Visualization of precut DSAEK and pre-stripped DMEK donor corneas by intraoperative optical coherence tomography using the RESCAN 700

Effect of Anterior Chamber Air on Central Corneal Thickness in Human Donor Eyes

PURPOSE

The purpose of this study was to describe the effects of intracameral air on corneal edema.

METHODS

A laboratory investigation was performed on human donor corneas. Baseline pachymetry measurements through anterior segment optical coherence tomography and endothelial cell density were obtained for all corneas. Each pair of corneas was separated and randomly assigned to undergo air injection or Optisol-GS into a BIONIKO artificial anterior chamber for 5 minutes at physiologic intraocular pressure confirmed by digital palpation. Photographs were obtained immediately on connection of the cornea to the artificial anterior chamber and on completion of the 5 minutes of treatment, with anterior chamber air being exchanged for Optisol-GS. Pretreatment and posttreatment photographs were obtained. Immediately after treatment, pachymetry was again obtained on all corneas. Pachymetry data underwent statistical analysis.

RESULTS

Corneal pachymetry improved from 690.5 ± 126.6 to 576.1 ± 87.2 μm, yielding a 114.4 ± 50.4 μm improvement of pachymetry in the group with air injected into the anterior chamber. This was a significant improvement of pachymetry when compared with the group with Optisol-GS injected into the anterior chamber, which showed an improvement from 662.3 ± 126.5 to 613.5 ± 108.0 μm, yielding an improvement of 48.8 ± 34.3 μm.

CONCLUSIONS

Injection of air into the anterior chamber leads to a significant decrease in corneal pachymetry. We thereby propose that injecting air intracamerally is an effective intraoperative intervention when visualization is negatively affected by corneal edema.

Intraoperative OCT for Lamellar Corneal Surgery: A User Guide

Intraoperative OCT is an innovative and promising technology which allows anterior and posterior segment ocular surgeons to obtain a near-histologic cross-sectional and tomographic image of the tissues. Intraoperative OCT has several applications in ocular surgery which are particularly interesting in the context of corneal transplantation. Indeed, iOCT images provide a direct and meticulous visualization of the anatomy, which could guide surgical decisions. In particular, during both big-bubble and manual DALK, the visualization of the relationship between the corneal layers and instruments allows the surgeon to obtain a more desirable depth of the trephination, thus achieving more type 1 bubbles, better regularity of the plane, and a reduced risk of DM perforation. During EK procedures, iOCT supplies information about proper descemetorhexis, graft orientation, and interface quality in order to optimize the postoperative adhesion and reduce the need for re-bubbling. Finally, mushroom PK, a challenging technique for many surgeons, can be aided through the use of iOCT since it guides the correct apposition of the lamellae and their centration. The technology of iOCT is still evolving: a larger field of view could allow for the visualization of all surgical fields, and automated tracking and iOCT autofocusing guarantee the continued centration of the image.

The predictability of graft thickness for Descemet's stripping automated endothelial keratoplasty using a mechanical microkeratome system

Descemet's stripping automated endothelial keratoplasty (DSAEK) is used for treating corneal endothelial dysfunction, and the postoperative visual acuity outcome depends on the thickness of the graft. We created a simple nomogram using factors affecting the cutting thickness during graft preparation via a mechanical microkeratome system for DSAEK. This retrospective study was conducted from May 2018 through October 2022 and included donor eyes cut by automatic methods. We measured the graft thickness, cutting accuracy, and assessed ten variables with donor/cornea-related factors potentially affecting the cutting thickness. Subsequently, we created a simple nomogram. We analyzed 81 donor tissues, and the donor median age was 76 years. The mean central graft thickness was 122.2 μm, with 62% of the grafts that could be cut within the target central graft thickness range. Comparatively, donor corneas from those with cardiac diseases were cut deeper (P = 0.007). The developed nomogram provided a 83% probability of estimating the post-cutting graft thickness within 25 µm. Our nomogram, which considers cause of death, enables reproducible production of graft of a desired thickness. A detailed analysis of donor tissues, including the cause of donor death and the characteristics from pressurization to cutting, will enable more precise DSAEK graft preparation.

Intraoperative optical coherence tomography-guided donor corneal tissue assessment and preparation

Purpose

To evaluate the role of intraoperative optical coherence tomography (i-OCT) in donor grading, selection, and preparation during different types of keratoplasty.

Methods

Seventy-one consecutive donor corneas collected over 6 months, after clinical grading, were observed by an experienced corneal surgeon under an i-OCT equipped microscope. The donor preparation (manual/automated) for different types of keratoplasty procedures was also undertaken under i-OCT.

