Ectasia following small-incision lenticule extraction (SMILE): a review of the literature

Abstract

PurposeFour cases of corneal ectasia after small-incision lenticule extraction (SMILE) have been reported. In this review, we provide an overview of the published literature on corneal ectasia after SMILE and risk factors associated with this complication.MethodsCase reports were identified by a search of seven electronic databases for pertinent heading terms between 2011 and July 2017. We identified patient characteristics and surgical details including preoperative topography, central corneal thickness, and anterior keratometry (Km). Residual stromal bed (RSB) values not reported were computed using VisuMax ReLEx SMILE software Version 2.10.10. Preoperative ectasia risk was measured using the Randleman Ectasia Risk Score System (ERSS). Percent tissue alteration was calculated for each patient as described by Santhiago et al.ResultsSeven eyes of four patients developed corneal ectasia post SMILE. Two patients had abnormal topography in both eyes. One patient had abnormal topography in one eye. Only one patient was noted to have normal topography in both eyes and later developed ectasia in one eye in the absence of any known risk factors. The mean Randleman ectasia risk score was 4±3 (range: 1–8). The mean calculated percent tissue altered (PTA) was 38%±6% (range: 30%–47%).ConclusionA majority of reported ectasia cases occurred in patients with subclinical keratoconus. These conditions may be exacerbated by SMILE and should be considered absolute contraindications to the procedure. Three patients were identified to have high risk based on the ERSS, and one patient exhibited a PTA ≥40%. We formulated a modification to the current calculation of PTA that takes into account the differences in tissue altered between SMILE and laser in situ keratomileusis (LASIK). More studies are needed to fully quantify the risk of ectasia. For now, we propose adopting the same exclusion criteria used for LASIK in the SMILE procedure until more specific metrics have been validated.

Corneal tomographic features of postrefractive surgery ectasia

“…For the left eye, these indices were 47% and 32%, respectively . Thus, these corneas were at risk of development of ectasia based on amount of tissue removed . Thus, this reinforces the need to combine tomography and surgical parameters to screen corneas susceptible to ectasia, irrespective of the type of procedure .…”

“…Topography of the anterior surface of the cornea forms the basis of all ectasia detection indices and scores . Recently, tomography and biomechanical assessment was stressed for detection of corneas that may be predisposed to ectasia . From our earlier study, the tomographic features of A‐E had a strong correlation with E‐B in keratoconic eyes .…”

“…For the fifth patient who underwent SMILE, all preoperative Scheimpflug tomographic data indicated no susceptibility to ectasia . However, the percentage tissue altered (PTA) and modified PTA for the right eye were 45% and 30%, respectively . For the left eye, these indices were 47% and 32%, respectively .…”

“…However, the percentage tissue altered (PTA) and modified PTA for the right eye were 45% and 30%, respectively . For the left eye, these indices were 47% and 32%, respectively . Thus, these corneas were at risk of development of ectasia based on amount of tissue removed .…”

“…In some of these reports, subclinical keratoconus was the probable cause of postrefractive surgery . Therefore, risk scores and metrics were developed for preoperative evaluation of patient corneas . These scores considered preoperative topography, tomography and surgical parameters to determine the risk of development of ectasia after refractive surgery.…”