Transmission spectrums and retinal blue-light irradiance values of untinted and yellow-tinted intraocular lenses

LABORATORY SCIENCE

Transmission spectrums and retinal blue-light irradiance values of untinted and yellow-tinted intraocular lenses Masaki Tanito, MD, PhD, Tsutomu Okuno, PhD, Yoshihisa Ishiba, Akihiro Ohira, MD, PhD

PURPOSE: To record and compare the spectral transmission characteristics of foldable untinted and yellow-tinted intraocular lenses (IOLs) and evaluate the protective effects against retinal damage by sunlight. SETTING: Shimane University Faculty of Medicine, Izumo, Japan. METHODS: The study evaluated 3 untinted IOLs (SA60AT, VA-60BBR, AU6 K) and 3 yellow-tinted IOLs (SN60AT, YA-60BBR, AU6 N) of 3 lens powers (C10.0 diopters [D], C20.0 D, and C30.0 D). Spectral transmittance in the wavelength range of 300 to 800 nm was measured using a spectrophotometer through 2.5 mm and 4.5 mm diameter apertures. Retinal hazard indices, including bluelight irradiance and maximum permissible exposure duration per day (tmax) for viewing sunlight, were calculated. RESULTS: The untinted IOLs completely absorbed ultraviolet (UV) light and nearly completely absorbed transmitted visible light at wavelengths longer than 440 nm. Yellow-tinted IOLs absorbed more in the blue-light range (400 to 500 nm) than untinted IOLs. The blue-light irradiance was 34.2% to 56.0% lower with the SN60AT IOL than with the SA60AT IOL, 35.2% to 48.4% lower with the YA-60BBR IOL than with the VA-60BBR IOL, and 16.8% to 22.9% lower with the AU6 N IOL than with the AU6 K IOL. Blue-light irradiance values of SN60AT and YA-60BBR IOLs decreased as the lens power increased. CONCLUSIONS: Compared with aphakic eyes, UV-blocking untinted IOLs reduced the blue-light irradiance value by 60%; yellow-tinted IOLs conferred an additional 17% to 56% reduction. The difference in lens power was significantly related to the blue-light irradiance value of some yellowtinted IOLs. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2010; 36:299–307 Q 2010 ASCRS and ESCRS

Epidemiology studies suggest a significant association between light exposure and the progression and/or severity of age-related macular degeneration (AMD)1–3 and some forms of retinitis pigmentosa.4 The role of photochemical reactions in the pathogenesis of these diseases has also been hypothesized.5 The absorption properties of the cornea and the crystalline lens help protect the retina against the hazards of light; that is, the cornea blocks ultraviolet (UV) radiation at wavelengths below about 300 nm and the crystalline lens blocks UV radiation between about 300 and 400 nm.6 The aging human crystalline lens also blocks potentially phototoxic shorter-wavelength light (blue light).7,8 The yellowing of the crystalline lens with Q 2010 ASCRS and ESCRS Published by Elsevier Inc.

aging results in a progressive increase in absorbance within the blue range of visible light.8,9 Removing the crystalline lens during cataract surgery increases the amount of optical radiation that reaches the retina,10 and implanting an intraocular lens (IOL) can compromise the ocular defenses against photic retinopathy.10 Intraocular lenses with UV radiation–blocking dye bonded to optic polymers were introduced in the early 1980s10 and are commonly implanted during cataract surgery. The transmission properties of the colorless UV radiation–blocking IOLs may not be comparable to those of the aging crystalline lens in absorbance of blue light, which causes the type of retinal phototoxicity 0886-3350/10/$dsee front matter doi:10.1016/j.jcrs.2009.08.036

