SMILE Procedure vs. LASIK

08 Dec SMILE Procedure vs. LASIK

What is the SMILE procedure and how is it different from LASIK?

The SMILE procedure is purportedly an improvement on LASIK in that it only requires one laser that will cut a “lenticule” –the same amount and size of corneal tissue as would be removed in LASIK –that can then be removed through a small incision in the cornea. The only advantage that the manufacturer claims is that since an entire corneal flap is not being cut, it will better preserve the corneal nerves from damage:

“The corneal disc is removed through a very small incision. Since the surface of the cornea is minimally disturbed, long-term dry eye should be less common with SMILE.” -AAO website

In reality, the corneal nerves are just as vulnerable whether with the SMILE technique, LASIK, or even PRK. The reason is that the most up-to-date corneal micro-anatomy technology shows the pattern of nerve distribution in the cornea is they spread over the cornea and then turn downward to penetrate all the way through the thickness of the cornea. So whether there is a flap, or you laser the top of the cornea, or you cut a flap, you are going to be cutting nerves.

Another key difference is the inability to treat astigmatism and hyperopia.  With the SMILE procedure, you can really only treat simple myopia which is a very small percentage of patients.

Here are more references for those who are interested in more information

Architecture of Human Corneal Nerves

Linda J. Mutter, Gijs F.J. M. Vrensen, Liesbeth Pels, Bob Nunes Cardozo,

and Ben Willekens

Purpose. The corneal innervation, mainly analyzed in light microscopical studies, has been

described as radially oriented stromal nerve bundles that ramify as leashes in the sub basal

plexus. The current study aims to determine the orientation, the size, and the postmortem

changes of the nerve fibers in the sub basal plexus of the human cornea.

Methods. Before processing for light and electron microscopy, the position of the corneas

within the enucleated eyes of persons with melanoma and pairs of postmortem eyes was

marked. The orientation and postmortem changes of the fibers were studied in serial “en

face” semithin sections, and the size was determined in random, ultrathin cross-sections.

Results. Thirteen and a half hours after death, the majority of the nerve fibers were degenerated or gone. Nerve fiber bundles in the subbasal plexus run first in die 9-3 hours direction, then after bifurcation in the 12-3 hours direction and after a second bifurcation again in the 9-3 hours direction. From die main straight bundles, single-beaded fibers branch and run

obliquely. Quantification of the nerve fibers shows an equally dense innervated central and

central-peripheral cornea (mean fiber diameter, 0.4 /j,m) and a five to six times lower innervated peripheral cornea (mean fiber diameter, 0.67 fitn).

Conclusions. The nerve bundles in the sub basal plexus of the human cornea form a regular

dense meshwork with equal density over a large central and central-peripheral area. Because

of their size, the majority of the fibers can be classified as C-fibers. Invest Ophthalmol Vis

Sci. 1997;38:985-994.