Femtosecond astigmatic incisions ideal to correct astigmatism at time of cataract surgery
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There have been several studies on the use of femtosecond astigmatic incisions for the correction of astigmatism at the time of cataract surgery.
When performing astigmatic incisions with cataract surgery, we should ensure that we have appropriately treated patients with dry eye, that patients have excellent topographical measurements, and that patients are appropriate for incisional treatment of astigmatism. The most important qualifier for corneal astigmatism treatment is a healthy ocular surface with reproducible measurements.
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Retrospective study
In a retrospective case study, my colleagues and I evaluated the outcomes of femtosecond laser-assisted arcuate keratotomy combined with cataract surgery in patients with low to moderate corneal astigmatism with a range of cylinder treatment from 0.5 D to 1.9 D. We reviewed records of 189 eyes and found postoperative refractive astigmatism was reduced significantly to 0.14 D ± 0.23 D compared with preoperative corneal astigmatism of 0.92 ± 0.34 D (P < .001).
Preoperatively, all patients had greater than 0.5 D of corneal cylinder, and 95% of patients demonstrated postoperative refractive astigmatism of 0.5 D or less. The mean surgically induced change along the steep axis was –0.59 ± 0.56 D; the change along the orthogonal axis was 0.01 ± 0.35 D. Postoperatively, roughly 90% of patients had an astigmatism angle of error of 15° or less. The postoperative mean uncorrected distance visual acuity (UDVA) and corrected distance visual acuity were 0.09 ± 0.16 logMAR and 0.02 ± 0.05 logMAR, respectively. Ninety percent of eyes had a postoperative UDVA of 20/30 or better. The results were stable at 12 months postoperatively, and no intraoperative or postoperative arcuate keratotomy-related events were observed. The results indicate that femtosecond laser-assisted arcuate keratotomy can be an effective method for astigmatism correction during cataract surgery, and results are demonstrated to be stable for at least 1 year postoperatively.
Another analysis
Our initial study outlined above excluded any patient with 0.5 D or less of corneal cylinder preoperatively. Most of these patients in our practice who had low astigmatism treatment with femtosecond laser-assisted cataract surgery received a multifocal lens. If a patient chooses a multifocal lens, we want to make sure they have the absolute best vision by treating any and all cylinders. We questioned why we had different criteria for monofocal patients who can also benefit from the best visual outcomes. So, we looked at some more data.
We examined 100 consecutive patients with 0.61 D or less of astigmatism, which we classified as “mild.” We used our usual customized nomogram to apply the astigmatic incision with our femtosecond laser (Lensar). We plugged in the cylinder magnitude along with the axis into the laser program. The femtosecond laser performs an iris registration maneuver to place the arcuate incisions exactly on the intended axis. Because the nomogram is already in the femtosecond laser, the length of the arcs, incision depth and radius are automated for the desired correction.
We started out with a mean preoperative topographical astigmatism of 0.41 D, and the mean postoperative refractive cylinder was 0.05 D. Ninety-six percent of eyes achieved 0.25 D or less of residual refractive cylinder. Eighty percent of eyes were 20/25 or better uncorrected. The mean manifest spherical equivalent for all patients was 0.00 ± 0.35 D.
Most normal healthy eyes are sensitive to diopter changes of 0.25 D, so we use steps of 0.25 D to treat patients. Correcting 0.25 D of cylinder will give us an extra half line of vision on the ETDRS chart. We prescribe spectacles and contact lenses or perform laser vision correction on these eyes. We would not ask a LASIK patient whether they want a half line of vision in their procedure because we know the answer would be “yes.” Assuming that it is frivolous to do so for cataract surgery patients is not fair to the consumer. Seventeen percent of patients with preexisting astigmatism are between 0.25 D and 0.5 D, and correction should be presented as an option. With the availability of advanced techniques, achieving correction for low astigmatism for our cataract patients is feasible. With precise and reliable iris registration-guided arcuate incisions, we can deliver outcomes of 0.25 D in our patients with low to moderate astigmatism.
Incisional corneal surgery
The fascinating thing about incisional corneal surgery is that it can be predictable. You can look at the results and go back and titrate. That is how Casebeer’s incisional refractive surgery system was born because incisions on the cornea can have reproducible outcomes for refractive and astigmatic effect. Therefore, the astigmatic incision that is done by the femtosecond laser is the ideal incision because it has the same depth the entire cord length of the incision, which is what surgeons wanted to achieve with their diamond knives in radial keratotomy (RK). However, we learned some hard lessons with RK that we need to remember. Large radial incisions close to the visual axis cause corneal instability. However, astigmatic incisions that are made in the arcuate fashion, if they are not made too close to the visual axis and are not too long in cord length, are safe and predictable. My current limit for incisional cylinder treatment is 1.5 D with the rule and 1 D against the rule, and the incisions are always paired.
Part 2 of this article will look at the nomogram used in this procedure.
- Reference:
- Visco DM, et al. J Cataract Refract Surg. 2019;doi:10.1016/j.jcrs.2019.08.002.
- For more information:
- Denise M. Visco, MD, MBA, can be reached at Eyes of York, 1880 Kenneth Road, Suite 1, York, PA 17408; email: deniseviscoeyes@gmail.com.
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