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described by Ham et al.11 Results of recent epidemiology studies12–15 suggest that previous cataract surgery, aphakia, and pseudophakia are significant risk factors for late-stage AMD and that an increase in the amount of blue light reaching the retina postoperatively may be a major cause. To compensate for the reduction in the filtering of blue light by colorless UV radiation–blocking IOLs, blue light–filtering and UV radiation–filtering yellow-tinted rigid poly(methyl methacrylate) IOLs were introduced in the 1990s.16 Newer generation filtering IOLs are of foldable silicone or soft acrylic, and today there is great interest in using IOLs designed to block blue light.17 Experimental studies report the protective effects of yellow-tinted IOLs against retinal photooxidative stress in photosensitizing A2E-laden retinal pigment epithelial cells exposed to blue light18,19 and artificial sunlight20 in vitro and in rats21 and rabbits22 exposed to blue light in vivo. Although several studies5,23–27 report the transmission spectra and/or blue-light cutoff efficacy of yellow-tinted IOLs, to our knowledge a more comprehensive overview of currently available untinted and yellow-tinted IOLs with different lens powers has not been published. In the current study, we measured the spectral transmittance of 3 frequently used untinted and 3 frequently used yellow-tinted IOLs with 3 lens powers for each IOL through 2 aperture sizes. Based on the transmission data, we quantified the protective effects against possible retinal damage by sunlight. MATERIALS AND METHODS Intraocular Lenses Eighteen soft acrylic IOL models by 3 manufacturers were used, including untinted UV–blocking and yellow-tinted

IOLs with C10.0 diopter (D), C20.0 D, and C30.0 D lens powers (Figure 1). Three IOLs of each model were tested to ensure reproducibility. The models tested were the SA60AT (untinted) and SN60AT (yellow tinted) (Alcon, Inc.), the VA-60BBR (untinted) and YA-60BBR (yellow tinted) (Hoya), and the AU6 K (untinted) and AU6 N (yellow tinted) (Kowa). All IOLs had a 6.0 mm optic. Each pair of untinted IOLs and yellow-tinted IOLs was equivalent in shape and material except for lens color.

Spectral Transmittance of Intraocular Lenses The spectral transmittance of the IOLs was measured in the wavelength range of from 300 to 800 nm (1563 data points/scan) using a spectrophotometer (U-3410, Hitachi High-Technologies). An IOL was placed in a quartz cell filled with saline solution, and the quartz cell was put into the cell holder in the sample chamber of the spectrophotometer. The measurement beam was normally incident on the IOL. An accessory-integrating sphere was placed in front of the light detector in the sample chamber to collect all light refracted by the IOL, which allowed accurate measurement. The mean transmittance over the 2.5 mm and 4.5 mm diameter central areas of the IOL was measured by placing a thin stainless-steel plate with an aperture of corresponding diameter in front of the quartz cell. One hundred eight scans of 54 IOLs were performed.

Calculation of Retinal Hazardous Parameters Retinal hazard indices, including blue-light irradiance and maximum permissible exposure duration per day (tmax) for viewing sunlight, were calculated. The blue-light irradiance for small-viewing-angle light sources, such as the sun, and the tmax value were calculated for aphakic and phakic eyes based on the guidelines provided by the American Conference of Governmental Industrial Hygienists28 and the International Commission on Non-Ionizing Radiation Protection29 and for pseudophakic eyes using the percentage transmittance data for the IOLs obtained in the current study. Blue-light irradiance Eblue is defined as spectral irradiance El weighted by the blue-light hazard function B(l) of normal eyes by the equation Eblue Z

700 nm X

El  BðlÞ  Dl

(1)

lZ305 nm

Submitted: June 16, 2009. Accepted: August 7, 2009. From the Department of Ophthalmology (Tanito, Ohira), Shimane University Faculty of Medicine, Izumo, Shimane, National Institute of Occupational Safety and Health (Okuno), Kawasaki, and Technology Development Department (Ishiba), Yamamoto Kogaku Co. Ltd., Higashi-Osaka, Japan. Alcon Japan, Hoya, and Kowa, Tokyo, Japan, supplied the intraocular lenses for this study. Supported in part by the Grant-in-Aid for Young Scientist, The Ministry of Education, Culture, Sports, Science and Technology (Dr. Tanito).

