Microdistortions in Bowman’s Layer Following Femtosecond Laser Small Incision Lenticule Extraction Observed by Fourier-Domain OCT

Abstract

Microdistortions in Bowman's layer after SMILE were associated with the refractive lenticule thickness and surgery order. The microdistortions remained stable after 1 week and had no impact on long-term visual performance.

Semiautomated SD-OCT Measurements of Corneal Sublayer Thickness in Normal and Post-SMILE Eyes

“…However, automated image segmentation algorithms still experience difficulties in delineating this anatomical interface correctly. Particularly, alterations of the anatomic configuration of Bowman layer (eg, after SMILE) 18 or of its OCT signal reflectivity (eg, after phototherapeutic keratectomy) 14 can lead to unnoticed segmentation errors. These shortcomings might not hamper the diagnostic power of ET profile maps for early keratoconus 4,14 when Bowman membrane is widely unaltered.…”

“…16 Even though satisfactory repeatability of both systems has been demonstrated, 14,15,17 nevertheless, segmentation errors of the software algorithms still diminish the reliability of these techniques in clinical use. Particularly, alterations of Bowman membrane (eg, in keratoconus 14 or after corneal refractive surgery 16,18 ) can lead to faulty automated delineation of this fine anatomical layer. Hence, there is an impetus for accurate and robust means of measuring corneal ET.…”

New Developments in the Lenticule Extraction Procedure

“…The microdistorsions remained stable after 1 week but had no apparent impact on longterm visual performance. 24 In summary, safety after SMILE appears to be comparable to that reported after FS-LASIK, 25,26 although recovery may be prolonged in a few cases.…”

Association Between Corneal Deformation and Ease of Lenticule Separation From Residual Stroma in Small Incision Lenticule Extraction

“…These microdistortions were believed to be caused during the separation and extraction of the lenticule from the cornea and were purely mechanical effects. 10 A possible alternate method to the subjective grading may be to analyze the correlation between the magnitude of microdistortions in the Bowman layer after surgery and CD variables before surgery, that is, greater microdistortions in the Bowman layer may be caused in corneas with lower DA. Another potential confounder of the study could be the incision width because it may restrict the removal of the lenticule from the stroma.…”

“…[7][8][9] However, the process of separation of the anterior-posterior surfaces and extraction of the lenticule from the residual stroma can cause mechanical distortions in layers of the cornea. 10 Therefore, it was hypothesized that subjective gradation of the ease of separation of the anterior and posterior surfaces of the lenticule from the residual stroma may be correlated with the measured preoperative deformation of the cornea by air-puff applanation. Thus, corneas that had lower deformation, when adjusted for central corneal thickness (CCT) and intraocular pressure (IOP), were assumed to be stiffer and may correlate inversely with resistance to separation of the lenticule surfaces during the SMILE procedure.…”