Small incision lenticule extraction (SMILE) is a new keratomileusis technique for laser vision correction. In this technique, an intrastromal refractive lenticule is extracted through a small peripheral incision (2 to 4 mm), obviating the need for creation of a flap.1 The most crucial step in the SMILE procedure is dissecting the intrastromal lenticule from the anterior stromal cap. Inadvertent entry of the dissector posterior to the lenticule can result in cap–lenticule adhesion and difficult lenticule extraction.2 An inability to recognize cap–lenticule adhesion and repeated efforts to find the second plane of dissection may lead to prolonged tissue handling, creation of a false plane, retained lenticule, lenticule fragments, or even a need for second stage surgery to achieve desired refractive correction.3
We report a case of intraoperative optical coherence tomography (OCT)–guided management of difficult lenticule extraction due to cap–lenticule adhesion during SMILE.
A 22-year-old man had a refractive error of −5.00 −0.50 × 120° in the right eye and − 5.00 −0.75 × 60° in the left eye. The patient was scheduled for femtosecond laser–assisted SMILE with the VisuMax laser platform (Carl Zeiss Meditec, Jena, Germany). The cut energy index was kept at 34 (approximately 170 nJ) with spot spacing of 4.5 μm. The following parameters were used for the creation of the lenticule: 7-mm cap diameter, 110-μm cap thickness, 6-mm optical zone, and 4-mm incision width. The thinnest corneal thickness in the right eye was 498 μm and the lenticule thickness produced was 88 μm.
The lenticule extraction in the left eye was possible without any difficulty; however, during the lenticule removal in the right eye, the surgeon experienced difficulty in finding the second plane of dissection, which resulted in excessive maneuvering causing edema and haze in the anterior stromal cap that further deteriorated the lenticule visibility (Figure 1A, Video 1, available in the online version of this article). Instead of abandoning the procedure, the patient was immediately shifted under a surgical microscope integrated with intraoperative OCT (RESCAN 700; Carl Zeiss Meditec, Inc., Dublin CA) because it was available in our operating room. Under direct visualization of intraoperative OCT, the surgeon was able to discern the lenticule and its planes even through the hazy overlying anterior stromal cap. Intraoperative OCT showed two planes between which the lenticule was discerned. Under intraoperative OCT, the lamellar plane below the lenticule was distinctly hyperreflective compared to the lamellar plane, which was above the lenticule, suggestive of complete dissection and good separation of the lenticule from the underlying stromal bed (Figure 1A). The lenticule was still adherent to the anterior stromal cap, indicating cap–lenticule adhesion due to inadvertent posterior plane entry.
Intraoperative optical coherence tomography (OCT)–guided management of cap–lenticule adhesion during small incision lenticule extraction (SMILE). (A) Surgical view showing hazy, edematous overlying cap and intraoperative OCT feedback scans depicting the posterior lamellar plane distinctly hyperreflective compared to the anterior lamellar plane, suggesting cap–lenticule adhesion. (B) Under direct observation of intraoperative OCT feedback images, the peripheral edge of the lenticule is being separated and lifted off from the anterior stromal cap by using the sharp tip of the dissector. (C) The freed peripheral edge of the lenticule is grasped with microforceps and rotated in a centripetal fashion. (D) Continuous curvilinear lenticulerrhexis helped in breaking the remaining peripheral adhesion of the lenticule from the side-cut incision. (E) At the end of surgery, intraoperative OCT feedback scans showed a well-apposed intrastromal pocket without any lenticule remnants, ensuring complete removal of the lenticule that was correlated clinically by examining the extracted lenticule for its complete intactness.
The sharp end of the dissector (SMILE Double Ended Dissector with spoon tip, product number 6–836; Duckworth & Kent Ltd., Baldock, United Kingdom) was then used to lift the peripheral edge of the intrastromal lenticule under direct visualization of intraoperative OCT feedback images (Figure 1B). The dissector was passed through the cap opening incision in the posterior plane until the peripheral edge of the lenticule was reached, and it was then pushed up with a simultaneous centripetal rotation of the dissector with the support of the overlying stromal cap. The aforementioned maneuver led to the detachment of the lenticular edge from the side-cut adhesions and some area of the anterior stromal cap. A similar maneuver was repeated on another side of the cap opening incision. The freed edge of the lenticule was grasped with microforceps (SMILE Lenticule Removal Forceps, 23 Gauge, product number 2–837; Duckworth & Kent Ltd.) and it was then slowly rotated in centripetal fashion to free it from any remaining attachments of overlying stroma and the side-cut incision of the lenticule (Figures 1C–1D).
Because of the continuous curvilinear lenticulerrhexis technique, it was possible to extract the lenticule in toto even with the partially separated lenticule from the anterior stromal cap. The extracted lenticule was then examined for its complete intactness and the intrastromal pocket was screened for any lenticule remnants left behind in the interface by moving the intraoperative OCT crosshair throughout the cap diameter (Figure 1E).
At postoperative day 1, uncorrected distance visual acuity was 20/40, which improved to 20/20 on day 7. Anterior segment OCT showed a smooth, regular, well-apposed interface without any lenticule remnants (Figure 2).
