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White ring sign confirms plane of dissection during SMILE
If the planes are not differentiated, complications such as epithelial defects, torn caps and difficult dissection may occur.
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Difficult lenticular extraction may sometimes occur in small incision lenticule extraction, especially if the posterior lenticular plane is inadvertently dissected before the anterior plane. Dr. Jacob has described the white ring sign as a means to facilitate easy identification of the anterior plane from the posterior plane of dissection and thereby prevent difficult and complicated SMILE lenticule extraction.
Differentiating the posterior plane from the anterior plane of dissection may sometimes be difficult, and inadvertent dissection of the posterior plane first results in a lenticule that is stuck to the cap. This can then be difficult to separate and may result in complications such as epithelial defects, torn caps, prolonged and lengthy dissection, and partially dissected lenticules. Keeping an eye out for the white ring sign while initiating and continuing the dissection helps the surgeon verify the plane of dissection with certainty.
Technique
Once the femtosecond laser application is over for the SMILE procedure, a semi-sharp pointed dissector is used to open the cap side-cut incision. The white ring sign is then utilized. The white ring refers to the circular light reflex that is seen around the edge of the SMILE lenticule created by the lenticular side cut. The anterior plane is first dissected in a small area by inserting the dissector in such a manner that the instrument lies anterior to the white ring. This is followed by dissection of a small area of the posterior plane, which again is identified by the instrument lying posterior to the white ring. These two planes are then further enlarged using a circular flat-tipped blunt dissector. The same principle of noting the relationship of the white ring reflex (edge of the lenticule) to the dissecting instrument whenever the instrument goes beyond the extent of the lenticular side cut is used throughout dissection. An oblique external light may be helpful in further enhancing illumination in dark-colored eyes.
Source: Soosan Jacob, MS, FRCS, DNB, and Amar Agarwal, MS, FRCS, FRCOphth
Dissection should be started after verifying that the instrument is seen anterior to the white ring reflex, which confirms an anterior plane dissection. Once the anterior plane is completely dissected, the posterior plane dissection is initiated, again after confirming placement by seeing the instrument posterior to the white ring. Once the lenticule is thus completely freed up on both sides, it is then extracted with microforceps.
Discussion
SMILE is a relatively newer technology for refractive correction and has FDA approval in the U.S. for myopic correction. It involves extraction of a femtosecond laser-carved lenticule from the patient’s stroma to obtain myopic correction. Although the procedure is generally easy to perform, failure to follow certain general principles of dissection can lead to complications such as difficult and complicated dissection, epithelial defects, cap tears, lenticular tears, partial lenticular dissection and retained lenticular fragments.
The basic general principle of SMILE lenticule dissection is to free the lenticule from the overlying cap first before dissecting it off the underlying residual stromal bed. This can sometimes be difficult to perform, especially because differentiating these two planes clearly and distinctly may not always be possible because of the transparent nature of the cornea. The white ring sign makes use of the white circular reflex created by the lenticular side cut and its relationship to the dissecting instrument to allow smooth and accurate dissection. Keeping this sign in mind and looking for it whenever the instrument crosses the margins of the lenticular side cut both anterior and posterior to the lenticule allows smooth dissection and extraction of the SMILE lenticule. It also helps ease the learning curve for a beginner surgeon.
- Reference:
- Jacob S, et al. J Cataract Refract Surg. 2016;doi:10.1016/j.jcrs.2016.07.018.
- 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.