Lenticule extraction

Femtosecond laser lenticule extraction (FLEX) and small-incision lenticule extraction (SMILE) for hyperopia have evolved to the point where they are at least as good as LASIK in terms of visual acuity and accuracy and postoperative refractive stability, although some problems with corneal haze remain, reports Walter Sekundo MD, Phillips University of Marburg, Germany “There are many problems to solve but we have been very good at getting ahead with these techniques,” Dr Sekundo told the XXXV ESCRS Congress in Lisbon Portugal. He noted that he and his associates first established the feasibility of correcting hyperopia using FLEX in a series of 47 highly hyperopic eyes as published by Blum et al. in 2012. They found that the refractive results were reasonably predictable initially. At nine months, 64% of eyes were within ±1.0D, and 38% were within 0.5D of intended correction. However, over the follow-up period there was mean of 0.51D regression, and roughly half of the patients had to be re-treated. To address the problem, Dr Sekundo recruited the help of the technicians and engineers from Carl Zeiss Meditec who designed the ablation pattern for treating hyperopia with the Mel 80 Excimer laser. Together they developed a new profile for hyperopia using the FLEX technique.

The advantage with the M treatment cone is that you can implement a large transition zone, and a large transition zone is a key for a stable correction of hyperopia

LARGE TRANSITION ZONE The new laser profile requires a larger “M” cone instead of an “S” cone (as was used in the initial study). “The advantage with the M treatment cone is that you can implement a large transition zone, and a large transition zone is a key for a stable correction of hyperopia. However, the disadvantage is that using a large treatment pattern on a small cornea presents a higher risk of suction loss,” Dr Sekundo explained. A pilot study involving nine patients who underwent FLEX for spherical hyperopia with the new profile using a VisuMax femtosecond laser (Carl Zeiss Meditec) showed that the treatment provided larger optical zones than the previous profile 
and refractive stability similar to that of LASIK, he said. In fact, a mean optic zone of 5.7mm and an adjustable transition zone between 1.9mm and 2.5mm, depending on the range of correction required, was successfully applied. At nine months’ follow-up, 33% were within ±0.50D and 78% within ±1.00D of intended correction. Regression was minimal, as the mean spherical equivalent changed from +0.14 at one month to +0.17 at nine months. At the same time, the investigators noted a systematic undercorrection of about 0.5D when using the first nomogram of the new profile. Dr Sekundo, Dr Blum and their associates then conducted a second, phase II study involving 40 eyes with hyperopia and astigmatism. The patients had a mean age of 49 years and a mean preoperative spherical equivalent of +1.94D (range, 0.63D to 4.5D). The target refraction was between plano and -1.0D, depending on age. In addition, 0.5D of overcorrection was added to the treatment taking into account the experience of the phase I. At the conclusion of this prospective study, which was nine months post-op, 70% were within half a dioptre and roughly 90% were within one dioptre of intended correction. Furthermore, regression was slight and similar to that commonly achieved with hyperopic excimer laser surgery, with the mean spherical equivalent changing from 0.2D to 0.0D when comparing the six- and nine-months follow-up. In terms of safety, best corrected visual acuity remained unchanged in 78% of eyes, 10% gained one line and 13% lost one line. In addition, there were no decentred treatments, no instances of suction loss and no patients reported halos. Dr Sekundo noted that there were a higher proportion of patients with dry eyes than is the case with SMILE for myopia, most likely because of the 
older age of the patients treated and the FLEX technique requiring flap. In addition, one-in-five patients had trace haze in the interface. That is probably because the lenticule is thinnest in the middle in hyperopic treatments, whereas in myopia the lenticule is thickest in the centre, he said. Research into the use of SMILE for hyperopia is also under way, he noted. Dr Pradhan, Dr Reinstein and Dr Carp at the Tilganga Institute of Ophthalmology in Kathmandu, Nepal, are carrying out studies using a VisuMax femtosecond laser and a similar profile with an optical zone between 6.3mm and 6.7mm and a 2.0mm transition zone. As part of the study, Dan Reinstein MD in London matched a group of eyes undergoing hyperopic LASIK with the MEL 80 excimer lasers (Carl Zeiss Meditec) and compared both the centration and the optical zone size. REFRACTIVE ACCURACY The British-Nepalese investigators carried out a study in which 31 eyes underwent hyperopic SMILE and were matched to 93 eyes after LASIK. At nine months of follow-up, UCVA was the same or better than preoperative corrected visual acuity in 47% of those who underwent SMILE and in 50% of those who underwent LASIK, Dr Sekundo said. Refractive accuracy was also similar in the two groups. In the SMILE group, 65% were within half a dioptre and 87% within one dioptre, whereas in the LASIK group 53% were within one half a dioptre and 81% were within one dioptre, he added. The results were recently published in the Journal of Refractive Surgery. The above-mentioned investigations paved the way to a worldwide multi-centre prospective study on SMILE for hyperopia that has been initiated very recently. The refractive community can expect the first results of a large cohort in one-to-two years' time. Walter Sekundo: 
sekundo@med.uni-marburg.de