or by the aphakic hazard function A(l) of aphakic eyes by the equation Eblue Z

700 nm X

El  AðlÞ  Dl

(2)

lZ305 nm

The standards do not define the blue-light irradiance of eyes with an IOL (ie, pseudophakic eyes). However, compared with aphakic eyes, in pseudophakic eyes the retina is exposed to light attenuated by the IOL; thus, it is reasonable to assume that for pseudophakic eyes Eblue Z

700 nm X

El  TðlÞ  AðlÞ  Dl

(3)

lZ305 nm

Corresponding author: Masaki Tanito, MD, PhD, Department of Ophthalmology, Shimane University Faculty of Medicine, Enya 89-1, Izumo, Shimane, 693-8501, Japan. E-mail: tanito-oph@ umin.ac.jp.

where T(l) is the spectral transmittance (dimensionless) of the IOL. For each IOL, the blue-light irradiance was calculated by substituting the measured spectral transmittance of the

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Figure 1. The IOLs analyzed in this study. In 2 of the 3 yellow-tinted IOLs (SN60AT and YA-60BBR), the yellow tinting becomes denser with increasing lens power; the yellow tinting remains virtually unchanged in the AU6 N IOL.

IOL and solar spectral irradiance in equation 3. The direct normal solar spectral irradiance defined by the American Society for Testing and Materials G159-9830 was used for solar spectral irradiance (Figure 2).28–30 For comparison, the bluelight irradiance of sunlight of normal eyes and aphakic eyes was also calculated using equation 1 and equation 2, respectively. Possible protection by the IOLs in aphakic eyes was estimated as a percentage cutoff value of solar radiation. The tmax value was obtained for each eye condition by dividing 10 mJcm2 by the obtained blue-light irradiance.28,29 Statistical analysis was performed using StatView software (version 5.0, SAS Institute Inc.) on a Macintosh personal computer (Apple Inc.).

IOLs showed nearly complete transmission (R95%) at 525 nm and longer wavelengths. The yellow-tinted IOLs showed greater absorption than the corresponding untinted IOLs in the UVB range (400 to 500 nm). The percentage transmittance values of the SN60AT, YA-60BBR, and AU6 N IOLs were 34%, 25%, and 56%, respectively, at 420 nm; 47%, 48%, and 74%, respectively, at 440 nm; 64%, 72%, and 77%, respectively, at 460 nm; and 91%, 95%, and 85%, respectively,

RESULTS Figure 3 shows the transmittance curves of the C20.0 D IOLs. The transmittance curves did not differ significantly between the 3 untinted IOLs; the curves showed nearly complete absorption in the ultraviolet B (UVB) range (320 nm) and ultraviolet A (UVA) range (320 to 400 nm) and nearly complete transmission (R98%) in the visible light spectrum at wavelengths of 440 nm and longer (Figure 3, A to C). However, the 3 yellow-tinted IOLs had unique transmittance curves. They showed complete absorption in the UVB range, with the SN60AT and AU6 N IOLs also having complete absorption in the UVA range. The YA-60BBR IOL showed transmission at the longer wavelength end of the UVA range (8% transmittance at 390 nm) (Figure 3, B). In the visible-light range, all yellow-tinted

Figure 2. Aphakic hazard function, blue-light hazard function,28,29 and solar spectral irradiance.30 The aphakic hazard function and the blue-light function show the effectiveness of optical radiation in producing photochemical retinal damage as a function of wavelength (left axis). The solar spectral irradiance shows the distribution of the radiant power of sunlight over a 37-degree tilted hemispherical surface with an air-mass coefficient of 1.5 (right axis).