(A) Postoperative day 1 clinical picture showing mild interface haze. (B) Anterior segment optical coherence tomography confirmed the well-apposed, smooth, regular interface without any lenticule remnants.
Cap–lenticule adhesion is a known complication of SMILE due to the inadvertent posterior plane entry or inability to find the correct plane of dissection. It may result in suboptimal anatomical and visual recovery in the postoperative period. Various factors such as an inexperienced surgeon, excessive eye movements, opaque bubble layer, and black spots or skip areas during femtosecond laser firing can lead to a lenticule adherent to the anterior stromal cap, which may lead to partial separation and hence difficult extraction.4 Similarly, lower amplitude of refractive errors leads to extremely thin lenticule formation, which may cause difficulty in searching the desired plane of dissection.2
Various clinical signs and techniques have been described for preventing cap–lenticule adhesion and difficult lenticule extraction. White ring sign is the earliest clinical sign by which the surgeon may become aware of the wrong plane of dissection entry.5 Similarly, sequential segmental terminal lenticular side-cut dissection has been described in cases with thinner lenticules to avoid the lenticule being folded over itself and resultant partial separation of the lenticule.6 Also, anterior segment OCT can be useful in managing this difficult situation and postoperatively to localize retained lenticule fragments.7
The photodisruptive nature of the femtosecond laser leaves bubbles in the interface, which helps identify the desired plane of dissection. As the time between the creation of the lenticule and its manual separation increases, the difficulty level rises due to the disappearance of bubbles. Inadvertent posterior plane entry and its dissection can push the lenticule against the cap, leading to cap–lenticule adhesion. Recognizing cap–lenticule adhesion and the anterior plane in such cases increases overall surgical time. The intraoperative OCT provides dynamic feedback images of surgical maneuvering and helps in the localization of the lenticule even through a hazy anterior stromal cap. In our experience, because of the extra advantage of real-time visualization with intraoperative OCT, a simple instrument like the tip of a dissector can be used to dislodge the lenticule from its peripheral attachments of the side-cut incision and overlying cap, avoiding the need for dedicated instruments to tackle the cap–lenticule adhesion.
The continuous curvilinear lenticulerrhexis technique has been described for lenticule extraction and the prerequisite for the continuous curvilinear lenticulerrhexis technique is complete separation of the lenticule from the cap and small posterior plane dissection.8 Our case was a reverse scenario; the lenticule was completely separated from the underlying stromal bed and small anterior separation was achieved under intraoperative OCT to enable the microforceps to grasp the lenticule followed by the slow motion, controlled continuous curvilinear lenticulerrhexis technique, successfully extracting the lenticule in toto. Further intraoperative OCT helps ensure complete removal of the lenticule and good apposition of the intrastromal pocket.
Intraoperative OCT helps in early detection of cap–lenticule adhesion and subsequent lenticule extraction with ease, even in hazy edematous corneas. This decreases surgical tissue handling, overall intraoperative time, patient discomfort, and postoperative suboptimal visual recovery. Also, by using a combined approach with continuous intraoperative OCT and the continuous curvilinear lenticulerrhexis technique in cases with cap–lenticule adhesion, the desired surgical outcomes can still be achieved, thereby avoiding the need for a second surgery and re-treatment in such cases.
- Shah R, Shah S, Sengupta S. Results of small incision lenticule extraction: all-in-one femtosecond laser refractive surgery. J Cataract Refract Surg. 2011;37:127–137. doi:10.1016/j.jcrs.2010.07.033 [CrossRef]
- Shetty R, Negalur N, Shroff R, Deshpande K, Jayadev C. Cap lenticular adhesion during small incision lenticular extraction surgery: causative factors and outcomes. Asia Pac J Ophthalmol (Phila). 2017;6:233–237. doi:10.22608/APO.201619 [CrossRef]
- Ivarsen A, Asp S, Hjortdal J. Safety and complications of more than 1500 small-incision lenticule extraction procedures. Ophthalmology. 2014;121:822–828. doi:10.1016/j.ophtha.2013.11.006 [CrossRef]
- Ramirez-Miranda A, Ramirez-Luquin T, Navas A, Graue-Hernandez EO. Refractive lenticule extraction complications. Cornea. 2015;34:S65–S67. Erratum in: Cornea. 2015;34:e37. doi:10.1097/ICO.0000000000000569 [CrossRef]
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- Jacob S, Agarwal A, Mazzotta C, Agarwal A, Raj JM. Sequential segmental terminal lenticular side-cut dissection for safe and effective small-incision lenticule extraction in thin lenticules. J Cataract Refract Surg. 2017;43:443–448. doi:10.1016/j.jcrs.2017.04.002 [CrossRef]
- Titiyal JS, Rathi A, Kaur M, Falera R. AS-OCT as a rescue tool during difficult lenticule extraction in SMILE. J Refract Surg. 2017;33:352–354. doi:10.3928/1081597X-20170216-01 [CrossRef]
- Zhao Y, Li M, Yao P, Shah R, Knorz MC, Zhou X. Development of the continuous curvilinear lenticulerrhexis technique for small incision lenticule extraction. J Refract Surg. 2015;31:16–21. doi:10.3928/1081597X-20141218-02 [CrossRef]