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Which emerging technology is more promising for achieving good vision at all distances?
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Accommodating IOLs are potentially a perfect fit
They say technology reaches its pinnacle when it becomes invisible. In other words, the best technologies work for us without requiring any conscious attention. Current presbyopia-correcting lens implants require us to make a choice between some degree of monovision and the limited optics of diffractive or extended depth of focus designs. Both of these compromises can lead to frustration for at least some patients some of the time. An adjustable lens such as the RxSight Light Adjustable Lens can offer a much higher degree of surgical accuracy. In clinical trials, 92% of patients were within 0.5 D of their refractive target, and 70% saw 20/20 unaided. The Perfect Lens (Perfect Lens), which uses a femtosecond laser to adjust the refractive index of an acrylic lens inside the eye, has the potential to refine refractive outcomes within 0.1 D of target refraction, although no clinical trial results are yet available. This kind of refractive accuracy is worth a lot. But so far, these lenses do not correct presbyopia and therefore require significant patient counseling and careful selection to find the right fit for monovision.
Accommodating lenses such as the Juvene (LensGen), FluidVision (Alcon) and AkkoLens (AkkoLens) are potentially a perfect fit for every patient because they mimic what nature gives us at birth: a wide range of balanced, binocular focus for distance, intermediate and near without splitting light. Clinical trials have shown between 2 D and 5 D of accommodation, according to the companies’ press releases. That sounds a lot like a technology that is blissfully invisible.
John A. Hovanesian, MD, FACS, is OSN Cataract Surgery Section Editor. Disclosure: Hovanesian reports he is an investor in RxSight.
Mini-monovision with adjustable IOLs low risk, reversible
As a pseudophakic strategy to reduce spectacle dependence, mini-monovision using monofocal IOLs is consistently the most popular choice among ASCRS Clinical Survey respondents. Monofocal IOLs provide the best optical quality and avoid nighttime halos and starbursts. Spectacles solve any visual problems with mini-monovision, which cannot be said about unwanted nighttime images or reduced contrast sensitivity. Adjustability will significantly improve outcomes with this strategy, and the RxSight Light Adjustable Lens is now available in the United States. Refining residual cylinder and sphere postoperatively will improve our ability to achieve emmetropia in the distant eye, especially in post-LASIK eyes. We will no longer rely on predictions of effective lens position, surgically induced astigmatism or posterior corneal astigmatism; we also avoid the problems of surgical misalignment or postoperative rotation of a toric IOL.
Next, we can allow the bilaterally pseudophakic patient to preview different amounts of myopia in the near eye postoperatively and then adjust in that optimal amount. As we know from contact lens monovision, some patients tolerate and prefer more anisometropia than others. Knowing that we can experiment with and then modify or reverse different amounts of myopia in the distance and near eye should allow us to replicate the high patient satisfaction with contact lens monovision. This “low-risk” strategy will appeal to both patients and their ophthalmologists and optometrists, who otherwise collectively face the unsettling possibility of dissatisfaction with diffractive IOLs despite perfectly performed calculations and surgery. Finally, RxSight has recently released an EDOF presbyopia treatment for the LAL in Europe, which will further improve depth of focus.
An FDA-approved accommodating IOL is still many years away, and there is not even a single U.S. phase 3 trial currently underway. Among the challenges to be overcome will be hitting emmetropia, inconsistent or unpredictable accommodative amplitudes, and long-term efficacy that relies on poorly understood ciliary-capsular dynamics. It will take many years to determine how well accommodating IOLs perform long term and whether unforeseen late complications might arise from these completely novel designs.
David F. Chang, MD, is an OSN Cataract Surgery Board Member. Disclosure: Chang reports he is a consultant for RxSight and Perfect Lens.