Here we proposed a designed, built, and evaluated 20G vertically inserted razor edge cannula (VIREC) robotic device guided by optical coherence tomography (OCT) for pneumatic dissection. The fiber sensor was glued inside the needle at a fixed offset of ~500 um. During the experiment, the robotic needle driver precisely moves the VIREC based on the surgeon input which is carefully monitored by the M-mode OCT system. Once the needle is inserted into the desired depth, the air is injected by the surgeon to separate stroma from Descemet’s membrane (DM). During in vivo study (N=8), the “big bubble” was effectively generated in six of eight eyes tested and DM was perforated in two eyes. This demonstrated the reliability and effectiveness of VIREC for “big bubble” DALK.
We reported a design and evaluation of an optical coherence tomography (OCT) sensor-integrated 27 gauge vertically inserted razor edge cannula (VIREC) for pneumatic dissection of Descemet’s membrane (DM) from the stromal layer. The VIREC was inserted vertically at the apex of the cornea to the desired depth near DM. The study was performed using ex vivo bovine corneas (N = 5) and rabbit corneas (N = 5). A clean penumodissection of a stromal layer was successfully performed using VIREC without any stomal blanching on bovine eyes. The “big bubble” was generated in all five tests without perforation. Only micro bubbles were observed on rabbit eyes. The results proved that VIREC can be an effective surgical option for “big bubble” DALK.
Deep anterior lamellar keratoplasty (DALK) is a partial-thickness cornea transplant procedure in which only the recipient’s stroma is replaced, leaving the host’s Descemet’s membrane (DM) and endothelium intact. This highly challenging “Big Bubble” procedure requires micron accuracy to insert a hydro-dissection needle as close as possible to the DM. Here, we report the design and evaluation of a downward viewing common-path optical coherence tomography (OCT) guided hydro-dissection needle for DALK. This design offers the flexibility of using different insertion angles and needle sizes. With the fiber situated outside the needle and eye, the needle can use its’ full lumen for a smoother air/fluid injection and image quality is improved. The common-path OCT probe uses a bare optical fiber with its tip cleaved at the right angle for both reference and sample arm which is encapsulated in a 25-gauge stainless still tube. The fiber was set up vertically with a half-ball epoxy lens at the end to provide an A-scan with an 11-degree downward field of view. The hydro dissection needle was set up at 70 degrees from vertical and the relative position between the fiber end and the needle tip remained constant during the insertion. The fiber and needle were aligned by a customized needle driver to allow the needle tip and tissue underneath to both be imaged within the same A-scan. Fresh porcine eyes (N = 5) were used for the studies. The needle tip position, the stroma, and DM were successfully identified from the A-scan during the whole insertion process. The results showed the downward viewing OCT distal sensor can accurately guide the needle insertion for DALK and improved the average insertion depth compared to freehand insertion.
The most challenging aspect of deep anterior lamellar keratoplasty (DALK), is what’s known as “Big Bubble” technique which injects air/fluid to fully separate the Descemet’s Membrane and stroma with a hydro-dissection needle. Big bubble technique requires micron accuracy to guide the needle to approximately 90% depth of cornea. Here, we developed and tested common-path swept source optical coherence tomography (CP-SSOCT) distal-sensor integrated hydro-dissection needles, which can accurately detect the needle position relative to corneal tissues with micron accuracy. The OCT distal-sensor was put inside a 30-gauge needle, which was also used for hydro dissection. A high-index elliptical epoxy lens was attached to the end of the single mode fiber to increase the signal to noise ratio inside the cornea. To control the position and insertion angle of the sensor, we customized the eye mount with an angular slide and a precise linear motor with Luer-slip. The needle was fixed outside, 100um from epithelium layer, to obtain the A-scan image to identify both epithelium and endothelium membranes at every 10° from 0° to 70° insertion angles. The needle was then inserted into bovine cornea and recorded A-scan images at each step. Freehand insertion test was performed with and without sensor guided needles. The results showed that the position of the epithelium and endothelium membranes were still identified from A-scan even at 70°. Sensor guided freehand test can reach 95% of cornea thickness on average without any perforation. These results are consistent with our hypothesis that CP-SSOCT fiber sensor can guide a needle insertion inside a cornea for Big Bubble technique.
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