By Ioannis Pallikaris, MD, Ph.D.

Over the past year, ophthalmic journals, medical device brochures, and headlines at professional meetings have saturated us with expressions such as "super normal vision", "eagle vision", "20/10 in 2010", "super custom eyes", "super, super…, etc." If you are not familiar with the subject, one may get the impression that science has miraculously discovered the technology capable of giving humans the supernatural capacity to see beyond what has to date been considered physiologically normal. These reports suggest that with the evolution of customised ablation and the ability to perform Topolink or wavefront-guided keratectomies it seems theoretically feasible to supercede Mother Nature.

Misplaced Expectations?
Before we even have a solid understanding of how related aberrations impact on vision quality, there has developed a sort of hyper-enthusiasm which has, unfortunately, captured the imagination not only of ophthalmologists but has disseminated this message to the general public. We may come to find, however, that our hopes are farther from reality and may instead be providing false impressions of what medicine and science can truly offer. These personal thoughts are based, in part, on several facts and on certain philosophical beliefs as to nature's role in the evolution of various beings, within which are included humans. That which appears accepted to scientists and researchers is that each living being that has evolved over hundreds of thousands of years has adapted its function according to its needs. Humans are foveate animals that combine sharp central acuity and a system of accommodation to accomplish a multitude of tasks both near and far in their everyday lives. Much like eagles or chameleons, the human visual system has evolved teleologically to fulfill a specific need.

The efforts by many to show a need for an aberration-free optical system as an ultimate technological endpoint are misplaced. Imagine a perfectly spherical and aberration- free optical system where only the spherical component would change during the process of accommodation. Such a system would need to continuously adjust itself for fixing on objects at different distances. Simply put, in order to have a sharp image projected on to the retina for near work, this spherical aberration-free system would need to be continuously working, with high velocity reaction and feedback times. This obviously does not occur in a physiologic eye; that is, one with multiple aberrations.

It is obvious that when we use our system of accommodation to focus on an object up close, switching to an object even closer would require rapid transfer of information and an even quicker end-organ response. If this were to occur in an aberration-free system the process of accommodation would take a long time in order to project a sharp image onto the retina for the brain to interpret. But having a system with an inherent wide range of aberrations, the retina can receive almost instantaneously a "multifocal" image projection. Those areas with higher levels of sharpness and contrast will be prioritised and processed by the brain much faster than those projected onto the retina after the time needed for accommodation. This is beneficial if one changes the point of focus frequently when carrying out a given task, as most of us do on a daily basis.

On the other hand, when one wants to read or focus on something at a fixed near plane for extended periods of time (and not need to make the microadjustments described above), an aberration-free system would be helpful. In that case the brain would have at its disposal a higher number of sharp images projected through the aberration free system onto the retina. So having said that, we can see how an aberration-free system with "superoptics" may create problems in those who receive it.

During accommodation the aberrations of the eye change. These changes are related to age and density of the crystalline lens. The dynamic variable in accommodation is the lens since the cornea theoretically does not change curvature. This does not necessarily mean that changes for the worse are attributed only to the lens, given that nature has made our optical system in such a way that the lens and cornea complement each other, at least in the peripheral part of the optics. In other words, aberrations and more importantly "higher order" aberrations change continuously, both during everyday use of vision as well as in the aging process.

It becomes apparent that we will need to inform, from the outset, any new patients who desire an aberration-free correction, the likelihood of a second procedure after age 40 when their "range of aberration" will change due to presbyopia. A third surgical intervention will entail removal of a cataractous lens and placement of an intraocular lens, a component of the optical system that would then become theoretically aberration-free. Following this, we would need to correct the corneal aberrations that have been "unmasked" by the synthetic lens that had previously been accounted for by the native lens. In other words, aberrations in general, and higher order ones in particular, are in flux during the dynamic use of vision as well as the aging process.

This whole ordeal brings us to a new age where the technology for development of a super optical system is certainly available. However, any given patient that may "benefit" from such advancements is an ongoing candidate for a series of surgical procedures, something they may not find very agreeable. Further, an aberration-free super system could bring about asthenopic symptoms when objects at varying planes of focus need to constantly be brought into focus.

Do We Really Need Wave Front Analysis?
The larger question we are left with is to what degree we truly need wavefront analysis and how can such a technological advancement be practically applied to the human eye. This technology will likely give us a better understanding of the visual system and could conceivably improve one's quality of vision, but in our given instance we are dealing with improving the quality of vision in a dynamic, everyday model, not a static one. I believe, therefore, that in the future, a parameter will need to be introduced which encompasses a "Dynamic Vision Range." This factor will need to take into account, among other variables, information such as range of accommodation, RMS values at different stages of accommodation, degree of change in wavefront information at different level orders of aberration, etc. This Functional Vision Factor (F.V.F.) will appropriately be applied with respect to the needs of a specific individual. So, the future contribution of wavefront technology in conjunction with super vision correction will be an end point of "functional" vision correction. In such a scenario, each individual would receive a correction, based on the F.V.F. factor, specified to their visual needs, much as Mother Nature intended.

Dr Pallikaris is Professor and Head of Department of Ophthalmology, University Hospital, Heraklion, Crete, Greece.