ABSTRACT
Epithelial ingrowth is a rare condition that is generally seen after laser in situ keratomileusis (LASIK) and has been reported in the literature in a small number of cases after small-incision lenticule extraction (SMILE) surgery. “Epithelial inoculation” should also be considered in patients presenting with decreased vision and an appearance similar to epithelial ingrowth in the early period after SMILE surgery. A 23-year-old woman presented to our clinic with a request for refractive surgery. Her manifest refractions were -7.50 -1.00 x 180° in the right eye and -7.25 -1.00 x 150° in the left eye, and best corrected distance visual acuity was 10/10 in both eyes. The SMILE procedure was performed with the Visumax femtosecond laser (Carl Zeiss Meditec AG). Slit-lamp examination at postoperative 1 week revealed a small grayish-white intrastromal opacity resembling epithelial ingrowth in the central optic axis of the right eye. Irrigation of the interface was performed with balanced salt solution using an irrigation cannula and the epithelial cluster was removed. The patient remained clinically stable 6 months after surgery and has experienced no recurrence. When epithelial inoculation is observed early after SMILE surgery, immediate irrigation of the interface appears to be an effective and safe treatment.
Introduction
Small-incision lenticule extraction (SMILE) surgery has been used in the surgical treatment of refractive errors such as myopia and myopic astigmatism since 2008. Flapless removal of an intrastromal lenticule with SMILE has led to a paradigm shift in which the complications of traditional flap-based ablation methods can be avoided.1,2 Epithelial ingrowth, a flap-related complication, is common after laser in situ keratomileusis (LASIK).3 In contrast to LASIK, a small lateral incision ranging from 3 to 5 mm is made to remove the lenticule created in SMILE, so it is expected that interface epithelial ingrowth will be less likely.4 However, in SMILE, epithelial cells can still be seeded into the interface by surgical instruments and epithelial cell proliferation can follow, leading to an ingrowth-like appearance. The result can be corneal irregularity and decreased vision, especially if the affected area is close to the visual axis.5
In this case report, we present a case of epithelial inoculation following SMILE surgery that was managed with interface irrigation.
Discussion
Epithelium at the interface is frequently encountered as a postoperative complication in the form of epithelial ingrowth after femto-LASIK surgery.6 Since SMILE does not require a corneal flap like LASIK, epithelial ingrowth is a rare postoperative complication.7 The possible causes of epithelial cell migration to the interface during SMILE are varied: a) frequent instillation of topical anesthetic drops, resulting in a loose epithelium-like state, b) migration of corneal epithelium from the lateral incision to the interface, c) disruption of the epithelium close to the incision site and seeding of disrupted epithelial cells via severe and repetitive surgical manipulations,5 and d) migration of epithelial cells to the interface through a fistula formed between the interface and epithelium by a vertical epithelial gas breakthrough.8,9 Each of these may be the cause or multiple causes may coexist.
Loose epithelium that is not detected in the preoperative biomicroscopic evaluation may be encountered intraoperatively. During entry into the interface through the side cut, the dissector may be directed under the epithelium due to loose epithelium and surgical manipulations may increase during the operation. Therefore, with epithelial cells detached from the loose epithelium, interfacial inoculation can take place through a side incision. In the present case, while intending to enter the interface, the dissector went under the epithelium due to the presence of loose epithelium. Then, although the surgery proceeded correctly, the epithelial cells detached from this loose epithelium around the side cut were planted at the interface during lenticule dissection. The fact that the epithelial accumulation was distant from the incision site and not associated with the side cut supports the diagnosis of epithelial inoculation rather than ingrowth.
It is a common approach to observe epithelial ingrowth seen after LASIK without treatment. If the visual axis is affected, the surface becomes irregular, visual acuity is reduced, or stromal melting is observed, a more aggressive approach is required. Many treatment options have been described for epithelial ingrowth. The flap can be lifted and mechanically debrided, and adjuvant treatments such as mitomycin C or alcohol can be used. In addition, phototherapeutic keratectomy can be performed on the residual stromal bed after flap removal. Following these methods, the flap can be closed with sutures or tissue glue to prevent recurrence.10 Although epithelial ingrowth is less common in SMILE, certain complications that affect the optical axis or reduce vision require treatment. Compared to LASIK, the epithelial infiltration area is relatively smaller in SMILE and therefore less aggressive methods may be sufficient.5 Intervention is necessary when the optical axis is affected because it leads to an irregular ocular surface and reduced visual acuity. The treatment decision depends on the size of the epithelial ingrowth area, its connection with the side cut, and its distance from the side cut. In our case, the epithelial debris was easily detached and removed from the interface by irrigation and was not connected to the side cut, facts strongly suggestive of epithelial inoculation rather than ingrowth. Prompt action was taken as the condition was interfering with the optical axis and creating topographic irregularity. After irrigating the interface, a dramatic increase in visual acuity was observed which confirmed that our diagnosis and intervention were appropriate.
In conclusion, in the presence of loose epithelium that was not detected in the preoperative examination, as in our case, or when access is repeatedly attempted during the procedure, the interface should always be checked immediately after surgery with the slit lamp of the device or biomicroscope, and the patient should be followed closely after surgery. When epithelial inoculation occurs after SMILE, treatment is planned depending on factors such as the location of epithelial cells and the amount of epithelial proliferation, necrosis, or progression at the inoculation site. If epithelial inoculation is in the optic axis, interfacial irrigation and scraping may improve visual acuity and reduce topographically irregular astigmatism. As epithelial inoculation is observed early after SMILE surgery, immediate irrigation of the interface appears to be an effective and safe treatment.5
