscopic heads-up display for intrasurgical optical coherence

[24] Shen L, Carrasco-Zevallos O, Keller B, et al. Novel microscope-

endothelial keratoplasty using intraoperative optical coherence tomography. JAMA Ophthalmology.

2013;**131**:1135-1142

2015;**6**:3014-3031

*Intraoperative Optical Coherence Tomography DOI: http://dx.doi.org/10.5772/intechopen.81515*

and utility of microscope-integrated optical coherence tomography during ophthalmic surgery: The DISCOVER study RESCAN results. JAMA Ophthalmology. 2015;**133**:1124-1132

[18] Ehlers JP, Kaiser PK, Srivastava SK. Intraoperative optical coherence tomography using the RESCAN 700: Preliminary results from the DISCOVER study. The British Journal of Ophthalmology. 2014;**98**:1329-1332

[19] Steven P, Le Blanc C, Velten K, et al. Optimizing descemet membrane endothelial keratoplasty using intraoperative optical coherence tomography. JAMA Ophthalmology. 2013;**131**:1135-1142

[20] Ehlers JP, Modi YS, Pecen PE, et al. The DISCOVER study 3-year results: Feasibility and usefulness of microscope-integrated intraoperative OCT during ophthalmic surgery. Ophthalmology. 2018;**125**:1014-1027

[21] Ehlers JP, Tao YK, Farsiu S, et al. Integration of a spectral domain optical coherence tomography system into a surgical microscope for intraoperative imaging. Investigative Ophthalmology & Visual Science. 2011;**52**:3153-3159

[22] El-Haddad MT, Tao YK. Automated stereo vision instrument tracking for intraoperative OCT guided anterior segment ophthalmic surgical maneuvers. Biomedical Optics Express. 2015;**6**:3014-3031

[23] Carrasco-Zevallos OM, Keller B, Viehland C, et al. Optical coherence tomography for retinal surgery: Perioperative analysis to real-time fourdimensional image-guided surgery. Investigative Ophthalmology & Visual Science. 2016;**57**:OCT37-OCT50

[24] Shen L, Carrasco-Zevallos O, Keller B, et al. Novel microscopeintegrated stereoscopic heads-up display for intrasurgical optical coherence

tomography. Biomedical Optics Express. 2016;**7**:1711-1726

[25] Tao YK, Ehlers JP, Toth CA, et al. Intraoperative spectral domain optical coherence tomography for vitreoretinal surgery. Optics Letters. 2010;**35**:3315-3317

[26] Eguchi H, Kusaka S, Arimura-Koike E, et al. Intraoperative optical coherence tomography (RESCAN((R)) 700) for detecting iris incarceration and iridocorneal adhesion during keratoplasty. International Ophthalmology. 2017;**37**:761-765

[27] Titiyal JS, Kaur M, Falera R. Intraoperative optical coherence tomography in anterior segment surgeries. Indian Journal of Ophthalmology. 2017;**65**:116-121

[28] Au J, Goshe J, Dupps WJ Jr, et al. Intraoperative optical coherence tomography for enhanced depth visualization in deep anterior lamellar keratoplasty from the PIONEER study. Cornea. 2015;**34**:1039-1043

[29] Steven P, Le Blanc C, Lankenau E, et al. Optimising deep anterior lamellar keratoplasty (DALK) using intraoperative online optical coherence tomography (iOCT). The British Journal of Ophthalmology. 2014;**98**:900-904

[30] Kobayashi A, Yokogawa H, Mori N, et al. Visualization of precut DSAEK and pre-stripped DMEK donor corneas by intraoperative optical coherence tomography using the RESCAN 700. BMC Ophthalmology. 2016;**16**:135

[31] Saad A, Guilbert E, Grise-Dulac A, et al. Intraoperative OCT-assisted DMEK: 14 consecutive cases. Cornea. 2015;**34**:802-807

[32] Das S, Kummelil MK, Kharbanda V, et al. Microscope integrated intraoperative spectral domain optical coherence tomography for cataract

**28**

*Novel Diagnostic Methods in Ophthalmology*

[1] Huang D, Swanson EA, Lin CP, et al. Optical coherence tomography. Science. coherence tomography. Annals of the New York Academy of Sciences.

[10] Shakhov AV, Terentjeva AB, Kamensky VA, et al. Optical coherence tomography monitoring for laser surgery of laryngeal carcinoma. Journal of Surgical Oncology. 2001;**77**:253-258

of prematurity using handheld spectral domain optical coherence tomography imaging. Ophthalmology.

2009;**116**:2448-2456

[11] Chavala SH, Farsiu S, Maldonado R, et al. Insights into advanced retinopathy

[12] Dayani PN, Maldonado R, Farsiu S, et al. Intraoperative use of handheld spectral domain optical coherence tomography imaging in macular surgery. Retina. 2009;**29**:1457-1468

[13] Pichi F, Alkabes M, Nucci P, et al. Intraoperative SD-OCT in macular surgery. Ophthalmic Surgery, Lasers &

[14] Scott AW, Farsiu S, Enyedi LB, et al. Imaging the infant retina with a handheld spectral-domain optical coherence tomography device. American Journal of Ophthalmology. 2009;**147**:364-373

Imaging. 2012;**43**:S54-S60

[15] Hirnschall N, Amir-Asgari S, Maedel S, et al. Predicting the postoperative intraocular lens position using continuous intraoperative optical coherence tomography measurements. Investigative Ophthalmology & Visual

Science. 2013;**54**:5196-5203

2015;**99**:7-10

[16] Hirnschall N, Norrby S, Weber M, et al. Using continuous intraoperative optical coherence tomography measurements of the aphakic eye for intraocular lens power calculation. The British Journal of Ophthalmology.

