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Laser intrastromal astigmatic keratotomy yields stable correction up to 6 months
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Femtosecond laser-assisted cataract surgery with or without intrastromal astigmatic keratotomy yielded small but statistically significant regressions in surgically induced astigmatism, according to a study.
One of the potential advantages of femtosecond laser-assisted cataract surgery, other than consistent capsulotomy creation, is femtosecond laser astigmatic keratotomy, which can be either penetrating or intrastromal, the study authors said.
“We found that there appeared to be minimal regression of [intrastromal astigmatic keratotomy] effect between 1 and 6 months following laser-assisted cataract surgery,” corresponding author Alexander C. Day, PhD, FRCOphth, told Ocular Surgery News. “The main advantage of ISAK is that if you are already using laser-assisted cataract surgery, it is quickly programmed and delivered for no extra cost. Compared to manual LRI, as the corneal epithelium is not opened, you would expect less postoperative pain and a lower infection risk. Additionally, you would expect laser-produced AK to be more precisely and reproducibly made than manual LRI.”
Intrastromal astigmatic keratotomy (ISAK) appears to be suitable for modest amounts of corneal cylinder, Day said.
“Femtosecond ISAK is a new, evolving technique for corneal astigmatism reduction, and so there is no direct evidence yet comparing it to other methods of astigmatism correction,” he said. “However, based on what we know, it appears useful for cases with low to moderate amounts of corneal cylinder correction where you would not use a toric IOL or choose to perform bioptics.”
Patients and procedures
The prospective study by Day and Julian Stevens from Moorfields Eye Hospital, UK, published in the Journal of Refractive Surgery, included 263 eyes that underwent femtosecond laser-assisted cataract surgery; 87 eyes underwent concurrent ISAK and a comparator group of 176 eyes did not undergo ISAK.
Mean preoperative keratometric cylinder was 0.65 D in the ISAK group and 1.23 D in the non-ISAK group.
The Catalys Precision femtosecond laser (Abbott Medical Optics) was used to perform anterior capsulotomy, lens fragmentation and ISAK. The Whitestar Signature system (Abbott Medical Optics) was used to perform phacoemulsification.
The keratotomies were 8-mm diameter paired limbal-centered symmetric arcs, with arc lengths ranging from 30° to 90°.
The Alpins method was used to perform astigmatic analyses and calculate surgically induced astigmatism.
Outcomes
Mean magnitude of surgically induced astigmatism was 0.78 D cylinder at 1 month and 0.69 D cylinder at 6 months in the ISAK group. The 0.09 D regression in cylinder was statistically significant (P = .009). Accounting for magnitude and angular direction of surgically induced astigmatism, the mean change in surgically induced astigmatism from 1 month to 6 months was 0.08 D at 94°.
Mean surgically induced astigmatism in the control group regressed from 0.43 D at 1 month to 0.32 D at 6 months. The 0.11 D regression in cylinder was statistically significant (P < .001). Accounting for magnitude and angular direction of surgically induced astigmatism, the mean change in surgically induced astigmatism from 1 month to 6 months was 0.14 D at 88°.
The difference in the amount of surgically induced astigmatism regression between the ISAK group and control group was not significant.
“The overall 1- to 6-month change in [surgically induced astigmatism] for ISAK cases was similar to that for cases without ISAK and was in the region of about 0.1 D regression,” Day said.
No complications were associated with ISAK between 1 month and 6 months. Changes in corneal endothelial cell count or corneal sensation were not recorded.
The main limitation of the study was short follow-up time of 6 months. ISAK may present long-term consequences such as reduced corneal sensation within the arcs that may induce secondary dry eye. In addition, the close proximity of femtosecond laser energy to the corneal endothelium may affect endothelial cell survival. – by Matt Hasson
- Reference:
- Day AC, et al. J Refract Surg. 2016;doi:10.3928/1081597X-20160204-01.
- For more information:
- Alexander C. Day, PhD, FRCOphth, can be reached at UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 2PD, United Kingdom; email: alex.day@ucl.ac.uk.
Disclosure: Day reports no relevant financial disclosures.
Perspective
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Noel A. Alpins, MD
This comparative and prospective study examines a total of 263 eyes treated with femto cataract surgery, 87 of whom also had two opposing intrastromal astigmatic keratotomies (ISAK) as part of their treatment for coexisting astigmatism. These incisions extended for 60% of corneal thickness from 20% to 80% depth and 30° to 90° of subtended arc. The individual groups were examined for the relative change of regression in surgically induced astigmatism between the 1-month and 6-month visits. Comparisons were made between the mean magnitudes as well as the summated vector means of the surgically induced astigmatism at each of these time frames. Corneal readings were taken with a Topcon autokeratometer.
The differences in rates of regression between the two sets of pairings was clinically insignificant, confirming the commonly held belief that corneas undergoing ISAK at the time of femto cataract surgery are equally stable to the phaco incision alone. No separate visual or astigmatic results were provided on the success or otherwise of the femto cataract surgery group who also underwent ISAK for the coexistent astigmatism at the time of cataract surgery. As a group these eyes had a larger amount of astigmatism than those that had the femto incision alone.
Take-home message: Femto ISAK treatment of astigmatism has an equivalent regression to femto phaco incisions alone.
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