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Figure 3. Transmission curves of C20.0 D IOLs measured through a 2.5 mm diameter aperture. The mean values derived from 3 independent measurements of 3 IOLs of each model were used to generate the curves.

at 500 nm. Thus, the SN60AT and YA-60BBR IOLs absorbed more light than the AU6 N IOL in the UVB region. Table 1 shows the blue-light irradiance and tmax values for blocking solar radiation in aphakic eyes and phakic eyes. Table 2 shows the blue-light irradiance values and Table 3 the tmax values of the IOLs

for blocking solar radiation. For most IOLs tested, the blue-light irradiance values were larger and the tmax values were shorter with the 4.5 mm aperture than with the 2.5 mm aperture; however, the difference in values between the 2 measurements was relatively small (!6%) and reached statistical significance for blue-light irradiance and tmax with only the C20.0 D VA-60BBR, C10.0 D SN60AT, and C30.0 D AU6 N IOLs (P!.05, all comparisons). All IOLs tested had smaller blue-light irradiance values and longer tmax values than aphakic eyes. Compared with phakic eyes, the blue-light irradiance values were larger and the tmax values were shorter for 2 of the 3 untinted IOLs (ie, SA60AT and VA-60BBR) but were almost the same or more preferable for the AU6 K IOL. However, all yellow-tinted IOLs had much smaller bluelight irradiance values (2.68 to 4.55 mW/cm2) and longer tmax values (2.20 to 3.73 seconds) than phakic eyes. Table 4 shows the percentage cutoff of solar radiation of untinted IOLs and yellow-tinted IOLs compared with the blue-light irradiance values of aphakic eyes. The percentage cutoff values for untinted IOLs ranged from 57.3% to 63.6% and of yellow-tinted IOLs, from 69.7% to 82.1%. Table 5 compares the percentage cutoff values between the untinted IOLs and the yellow-tinted IOLs. The yellow-tinted IOLs had statistically significantly lower blue-light irradiance values than the untinted IOLs (P!.0001, all comparisons); the percentage cutoff values over the untinted IOLs ranged from 34.2% to 56.0% for the SN60AT IOL, from 35.2% to 48.4% for the YA-60BBR IOL, and from 16.8% to 22.9% for the AU6 N IOL. Table 6 compares the percentage cutoff values of the 3 lens powers. The percentage cutoff did not differ significantly between the 3 lens powers for any untinted IOL. Two of the 3 yellow-tinted IOLs (SN60AT and YA-60BBR) had larger percentage cutoff values with a higher lens power than those with a lower lens power; the C30.0 D IOLs had decreased blue-light irradiance (34.6%, SN60AT, P!.0001; 22.4%, YA-60BBR, P Z .0131) compared with the corresponding C10.0 D IOLs. However, the percentage cutoff did not differ significantly between the 3 IOL powers for the AU6 N IOL (P Z .5925 to P Z .9674). Increased yellow tinting was seen with increasing lens power with the SN60AT and YA-60BBR IOLs, while the yellow tinting was virtually unchanged with the AU6 N IOL (Figure 1), explaining the reason for this discrepancy. Table 7 compares the percentage cutoff values between 3 IOL pairs. Of the untinted IOLs, the blue-light irradiance value of the AU6 K IOL was statistically significantly lower than those of the other 2 IOLs; the differences in percentage cutoff were 11.4% to 13.3% compared with the SN60AT IOL (P!.0001 to P!.0002) and 7.4% to 9.4% compared

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Table 1. Blue-light irradiance and tmax values for blocking solar radiation in aphakic eyes and phakic eyes.* Lens Status Aphakic Phakic

BLI (mW/cm2)

tmax (Seconds)

