Blue-blocking spectacles lenses for retinal damage protection and circadian rhythm: evaluation parameters
BBlue-blocking spectacles lenses for retinaldamage protection and circadian rhythm: evaluation parameters
Regina Comparetto Alessandro Farini University of Florence, degree in Optics and Optometry CNR-National Institute of Optics, Largo Enrico Fermi 6, 50125 Firenze
June 14, 2018
Abstract
There is evidence for the effect of blue light on circadian cycle andocular pathologies. Moreover the introduction of LED lamps has in-creased the presence of blue light. In the last two years many differentblue blocking ophthalmic lens have been introduced Due to the differ-ent effect of blue light on ocular media and circadian rhythm we havedefined two indices that describe the level of protection of the lenses to-wards the retina and the circadian cycle under different lighting as forexample daylight and tablet. These indexes can help in individuatingthe right lens for ocular protection.
The invention of the Light Emitting Diode (LED) has completely changedthe world of light sources. LEDs have replaced the old type of light sources,and they have been massively adopted in the production of screens of allkind of electronic devices with which many of us deal everyday, such as TVs,PCs, smartphones, and tablets. A particularity of the commonly used whiteLED is its significant emission of short-wavelength blue light [1]. Thus, it is1 a r X i v : . [ q - b i o . O T ] J un mportant to fully understand the consequences of this type of radiation onour health.Recent investigations on the third retinal receptor have shed some light onthe importance of blue light (i.e. short-wavelength visible radiation mainly inthe range 400 nm ≤ λ ≤
450 nm) for our life cycles. Berson et al. [2] showedthat this receptor has a huge impact on the control of the circadian cycle, i.e.the set of all the physiological cycles of our body within 24 hours, such as theregulation of arterial pressure or the production of melatonin. Several studiesconfirmed that an unnatural exposition to short-wavelength radiation canhave a negative impact on our health. For example, an insufficient exposureto blue light during the day has been related to sleep disorders [3, 4], whilea strong exposure to blue light during the evening is known to cause theinhibition of melatonin production which damages the quality of sleep [5,6, 7]. Lots of studies [8, 9, 10, 11, 12, 13, 14, 15, 16] have shown how anexcessive and prolonged exposure to this kind of radiation can lead to theonset of ocular pathologies, such as senile macular degeneration or cataract.Optical devices such as ophthalmic, contact, or intra-ocular lenses can beused as a protection from the effects of the blue radiation. Due to the ubiq-uitous presence of LED devices, we witnessed an increasing interest aroundthose aspects of blue light, with the result of the market introduction overthe last few years of many blue-blocking ophthalmic lenses by lens manu-facturers. However, there is still a debate in the scientific community andno strict regulations on how short-wavelength visible light should be treated.Thus, it is not clear how lenses should protect us from the negative effectsof the blue light (by blocking it) while preserving the positive effects on thecircadian cycle.In this work, we propose a novel approach to characterize the interactionof lenses with blue light through the introduction of two numerical indexes.Those are meant to quantify the behavior of lenses when exposed to the blueradiation and to estimate both the risks of retinal damage and disruption ofthe circadian cycle. We evaluate a set of commercially available lenses withdifferent types of blue-blocking treatments, comparing them with a groupof lenses without this type of treatment. Computing our indexes for theanalyzed lenses, we were able not only to compare treated and non-treatedlenses, but also to capture the heterogeneity of the behaviors of the differentblue-blocking lenses.The paper is structured as follows. In section 2, we briefly introduce thenumerical parameters used for the analysis of the lenses, giving the definition2f the two novel indexes we propose in this work. In section 3 we report theexperimental settings, in section 4 we expose and discuss the results of thisstudy, and section 5 concludes the paper.
In this section, we describe the two proposed indexes to characterize theresponse of lenses to the exposure to blue light, respectively named
RetinalIndex (RI) and
Circadian Index (CI).
