SMILE Laser Surgery for Vision Correction

What is SMILE eye surgery ?

SMILE is an easy to remember acronym used for a laser eye surgery known as Small Incision Lenticulate Extraction. After the introduction of LASIK surgery for eye surgery, many new advancements have been made so far. One of these is SMILE which has been said to be the world’s most advanced laser eye surgery.

FDA approved its usage in the United stated in September 2016. More than 1 million SMILE procedures have been performed worldwide. SMILE laser surgery is performed using a single laser called as VisuMax femtosecond laser which is the proprietary technology owned by Carl Zeiss Meditec.

What are the indications for SMILE ?

SMILE procedures can be used to correct short-sightedness alone or short-sightedness along with some amount of astigmatism. The US FDA approved indications are as follows:

• Near-sightedness ranging from -1.00 D (dioptre) to -8.00 D
• Astigmatism which is equal to or less than – 0.50 D

There are several another prerequisite to be able to qualify for the surgery like

• Age over 18 years
• Eyeglass prescription must be stable for at least 12 months etc.

Patients will undergo a series of tests to determine if they are good candidates for the procedure. In general, people who are good candidates for LASIK will likely be good candidates for SMILE as well. In fact, some individuals who are not suitable for LASIK may be covered by SMILE like

• People having thin or irregularly shaped corneas.
• People who perform jobs and pursue sports with a lot of direct contact to the eyes e.g. fighters, boxers etc
• Predisposition to dry-eye or chronic dry eye syndrome.

Comparison of SMILE vs LASIK procedure

The objective of the refractive eye surgery to reduce the thickness of corneal tissue. This is achieved by reshaping the cornea with the help of laser. Cornea is comprised of 5 layers. It is the middle stromal layer that is reshaped. We will be comparing the procedure of SMILE and LASIK surgery. 

In SMILE surgery

• The laser creates bubbles above and below the desired amount of stroma layer. It will create a lens shaped (lenticular) piece of stroma layer. The thickness of the stroma layer to be removed is determined by the amount of specs power correction. 
• With the same laser, a small incision ranging from 2mm to 4mm is created to extract that lenticular piece of stroma which have been created above with the help of laser.

The entire procedure duration varies from 10 to 15 minutes but the time duration for which laser is used is much lesser which is around 25 seconds.

In LASIK surgery

• a circumferential flap is created with the help of laser to expose the stroma layer. Around 20 mm length of the incision is needed for it. 
• With the help of another laser called an excimer laser, the stromal layer is reshaped and the flap is reclosed.

Benefits of SMILE over lasik

• Precision: SMILE uses only one type of laser and a very small incision area is created when compared to LASIK
• Flapless surgery: No flap is created in SMILE as compared to LASIK. This is the biggest advantage of SMILE over LASIK and it has reduced the chances of several flap related complications.
• Reduced flap related complications: Reduced chances of postoperative dry eyes symptoms as less corneal nerves are cut down owing to the small incision. The small incision may also enable the cornea to have more biochemical stability when compared with LASIK which helps in maintaining shape, especially after trauma.

Recovery after SMILE

It has been found that the SMILE is as safe and accurate as LASIK but there is no WOW effect since the visual recovery is slow. Wow effect is referred to the speedy recovery in clarity of vision after a laser procedure like LASIK, usually within 30 minutes of the procedure but the patient recovery is quick, most people will be feeling great the very next day.

Limitations of SMILE laser eye surgery

It cannot be used to treat the conditions like 

• far-sightedness  
• higher astigmatism
• High order aberrations (HOAs) that can affect night vision

After undergoing a SMILE procedure if someone has a residual refractive error than the best choice to treat additional vision correction would be PRK. High order aberrations (HOAs) that can affect night vision can be treated by LASIK and PRK but not by SMILE. 

Summary

The SMILE procedure like LASIK is a safe, predictable and effective surgical option for the treatment of near-sightedness with reduced chances of flap related complications when compared to LASIK.

Reference

• VisuMax® Femtosecond Laser - P150040. U.S. Food and Drug Administration.

• Kamiya K, Shimizu K, Igarashi A, Kobashi H. Visual and refractive outcomes of femtosecond lenticule extraction and small-incision lenticule extraction for myopia. Am J Ophthalmol. 2014 Jan. 157 (1):128-134.e2
• J Zhao, L He, P Yao, et al. Diffuse lamellar keratitis after small-incision lenticule extraction. J Cataract Refract Surg. 2015. 41:400-307.
• G Sachdev, M Sachdev, R Sachdev, et al. Unilateral corneal ectasia following small-incision lenticule extraction. J Cataract Refract Surg. 2015. 41:2014-2018.
• Shen Z, Shi K, Yu Y, Yu X, Lin Y, Yao K. Small Incision Lenticule Extraction (SMILE) versus Femtosecond Laser-Assisted In Situ Keratomileusis (FS-LASIK) for Myopia: A Systematic Review and Meta-Analysis. PLoS One.