Femtosecond laser-assisted cataract surgery will continue to lead the transition to a new era in ophthalmology with more precise, customizable, and reproducible capsulotomies.
Take-home message: Femtosecond laser-assisted cataract surgery will continue to lead the transition to a new era in ophthalmology with more precise, customizable, and reproducible capsulotomies.
By George O. Waring IV, MD, FACS, Special to Ophthalmology Times
In the short time surgeons have been performing femtosecond laser-assisted cataract surgery (FLACS), it has become obvious the technology facilitates creation of a precise and accurate capsulotomy.
As settings continue to be refined, surgeons will almost certainly see further improvements in clinical outcomes with femtosecond laser capsulotomy.
For example, Wendell Scott, MD, has explored the effects of different vertical spacing and incision depth settings on the quality and speed of the laser capsulotomy.1
Work like this mirrors what surgeons saw in the evolution of femtosecond laser LASIK flaps. Early flaps were not superior to manual flaps but as settings were refined and surgeon experience with the lasers grew, laser flaps quickly outpaced what had been previously possible with manual flaps.
Ophthalmology is heading into a new era where eventually FLACS will gain majority market share compared with manual surgery, just as was observed in corneal refractive surgery. More precise, customizable, and reproducible capsulotomies will be a big part of that transition.
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Size, shape, and strength
The size of laser capsulotomies has been shown to be more uniform and predictable as well as more circular than manual capsulotomies.2 Debate still exists on the overall clinical utility of femtosecond laser-enabled capsulotomies.
Several distinct clinical advantages may result from these attributes. Perhaps the most important benefit may be the increased likelihood of achieving a uniform, 360Ë anterior capsule-optic overlap which should reduce lens tilt and decentration-both of which are particularly important when implanting tilt-intolerant toric or multifocal lenses.
If there is a less-than-perfect or non-circular manual rhexis that extends to or beyond the optic edge, the potential for anterior optic capture (leading to tilt) increases.
Uniform capsulotomy size and shape could also contribute to more uniform capsular contraction, which may be important in controlling for effective lens position (ELP).
However, that may not entirely solve the riddle of ELP. For that, it may be necessary to truly modulate the wound-healing process by eradicating lens capsule epithelial cells or by removing the scaffold for LEC proliferation via primary posterior capsulotomy, as described by Dick and Schultz.3 Although patient and surgical flow issues still remain, the femtosecond laser has the potential to make primary posterior capsulotomies more routine.
Finally, the consistency of the laser capsulotomy can be beneficial in complex cases. Patients with short eyes, tight anterior chambers, and poor dilation benefit from the predictability of the femtosecond laser.
In the rare event of posterior capsular compromise, the femtosecond-enabled uniform size and shape capsulotomy lends itself well to optic capture, where consistent apposition of the optic and capsule is essential for successful sulcus placement and maintenance of centration and proper positioning of a three-piece lens.
The same line of reasoning applies in the rare event of negative dysphotopsia or a consistently rotating toric IOL, where a patient may benefit from a reverse optic capture maneuver, in which the optic is maneuvered to rest anterior to the anterior capsule. In such a case, a perfectly circular and sized anterior capsule is more likely to capture the optic in a uniform, planar configuration with less chance of tilt.
There is conflicting evidence on the strength of laser versus manual capsulotomies. Further studies are needed, but I am fairly confident that as laser hardware and settings are optimized-such as increasing the spot and line separation, increasing the laser speed, and with improvement in patient interfaces-the tensile strength of laser capsulotomies should continue to improve from what is already excellent.
Proper centration of IOLs-particularly multifocal IOLs-is key to success. Surgeons and the ophthalmic industry are working to improve IOL centration on a number of fronts, ranging from better centration techniques that rely on the subject-fixated coaxially sighted corneal light reflex (SFCSCLR) 4 to the use of advanced surgical guidance systems.
Femtosecond laser capsulotomies can be beneficial, as well.