15.00 5.76

0.67 1.73

BLI Z blue-light irradiance; tmax Z maximum permissible exposure duration per day *Calculated according to the guidelines of the American Conference of Industrial Hygienists28 and the International Commission on Non-Ionizing Radiation Protection29

with the VA-60BBR IOL (P!.0001 to P!.0019). Of the yellow-tinted IOLs, the blue-light irradiance values of the SN60AT and YA-60BBR IOLs were significantly lower compared with the AU6 N IOL; the differences in the percentage cutoff values at C10.0 D, C20.0 D, and C30.0 D were 5.8%, 20.7%, and 39.7%, respectively, when the SN60AT IOL was compared with the AU6 N IOL (P!.0001 to P!.0063) and 8.7%, 16.6%, and 30.7%, respectively, when the YA-60BBR IOL was compared with the AU6 N IOL (P Z .0002 to P Z .0036). Thus, the differences increased with increasing lens powers. There was no statistically significant difference in blue-light irradiance values estimated by the percentage cutoff between the SN60AT IOL and YA-60BBR IOL in any comparison of different lens powers (P Z .0796 to P Z .4171). DISCUSSION We measured the spectral transmittance values of 54 IOLs and estimated the retinal hazard indices. This study compared currently available untinted IOLs and yellow-tinted IOLs with different lens powers using different aperture sizes and calculated the

transmission curves and blue-light irradiance and tmax values of the IOLs. Previous studies20,23,24,26,27 report the spectral transmittance values of untinted and/or yellow-tinted IOLs used in our study. The transmission characteristics in the current study were generally comparable with those reported previously. In the previous studies, however, the maximum transmission of IOLs in the longer visible light range (eg, O550 nm) sometimes peaked around 90%.16,23 The maximum transmission values reached 98% or greater for all IOLs tested in the current study. Use of the spectrophotometer equipped with an integrating sphere to collect all light refracted by the IOL may have allowed us to obtain higher transmission values than those reported previously. We found that transmittal of UVA at the longer wavelength end was greater with the YA-60BBR IOL than with the VA-60BBR IOL (8.0% versus !0.1% transmittance at 390 nm), suggesting that the YA-60BBR IOL has less UV–blocking dye than the VA-60BBR IOL or that a different UV–blocking dye is used in each IOL. Although the reason the YA-60BBR IOL had higher transmittance of UVA has to be clarified, the retinal protection afforded by this IOL would increase if the efficacy of longer UVA absorption were at the same level as that of the VA-60BBR IOL. For most IOLs tested, the blue-light irradiance values were larger and the tmax values were shorter with the 4.5 mm aperture than with the 2.5 mm aperture; however, the difference in values between the 2 apertures was relatively small (!6%), suggesting that the difference in aperture size is not likely to significantly affect IOL transmission characteristics in experimental settings, such as the current study. The coefficient of variation for the 3 independent measurements of each model was calculated to be,

Table 2. Blue-light irradiance values for blocking solar radiation. Mean Blue-Light Irradiance (mW/cm2) G SD 2.5 mm Aperture Diameter IOL Nontined SA60AT VA-60BBR AU6K Yellow tinted SN60AT YA-60BBR AU6N

4.5 mm Aperture Diameter

C10.0 D

C20.0 D

C30.0 D

C10.0 D

C20.0 D

C30.0 D

6.41 G 0.16 6.16 G 0.02 5.66 G 0.04

6.27 G 0.02 6.05 G 0.00 5.63 G 0.03

6.11 G 0.04 5.99 G 0.04 5.48 G 0.11

6.50 G 0.01 6.17 G 0.08 5.69 G 0.07

6.31 G 0.09 6.12 G 0.02* 5.69 G 0.06

6.17 G 0.03 5.98 G 0.07 5.45 G 0.01

4.11 G 0.09 3.98 G 0.06 4.36 G 0.01

3.52 G 0.08 3.70 G 0.18 4.44 G 0.19

2.69 G 0.21 3.09 G 0.22 4.46 G 0.02

4.28 G 0.08* 4.00 G 0.14 4.43 G 0.05

3.62 G 0.10 3.82 G 0.04 4.51 G 0.04

2.85 G 0.18 3.15 G 0.06 4.55 G 0.04*

IOL Z intraocular lens *P!.05 between measurements through 2.5 mm and 4.5 mm aperture diameters with each IOL (paired t test)

