The cornea protects the retina from UV radiation (<300 nm). The crystalline lens blocks additional UV light (between 300 nm and 400 nm). With the development of brunescent nuclear sclerosis and aging, there is progressive additional attenuation of violet light (between 400 nm and 440 nm) along with some blue light (up to 500 nm). Removing the crystalline lens with surgery potentially exposes the macula to UV, violet and blue light, raising fears that this may accelerate macular degeneration.
Because of the possibility of chronic phototoxicity that may result from the transmission of light exposure following the surgery, most of the IOLs implanted after 1996 utilized UV-blocking chromophores, although an action spectrum for macular degeneration has never been determined. More recently, lenses that block UV, violet, blue and even some green light have been introduced (eg, Acrysof Natural [Alcon Laboratories, Fort Worth, Texas]).
DAILY AMBIENT EXPOSURE
Although the retina's defense against phototoxicity declines with aging, there is no convincing evidence that daily ambient light exposure injures the retina of those with implanted clear IOLs that block only the ultraviolet.1,2 Review of the epidemiologic literature on age-related macular degeneration (AMD) indicates that most of the risk is genetic inheritance; a relationship between AMD and chronic accumulated light exposure has not been established. Large population-based studies — including the well-defined population of the Age-Related Eye Disease Study (AREDS) — as well as two AMD case-control studies have found no relationship between AMD and cataract surgery or significantly less than that associated with genetic markers, inflammation, smoking, atherosclerosis or overall metabolic health risk factors.3-10
There is, however, a substantial downside to blue-blocking IOLs: These IOLs impact the function of elderly patients under mesopic or scotopic conditions. Vision under scotopic conditions versus photopic vision declines more rapidly in the elderly than their photopic vision.11,12 Many environments in which older people must function represent mesopic or scotopic conditions with significantly reduced visual function. We are aware that many older drivers (even those with a normal-appearing macula) often limit or stop driving because of nighttime vision difficulties, and although they continue to go to restaurants, they often are frustrated with not being able to function under the dim lighting conditions. Unless physicians ask their patients about such problems, they often go unrealized.
DIM ENVIRONMENT
What is commonly understood in the rehabilitation industry, but I suspect largely ignored by eye care providers, is the significant association between reduced vision in dimmer environments and the increased risk of automobile accidents or other general accidents (eg, falling). A hip fracture, the most common result of a fall, may lead to long-term debilitation or requirement for care as well as risk of death.
The vision difficulties under mesopic and scotopic conditions among patients with even mild forms of macular degeneration are worse. The incidence of macular degeneration in the elderly is staggering, with one in four patients aged >65 years affected with some degree of macular degeneration and one in four aged >75 years affected with severe vision loss. With any manifestation of macular degeneration, most eye care providers realize that contrast sensitivity in good lighting conditions is reduced, but what most eye care providers do not realize is that under mesopic or scotopic conditions, the contrast of their vision is severely impaired. We do not measure the vision of our patients under these conditions, and as vision professionals, we do not realize their real risk of motor vehicle or other accidents or their well-founded fear of such accidents.
I am significantly concerned that IOLs that block blue light in addition to UV light may worsen the function of the elderly under such mesopic and scotopic environments. Because of the shift of the action spectrum with a peak at 555 nm in photopic well-lit conditions to the more blue 506 nm under mesopic or scotopic conditions, blue-blocking lenses reduce the overall light reaching the macula by >25%,1,2 which I believe will have a profound effect on vision in the elderly (with or without AMD). Most tests that claim to measure vision under mesopic conditions, in truth, measure under low photopic conditions.
We have been testing phakic and pseudophakic elderly patients under such real-world mesopic and scotopic conditions, and they both show more severe reduced visual function than we had anticipated, although the pseudophakic eyes with clear UV-blocking lenses were less severely encumbered. Reducing the ambient light by 25% in these individuals would substantially increase the risk of voluntarily ceasing of activities under dim illumination conditions. Even more problematic, these individuals may be involved in more accidents.
IMPLANT IOLs TO BLOCK UV, VIOLET LIGHT
I would argue that in order to maintain optimal visual function for our elderly patients — especially those with manifestations of AMD —we should implant IOLs that block UV and violet light (shorter than 440 nm) because these wavelengths do not actively play a role in mesopic or scotopic visual function. We should also attempt to correct them with the most optimal IOL optics possible (eg, aspheric design or customized optics that reduce even higher-order aberrations). In brightly lit environments, in order to reduce glare and enhance contrast, I believe we should certainly continue to encourage our patients to wear adequate blue light-filtering spectacles.
In addition, since there is the potential for macular acute phototoxicity from microscope light levels, I believe that every surgeon should be mindful about the amount of light that impinges upon the eye during cataract surgery and should take steps to reduce the acute light toxicity associated with the surgery.
