There have been remarkable advances in cataract surgery since the development of
phacoemulsification. However, significant limitations still exist because the critical steps are manual procedures: corneal incisions are created with metal or diamond knives, the capsulorrhexis is performed with cystotomes and forceps, and nucleus disassembly is accomplished with various manual cracking or chopping techniques. Cataract surgery is highly surgeon dependent, and although experienced surgeons can consistently achieve excellent outcomes, there is a need for increased precision and safety to improve results, particularly for premium IOL surgery.
Femtosecond (FS) lasers have the potential to accomplish this.
We can evaluate precision and safety by looking at outcomes. Precision can be measured by the postoperative residual refractive error. Many factors contribute to an error in predicted postoperative refraction. The most common cause of such a refractive surprise is usually an error in axial length (AL) or average keratometry (K) measurement. However, by using the best technology for preoperative measurements and IOL calculations, we can improve the predictability in refractive target to about 0.25 D for each factor. Thus, the main source of unpredictability becomes the final position of the IOL optic. This effective lens position (ELP) is derived from anterior chamber depth (ACD) values and IOL formulas, but the most important variable is the capsulorhexis.
A 0.5 mm difference in IOL position results in approximately a 1 D change in refractive error. This underscores the importance of the capsulorrhexis size and location. Ideally, the capsulorhexis should completely overlap the edge of the IOL optic to ensure the proper position of the IOL in the capsular bag. A decentered, asymmetric, or large capsulorrhexis allows the IOL to rest anterior to the predicted location causing a myopic shift. In addition, astigmatism can be induced by optic tilt. One study examining the effect of capsulorhexis size found that a larger capsulorhexis (6 mm vs. 4 mm) resulted in an average anterior shift of the IOL optic of 0.23 mm or approximately 0.5 D (Cekic, Batman. Ophthalmic Surg Lasers. 1999). The main reason we need to optimize IOL formulas is that we are unable to always make a perfect capsulorrhexis and this adds the most inconsistency to our refractive results. If we were able to guarantee the position of the IOL optic, the accuracy of our outcomes would improve tremendously.
Safety can be assessed by adverse events or complications. Improved phaco technology and smaller incision surgery has reduced the amount of surgical trauma delivered to the ocular tissues. However, we can make cataract surgery even safer by further decreasing surgical time, phaco energy, amount of irrigating fluid running through the eye, and minimizing or eliminating manual intraocular manipulations. Furthermore, clear corneal wound integrity has been a concern with respect to an increased risk of endophthalmitis. As we know, not all clear corneal cataract incisions are created equal, and any wound that is not watertight may increase the potential for this devastating complication. Having the ability to create precise and reproducible incisions with the proper architecture is critical. All of this can be achieved with FS laser technology.
FS lasers act like a laser scalpel, producing precise cutting without adjacent tissue damage. These are near infrared lasers with ultrashort pulse durations (10-15) that cause photodisruption. We are familiar with the benefits of these lasers for LASIK flap creation and corneal transplant trephination. FS lasers have revolutionized refractive surgery, and I believe they have the potential to also dramatically change the way we perform cataract surgery.
There are three companies—LensAR Inc. (Winter Park, FL), LenSx Lasers Inc. (Aliso Viejo, CA), and OptiMedica Corp. (Santa Clara, CA)—developing FS laser devices to cut the cornea and lens. After docking the patient’s eye, the anterior segment structures are imaged and registered, and then the laser is guided to create the desired incisions. The LensAR machine uses Scheimpflug imaging technology to register the cornea and lens, while the LenSx and OptiMedica devices use OCT technology to accomplish this essential step. All 3 companies have demonstrated safety and efficacy with their respective FS lasers in feasibility studies in Mexico (LensAR), Hungary (LenSx), and Dominican Republic (OptiMedica). LenSx recently received 510(k) clearance from the FDA for the capsulotomy, corneal incisions, and lens fragmentation. LensAR has received the FDA’s 510(k) clearance for conducting anterior capsulotomy during cataract surgery.
FS lasers are capable of producing corneal relaxing incisions, cataract incisions, side port incisions, capsulotomies, and lens fragmentation. Each cut is exquisitely accurate and can be customized (i.e. size, shape, depth, position, etc.) according to surgeon preference, patient anatomy, and phaco and IOL technology. Novel designs and patterns unachievable with manual devices can also be created (i.e., tongue-and-groove incisions). I had the opportunity to perform surgery with the OptiMedica device as part of the study in the Dominical Republic and was amazed at the results. The laser cut perfect incisions that facilitated surgery and guaranteed complete capsule overlap of the IOL optic edge. This is an exciting time in ophthalmology and we eagerly await commercialization of this technology, since FS lasers will clearly make cataract surgery safer, more precise and reproducible.