By Lisa B. Arbisser, MD
The authors of this study report on a novel anterior capsulotomy technique with an optical coherence tomography (OCT)-guided femtosecond pattern-scanning laser (Catalys Precision Laser System, OptiMedica Corp.). They believe that this system significantly increases the precision and reproducibility of cataract surgery, compared with manual capsulorhexis. However, they tested capsulotomy strength only in porcine eyes, which have thicker and more elastic capsules than do human eyes, so the jury is still out on this issue.
An essential aspect of the femtosecond laser system used in this study that differentiates it from femtosecond lasers designed to create laser in situ keratomileusis flaps is the integrated OCT that performs 3-D mapping of the cornea and lens. The system automatically aligns all incision patterns in 3-D to follow the contour of ocular structures, which minimizes the degree of required cutting overlap and optimizes the safety zone distances.
During the experimental portion of the study, 33 porcine eyes underwent laser capsulotomy and 13 had manual capsulorhexis. Subsequently, the laser procedure was performed in 39 patients (39 eyes), with the fellow eye serving as a control for manual cataract surgery in 24 patients (24 eyes).
The authors found that the integrated OCT-guided femtosecond laser system enabled precise cutting of the anterior lens capsule and created continuous sharp-edged anterior capsulotomies of exact size, shape and position. Compared with manual capsulorhexis, the laser method improved precision in capsulotomy sizing by 12 times and accuracy in capsulotomy shaping by a factor of approximately three. They conclude that laser-created capsulotomies may be more than twice as strong, which could decrease the risk for inadvertent rupture during subsequent steps of cataract surgery.
The strength of the laser capsulotomies in the porcine eyes decreased with increasing pulse energy: 152 ± 21 mN with 3 µJ, 121 ± 16 mN with 6 µJ and 113 ± 23 mN with 10 µJ. The strength of the manual capsulorhexes in the porcine eyes was 65 ± 21 mN, significantly lower than the mean laser capsulotomy strength (P < 0.05).
In the patients, the deviation from the intended diameter of the resected capsule disk was 29 ± 26 (SD) µm with the laser technique and 337 ± 258 µm with the manual technique. The mean deviation from circularity was 6 percent and 20 percent, respectively (P < 0.05), and the difference between the mean shape (circularity ratio) of the manual capsulorhexes and the laser capsulotomies was statistically significant (P < 0.05).
The center of the laser capsulotomies was within 77 ± 47 µm of the intended position. They were all complete, with no radial nicks or tears. Slit lamp examination the day after surgery demonstrated more precise central position and proper sizing of the capsule openings created with the laser, resulting in complete and symmetric 0.7 mm overlap of the capsular bag on the edge of the 6.0-mm IOL optic.