Mathematician Edward Lorenz is famous for coining the term butterfly effect, the most common metaphorical example of chaos theory. This is the branch of mathematics that deals with complex systems whose behavior is highly sensitive to slight changes in conditions, so that small alterations can give rise to strikingly great consequences.
Case in point, the butterfly effect describes the effects of a butterfly flapping its wings on one side of the globe, setting into motion a tornado on the opposite side. The field of meteorology has developed advanced measurement tools and algorithms designed to predict future weather events in spite of the chaos that seems to control them. Even with the progress, inaccuracies occur, leading to ridicule of the meteorologist by the common man, who is unaware of the inherent challenges of the complex field.
The modern refractive cataract surgeon has some things in common with the poor weatherman. Despite sophisticated technologies including optical biometry, corneal topography, OCT, and high-powered mathematical formulas, most of us achieve refractive outcomes within ±0.50 D of intended target only 50% to 80% of the time.1
Chaos theory has not yet been mastered in our field. The butterfly wings flapping during cataract surgery may be the patient’s tear film quality at the time of testing, or the exact angle of approach we use when making the main incision, or perhaps the orientation of zonules affecting the effective lens position (ELP) of the IOL after implantation.
Regardless of the cause, we are frequently surprised by an imperfect refractive outcome—despite our most sincere efforts before, during, and after surgery. Unfortunately, patients who end up with these imperfect outcomes rarely have the capacity or perspective to understand why, and regardless of all of our efforts (and in many cases their extra money spent), their metaphorical picnics have been rained upon. In essence, there is often a gap between the expectations of our patients and the realities achieved after surgery. The larger the gap, the greater the frustration, and we have but two choices: Either lower patient expectations or change their realities by achieving better postoperative outcomes.
Thankfully a new category of IOL technologies—adjustable and exchangeable lenses—is taking aim squarely at the latter through novel strategic designs that give doctors and patients better options for fine-tuning their vision after the initial cataract surgery.
ADJUSTABLE IOLs
Light Adjustable Lens (RxLAL). The three-piece silicone »RxLAL (RxSight) is designed for in-the-bag placement. The material has a proprietary property technology that allows refractive changes to be induced by a UV light source (Light Delivery Device [LDD], RxSight). This adjustment is typically performed in the office after the refraction has stabilized. The RxLAL is the first of this new generation of adjustable IOLs to achieve FDA approval; the lens and LDD were approved in November 2017.2
Early clinical results showed that 91.8% of patients were within ±0.50 D of target refraction after LDD lock-in.1 The LDD is approved to correct up to 2.00 D of residual sphere and -0.75 to -2.00 D of residual astigmatism. The real-world results may be even better once we are able to correct lower levels of residual astigmatism (currently an off-label use).
The ability to noninvasively correct refractive error postoperatively is a distinct advantage of this technology. Being able to create customized monovision for patients is another application with a significant upside. The only downsides are the potential costs of the LDD and lens, along with ensuring that patients comply with UV light protection prior to the lock-in procedure. (Editor’s note: Phillips Kirk Labor, MD, FACS, FICS, ABES, provides further insights on the RxLAL.)
Perfect Lens. The startup company Perfect Lens is developing a femtosecond laser technology to noninvasively change the optical power of any acrylic lens. Using a concept called phase wrapping, the laser creates a change in the refractive index of an acrylic IOL in vivo. Sphere, cylinder, and even multifocality can be either induced or reversed using this process in dioptric ranges that would perhaps place all but the most extreme cases within its capabilities.3,4
Because each IOL company has a proprietary acrylic, the treatment algorithms would have to be specifically tailored for each type and power of lens. However, if the bench work to date is confirmed through human testing, this technology could become the refractive cataract surgeon’s best friend. No longer would we need to spend hours preoperatively counseling patients and finding out which IOL they would like to have implanted. Imagine a day when every patient receives a standard IOL, and the upgrade conversation happens postoperatively, when the patient is no longer contending with the cataract and is in a better position to make a decision that is right for his or her lifestyle. Plus, if the patient chooses a multifocal IOL and is unable to adapt, the multifocality could be erased without a lens exchange (bit.ly/waring0518).
Blake K. Williamson, MD, MPH, MS; and George O. Waring IV, MD, FACS, discuss the concept of refractive indexing.
Harvard Business School Professor Clayton Christensen defined disruptive innovation as a process by which a product or service takes root initially in simple applications at the bottom of a market and then relentlessly moves upmarket, eventually displacing established competitors. If the Perfect Lens technology is eventually approved, it could render all other lenses obsolete. With any intervention, however, the possibility of risk is present. It will be interesting to see clinical results with this technology to allow us to evaluate it in a better light. <strong">(Editor’s note: Dan B. Tran, MD, provides further insights on the Perfect Lens.)
