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Surgeon: Give up the surgical limbus and use clear cornea instead
Arcuate and clear corneal incisions can help eliminate postoperative corneal astigmatism.
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Femtosecond laser entry into the cataract surgery arena had a positive influence on the key steps of cataract surgery, namely anterior capsulotomy, softening of the lens nucleus, lens fragmentation and self-sealing corneal incisions. A full-thickness corneal incision is a must for cataract surgery in order to gain access to the cataractous lens nucleus and surrounding cortex and to implant an IOL within the capsular bag. In doing so, there can be induced iatrogenic corneal astigmatism. Ophthalmic surgeons have long focused on decreasing the size and location of corneal incisions to obtain the best access to the lens while trying to achieve an astigmatically neutral corneal incision or targeting the least amount of induced iatrogenic corneal astigmatism.
Femtosecond laser-assisted cataract surgery permits making, in a reproducible manner, corneal incisions that are more precise, which is clearly considered superior to any of the manual corneal incisions. Additionally, surgeons also have the option of making these anterior chamber entry incisions in the plus axis to decrease pre-existing corneal astigmatism, which can be combined with additional corneal incisions as needed, all in an effort to decrease corneal astigmatism to zero or near zero without flipping the axis of astigmatism. This is in line with what our present-day cataract surgery patients would like, namely the best quality of vision, as we now intentionally drift from routine cataract surgery to femtosecond laser-assisted refractive cataract surgery.
In this column, Dr. Siepser explains why ophthalmic surgeons, when using a femtosecond laser for cataract surgery, should move away from the region of comfort, namely the surgical limbus, and embrace the region of the clear cornea to obtain maximum benefit of the laser effect in making cataract incisions and refractive corneal incisions.
Thomas John, MD OSN Surgical Maneuvers Editor
In my early experience with femtosecond lasers, I continually wanted to move the incision out to the limbus, a spot I am more comfortable with when entering the eye. After all, during my residency, finding that there actually was a “blue line” and ending up anterior to the iris was a major challenge, something that was hard fought and hard to give up. Years of limbus-based, fornix-based conjunctival incisions, scleral tunnels, radial transverse incisions and finally what appeared to be “clear cornea” get a surgeon in a groove, no pun intended.
Images: Siepser S
Striving for years to reduce the incision size and make it astigmatically neutral weighs heavily on any accomplished surgeon. Leaving this area of comfort is certainly not easy, but it is the best way to use the newer femtosecond technology.
Femtosecond lasers are optical breakdown lasers. They must operate through transparent structures in order to work at all. Thinking otherwise is assuming that a flashlight can penetrate an opaque shade. It cannot, and anything that colors, limits or blurs a laser, reduces the transmission of light energy and decreases the intensity of the optical breakdown. Think about how hard it is to YAG an opaque membrane. The femtosecond lasers are actually high-speed YAG-like focusing destructive cavitation lasers that must work in clear media. Would you ever consider doing a capsulotomy through a cloudy cornea? It will not work, and trying to work through any corneal opacity with an optical breakdown laser will not either. There may be other types of lasers that can cut through opaque tissue such as the surgical limbus, but they are not optical breakdown lasers — they are cutting unfocused collimating beams. It might help you get the basic idea of what we are dealing with when we operate with the present generation of femtosecond lasers.
Femtosecond lasers work best in clear cornea, which is something we will have to live with and possibly even use to our advantage. It struck me that this is an opportunity for a refractive cataract surgeon and a definite change in perspective, which will improve surgical results. It is truly a paradigm shift. We are now going to operate like RK surgeons and make arcuate cataract incisions serve as refractive opportunities.
In order to get consistent and well-structured incisions, they should begin in clear cornea. This runs a bit against the grain of any senior surgeon who, not too many years ago, used to start incisions in the sclera. Aimed at reducing astigmatism, an astigmatically neutral incision was the way to go. Now my thoughts have changed. How can I use an incision to adjust and control astigmatism, and how do I use an arcuate incision to neutralize the surgically induced astigmatism?
The answer is simple: Use the corneal incision as part of the arcuate armamentarium. Because I am ambidextrous and have always operated from the head of the patient, it has been my tried and true astigmatism reduction method to place my limbal incision in the plus axis. I can easily move my incision 90° with little change in technique and pair this with an opposite arcuate incision to increase the effect. This measured carefully with the ORA (Alcon) allows me to titrate the astigmatic effect right on the table.
The active use of a clear corneal incision has been effective in treating astigmatism in my refractive cataract patients; however, there is also an unintended consequence. When there is little corneal astigmatism, a clear corneal incision can induce up to 1 D of unwanted positive astigmatism, 90° from the incision site. I adjust this by placing two opposing arcuate incisions of 25° at the 4.5 radius position to reduce the surgically induced astigmatism of the incision. The placement of an arcuate incision in the perpendicular meridian increases the effect even greater than two arcuate incisions. Relying on the intraoperative ORA readings helps titrate the opening of these femtosecond laser-created arcuate tracts.
In some ways, femtosecond laser marketers have wanted us to believe that we can approach the surgical limbus. This leads to surgeons going back to blades, settling for a laser capsulotomy and fracturing of the cataract. Nice, but not worth $500,000. Everyone should understand that any clouding of the cornea, arcus or vessels, Fuchs’ dystrophy and edematous changes in the cornea make it impossible to create a “corneal” incision. These machines should be clearly labeled, like our air bags: Do not operate when there is any hint of loss of corneal clarity! Do not attempt to operate through blood vessels or any blurred area! You are headed for trouble!
With good planning, we can conciliate a sometimes troublesome incision with refractive techniques to improve our overall visual results. By moving this incision into the positive axis at the 4- to 5-mm radius, beautiful arcuate and clear corneal incisions can be achieved almost 100% of the time. It only takes a few cases to get comfortable with the “oar lock” and different technique needed to capture the nucleus and cortex through these anterior incisions. Properly placed, they can eliminate postoperative corneal astigmatism. Shifting this paradigm from trying to march toward the limbus to what any RK surgeon already knows, arcuate full-thickness incisions are powerful refractive tools that now are part and parcel of femtosecond clear corneal incisions. Effectively managing their effect is the way to get to those LASIK-like results we are all striving to achieve.
- References:
- Abell RG, et al. J Cataract Refract Surg. 2015;doi:10.1016/j.jcrs.2014.06.025.
- Abouzeid H, et al. Acta Ophthalmol. 2014;doi:10.1111/aos.12416.
- Blum M, et al. J Cataract Refract Surg. 2014;doi:10.1016/j.jcrs.2014.01.034.
- Mastropasqua L, et al. J Refract Surg. 2014;doi:10.3928/1081597X-20131217-03.
- Serrao S, et al. J Refract Surg. 2013;doi:10.3928/1081597X-20130430-01.
- For more information:
- Steven B. Siepser, MD, FACS, can be reached at Siepser Laser Eyecare, 860 E. Swedesford Road, Wayne, PA 19087; email: ssiepser@clear-sight.com.
- Edited by Thomas “TJ” John, MD, a clinical associate professor at Loyola University at Chicago and in private practice in Oak Brook, Tinley Park and Oak Lawn, Ill. He can be reached at tjcornea@gmail.com.
Disclosures: Siepser reports he receives minimal royalties for the instrumentation made by Escalon Trek and Moria. John reports no relevant financial disclosures.