Laser Cataract Surgery

Proponents say it's safer and more precise. Is it? Here's a preview and status report.

BY WILLIAM W. CULBERTSON, MD

For over 40 years since the advent of small-incision phaco by Dr. Charles Kelman, many of the important aspects of cataract surgery have been performed manually — hampered by the possibility of imprecision and rare occasional complications.

Our initial incision into the eye through the clear cornea serves as the foundation on which to build the rest of the surgical procedure and requires difficult maneuvers and control. As refractive cataract surgeons, we want to control the placement, architecture, size and shape of our cataract incisions to create the desired astigmatic effect and optimal wound construction for healing. Additionally, we maintain intraoperative and postoperative anterior chamber pressure through our clear corneal incisions and reduce risk of endophthalmitis by creating tightly sealed wounds, ideally watertight and self sealing without the need for sutures. Amazingly, we accomplish this in the majority of cases with simple keratomes of various materials and sizes.

Clearly, creating a clean, centered capsulorhexis is the key to successful cataract surgery. An errant capsulorhexis increases the subsequent surgical difficulty and risks for complications. As it is presently performed manually, the capsulorhexis is hard to size and difficult to center due to parallax error. In addition to traditional capsulorhexis sizing, novel IOLs have presented additional requirements to prevent posterior capsule opacification, tilt and decentration.

As surgeons, we have to estimate the capsulorhexis position and size so that the desired aperture in the capsular bag after healing, with possible fibrosis, matches the design objective of the intraocular lens. For square-edged IOLs, the capsulorhexis is sized for optimal overlap but for some of the accommodating IOLs such as the Crystalens, the capsulorhexis is oversized to allow for hinged movement. Additionally, placement of the capsulorhexis is thought to aid IOL centration and yet we have few tools to help us center the capsulorhexis besides anatomical landmarks such as the dilated pupil or limbal edge. This can be challenging given irregular dilation and pharmacologically induced inferotemporal pupil dilation prior to phaco surgery. Decentration of multifocal lenses is debilitating for our patients, causing double vision, glare, halos, etc. Our current tools consist of cystotomes and forceps used to manually tear the capsulorhexis and a variety of aid devices for sizing, such as capsulorhexis rings, markers and the Seibel ruler. If you add the surgical challenges of floppy irises, shallow chambers and zonular weaknesses, the capsulorhexis becomes increasingly difficult, even for the experienced surgeon.

During phacoemulsification, we rely today on a variety of cracking and chopping techniques to disassemble the lens nucleus while maintaining the structural integrity of the capsular bag and supporting zonules. Perhaps the sheer number of surgical phacoemulsification techniques for soft lenses, hard lenses and complicated cases indicate that there is still room for improvement. The number and degree of instrument manipulations required to disassemble the lens, remove the cortex and polish the capsular bag poses additional risk of corneal phaco burn, iris and endothelial damage and reduced integrity of wound size and architecture.

As refractive cataract surgeons, our goal is to provide minimal astigmatism required for optimal uncorrected vision, a target of less than 0.75 D of residual astigmatism after surgery. While cataract surgery is safe and dependable today, there is still much room for improvement. Increased precision and safety will improve the results of both standard and premium IOL surgery.

Femtosecond Lasers in Ophthalmology

Femtosecond lasers have already proven to be a powerful tool in ophthalmology. The pulses of light of extremely short duration (10^-15s) create bubbles that separate tissue through plasma expansion, shock wave pressure and ultimately cavitation bubble creation. Decreased pulse duration reduces the photodisruption threshold and secondary effects allowing closer placement of pulses to create a precise cutting instrument. Almost six years ago, I adopted the IntraLase femtosecond laser (Abbott Medical Optics) with the dual goals of reducing the potential for serious flap-related complications and improving the consistency of flap dimensions. The use of femtosecond laser technology for corneal cutting improved the ability of the surgeon to customize the precise dimensions and orientation using computer-controlled registration and treatment software. The result has been years of consistent and predictable outcomes. Refractive surgeons are becoming increasingly skilled, diagnostic tools are expanding and treatments are becoming more and more refined. Femtosecond lasers (AMO/Intralase, Zeiss/Visumax, Zeimer/LDV) are used today in corneal surgery for LASIK flaps, keratoplasty, investigation of corneal relaxing incisions and cataract surgery incisions.

