VisuMax 800: latest generation Femtosecond laser

When an individual’s vision is perfect at any distance, it is primarily because the light rays passing through the eye are focused to a single point located exactly on the surface of the retina.

This phenomenon—where the direction of light is altered as it travels through the eyeball—is called “refraction.” Refraction is performed by the cornea and the lens, the eye’s two natural converging lenses. The cornea accounts for about 70% of the eye’s refractive power, with the lens providing the remainder. Additionally, the lens can change shape—becoming more convex for near vision or flatter for distance vision—thus allowing the eye to focus, much like a camera lens.

Refractive errors, or “ametropias”, occur when the combined refraction of the cornea and lens fails to focus light rays to a single point on the retina.

• Myopia (Nearsightedness): When the eye refracts light too strongly, often due to an excessively curved cornea, the focal point falls in front of the retina. This causes distant objects to appear blurry, while near vision remains clear.
• Hyperopia (Farsightedness): In hyperopic individuals, light rays are focused behind the retina, typically due to a flatter cornea or a shorter eyeball. This results in poor near vision and sometimes poor distance vision.
• Astigmatism: In astigmatism, the cornea is oval-shaped, resembling a rugby ball, with different curvatures along different meridians. This leads to a blurred image along the eye’s anteroposterior axis, causing vision to be impaired at all distances.

Refractive surgery aims to correct ametropias. There are several methods to achieve this:

• Intraocular lenses: Some techniques involve implanting artificial lenses inside the eye.
• Laser procedures: Others use laser beams to reshape the cornea.

 

Depending on the chosen laser technique, optical correction can be achieved by:

• Excimer laser photorefractive procedures (e.g., PRK): Modifying the corneal curvature through photoablation.
• SMILE procedure: Removing a pre-cut corneal lenticule with a femtosecond laser.

The VisuMax 800 is the latest device for these applications.

In addition to presbyopia treatment, the LASIK method allows correction of myopia up to 10 diopters (D), and astigmatism and hyperopia up to 6D. This broad applicability, combined with typically rapid visual recovery and pain-free postoperative course, makes LASIK the most widely performed refractive laser surgery technique in France and worldwide.

Like PRK, LASIK works by reshaping the cornea through photoablation with an excimer laser. However, the ablation in LASIK is performed on deeper corneal layers. The first step is to create a very thin flap in the superficial corneal layers—the “stromal flap.” This flap remains attached at one side and is lifted to expose the deeper layers, where the excimer laser is then applied to achieve the necessary optical correction. At the end of the procedure, the flap is repositioned.

Originally, the stromal flap was created using a microkeratome, a type of manual micro-blade. Today, this tool is increasingly replaced by the femtosecond laser, an extremely precise cutting device. This all-laser LASIK approach makes the procedure more accurate, safer, and less invasive, as it eliminates mechanical contact with the eye.

Studies indicate that using a femtosecond laser for flap creation significantly reduces the risk of postoperative inflammation or infection and minimizes the incidence of temporary dry eye, a common side effect after conventional LASIK. Furthermore, the femtosecond laser allows for optimal customization of the flap’s characteristics to each patient’s needs.

Among all laser refractive surgery methods, the SMILE procedure is the most recent and follows a different strategy than LASIK, which uses excimer laser photoablation.

In SMILE, the surgeon uses a femtosecond laser to cut a disc-shaped lenticule within the cornea. The lenticule’s shape, thickness, and orientation are calculated during the preoperative assessment. After the lenticule is cut, the surgeon manually separates any adhesions and extracts it under a microscope.

Like other refractive surgeries, SMILE is performed under local anesthesia with eye drops, and patients can return home the same day.

Thanks to its technological advancements, the VisuMax 800 (Zeiss) expands the range of treatments possible with the SMILE protocol. Until recently, SMILE was used only for myopia up to 10 diopters. With the VisuMax 800, routine treatment of astigmatism up to 5 diopters is now possible, notably due to the CentraLign® system, which controls cyclotorsion—a rotation of the eye that occurs when a patient moves from a seated to a lying position for surgery. This system addresses previous challenges in treating astigmatism with SMILE.

Additionally, the range of indications continues to grow, with hyperopia correction via SMILE using the VisuMax 800 currently in development.

Another notable advantage of the VisuMax 800 is its increased speed, thanks to a higher laser pulse frequency—2 MHz compared to 0.5 MHz in the earlier VisuMax 500 (released in 2007). In practice, this means shorter procedures and greater patient comfort. For example, the time required to cut a SMILE lenticule has dropped from 30 seconds to just 10 seconds. Similarly, creating the stromal flap for LASIK now takes only 7 seconds, versus 20 seconds with the VisuMax 500.