Microscopes in many general operating rooms are often used for a multiplicity of subspecialty procedures. Light settings and filters are often ignored. Make sure the microscope has adequate UV- and violet-filtering, and turn the light levels down to the minimum required to perform the procedure. Adopt off-axis lighting optics that enhance the 3D view of lens structures while reducing the axial light impinging on the macula.
Finally, to understand the visual complaints of our patients, we need to pursue vision measurements under the actual lighting and contrast conditions that cause our patients' visual problems. There is an old adage in medicine: Physicians do not pay attention to those factors that they cannot measure. I believe this may be the case in this industry. I think it is inadequate to measure the vision of a person in a well-lit office with high (or low) contrast letters and then profess to understand how well they may function under other conditions or to understand how we may help them.
Stephen H. Sinclair, MD, is a vitreoretinal surgeon in private practice in Philadelphia, and is adjunct professor of ophthalmology at Drexel University School of Medicine, Philadelphia. He has spent more than 10 years developing new methods to evaluate vision and has financial interests in Vimetrics LLC (Media, Pennsylvania), which will market instruments that measure vision under the real-world conditions discussed in the article. Dr. Sinclair may be reached at Stephen@StephenSinclairMD.com or +1 610 892 1708.
BLUE LIGHT-FILTERING IOLS MAY OFFER RETINAL PROTECTION.
By Albert J. Augustin, MD
The use of blue light-filtering IOLs remains a subject of debate. Although most ophthalmologists agree that filtering high-energy blue light is advantageous for cataract patients, some believe that these IOLs compromise visual performance.
The human crystalline lens protects the retina from hazardous UV and high-energy blue light, however, lens removal during cataract surgery leaves the retina unprotected. When the retina does not have protection, the eye may be at greater risk of incurring phototoxic damage.
LIGHT EXPOSURE AND AMD
It has been shown that age-related macular degeneration (AMD) progresses more frequently after cataract extraction and traditional UV-absorbing IOL implantation compared with nonsurgical eyes.1 Pollack and colleagues evaluated the progression of AMD in 47 patients with bilateral and symmetrical early AMD. Patients underwent extracapsular cataract extraction and implantation of a traditional UV-absorbing IOL in one eye. The other eye (control eye) remained untreated. Almost 20% of treated eyes progressed to wet AMD, compared with only 4% of control eyes.
Pooled data from two large population-based studies found that cataract surgery may be associated with an increased risk for AMD progression, specifically to neovascular age-related maculopathy (ARM).2 These two studies were the Beaver Dam Eye Study and the Blue Mountains Eye Study. In the Beaver Dam Eye Study, 3,684 patients were re-examined after 5 years; in the Blue Mountains Eye Study, 2,335 were re-examined after 5 years.
Of the 6,019 patients (12,038 eyes) who were examined after 5 years, 11,391 eyes (315 nonphakic eyes and 11,076 phakic eyes) were considered at risk for developing late-stage ARM, and 21 nonphakic eyes (6% of right eyes and 7.5% of left eyes) and 77 phakic eyes (0.7%) developed late-stage ARM during the 5-year period. After adjusting for age, study site, gender, smoking and the presence of indistinct or reticular drusen or pigmentary abnormalities at baseline, nonphakic eyes had a significantly higher risk of developing a late-stage ARM lesion compared with phakic eyes.
Results from retrospective evaluations of epidemiological data, however, are inconsistent. A recent evaluation of the Age-Related Eye Disease Study (AREDS) population did not show correlation between cataract surgery and/or pseudophakia and AMD progression.3 On the other hand, the importance of light in the development of AMD and cataract is shown by subgroup analyses of the Beaver Dam population.4 Significant associations were found between extended exposure to the summer sun and the incidence of AMD changes. In addition, sufficient protection prevented such changes.
BLUE-LIGHT FILTERING IOLs: STABLE BLOOD-RETINAL BARRIER
Eyes implanted with blue light-filtering IOLs have a low incidence of blood retinal barrier (BRB) disruption. In fact, a retrospective case-controlled study conducted by Miyake and colleagues5 found that eyes implanted with these lenses had a significantly lower incidence of BRB disruption than eyes with an untreated IOL. Autofluo-rescence also increased with age, even in eyes implanted with UV-filtering IOLs.
In the 31 eyes that received untreated IOLs (followed for 5 years), the mean sodium fluorescein transmittance was 4.2 ±1.9 ng/mL. In the 30 eyes that received UV-absorbing IOLs, the mean fluorescein concentration was 3.2 ±2.1 ng/mL. The mean fluorescein concentration in the 20 eyes that received one version of blue light-filtering IOL was 2.8 ±1.9 ng/mL, and in the 21 eyes that received another version of a blue light-filtering IOL, it was 2.6 ±1.8 ng/mL.
