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Femtosecond laser arcuate incisions being incorporated into refractive surgery practices
A surgeon explains which patients are good candidates for the procedure and shares case examples and studies.
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Surgeons can now market themselves as being able to perform bladeless cataract surgery, which has the potential benefits of being safer and more predictable than traditional cataract surgery. The iFS laser from Abbott Medical Optics is now approved for arcuate incisions. Because many refractive surgeons already have the iFS laser in their offices, they have begun to perform arcuate incisions with positive results.
Arcuate incisions
There are basically three groups of patients who are good candidates for arcuate incisions at a refractive surgery practice. The first and probably largest group of patients is cataract patients who have clinically relevant astigmatism. These are the cataract patients who in the past would have received a limbal relaxing incision (LRI) or considered a toric IOL. In other words, these patients may decline a toric IOL, or they may have just enough astigmatism that it requires treatment but may not warrant a toric IOL. Previously, these patients would have been treated with LRIs; however, LRIs are not always predictable. Now, surgeons have a device that has good precision with regard to the depth of the incision, the arc length and the diameter at which the incision is made. In other words, when making a 90° arc length incision, femtosecond lasers are obviously much more precise than the human hand. As much as surgeons would like to think that we have great hands, the laser is more precise.
The other two groups of patients who are good candidates for arcuate incisions are those with congenital astigmatism and those with high levels of astigmatism after penetrating keratoplasty. For patients with more than 3 D of congenital astigmatism, first decreasing astigmatism via femtosecond laser-created arcuate incisions can allow the possibility of performing a wavefront-guided LASIK procedure.
Christopher L. Blanton
In my practice, I have used arcuate incisions with positive results in patients who fall into all three of these groups.
Case example
A recent case was a 35-year-old woman who presented with 7 D of refractive astigmatism several months after suture removal from PK. Her refraction was +3.5 –7.00 D at 010°. We programmed two incisions of 70° arc length centered at 100° and 280°. The diameter of the cuts was 6 mm, and the cuts were located just inside the graft-host junction. Depth was set for 475 µm. Side-cut angles were 90°, and the incisions came up through Bowman’s membrane and the epithelium ending in the glass cone (penetrating). One week after receiving arcuate incisions, the patients had a refraction of +0.25 –0.75 D at 028°, a reduction of almost 90%. A similar reduction was noted on her preoperative and postoperative topographies (Figures 1 and 2). Her uncorrected visual acuity went from 20/80 to 20/30. She was, of course, extremely happy.
Figure 1. Patient’s topography before receiving arcuate incisions.
Images: Blanton CL
Figure 2. Patient’s topography after receiving arcuate incisions.
Intrastromal incisions
Additionally, surgeons are now able to make incisions with a laser that cannot be made with a blade. For example, we can make an intrastromal incision, meaning the incision begins anterior to Descemet’s membrane and is completed before it reaches Bowman’s membrane. The incision stays completely within the stroma, and it corrects astigmatism.
There are multiple advantages of intrastromal incisions. Because there is no break in the surface of the cornea, the chances of infection are basically nonexistent. The patient is also less likely to have discomfort and suffer dry eye symptoms because the surface of the eye is undisturbed. Also, with either intrastromal or penetrating incisions, the angle of the incision can be adjusted. Normally, with a blade, the incisions are made 90° or perpendicular to the surface of the cornea. With a laser, the incision can be angulated with relationship to the surface of the cornea, anywhere from 30° to 150°. Surgeons are currently in the process of determining whether there is an advantage to using an angulated cut — possibly less wound gape, possibly a better effect.
The learning curve
For surgeons who are comfortable using IntraLase to make LASIK flaps, the transition to performing arcuate incisions will be smooth. Many of the steps are the same as creating a bladed arcuate incision. We are simply substituting a significantly more precise device. For example, the surgeon still needs to mark the cornea. The most common questions I have received are regarding the nomograms. Two recently published articles that have undergone peer review and utilize the AMO IntraLase laser are available. They represent an excellent starting point for the surgeon who is new to femtosecond arcuate incisions.
The first article was a case study. Surgeons used flap mode software to create two anterior arcuate side cuts in each eye using IntraLase in a 30-year-old woman with naturally occurring high astigmatism (with-the-rule, 5.25 D) in both eyes. In the right eye, the manifest refraction improved from –3.5 +5.25 × 89 preoperatively, with an uncorrected visual acuity of counting fingers and best corrected visual acuity of 20/25, to –1.75 +2.75 × 90 postoperatively, with UCVA of 20/50 and BCVA of 20/20. In the left eye, the manifest refraction improved from –3.5 +5.25 × 83 preoperatively, with UCVA of 20/200 and BCVA of 20/20, to –1.75 +2.25 × 85 postoperatively, with UCVA of 20/30 and BCVA of 20/20.
In the second study, 37 eyes of 34 patients underwent IntraLase-enabled astigmatic keratotomy for high astigmatism (more than 5 D) after penetrating keratoplasty. After a mean follow-up of 7.2 months, UCVA improved from a mean of 1.08 ± 0.34 logMAR preoperatively to a mean of 0.80 ± 0.42 logMAR postoperatively. BCVA improved from a mean of 0.45 ± 0.27 logMAR preoperatively to 0.37 ± 0.27 logMAR postoperatively. The defocus equivalent was significantly reduced by more than 1 D. Absolute astigmatism was reduced from 7.46 ± 2.70 D preoperatively to 4.77 ± 3.29 D postoperatively. In this nomogram for PK, the incisions are placed 0.5 mm within the graft-host junction, and the primary variable is the arc length. Once again, 90% of the pachymetry is the programmed depth of the incisions.