Only weak evidence supports the use of IOLs that filter visible blue light, researchers say.
“On the basis of currently available evidence, one cannot advocate for the use of blue-light-filtering IOLs over UV-only filtering IOLs,” wroite X. Li, Waterford Institute of Technology, Waterford, Ireland, and colleagues.
They published their review of the research on the lenses in the journal Eye
Manufacturers and distributers have been claiming benefits for IOLs that filter visible short-wavelength light.
Blue light is scattered more than light of longer wavelengths, Li and colleagues wrote, and blue light scatter is the predominant cause of veiling luminance and glare disability.
In a healthy eye, lutein, zeaxanthin, and mesozeaxanthin—collectively referred to as macular pigment—absorb blue light peaking at 460 nm. An average amount of macular pigment filters out about 40% of blue light incident on the macula.
Hypothetically, increasing macular pigment would improve contrast between a background consisting of blue haze and a target, thereby increasing visual range and improving discernibiltiy of a target’s low-contrast internal details.
The crystalline lens blocks ultraviolet (UV) radiation between about 300 and 400 nm. Over time, the damage caused by radiation, oxidation, and post-translational modification increases light scatter, fluorescence, and spectral absorption, especially at the short-wavelength end of the visible spectrum.
As a consequence, a 53-year-old lens transmits about 70% of visible blue light, while a 75-year-old lens transmits about 25% of blue light.
Early IOLs did not include chromophores to block UV radiation, but by 1978 researchers realized that UV radiation was damaging retinas in eyes implanted with these lenses, and by 1980 most IOLs contained UV-blocking chromophores.
A standard IOL now absorbs wavelengths up to 420 nm. Blue light-filtering IOLs block wavelengths between 400 and 500 nm. They are subdivided into blue-blockers, which absorb visible light in the 450-500 nm range and violet-blockers, that absorb visible light in the 410-440 nm range.
Li and colleagues could not find any studies on violet-blocking IOLs. They found 21 studies reporting on outcomes following implantation of blue-light-filtering IOLs. The studies involved a total of 8,914 patients and 12,919 study eyes undergoing cataract surgery.
The researchers classified 7 of these as individual cohort studies or low-quality randomized controlled trials. There were no systematic reviews of cohort studies or individual randomized-controlled trials with narrow confidence intervals.
Of these 7 best studies, only one found better vision with blue-light-filtering IOLs than UV-only filtering IOLs. In this study, researchers randomly selected 30 eyes for implantation with UV-only light filtering IOLs and 30 for implantation with blue-light filtering IOLs. There were no differences in visual acuity or colour vision up to 6 months after surgery, but the blue-light filtered eyes scored better in contrast sensitivity at select frequencies.
This study did not measure or report contrast sensitivity preoperatively in either group, so Li et. al. reasoned the finding may simply reflect better preoperative contrast sensitivity in the eyes scheduled to be implanted with the blue-light-filtering IOL.
In another study, patients implanted with standard IOLs that block UV light only wore either clip-on blue light-filtering spectacles of clip-on UV-only filtering spectacles. The researchers found that the blue-light filtering spectacles increased the patient’s ability to tolerate glare and enhanced their recovery following photostress under conditions of intense light. It is hard to determine how well the results of this experiment applies to actual blue light-filtering IOLs, Li and colleagues noted.
On the other hand, a comparison of another IOL (AcrySof Natural IOL, Alcon), which filters blue light, to single-piece IOLs (single-piece AcrySof IOL, Alcon), which filter only UV light, showed no difference between them in visual acuity, contrast sensitivity, or colour perception among the 93 patients implanted with one or the other.
Likewise, researchers implanted each of 30 patients with UV-only filtering lenses (AcrySof SA60AT lenses, Alcon) in one eye and blue light-filtering lenses (AcrySof SN60WF, Alcon) in the other eye. Two years later they found no differences in visual acuity, colour vision, contrast sensitivity, macular thickness, or macular volume.
Some researchers have tested the influence of blue-light filtering IOLs on night vision, which depends on blue light. In one study, 22 patients with bilateral pseudophakia and early age-related macular degeneration were less able to sort blue socks from navy socks while wearing blue light-filtering spectacles than without the spectacles in dim conditions.
Other studies found no such differences. These studies, however, all used luminance values of at least 1 cd/m2, which means the subjects’ vision was at least partly mediated by cones rather than rods, Li and colleagues wrote.