Results

The mean central corneal thickness of optical and nonoptical grade tissues was 533 ± 19 and 662 ± 52 μm, respectively. The i-OCT-based grading matched with clinical grading in 98.5% cases. Irregular thickness, anterior stromal hyperreflectivity, and previous scars were appreciated in 1.4, 1.4, and 7.04% donors, respectively. During Descemet stripping automated endothelial keratoplasty, i-OCT facilitated selection of appropriate microkeratome head for automated donor preparation in all cases, besides allowing manual dissection of partially dissected lenticule, identification of site of inadvertent perforation, and eccentric trephination in one case each. During Descemet membrane endothelial keratoplasty, i-OCT-based assessment of preexisting scar (five cases) guided careful tissue selection (2/5) and preparation. During predescemetic endothelial keratoplasty, precise needle advancement allowed successful type-1 bubble formation in all cases. All manually punched donors demonstrated an extra endothelial ledge, while those with automated preparation showed tapering donor margins.

Conclusion

i-OCT might serve as a useful imaging tool for objective assessment of donor characteristics. The modality may complement clinical evaluation for donor grading, selection, and preparation.

Application of Intraoperative Optical Coherence Tomography Technology in Anterior Segment Surgery

The use of optical coherence tomography (OCT) technology in anterior segment diseases allows for precise assessment of the changes following anterior segment surgery. Advances in microscope-integrated OCT systems have allowed the utilization of intraoperative OCT (iOCT) in anterior segment surgeries, i.e., cornea, cataract, and refractive surgery. iOCT has enabled real-time precise visualization of anterior segment tissues as well as interactions between surgical instruments and ocular tissue; thus, the device can facilitate surgical procedures and provide valuable information for decision-making during anterior segment surgeries. In this review, the authors will introduce studies regarding the development of iOCT technology and its application in various anterior segment surgeries. Multiple studies have shown the efficacy of the iOCT for intraoperative assistance and guidance, suggesting the potential of the device for optimizing the surgical outcomes after cornea, cataract, and refractive surgery.

An Overview of Intraoperative OCT-Assisted Lamellar Corneal Transplants: A Game Changer?

Intraoperative optical coherence tomography (iOCT) is a noninvasive imaging technique that gives real-time dynamic feedback on surgical procedures. iOCT was first employed in vitreoretinal surgery, but successively served as a guidance in several anterior segment surgical approaches: keratoplasty, implantable Collamer lens (ICL) implantation, and cataract surgery. Among all of those approaches, the unbeatable features of iOCT are fully exploited in anterior and posterior lamellar keratoplasty, and the purpose of this review is to focus on the advantages and shortfalls of iOCT in these techniques, in order to assess whether this technology could be a real step forward. In deep anterior lamellar keratoplasty (DALK), iOCT is useful to evaluate the needle depth into the corneal stroma, the big bubble dissection plane, and residual stromal bed, thus aiding the standardization of the technique and the reduction of failures. In Descemet stripping automated endothelial keratoplasty (DSAEK), iOCT allowed for clear visibility of fluid at the graft/host interface, allowing for immediate rescue maneuvers and granting the best graft apposition. In Descemet membrane endothelial keratoplasty (DMEK), iOCT can track the lenticule unfolding in real time and assess graft orientation even in severe hazy corneas, thus optimizing surgical times, as well as avoiding the use of potentially hazardous exterior markers (such as the “S” stamp) and preventing unnecessary manipulation of the graft. Overall, the role of iOCT appeared crucial in several complicated cases, overcoming the difficulties of poor visualization in a fast, non-invasive way, thus raising this approach as possible gold standard for challenging conditions. Further improvements in the technology may enable autonomous centering and tracking, overcoming the current constraint of instrument-induced shadowing.

