EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/387844
Steven J. Dell, MD by Steven J. Dell, MD The impact of reducing or eliminating ultrasound energy on inflammatio Reducing the impact of cataract surgical stress by mitigating inflammation and reducing ultrasound energy The less surgical stress that is introduced into the ocular system during surgery, the lower the risk of postop inflammation S urgical stress on the eye begins before the first inc - sion is ever made. Topical anesthetics, antibiotics and other topical agents begin a cascade that releases inflammato y mediators. Postoperative corneal edema is related to some aspects of the cataract procedure itself, includ- ing ultrasound time and the volume of irrigation/aspiration (I/A), but also to non-surgical factors, such as cataract density or ocular comor- bidities. 1 But at its heart, postop inflammation is a direct result of the surgical stress the eye undergoes during surgery. 2 There are various techniques for lens removal that all attempt to produce a gentler surgery. Pre-slicing techniques have better outcomes than stop-and-chop techniques in terms of cumulative ultrasound, cumulative delivered energy. Divide-and-conquer takes more time and uses more energy than chopping techniques. 3–8 A 2008 clinical trial demonstrated ultrasound energy consumption (phacoemulsification time, powe , and EPT) was significantly higher in a stop-and-chop group vs. the nuclear pre-slice technique. Both techniques had similar results including endothelial cell loss. 9 Further, whenever ultrasound energy is used, there is the potential for wound burn. 10 However, Sorensen et al. found phacoemulsification-induced wound burns are inversely correlated to a surgeon's experience, and can be reduced by nucleus disassembly choice, ophthalmic viscosurgical de- vice (OVD) choice, and by reducing or eliminating ultrasound altogether when the anterior chamber is filled Figure 1. An example of a geometric shape created by a femtosecond laser. Multiple microscopic pulses form the desired ablation geometry. Source: Bausch + Lomb with OVD. 2 OVDs can factor into the stress introduced, as exothermic dispersive OVDs create more heat production than cohesive forms. There are 3 principal sources of corneal surgical stress introduced during cataract surgery: the incision, epithelial trauma, and endothelium loss. 2 Minimizing these will result in a gentler surgery. Pupil dilation, anesthetic drops, and commonly used povidone iodine preparations result in epithelial trauma. Endothe- lial cell loss is increased in eyes with shorter axial lengths and is higher with longer active phaco time. The choice between scleral tunnel or clear corneal incision affects endothelium loss as well. Femtosecond laser- assisted cataract surgery Femtosecond laser-assisted cataract surgery has the potential to reduce the phaco energy delivered to the eye by orders of magnitude over ultrasound, as its ability to pre-frag- ment or soften the lens may result in the reduction or elimination of ultrasound altogether. 11,12 Femtosecond lasers use a tightly focused, ultra-short pulse of light that causes photodisruption by creating high energy density in whatever tissue they are trying to penetrate. Each "plasma explosion" is a few microns in diameter, which do not cause thermal damage. Geo- metric shapes are easily created by arranging thousands of these pulses into various shapes (see Figure 1). Laser-assisted cataract surgery (LACS) utilizes a femtosecond laser to perform several functions in cataract surgery, including creation of the capsulotomy, entry wounds, astigmatic incisions, and lens frag- mentation. In the first 3 mentioned steps, surgeons are using the laser primarily to improve the precision of what we could do manually. Lens fragmentation is unique in that it pre-softens the lens, considerably altering the conditions that are