Femtosecond laser assisted cataract surgery has been one of the most exciting topics in ophthalmology for the past several years.
By optimizing the critical steps of cataract surgery to create accurate, reproducible, and customized corneal and lenticular incisions, these lasers add an element of precision to cataract surgery that is unattainable with a traditional manual technique. The technology facilitates the subsequent intraocular steps of the cataract procedure, but some modifications to surgical technique need to be made.
The femtosecond laser devices currently available in the United States include Alcon LenSx Laser, AMO’s Catalys Precision Laser System, the LENSAR Laser System and Bausch + Lomb’s VICTUS Femtosecond Laser Platform.
When discussing femtosecond laser procedures and particularly when comparing different systems, I think it is easiest to look at the individual steps that comprise the laser treatment and then evaluate the system’s advantages and disadvantages for each step. The laser procedure consists of the following components:
- Plan/Customize via graphic user interface (GUI)
- Dock with Patient Interface (PI)
- Image via OCT scan
- Analyze (either automated or manual)
- Treat with the femtosecond laser
All of the companies have taken different approaches in designing their technology, so the patient interface, imaging modality, user interface and software, and laser vary considerably across the platforms. All have strengths and weaknesses. I have had the opportunity to use two of the systems, first the Catalys and then the LenSx, and I am certified on both devices.
In this two part article, I review my experience with these machines. In this part of the article I will cover Treatment Planning and Customization, Patient Interfaces and Docking, Imaging and Analysis of the images. Part 2 will take on the way the lasers actually work while treating patients.
Treatment Planning
Planning and customizing the treatment is performed on the GUI. I believe the Catalys GUI is more intuitive and easier to navigate because the screens are simpler and more user friendly. Since these are computers, the analogy that seems most relevant is to the operating systems we are all familiar with (Mac and PC). The look and feel of the Catalys is akin to the Mac, while the LenSx is more similar to a PC. In my experience, planning treatments initially and then customizing them while the patient is docked is faster and more efficient with the Catalys.
Patient Interface
Docking the eye to the system is achieved with the PI and utilizes suction to stabilize the eye and provide a clear optical pathway for imaging and laser delivery. The Catalys accomplishes this step with a liquid filled interface that does not contact the corneal surface and produces the smallest elevation in IOP. This prevents any deformation of the cornea and minimizes subconjunctival hemorrhages and patient discomfort. The LenSx uses a curved PI that applanates the cornea and thereby can create posterior corneal folds. In my experience with the system, this can interfere with its ability to image and effectively cut the lens tissue. Although the SoftFit contact lens insert significantly reduces the occurrence of corneal folds, it does not eliminate them, particularly in eyes with steep corneas. Posterior corneal folds can lead to incomplete capsulotomies from focal areas of uncut capsule; therefore, when these folds are seen on the OCT images, the laser power should be increased from 5 microJ to 10 microJ.
The Catalys liquid patient interface (top) and the LenSx SoftFit patient interface (bottom).
In my first 10 cases with each system, all of the Catalys cases had free-floating capsulotomies, but two of the LenSx cases had capsulotomies with a small “postage stamp” micro-adhesion.
The actual docking procedure I find to be easier with the LenSx laser. Docking with the Catalys is similar to docking with the Intralase laser in that it requires the surgeon to hold and manually place the suction ring on the eye, usually without a lid speculum. This can be challenging in patients who have small palpebral fissures or difficulty fixating, and I had one patient in whom I could not insert the PI. This issue may be eliminated later this year when a smaller diameter PI will be available. Once the suction ring is on the eye, the joystick and video image on the GUI are used to dock the laser to the suction ring.
Conversely, the LenSx PI is attached to the machine and then docked to the eye using the joystick and the video image on the GUI. This one step process is easier owing to a smaller diameter suction ring and excellent exposure of the globe from a lid speculum. However, the technician must manually change the video focus as the PI descends toward the patient’s eye. Loss of suction can occur, and has happened to me with both systems. The Catalys is more prone to suction break, but the surgeon is alerted to such an occurrence because there are force sensor indicators that are monitored on the GUI. However, the head restraints and hard headrest on the Catalys’ fixed bed prevent head movement in the anterior-posterior direction (z-axis). With the LenSx system, the patient is on a gurney and even with a firm donut head rest it is not uncommon to see some posterior movement of the head, which is evident on the GUI as a downward movement of the white applanation force indicator (i.e., falling lower in the green zone or into the yellow zone).
Imaging
Imaging of the ocular structures is performed with OCT for both the Catalys and LenSx devices. The Catalys scans the entire cornea and the lens within the pupil to create a 3D image of the eye that is automatically analyzed and then displayed as an axial and a sagittal cross-section through the center of the lens. The LenSx performs a more limited OCT imaging of the eye. A circular scan is produced through the lens underlying the boundary of the capsulotomy and a cross-sectional scan is performed through the lens in the meridian of maximum lens tilt as identified by the highest point of the posterior capsule on the circular scan. These images are then displayed for manual verification by the surgeon. Therefore, the scan time is significantly faster for the LenSx than it is for the Catalys.
Analysis
An image analysis on the Catalys Precision Laser System.
Analysis is automated for the Catalys and manual for the LenSx. One of the most important safety features of the Catalys is the Integral Guidance system—sophisticated algorithms that process the OCT image, automatically and accurately detect the tissue surfaces, and then create safety zones to maintain adequate distance from the posterior capsule and iris and automatically compensate for any lens tilt or decentration from docking. The displayed images can be rapidly verified by the surgeon and customized if necessary. The Catalys also allows the surgeon to choose from a number of automatic centering methods for the capsulotomy (i.e., pupil, limbus, scanned capsule, custom, or maximized) and the arcuate incisions (i.e., pupil, limbus, or custom).
Treatment planning on the LenSx Laser.
The LenSx system produces the OCT scans more quickly, but there is no boundary identification or choice of centering method by the device. All the incisions must be manually verified and often adjusted by the surgeon (i.e., size and centration of the capsulotomy and lens patterns, location of the highest point of the posterior capsule, and centration, orientation and location of all the corneal incisions). Therefore, I find that even though the OCT scanning requires more time for the Catalys, the analysis and surgeon customization is much quicker, so the total time for scanning and analysis is similar for the two devices.
In many areas these two femtosecond lasers are designed and function in discrete ways. They each have advantages and disadvantages in the design of their software interfaces, the ways they dock to the patient and how they image and use those images to help the clinician plan treatment. In Part 2 of this article I will share my experiences with both the Catalys and LenSx lasers during clinical treatment.
Disclosure: Dr. Friedman is a consultant to OptiMedica.