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Table 3. The tmax values for blocking solar radiation. Mean tmax (Seconds)* G SD 2.5 mm Aperture Diameter IOL Untinted SA60AT VA-60BBR AU6K Yellow tinted SN60AT YA-60BBR AU6N

4.5 mm Aperture Diameter

C10.0 D

C20.0 D

C30.0 D

C10.0 D

C20.0 D

C30.0 D

1.56 G 0.05 1.62 G 0.00 1.77 G 0.01

1.59 G 0.00 1.65 G 0.00 1.78 G 0.01

1.64 G 0.01 1.67 G 0.01 1.83 G 0.04

1.54 G 0.00 1.62 G 0.02 1.76 G 0.02

1.58 G 0.02 1.63 G 0.01† 1.76 G 0.02

1.62 G 0.01 1.67 G 0.02 1.83 G 0.00

2.44 G 0.05 2.51 G 0.04 2.29 G 0.01

2.85 G 0.06 2.71 G 0.13 2.26 G 0.10

3.73 G 0.29 3.24 G 0.22 2.24 G 0.01

2.34 G 0.04† 2.50 G 0.80 2.26 G 0.03

2.77 G 0.07 2.62 G 0.03 2.22 G 0.02

3.52 G 0.22 3.17 G 0.06 2.20 G 0.02†

IOL Z intraocular lens; tmax Z maximum permissible exposure duration per day *Mean of 3 independent measurements † P!.05 between measurements through 2.5 mm and 4.5 mm aperture diameters with each IOL (paired t test)

at most, 7.8% (for C30.0 D SN60AT) and to be 2.0% or less for most IOL models, suggesting good reproducibility of measurements in the current study and excellent uniformity of products among the currently available IOLs. The blue-light irradiance values of any of the untinted IOLs were approximately 60% lower than the aphakic eye values. Thus, implantation of a UV–filtering IOL could provide greater retinal protection from solar radiation, as previously suggested.31,32 The yellow-tinted IOLs had greater reductions in blue-light irradiance than the untinted IOLs. The blue-light irradiance value of the SN60AT IOL decreased by 34.2% to 56.0% compared with the SA60AT IOL, of the YA-60BBR IOL by 35.2% to 48.4% compared with the VA-60BBR IOL, and of the AU6 N IOL by 6.8% to 22.9% compared with the AU6 K IOL. In the SN60AT IOL and YA-60BBR

IOL, the blue-light irradiance values differed significantly between lens powers; that is, more blue light was absorbed with higher lens powers due to increased lens thickness and yellow tinting. Thus, the effect of the difference in lens power must be considered when these IOLs are analyzed. However, the efficacy of the blue light–filtering AU6 N IOL did not differ significantly between lens powers, suggesting that the composition of the blue light–filtering dye could be adjusted for each lens power to keep the constant yellow density in this lens. Although previous evidence has suggested but has not confirmed that blue light is a risk factor for AMD,24,33 the yellowtinted IOL could protect the retina from phototoxicity if the blue-light theory is valid in the pathogenesis of retinal degeneration. One of the earliest studies16 suggested that contrast sensitivity improves in photopic and mesopic

Table 4. Percentage cutoff of solar radiation by untinted IOLs and yellow-tinted IOLs compared with blue-light irradiance values of aphakic eyes. Percentage Cutoff* 2.5 mm Aperture Diameter IOL Untinted SA60AT VA-60BBR AU6K Yellow tinted SN60AT YA-60BBR AU6N

4.5 mm Aperture Diameter

C10.0 D

C20.0 D

C30.0 D

C10.0 D

C20.0 D

C30.0 D

57.3 58.9 62.3

58.2 59.7 62.5

59.3 60.1 63.5

56.6 58.8 62.1

57.9 59.2 62.1

58.9 60.1 63.6

72.6 73.4 70.9

76.6 75.4 70.4

82.1 79.4 70.3

71.5 73.3 70.5

75.9 74.6 70.0

81.0 79.0 69.7

IOL Z intraocular lens Percentage cutoff by IOL Z (BLI of aphakic eye  BLI of IOL)/BLI of aphakic eye  100; where BLI is blue-light irradiance of aphakic eye (15.0 mW/cm2)

