Dr Roger F. Steinert
Dr Schwartz and his colleagues have described another key step in their development of a novel technology. The ability to adjust the power and possibly other optical characteristics of an IOL, such as modifying multifocality and reducing high-order aberrations, has captured the imagination of cataract and refractive surgeons worldwide. Rarely is pre-clinical technology so well known and repeatedly discussed by clinicians. From the point of view of an outside observer keenly intrigued by the potential for this device, the process of this development has been characterized by a rigorously designed and meticulously achieved series of milestones.
The current presentation is essentially a proof of concept. After conceiving the chemical principle of migrating macromolecules that could be polymerized after IOL implantation by light, and then developing the material in a form suitable for a lens, the inventors faced the challenge of precise control of the delivery of the light energy. This required the development of the digital light delivery system whose key component is the digital mirror device (DMD).
In an in-vitro laboratory setting, Dr. Schwartz and his coworkers have now developed nomograms for control of both hyperopic and myopic lens power changes presented here. The standard deviations are impressively tight, well within clinically acceptable levels. Details about methodology need to be expanded, however. The text indicates that “each point on the nomogram consists of a minimum of 16 LALs/dose,” implying that the number of lenses tested varied from group to group. Why? Were some results unexpected and the outliers discarded? If so, the standard deviation is artificially small. Similarly, we would like much more detail about the lenses that were photo locked and then tested for optical stability and resolution. Summary results are presented on 48 photo locked LALs, again with apparently tight variability, but the text is silent on the underlying data and method of statistical analysis as well as the possibility of discarded data points.
Beyond these technical points, however, the authors appropriately alert us to some of the future challenges. One key question is the consistency of transmission of the 365-nanometer light by corneas of different patients. Another major issue is safety. While safety concerns are beyond the scope of the current presentation, the inventors will need to demonstrate the short- and long-term safety of both the material and the ultraviolet light, whose wavelength is toxic to the retina and the corneal epithelium. I have been assured that these concerns are well known and being satisfactorily addressed by the researchers.
Other issues will arise as this technology moves into clinical testing. Some of these issues are practical, such as the need for patients to wear UV absorbing spectacles, at least outdoors, in the days or weeks prior to photo locking, and whether patients will comply with this.
Many other issues are socioeconomic. The technology of the digital light delivery system, the IOL material itself, and the considerable extra surgeon and technician time involved in the postoperative interventions all add considerable expense. As with some other new IOL technologies, such as the accommodating IOL, the restrictions on balance billing of cataract patients have forced a business model in the U.S. where these expensive technologies are marketed for refractive lens exchange in patients without lens opacities. How much extra is such a patient willing to pay for optical perfection?
Notwithstanding these challenges, known and unknown, Dr Schwartz and his coworkers are to be congratulated both for their innovative technology and for their methodical scientific development of its potential.
Dr David L. Guyton
To do the lock-in process, you have to have a very widely dilated pupil to irradiate the whole lens. There are many cataract patients whose pupils do not dilate well. How critical do you view this problem and do you have a solution for those cases where the pupil just won’t dilate?
Dr Michael Nork
As a retinal specialist, I was hoping that we had seen the end of silicone lenses since these hydrophobic lenses present a difficulty when performing retinal operations. The lenses develop condensation, making it difficult to see the retina once you perform an air-fluid exchange. Although it is true that most people with implants will never require a vitrectomy procedure, on the other hand, most people that need vitrectomy surgery are pseudophakic. Is there any way to coat the lens or technologies to prevent condensation from forming during air-fluid exchanges?
Dr George L. Spaeth
From the point of view of quality of life, what would be the benefit to the patient? Resources are limited. Is the investment in this type of technology justified in terms of other issues that need to be solved?
Dr Daniel M. Schwartz
First, I would like to address the issue of the number of lenses used for adjustment nomograms and lock-in. As Dr Steinert notes, there were variable numbers of lenses used to develop each point of the nomograms. Our in-vitro lens adjustments/lock-ins are performed in groups of eight lenses by one to three scientists. The nomogram data reported ranged from 16 to 48 lenses for each point generated by a minimum of two different operators and represents the total number of lenses tested under each condition. All data collected were reported with no data points rejected. In spite of the different operators, the data remained reproducible with small standard deviations.
