Side-cut dissection technique aids in lenticule extraction in SMILE

This method can be used in all cases but is especially important for thin lenticules.

Issue: October 10, 2017

ByAmar Agarwal, MS, FRCS, FRCOphth

BySoosan Jacob, MS, FRCS, DNB

Small incision lenticule extraction is a newer refractive procedure that involves refractive correction by means of femtosecond laser dissection of an intrastromal lenticule that is then extracted manually. Manual extraction of this lenticule, if not performed appropriately, may result in complications, more so with thin lenticules. Soosan Jacob has described a sequential segmental terminal lenticular side-cut dissection technique for SMILE lenticule extraction. It is applicable in all cases but is especially important for thin lenticules, which are more difficult to dissect and prone to tears.

This technique together with the white ring sign, also described by Jacob, helps with easy, safe and rapid dissection and extraction of the SMILE lenticule, even in thin corneas, without the fear of complications such as difficult dissection, torn lenticule or partial extraction.

Technique
Figure 1 shows the sequence of terminal segmental lenticular side-cut dissection.

Source: Soosan Jacob, MS, FRCS, DNB, and Amar Agarwal, MS, FRCS, FRCOphth

Figure 2. A: Anterior plane is first dissected utilizing the white ring sign. The posterior surface is then dissected, leaving a very thin rim of posterior plane and the LSC undissected. White arrow points to the extent of central posterior plane dissection, yellow arrow points to the undissected LSC, and black arrow points to the peripheral extent of anterior plane dissection. B and C: The LSC over a small segment from 8 o’clock to about 6 o’clock is dissected counterclockwise followed by sequential short segmental clockwise dissection performed multiple times from left to right, from 4 to 6 o’clock, followed by 2 to 4 o’clock. The uncut LSC on either side (from 8 o’clock and 2 o’clock to the cap side cut, respectively) holds the lenticule in place during this dissection and prevents sliding, folding and unwanted movements of the lenticule during dissection. D and E: The lenticule is freed up on either side by dissecting the LSC counterclockwise from 2 to 12 o’clock (d) and then clockwise from 8 to 10 o’clock (e) to meet the SMILE incision on either side. F: A completely separated well-dissected lenticule without tears or frayed edges is seen under the cap (outline marked by white arrows). The outline of the dissected lenticular side cut is marked by yellow arrows.

First, femtosecond SMILE laser application is completed. For right-handed surgeons, the patient looks downward and to the left and the eye is held at the limbus with toothed forceps to prevent any sudden movements and consequent cap tears. The cap side-cut incision is opened with a semi-sharp pointed dissector, and using the white ring sign as a guide, a small lamellar channel is created anterior to the lenticule at the right and posterior to the lenticule at the left of the cap side cut. The white ring sign makes use of the circular white reflex from the edges of the SMILE lenticule and is the lenticular side cut (LSC). Its relationship to the dissecting instrument allows identification of anterior vs. posterior plane of dissection. The dissecting instrument seen anterior to the white ring indicates anterior plane of dissection, and the dissecting instrument seen posterior to the white ring indicates posterior plane of dissection. After thus confirming anterior placement of the instrument, anterior plane dissection is completed in a relatively straightforward manner by using broad sweeping movements from right to left using a circular, flat-tipped blunt spatula.

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The sequential segmental terminal LSC dissection technique is utilized for posterior plane dissection. The central area is dissected first, leaving a thin band of peripheral rim undissected all around. The LSC is also left intact and not broken through. Next, the LSC is dissected in a small segment from 8 o’clock to about 6 o’clock counterclockwise. The LSC from 8 o’clock to the right edge of the cap side cut is left intact. Sequential short segmental clockwise dissection is then performed multiple times from left to right, from 4 to 6 o’clock, followed by 2 to 4 o’clock. This may be broken down into smaller segments in very thin lenticules. The uncut LSC on either side (from 8 o’clock and 2 o’clock to the cap side cut, respectively) helps hold the lenticule in place during this dissection and prevents sliding, folding and unwanted movements of the lenticule during dissection. Only at the end is the lenticule finally freed up on either side by dissecting the LSC counterclockwise from 2 to 12 o’clock and finally clockwise from 8 to 10 o’clock to meet the SMILE incision on either side. The SMILE lenticule is then extracted using microforceps. In case the final segmental dissection between 8 o’clock to the cap side cut is difficult because of a mobile lenticule, a clockwise lenticulorhexis maneuver may be used to free the lenticule and remove it. The LSC dissection should always be completed in this sequential segmental manner in thin lenticules less than 100 µm to avoid lenticular tears. A similar general principle may be used in thick lenticules even though these are less likely to tear.

Discussion

Various advantages of SMILE over LASIK include decreased disruption of the anterior corneal innervation, faster recovery of dryness and corneal sensitivity, better biomechanical stability as well as decreased flap-related complications such as striae, flap dislodgement and epithelial ingrowth. However, dissection of the femtosecond cut lamellar plane is performed manually, and any difficulty in this step may result in complications such as difficult dissection, torn lenticule and partial extraction. This is more likely to occur in thin lenticules, which are more fragile and can tear easily even during dissection. Ways to avoid tears and facilitate smooth lenticular dissection include complete dissection of the anterior surface of the lenticule followed by dissection of the posterior surface, leaving a very thin rim of posterior plane and the LSC undissected. The LSC dissection is then broken down into segments while leaving it attached on either side to avoid lenticular movements that can make complete dissection difficult. The two sides of the LSC are finally freed in the end, resulting in a completely free lenticule that can be extracted with ease.

Reference:
Jacob S, et al. J Cataract Refract Surg. 2017;doi:10.1016/j.jcrs.2017.04.002.

For more information:
Amar Agarwal, MS, FRCS, FRCOphth, is director of Dr. Agarwal’s Eye Hospital and Eye Research Centre. Agarwal is the author of several books published by SLACK Incorporated, publisher of Ocular Surgery News, including Phaco Nightmares: Conquering Cataract Catastrophes, Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery and Presbyopia: A Surgical Textbook. He can be reached at 19 Cathedral Road, Chennai 600 086, India; email: dragarwal@vsnl.com; website: www.dragarwal.com.
Soosan Jacob, MS, FRCS, DNB, is director and chief of Dr. Agarwal’s Refractive and Cornea Foundation at Dr. Agarwal’s Eye Hospital, Chennai, India. She can be reached at email: dr_soosanj@hotmail.com.

Disclosures: Agarwal and Jacob report no relevant financial disclosures.