Blue light can suppress melatonin, so some researchers have speculated that blue-filtering IOLs might affect sleep patterns. Studies on UV-only filtering IOLs show improvements in sleep patterns, perhaps because the procedure replaced yellow lenses. One study comparing patients implanted with UV-only filtering IOLs and blue-light filtering IOLs found improvements in sleep only for those with the UV-only filtering IOLs. Other similar studies have also found no differences.
Could blue light filtering lenses affect macular degeneration? It is difficult to design a study answering that question, Li et. al. wrote, because “it would be impossible to control for the cumulative exposure to such visible wavelengths before surgery.”
However, one small, observational study found increased fundus autofluorescence, a marker for geographic atrophy and neovascular age-related macular degeneration, in eyes implanted with UV-only filtering IOLs and not in eyes implanted with blue light-filtering IOLs. Li and colleagues noted measures of autofluorescence are influenced by the nature and density for a cataract before surgery and the absorbance properties of the IOL.
Another study found geographic atrophy progressed more slowly in eyes implanted with blue light-filtering IOLs. However, the study did not control for age, genetic background, and other confounding factors.
“In general, the quality of evidence informing the surgeon’s selection of IOLs on the basis of light transmittance properties is deficient,” Li and colleagues concluded.
1A. This is a lower impact factor-journal but of interest:
Color of Intra-Ocular Lens and Cataract Type Are Prognostic Determinants of Health Indices After Visual and Photoreceptive Restoration by Surgery
Background: This study compared post-operative quality of life and sleep according to the type of cataract opacity and color of the implanted intra-ocular lens (IOL).
Methods: This is a cohort study and participants were 206 patients (average age 74.1 years) undergoing cataract surgery with the implantation of a clear ultra-violet (UV)-blocking IOL (C) or a yellow blue-light-blocking IOL (Y). Participants were evaluated using the National Eye Institute Visual Function Questionnaire (VFQ-25) and Pittsburgh Sleep Quality Index (PSQI) before surgery and 2 and 7 months after surgery. Changes in sub-scale scores of VFQ-25 and PSQI were compared.
Results: Sub-scale analyses for improvement after surgery revealed significant differences in ocular pain scores on the VFQ-25 (Y>C; the higher the score, the better the outcome). Furthermore, there were significant differences between the two IOLs in terms of the sleep latency score (C>Y) and sleep disturbances score (C>Y). A posterior sub-capsular cataract was significantly correlated with improvements in ocular pain and sleep latency scores. These effects were successfully represented by the change in scores rather than absolute post-operative scores because individual standard of response may often change after intervention, recognized as a response shift phenomenon in patient-reported outcome study. Regarding seasonal differences, patients who had surgery in summer exhibited relatively better sleep quality than those who had surgery in winter.
Conclusions: Analysis of sub-scales of health indices demonstrated characteristic prognoses for each IOL and cataract type. Cataract surgery may potentially contribute to systemic health in older adults.
The color of an intra-ocular lens (IOL) is an emerging topic of interest among cataract surgeons, particularly the question as to whether a blue-light filter has any beneficial effects in terms of visual function, age-related macular degeneration, and circadian rhythm.7–10 Theoretically, a blue-light filter should effectively reduce phototoxicity and glare originating from blue light, as well as photophobia characterized by an excessive sensitivity to light that causes ocular pain and headache.11,12However, blue-light filters are yellow-tinted in appearance (yellow being the complementary color), and this may have adverse effects on color and scotopic vision, as well as disrupting circadian photoentrainment.13,14 There is one large comparative study that has investigated this issue, and, in that study, overall sleep quality and sleep latency improved after removal of cataract regardless of the type of IOL implanted.15 The authors of that study concluded that implantation of a blue-light filter IOL did not have a negative impact on the sleep–wake cycle. In ophthalmologic practice, cataract surgeons can now select any one of three types of IOL, namely those that block UV, violet, or blue light. Previous studies reported that both UV- and blue-light-blocking IOLs had beneficial effects on systemic health in terms of vision-related QOL, sleep quality, and gait speed.16–18
The major limitations of the present study relate to the use of two separate study groups and the lack of randomization. The study was performed in two different medical centers, 20 km apart, in the same region. Although the surgeon, medical service, chronological factors, race, education, and insurance were exactly same for patients at both centers, there may have been differences in patient lifestyles and occupation. The sample sizes of the groups allocated a clear or yellow IOL were different (n=71 and n=135, respectively), but the groups were statistically comparable because the enrollment of consecutive surgical cases was not biased and appropriate statistical analyses were used. The present study was based on the results of questionnaires only. Restoration of photoreception in the eyes needs to be confirmed by a pupillometer, electroretinogram, optical coherence tomography, and/or other retinal and neurological examinations. Further investigation in large randomized control studies is necessary to confirm the different effects on systemic health of different-colored IOL.
