Surgeons offer overview of femtosecond laser-assisted refractive cataract surgery

Highlights of this technology and possible complications and risks are reviewed.

Introduction

Amar Agarwal

The main objective in the surgical management of cataracts has always been the treatment of a disease. Residual refractive errors, delayed recovery and complications were accepted and even expected by both patients and physicians. Following the development of IOLs and small-incision surgical technique, patients and physicians became less tolerant of imperfect or unexpected results. The drive within our profession to continually improve efficacy and safety is pushing to what will likely become the greatest paradigm shift in cataract surgery since the development of ultrasonic phacoemulsification: femtosecond laser-assisted refractive cataract surgery. My special guests in this column are Glauco Reggiani Mello, MD, Jonathan H. Talamo, MD, and Ronald R. Krueger, MD, MSE, who have worked on this.

– Amar Agarwal, MS, FRCS, FRCOphth
OSN Complications Consult Editor

Femtosecond laser technology is expected to improve safety and uncorrected visual acuity results, due to a reduction in postoperative astigmatism, wound dehiscence, IOL decentration and potentially visually disabling complications such as capsular tears and vitreous loss. This technology is able to correct pre-existing and induced astigmatism with corneal incisions, using precisely created multiplanar clear corneal entry and limbal relaxing incisions of uniform depth and radius, and likely improve effective IOL positioning through the use of fastidiously sized, centered and shaped anterior capsulorrhexis incisions.

Femtosecond laser-assisted refractive cataract surgery

Currently, three companies, LensAR, Alcon/LenSx and OptiMedica, are developing femtosecond technology to make primary clear corneal incisions, paracenteses, capsulotomies, lens fragmentations and limbal relaxing incisions.

The primary incision and the paracentesis shape, size and location can be customized (Figure 1). The cutting geometry profile is limitless, and the ideal incision shape is yet to be determined.

A reproducible, centered and precisely sized and shaped capsulotomy is one of the obvious advantages of using a femtosecond laser in cataract surgery. Initial studies showed a high accuracy and low standard deviation in laser-performed capsulotomies, with the same or better strength resistance compared with the manual technique.

Figure 1. Clear corneal incision design can be programmed into the machine. Image: OptiMedica

Figure 2. The cube pattern of nuclear fragmentation in a softer lens allows easier aspiration. Image: LensAR

Figure 3. Limbal relaxing incisions can be customized to a micron precision. Image: OptiMedica

The femtosecond laser causes little damage in the surrounding tissue, extending to no more than 100 µm from the desired focus of the beam (very far from the endothelium, which is likely unaffected). However, the femtosecond laser is a cutting device that can only fracture and soften the lens to a point, with phaco energy still being needed to emulsify the nucleus in some cases. The reduction in ultrasound energy is greater in softer nuclei, but even in hard ones, a decrease in total amount of energy used is observed. Several different patterns, such as cubes, crosses, circles and many other shapes, of nucleus disassembly are being studied to determine which is most effective. The cube pattern (Figure 2) has been shown to be one of easiest to aspirate with lower phaco energy. However, it is possible that different patterns and combinations would be optimal for different densities of nuclear sclerosis.

The safety concerns with femtosecond lasers are primarily related to displacement of the laser pulses, which can damage the posterior capsule. As such, it is important to program a safety zone, or buffer, between the lens tissue targeted for photodisruption and the posterior capsule. The profiles of fragmentation are using a safe distance of about 300 µm to 500 µm from the capsule.

Initial studies of femtosecond laser-assisted astigmatism correction have begun with promising results. Besides the precision involved in a laser incision compared with manual limbal relaxing incisions (Figure 3), another great advantage of using femtosecond laser-assisted astigmatic incision compared with excimer laser photoablation in cataract patients is that there would be just one procedure. In addition, femtosecond lasers can create intrastromal-only astigmatic incisions. Although these are expected to be less effective, they may prove to be safer and more stable because Bowman’s layer remains intact; however, these benefits need to be proven through further clinical studies.

Complications, risks and limitations

The major risks involved in the surgery are loss of suction during the procedure and displacement of the laser pulses. This can lead to posterior capsular rupture and, in an eye with increased pressure due to suction, potential migration of nucleus fragments into the vitreous. Displaced laser pulses could also damage the iris, causing hemorrhage in the anterior segment or damage the corneal endothelium. Irregular astigmatism could also occur with displaced limbal relaxing incisions. To minimize the chance of misplaced laser energy within the eye, sophisticated imaging platforms have been developed by each company to ensure accurate guidance of laser pulses inside the eye after coupling of the laser to the eye has occurred using a suction device.

Complex cataract cases, such as those with opaque nuclei, corneal opacity or edema, conjunctival bleb due to previous filtration surgery, or poor iris dilation, are contraindications for the procedure.

Conclusion

The surgical precision offered by femtosecond lasers promises a safer and more predictable cataract surgery. The first results show a more reproducible and stronger capsulotomy, excellent incision architecture and less ultrasound energy used. Future research with femtosecond laser technology will focus on enhancing the concept of these systems as precise intraocular cutting tools and determining the best nomograms for relaxing incisions, the best architecture for cataract incisions and capsulotomies, and the ideal energy parameters for each of these steps and circumstances.

• Amar Agarwal, MS, FRCS, FRCOphth, is director of Dr. Agarwal’s Eye Hospital and Eye Research Centre. Prof. Agarwal is the author of several books published by SLACK Incorporated, publisher of Ocular Surgery News, including Phaco Nightmares: Conquering Cataract Catastrophes, Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery and Presbyopia: A Surgical Textbook. He can be reached at 19 Cathedral Road, Chennai 600 086, India; fax: 91-44-28115871; e-mail: dragarwal@vsnl.com; website: www.dragarwal.com.
• Glauco Reggiani Mello, MD, can be reached at Cleveland Clinic Foundation, 9500 Euclid Ave., Room i32, Cleveland, OH 44195; e-mail: glaucohrm@gmail.com.
• Jonathan H. Talamo, MD, can be reached at Talamo Laser Eye Consultants, 1601 Trapelo Road, Suite 184, Waltham, MA 02451-7356; 781-890-1023; e-mail: jtalamo@lasikofboston.com. Dr. Talamo is a consultant to OptiMedica.
• Ronald K. Krueger, MD, can be reached at the Cleveland Clinic Foundation, 9500 Euclid Ave., Room i32, Cleveland, OH 44195; 216-444-8158; e-mail: Krueger@ccf.org. Dr. Krueger is a cofounder and investor in LensAR.