Femtosecond laser-assisted astigmatic incisions vs. blade incisions
Surgeons weigh which technique is better for treating astigmatism during cataract surgery.
CEDARS Debates is a monthly feature in Ocular Surgery News. CEDARS — Cornea, External Disease, and Refractive Surgery Society — is a group of cornea, cataract and refractive surgery specialists, here to discuss some of the latest hot topics in ophthalmology.
This month, William F. Wiley, MD, and George O. Waring IV, MD, FACS, discuss the pros and cons of femtosecond laser-assisted astigmatic incisions vs. blade incisions for the treatment of astigmatism during cataract surgery. Astigmatic correction with blades has been utilized for years with varying degrees of success. With improved nomograms and now with intraoperative aberrometry, the opportunity for success continues to grow. Of course, with the availability of the femtosecond laser, unprecedented precision with these incisions may be possible. Which method is superior? We hope you enjoy this discussion.
Kenneth A. Beckman, MD, FACS
OSN CEDARS Debates Editor
Femtosecond laser astigmatic keratotomy leads to more accurate, reproducible outcomes
Astigmatic keratotomy has been a mainstay of low to moderate surgical astigmatism management during cataract surgery for years. Although effective, results with manual incisions can be unpredictable, even with advanced nomograms. The use of intraoperative aberrometry has improved predictability of manual incisions; however, results are subject to multiple intraoperative factors. The use of femtosecond lasers for limbal relaxing incisions (LRIs) has been described previously, with femtosecond lasers designed for corneal lamellar flap surgery. With the advent of femtosecond lasers for refractive laser-assisted cataract surgery, more surgeons have been able to take advantage of this technology and refine their nomograms and algorithms.
My experience with the Catalys (Abbott Medical Optics) has been excellent. One reason for this is the improvement in my refractive outcomes during management of low to moderate amounts of astigmatism with femtosecond laser-assisted LRIs. I practice with the motto of “under promise and over deliver,” and manual LRIs are a great example in which I routinely counsel patients that I can debulk or reduce their astigmatism, which was often the case on both postoperative manifest refraction and topography. Since adopting laser cataract surgery and employing femtosecond laser-assisted astigmatic keratotomy, however, complete treatment is the rule, and I encounter postoperative residual astigmatism much less often. More so, where I would commonly observe some residual topographic astigmatism with manual incisions, which may have been partially related to posterior corneal astigmatism, I am observing postoperative topographic resolution much more often with femtosecond-enabled incisions. I am able to offer patients with astigmatism who desire multifocal IOLs this option more often because we can more reliably treat their astigmatism. I use a simple nomogram with a 9-mm optical zone and 80% incision depth that penetrates Bowman’s layer. For post-LASIK eyes, I program a 10.5-mm optical zone to stay outside the lamellar flap and account for this in a chord length adjustment. I typically operate on axis and couple the incision. I am more aggressive with against-the-rule treatments to account for posterior corneal astigmatism and open these during surgery. I leave with-the-rule treatments closed and titrate the opening 1 month postoperatively at the slit lamp to effect, which is uncommonly needed. The precise and reproducible outcomes are likely related to the incision architecture, and this makes sense when examined under high magnification (Figure).
Image: Waring GO
Future advancements in incision architecture and their effect on minimizing higher-order aberration induction will be much easier with laser-assisted incisions due to the ability to customize the incisions. The major limitation at this time is the inability to utilize intraoperative aberrometry at the time of laser-assisted incision creation. This not only limits the magnitude of correction, but also registration with cyclotorsion. With outcomes as good as they are, the prospect of intraoperative astigmatism guidance during femtosecond laser incision creation with aberrometry or optical coherence tomography feedback is particularly exciting and may represent the future of corneal astigmatism correction.
Blade can offer unique advantages
Undoubtedly, the femtosecond laser has allowed for a dramatic increase in precision of depth, length and size of arcuate incisions. The concern I have noticed with the current use of the femtosecond arcuate incision is that the surgeon is placing the incision based on preoperative information with questionable accuracy. I argue that one does not know the true astigmatism to be treated until it can be measured with intraoperative aberrometry. Further compounding the inaccuracy of the femtosecond laser is the fact that it cannot take into account the variables of tissue response, which can be affected by corneal rigidity and/or elasticity. Intraoperative aberrometry-guided blade incisions can take into account the surgically induced incision and posterior corneal astigmatism and can measure the tissue response directly with real-time readings.
Doug Koch’s work has shown that posterior corneal astigmatism is prominent, which I have witnessed through the use of intraoperative aberrometry. The issue I have experienced with posterior corneal astigmatism is that it is both prominent and variable. Furthermore, surgically induced astigmatism is quite variable because of variable tissue response from patient to patient, which can be compounded by the placement of the incision on the cornea. By waiting to do a blade-created limbal relaxing incision at the end of the case, one can treat the true corneal astigmatism that is present. Furthermore, by using VerifEye (WaveTec Vision), which displays real-time aberrometry, one can observe the immediate effect that the incision has and then titrate this effect by lengthening or creating new arcuate incisions. With this method, precision in depth becomes less important because one can track the effect of the incision immediately.
In theory, a femtosecond laser incision can be created and not opened, and thus the effect can be titrated through intraoperative aberrometry. However, the process of making the incision with the femtosecond laser creates a layer of bubbles that may introduce a temporary variable that may make the intraoperative aberrometry readings unreliable. One could wait to open the incisions postoperatively, but that requires additional manipulation not too different from using a blade at a later time to treat astigmatism.
In the future, I foresee we will have the ability to take advantage of both techniques. I predict we will use intraoperative aberrometry to diagnose the true astigmatism, providing accuracy, and then treat this astigmatism with a more portable OR-friendly version of the femtosecond laser, allowing for precision. In combination, this should allow for a clinical improvement over our current techniques. Until that time, I believe the advantages of real-time measurement of the amount of astigmatism and the response observation to treatment by blade can offer unique advantages when compared with a femtosecond laser treatment based on questionable preoperative diagnostic measurements.