Retinal Index (RI)
The Retinal Index (RI) quantifies the possible dam-age of the retina due to the exposure to the short-wavelength radiation. Wedefine RI as: RI = (cid:90) nm nm T ( λ ) I ( λ ) B ( λ ) dλ (cid:90) nm nm I ( λ ) B ( λ ) dλ (1)where T ( λ ) is spectral transmittance of a lens in the visible spectrum (380 –780 nm), defined as the ratio between the transmitted flux and the incidentflux [17], I ( λ ) is a generic illuminant, and B ( λ ) is the blue light hazard func-tion (depicted in Fig. 1). B ( λ ) represents the risk of damaging the retina ifexposed to a blue-light radiation [18]. RI ranges from 0 to 1, where a RI = 0identifies a totally protective lens against the photochemical retinal damagedue to blue light, while RI = 1 identifies a totally non-protective lens. Circadian Index (CI)
The Circadian Index (CI) quantifies the ability ofa lens to inhibit the effect of the light radiation in the circadian cycle. Wedefine CI as the weighted average of the spectral transmittance of the lens: CI = (cid:90) nm nm T ( λ ) I ( λ ) M λ dλ (cid:90) nm nm I ( λ ) M λ dλ (2)where T ( λ ) is the spectral transmittance, I ( λ ) is the emission spectrum ageneric illuminant, and M λ (depicted in Fig. 1) is a relative spectral efficiencyfunction that represents the response of the third retinal receptor to the3igure 1: Comparison between B ( λ ) , Blue Light Hazard Function, and M λ ,a relative spectral efficiency function which represents the represents theresponse of the third retinal receptor to radiation.light radiation [19, 20]. The function M λ takes into account how much thecircadian cycle is influenced by the received radiation. CI ranges from 0 to 1,where a CI = 0 identifies a lens that completely blocks the effects of the bluelight radiation on the circadian cycle, and CI = 1 identifies a lens that doesnot interfere with those effects. When using a lens with CI = 1, the naturalcircadian cycle could be altered by the exposure to the artificial blue light ofdigital devices, but the same lens allows the natural rhythm of the circadiancycle in the case of natural, solar light exposure. On the other hand, a lenswith CI = 0 protects from the damages caused by the artificial blue light,but, at the same time, does not allow the natural blue light to reach the thirdretinal receptor. UV Transmission Factor ( τ UV ) To fully characterize the quality of alens, we also measure and report the
Solar UV transmission factor, τ UV ,defined as 4 UV = (cid:90) nm nm T ( λ ) W λ ( λ ) dλ (cid:90) nm nm W λ ( λ ) dλ (3)where T ( λ ) is the spectral transmittance of a lens, and W λ ( λ ) is theweighting function for UV transmission as defined in (European RegulationUNI EN 1836) []. This index takes into consideration the percentage ofultraviolet radiation that a medium is able to transmit. For this study, we analyzed 16 commercially available blue-blocking lensesfrom 8 different companies and 5 lenses without any blue-blocking treatment.The characteristics of the analyzed lenses are reported in Table 1.We measured the spectral transmittance T ( λ ) using the spectrophotome-ter Perkin Elmer Lambda 1050 UV/Vis/NIR double-bean with integratingsphere. Since we were interested in the behavior of the lenses in the visibleand UV spectra, we measured T ( λ ) for 280 nm ≤ λ ≤
830 nm, with a strideof 5 nm, in order to obtain a good compromise between measuring timesand preciseness, as suggested by the main ISO regulations. For each lens,we computed RI, CI, and τ UV using two different illuminants I ( λ ) , the stan-dard illuminant D65 ( RI D e CI D ), and the spectral emission of a LCDscreen, in particular the one of an iPad ( RI LCD e CI LCD ). By changing theilluminant it’s possible to study the behavior of a medium when exposed todifferent type of radiation. The MATLAB code for the computation of theindexes is publicly available . The computed indexes for all the lenses and both the illuminants are reportedin Table 1. Figure 2 shows the scatter plot of RI and CI of various lensescomputed using the spectral emission of the standard illuminant D65.Although it is clear that blue-blocking lenses are on average more pro-tective towards the effects of blue light with respect to non-treated ones, we https://github.com/ReginaComparetto/Retinal-and-Circadian-Indexes n ), whether they had a blue blocking treatment ( BB ),and the RI and CI computed with the standard illuminant D65 ( RI D , CI D ) and the spectral emission of a LCD screen ( RI LCD , CI LCD ). Lens n BB RI D CI D RI LCD CI LCD τ UV % .
