Legerton: Questions surround 'bionic lens' announcement

The promise of perfect vision is old news to eye care practitioners after the quest for correction of higher-order aberrations with corneal refractive surgery in the 1990s, spectacle lenses in the last decade and contact lenses more recently.

Campbell and Green in 1965, followed by Curcio and colleagues in 1990, Smith and Atchison in 1997, and Roorda and Williams in 1999, demonstrated and reported the retina brain limitation to visual acuity as being as good as 20/8 or 20/6 with the elimination of all optical aberrations of the eye.

The recent press describing the Ocumetrics Bionic Lens was certainly sensational while lacking as much balance as practitioners may prefer. Within minutes of the first posting I received email from Europe and Israel asking my opinion about the news. Within hours I also heard from a concerned contact lens distributor in Asia.

My first reflection was on my 26 years in practice and the inquiries I would get from patients following a sensational news piece. I had a busy low vision and contact lens specialty practice, so the first folks to inquire were those with reduced best-corrected visual acuity. The contact lens wearers followed closely, and the next group was made up of the more compulsive folks who always wanted vision better than their habitual best correction was delivering.

Jerome A. Legerton

Patients as consumers are becoming accustomed to rapid advances in technology and come closer to believing the otherwise unbelievable. The proclivity to believe may create a higher risk for mistaking an incomplete news piece and a higher responsibility for deciding to publish one. The time consumption alone in responding to patients carries a cumulative high economic cost. This is made worse when practitioners find themselves in the position of being nay-sayers. This example is most egregious.

A headline about this technology speaks to perfect vision at every age. A closer read indicates that the technology is a surgical device and, in fact, is taught by the inventor as an intraocular lens for clear lens replacement. So, is this so phenomenal that we will perform lens extraction and IOL replacement on children as suggested? Will this “bionic” lens provide perfect accommodation for the recipients as well as correct all higher-order aberrations (HOAs)? Will there never be an infection, a surgical mishap, a loss of vision, a loss of an eye or other pain and suffering?

Will all eyes gain vision to the level of 20/8 or better as stated by the inventor? While this level of vision is accepted as possible if all aberrations are corrected, is it actually possible to correct all aberrations?

During my 8 years consulting in the corneal refractive surgery technology space I learned that the biomechanical aspects of healing were relatively equivalent to the wavefront features that we were attempting to correct with laser surgery. In other words, the submicron features that we intend to guide with the ablation are often sabotaged by flap interface aberrations and aberrations from physical changes in healing. Studies have failed to show the ability to deliver on the full promise of perfect vision with corneal refractive surgery.

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Wavefront aberrometers can measure the eye consistently and precisely for HOAs. Even so, the ability to place these corrections in spectacle lenses has not yet proven to be successful. We have also learned that the aberrations of the eye change over time, with natural accommodation and with different pupil sizes. Further, “perfect vision” requires excellent registration of the HOA correction over the optical system of the eye. A failure to register the features actually induces a new set of HOAs that may be equal to or worse than the pre-existing state. This is not easy work nor is it the low hanging fruit.

Several researchers have tried to develop wavefront-guided contact lenses over the last decade. We know we can manufacture lenses to an accuracy of a quarter of the wavelength of light. Even so, the challenges of lens flexure, lens orientation and stability, dimensional changes in soft lenses during manufacturing and changes in water content during wearing can all be at or greater than the order of magnitude of the HOA correction we are attempting to correct. Nature simply hides on the side of the flaw.

A final challenge is that of chromatic aberration. The previously mentioned researchers measured their retina brain visual acuity limit using high contrast black and white sinusoidal wave patterns or by measuring photoreceptor spacing. Our world is polychromatic, and the longitudinal chromatic aberration of the eye is quite significant and counters the effort to deliver retina and brain limit visual acuity. Longitudinal chromatic aberration damages the retinal image even in the presence of full correction of HOA.

The patents referenced are titled: “Inflatable intraocular lens/lens retainer” and “Method and apparatus for modulating prism and curvature change of refractive interfaces.” Both teach an accommodating IOL with either gas or fluid in multiple chambers and a mechanism for triggering mechanical, piezoelectric or electromagnetic controlled accommodation that involves the ciliary body. While this technology may be commercialized as an excellent accommodating IOL, one must wonder how it will correct the HOA of the optical system to provide perfect vision three times better than normal.

It is well understood that the HOAs of the optical system of the eye are not limited to the crystalline lens; rather, the anterior and posterior corneal surfaces induce HOA as well as the other media of the eye. There is no discussion for how this lens will not itself induce HOA when it accommodates and how issues of inadvertent tip, tilt and registration error-induced aberrations will be managed.

Unfortunately, this news release did not include a fair balance of counterpoints that would likely have saved our colleagues the need to answer questions from their stimulated and concerned patients. To its credit, it did state that clinical investigations on animals and blind eyes were being arranged and are not complete. Then again, how would a clinical investigation on an animal or blind eye support the claim of the inventor: “If you can just barely see the clock at 10 feet, when you get the Bionic Lens you can see the clock at 30 feet away”? -- Jerome A. Legerton, OD, MS, MBA, FAACO

References:

Atchison DA, et al. Am J Optom Physiol Opt. 1979;56:315–323.

Campbell FW, et al. J Physiol. 1965;181:576–593.

Curcio CA, et al. J Comp Neurol. 1990;292:497–523.

Roorda A, et al. Nature. 1999;397:520–522.

Smith G, et al. The Eye and Visual Optical Instrument. New York: Cambridge University Press. 1997