Dr Steinert also raises the important potential problem of variable corneal transmission of 365-nanometer light used to irradiate the lenses. This is an important issue because if there is variability from patient to patient, it’s going to make this technology very difficult to adopt by the practitioner. With the data to date, we don’t know how much variability there’s going to be from patient to patient. However, we have adjusted eight consecutive patients since the manuscript was submitted. Four were adjusted with an intended refractive change of +1.5 diopters, 2 for +1.0 diopters, and 2 for −1.0 diopters. After adjustment, all were within 0.25 diopters of the intended refractive outcome. One of the patients we adjusted for +1.5 diopters was 50 years old and one was 85, and yet we achieved the same dioptric change. We are using pachymetry measurements before and after surgery to confirm that patients recover to their pre-op pachymetry levels, thus minimizing corneal edema as a variable. Fortunately, the technology is somewhat tolerant of these differences. We can get the same power changes with about a 10 percent difference in corneal light transmission.
There are concerns about irradiation safety, and these relate to potential damage to the cornea with photokeratitis or damage to the retina from these UV light sources. There is animal and human data on these potential toxicities. The threshold for toxicity for photokeratitis is approximately 70 joules per cm2 at 365 nm. We have not encountered any cases of photokeratitis either in our rabbit studies for preclinical submission to the FDA or in the patients that we have treated.
We also are concerned about retinal toxicity, and the retinal threshold in primates at this wavelength is approximately 5.5 joules per cm2. Dr David Sliney is widely published on the subject of the effects of UV radiation on the eye and serves as member, advisor and chairman of numerous committees and institutions which are active in the establishment of safety standards for protection against non-ionizing radiation (ANSI, ISO, ICNIRP, ACGIH, IEC, WHO, NCRP). He has advised that we not exceed 2 joules per cm2 at the retina, and light treatments are within that guideline.
Dr Steinert raised some important issues about the expense of the technology and the time requirement for practitioners. I do not have detailed information about these issues, but I can say the lens material itself is surprisingly inexpensive. It costs just a few dollars more to make this lens than conventional silicone lenses. The sales price for the digital light delivery device is approximately $80,000, which compares favorably with the excimer laser.
As Dr Guyton notes, pupillary dilation is very important. For typical adjustment and lock-in, spatial intensity profiles are projected onto nearly the entire 6mm diameter of the IOL. We can customize the size of the adjustment profile to accommodate smaller pupils; however, the entire lens must be irradiated for lock-in. At this time we are limiting the technology to patients who dilate 7mm or more preoperatively. Undoubtedly there will be some patients who dilate less after surgery. For those patients, we could use a gonioscopic-type lens that would direct light around the edges of the pupil to achieve lock-in. We are also developing a second-generation lens formulation that will not require lock-in. Pupillary dilation would not be an issue with such a formulation since lock-in would not be necessary.
Dr Nork raises an important issue about condensations that can form on silicone IOLs during vitrectomy surgery, especially when silicone oil is used. The development of proliferative vitreoretinopathy (PVR) requiring vitrectomy among those patients who develop pseudophakic retinal detachments is probably on the order of 5 to 7 percent. With PVR, equal success is achieved using either gas or silicone oil, so silicone oil would be avoided in patients with a silicone light adjustable lens. For those patients in whom there is an increased risk of retinal detachment recognized prior to the cataract surgery, an adjustable silicone lens may not be indicated. We are not restricted to silicone lenses and we can adapt our technology to acrylic lenses, thereby avoiding these condensation issues. We have developed a prototype acrylic formulation that has been successfully adjusted.
Dr Spaeth asks how is this going to make our patients’ lives better, and is it really worth the cost? I do believe that there is a need for this technology since more patients would like to be spectacle-free both at near and distance. I have discussed a monofocal version of this lens, but we can also make a customized multi-focal version of the lens. Using the digital light delivery device, we can emmetropize the eye and then create a multi-focal optic in situ. Furthermore, if a patient will not tolerate multi-focality, the multi-focal optic is potentially reversible. Because of the ability to modify lens power multiple times until it is locked in, we can also try a patient with monovision and then reverse it if the patient wishes. As discussed above, the technology is going to be a fairly insignificant increase in cost in terms of the IOL material. Whether patients themselves will want to undergo implantation with an adjustable IOL given the extra cost related to financing the light delivery device and physician time, only the market will provide the answer. You still have to perform a refraction, but the physician time for adjustment and lock-in is minimal. Treatments are on the order of 30 seconds to two minutes each for adjustment and lock-in.