Identification of separated lenticular planes using optical coherence tomography

Three patterns for identifying the posterior plane of a lenticule during SMILE

PURPOSE

To describe three patterns of posterior plane edge identification in small-incision lenticule extraction and to prevent lenticule mis-dissection.

METHODS

Femtosecond laser application was performed for small-incision lenticule extraction (SMILE) by one surgeon. The surgical videos of SMILE were recorded and re-watched by the surgeon after operation.

RESULTS

Small-incision lenticule extraction was performed in 52 eyes of 28 patients, and no patient had cap-lenticular adhesion. Three patterns of posterior plane of lenticule were noticed when the surgical videos were re-watched. A "double lines" attached to the dissector were visible, signifying the reflective tape of the edge of the lenticule and the cap. During the expansion of the posterior lamellar separation, a fusiform opening between the lenticule edge and the underlying matrix layer was assumed to be a "leaf sign." With some unintentional operation, the posterior lamella was pushed away from the surgeon. The edge of the lenticule away from the anatomical part, the marking of the femtosecond laser cut, and the edge of the cap layer showed three reflective bands, which formed a "triple lines." The "double lines," "leaf sign," and "triple lines" were observed in 30 eyes (57.7%), 21 eyes (40.4%), and 1 eye (1.9%), respectively.

CONCLUSION

These three signs cover possible situations and provide visual landmarks to identify the correct dissection of the posterior plane, which can help shorten the learning curve of novice doctors.

Cap recovery technique and double-edge sign during small-incision lenticule extraction

PURPOSE

To describe a new technique for identifying the upper (cap) interface during small-incision lenticule extraction (SMILE). If the lower interface is dissected first it can be challenging to locate the cap interface and complete the lenticule separation.

SETTING

London Vision Clinic, London, United Kingdom.

DESIGN

Retrospective analysis.

METHODS

The routine protocol was to open the primary small incision and separate the cap interface, followed by the lenticule interface. If the lenticule interface was dissected first, the modified Sinskey tip was inserted through the superior end of the incision, tangentially along the cap edge interface and then rotated anteriorly to engage the edge of the lenticule adherent to the underside of the cap. The Sinskey tip is then drawn inferiorly, creating a pocket of separation of the lenticule from the cap, enabling the dissection bulb and spatula to be used to dissect the upper interface.

RESULTS

A total of 629 consecutive eyes undergoing SMILE using the VisuMax femtosecond laser were included. The routine surgical protocol (cap interface first) was followed in 88% of eyes and the lenticule interface first in 12% of eyes. The lenticule was extracted successfully in all cases. Uncorrected distance visual acuity at the 1-day postoperative visit was 20/25 or better in 81% of the cap interface first group and 86% of the lenticule interface first group.

CONCLUSIONS

The visual results using this cap recovery technique were equivalent to those when a routine SMILE dissection was performed. The technique allowed surgeons to rescue more challenging cases where identifying the different interfaces was difficult. This technique meant that separating the lenticule interface first should no longer be considered a complication of SMILE.

Analysis of factors associated with unintended initial dissection of the posterior plane during small incision lenticule extraction

Background

To investigate potential risk factors for unintended initial dissection of the posterior plane in the initial learning curve of small incision lenticule extraction (SMILE).

Methods

Data were derived from consecutive 263 eyes of 136 patients who underwent SMILE at the beginning of the surgeon's learning curve. Probabilities of unintended initial dissection of the posterior plane in left and right eyes were analyzed. Preoperative sphere, cylinder, spherical equivalent (SE), J0, J45, lenticular diameter, lenticular thickness, corneal thickness, and axial length were assessed between eyes in which posterior plane dissection was unintended and those in which it was not.

Results

Unintended initial dissection of the posterior plane occurred in 29 eyes, corresponding to an incidence rate of 11.03%. The probability of difficulty in plane dissection in the left eye was significantly higher than that in the right eye (P=0.003). Significant differences were found in sphere (T =2.8, P=0.006), SE (T =2.37, P=0.019), J0 (T =2.05, P=0.043) and axial length (T =-2.79, P=0.006) between eyes with and without unintended initial dissection of the posterior plane.

Conclusions

In the present study, difficulty in plane dissection during SMILE was encountered significantly more often in left eyes for a right-hand doctor, and in eyes with low SE or high J0 values. Special attention should be paid to prevent unintended initial dissection of the posterior plane in such situations.