Coming of Age
Why SMILE is my procedure of choice for low-to-moderate myopia
Dan Reinstein |
When it comes to choosing between LASIK and small incision lenticule extraction (SMILE), I think of this as being similar to choosing between a Ferrari and an Aston Martin. LASIK is a great procedure: it is mature, highly developed and highly sophisticated – over 51 million have been performed worldwide, and outcomes today are great. Indeed, my clinic still performs LASIK, but today, we mostly perform SMILE for myopic patients. Let me explain why.
I think that SMILE has come of age – when you look at the SMILE literature, it is clear that SMILE is as effective as LASIK for the correction of low-to-moderate myopia, and has comparable safety outcomes. Some might say that SMILE is not suitable for low myopia because the lenticule is too thin, which people say can make it difficult to handle and there may be a distortion of the second cut caused by an interaction between the two bubble layers. But this can be easily avoided simply by increasing the lenticule thickness by using a larger optical zone (≥7 mm), and using a minimum lenticule thickness of 20–25 µm instead of the normal 10 µm. We’ve published our results using this approach (1), and 96 percent of our low myopia (-1 to 3.5 D) patients saw 20/20 afterwards – an efficacy that’s equivalent to LASIK.
Clearly, the “flapless” nature of SMILE brings a number of advantages. The keyhole aspect appeals to patients because they don’t have to wait for a flap to adhere, there are almost no post-operative restrictions and they can resume their normal activities almost straight away. Furthermore, the procedure damages fewer corneal nerves. Although SMILE cuts some nerves at the lenticular interface, there’s clear evidence demonstrating that the nerve plexus is for the most part preserved with SMILE, and severed by LASIK, and that corneal sensitivity recovers faster with SMILE (3–6 months versus 6–12 months for LASIK) (2). SMILE also has potential biomechanical advantages because the stronger anterior stroma is left uncut. This means we can use larger optical zones without affecting corneal strength, and as biomechanics are more predictable with SMILE, we induce less spherical aberration than we do with LASIK (3).
But despite these advantages, there are still many myths out there about SMILE, such as: centration is not accurate, it can’t treat cylinder, you can’t perform custom or wavefront-guided ablation, or that retreatment options are limited and difficult. These are either irrelevant to the technique or simply untrue. Just like the early days of LASIK, there were some issues when SMILE was first introduced, but in my view most of these issues have gone – they’re now obsolete. With SMILE, you can center on the visual axis, cylinder is perfectly correctable, custom ablation isn’t actually necessary, and you can retreat after SMILE. Indeed, a LASIK enhancement after SMILE is actually better than LASIK after LASIK because the risk of epithelial ingrowth is massively reduced. We’ve also seen the first SMILE re-treatment (4) – only the lenticule cut was performed and the same cap was used for the enhancement, and the outcome was excellent.
I am not saying there’s anything wrong with LASIK, I’ve even had PRESBYOND Laser Blended Vision (5) myself – if SMILE were to magically disappear off the face of the earth I’d still be very happy to perform LASIK. But SMILE is my technique of choice, and in my view, it is set to become the “go-to” procedure for low to moderate myopia below -6 D, as well as high myopia in place of phakic IOL.
- DZ Reinstein et al., J Refract Surg, 30, 812–818 (2014). PMID: 25437479.
- DZ Reinstein et al., J Cataract Refract Surg, 41, 1580–1587 (2015). PMID: 26432113.
- F Lin et al., J Refract Surg, 30, 248–254 (2014). PMID: 24702576.
- D Donate, R Thaëron. J Refract Surg, 31, 708–710 (2015). PMID: 26469078.
- DZ Reinstein et al., J Refract Surg, 28, 531–541 (2012). PMID: 22869232.