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Femtosecond arcuate incisions improve best corrected vision after keratoplasty
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Full-thickness penetrating keratoplasty results in iatrogenically introduced corneal astigmatism and degradation of the final quality of postoperative visual acuity in our patients. Corrective steps often entail rigid gas-permeable contact lenses, requiring an expanded skill set in order to fit the contact lenses on an irregular corneal surface and provide patient comfort. Surgeons have treated this postoperative astigmatism with manual incisional astigmatic keratotomy procedures using either diamond or steel blades with variable postoperative results.
The introduction and approval of laser technology for incisional corneal surgery marks a new era in the surgical correction of corneal astigmatism. Additionally, laser technology allows the surgeon to adjust the procedure to some degree by avoiding full opening of both arcuate incisions at the time of the procedure. This allows some room for surgeon adjustment of the postoperative result, which was not possible with the manual techniques of astigmatism correction. The goal is patient satisfaction, and any residual astigmatism after surgical correction that the patient does not complain about may be left as residual cylinder. However, if the patient continues to be symptomatic after laser-assisted astigmatic keratotomy, then additional options include PRK or repeat keratoplasty, as the individual case may require. Thus, we can now offer a stepladder, patient-tailored surgical approach for the management of postoperative keratoplasty astigmatism.
In this column, Reilly describes his technique of femtosecond arcuate incisions for treating post-keratoplasty astigmatism.
Thomas John, MD
OSN Surgical Maneuvers Editor
Following corneal transplant, some patients are left with very high astigmatism that is difficult to correct with spectacles or contact lenses. We would like for any further surgical correction in these challenging eyes to be as predictable, precise and safe as possible.
The recent approval of the iFS femtosecond laser (Abbott Medical Optics) for arcuate incisions offers the potential to increase surgeon and patient confidence and improve outcomes in post-keratoplasty astigmatic corrections.
Case history
A 77-year-old pseudophakic woman with a history of open-angle glaucoma and Fuchs’ dystrophy was referred for possible refractive surgery in March 2012. The patient had had several corneal transplants in each eye, with the most recent one 3 years prior. Although the grafts were successful, she had 11 D of topographic cylinder in the left eye, with a manifest refraction of +7.75 –8.00 × 180 and best corrected visual acuity of only 20/60 (Figure 1). Her vision had been better in the past with a rigid gas-permeable lens in that eye, but at the time of our consultation she was no longer able to tolerate the contact lens.
Figure 1. Preoperative topography. Following a corneal transplant, this patient had 11 D of topographic cylinder in the left eye and reduced BCVA.
Images: Reilly CD
Options for this patient included a repeat keratoplasty to improve the refractive result, PRK and incisional correction of the astigmatism with either a diamond blade or the iFS laser. After extensive discussion, we opted for femtosecond arcuate incisions.
Surgical procedure
Preoperative planning is very similar to that for bladed astigmatic keratotomy. Intraoperatively, the procedure is very similar to keratoplasty or cutting a LASIK flap with the IntraLase femtosecond laser (AMO).
Using the iFS laser’s IntraLase-enabled keratoplasty software, I programmed it to perform paired arcuate incisions in the steep axis of astigmatism at a posterior depth of 450 µm (about 75% depth of her cornea), an arc length of 80° and a diameter of 6 mm, which kept the incisions well inside the patient’s 8-mm graft. I elected to make vertical 90° side cuts.
Prior to docking the laser, I marked the optical center of the eye and the axes of the planned incisions, 93° and 273° in this case. The marks are easily visible under the cone of the laser, ensuring accurate positioning. The femtosecond procedure itself takes only a few seconds — less time than for a LASIK flap.
I performed this procedure in our laser suite. After creating the incisions at the femtosecond laser, I swiveled the patient under the excimer laser and used its microscope to inspect the quality and depth of the cuts and to open up the incisions with a Sinskey hook. With this patient, I opened the inferior incision fully and the superior incision only about 80%.
I placed a bandage contact lens and gave the patient topical antibiotic and steroid drops. She experienced no pain or discomfort during or after the procedure. Other than a mild subconjunctival hemorrhage that resolved within 3 weeks, recovery was uneventful.
One week postoperatively, her manifest refraction was +2.50 –5.75 × 177, with BCVA of 20/70. At this visit, I opened the superior incision the rest of the way, another 20°, at the slit lamp to achieve greater effect.
Her final refraction at 7 weeks postop was +1.75 –3.25 × 180, with BCVA of 20/40. In all, we were able to reduce her manifest cylinder from 8 D to 3.25 D and topographical cylinder from 11 D to 5 D. The incisions look perfectly constructed and pristine at the slit lamp (Figure 2). The pattern of astigmatism is a little more irregular (Figure 3), which we might expect, but her best corrected vision has improved and the patient is much happier with her vision.
Figure 2. At the slit lamp, the femtosecond laser arcuate incisions look pristine and precise.
Figure 3. Postoperative topography shows somewhat more irregular astigmatism but a significant reduction in manifest astigmatism from 8 D preop to 3.25 D at 7 weeks postop.
Importantly, we were able to improve the patient’s vision without the risks and longer recovery time of a repeat transplant or even surface ablation. Both options are preserved for the future, should additional correction be necessary.
Advantages
Compared to bladed arcuate incisions, the femtosecond laser offers several advantages. First is the customizability of the procedure to each case. Depending on the eye and the degree of astigmatism to be corrected, we can vary the optical zone, location, length and depth of the cuts, and the incision’s bevel of angle (from a 60° to 130° side cut). The ability to alter the optical zone during surgical planning is very nice, allowing one to work around the graft, whatever size it may be. Because the laser is computer programmed, one can preview the cuts before making them, which enhances confidence.
I also particularly like the flexibility that the laser affords in adjusting the effect. One can make large incisions, then simply not open them fully until the initial effect is determined, as I did in the case described here.
Just as femtosecond lasers have allowed for greater precision and predictability in creating lamellar flaps, I think we will find the same results with arcuate incisions, particularly as nomograms become better developed. The ability to accurately achieve the desired posterior depth of the incision, for example, is a huge advantage. This should lead to more consistent results.
As a surgeon, it definitely gives me greater confidence in my ability to place the incisions exactly where I want them. We also cannot discount the confidence that a laser gives to post-keratoplasty patients who have already undergone one or more ocular surgeries with poor visual results.
Pearls
Preoperatively, one must be careful to manage the expectations of the patient and referring providers. It can be challenging to predict the true visual potential of older post-keratoplasty eyes. One should also be sure to treat any ocular surface problems prior to surgery, both to facilitate healing of the arcuate incisions and to maximize the quality of vision.
Excellent pachymetry is required for this procedure. I prefer to use Pentacam (Oculus) data for planning because it provides me with pachymetry for points all across the cornea. I also confirm the tissue depth at the incision site with an ultrasound pachymeter just prior to making the incisions.
I strongly recommend previewing the arcuate incisions on the planning screen before the patient is even in the room. This allows the surgeon to confirm where the arcs will be placed and make adjustments, if desired, before the patient is present. Finally, using markings, take care to align the patient properly underneath the laser.
Femtosecond laser arcuate incisions offer a simple, effective step on the post-keratoplasty patient’s road to visual rehabilitation. There is still much to explore in the continuing evolution of the capabilities of this laser platform, including the effect of different side-cut angles and the potential to make nonpenetrating stromal incisions and optimal nomograms. However, I am enthusiastic about the potential of the femtosecond laser to enhance the accuracy of astigmatic correction in post-keratoplasty and other patients.