Femtosecond Laser Technology Applied to Lens-Based Surgery
Louis D. “Skip” Nichamin, M.D.
Arguably the last global Milestone within the field of cataract surgery was the introduction of phacoemulsification by Kelman. Through his pioneering work phacoemulsification became a reality as a means by which surgeons could break up the cataractous lens and remove it through a small incision. Over the ensuing 40 years this led to further refinements in surgical technology and technique, yielding additional reduction in incision size, sutureless wound closure, the development of ophthalmic viscoelastic agents, and intraocular lenses that now achieve unprecedented levels of visual function. The introduction of phaco affected every aspect of cataract surgery and led to the present day standard of care.
Laser Cataract Surgery
Recently, an emerging new technology appears to represent a similar paradigm shift in the world of refractive cataract surgery: the introduction of ultra-short pulse (femtosecond) lasers. Since their introduction, there has been a move towards the development and use of such lasers in order to make precise cuts that can enhance the safety and efficacy of ophthalmic surgery. It is well accepted that short pulse lasers have advanced corneal flap creation for keratorefractive surgery, in part, by greatly increasing the predictability and consistency of the corneal cut compared to that of a manual microkeratome blade cut . However, the newest innovation in anterior segment surgery is the use of ultra-short pulse lasers in cataract surgery. Instead of a manually torn capsulorhexis the laser can create a precise, laser- cut anterior capsulotomy which is well centered, of exact size and of perfect shape. Using the laser to fragment the lens prior to aspiration and making the necessary corneal incisions can create a laser-based cataract surgery that should reflect the precision and accuracy normally associated with other all laser-based procedures. The new LensAR Laser System™ introduces the possibility of entering the operating room with the knowledge that the cataract patient will have the exact capsulotomy, clear corneal incision and astigmatic corneal relaxing incisions that are desired along with a laser-treated cataract that requires little or no ultrasonic energy to remove.
Studies have shown the benefits of the laser-based procedures. Nichamin  reported on an assessment of anterior capsulotomy when compared to manual capsulorhexis. It was found that the laser capsulotomy was not only significantly closer to the intended diameter by a factor of almost three, but the shape was also significantly rounder than the manually torn rhexis.
More recently, data has been presented that shows the benefits of fragmenting the lens with the laser prior to lens extraction thereby reducing the amount of ultrasound energy used during the surgery. Fishkind presented results that showed phaco energy (expressed as Cumulative Dissipated Energy or CDE) in a group with the lens fragmented with the LensAR Laser System was reduced compared to a control group which underwent conventional phacoemulsification. Reductions in CDE ranged from 40% for LOCS III Grade 4+ cataracts to 95% for LOCS III Grade 2 cataracts. In particular, the ability to fragment and remove higher grade (Grades 3 & 4) cataract has surgeons particularly excited, especially since LensAR is the only company to have presented such data. Since invasive surgery is associated with a breakdown in the blood-aqueous-barrier (BAB) and Pande has suggested that less invasive procedures result in less BAB disruption, it might be expected that laser lens fragmentation could result in less anterior chamber reaction than conventional phacoemulsification if the ultrasound energy is reduced. Early clinical results from a clinical study with the LensAR Laser System  suggest that this might be the case. Earlier visual rehabilitation with ultra-short pulse lasers may also be expected and has been seen in early data with the LensAR Laser System.
Clear Corneal Incisions
As noted, the precision of the laser has been well documented in making lamellar incisions in the fields of keratorefractive and corneal transplant. Their application to cataract-related corneal incisions is a logical extension to this indication. While clear corneal incisions offer significant surgical advantages there has been a purported increase in the incidence of endophthalmitis with their use.[8, 9]. The potential for sutureless wounds to leak after the completion of surgery is linked directly to the architecture of the incision, the complexity of the case (with the resulting increased manipulation through the wound) and the care with which the wound is hydrated at the end of the case. While a skilled surgeon can manually create the required wound architecture, other factors such as placement of incision, blade type and patient factors such as deep set eyes, etc . may impact the repeatability of the procedure. The laser can produce a consistent incision of the required dimensions regardless of placement or patient features. More importantly, the characteristics of the incision, including size and length, can be adjusted to suit individual cases. A tongue-and-groove design may further help to ensure a total seal at the end of surgery.
Limbal Relaxing Incisions
As the premium lens share of the cataract market increases, so the need for exceptional postoperative uncorrected visual acuity increases with it. Corneal astigmatism can limit the quality of post-operative vision and presbyopic-correcting lenses often require this astigmatism to be minimized if optimum results are to be obtained. Since toric lens options are not common for presbyopic lenses, limbal relaxing incisions remain an integral part of the refractive cataract procedure. They have been shown to be a relatively simple, safe and effective way to correct astigmatism, [10, 11] but the need for individual nomograms  suggests that there is some inter-surgeon variability to the technique. The femtosecond laser can create limbal relaxing incisions and has the precision and repeatability necessary for consistent outcomes that cannot easily be achieved with a manual method using a blade. A recent review  showed how the effect of laser-induced incisions can be predicted from finite element analysis models and can then be compared to untreated eyes or manually treated eyes to demonstrate effectiveness.
One final area of research is the correction of presbyopia. The potential for the LensAR Laser System to use photodisruption to create shaped structural weakening within the lens and thus to restore some flexibility, is the subject of ongoing clinical research. Having demonstrated the feasibility of the technique,  work has continued in order to demonstrate safety in animal models before human trials could begin . A review of this work  earned Dr. Ronald Krueger the best paper in the session award at ASCRS 2010. Laser lens treatment has been shown to reduce the rigidity of the lens and allow it to take up more change in shape than without treatment. Animal studies have shown that there is no progressive cataract as a result of the photodisruption. As a result, human clinical feasibility trials are underway and it is anticipated that results will be published in the near future. This is an exciting application of ultra-short pulse lasers that increases the potential to enhance patient visual performance and LensAR is the only company worldwide to be conducting clinical trials in human subjects.
The application of femtosecond laser technology to cataract surgery and presbyopia treatment is the latest enhancement of ophthalmic surgery. The increased precision of the technology can help in the improvement of surgical outcomes while assisting exp
erienced and inexperienced surgeons achieve more consistent results.
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16. Krueger RR, (2010) “Restoring accommodation using intralenticular laser photodisruption” paper presented to the Annual Meeting of the American Society of Cataract & Refractive Surgery, Boston.