In conclusion, the results of the present study indicate that the color of the IOL and cataract type are significantly correlated with non-visual prognosis. Ophthalmologists are encouraged to check for the presence of a PSC, photophobia, and sleep quality pre-operatively, because these factors could potentially be related to post-operative QOL after restoration of light transmittance in the eye.
2. Br J Ophthalmol. 2006 Jun;90(6):784-92.
Violet and blue light blocking intraocular lenses: photoprotection versus photoreception.
To analyse how intraocular lens (IOL) chromophores affect retinal photoprotection and the sensitivity of scotopic vision, melanopsin photoreception, and melatonin suppression.
Transmittance spectra of IOLs, high pass spectral filters, human crystalline lenses, and sunglasses are used with spectral data for acute ultraviolet (UV)-blue photic retinopathy (“blue light hazard” phototoxicity), aphakic scotopic luminous efficiency, melanopsin sensitivity, and melatonin suppression to compute the effect of spectral filters on retinal photoprotection, scotopic sensitivity, and circadian photoentrainment.
Retinal photoprotection increases and photoreception decreases as high pass filters progressively attenuate additional short wavelength light. Violet blocking IOLs reduce retinal exposure to UV (200-400 nm) radiation and violet (400-440 nm) light. Blue blocking IOLsattenuate blue (440-500 nm) and shorter wavelength optical radiation. Blue blocking IOLs theoretically provide better photoprotection but worse photoreception than conventional UV only blocking IOLs. Violet blocking IOLs offer similar UV-blue photoprotection but better scotopic and melanopsin photoreception than blue blocking IOLs. Sunglasses provide roughly 50% more UV-blue photoprotection than either violet or blue blocking IOLs.
Action spectra for most retinal photosensitisers increase or peak in the violet part of the spectrum. Melanopsin, melatonin suppression, and rhodopsin sensitivities are all maximal in the blue part of the spectrum. Scotopic sensitivity and circadian photoentrainment decline with ageing. UV blocking IOLs provide older adults with the best possible rhodopsin and melanopsin sensitivity. Blue and violetblocking IOLs provide less photoprotection than middle aged crystalline lenses, which do not prevent age related macular degeneration (AMD). Thus, pseudophakes should wear sunglasses in bright environments if the unproved phototoxicity-AMD hypothesis is valid.
3. Surv Ophthalmol. 2010 May-Jun;55(3):272-89. doi: 10.1016/j.survophthal.2009.07.006. Epub 2009 Nov 1.
Blue-blocking IOLs decrease photoreception without providing significant photoprotection.
Violet and blue light are responsible for 45% of scotopic, 67% of melanopsin, 83% of human circadian (melatonin suppression) and 94% of S-cone photoreception in pseudophakic eyes (isoilluminance source). Yellow chromophores in blue-blocking intraocular lenses (IOLs) eliminate between 43 and 57% of violet and blue light between 400 and 500 nm, depending on their dioptric power. This restriction adversely affects pseudophakic photopic luminance contrast, photopic S-cone foveal threshold, mesopic contrast acuity, scotopic short-wavelength sensitivity and circadian photoreception. Yellow IOL chromophores provide no tangible clinical benefits in exchange for the photoreception losses they cause. They fail to decrease disability glare or improve contrast sensitivity. Most epidemiological evidence shows that environmental light exposure and cataract surgery are not significant risk factors for the progression of age-related macular degeneration (AMD). Thus, the use of blue-blocking IOLs is not evidence-based medicine. Most AMD occurs in phakic adults over 60 years of age, despite crystalline lens photoprotection far greater than that of blue-blocking IOLs. Therefore, if light does play some role in the pathogenesis of AMD, then 1) senescent crystalline lenses do not prevent it, so neither can blue-blocking IOLs that offer far less photoprotection, and 2) all pseudophakes should wear sunglasses in bright environments. Pseudophakes have the freedom to remove their sunglasses for optimal photoreception whenever they choose to do so, provided that they are not encumbered permanently by yellow IOL chromophores. In essence, yellow chromophores are placebos for prevention of AMD that permanently restrict a pseudophake’s dim light and circadian photoreception at ages when they are needed most. If yellow IOLs had been the standard of care, then colorless UV-blocking IOLs could be advocated now as “premium” IOLs because they offer dim light and circadian photoreception roughly 15-20 years more youthful than blue-blocking IOLs.