Indications for intraoperative anterior segment optical coherence tomography in corneal surgery

Recently, intraoperative optical coherence tomography (iOCT) was established in the field of ophthalmic surgery. The first studies reported on the use of handheld iOCT devices [1, 2]. However, a more feasible option seems to be the use of microscope mounted devices [3]. First reports of intraoperative OCT use were mainly focused on vitreoretinal surgery [3‐5], including macular hole surgery [2] and retinal detachment [6].In anterior segment surgery, the use of iOCT was reported for lamellar keratoplasty. In deep anterior lamellar keratoplasty (DALK), the iOCT can be used to visualize the placement of the needle for the injection of the big bubble. Also the preparation of the bare Descemet’s membrane and the visualization of interface fluids can be assisted with iOCT [7, 8]. The use of iOCT for big bubble formation in DALK has been reported [9].

In posterior lamellar keratoplasty, the Prospective Intraoperative and Perioperative Ophthalmic ImagiNg with Optical CoherEncE TomogRaphy (PIONEER) study [10] examined the usefulness of iOCT in Descemet stripping automated endothelial keratoplasty (DSAEK). In this study, the iOCT was used to detect interface fluid during surgery, which correlated with interface opacity [10].

In Descemet membrane endothelial keratoplasty (DMEK), the iOCT can be used to enhance the visibility of the graft and can therefore support graft orientation and unfolding [11].

Lately, the iOCT also was introduced to the field of glaucoma surgery by enabling visualization of trabecular aspiration or ab interno trabeculotomy; however, adjustments of wavelengths and oblique scanning are necessary for intraoperative use [12].

The aim of this study is to report our experiences with the new iOCT Rescan® technique in anterior segment surgery, including DALK and DMEK and to evaluate new possibilities of this application.

We used the iOCT (OPMI Lumera 700 RESCAN 700, Carl Zeiss Meditec AG, Jena, Germany) in 18 patients. The respective surgeries include two DALK, 8 DMEK, two penetrating keratoplasties, one autologous limbal transplantation, one transscleral suture fixation of a posterior chamber lens, two removals of corneal surface pannus, one examination of Peters’ anomaly in a newborn child and pterygium surgery. The iOCT scans can be directly viewed through the eyepiece of the microscope as well as on the observation monitor, simultaneously to the live surgery images. The scan location marker can be positioned with the foot control panel. The A-scan depth is 2.0 mm, and the axial resolution is 5.5 µm. Scan length can be adjusted between 3 and 16 mm. The scan can be rotated 360°. There are different scan modes available, including 1-line, 5-lines and a cross hair. We obtained the anonymized video data for all procedures. Intra- and postoperative video analysis was performed concerning the importance of the visualization during crucial surgical steps during different surgical procedures. Ethics committee statement for the analysis of anonymized was obtained by the ethics committee of the Albert-Ludwigs-University of Freiburg (10015/19).

The iOCT used in this case series enabled visualization of the complete anterior segment assisting far more surgical procedures than the previous reported DALK, DMEK and DSAEK including sclera for example. The visualization of the cannula and the bubble formation during DALK preparation can indeed be helpful for the surgeon, especially since the cornea may become opaque during the air injection. This is concordant to the findings of previous studies [7, 13]. The big bubble formation was assessed in a retrospective study in 100 eyes by Scorcia et al. [13]. They described that depending on the iOCT findings a repositioning of the cannula may improve the outcome of DALK surgery [13]. The combination with femto-second laser has also been reported in the literature [14]. The technique of deep trephination for DALK enhances the success rate of the type 1 bubble formation [15]. Possibly, the additional depth information gained from iOCT might further increase the success rate. In cases where iOCT is not possible or does not deliver adequate information for cannula placement, the red reflex can help to locate the depth of the cannula when penetrating the stroma as described by Scorcia et al. [16].

The share of posterior lamellar keratoplasty is growing in the recent years [17], and regular anterior segment OCT is already established in postoperative examination of posterior lamellar keratoplasty [18]. During DMEK surgery, the iOCT has been reported to help with the graft orientation and the unfolding of the graft [11]. We found this especially helpful in cases with corneal edema and impaired visibility for the surgeon. Beneficial effects of iOCT have also been described by other authors [19, 20]. Possible beneficial effects regarding the rebubbling rate should be evaluated in studies comparing iOCT to standard methods.

Also, conventional penetrating keratoplasty may benefit from the use of iOCT. The evaluation of the corneal stroma and the anterior chamber can be helpful in cases of scarred and therefore opaque corneas to find the best trephination diameter and position in order to allow for safe suturing of the graft by avoiding trephination in thin areas of the recipient’s cornea. Also, the visualization of the interface during and after suturing may be helpful in special cases.

Furthermore, the iOCT provides the opportunity of live assessment of the preparation depth in all cases of lamellar preparation in the anterior segment. This includes scleral flap preparation that is done for transscleral suture fixation of a posterior chamber lens or the lamellar graft preparation for an autologous limbal tissue graft. Corneal pannus or pterygium can be visualized during preparation to allow for an exact preparation depth to remove the diseased tissue completely and to avoid penetration of the globe. This may be especially helpful in cases of severe recurrent pterygium with deep infiltration of the cornea and the sclera and even in performing corneal biopsies [21]. The iOCT provides immediate visual feedback to the surgeon during the surgery and may prevent accidental perforation, especially in complicated surgical situations. In contrast to conventional OCT devices, the mounted iOCT device also enables anterior segment imaging in lying patients like newborn or infants. This is also helpful for uncooperative patients that can only be examined in general anesthesia.

Disadvantages of the iOCT tested in this case series are the need for an additional person in the operating room, handling the iOCT. This might improve as all surgeons were at the beginning of their personal learning curve using iOCT. Furthermore, the iOCT-operator had to describe the OCT pictures to the surgeon in certain complicated surgical situations. Finally, the additional costs of the system have to be taken into account.

In conclusion, the iOCT is a helpful device, not only for vitreoretinal surgery [3, 4], but also for anterior segment imaging [7, 11, 22] and child/newborn examination. The range of surgical techniques that may improve does not only include DALK and DMEK, but also conventional penetrating keratoplasty and every kind of lamellar preparation like in autologous limbal transplantation or pannus, pterygium or tumor removal.