IMPROVING QUALITY OF LIFE
One of the most important measures of successful surgery is how patients function in their daily lives. Blue light-filtering IOLs improve color vision, driving ability, and quality of life/health-related functioning similar to that of a lens that does not filter blue light.6 A prospective randomized study including 291 patients who underwent bilateral cataract extraction were implanted with either the blue light-filtering Acrysof Natural IOL (Alcon Laboratories, Fort Worth, Texas) or a clear IOL (Acrysof single-piece). A total of 257 patients completed baseline health-related quality-of-life assessment and at least one of two assessments after IOL implantation. Health-related functioning and quality of life was measured with the 39-item National Eye Institute Visual Functioning Questionnaire (NEI VFQ-39) and the 12-item Short Form Health Survey (SF-12).
The primary analysis included change in NEI VFQ-39 composite score, color vision, driving scales, and the SF-12 physical and mental component summary scales. Outcomes for the blue light-filtering IOL group and the clear IOL group were not statistically significant for these five areas. Importantly, both lenses demonstrated statistically significant improvements in difficulty driving at daytime and nighttime and in difficult conditions; there were no statistically significant differences between the lens types. The same improvements were seen for the NEI VFQ-39 item asking about "difficulty going down steps, stairs or curbs in dim light or at night."
The investigators concluded that because no statistically significant differences in improved NEI VFQ-39 color vision and driving scales were seen between the blue light-filtering IOL and the clear IOL, the former IOL did not impair color vision. Furthermore, compared with bilateral cataracts, the investigators concluded that improved color vision and driving in the former IOL was comparable to a clear IOL.
CONTRAST SENSITIVITY AND DIABETES
In patients with diabetes, blue light-filtering IOLs provide better contrast sensitivity than an IOL that does not filter blue light, according to a recent study of 22 diabetic patients (44 eyes).7 Patients received the Acrysof Natural in one eye and the Acrysof SA60AT in the fellow eye. Three months after surgery, monocular contrast sensitivity function was measured (CSV 1000-E contrast sensitivity chart) at distance, and color discrimination was measured (Farnsworth-Munsell 100-hue test).
Eyes implanted with the Acrysof Natural IOL had better contrast sensitivity values (10% increment) than fellow eyes implanted with Acrysof SA60AT IOLs. The investigators concluded that yellow-filter IOLs improved contrast sensitivity at every spatial frequency.
SCOTOPIC VISION
Mainster and Sparrow8 postulated that blocking blue light may adversely affect scotopic vision. Because rods have a different excitation spectrum than cones, with a peak more in the blue range, acceptable night vision is a concern. Decreased scotopic vision in pseudophakic patients was found for a UV-blue filtering IOL in an artificial setting using isolated spectral frequencies.9 A more recent report by Werner10 compared the Acrysof Natural IOL with the Acrysof SA60AT IOL. Benefits of the Acrysof Natural were important, however, the loss in scotopic sensitivity was not. Werner concluded that at absolute threshold, scoptic spectral sensitivity only caused a 0.07 log unit reduction; due to the range of scotopic sensitivity, this is not significant.
The investigators wrote: "More relevant to everyday visual performance is a loss of only 0.01 log unit in contrast sensitivity under the worst case. This is visually insignificant, and given the measurement error in psychophysical experiments with naïve observers under scotopic conditions, it is unlikely that a difference between the Natural and conventional IOLs could be reliably detected with normal sampling using broadband illuminants."
Additionally, Braunstein and Sparrow11 noted that older adults experience the greatest reduction in scotopic sensitivity in the violet-blue region of the spectrum, and scotopic sensitivity is greatest when light is of wavelengths near 507 nm. They also noted that at these wavelengths, the Acrysof Natural transmits only slightly less light versus conventional Acrysof IOLs (85% of 500-nm light vs 90% of 500-nm light, respectively). The Acrysof Natural and conventional Acrysof IOLs have the same transmission in the visible range above 520 nm.
Olson et al12 determined it necessary to show that white light impacts rod vision, presenting a noticeable change in scotopic function, in order to clinically validate the concern of night vision. The investigators noted that as of yet, there is no clinical evidence or study that show a decreased scotopic visual function with the IOL.
Because cataract patients are at risk for developing AMD and because the benefits of blue light-filtering IOLs may serve to mitigate some of the risk, I believe that it is prudent to replace cataractous crystalline lenses with IOLs that filter blue light similarly to the adult natural human lens.