EXCHANGEABLE IOLS
Gemini Refractive Capsule. The »Gemini Refractive Capsule (Omega Ophthalmics) takes an open-source approach to providing the option of exchangeability to any modern lens design while also stabilizing ELP. The product is an implant that lines the circumference of the capsular bag and provides a defined plane in the middle of the capsule to securely hold a traditional IOL in place. The company is also developing a proprietary hydrophobic acrylic optic that could be used in conjunction with the Gemini Refractive Capsule, either alone or in combination with traditional IOLs, to create new optical systems for low-vision patients or simply to fine-tune refractive outcomes.
Additionally, by keeping the capsular bag open, the Gemini Refractive Capsule has been shown to dramatically reduce posterior capsular opacification (PCO). Other nonrefractive devices, such as biometric sensors, are also being developed to fit inside the real estate that is protected by the Gemini Refractive Capsule. With a protected environment inside the capsule, adding or exchanging lenses or other technologies would become a simple proposition without the traditional risks of damage to zonules or the natural capsule. Human trials demonstrating the implantation of the Omega Gemini plus an additional IOL were first presented at the OIS ASCRS meeting in 2017. While the intent of the device has remained constant, the design has evolved since then and was shown to be safe and effective through another human trial presented in April of this year.5 An expanded human trial is currently being scheduled in El Salvador. (Editor’s note: William F. Wiley, MD, provides further insights on the Gemini.)
Harmoni Modular IOL System. The Harmoni Modular IOL System (ClarVista Medical) is a two-part hydrophobic acrylic lens system that sits inside the capsular bag. This well-designed technology uniquely solves the problem of lens exchange. On an annual basis, the most common reason for IOL exchange is implantation of an IOL with the wrong power. As we know, lens exchanges become more complicated once the anterior and posterior capsules fuse. With the Harmoni system, the optic is separate from the haptic and base, and late exchange of the optic component would theoretically be easier than a full IOL exchange, should the patient desire a change.
With a proprietary clip-in optic, the worries over complications from an optic exchange are greatly mitigated. There have also been reports of dramatic PCO reduction, which is an added bonus. Bench and animal study results have been published,6,7 and clinical trials are said to be under way. (Editor’s note: Liliana Werner, MD, PhD, provides further insights on the Harmoni in her accompanying sidebar.)
Precisight IOL. Originally designed by ophthalmologist Theodore P. Werblin, MD, PhD, the Precisight lens (InfiniteVision Optics) was conceived well ahead of its time. This two-piece hydrophobic acrylic lens system is designed to have a posterior lens with a plate-style haptic that sits in the capsular bag and an anterior lens component that is connected to the posterior component through the capsulorrhexis but that resides in the ciliary sulcus.8,9
This system also nicely solves the problem of lens exchange by eliminating the need to remove haptics that have become fixated by a fibrosed capsule. The front lens can be exchanged while the posterior lens remains in place. This lens has received the CE Mark and is commercially available in Europe. (Editor’s note: Harvey Siy Uy, MD, provides further insights on the Precisight in his accompanying sidebar.)
ON TO NIRVANA
As we have seen, there are multiple technologies in development that promise to assist in conquering the chaos theory of refractive cataract surgery. May we all someday find ourselves together in the nirvana of routinely exceeding patient expectations and being properly recognized for the hard work and effort we apply to helping our patients.
1. Sheard R. Optimizing biometry for best outcomes in cataract surgery. Eye (Lond). 2014;28(2):118-125.
2. Light Adjustable Lens (LAL)/Light Delivery Device (LDD). Summary of Safety and Effectiveness Data. US Food and Drug Administration. November 22, 2017. https://www.accessdata.fda.gov/cdrh_docs/pdf16/P160055B.pdf. Accessed April 9, 2018.
3. Sahler R, Bille J, Sean E, Chhoeung S, Chan K. Creation of a refractive lens within an existing intraocular lens using a femtosecond laser. J Cataract Refract Surg. 2016;42(8):1207-1215.
4. Werner L, Ludlow J, Nguyen J, et al. Biocompatibility of intraocular lens power adjustment using a femtosecond laser in a rabbit model. J Cataract Refract Surg. 2017;43(8):1100-1106.
5. Waltz K. First-in-man experience with a device to maintain an open capsule long-term after cataract surgery. Paper presented at: the 2018 ASCRS annual meeting; April 16, 2018; Washington DC.
6. Guan JJ, Kramer GD, MacLean K, et al. Optic replacement in a novel modular intraocular lens system. Clin Exp Ophthalmol. 2016;44(9):817-823.
7. Ludlow J, Nguyen J, Aliancy J, et al. Long-term uveal and capsular biocompatibility of a novel modular intraocular lens system [published online ahead of print January 25, 2018]. Acta Ophthalmol.
8. Fuchs HA, Frohn A, Dean K, Werblin TP. Multiple component intraocular lens: first human implantation. J Refract Surg. 2009;25(4):390-393.
9. Portaliou DM, Grentzelos MA, Pallikaris IG. Multicomponent intraocular lens implantation: two-year follow-up. J Cataract Refract Surg. 2013;39(4):578-584.
