Purpose
Intraoperative optical coherence tomography (iOCT) may facilitate successful transition to Descemet membrane endothelial keratoplasty (DMEK) surgery via improved efficiency of tissue orientation. The purpose of this study is to report a large consecutive series of iOCT-assisted DMEK, inclusive of all learning curve cases.
Design
Prospective consecutive case series.
Methods
The Determination of Feasibility of Intraoperative Spectral Domain Microscope Combined/Integrated OCT Visualization During En Face Retinal and Ophthalmic Surgery (DISCOVER) study is a single-site, multisurgeon, IRB-approved investigational device prospective study. The first 100 consecutive iOCT-assisted DMEK surgeries performed by 1 attending corneal surgeon (JMG) and 6 novice surgeons (cornea fellows under supervision) were reviewed. iOCT was utilized for tissue orientation. Patient demographics, tissue characteristics, intraoperative parameters, and postoperative complications are reported.
Outcomes
(1) Utility of iOCT based on surgeon reporting during surgery, (2) intraoperative graft unscrolling efficiency, and (3) frequency of postoperative complications.
Results
One hundred eyes of 76 patients were enrolled. Forty-three cases were performed by 1 staff physician and 57 cases were performed by 6 cornea fellows. Concurrent phacoemulsification with lens implantation was performed in 52 cases (52%). Nine eyes (9%) required rebubbling. Two eyes (2.0%) experienced primary graft failure. One graft failure resulted from surgeon error in interpreting the iOCT. Average unscrolling time was 4.4 ± 4.1 minutes (range: 0.7-27.6 minutes).
Conclusions
iOCT facilitates DMEK orientation without the need for external markings. For novice DMEK surgeons, complication rates and unscrolling times compare favorably with alternative tissue orientation methods.
Descemet membrane endothelial keratoplasty (DMEK) provides superior results compared to Descemet stripping automated endothelial keratoplasty (DSAEK) for the treatment of corneal endothelial diseases. Specifically, DMEK has been shown to provide faster visual rehabilitation, better visual acuity, and a lower rate of corneal rejection. Despite its advantages, DMEK requires a surgeon to acquire new skills and may result in in a steep learning curve. , , As such, a number of strategies have been developed to improve surgeons’ confidence and success with DMEK surgery.
Intraoperative optical coherence tomography (iOCT) has been previously shown to facilitate DMEK surgery. iOCT allows real-time visualization and identification of DMEK scroll orientation. iOCT achieves this without potentially harmful external markings (eg, s-stamp or peripheral notches) and may be helpful in instances of corneal opacity or advanced corneal edema when visualization is compromised.
Although its use has been previously described, there have been no large studies as of this writing reporting the clinical outcomes of intraoperative OCT-assisted DMEK. The purpose of this study is to report the results of a single consecutive series of DMEK surgeries, including all “learning curve” cases. We previously reported our initial experience with 8 eyes undergoing DMEK surgery with iOCT that suggested a potential role for iOCT in identification of graft orientation and confirmation of graft placement. Herein, we examine our first 100 cases of iOCT-assisted DMEK surgery performed by either a single attending surgeon (J.M.G.) or cornea fellows under supervision.
Methods
All cases were performed between August 2014 and February 2018 as part of the D etermination of feasibility of I ntraoperative S pectral domain microscope C ombined/integrated O CT V isualization during E n face R etinal and ophthalmic surgery (DISCOVER) study, a single-site, prospective multisurgeon investigational device interventional case series assessing the utility intraoperative OCT for ophthalmic surgery. The study was approved by the Cleveland Clinic Institutional Review Board and adhered to the tenets of the Declaration of Helsinki. Written informed consent was obtained from all patients prior to enrollment.
Donor Tissue
All donor tissue was provided by Eversight eye bank (Ann Arbor, Michigan, USA). Corneas were “pre-stripped” by a certified eye bank technician, employing a 9.5-mm partial trephination and then stripping Descemet membrane with non-toothed forceps, leaving a small (<20%) undisturbed peripheral “hinge.” For the first 20 cases, “fold-over” micro S-stamping was performed during eye bank preparation as an aid for tissue orientation using a previously described technique. iOCT was employed as the sole method for tissue orientation for the subsequent 80 cases. All tissue was stored in Optisol GS (Bausch & Lomb, Rochester, New York, USA) prior to surgical use.
Surgical Technique
All surgery was performed under retrobulbar anesthesia based on surgeon preference for patient comfort and akinesia. For cases with concurrent phacoemulsification, dilation was achieved via preoperative topical administration of a compounded solution consisting of 0.5% tropicamide, 0.5% cyclopentolate, and 2.5% phenylephrine (our institution’s standard regimen for cataract surgical patients). No intracameral pharmacologic dilating agents were employed. When pupillary dilation was deemed insufficient for cataract surgery, mechanical dilation was achieved with the use of a disposable pupil expansion device.
Healon (Johnson & Johnson Surgical Vision, Inc, Santa Ana, California, USA) was the only viscoelastic employed for all cases, owing to its highly cohesive property. After marking the desired graft position on the corneal surface, a reverse Terry-Sinskey hook (Bausch & Lomb, St Louis, Missouri, USA) was used to strip the host Descemet membrane in a circular diameter approximately 0.25 mm larger than the intended graft diameter. Viscoelastic was removed using irrigation and aspiration, and Miochol (Bausch & Lomb, Rochester, New York, USA) was instilled to constrict the pupil. For all cases, a small peripheral iridectomy was created by excising a small piece of iris with Vannas scissors via a 1-mm inferior limbal incision.
