In early September, the OptiMedica Catalys Precision Laser System was approved to perform corneal incisions by the Food and Drug Administration, meaning U.S. surgeons can now get reimbursed for using it, since astigmatic keratotomy is currently the only aspect of femtosecond cataract surgery surgeons can charge separately for. In this article, surgeons well-versed in the use of the Catalys give you an idea of what to expect if you decide to start using it.
The Docking Step
Surgeons who perform femtosecond surgery, either for cornea or cataract applications, say that the initial docking of the device with the eye is critical. Here are surgeons’ impressions of the Catalys’ approach to this key step.
“The laser’s Liquid Patient Interface functions as a little immersion system,” explains William Culbertson, MD, head of OptiMedica’s medical advisory board. (Dr. Culbertson has a financial interest in the device.) “The part that couples to the eye is a little reservoir into which we pour balanced salt solution. We then bring down the focusing cone that’s connected to the laser and couple it with the patient interface/water bath. In this way, the laser doesn’t distort the cornea by pressing it up against a cone or plate. This lets the laser focus its treatment more accurately. What’s more, the patient interface operates under low vacuum, only raising the patient’s intraocular pressure by 8 mmHg. It also allows us to treat out to 11 mm diameter, such as when creating relaxing incisions.”
The laser also has a force-sensing function that will try to compensate for any forces exerted against the patient interface, such as patient movement from breathing.
Placing the Treatment
To place the femtosecond treatment, the laser uses a high-definition 3D optical coherence tomographer and a feature called the Integral Guidance System.
“The 3D optical coherence tomographer gives a precise image of such features as the anterior and posterior corneal surfaces, the iris plane and the pupil,” says Robert Rivera, MD, a Catalys user from Salt Lake City. “You get an axial and sagittal view of the structures so, in the case of lens tilt, the laser automatically adjusts for the tilt and tilts the anterior capsulotomy treatment. It also automatically creates a 500-µm safe zone to keep the treatment away from the posterior capsule.” Once the laser finds the center of the pupil, the center of the limbus and the recess of the capsular bag, the surgeon can use the system’s Integral Guidance and touch screen to make fine adjustments to where the treatment will be laid down.
Surgeons say the liquid interface aids in the capsulotomy creation. “When we had a fixed-curved applanation plate, we were getting too many incomplete capsulotomies, with the attendant risks of radial tears, and which were difficult to advance due to the problem of folds and distortion created by coupling a fixed cone to the cornea,” explains Dr. Culbertson. “You’d get these uncut places on the anterior capsule that corresponded exactly to the location of the corneal fold on applanation. This is why we switched to the immersion interface.”
For nuclear softening, the laser allows the surgeon to choose a pattern, such as two intersecting lines creating four quadrants or three lines creating six segments. Then, within those segments, the laser will create smaller segments. “In the treatment that I use, it creates a series of square columns throughout the lens similar in shape to French fries,” says Dr. Rivera. “I then use a Chang chopper to feed the segments into the I/A port. I’d estimate that, on average, I use two-thirds less phaco energy in removing the nucleus than I did before.”
In addition to allowing surgeons to charge extra for the use of the Catalys in conjunction with cataract surgery, the FDA approval of the creation of corneal incisions also means that users can create more consistent incisions, say surgeons.
“With a standard manual astigmatic keratotomy incision, there’s some inconsistency as the blade ‘porpoises’ up and down in the cornea as you drag it across, so you’re not exactly sure how deep you’re cutting, how long it is or what bevel you’ve made it at,” says Dr. Culbertson. “But these variables are precisely made with the laser. I presented a paper at the 2012 meeting of the European Society of Cataract and Refractive Surgeons that found when we made Catalys incisions in plastic, animal models and in clinical cases, the accuracy of the incision length was within 1 degree of the intended arc, the optical zone was within 0.1 mm of intended and the depth was within 20 µm.” Dr. Culbertson adds that after the AK incisions are made, there’s very little effect from them until you open them with a blunt instrument. “So you can use an intraoperative aberrometer or topographer to monitor the incisions as you slowly open them on the table until you get the exact effect you want,” he says. The laser is also capable of creating intrastromal incisions. Though intrastromal AK can only treat up to about 1.5 D of cylinder, says Dr. Culbertson, they cause less pain than full-thickness wounds and there’s no risk of infection.
Experienced users say you’ll have to adjust your current AK nomogram to compensate for the laser’s increased power. “You get more effect from a laser incision due to the uniformity of the depth created by the laser,” Dr. Culbertson explains. “We adjust our AK nomograms down by 30 percent. So, if we have 1 D of astigmatism to correct, we subtract 30 percent, or 0.3 D, and treat for 0.7 D.”
Dr. Culbertson says a reliable AK nomogram will come in time. “We haven’t done enough incisions to develop a nomogram for it yet,” he says. “We’re working off of our existing nomograms right now. Factors such as age and the orientation of the astigmatism will have to be derived empirically by simply doing a lot of cases.” REVIEW
Dr. Rivera has no financial interest in the Catalys.