77 0 .
84 0 .
78 0 .
84 3 . .
86 0 .
92 0 .
92 0 .
93 3 . .
86 0 .
92 0 .
88 0 .
92 1 . .
90 0 .
93 0 .
90 0 .
93 4 . .
10 0 .
23 0 .
09 0 .
24 0 . .
84 0 .
85 0 .
85 0 .
85 4 . .
79 0 .
86 0 .
81 0 .
87 0 . .
79 0 .
87 0 .
85 0 .
89 0 . .
74 0 .
82 0 .
77 0 .
83 0 .
10 1.67 y .
78 0 .
86 0 .
83 0 .
88 0 .
11 1.59 y .
85 0 .
91 0 .
92 0 .
93 0 .
12 1.60 y .
83 0 .
89 0 .
91 0 .
93 0 .
13 1.67 y .
82 0 .
89 0 .
91 0 .
92 0 .
14 1.50 y .
84 0 .
90 0 .
90 0 .
93 0 .
15 1.50 y .
75 0 .
87 0 .
92 0 .
93 0 .
16 1.60 y .
80 0 .
90 0 .
96 0 .
96 0 .
17 1.60 y .
82 0 .
91 0 .
97 0 .
97 0 .
18 - n .
97 0 .
97 0 .
98 0 .
98 5 .
19 1.50 n .
88 0 .
90 0 .
89 0 .
90 2 .
20 1.50 n .
87 0 .
89 0 .
88 0 .
89 2 .
21 1.50 n .
92 0 .
92 0 .
92 0 .
92 66 . † * Lens 5 is an orange-tinted lens. † Lens 21 is a non-organic glass lens without any treatment.6 lue Blocking Lenses Lenses without any treatment
Treatment BTreatment A
Figure 2: Scatter plot of RI and CI some of the evaluated lenses. Thereported indexes are calculated using the standard illuminant D65.notice a heterogeneity in the RI and CI values among treated lenses that isnot reported by lens manufactures. For example, lenses with a different CIshould be used for different needs, e.g. lower CI lenses might be used withelectronic devices in the evening to prevent sleep disorders, while they are notrecommended in the day-light in order to preserve the natural circadian cy-cle. Instead, lens manufactures generally advertise lenses with blue-blockingtreatments as globally protective against blue light without distinguish thoseaspects.