In addition to the benefits of uniform capsular overlap described above, the Catalys laser (Abbott Medical Optics) provides the ability to center the capsular opening on the capsule itself, rather than on the pupil. In my practice, the “scanned capsule” capsulotomy setting has become the default in most cases, except those with very small pupils. It is important to note that in addition to centering on the scanned capsule, multifocal IOLs can be centered on the SFCSCLR intraoperatively (see video).
I prefer a relatively tight range for the capsule diameter. My ideal capsulotomy is 4.9 mm in diameter, which is easier to routinely achieve with a programmable, automated laser capsulotomy. My minimum femtosecond enabled diameter in eyes with poor dilation is 4.7 mm, and I will sometimes go as high as 5.1 mm, particularly in mature cataracts.
In eyes with poor dilation due to use of tamsulosin or other medications, it can be challenging to get the desired size capsulotomy with capsule-centered because of the system’s safety zones that prevent encroaching on the iris margin. In such eyes, my default setting is maximized and centered on the pupil.
In cases where sufficient diameter is still not realized, I use a manual override technique to optimize the diameter, in which the captured iris boarder is enlarged to larger than what is captured, which allows the rhexis to expand out to the iris margin when necessary.
The goal is always a uniform shape that produces a uniform overlap. Being able to manipulate the laser’s diameter and centration settings helps to avoid decentration in these challenging eyes.
Femtosecond laser capsulotomies may also make entirely new approaches a reality in the future. For example, better understanding the biometric data that laser systems are gathering from OCT scans of the capsule can provide new insights into anterior-posterior ELP, the cause of refractive surprises, and how best to use this data for improved outcomes.
Already, much has been learned about the variation of crystalline lens anatomy. Not only is there wide inter-patient and inter-eye variation in capsule dimensions, but there is also the finding that capsule dimensions relative to axial length may be important. It is possible that in the future, IOL companies may begin to focus more on the potential for sizing lenses to the capsule in order to improve ELP. The concept of a primary posterior capsulotomy to reduce capsular contraction and possibly primary optic capture techniques is also exciting. Much of this is due to the fact that this is now imaged-guided surgery.
Capsulotomy-fixated IOL designs have also been proposed by a number of surgeons, including Julian Stevens, MD; Burkhard Dick, MD; Sam Masket, MD; and Roberto Zaldivar, MD. The aforementioned femtosecond laser capsulotomy benefits are desirable and possibly necessary for these IOL innovations.
Femtosecond-enabled laser capsulotomy is one of many benefits of FLACS. With the precision of laser-enabled limbal-relaxing incisions, the customizable lens fragmentation patterns and softening, and image-guided surgery, FLACS is an important innovation in anterior segment surgery.
Centering a multifocal IOL on the subject-fixated coaxially sighted corneal light reflex (Video courtesy of George O. Waring IV, MD, FACS)
1. Scott W, Tauber S, Gessler JA, et al. Clinical comparison of effect of sub-one second femtosecond laser capsulotomy on capsulotomy irregularities. Paper presentation, ASCRS 2015.
2. Friedman NJ, Palanker DV, Schuele G, et al. Femtosecond laser capsulotomy. J Cataract Refract Surg. 2011;37:1189-1198.
3. Dick H, Schultz T. Primary posterior laser-assisted capsulotomy. J Refract Surg. 2014;30:128-133.
4. Chang DH, Waring GO IV. The subject-fixated coaxially sighted corneal light reflex: A clinical marker for centration of refractive treatments and devices. Am J Ophthalmol. 2014;158:863-874.
George O. Waring IV, MD, FACS
Dr. Waring is associate professor of ophthalmology and director of refractive surgery, Storm Eye Institute, Medical University of South Carolina (MUSC), Charleston, and serves as medical director at MUSC’s Magill Vision Center. Dr. Waring also serves as adjunct assistant professor of bioengineering, College of Engineering and Science, Clemson University, Clemson, SC.