I read the following writeup on the use of femtosecond lasers for cataract removal and thought it was especially well written. It also piqued my curiosity about some of the “new” applications suggested for femtosecond lasers, including the use of “laser photolysis” to remove lens opacities. That being the case, I got in touch with the author and received permission to reproduce it in this space.
In addition, I have written a short treatise on Photolysis of Lens Opacities. That’s a new one to me, so please see the attached addendum for additional information.
Femtosecond laser surgery of the lens: a second revolution?
by Joseph Colin, MD
Ocular Surgery News, European Edition Sept 1, 2010
The era of modern cataract surgery began in 1967, with the "phaco revolution" of Charles D. Kelman, MD. The radical changes brought by the use of ultrasound energy were slowly accepted and gradually adopted by the ophthalmic community. With the introduction of flexible implants, phacoemulsification eventually established its position as the state-of-the-art in cataract removal.
Over the following years technology has continued to evolve through incremental improvements, allowing the creation of increasingly smaller incisions.
At the same time, corneal refractive surgery witnessed a gradual switch from mechanical microkeratomes to femtosecond lasers. Ultrashort pulses now enable us to perform very accurate and reproducible LASIK flaps as well as intracorneal tunnels for intracorneal rings, and to carry out better quality keratoplasty procedures, both penetrating and lamellar.
It was obvious that sooner or later we would want to evaluate the possibility of applying femtosecond laser technology to cataract surgery. A femtosecond-assisted procedure, guided by anterior segment imaging (OCT or Scheimpflug), holds the potential for unprecedented precision, reproducibility and safety. Furthermore, it meets the higher requirements of premium IOLs – toric, accommodative and multifocal, creating the conditions in which they can guarantee the best refractive outcomes.
Several stages of the cataract procedure can be assisted by femtosecond laser, starting from inside the eye and reaching the surface: nucleus liquefaction, capsulorrhexis, corneal incision and, when needed, astigmatic relaxing incisions.
Nucleus liquefaction can be applied to cataracts grade 1 to 3 or even up to 4. Microphotolysis is carried out using a variety of dissection patterns, such as four quadrants, multiple concentric circles, microcubes or microspheres. Aspiration is then performed as in conventional phaco. The time the globe stays open is decreased considerably and the trauma caused to the ocular tissue (endothelium, capsule and iris) by ultrasound is entirely avoided.
Femtosecond lasers enable us to perform perfectly centered capsulorrhexes, with custom shapes and sizes. The same level of accuracy would never be achieved by manual techniques. In a study carried out in Budapest by Zoltan Nagy, MD, femtosecond and manual capsulorrhexes were compared in two groups of 60 patients. All laser-performed capsulorrhexes were within +/-0.5 mm of intended diameter. The same result was achieved in only 10% of the manual dissection group. This precision in diameter, size and centration can be crucial when using premium IOLs. Furthermore, in case of weak zonules, surgical stress is considerably decreased. Last but not least, with such a precise match between the anterior capsule and IOL optic, the rate of secondary cataracts is likely to decrease.
A simple step like corneal incision also can be improved by the use of femtosecond laser. Cut geometry and size can be precisely calculated. Roger Steinert, MD, compared femtosecond laser and manual incisions in two groups of eyes. He found that in the femtosecond laser group several incisions did not need sutures or stromal hydration for sealing.
Three companies, LenSx Lasers Inc. (recently acquired by Alcon), LensAR Inc. and Optimedica Corp., are currently investing in femtosecond technology for cataract surgery and have presented the results of their initial series. With all lasers, the procedure appears to be extremely promising in terms of increased accuracy, reproducibility and safety compared to conventional surgery.
Nevertheless, in some cases of advanced cataract, the need for ultrasound phaco still persists. It is still early days, and further advances are needed to optimize the efficiency of this new technique.
Although the cost of the procedure is likely to be higher compared to phacoemulsification, femtosecond laser cataract surgery is likely to become the gold standard in the near future. We are witnessing a second revolution that will bring enormous changes to our practice. Because some stages of the procedure need a clean but not necessarily sterile environment, we may be able to move toward shared care, with part of the procedure being carried out by specially trained non-medical staff outside the operating room. This will allow us to increase the volume of cataract procedures, to save medical time and to shorten wait lists.
Because change always stimulates ideas and brings new opportunities, we should expect this technology to open up new and unexplored possibilities. Already, the femtosecond laser platforms for cataract are finding applications in other lens-related, innovative techniques, such as phacophotomodulation to restore accommodation and photolysis to restore crystalline lens transparency. As we have heard many times before, this is an exciting time in cataract surgery, which never ceases to amaze us with its inner potential of expansion and growth.
* Kessel L, Eskildsen L, van der Poel M, Larsen M. Non-invasive bleaching of the human lens by femtosecond laser photolysis. PLoS One. 2010;16;5(3):e9711.
* Nagy Z et al. Initial clinical evaluation of an intraocular femtosecond laser in cataract surgery. J Refract Surg. 2009;25(12):1053-1056.
