Femtosecond laser capsulotomy is the latest development in the ongoing evolution of cataract surgery. Replacing manual creation of the capsulorrhexis with laser creation increases the precision of the opening’s size, shape, and position. This can have a significant impact on capsulotomy centration outcomes.
MACHINE OVER MAN
All physicians like to consider themselves highly skilled, but every surgery presents an opportunity for human error. Automating a process increases its precision.
The main goal of a manual capsulorrhexis or a laser capsulotomy is to create an exact circle of a specific size, in a precise position, to ensure the proper amount of optic-capsule overlap, thereby facilitating placement of the IOL. Daniel Palanker, MD, and colleagues have shown that performing anterior capsulotomy, lens segmentation, and corneal incisions with a laser that is guided by diagnostic imaging produces continuous incisions in the anterior capsule that are twice as strong and more than five times as precise in shape and size as a manual capsulorrhexis.1 Zolton Z. Nagy, MD, and colleagues reported that use of the laser resulted in fewer patients with incomplete IOL-capsule overlap.2 These investigators found incomplete overlap of capsulotomies in 28% of eyes (n = 57) that received manual continuous curvilinear capsulorrhexes, whereas only 11% of eyes (n = 54) that received an anterior capsulotomy created with a laser had incomplete overlap. The researchers also found that improved overlap parameters helped maintain proper positioning of the IOL.3
WHAT IS THE CENTER?
Establishing centration of the capsulotomy is not always straightforward, as there are myriad approaches. Pupillary centration is a common method, but opinions vary regarding whether the pupil should be dilated. I have found flaws with both approaches. A pharmacologically dilated pupil can be asymmetrical, providing an incorrect reference point. Similarly, although an undilated pupil represents the visual axis, it may also be uncentered relative to the capsular bag.
It is important to understand that the IOL is naturally going to migrate toward the center of the capsular bag based on the orientation of the lens haptics. Although, theoretically, a lens can be intentionally decentered, lenses tend to find their natural resting position inside the capsular bag. Thus, the capsulotomy should be positioned on top of the theoretically centered lens within the bag.
The Catalys Precision Laser System (Abbott Medical Optics Inc.) offers full-volume optical coherence tomography (OCT), allowing the capsulotomy to be centered over the scanned capsule (Figure 1), the pupil, and the limbus, among other options. My colleagues and I conducted a retrospective analysis of 50 consecutive eyes, randomly assigned to either pupillary centration or scanned capsular centration with the Catalys4. All eyes received a 5.1-mm capsulotomy (Figure 2) and were subsequently analyzed for relative position versus IOL optic position and optic coverage.
One hundred percent of the eyes centered over the scanned capsule had complete optic coverage, whereas 75% of the eyes with pupil-centered capsulotomies had complete optic coverage. For a video demonstration of the laser-assisted capsulotomy, visit eyetube.com/?v=hotuf.
In certain instances, one may not want to center the capsulotomy on the capsular bag. For example, if a particular pathology results in an irregular capsular bag or if an optical situation prevents a clear image of the bag, it would be reasonable to rely on pupillary centration as the landmark for placement of the capsulotomy. Additionally, certain surgeons, particularly in Europe, have access to IOLs that can be fitted around the capsulotomy. These capsulotomy-fixated or bag-in-lens implants are designed to fit inside the capsulotomy and, thus, are best centered on the undilated pupil.
THE LENS’ INFLUENCE
I find it beneficial to use the scanned-capsule centration technique for all IOLs, but it is particularly relevant for aspheric, multifocal, and toric IOLs. With some lenses, slight decentration may cause visual aberrations or decrease the patient’s quality of vision. Toric lenses are less prone to visual aberrations but, when poorly centered lose their ability to correct astigmatism.
Overall, I find that aspheric optics are somewhat forgiving in regard to the postoperative UCVA. In my experience, I observe more patients with 20/20 vision even when the final refraction is slightly off target. Anecdotally, I have seen patients whose outcomes are 0.50 to 0.75 D off target but are satisfied. This is in contrast to nonaspheric-optic IOLs, which seem to be less forgiving to off-target refractive outcomes. To maximize the quality of vision in aspheric optics, it is important to assure that they are well centered.5
Patients who choose premium services have high expectations. Although a lens may be perfectly centered after surgery, incomplete overlap of the capsular bag may allow the lens to shift or tilt as the capsulotomy starts to heal, changing the surgical result and decreasing the quality of vision at 3 or 6 months. Intraoperative 3-D OCT imaging makes it possible to align the capsulotomy with the natural resting place of the optic in the capsular bag, enhancing the benefits of femtosecond laser-assisted cataract surgery.
William F. Wiley, MD, is in practice at the Cleveland Eye Clinic and is an Assistant Clinical Professor of Ophthalmology at University Hospitals/ Case Western Reserve University in Cleveland, Ohio. Dr. Wiley states that he is a paid consultant to Abbott Medical Optics Inc., and has a financial interest in the ORA System (WaveTec Vision). He may be reached at tel: +1 440 840 2020; e-mail: email@example.com.
- Palanker DV, Blumenkranz MS, Andersen D, et al. Femtosecond laser-assisted cataract surgery with integrated optical coherence tomography. Sci Transl Med. 2010;17;2(58):58ra85.
- Nagy ZZ, Kránitz K, Takacs AI, et al. Comparison of intraocular lens decentration parameters after femtosecond and manual capsulotomies. J Refract Surg. 2011;27(8):564-569.
- Kránitz K, Takacs A, Miháltz K, et al. Femtosecond laser capsulotomy and manual continuous curvilinear capsulorrhexis parameters and their effects on intraocular lens centration. J Refract Surg. 2011;27(8):558-563.
- Wiley WF, Bafna S, Jones J. Optical coherence tomograghy guided capsule bag-centered femtosecond laser capsulotomy. Paper presented at: the ASCRS Annual Meeting; April 20, 2013; San Francisco.
- McKelvie J, McArdle B, McGhee C. The influence of tilt, decentration, and pupil size on the higher-order aberration profile of aspheric intraocular lenses. Ophthalmology. 2011 Sep;118(9):1724-31.