MiLoop: Micro-Interventional, Phaco-Free, Lens Fragmentation

16 MiLoop: Micro-Interventional, Phaco-Free, Lens Fragmentation

Tsontcho Ianchulev and Susan MacDonald

Abstract

The chapter describes a new device “miLoop” that is a micro-interventional device for cataract surgery that helps divide the nucleus with the “loop,” thereby reducing the phaco energy that is employed in cataract surgery and also has an added advantage of reducing the size of incision in a small-incision cataract surgery.

Keywords: miLoop, lens fragmentation, zero phaco lensectomy, endocapsular fragmentation

16.1 Rationale and Background

Dr. Kelman introduced phacoemulsification around 50 years ago and in the developed world it is currently the standard mode to perform cataract surgery. In the United States, more than 3.5 million cataract surgeries are performed every year, of which more than 95% are done with standard phacoemulsification. Incremental advances in phacoemulsification have led to minimally invasive, highly efficient, and safe cataract surgery with small clear corneal incisions (< 2.8 mm) that transmit reduced ultrasound energy to the eye (e.g., torsional phaco) with relatively few complications. More than 95% of eyes achieve better than 20/40 best-corrected visual acuity (BCVA) postoperatively. Nevertheless, the conventional phacoemulsification paradigm has plateaued on the innovation curve, and incremental changes have not been able to solve for the ever-increasing demands of both surgeons and patients. Patients undergo cataract surgery much earlier on the disease spectrum, often with very early cataracts (sometimes even clear lens extraction with BCVA 20/20), many well before the end of their life expectancy with 20% having cataract surgery before the age of 60 years 1 with more than 20 years of their lifespan remaining.

This is redefining the risk–benefit equation of cataract surgery, raising the safety bar to the level of refractive procedures such as laser in situ keratomileusis (LASIK). Yet, phacoemulsification continues to deliver significant amounts of heat-generating, burst energy to the eye ( Fig. 16.1, Fig. 16.2), which can permanently destroy more than 10 to 15% of the corneal endothelium—a fragile and important cellular layer of corneal tissue that does not regenerate and continues to undergo atrophic aging changes throughout life with 1 to 2% reduction per year. With more advanced cataracts, the changes are more prominent and endothelial cell loss can exceed 40%. Even with best-in-class equipment and surgical technique, patients continue to experience phaco-related complications such as capsular tear, corneal edema, iritis, and endothelial cell loss.

In the developing world, phacoemulsification has had a slow adoption. This is due to several factors, including the expense of the technology and disposables, the maintenance of the equipment and the steep, long learning curve of the surgical technique. The maturity and density of the cataracts make them technically difficult and require a substantial amount of phaco-ultrasound energy. In fact, there are many who believe small-incision cataract surgery (SICS) is a superior surgical choice for these cases, because dense cataracts are challenging even for the expert phaco surgeon and may be best served by extracapsular and manual small-incision cataract surgery (MSICS or SICS) techniques. In fact, a randomized control trial demonstrated SICS to be economical² and nearly as effective as phacoemulsification.^3,4 There is a difference of 0.3 to 0.5 diopter of astigmatism between SICS and phaco, but most significant was the substantial difference in cost. A version of SICS is being taught and popularized the world over by major international nongovernmental developmental organizations. SICS does reduce an extracapsular cataract incision size, to 7-mm external incision with a 9-mm internal width. This “small-incision” extracapsular is still a large incision (7 mm); many times, it may need to be sutured and/or may widen to safely remove the natural lens.

Fig. 16.1 Increasing levels of phaco energy used with higher grade cataracts.

Fig. 16.2 Demonstration of the current technique and principles of phacoemulsification. Conventional phaco chopping techniques are centrifugal (in–out) with significant tension on the capsular complex.

Fig. 16.3 (a,b) Miyake’s view of miLoop full-thickness endocapsular nucleus disassembly, demonstrating minimal stress of the capsular bag zonules.

Recently, the first micro-interventional device for cataract surgery, the miLoop, was developed and introduced by Dr. Ianchulev at the American Society of Cataract and Refractive Surgery (ASCRS) meeting (Los Angeles, 2017). Using first-in-class Nitinol technology, the miLoop is following the recent advent of micro-stents and minimally invasive glaucoma surgery (MIGS) technology, which are already changing the treatment paradigm for glaucoma (e.g., iStent, CyPass). This device has been used to reduce phaco energy in cataracts and recently has been used to reduce the size of SICS incision.

16.2 MiLoop Device

The miLoop is a super-elastic nitinol microthin filament around 300 μm in diameter. It can be introduced through a 1.5-mm incision and is designed for endocapsular deployment without exerting tension on the posterior capsule. In expanded position, it achieves a memory-shaped loop that encircles the lens and upon contraction creates full-thickness nuclear cuts that can be repeated for end-to-end cataract segmentation ( Fig. 16.3). When used as an adjunct to phacoemulsification (i.e., mi-phaco technique), it can facilitate the lens breakup and removal and minimize the need for phaco energy. This microthin nitinol filament allows the surgeon to do lens fragmentation with a new micro-interventional technique without using the phaco probe and without using a second instrument.

Conventional chopping or prechopping techniques that use centrifugal (in–out) forces are of variable effectiveness depending on the hardness of the lens nucleus.

It is a two-instrument technique that uses phaco energy to cleave the nucleus and is variable in achieving full-thickness reliable fragmentation because it relies on the propagation of a fragmentation cleavage plane ( Fig. 16.4) through the lenticular complex from a surface chop, which is highly dependent on the density and compliance of the nucleus. It is also invariably centrifugal in nature with out–in cleavage forces that can destabilize and exert tension on the capsular complex.

MiLoop’s endocapsular full-thickness lens fragmentation has several advantages. It allows nuclear disassembly of cataracts independent of cataract grade, utilizing out–in, centripetal cutting rather than centrifugal forces ( Fig. 16.5). The technique reduces stress on the zonules and reduces the risk of zonular dehiscence and capsular bag instability. It is a technique that is simple to learn and limits the stress on the capsular bag. It has been found to be a useful nuclear disassembly technique.

16.3 New Surgical Technique for Nucleus Disassembly

MiLoop fragmentation is unique and unconventional in its mechanistic approach to the nucleus. For the first time, it allows the ability to achieve zero-energy, centripetal (out–in) nucleus disassembly that is materially different from all conventional techniques of in–out, centrifugal chopping and fragmentation ( Fig. 16.5). It completes full-thickness microsegmentation and disassembly regardless of cataract grade through a single 1.5-mm incision. It also allows fragmentation to occur under viscoelastic control without phaco probe in the eye and any irrigation and aspiration, further protecting the endothelium from phacoemulsification-related exposure during the disassembly step of surgery.