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Table 5. Comparison of percentage cutoff of solar radiation between yellow-tinted IOLs and untinted IOLs. 2.5 mm Aperture Diameter C10.0 D IOL Comparison

4.5 mm Aperture Diameter

C20.0 D

C30.0 D

C10.0 D

C20.0 D

C30.0 D

% Cutoff % Cutoff % Cutoff % Cutoff % Cutoff % Cutoff by Tinted P by Tinted P by Tinted P by Tinted P by Tinted P by Tinted P IOL* Value† IOL* Value† IOL* Value† IOL* Value† IOL* Value† IOL* Value†

SA60AT vs SN60AT VA-60BBR vs YA-60BBR AU6K vs AU6N

35.90

!.0001

44.0

!.0001

56.0

!.0001

34.2

!.0001

42.7

!.0001

53.8

!.0001

35.4

!.0001

38.9

!.0001

48.4

!.0001

35.2

!.0001

37.7

!.0001

47.3

!.0001

22.9

!.0001

21.2

!.0001

18.6

!.0001

22.2

!.0001

20.8

!.0001

16.8

!.0001

IOL Z intraocular lens; Tinted IOL Z yellow-tinted intraocular lens *Percent cutoff by yellow-tinted IOL Z (BLI of untinted IOL  BLI of yellow IOL)/BLI of untinted IOL  100; where BLI is blue-light irradiance † Calculated using the unpaired t test between each pair of untinted IOL and yellow-tinted IOL (n Z 3 of each IOL)

Table 6. Comparisons of percentage cutoff of solar radiation by IOL power. Untinted IOLs SA60AT Power Comparison

Yellow-Tinted IOLs

VA-60BBR

AU6K

SN60AT

YA-60BBR

AU6N

% Cutoff*

P Value†

% Cutoff*

P Value†

% Cutoff*

P Value†

% Cutoff*

P Value†

% Cutoff*

P Value†

% Cutoff*

P Value†

2.2 2.7 4.8

0.2746 0.1732 0.0207

1.9 0.9 2.8

0.0060 0.0860 0.0006

0.5 2.7 3.3

0.8268 0.0795 0.0378

14.4 23.5 34.6

0.0055 0.0010 !0.0001

7.2 16.4 22.4

0.1928 0.0019 0.0131

1.7 0.5 2.2

0.7318 0.9674 0.5925

C10.0 D vs C20.0 Dz C20.0 D vs C30.0 Dx C10.0 D vs C30.0 D{

IOLs Z intraocular lenses *Percentage cutoff Z (BLI of IOL A  BLI of IOL B)/BLI of IOL A  100; where BLI is blue-light irradiance measured through the 2.5 mm diameter aperture † Calculated between IOLs with 3 different lens powers using 1-way analysis of variance followed by Scheffe´ post hoc tests (n Z 3 of each IOL. z Comparisons between C10.0 D lens (IOL A) and C20.0 D lens (IOL B) x Comparisons between C20.0 D lens (IOL A) and C30.0 D lens (IOL B) { Comparisons between C10.0 D lens (IOL A) and C30.0 D lens (IOL B)

Table 7. Comparisons of percentage cutoff of solar radiation by 3 untinted IOLs and 3 yellow-tinted IOLs. Untinted IOLs C10.0 D Pair Comparison Alcon vs Hoyaz Hoya vs Kowax Alcon vs Kowa{