INTRAOPERATIVE OPTICAL COHERENCE TOMOGRAPHY -AVAILABLE TECHNOLOGIES AND POSSIBILITIES OF USE. A REVIEW

Optical coherence tomography (OCT) is a non-contact and non-invasive imaging and diagnostic method, that allows the imaging of ocular tissues on transverse sections in extremely high quality of micrometer resolution. The physical principle of OCT is analogous to ultrasound, but it uses infrared radiation instead of acoustic waves. By using a low coherent radiation source, it is possible to achieve a higher resolution. Based on the obtained data, the computer can reconstruct two or three-dimensional images of the examined tissue. In recent years, we have seen a rapid development in ophthalmic surgery, especially in surgical instruments and imaging methods. However, the technology of surgical microscopes does not change significantly and thus becomes a limiting factor in the development of ophthalmic microsurgery. The integration of the OCT into surgical microscopes, so the introduction of the Intraoperative Optical Coherence Tomography (iOCT), opens up further possibilities for displaying/looking at the operating field and adapting surgical techniques to the current situation during the surgery. On the contrary, the disadvantage is the prolongation of the surgery time and thus the theoretical increase in possible complications related to the surgery. iOCT can be used for operations on the anterior and posterior segment of the eye. In anterior segment surgery, it is used mostly in penetrating and lamellar keratoplasty, glaucoma surgery and cataract surgery. In posterior segment surgery, it is used during pars plana vitrectomy. The aim of the article is to provide a comprehensive overview of the current possibilities of using iOCT in eye surgery.

Correlation between intraoperative and postoperative vaulting of the EVO implantable Collamer lens: a retrospective study of real-time observations of vaulting using the RESCAN 700 system

Background

Implantable Collamer lens (ICL) vaulting is one of the most important parameters for the safety, aqueous humor circulation, and lens transparency after ICL implantation. This study aimed to investigate the factors associated with the actual vaulting after refractive EVO-ICL surgery.

Methods

This retrospective study included patients who underwent EVO-ICL surgery at a tertiary eye hospital between October and December 2019. A RESCAN 700 was used for the intraoperative and CIRRUS HD-OCT was used for postoperative observation of vaulting. Subjective and objective refractions, anterior ocular segment, corneal morphology, intraocular pressure (IOP), anterior chamber volume (ACV), crystalline lens rise (CLR), white-to-white distance (WTW), anterior chamber depth (ACD), axial length, corneal endothelial cell density (ECD), and fundoscopy were examined. A multivariable analysis was performed to determine the factors independently associated with 1-month postoperative vaulting.

Results

Fifty-one patients (102 eyes) were included. Compared with the eyes with normal vaulting, those with high vaulting had higher preoperative diopter values (P = 0.039), lower preoperative corrected visual acuity (P = 0.006), lower preoperative IOP (P = 0.029), higher preoperative ACD (P = 0.004), lower preoperative CLR (P = 0.046), higher ICL spherical equivalent (P = 0.030), higher intraoperative vaulting (P < 0.001), and lower IOP at 1 month (P = 0.045). The multivariable analysis showed that the only factor independently associated with high vaulting at 1 month after surgery was the intraoperative vaulting value (odds ratio = 1.005, 95% confidence interval: 1.002–1.007, P < 0.001). The intraoperative and 1-month postoperative vaulting values were positively correlated (R² = 0.562).

Conclusions

The RESCAN700 system can be used to perform intraoperative optical coherence tomography to predict the vaulting value of ICL at 1 month.

Comprehensive review of surgical microscopes: technology development and medical applications

SIGNIFICANCE

Surgical microscopes provide adjustable magnification, bright illumination, and clear visualization of the surgical field and have been increasingly used in operating rooms. State-of-the-art surgical microscopes are integrated with various imaging modalities, such as optical coherence tomography (OCT), fluorescence imaging, and augmented reality (AR) for image-guided surgery.

AIM

This comprehensive review is based on the literature of over 500 papers that cover the technology development and applications of surgical microscopy over the past century. The aim of this review is threefold: (i) providing a comprehensive technical overview of surgical microscopes, (ii) providing critical references for microscope selection and system development, and (iii) providing an overview of various medical applications.

APPROACH

More than 500 references were collected and reviewed. A timeline of important milestones during the evolution of surgical microscope is provided in this study. An in-depth technical overview of the optical system, mechanical system, illumination, visualization, and integration with advanced imaging modalities is provided. Various medical applications of surgical microscopes in neurosurgery and spine surgery, ophthalmic surgery, ear-nose-throat (ENT) surgery, endodontics, and plastic and reconstructive surgery are described.

RESULTS

Surgical microscopy has been significantly advanced in the technical aspects of high-end optics, bright and shadow-free illumination, stable and flexible mechanical design, and versatile visualization. New imaging modalities, such as hyperspectral imaging, OCT, fluorescence imaging, photoacoustic microscopy, and laser speckle contrast imaging, are being integrated with surgical microscopes. Advanced visualization and AR are being added to surgical microscopes as new features that are changing clinical practices in the operating room.

CONCLUSIONS

The combination of new imaging technologies and surgical microscopy will enable surgeons to perform challenging procedures and improve surgical outcomes. With advanced visualization and improved ergonomics, the surgical microscope has become a powerful tool in neurosurgery, spinal, ENT, ophthalmic, plastic and reconstructive surgeries.