Initial Experience With OptiMedica Femtosecond Laser

Femtosecond lasers, already used in corneal surgery, can also be employed to photodisrupt tissue deeper in the eye such as the crystalline lens. There are at least three companies, OptiMedica, LensAR and LenSx, that are actively developing femtosecond lasers for cataract surgery. I have worked with a team of physicians, physicists and engineers to develop femtosecond laser-assisted cataract surgery to increase safety, improve precision and automate undependable components. I have participated in an IRB-approved feasibility study (OptiMedica, Santa Clara, Calif.) at Centro Laser in Santo Domingo, Dominican Republic in 50 sighted human eyes without anterior segment pathology and with grade 2-4 nuclear cataracts on the LOCS III scale. Our results indicate that the laser capsulotomy is achieved with the desired position and diameter, within 0.1 mm of intended and is strong under tensile strength testing and SEM analysis. A bi-planar laser cataract incision, opened with a third plane in the operating room, is self sealing upon completion of the surgery. Nuclear segmentation is facilitated and emulsification of the nucleus is enhanced turning a LOCS III grade 4 nucleus into the resemblance of a grade 2 nucleus that can be easily aspirated with minimal, if any, phaco energy.

Perioperative and Postoperative Safety and Performance

When I think about the possibilities of femtosecond laser-assisted cataract surgery, I think it is a tool that levels the surgical playing field by facilitating simplicity and reproducibility and also enables future innovation from our best and brightest surgeons. We are not just replacing manual methods with a more precise and controlled technique, but are also creating the ability to cut with architectural and locational control not possible with manual methods, keratomes, cystatomes, forceps, choppers and phaco tips.

The femtosecond laser enables precise cuts that have important safety and performance implications both peri-operatively and long term. Integrated imaging systems, such as on-board OCT, provide registration to direct the laser both laterally and in depth (Figure 1). For clear corneal incisions, the OCT can provide the corneal thickness at the desired incision location so the architecture for incisions can be properly customized for each patient (Figure 2). This can include the main cataract incision sized for surgical instrumentation, such as the phaco tip and lens injector, and is designed for a watertight seal. It can also include side port incisions. The depth and architecture for relaxing incisions can also be registered, calculated and accurately delivered on the desired axis.

Figure 1. OCT detection of dimensions of anterior chamber and position of anterior and posterior capsule with physician-directed placement of capsulotomy and lens softening-segmentation cuts. Real-time OCT detection of anterior and posterior surfaces of cornea (blue arrows), anterior surface of the lens (red arrows), posterior surface of lens (yellow arrows), planned position and diameter of anterior capsulotomy (white arrows), and the position and depth of the lens segmentation and softening (green arrows).

Figure 2. Clear-corneal incision made by the femtosecond laser (red arrows) with perfect tongue and groove apposition of edges of the incision).

For the capsulorhexis, the OCT detects the iris boundaries so the laser can be safely directed inside the iris even if it is not dilated symmetrically (Figure 3). Research has shown that the capsular edge tensile strength is equal to that of manual techniques (Figure 4). The laser incision formed with cavitation bubbles may have improved strength and resistance to manual trauma during phaco and lens implantation, which could reduce capsular extensions. Symmetrical uniform fibrosis and healing may also be important for accommodating IOLs that rely on symmetrical contractile forces to translate into axial movement.

Figure 3. Perfectly sized (5.0 mm) and positioned, round anterior capsulotomy (red arrows) with four-quadrant segmentation and softening (0.5 mm cubes) created by femtosecond laser.

Figure 4: Electron microscopy of edge of femtosecond laser-cut human anterior lens capsule showing smoothness of the cut (red arrows) comparable to manually created anterior capsulorhexis.

The OCT also provides improved references that enable algorithms to calculate desired capsulotomy centration, reducing surgeons' reliance on visible reference points and estimation for size, shape and position. With this registration information, the laser and control system can deliver precisely sized, custom-shaped and calculated centration of the capsule aperture.

Finally, the OCT detects the anterior and posterior surfaces of the capsule so customized laser patterns can be delivered to separate the lens (Figure 1). Detection of the posterior surface is critical to maintain a safety zone and prevent laser cuts in the posterior capsule, which could lead to rupture during phaco. The nuclear segmentation can be customized for the lens density to facilitate separation with traditional instruments such as simple spatulas without the need for sculpting or chopping (Figure 5). Additional patterns can soften the lens and match to preferred phaco techniques and lumen size so overall phaco time and energy can be reduced. Patterns can be optimized for followability for phaco dynamics to reduce flow, trampolining, iris prolapse and endothelial cell damage from lens fragments. We have found that quadrant segmentation with a cube-softening pattern can turn a LOCS III grade 4 nucleus into that which resembles irrigation and aspiration needs for a grade 2 nuclear cataract. (Figure 6) There may be added safety benefits with less instrument manipulation from fewer instruments and fewer insertion and removal motions. The integration of advanced imaging technology and customized algorithms with femtosecond laser pulse cutting precision in the cornea, capsule and cataractous crystalline lens provides a new level of safety and security for the cataract surgeon.

