ReLEx and Femtosecond LASIK: A Comparison of Two Approaches for Laser Vision Correction

A new single-step, single-instrument technique for laser vision correction may offer advantages in the correction of myopia.

By Osama Ibrahim, MD

Refractive surgery via LASIK is highly successful. Modern innovations in technology and techniques have improved the procedure’s safety, efficacy, predictability, and repeatability. Still, an even less invasive laser procedure for the correction of refractive error may be of great benefit to patients.

ReLEx smile, a procedure performed exclusively with the VisuMax femtosecond laser platform (Carl Zeiss Meditec, Inc.), constitutes a milestone in minimally invasive laser vision correction surgery (the procedure has not been evaluated by the US Food and Drug Administration). With this procedure, an intrastromal lenticule is created with the VisuMax within the intact cornea and is separated and removed manually through a small incision. Thus, ReLEx smile distinguishes itself from other techniques because it uses tissue removal instead of tissue ablation. It achieves high precision cutting that contributes to the predictability of the procedure. The size and shape of the created lenticule corresponds to the desired refractive correction, and it requires only a small opening incision for the dissection and removal of the lenticule.


ReLEx: Smile Versus Flex
In the past 2 years, I have performed about 200 procedures with ReLEx flex and more than 400 cases of ReLEx smile. There are slight differences between the flex and smile approaches. ReLEx flex represented the first step toward the development of a minimally invasive laser vision correction procedure. Like the smile technique, flex is a procedure in which an intrastromal lenticule is created in the intact cornea. The difference is that flex is performed with a corneal flap-like access cut to dissect and extract the lenticule, although the flap is smaller than that used in LASIK.

Our practice was involved in clinical studies of both ReLEx procedures. As our experience grew over the course of the clinical study, we were able to titrate the energy levels of the VisuMax femtosecond laser as well as its spot distance and size to make the system more individualized. These adjustments gave us more repeatable and reproducible results. Since that time, we have also fine-tuned the lenticule geometry, resulting in more accurate astigmatic correction.

ReLEx Versus LASIK
ReLEx smile has a slightly steeper learning curve compared with femtosecond LASIK. After mastering it, however, smile is a much easier and less timecosuming procedure. It consists of a single step where the lenticule and side cut are created at once. Because both steps are performed using the VisuMax, there is no need to move the patient between two lasers. Thus, the procedure minimizes stress for the patient. Additionally, the laser treatment time (ie, the time it takes to create the lenticule) is independent of the patient’s myopia. I can treat -10.00 D of myopia in the same amount of time it takes me to treat -1.00 D, provided the eyes have the same cap diameter and optical zone.

The long-term results after LASIK or ReLEx smile are similar, but in our experience, visual recovery can take a bit longer with the latter in some patients, and there is less incidence of dry eye after ReLEx smile compared with LASIK.


The major advantage of ReLEx smile is that there is no flap cutting, which may minimize the induction of spherical aberration and eliminates the incidence of striae. Without the potential for spherical aberration, patients treated using the smile technique are more likely to achieve better quality of vision than patients treated with an excimer laser. This is especially true for those with high myopia. ReLEx smile may also offer better biomechanical stability than procedures employing flap creation, along with less postoperative discomfort and a lower incidence of dry eye. With no potential for flap displacement, even after trauma, smile is the best procedure for those who are involved in contact sports.

Unlike excimer laser-based procedures, ReLEx smile uses a solid-state laser, and therefore, there is no need for consumable gases or tight environmental humidity control. The VisuMax is a silent, soft, and gentle laser. It does not produce a smell, there is no vision blackout during the procedure, and the cornea is not forced into a nonphysiological planar shape. As a result, deformation and artifacts can be avoided in the cutting results as well as unnecessarily high intraocular pressure.


After general treatment planning, the first step for performing ReLEx smile is to attach a disposable curved contact glass onto the laser aperture cone of the VisuMax femtosecond laser. The spherical patient interface of the contact glass is designed to provide the best fit with the anatomical shape of the cornea, minimizing tissue compression and ocular irritation. After the contact glass is attached, the system self-calibrates. Keratometry data can then be entered to account for the difference between the relaxed cornea and the contact glass curvature. This calculation allows the system to determine the ratio between the intended clinical treatment and the cap’s diameter on the relaxed eye, as well as the incisional diameter, when cutting the eye coupled to the contact glass.

With the patient fixating on a flashing green light, the surgeon manually repositions the bed so that the cornea meets with the contact glass. The patient will then notice a flashing fixation target in clear focus. This target uses the manifest refraction of each individual eye to adjust the target’s visibility. The patient’s bed is raised vertically, and the surgeon observes the alignment of the contact glass application through the operating microscope and the side screen during the entire docking process.

The cornea slightly applanates and centers as the surgeon aims for the corneal vertex, and suction is applied to immobilize the globe. The increase in intraocular pressure with the VisuMax is low enough that the patient can see throughout the procedure. The laser is activated when the surgeon presses on the foot pedal. After the lenticule and a small incision are created with the laser, the patient is moved to the observation microscope, where manual dissection is performed. This process starts with dissection of the upper surface (ie, the cap) from the lenticule, followed by separation of the lenticule from the intrastromal bed. The lenticule is removed with a forceps through a 3- or 4-mm incision.


ReLEx smile is a novel approach to laser vision correction in myopic patients. Considering that the evolution of refractive surgery is heading closer to the preservation of corneal biomechanics to increase safety and achieve aberration-free results, ReLEx smile appears to be a reasonable technique worthy of future study and consideration.

Osama Ibrahim, MD, is a professor of ophthalmology, and President of Alexandria University, Egypt, and chairman, Roayah Vision Correction Centers, Middle East. He is a consultant to Carl Zeiss Meditec, Inc. Dr. Ibrahim may be reached at