Intraoperative Optical Coherence Tomography Imaging in Corneal Surgery: A Literature Review and Proposal of Novel Applications

Intraoperative optical coherence tomography (iOCT) is widely used in ophthalmic surgeries for cross-sectional imaging of ocular tissues. The greatest advantage of iOCT is its adjunct diagnostic efficacy, which facilitates to decision-making during surgery. Since the development of microscopic-integrated iOCT (MIOCT), it has been widely used mainly for vitreoretinal and anterior segment surgeries. In corneal transplantation, MIOCT allows surgeons to visualise structure underneath the turbid and distorted cornea, which are impossible to visualise with a usual microscope. Real-time visualisation of hard-to-see area reduces the operation time and leads to favorable surgical outcomes. The use of MIOCT is advantageous for a variety of corneal surgical procedures. Here, we have reviewed articles focusing on the utility of iOCT  and MIOCT in penetrating keratoplasty, deep anterior lamellar keratoplasty, Descemet stripping automated endothelial keratoplasty, and Descemet membrane endothelial keratoplasty. The applications of MIOCT to corneal surgery in terms of surgical education for trainees, emergency surgery, and novel surgery are also discussed, with our cases performed using RESCAN^® 700.

Intraoperative Optical Coherence Tomography Guided Ocular Surgeries: Critical Analysis of Clinical Role and Future Perspectives

Intraoperative imaging of ocular tissues for diagnostic and therapeutic applications has gained immense admiration in recent years. The real time cross-sectional imaging, as well as three and four dimensional reconstruction abilities of intraoperative optical coherence tomography (iOCT), has enhanced our knowledge on many fronts in surgical maneuvers. In this review, we discuss the iOCT discovered constructive knowledge in the cornea, cataract, refractive, glaucoma, pediatric ocular, and various retinal conditions. The practical utility with decision modifying aspects along the specified ocular tissues and with respect to specific ocular entities have been narrated. Moreover, limitations and future directions have also been emphasized to make ophthalmic care more comprehensive in the future.

Observation of Gonio Structures during Microhook Ab Interno Trabeculotomy Using a Novel Digital Microscope with Integrated Intraoperative Optical Coherence Tomography

Purpose

Observation of ocular structures using microscope-integrated intraoperative optical coherence tomography (iOCT) has been adopted. Using the novel digital ophthalmic microscope, ARTEVO 800 with iOCT, we tested the feasibility of trabecular meshwork (TM) imaging during microhook ab interno trabeculotomy, a minimally invasive glaucoma surgery.

Methods

The nasal and temporal sides of the TM/inner wall of Schlemm's canal were incised more than 3 clock hours in 14 glaucomatous eyes of 10 patients. To observe the trabeculotomy site, iOCT was performed with the real-time five-line scan mode under observation using a Swan-Jacob gonioprism lens. The success of the imaging and visibility of the trabeculotomy cleft and its incisional patterns (i.e., anterior, middle, or posterior pattern) were determined by reviewing the iOCT video files.

Results

OCT images of the region of interest were acquired successfully in 100% of the 28 nasal or temporal sides in 14 eyes, although the trabeculotomy cleft was not visualized in four (14%) sides due to blockage of the OCT signal by a blood clot. Based on the predominant locations of the TM flaps in 24 of the acquired images, the trabeculotomy clefts were classified as anterior incisional patterns in 13 (54%), middle incisional patterns in nine (38%), and posterior incisional patterns in two (8%).

Conclusion

Intraoperative imaging of the gonio structures including the trabeculotomy cleft was feasible using the ARTEVO 800 with iOCT in combination with a gonioprism.

What Is the Impact of Intraoperative Microscope-Integrated OCT in Ophthalmic Surgery? Relevant Applications and Outcomes. A Systematic Review

Background: Optical coherence tomography (OCT) has recently been introduced in the operating theatre. The aim of this review is to present the actual role of microscope-integrated optical coherence tomography (MI-OCT) in ophthalmology. Method: A total of 314 studies were identified, following a literature search adhering to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. After full-text evaluation, 81 studies discussing MI-OCT applications in ophthalmology were included. Results: At present, three microscope-integrated optical coherence tomography systems are commercially available. MI-OCT can help anterior and posterior segment surgeons in the decision-making process, providing direct visualization of anatomic planes before and after surgical manoeuvres, assisting in complex cases, and detecting or confirming intraoperative complications. Applications range from corneal transplant to macular surgery, including cataract surgery, glaucoma surgery, paediatric examination, proliferative diabetic retinopathy surgery, and retinal detachment surgery. Conclusion: The use of MI-OCT in ophthalmic surgery is becoming increasingly prevalent and has been applied in almost all procedures. However, there are still limitations to be overcome and the technology involved remains difficult to access and use.

