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CASE REPORT
Year : 2023 | Volume
: 13
| Issue : 1 | Page : 106-109
Intraoperative optical coherence tomography-guided deep anterior lamellar keratoplasty
Charles C Lin, Wen-Shin Lee
Department of Ophthalmology, Byers Eye Institute at Stanford University, Palo Alto, CA, USA
Correspondence Address:
Dr. Charles C Lin
2452 Watson Court, Palo Alto, CA 94303
USA
Source of Support: None, Conflict of Interest: None
DOI: 10.4103/tjo.TJO-D-22-00151
Gauging stromal dissection depth is crucial to successfully perform deep anterior lamellar keratoplasty (DALK) surgery. Intraoperative optical coherence tomography (iOCT) offers a promising tool to aid DALK surgery but visualization of surgical maneuvers is impaired due to artifacts from metallic instruments. We describe a novel surgical technique utilizing suture-assisted iOCT guidance that facilitates clear visualization of corneal dissection planes during DALK. A stromal dissection tunnel is performed with a Fogla probe and its depth is subsequently identified by threading a 1 cm segment of 8-0 nylon into the tunnel. In contrast to the Fogla probe, the 8-0 nylon is conspicuously highlighted on iOCT. If the tunnel is too superficial, a separate, deeper stromal tunnel can be created and visualized again with the 8-0 nylon suture and iOCT. This iterative process facilitates a deep stromal dissection, increasing the probability of successful big-bubble formation and Descemet baring DALK surgery. This technique was utilized for a successful big-bubble DALK in a patient with severe keratoconus.
Keywords: Deep anterior lamellar keratoplasty, intraoperative optical coherence tomography, keratoconus
For isolated corneal stromal pathology, deep anterior lamellar keratoplasty (DALK) is favored over penetrating keratoplasty (PKP) due to several advantages including decreased risk of rejection and safety.[1] However, the technical difficulty and increased operative time of DALK can dissuade surgeons from performing DALK. Among the technical challenges inherent to DALK, the baring of the host Descemet membrane is the most difficult yet critical step to optimizing visual outcomes. Addressing this challenge requires accurate identification and dissection of surgical planes.
Intraoperative optical coherence tomography (OCT) has emerged in recent years as an adjunctive tool for anterior segment surgery requiring accurate identification of precise surgical planes.[2] Intraoperative OCT (iOCT) has been used to provide step-by-step visualization of DALK surgery.[3],[4] However, imaging artifacts from metallic instruments impair clear real-time OCT visualization of intraoperative maneuvers. Here, we report a novel technique utilizing suture-assisted iOCT that provides precise visualization of dissection planes. This technique guides real-time stromal dissection, facilitating big-bubble creation and Descemet baring during DALK surgery.
Case ReportIn one example utilizing this technique, a 43-year-old woman with advanced keratoconus refractory to contact lens wear underwent a planned DALK surgery. Following partial depth trephination of the recipient cornea and removal of the anterior stroma, a Fogla probe is introduced into the deep stromal bed to dissect toward the paracentral cornea [Video 1, accessible at https://tinyurl.com/mum8dju5]. With the metallic Fogla probe in place, OCT images demonstrate significant shadow artifacts [Figure 1] preventing an accurate assessment of the depth of the dissection plane. With the Folga probe removed, the dissected stromal tunnel collapses, precluding clear visualization of its depth. To overcome this, various sutures were threaded into the stromal tunnel. A 6-0 Prolene easily passed into the tunnel but its thicker gauge precluded precise localization of stromal depth. A 10-0 nylon was used but too flimsy to easily thread into the tunnel. An 8-0 nylon suture provided the right balance of a small gauge suture with enough rigidity and it was threaded into the pre-dissected stromal tunnel and spectral domain OCT images (Zeiss Rescan 700 operating microscope, Carl Zeiss Meditec, Jena, Germany) revealed that it was located at approximately 50% depth [Figure 2]. The Fogla probe was used to create a second deeper stromal tunnel adjacent to the first. This time, OCT images showed that the stromal tunnel, identified with the 8-0 nylon suture was located in the very deep posterior stroma, nearly abutting the Descemet membrane [Figure 3]. A Fogla cannula was inserted into this tunnel and air insufflation readily produced a big bubble [Figure 4]. Removal of the residual overlying stroma left behind bare Descemet membrane. Endothelial cells were wiped off of the donor cornea with Weck-Cell sponges and the graft was sutured in place with interrupted 10-0 nylon sutures to complete the DALK. Nine months after her surgery, the patient's uncorrected visual acuity had improved to 20/50, an improvement from 20/400 preoperatively.
