Femtosecond Laser Arcuate Incisions help reduce refractive astigmatism after cataract surgery
The presence of a low to moderate level of corneal astigmatism at the time of cataract surgery is very common. It is estimated that two-thirds of eyes presenting for cataract surgery will have between 0.50D and 1.50D of corneal astigmatism. With a non-toric intraocular lens (IOL), such levels of corneal astigmatism may contribute to a level of refractive astigmatism that is likely to compromise uncorrected vision.
The primary surgical options for reducing astigmatism at the time of cataract surgery include implantation of a toric IOL or the use of corneal arcuate incisions to alter the topography of the cornea. The decision of which method to use may be affected by IOL availability, cost considerations and the magnitude of the corneal astigmatism measured. Corneal relaxing incisions have traditionally been created manually, using a hand-held blade. This increases the level of surgical skill required for cataract surgery.
Recently, femtosecond laser systems with image guidance capability have been developed for use during cataract surgery. While primarily developed to assist with lens fragmentation and creation of the capsulorhexis, they can also be used to create corneal arcuate incisions.
With such a laser system, the location, depth and extent of the incisions can be more precisely controlled, and the measurement of the anterior and posterior corneal positions can prevent inadvertent full-thickness perforation. In addition, associated image guidance systems can improve alignment of the incision; if the image guidance system registers corneal astigmatism in the upright state, compensation for cyclotorsion is possible when the laser is used in the supine position. These features are likely to improve the predictability, safety and effectiveness of any astigmatism correction. Laser arcuate incisions have been demonstrated to significantly reduce corneal astigmatism.
Blehm and Potvin carried out a study, "Clinical Outcomes After Femtosecond Laser-Assisted Arcuate Corneal Incisions versus Manual Incisions". The purpose of this study was to compare the relative effectiveness of corneal arcuate incisions made with a manual (blade) technique to those planned using an image guided system and created using a femtosecond laser system.
This study was a contralateral eye, prospective study that included subjects with 0.50 D to 1.75 D of corneal astigmatism who wanted less refractive astigmatism post cataract surgery. The surgeon used anterior keratometry and the Woodcock astigmatism nomogram for preoperative planning, while the LenSx femtosecond laser with the Verion Image Guided System was used to create all laser arcuate incisions. Manual incisions were planned using the Donnenfeld nomogram and made with a fixed-depth diamond knife. The primary outcome measure was the residual refractive astigmatism at 3 months postoperative. Secondary outcome measures included the manifest refraction, uncorrected distance visual acuity and the change in corneal astigmatism from 1 to 3 months postoperative.
- Forty-one subjects were successfully enrolled in the study, with data from 38 subjects available at 3 months.
- There were no statistically significant differences in refractive astigmatism, corneal astigmatism, uncorrected distance visual acuity or manifest refraction between the Manual and Femto groups at either 1 month or 3 months.
- Significant changes in refractive and corneal astigmatism were noted between 1 months and 3 months. Ninety percent of eyes in both groups had ≤0.50 D of refractive astigmatism at 3 months.
- Two minor non-serious adverse events (full-thickness incisions of the cornea) occurred in two eyes of two different subjects in the Manual group; they were resolved without incident.
The study compared visual outcomes between corneal arcuate incisions made manually with a blade to those made with a femtosecond laser system, with treatment assigned to contralateral eyes. As noted in the results, there was no statistically significant difference between the groups with regard to refractive astigmatism at 3 months postoperative. There was, however, a statistically significant reduction in refractive astigmatism from 1 month to 3 months in both groups. This emphasizes the need for a minimum follow-up of 3 months when evaluating corneal arcuate incisions for the correction of astigmatism.
"In conclusion, laser arcuate incisions appear to be an effective means of reducing postoperative refractive astigmatism at the time of cataract surgery. No significant clinical differences were observed between incisions made manually and those made with an image-guided femto-second laser system. The lower number of minor adverse events experienced with the femtosecond laser system is an apparent advantage."
Source: Blehm and Potvin; Clinical Ophthalmology 2021:15 2635–2641