Characterization of Corneal Donor Tissue Lesions by Anterior Segment Optical Coherence Tomography Compared With Eye Bank Technician Slit-Lamp Examination

PURPOSE

To compare anterior segment spectral-domain optical coherence tomography (OCT) with eye bank technician slit-lamp examination (SLE) in characterizing lesions in donor corneas.

METHODS

Twenty-nine donor corneas identified by eye bank technicians to have opacities or lesions potentially representing pathologic findings affecting the stroma were evaluated through the use of technician SLE, SLE photography, and OCT. Technicians were tasked with describing the lesion, estimating the lesion depth, and photographing their SLE findings. A masked grader evaluated the OCT images and measured the lesion depth using customized software. The lesions identified on OCT were then compared with those identified on SLE.

RESULTS

A total of 37 lesions were detected on SLE; 25 of the 37 lesions identified on SLE were matched to a lesion on OCT. SLE and OCT depth measurements were statistically significantly different (P = 0.0042, mean difference 4.8% ± 6.5%), and OCT graded lesions as slightly deeper. Of the 12 out of the 37 lesions that were noted on SLE (but not identified on OCT), these included 2 central and paracentral anterior stromal lesions (OCT showed loose epithelium), 5 peripheral anterior stromal lesions, and 5 corneas with LASIK.

CONCLUSIONS

Our study highlights both advantages and limitations of OCT compared with technician SLE in the evaluation of donor corneal tissue. Although OCT may miss some peripheral lesions and LASIK scars that are identifiable on SLE, OCT's depth resolution is helpful in differentiating whether shallow anterior opacities actually extend deeper into the stroma or are confined superficially to the epithelium.

Intraoperative optical coherence tomography in anterior segment surgeries

Intraoperative optical coherence tomography (iOCT) is a noninvasive imaging modality that provides a real-time dynamic feedback of the various surgical steps. Comprehensive literature search was performed in MEDLINE using “intraoperative optical coherence tomography” and “iOCT” as keywords. The use of iOCT as an aid to decision-making has been successfully reported in cases undergoing keratoplasty, implantable Collamer lens (ICL) implantation as well as cataract surgery. iOCT helps to assess the graft-host relationship in penetrating keratoplasty. It helps confirm the presence of a big bubble, detect subclinical big bubbles and guide layer by layer stromal dissection in cases of deep anterior lamellar keratoplasty. It acts as a guide during crucial surgical steps in endothelial keratoplasty, right from scoring of the Descemet membrane to ensuring graft apposition at the end of surgery. The morphological features of the corneal incision in phacoemulsification may be assessed. iOCT is a useful tool in assessing the status of the posterior capsule and may help identify preexisting posterior capsular defects during cataract surgery in various clinical scenarios such as posterior polar cataract, traumatic cataract, and vitrectomized eyes. It allows on-table assessment of the ICL vault and potentially facilitates exchange of ICL in the same sitting in extremes of vault. Ocular surface disorders such as ocular surface squamous neoplasia, pterygium, and dermoid may find an application for iOCT, wherein an iOCT-guided stromal dissection will ensure adequate depth of dissection. Further technological advancements may allow for automatic centration and tracking and address the present limitation of instrument-induced shadowing.

Optical Coherence Tomography Observation of Gonio Structures during Microhook Ab Interno Trabeculotomy

INTRODUCTION

Intraoperative observation of ocular structures using microscope-integrated optical coherence tomography (iOCT) has been adopted recently. I report my initial feasibility assessment of iOCT for the incised trabecular meshwork observation during microhook ab interno trabeculotomy.

CASE SERIES

Both the nasal and temporal sides or either side of the trabecular meshwork/inner wall of Schlemm's canal was incised more than 3 clock hours. After then, under observation using a Swan-Jacob gonioprism lens with the real-time 5-line scan mode, OCT images of the area were successfully acquired in 10 (83%) of 12 sides in nine eyes. Based on the appearance of the acquired images of the 10 sides, the trabeculotomy cleft could be classified into three incisional patterns, that is, six (60%) anterior-opening patterns (posterior-based flap), three (30%) middle-opening patterns (posterior- and anterior-based flaps), and one (10%) posterior-opening pattern (anterior-based flap), according to the predominant locations of the trabecular meshwork flaps.

CONCLUSION

Intraoperative observation of the gonio structures including the trabeculotomy cleft was feasible using the RESCAN 700 in combination with a gonioprism.