The prestripped tissue was cut by the surgeon using a disposable corneal punch (Moria SA, Antony, France) and then lifted from the stromal bed with tying forceps. The tissue was stained with trypan blue (0.06%, VisionBlue; DORC International BV, Zuidland, South Holland, Netherlands) for 3 minutes, rinsed with balanced salt solution, and then drawn into an insertion apparatus consisting of a Straiko Modified Jones Tube (Gunther Weiss Scientific, Portland, Oregon, USA) connected to a 3-mL syringe. The scroll was injected into the anterior chamber through a 3.0-mm temporal clear corneal incision that was sutured prior to graft manipulation. Grafts were unscrolled using a “no-touch” technique in which the anterior chamber was kept shallow and the graft is manipulated by external tapping or sweeping gestures.
Using a microscope-integrated system (RESCAN 700; Carl Zeiss Meditec, Oberkochen, Germany), iOCT was used during the unscrolling process to verify tissue orientation. iOCT images are viewable via a “heads-up” display in the surgeon’s right ocular or with an external video monitor on the display panel. The iOCT can be controlled with the microscope foot pedal or via an assistant on the video monitor. Tissue orientation was determined by orienting the raster perpendicular to the long axis of the scroll and observing the curling behavior of the tissue margins. Clear evidence of curling toward the anterior aspect of the graft (eg, “scrolls on top”) was considered evidence of correct tissue orientation ( Figure 1 ).
After unscrolling, 20% sulfur hexafluoride was injected to attach the graft to the host cornea. Ten minutes were allowed to pass with a complete gas fill with intraocular pressure in the range of 30-40 mm Hg before a gas-fluid exchange was performed. The anterior chamber was left with an approximately 80% to 90% gas fill to allow passage of aqueous through the peripheral iridectomy to avoid pupillary block. The patient was instructed to remain supine as much as possible during the first 24 hours after the surgery and for 4 hours daily for the subsequent week. The typical postoperative visits occurred on day 1, week 1, month 1, then every 3 months for the first year.
Surgeon Feedback Assessment and Statistical Analysis
A surgeon feedback questionnaire was completed intraoperatively by the attending surgeon that reviewed the overall impact of iOCT on the surgical procedure and perceived value of the imaging to the surgical procedure. Statistical analysis was performed using independent sample t tests for continuous variables and Fisher exact tests for proportions where appropriate with GraphPad InStat Software (GraphPad Software, La Jolla, California, USA; www.graphpad.com ).
Results
One hundred consecutive eyes of 76 patients (28 male, 48 female) were enrolled and included in the analysis. Median follow-up duration was 2.0 years (range 0.9-4.5 years). The mean patient age was 67.6 years (range: 49-90). The indications for DMEK in this series were Fuchs endothelial dystrophy (n = 87), failed prior graft (n = 6), pseudophakic bullous keratopathy (n = 5), posterior polymorphous corneal dystrophy (n = 1), and endothelial decompensation from previous refractive surgery (n = 1). No eyes with anterior chamber intraocular lenses, a history of pars plana vitrectomy, or glaucoma drainage devices underwent DMEK surgery in the study.
All surgeries were performed by either a single attending corneal surgeon (n = 43) or by novice surgeons (6 cornea fellows under the supervision of the attending surgeon, n = 57). The median number of DMEK cases performed by individual fellows was 10 (range 1-15). DMEK was performed in combination with phacoemulsification and posterior chamber intraocular lens implantation in 52 cases (52%). Forty-six (46%) eyes were pseudophakic prior to DMEK surgery. Two (2%) eyes remained phakic at the time of DMEK surgery.
The mean donor age was 64.8 years (range: 55-75 years). The mean preoperative donor endothelial cell density was 2693 cells/mm 2 (range: 2278-3484 cells/mm 2 ). The average implanted graft diameter was 7.7 ± 0.1 mm (range: 7.0-7.75 mm). Twenty (20%) donor grafts (representing the first 20 cases in the series) also received a micro “S-stamp” at the time of preparation. For 3 (15%) of the cases in which an S-stamp was employed, the visibility of the S-stamp was poor enough (either due to reduced host corneal clarity or poor S-stamp quality) such that iOCT was used exclusively to determine tissue orientation.
In all cases (100%), the surgeon reported that iOCT provided useful real-time feedback and did not interfere with the surgical procedure in any way. For determining graft orientation, the iOCT image on the attached external video monitor (rather than the “heads-up” overlay in the surgeon’s right ocular) was used preferentially in all cases. The external monitor was preferred because the smaller, lower-resolution image in the ocular was often insufficient to readily visualize the graft and required dimming the microscope lights to enhance visibility.
Nine eyes (9%) required rebubbling because of postoperative graft maladherence as judged by the attending surgeon (>25% graft detachment or any detachment involving the visual axis). The frequency of rebubbling was 9.5% (4/42) for attending cases and 8.9% (5/56) for fellow cases (Fisher exact test, P > .99). ∗
∗ For the purpose of calculating rebubbling rates, the 2 cases of primary graft failure were excluded.
The rebubbling rates for S-stamp cases compared to non–S-stamp cases were 20.0% (4/20) and 6.4% (5/78), respectively (Fisher exact test, P = .08 ) . For 3 of the 4 cases in which an S-stamped tissue required rebubbling, the area of detachment was centered around the S-stamp ( Figure 2 ). In the remaining case, the stamp could not be visualized, and its location was indeterminate.