[17] Ehlers JP, Goshe J, Dupps WJ, et al. Determination of feasibility

1998;**838**:68-74

[3] Binder S, Falkner-Radler CI, Hauger C, et al. Feasibility of intrasurgical spectral-domain optical coherence tomography. Retina. 2011;**31**:1332-1336

[4] Ehlers JP, Dupps WJ, Kaiser PK, et al. The prospective intraoperative and perioperative ophthalmic ImagiNg with optical coherence tomography (PIONEER) study: 2-year results. American Journal of Ophthalmology.

[5] Ehlers JP, Ohr MP, Kaiser PK, et al. Novel microarchitectural dynamics in rhegmatogenous retinal detachments identified with intraoperative optical coherence tomography. Retina.

[6] Ray R, Baranano DE, Fortun JA, et al. Intraoperative microscopemounted spectral domain optical coherence tomography for evaluation of retinal anatomy during macular surgery. Ophthalmology. 2011;**118**:2212-2217

[7] Boppart SA, Bouma BE, Pitris C, et al. Intraoperative assessment of microsurgery with three-dimensional optical coherence tomography. Radiology. 1998;**208**:81-86

[8] Boppart SA, Herrmann JM, Pitris C, et al. Real-time optical coherence tomography for minimally invasive imaging of prostate ablation. Computer

[9] Brezinski ME, Tearney GJ, Bouma B, et al. Optical biopsy with optical

Aided Surgery. 2001;**6**:94-103

[2] Choma M, Sarunic M, Yang C, et al. Sensitivity advantage of swept source and Fourier domain optical coherence tomography. Optics Express.

1991;**254**:1178-1181

**References**

2003;**11**:2183-2189

2014;**158**:999-1007

2013;**33**:1428-1434

surgery: Uses and applications. Current Eye Research. 2016;**41**:643-652

[33] Almutlak MA, Aloniazan T, May W. Real-time optical coherence tomography incorporated in the operating microscope during cataract surgery. Middle East African Journal of Ophthalmology. 2017;**24**:156-158

[34] Ruland K, Bouldin TW, Davis RM, et al. Intraoperative optical coherence tomography-assisted retrocorneal fibrous membrane biopsy and excision. American Journal of Ophthalmology Case Reports. 2018;**11**:101-104

[35] Siebelmann S, Horstmann J, Scholz P, et al. Intraoperative changes in corneal structure during excimer laser phototherapeutic keratectomy (PTK) assessed by intraoperative optical coherence tomography. Graefe's Archive for Clinical and Experimental Ophthalmology. 2018;**256**:575-581

[36] Falkner-Radler CI, Glittenberg C, Gabriel M, et al. Intrasurgical microscope-integrated spectral domain optical coherence tomographyassisted membrane peeling. Retina. 2015;**35**:2100-2106

[37] Xu D, Yuan A, Kaiser PK, et al. A novel segmentation algorithm for volumetric analysis of macular hole boundaries identified with optical coherence tomography. Investigative Ophthalmology & Visual Science. 2013;**54**:163-169

[38] Ehlers JP, Griffith JF, Srivastava SK. Intraoperative optical coherence tomography during vitreoretinal surgery for dense vitreous hemorrhage in the pioneer study. Retina. 2015;**35**:2537-2542

[39] Khan M, Srivastava SK, Reese JL, et al. Intraoperative OCT-assisted surgery for proliferative diabetic retinopathy in the DISCOVER study. Ophthalmology Retina. 2018;**2**:411-417 [40] Itoh Y, Vasanji A, Ehlers JP. Volumetric ellipsoid zone mapping for enhanced visualisation of outer retinal integrity with optical coherence tomography. The British Journal of Ophthalmology. 2016;**100**:295-299

[41] Browne AW, Ehlers JP, Sharma S, et al. Intraoperative optical coherence tomography-assisted chorioretinal biopsy in the DISCOVER study. Retina. 2017;**37**:2183-2187

[42] Rachitskaya AV, Yuan A, Marino MJ, et al. Intraoperative OCT imaging of the argus II retinal prosthesis system. Ophthalmic Surgery, Lasers and Imaging Retina. 2016;**47**:999-1003

[43] Gregori NZ, Lam BL, Davis JL. Intraoperative use of microscopeintegrated optical coherence tomography for subretinal gene therapy delivery. Retina. 2017. [Epub ahead of print]

[44] Mandai M, Kurimoto Y, Takahashi M. Autologous induced stem-cellderived retinal cells for macular degeneration. The New England Journal of Medicine. 2017;**377**:792-793

**31**

**Chapter 3**

**Abstract**

ment for each patient.