Indexes Correlation
We can observe that there is a positive correlationbetween the two indexes. This is reasonable since the peak values of B ( λ ) and M λ (on which the definition of RI and CI are based) are near in thespectrum, and there is a significant overlap of the areas under the two curves(see Fig. 1). This means that the two aspects of the blue light, i.e. the effecton the circadian cycle and the damages of the retina, are difficult to separate.In Figure 3, the two curves B ( λ ) and M λ are shown together with thespectral transmittance of two chosen lenses (Lens 1 and 2). These lensesare two samples of the same material and made by the same company, but7ith two different blue-blocking treatments, which we refer to as TreatmentA and
Treatment B . We can observe that the spectral transmittance of thelens with Treatment B reaches a high value near the higher point of M λ curve (450 nm ≤ λ ≤ nm ); thus, it has a higher CI D than the lens withTreatment A. On the other hand, a side effect of Treatment B is that thespectral transmittance near the peak of B ( λ ) curve (400 nm ≤ λ ≤ nm ) isequally high, yielding a higher RI D with respect to Treatment A. However,we can notice that there is a clear depression in the spectral transmittanceunder the B ( λ ) curve right before its peak, which prevents the retinal indexto further increase.Figure 3: Comparison between B ( λ ) , M λ , and the spectral transmittance T ( λ ) of two blue-blocking lenses (Lens 1 and 2) of the same material withdifferent treatment (Treatment A and Treatment B highlighted in Figure 2). Relation to UV transmittance
In Figure 4, the spectral transmittancesof all the analyzed lenses with blue blocking treatment are shown, with partic-ular attention to the cut-off wavelength. We notice that four lenses (Lens 1 to4) have a lower cut-off wavelength and thus present a higher UV transmissionfactor τ UV . Despite being advertised as a protective lens with blue-blocking8igure 4: The detail of the spectral transmittance of all blue-blocking lensesaround the cut-off wavelength λ cut .treatment, Lens 4 have the highest values of RI D , CI D , and τ UV amongall lenses with blue-blocking treatment; thus it offers a very limited protec-tion against the effects of the exposure to blue light. Moreover, it is the lessprotective less against UV radiation among all the treated ones, with a τ UV value comparable to the ones of non-treated lenses. Lens 1, which is the onewith the Treatment A, has a lower value of RI D and CI D , but still hasa high value of τ UV , which is comparable to the one of lenses without blueblocking treatment. It is important to notice that the values of RI and CI areindependent from τ UV ; thus the proposed indexes are not meant to describein any way the behavior of the sample to the ultraviolet radiation. Chromaticity of Lenses
In Figure 5, we highlight the chromatic coordi-nates of three lenses of interest in the CIE color space chromaticity diagram.The curve in the center of the diagram delimits the set of chromatic coor-dinates for which the color perception is not altered [22]. We observed thatlenses with blue-blocking treatments do not lead to an altered color percep-tion; in fact, all blue-blocking lenses fall inside the delimited area. Lens 1,9igure 5: The CIE color space chromaticity diagram. The points representedthree out of all the analyzed lenses (with and without blue blocking treat-ment. The CIE spectral locus was generated using the software described in[21]treated with Treatment A, is the most yellow lens out of all the one in theacceptance area; still, it is very near in the chromaticity space to Lens 6, anon-treated lens which is the most white of all the analyzed lenses. The onlylens that lies outside the acceptance area is Lens 5. Since it is an orange-tinted lens, we expected it to alter the perception of color. This accounts alsofor the low values of RI D and CI D , since the strong orange tint blocksthe majority of the blue radiation. All the other lenses had color coordinatesthat lie approximately between the coordinates of Lens 1 and Lens 6. In this work, we proposed two numerical indexes, namely the Circadian In-dex and the Retinal Index, to quantify the effects of the exposure to short-wavelength visible radiation to the human health. Given a lens, the formersummarizes impact of the transmitted light on the circadian cycle, while thelatter summarizes the risk of retinal damage when exposed to same trans-mitted radiation. 10sing these indexes, we performed a comparative analysis between com-mercially available lenses with blue-blocking treatment and non-treated lenses.Results shown there is a large dispersion of behaviors among differenttreatments. Our proposed indexes are able to efficiently capture those dif-ferences, and they could be useful as a metric to characterize blue-blockingoptical media.Differently from already proposed index measuring global blue light trans-mission, we argue that having two separated metrics could help to easilyidentify the optimal lens for a particular usage. While it is always desirableto have a lens protecting from retinal damage, i.e. with a low RI, we maywant to choose whether to block the effects of blue light to the circadiancircle (with a low CI) or not to (with a high CI), depending on the needs ofthe user.In order to encourage further research in this field, we released the dataand MATLAB code to compute the proposed indexes and to replicate theexperimental results.
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