July 2019

REFRACTIVE

Presentation Spotlight
Pros and cons of femtosecond laser in different applications


by Stefanie Petrou Binder, MD EyeWorld Contributing Writer


SMILE is a predictable non-flap procedure for the treatment of myopia and myopic astigmatism.

Femtosecond LASIK has fewer safety issues than manual.
Source (all): Jesper Hjortdal, MD

 

Femtosecond lasers offer precision and reliability for a number of procedures. At the 36th Congress of the European Society of Cataract and Refractive Surgeons, Jesper Hjortdal, MD, shared the upsides and downsides of using the femtosecond laser for its top applications in ophthalmology.
“Femtosecond laser is about precision and achieving the best refractive outcomes in cataract and refractive surgery,” Dr. Hjortdal said. “We have four main applications for the femtosecond laser in refractive surgery: relaxing incisions, channels for intracorneal rings segments, LASIK flaps, and small incision lenticule extraction (SMILE).”

Non-precision surgery

Arcuate relaxing incisions are non-penetrating cuts in the mid-periphery of the cornea that achieve a flattening of the cornea in one meridian and a steepening in the other. Relaxing incisions can be cut manually with a diamond knife (traditionally) or using the femtosecond laser.
In Dr. Hjortdal’s experience, performing manual arcuate relaxing incisions in the context of paired arcuate keratotomy in patients with congenital and post-keratoplasty astigmatism is safe and effective. He explained, “The spherical equivalent refraction is unaffected by the procedure. Manual incisions successfully reduce the cylinder, which is the target of the surgery, although there is often also some scatter. We found that manual astigmatic keratotomy is safe and could halve the astigmatism in post-PK eyes in our studies.”
Evidence suggests that the femtosecond laser is just as effective in cases of astigmatic keratotomy. Data suggest safe, reproducible results using the femtosecond laser for relaxing incisions with no change in the spherical equivalent and a decrease in the mean keratometric cylinder of about half, matching the effects of manual relaxing incisions. Although not precision surgery, the femtosecond laser can reduce the risk of perforation over manual incisions, Dr. Hjortdal said.
Manual and femtosecond laser cutting techniques have been shown to be equally effective in the creation of channels for intracorneal ring segments (ICRS) as well. ICRS were developed for the correction of low myopia, with an arc-shortening effect on collagen fibers. Studies on correcting keratoconus with intracorneal rings show lower irregular astigmatism as a result of the procedure in patients with stable keratoconus or keratectasia, with poor visual acuity, and contact lens intolerance. ICRS are contraindicated in very steep corneas >70 D, hydrops, and in eyes with extensive corneal scarring.
According to Dr. Hjortdal, ICRS channels can be cut manually, however, with a risk of perforation (in or out) and epithelial defects. The femtosecond laser helps avoid these complications. “Femtosecond laser is much better for ICRS,” he said. “We implanted ICRS mostly in keratoconic eyes, improving visual acuity. Although femtosecond laser is more reproducible and safer than manual, the results can be quite variable.”
A number of clinical trials confirm that the femtosecond laser is safer for creating ICRS channels. Predictability of ICRS, however, remains a key challenge as current nomograms are insufficient to cover the spectrum of cases. According to Dr. Hjortdal, outcomes are better in patients with more severe keratoconus and poor preoperative visual acuity, and the coincidence between refractive and topographic axes seems to improve outcomes as well.

LASIK and SMILE

LASIK flaps can be created manually with a microkeratome or by femtosecond laser. Manual LASIK flap creation is effective, however, complications like flap folds, plastic mask particles in the surgical interface, epithelial ingrowth, and ectasia (if the flap is cut too deep) have been documented.
Comparative studies from the literature demonstrate that the femtosecond laser is associated with fewer safety issues like epithelial ingrowth and flap thickness inconsistencies. The laser creates a more reproducible flap thickness and a well-defined LASIK flap. A disadvantage of the femtosecond laser in this application is expense. The two approaches are comparable overall in terms of endothelial cell density, dry eye events, corneal aberrations, efficacy, predictability, and contrast sensitivity, Dr. Hjortdal said.
SMILE is a unique femtosecond laser keyhole treatment. Dr. Hjortdal’s own data comparing SMILE to femto-LASIK in more than 3,000 cases show that SMILE achieves good predictability with 95% of eyes within
±1 D. This non-flap procedure avoids the risk of epithelial ingrowth associated with LASIK and has a lower risk of ectasia.
“In higher myopes (>7 D), SMILE efficacy is approximately the same as with LASIK and surface PRK. Safety is similar, too, as different studies show. We followed our SMILE patients between 3 and 7 years and saw stable eyes for 3 years after surgery, with a regression tendency in later years in myopia over –8 D,” he said.

About the doctor

Jesper Hjortdal, MD

Department of Ophthalmology
Aarhus University Hospital
Aarhus, Denmark

Financial interests

Hjortdal: Carl Zeiss Meditec

Contact information

Hjortdal: jesper.hjortdal@dadlnet.dk

Pros and cons of femtosecond laser in different applications Pros and cons of femtosecond laser in different applications
Ophthalmology News - EyeWorld Magazine
283 110
220 199
,
2019-07-01T08:20:31Z
True, 7