* Schumacher S, Fromm M, Oberheide U, Gerten G, Wegener A, Lubatschowski H. In vivo application and imaging of intralenticular femtosecond laser pulses for the restoration of accommodation. J Refract Surg. 2008;24(9):991-995.
About the Author
Joseph Colin, MD
Dr Joseph Colin received his MD in 1977 from the Brest University; he completed his ophthalmology residency and fellowship in Brest University Medical School and Nantes University, France, where he specialized in anterior segment surgery.
Promoted to Professor of Ophthalmology in 1982, he was Chairman of the Department of Ophthalmology at Brest University Medical School until September 2000. He is currently Chairman of the Department of Ophthalmology at Bordeaux University Medical School.
He was president of the French National University Council for Ophthalmology (1995-2003).
He currently serves on the Board of the French Society of Refractive Surgery (SAFIR). He also serves on the Board of the French Eye Bank.
He was a member of the board of the National French Ophthalmological society (SFO) from 2001 to 2008 and president of the SFO for three years
OK, What is Laser Photolysis?
After reading Dr. Colin’s article about the new uses for femtosecond lasers, including his mention of “laser photolysis” (and having just written about laser vitreolysis), it piqued my curiosity and I decided to learn more about this term that I had not heard of before.
In doing an online search, I came across three articles discussing this phenomenon, including the first article cited by Dr. Colin, by Dr. Kessel et al, from the March 2010 issue of PloS One (The Public Library of Science), on “Non-Invasive Bleaching of the Human Lens by Femtosecond Laser Photolysis”.
It turns out that Kessel and her colleagues at the University of Copenhagen and the University of Denmark, discovered that they could use a femtosecond laser (Mira 900 from Coherent) to “bleach” naturally occurring “chromophores” that have accumulated due to the ageing process in the natural lens. Or, as they put it, “With time the structural lens proteins are subjected to post-translational modifications by non-enzymatic glycation and other biochemical and biophysical pathways leading to an accumulation of chromophores that absorb visible light preferentially in the blue end of the spectrum, giving the aged human lens its characteristic yellow-brown color. “
“Photoactive molecules, such as chromophores, will eventually degrade upon the interaction with light. Chromophore bleaching is a phenomenon of fundamental importance for multiple life functions such as vision that is based on the photobleaching of photopigments, opsins, in the retina. The fluorescent chromophores of the human lens can be bleached in vitro by broad-band ultraviolet radiation, demonstrating that lenses can be optically rejuvenated by chromophore bleaching. Ultraviolet treatment of the lens is, however, not possible in a clinical setting because of retinal phototoxicity.”
What they chose to do instead, was to apply the radiation output of a femtosecond laser, scanned across nine donor human lenses, to achieve photobleaching of those lenses. As they reported, “Photobleaching was visible to the unaided observer in the treated area with no signs of damage to the untreated parts of the lens.”
They went on to say, “After laser treatment the transmission of light through the lens was increased over the entire visible spectrum and most prominently in the blue-green part, where the age-related loss of transmission is also most pronounced. The effect of the laser treatment showed a clear dose response with the number of scans applied to the lens.”
They concluded that, “We have shown that the age-induced yellow discoloration of human donor lenses can be bleached by a non-invasive procedure using femtosecond pulsed infra-red laser light. Even with the current primitive set-up, clinically relevant effects corresponding to a lens rejuvenation of 3 to 7 years was obtained. (See Table 1.) Cataract is a disease associated with old age and by postponing the need for surgery by 5 years the number of surgeries performed can be reduced by 35%. Treating the entire lens volume is expected to eliminate the effect of several decades of optical aging.”
So, now we know why Dr. Colin was so excited about one of the future applications of the femtosecond laser. It might be possible in the future, to scan the lenses of those with early-stage cataracts and remove the milkiness/yellowness of the cataracts by photobleaching, or laser photolysis and thus extend the time – in years – before cataract surgery is needed!
By the way, Wolfram, Waring and Mamalis, writing in the June 2010 issue of the Journal of Cataract & Refractive Surgery (and also the March 2010 issue of C&RSToday), also discuss laser photolysis. But, in this case, they are discussing using the Dodick YAG photolysis laser (a Nd-YAG, from ARC GmbH) to prevent posterior lens capsule opacification by photodisrupting lens epithelial cells and proteoglycan attachment molecules on the anterior capsule.
This work is noteworthy, but not as much as the work described above by Kessel et al, in photobleaching the lens itself, to prevent cataract formation and extend the time before cataract removal becomes necessary.
3. Capsular Cleaning to Remove Lens Epithelial Cells: Results of Nd:YAG laser photolysis at 3 years are promising
; Wolfram Wehner, MD, George O. Warning III, MD, FACS, FRCOPTH, Rudoph Walker, PHD, and Reinhardt Thyzel; Cataract & Refractive Surgery Today, Europe, March 2010.
Additional Information about Femtosecond Lasers from this Journal:
Intrastromal Ablation: A Technology Whose Time Has Come?
Another Approach to Intrastromal Ablation
Femtosecond Lasers Proposed for Use in Cataract Surgery