29 The Femtosecond Laser: Future Directions

Wendell John Scott

Keywords: Synergy, real-time imaging, team delivery system, patient interface, capsulotomy, after-cataract prevention, customization, primary posterior laser capsulotomy, intraocular lens design, phacoemulsification machine, laser system location

29.1 Future Directions

When it comes to cataract surgery, what do we, as ophthalmologists, want? How will femtosecond laser cataract surgery (LCS) help us accomplish it? We want reproducible cornea incisions that are watertight and consistent. We want a perfect capsulotomy. We want our lens removal to require no energy or minimal energy in order to reduce damage to the ocular tissues. We want implants that are designed for optimal optical quality and function without the need to compromise. For example, current intraocular lens (IOL) edge designs intended to decrease posterior capsule opacity also cause dysphotopsia. In fact, we want to eliminate the most common complication of cataract surgery, posterior capsule opacification. We want real-time quantitative biometrics, intelligent software with adaptive learning, and integrated real-time computer-guided treatment and safety monitoring. We want individualized IOL power determination that eliminates refractive error. We want to reduce complications and human error. We want technology that helps make us better surgeons.

The dawn of femtosecond laser–assisted cataract surgery has helped ophthalmologists further the desire for perfect surgery and has shed light on improvements in each step of the procedure. Cataract surgery has come a long way. The conversion to extracapsular procedures was criticized due to posterior capsule opacification that, at the time, required a return to surgery. However, IOL development advanced due to the extracapsular cataract extraction with an intact posterior capsule and the ability to place the IOL in the capsular bag. The advent of the YAG (yttrium aluminum garnet) laser, which was the first noninvasive way to deal with posterior capsule opacification, removed a philosophical barrier and argument made by those opposed to extracapsular cataract surgery. Consecutive to this, phacoemulsification was developed, and along with it, the foldable IOL. These advances led to small incision no stitch cataract surgery. Along the way, there were many controversies and pundits argued that the procedure was already highly successful and that new procedures were unnecessary and possibly harmful, especially in the case of phacoemulsification. Sound familiar? Indeed, the learning curve was steep and the phacoemulsification equipment was not sophisticated by today’s standards. Even after many technology advancements, the initial complication rate for experienced surgeons transitioning to phacoemulsification in 1997 was reported to be 21.7%. ¹ It took over 20 years for the majority of ophthalmologists to adopt phacoemulsification. Like phacoemulsification, LCS represents a major technology breakthrough, and like phacoemulsification, it is disruptive because it changes the essential way ophthalmologists perform cataract surgery and forces us to re-think every step of the procedure. Fortunately, unlike phacoemulsification, the learning curve of LCS is not a significant barrier and adoption of the procedure is proceeding more rapidly.

The LCS procedure is made possible by the synergy of many technologies, including three-dimensional eye imaging systems that locate the surgical tissue target and display it on a graphical interface for the surgeon. The challenge is to make this imaging real time, including the actual treatment. In this way, the laser reacts more like the surgeon, for example, visualizing the target tissue and making adjustments as necessary. Currently, it is possible for the position of the eye, relative to the eye image, to change prior to delivery of the laser beam because slight eye movement is possible. With real-time imaging providing constant and linked feedback to the surgical beam delivery system, accuracy, treatment speed, and safety will be further improved.

Power and performance are two important features of the femtosecond laser. In comparison to the cornea, the energy delivery needed for lens treatment is several times higher. For instance, if you have a racecar, you cannot hope to win the race if your engine is too small. Many of the laser systems were developed from lasers used for cornea systems. These lasers only require treatment to 150 μm, small spot sizes, and low energy with a high repetition rate. Treatment of the lens requires treatment depths as great as 8 to 9 mm and higher energy due to loss during beam propagation. Higher energy is also needed because the achievable spot size is larger due to cone angle focus limitations at the greater depth level. Thus, like the race car, the size of the engine matters and new generations of some cataract femtosecond lasers will have bigger laser engines than the preceding generation, particularly those developed from cornea-based systems.

Of course, there is more to performance than power alone. Equally important is the beam delivery system. The targeting of cornea tissue, which can be directly applanated and is of limited depth, is much different than the cataract procedure in which the target tissue includes the cornea, capsule, and lens. This laser beam depth range, along with the integrated imaging, makes the complexity of the delivery system significant and also is a major factor that differentiates laser performance between systems. Current systems use a fixed cone focusing angle for all target tissue depths. This leads to compromise. If the delivery system is optimal for cornea incision depth, it may not be as efficient at the depth of the lens and vice versa. Improved laser beam focus, such as a delivery system with a variable cone focusing angle that optimizes beam delivery to each targeted tissue depth, is needed to improve current systems.

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