Figure 5. Femtosecond laser presegmented (four quadrants) and presoftened (0.5 mm cubes) grade four nuclear cataract ready for easy phacoaspiration.

Figure 6. Femtosecond laser facilitated aspiration of first quarter of presegmented and softened grade four cataract.

Adoption Challenges

I see a few challenges for adoption of femtosecond technology for cataract surgery, all of which are encompassed in workflow and practice integration. While femtosecond lasers at customer-centered private outpatient refractive centers were afforded private funding, space and time, we will need to integrate this technology into crowded, CMS-regulated, ambulatory surgery centers that are driven by cost and efficiency.

Femtosecond technology is expensive and, for the safety and control necessary for cataract surgery, we will also be paying for integrated imaging systems. In this time of healthcare reform, how will we finance this technology? I believe the procedural cost will initially be absorbed in the premium lens and refractive channel where the price is set by the surgeon. The challenge will be in finding a way to pay for the advantages of this technology for all lens implants, both standard monofocals and toric, multifocal and novel lenses.

Another disadvantage of this technology is the added procedure time. While the laser procedure time is short, it will add time to our overall workflow. Skilled high-volume surgeons complete a capsulorhexis in less than one minute and can complete the whole procedure in 10 minutes. I do not expect that overall time in the operating room will be reduced for highly efficient centers and surgeons. However, a surgeon who currently spends 30 to 45 minutes on a case may realize significant savings in time. Given the procedural time and technology expense, how do we seamlessly bring this laser into our operating rooms? The four pieces to this puzzle will be the number of operating rooms at your facility, the number of laser systems available, the number of surgeons operating at the same time and the number of operating rooms used by a given surgeon. We will want to optimize the workflow so the laser system can be used by all operating surgeons to pre-treat the maximum number of patients without multiple large capital equipment expenses.

Another key difference from refractive surgery in workflow integration is the cataract patient population. The aging population with comorbidities requires more attention to safety and patient comfort. Additionally, we have the challenge, and therefore the opportunity, to create a premium surgical experience for these patients.

As a surgical community, we will need to find creative solutions to elevate the safety and results of refractive cataract surgery A good first step is to figure out how to integrate femtosecond technology into our cost and efficiency-driven workflow.

Femtosecond Laser for Refractive Cataract Surgery: Equalizer or Enabler?

There is no doubt that femtosecond laser-assisted cataract surgery is the future — the near future — of ophthalmology. Femtosecond laser-assisted cataract surgery is a promising improvement on standard contemporary phacoemulsification cataract surgery It has the potential advantages of improved safety increased precisions and enhanced reproducibility.

What does this mean for us, the surgeons, our practices and ASCs, and our patients? Will this technology obsolesce the years of experience that we have acquired? Will the challenges of modern refractive and cataract surgery still attract the best and the brightest?

With femtosecond lasers, we now have the ability to standardize cataract surgery across the world and provide all surgeons with the ability to create a perfectly sized and centered capsulorhexis with reduced risk of radial tears and rupture of the posterior capsule. Femtosecond lasers offer the opportunity to bring a surgeon's talent and expertise to the forefront of every surgery, less hampered by imperfect surgical tools. In an age in which cataract surgeons cannot keep up with the growing aging population around the world, this technology holds promise of better vision for those with limited access to world-class surgeons. More importantly, this technology will enable innovation from the surgical community and our partners in industry, particularly those in the lens design and manufacturing business.

We will soon have a tool that will allow us to create controlled relaxing incisions sub-Bowman's layer, complex cataract incisions, customized capsulotomies, capsulotomies integrating with IOLs such as “Capsule in the Lens,” new methods for toric IOL orientation and even lens refilling surgery. Our goal is to provide a tool that facilitates this future innovation and improves precision and reproducibility today for all stages of the surgical process from cataract removal to IOL implantation and wound healing. Through enabling IOL performance, and reducing surgical complications, we will increase patient satisfaction through emmetropic refractive outcomes that improve quality of life. OM

William W. Culbertson, MD, is the Lou Higgins Professor of Ophthalmology and Director of the Cornea Service and Refractive Surgery at Bascom Palmer Eye Institute, University of Miami. He is a consultant for OptiMedica. He can be reached via e-mail at wculbertson@med.miami.edu.