C20.0 D

Yellow-Tinted IOLs C30.0 D

C10.0 D

C20.0 D

C30.0 D

% Cutoff*

P Value†

% Cutoff*

P Value†

% Cutoff*

P Value†

% Cutoff*

P Value†

% Cutoff*

P Value†

% Cutoff*

P Value †

4.0 8.9 13.3

.0478 .0019 .0002

3.7 7.4 11.4

!.0001 !.0001 !.0001

1.9 9.4 11.5

.2139 .0003 .0001

3.1 8.7 5.8

.1216 .0008 .0063

4.9 16.6 20.7

.4171 .0036 .0011

13.0 30.7 39.7

.0796 .0002 !.0001

IOLs Z intraocular lenses *Percentage cutoff Z (BLI of IOL A  BLI of IOL B)/BLI of IOL A  100; where BLI is blue-light irradiance measured through the 2.5 mm diameter aperture † Calculated between 3 IOLs (SA60AT, VA-60BBR, and AU6K for untinted IOL comparison; SN60AT, YA-60BBR, and AU6N for yellow-tinted IOL comparison) using 1-way analysis of variance followed by Scheffe´ post hoc tests (n Z 3 of each IOL) z Comparisons between SA60AT (IOL B) and VA-60BBR (IOL A) for untinted IOLs and between SN60AT (IOL B) and YA-60-BBR (IOL A) for yellow-tinted IOLs x Comparisons between VA-60BBR (IOL B) and AU6K (IOL A) for untinted IOLs and between YA-60-BBR (IOL B) and AU6N (IOL A) for yellow-tinted IOLs { Comparisons between SA60AT (IOL B) and AU6K (IOL A) for untinted IOLs and between SN60AT (IOL B) and AU6N (IOL A) for yellow-tinted IOLs

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conditions and that glare decreases when yellowtinted IOLs are used versus when untinted IOLs are used. A more recent study34 found that the visual function in eyes with a yellow-tinted IOL did not differ significantly from that in eyes with untinted IOLs in terms of photopic and mesopic contrast visual acuity with and without a glare source. Other recent studies report decreased blue color perception35 or photoreception24 with yellow-tinted IOLs. Thus, a large-scale clinical trial is needed to evaluate the effect of blue– blocking filters on AMD development and progression and the best balance of filtering spectrums for visual function. In the current study, retinal hazards in phakic, aphakic, and pseudophakic eyes were estimated by blue-light irradiance values, as in previous reports.25,36 The blue-light irradiance value is characterized by an action spectrum called the hazard function, which represents the relative weight of each wavelength in terms of the potential damage it can cause to the retina. The merit of using the blue-light irradiance value to assess retinal hazard is that the value permits a direct comparison of different radiation sources to determine the relative effectiveness or the individual potential hazards.25 The hazard function on which to base the blue-light irradiance value was derived from data from relatively young monkey eyes.37–39 Yellowing of the crystalline lens with age results in a progressive increase in the absorption of blue light.8,9 Although the current study showed much smaller blue-light irradiance values and longer tmax values for the 3 yellowtinted IOLs than for young phakic monkey eyes, this may not be directly applicable to human eyes with an IOL at older ages. Some studies5,24 recommend that pseudophakic persons should wear sunglasses in bright light because yellow-tinted IOLs provide less photoprotection than the middle-aged crystalline lens. More recently, a new approach to evaluate retinal protection was proposed; the technique uses spectral filtering to protect against photooxidative stress with the functions of age-related yellowing of the crystalline lens and A2E accumulation.5,27 Thus, the transmission results in the current study could be applicable to new approaches in the near future. In the current study, we measured the spectral transmittance of currently available untinted and yellow-tinted IOLs and calculated the blue-light irradiance values and tmax values to estimate the possible retinal hazard from sunlight in pseudophakic eyes. Compared with aphakic eyes, UV–blocking untinted IOLs conferred a 60% reduction in the blue-light irradiance value and yellow-tinted IOLs conferred further reductions in the blue-light irradiance value. The difference in aperture size did not greatly affect measurements of spectral transmittance. The difference in the

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