Figure 1: Significant shadow artifact from the Fogla probe (white arrow) hinders precise determination of dissection depth in the optical cross-section
Figure 2: With an 8-0 nylon suture passed into the stromal tunnel created by the Fogla probe, there is minimal shadow artifact and the depth of the tunnel can be clearly visualized in the mid-stroma (white arrows)
Figure 3: With an 8-0 nylon suture passed into a deeper stromal tunnel, optical cross-section reveals that the tunnel is located in the deep stroma (white arrows), nearly adjacent to the Descemet membrane, indicating an appropriately deep plane for pneumatic dissection
Figure 4: A successful big bubble has been achieved, with pneumatic separation of overlying stroma from Descemet membrane (white asterisks) Discussion Even as DALK has emerged as the treatment of choice for isolated stromal pathology, the technical difficulty of the surgery remains a challenge for even experienced cornea surgeons. To achieve visual outcomes equivalent to PKP, a successful DALK surgery must bare Descemet membrane or leave <20 um of the residual stroma.[5] Advances in technique including Anwar's “big-bubble” approach, the small-bubble modification, and the use of ophthalmic viscosurgical devices for lamellar dissection have certainly helped.[6],[7],[8] Achieving the big bubble significantly improves the success rate of DALK but failure to do so relegates the surgeon to perform manual lamellar dissection, a laborious and delicate technique that often results in micro- and macro-perforations. Descemet membrane perforations are still fairly common, averaging 11.7% in the studies assessed by an ophthalmic technology assessment published by the American Academy of Ophthalmology.[1] The same study found a total conversion rate to PKP of 2.4%.[1] However, most case series assessed were published by high-volume corneal surgeons and thus the true overall conversion rate is likely higher than what has been reported. Even for experienced surgeons, consistently performing successful DALK surgery remains formidable.[9]
The key to successful big-bubble formation lies in creating a deep stromal dissection plane. If the plane is insufficiently deep, air insufflation often results in intrastromal emphysema rather than a successful big bubble. However, the en-face view of the cornea through the operating microscope makes it difficult to accurately gauge the depth of stromal dissection. Moreover, each successive failed attempt at creating the big bubble further opacifies the cornea and obscures the surgeon's depth perception. Thus, the first attempt presents the best opportunity for success.
Several groups have utilized various imaging modalities to better identify stromal dissection planes. Preoperative measurement of corneal thickness with Pentacam, followed by lamellar trephination of 90% of measured corneal thickness was associated with an 84% success rate of big-bubble formation.[10] Intraoperative use of ultrasound pachymetry followed by trephination to 90% of the measured corneal thickness was found to result in an 81.8% success rate of big-bubble formation.[11],[12] Similarly, iOCT has been used to guide trephination depth in DALK.[13] In another study, intraoperative use of a sideways-mounted anterior segment OCT to evaluate the depth reached by the cannula before air injection was associated with a 70% success rate of big-bubble formation.[14] The successful big-bubble formation was associated with a deeper dissection plane, averaging 90 μ from the internal corneal surface compared with 136 μ for failed procedures.[14] However, this technique did not use a microscope-mounted OCT and required pausing the surgery to obtain OCT images. Microscope-mounted iOCT has been shown to provide accurate real-time visualization of all the steps of DALK,[3],[4] but shadow artifact from the metallic cannula before the big-bubble attempt hinders precise determination of the depth of the dissection plane with this technique.
Here, we describe a novel iOCT DALK technique utilizing suture assistance to visualize real-time surgical maneuvers and stromal dissection depth before pneumatic dissection. Two characteristics make 8-0 nylon suture appropriate for this purpose. First, it is rigid enough to be threaded into a predissected stromal plane using tying forceps. Second, it is thin enough to not create shadow artifacts, thus permitting precise determination of dissection depth. As such, we propose this technique as an improvement of iOCT-guided DALK that will allow for deeper stromal dissection, more consistent big-bubble formation, and ultimately a higher success rate of DALK surgery.
Ethical approval
Approval from the Institutional Review Board at Stanford University was obtained for this study. (approval number: 38636).
Declaration of patient consent
The authors certify that they have obtained appropriate patient consent form. In the form, the patient has given her consent for the images and other clinical information to be reported in the journal. The patient understands that her name and initial will not be published and due efforts will be made to conceal the identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
This work was supported by the National Eye Institute core grant P30-026877 and Research to Prevent Blindness.
Conflicts of interest
The authors declare that there are no conflicts of interests of this paper.
References
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