Eyeworld

30 | EYEWORLD | JULY 2019 R EFRACTIVE PRESENTATION SPOTLIGHT by Stefanie Petrou Binder, MD EyeWorld Contributing Writer Contact information Hjortdal: jesper.hjortdal@dadlnet.dk F emtosecond lasers offer precision and reliability for a number of procedures. At the 36th Congress of the Europe- an Society of Cataract and Refractive Surgeons, Jesper Hjortdal, MD, shared the upsides and downsides of using the femtosecond laser for its top applica- tions 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 seg- ments, 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 merid- ian and a steepening in the other. Relaxing inci- sions 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 spher- ical 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 equiva- lent and a decrease in the mean keratometric cylinder of about half, matching the effects of manual relaxing incisions. Although not preci- sion surgery, the femtosecond laser can reduce the risk of perforation over manual incisions, Dr. Hjortdal said. Manual and femtosecond laser cutting tech- niques 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 re- sult of the procedure in patients with stable ker- atoconus or keratectasia, with poor visual acuity, and contact lens intolerance. ICRS are contra- indicated 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 com- plications. "Femtosecond laser is much better for ICRS," he said. "We implanted ICRS mostly in keratoconic eyes, improving visual acuity. Al- though 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 coinci- dence 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, com- plications 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 asso- ciated with fewer safety issues like epithelial in- growth and flap thickness inconsistencies. The laser creates a more reproducible flap thickness Pros and cons of femtosecond laser in different applications About the doctor Jesper Hjortdal, MD Department of Ophthalmology Aarhus University Hospital Aarhus, Denmark Financial interests Hjortdal: Carl Zeiss Meditec

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