VITREORETINAL SURGERY AND BLUE-LIGHT FILTERING IOLs
Implanting a blue light-filtering lens into an eye that may undergo vitreoretinal surgery is debatable. Currently, no publications in peer-reviewed journals exist on this topic, however, according to the experience in our department and that of other surgeons, there is no impairment concerning visualization of retinal pathologies such as epiretinal membranes. This is true for the retinal periphery and the macula area as well as for conventional buckling surgery or vitrectomy.
SUMMARY
Blue light-filtering IOLs are still a subject of debate. Discussions on impairment of scotopic vision and/or circadian rhythm — mainly based on the Purkinje shift, the important role of melatonin and the alteration of melanopsin sensitivity with the latter being not fully understood13 — are mainly theoretical and deducted from retinal physiology. Evaluating newborn crystalline lens transmittance, however, shows that nature did not develop a blocker of visible light rather than a filter. Many prospective studies and case series have shown that blue light-filtering IOLs are not altering relevant physiological parameters. Future technologies (violet-absorbing or blue light-filtering) and prospective studies will help to further identify patients at high risk for AMD progression following cataract surgery. In addition, these studies will also have to show which concept of light protection is the best for our patients.
Albert J. Augustin, MD, is the director of Augenklinik, Karlsruhe, Germany. He states that he has no financial interest with any products or companies mentioned herein. Professor Augustin may be reached at 106020.560@compuserve.com or +49 721 9742001.
WHY YELLOW DOES NOT GO FAR ENOUGH.
By Augustinus V. Schulte, MD, PhD
The blue-blocking IOL is a great concept, but there are two key reasons why I think a different approach is warranted. First, there is no sound scientific evidence that yellow IOLs play a significant role in the prevention of age-related macular degeneration (AMD). Second, there is definite evidence that the yellow lenses do not go far enough in preventing visual discomfort and distorted color perception. In other words, the rationale for the partial absorption of visible light by an IOL is primarily the prevention of visual discomfort and color distortion, rather than the hypothetical prevention of AMD.
That is why I came up with the concept of an orange IOL. This new IOL really matches the absorption/transmission characteristics of the healthy middle-aged human lens. A recent clinical study has underpinned what was expected on a theoretical basis. Patients experience more visual comfort and a better-balanced color perception after implantation of this new IOL as compared with both the classic clear IOLs and the yellow blue-blocking IOLs. The new lens is now in production (Orange Series; Ophtec, Groningen, Netherlands) and will soon be available in the European market.
POSTCATARACT SURGERY DISCOMFORT
Over the years, I have noticed that many patients experience a certain level of visual discomfort after cataract surgery with IOL implantation. Often, this discomfort forces patients to wear sunglasses (even indoors) because of oversensitivity to light. These patients also tend to have a distortion of color perception with a relatively increased sensitivity for the shorter wavelengths of the spectrum (blue and green). When investigating why these problems occur, it was discovered that they are caused by the discrepancies in absorption/transmission qualities between the implanted artificial lens and the age-matched healthy human lens.
As a person ages, the retina's repair function declines. In other words, the light damage in the retina is repaired more slowly. Similarly, the natural lens progressively limits the transmission of light over the years. This transmission limitation pertains not only to the harder blue and green light. To a lesser extent, it also pertains to the relatively softer yellow and red. Thus, the aging lens protects the aging retina.
In normal eyes of elderly people, the toxic effects of light in the retina stay in balance with the retina's capability of repairing itself. After the implantation of a clear IOL, this delicate balance is impaired. The subsequent photophobia is a defense mechanism against retinal overexposure caused by the increased light flux, caused by nonphysiologically high lenticular transparency.
TEST THEORY
We tested this theory by using two kinds of filters in patients who had recently undergone cataract extraction with clear IOL implantation. The first filter had the absorption/transmission properties of a normal, healthy middle-aged human lens. The other filter had the absorption/transmission properties of the yellow blue-blocking IOLs. In a controlled environment, the patients were exposed to a series of daily life visual stimuli, with a luminance varying from that of outside clear sky conditions to scotopic luminance levels.
Fifty patients subjectively evaluated vision without any filter, with a yellow filter in front of their pseudo-phakic eyes or with an orange filter. Patients scored their visual comfort and color perception higher with the orange filter as compared with the yellow one. The worst scores were given when visual comfort and color perception were evaluated without the use of any filter.
Results of these initial tests with filters have been confirmed by psychophysical tests in patients with the orange IOL implanted in one or both eyes. Based on my experience with this lens, I think it has a great future. My patients are significantly more comfortable having been implanted with this lens and find that they can go about their daily lives as they did before developing cataracts.
Augustinus V. Schulte, MD, PhD, is from the Knokke and Blankenberge hospitals in Belgium. Dr. Schulte states that he has a patent ownership or part ownership as well as a royalty agreement with the company and/or product mentioned herein. He may be reached at schulte@skynet.be or +32 477 358470.
