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EW Interview by Joseph
Hoffman, ELS Executive Editor |
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EyeWorld: Does your 1999 paper in Ophthalmology, “The Mechanism of Accommodation in Primates”1 still represent your thinking on the subject of accommodation? Adrian Glasser, PhD: Absolutely. That paper describes the mechanism of accommodation in the rhesus monkey eye. The results show strong support for the classically described Helmholtz accommodative mechanism. Dr. Ronald Schachar [adjunct professor, University of Texas, Arlington] had come to Dr. Paul Kaufman, [professor, Department of Ophthalmology and Visual Sciences, University of Wisconsin – Madison and the Wisconsin Regional Primate Center] and me and suggested a number of experiments to verify his theory of the accommodative mechanism. He described the kinds of experiments we should do, and we did them to the best of our abilities. In fact, he was there for many of the experiments. The results refuted many of Schachar’s ideas about the accommodative mechanism. In those experiments, we found no evidence to support his theory of accommodation. EW: I also saw in Ophthalmology some letters2, 3 you wrote about how the supposed restoration of accommodation after scleral expansion band implantation was being documented. Glasser: Dr. Steven Matthews, [Department of Ophthalmology and Visual Sciences, Texas Tech. University Health Science Center, Lubbock, Texas] had undertaken an investigation of three patients who had undergone scleral expansion surgery.4 Schachar provided those three patients and, presumably, he had selected individuals in whom he believed accommodation truly was restored. Mathews used appropriate, objective instrumentation to attempt to measure accommodation in those three individuals and found no evidence that accommodation was restored. He found no evidence of a dynamic change in power of the eye, which is what accommodation is. Indeed, the methods employed are the best to objectively demonstrate whether accommodation is present. EW: What’s different about the findings of Schachar and others who are saying that these surgical techniques restore accommodation? Glasser: Although they claim that these procedures restore accommodation, they’re not attempting to truly measure accommodation. Accommodation is not simply the ability to see clearly at near. By definition, accommodation is a change in the optical power of the eye. For example, a presbyope with a bifocal spectacle lens or a multifocal contact lens on the eye can see both at distance and at near, but this is by no means accommodation. Accommodation is a dynamic process. Most individuals that I’m aware of who are performing scleral expansion procedures, either through scleral expansion bands, radial sclerotomy, or variations, aren’t actually doing objective measurements of accommodation. They do a push-up test, which does not measure accommodation. It may measure a functional near and distance vision, but not accommodation. Those of us who are interested in seeing these objective measurements are left to speculate about what may be happening with these procedures. Mathews had suggested in his article that some of the improved reading ability demonstrated with subjective push-up testing might be a result of inadequate testing procedures. It may be due to some kind of induced multifocality of the eye, either in the cornea or in the crystalline lens, as a consequence of these surgical procedures. Patients may be left with some kind of aberration, either astigmatism or higher-order aberrations of the eye, which allows them to have functional near and distance vision simultaneously. That may account for how these patients are apparently seeing at near after these surgical procedures. But let me further state that if these surgical procedures are introducing aberrations to the eye, there are excellent objective instruments available to measure these aberrations. The so-called wavefront sensors should be employed to try to identify whether these presbyopia reversal surgeries are introducing near vision by producing aberrations in the eye. EW: What about findings that when the procedure is done on one eye, there is an effect on the contralateral eye? Glasser: Well, they’re absolutely extraordinary. The immediate explanation that jumps to mind is that it’s a clear demonstration of inadequate or inappropriate testing. It’s relatively easy to explain how so-called accommodation — near vision, really — could be improved in the contralateral eye. The patients may be learning the near reading chart or the tests being done are inappropriate. It’s very difficult or impossible to find a physiological explanation for how a surgical procedure done on one eye should restore accommodation in the contralateral eye. EW: There are a number of intraocular lenses being designed that are attempting to take advantage of latent ciliary muscle action to induce movement of the lens and restore a type of accommodation. Are you familiar with any of those designs? Glasser: I’m a little familiar with some of them, just by virtue of what I hear at meetings and read in the press. EW: Does your understanding of the mechanism of accommodation fit in with some of the designs? Is there at least a theoretical basis for those lenses to work? Glasser: I believe that the research I’m involved in very directly addresses many of the questions about mechanisms of accommodation and the possible restoration of accommodation in presbyopia. First of all, I believe that it’s a fundamental necessity that we understand how accommodation occurs, that we understand precisely how the crystalline lens undergoes optical changes in the eye to allow accommodation to occur, and that we understand the aging of the eye. In other words, that we understand what is going wrong with the eye that leads to presbyopia. Much of my research is aimed at answering some of these fundamental physiological questions that remain. While it certainly may be possible to develop accommodative intraocular lenses, and it may be possible that some of the current designs actually work, ultimately, we could design far superior lenses that should work much better once we fully understand the physiology and the physiological optics of accommodation and presbyopia. So, my research on rhesus monkeys and on humans, including both in vivo and in vitro experiments in monkey and human eyes, is designed to try and understand some of the fundamentals. I am surprised at the general lack of understanding of the physiology of the accommodative apparatus. However, there is a tremendous eagerness amongst the ophthalmologists that I talk to, either individually or at meetings, in understanding and learning more. That gives me great encouragement. But it was a tremendous surprise to me that ophthalmologists are also very willing to accept new and unverified explanations of the accommodative mechanism and the causes of presbyopia. EW: What would you say is the best source of reliable information? Classic textbooks? The current peer-reviewed literature? Glasser: Obviously, there is a lot of controversy in this area right now, and it makes it that much more difficult for people to find the right information. It probably does require considerable effort on the part of individuals to get that information — even more so now that there is a lot of contradictory information being thrown out. But certainly the peer-reviewed journals are an ideal source for that information. Unfortunately, it’s very easy for somebody to stand up at a meeting and say whatever they think without providing substantial information. It’s necessary to be very critical and to compare and contrast the different sources of information before coming to a conclusion. I would like to reiterate that in this age of rapidly advancing technology, where things like wavefront sensors and wave-guided refractive surgery are becoming available, and new biomedical advances are being made, it should be considered totally unacceptable that a push-up technique be accepted for measurement of accommodation. The push-up test is inappropriate and inadequate to demonstrate restoration of accommodation. I hope ophthalmology clinicians, surgeons, venture capital investors, and patients demand that appropriate and objective measurements be done to verify the claims of new approaches to treat presbyopia. I think that will leave us all with a much healthier perspective on accommodation and accommodation restoration. Contact Information References:
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Adrian Glasser, PhD,
describes his experimental work on accommodation and evaluates surgical
techniques for presbyopia correction. |
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