**1. Introduction**

Microscope-Integrated

Intraoperative Optical Coherence

Tomography in Retinal Surgery

*Jesus Hernan Gonzalez-Cortes, Abraham Olvera-Barrios,*

**Keywords:** intraoperative optical coherence tomography, retinal surgery,

The development of microsurgery enhanced the precision with which ophthalmic surgical procedures are currently performed. Its origins date back to 1876, when the first binocular magnifying device was invented by T. Saemisch of Bonn [1]. It was not until 1953, with the manufacture of a microscope with coaxial illumination, that the use of the surgical microscope became more widely available and adapted to ocular surgery [2–4]. Three years later, in 1956, the term "microsurgery" was used for the first time by H. M. Dekking of Göningen [5]. Almost two decades before the use of binocular magnifying devices, Hermann von Helmholtz invented ophthalmoscopy in 1851 and allowed us to see, for the first

vitreomacular interface, membrane peeling, retinal detachment

*Jesus Emiliano Gonzalez-Cantu and Jesus Mohamed-Hamsho*

Imaging techniques of the posterior segment of the eye have gradually evolved and tremendously improved during the last decade. A widespread implementation of optical coherence tomography (OCT) for the management and diagnosis of retinal conditions, with a concurrent advance in integrative technology, led to the integration of the OCT into the microscope for its intraoperative use. Regarding posterior segment eye surgery, some of the most common diagnoses in which microscope-integrated OCT (MIOCT) can result of great value are epiretinal membrane, macular hole (MH), proliferative diabetic retinopathy (PDR) and, less frequently, for inflammatory diseases, chorioretinal biopsies, and retinal implants. The impact on the surgical procedure and, possibly, on the postoperative outcome could relate to the definition of whether or not a membrane has been entirely peeled, the presence of residual membranes, and the option to perform a dissection without the need of vital dyes. The possibility of correct topographical location of hemorrhages, suspect lesions, or implants can also facilitate the surgical decision-making during biopsies or prosthesis implantation. Microscope-integrated OCT is a feasible and useful tool that can provide valuable information during surgery impact on decision-making, anatomic results, surgical safety and provide opportunity to individualize surgical treat-

### **Chapter 3**

*Novel Diagnostic Methods in Ophthalmology*

surgery: Uses and applications. Current

[40] Itoh Y, Vasanji A, Ehlers

2017;**37**:2183-2187

JP. Volumetric ellipsoid zone mapping for enhanced visualisation of outer retinal integrity with optical coherence tomography. The British Journal of Ophthalmology. 2016;**100**:295-299

[41] Browne AW, Ehlers JP, Sharma S, et al. Intraoperative optical coherence tomography-assisted chorioretinal biopsy in the DISCOVER study. Retina.

[42] Rachitskaya AV, Yuan A, Marino MJ, et al. Intraoperative OCT imaging of the argus II retinal prosthesis system.

Ophthalmic Surgery, Lasers and Imaging Retina. 2016;**47**:999-1003

[43] Gregori NZ, Lam BL, Davis JL. Intraoperative use of microscope-

tomography for subretinal gene therapy delivery. Retina. 2017. [Epub ahead of

[44] Mandai M, Kurimoto Y, Takahashi M. Autologous induced stem-cellderived retinal cells for macular

degeneration. The New England Journal

of Medicine. 2017;**377**:792-793

integrated optical coherence

print]

[34] Ruland K, Bouldin TW, Davis RM, et al. Intraoperative optical coherence tomography-assisted retrocorneal fibrous membrane biopsy and excision. American Journal of Ophthalmology Case Reports. 2018;**11**:101-104

[35] Siebelmann S, Horstmann J, Scholz P, et al. Intraoperative changes in corneal structure during excimer laser phototherapeutic keratectomy (PTK) assessed by intraoperative optical coherence tomography. Graefe's Archive for Clinical and Experimental Ophthalmology. 2018;**256**:575-581

[36] Falkner-Radler CI, Glittenberg C, Gabriel M, et al. Intrasurgical microscope-integrated spectral

[37] Xu D, Yuan A, Kaiser PK, et al. A novel segmentation algorithm for volumetric analysis of macular hole boundaries identified with optical coherence tomography. Investigative Ophthalmology & Visual Science.

[38] Ehlers JP, Griffith JF, Srivastava SK. Intraoperative optical coherence tomography during vitreoretinal surgery for dense vitreous hemorrhage

in the pioneer study. Retina.

[39] Khan M, Srivastava SK, Reese JL, et al. Intraoperative OCT-assisted surgery for proliferative diabetic retinopathy in the DISCOVER study. Ophthalmology Retina. 2018;**2**:411-417

2015;**35**:2100-2106

2013;**54**:163-169

2015;**35**:2537-2542

domain optical coherence tomographyassisted membrane peeling. Retina.

Eye Research. 2016;**41**:643-652

[33] Almutlak MA, Aloniazan T, May W. Real-time optical coherence tomography incorporated in the operating microscope during cataract surgery. Middle East African Journal of Ophthalmology. 2017;**24**:156-158

**30**