- Email: [email protected]
Ultraviolet radiation absorption of intraocular lenses
Ultraviolet Radiation Absorption of Intraocular Lenses Thomas Laube, MD,1 Horst Apel, PhD,2 Hans-Reinhard Koch, MD3 Objectives: To record and compare the spectral transmittance curves of intraocular lenses (IOLs) made out of polymethyl methacrylate (PMMA), acrylic, hydrogel, and silicone from different manufacturers; to evaluate their ultraviolet radiation absorption capacities; and to contrast the recorded transmittance curves with that of the natural lens. Design: Experimental study. Methods: We studied 17 different 21-diopter IOLs. A high-performance spectrophotometer with a diffuse transmittance accessory was employed to measure the transmittance of wavelengths from 200 nm to 800 nm through a 1.5-mm aperture. Main Outcome Measures: Transmittance percentage and 10% transmittance cutoff wavelength. Results: All studied IOLs offered good ultraviolet radiation protection in the ultraviolet C (200 –280 nm) and ultraviolet B (280 –315 nm) ranges. A number of silicone, PMMA, and acrylic lenses showed different and, at times, only low degrees of absorption in the ultraviolet A (315– 400 nm) range. Conclusions: Intraocular lenses of different compositions have ultraviolet radiation absorption characteristics different from that of the crystalline lens. Ophthalmology 2004;111:880 – 885 © 2004 by the American Academy of Ophthalmology.
The different tissues of the eye absorb incoming ultraviolet radiation at varying degrees.1 Although ultraviolet C rays (200 –280 nm) are normally blocked by stratospheric ozone, holes that have formed in the protective ozone layer allow increased levels of ultraviolet C radiation to reach the earth’s surface, in addition to ultraviolet B (280 –315 nm) and ultraviolet A (315– 400 nm) radiation.2 A large portion of the ultraviolet B rays that enter the eye is absorbed by the cornea and has been shown to elicit structural damage to the corneal epithelial surface and stromal cells.3–5 Although the cornea, vitreous, and aqueous humor transmit wavelengths of 300 nm, the crystalline lens absorbs a large portion of the ultraviolet B and ultraviolet A spectra, up to 390 nm for the young eye and up to 400 nm in a 63-year-old lens.1 Chronic ultraviolet B exposure to the crystalline lens is well known to be associated with cortical cataract formation.6 –10 Numerous studies support these theories and advocate the further use of tinted contact lenses, sunglasses, or intraocular lenses (IOLs) with chromophore components to block Originally received: January 7, 2003. Accepted: August 25, 2003.
Manuscript no. 230015.
1
Department of Ophthalmology, Essen University, Essen, Germany. 2 Varian GmbH, Darmstadt, Germany. 3 Klinik Dardenne, Bonn-Bad Godesberg, Germany. First results partly presented as a poster at: American Academy of Ophthalmology Annual Meeting, October 26 –29, 1997; San Francisco. Drs Laube and Koch have no financial interest in any product mentioned in this article. Dr Apel was a collaborator with Varian GmbH until 2001. Correspondence to Thomas Laube, MD, Department of Ophthalmology, University of Essen, Hufelandstr. 55, 45147 Essen, Germany. E-mail: [email protected].
880
© 2004 by the American Academy of Ophthalmology Published by Elsevier Inc.
out damaging ultraviolet rays, especially when considering the state of reduced ozone protection, longer life expectancies (i.e., longer ultraviolet radiation exposure), and increased lifestyle-associated sun exposure.2,11–13 When the natural lens is removed and replaced by an IOL, however, the absorptive characteristics of an artificial lens may not be enough to block reliably the potentially harmful ultraviolet rays from reaching the retina. Although the precise effect of ultraviolet radiation on the retina is a subject of much debate, most would agree that the risk of ultraviolet radiation damage to the aphakic eye is dramatically increased. Both older and more recent investigations of chronic ultraviolet radiation exposure show evidence of reduced photoreceptor sensitivity and an association with cystoid macular edema and age-related macular degeneration.14 –20 Most authors therefore would agree that lenses with maximal ultraviolet radiation absorption should be implanted to protect this sensitive ocular layer. Although a number of investigations have substantiated the photostability of certain IOL materials and the integrity of the ultraviolet radiation–absorptive capacities of specific IOLs,15,21–25 a more comprehensive overview is lacking. The present comparative study was designed to illustrate the differences and similarities in the ultraviolet radiation absorption properties of IOLs of different compositions and to allow surgeons to contrast ultraviolet radiation transmission percentages of lenses made of like substances from different lens manufacturers. The lenses studied include currently used silicone, polymethyl methacrylate (PMMA), hydrophobic and hydrophilic acrylic, and hydrogel IOLs. ISSN 0161-6420/04/$–see front matter doi:10.1016/j.ophtha.2003.08.031
Laube et al 䡠 Ultraviolet Radiation Absorption of IOLs Table 1. Intraocular Lens (IOL) Manufacturers Manufacturer
Material
Name of Lens
Alcon IOLTECH Tomey Corneal Storz Mentor Dr. Schmidt Ophtec Pharmacia Pharmacia Pharmacia Allergan Chiron IOVISION Pharmacia Pharmacia Staar
Acrylic Acrylic Acrylic Acrylic Hydrogel HEMA/MMA PMMA PMMA PMMA PMMA ⫹ heparin PMMA Silicone Silicone Silicone Silicone Silicone Silicone
Acrysof MA60BM Acrystal Eyecryl HD Acrygel ACR6D Hydroview H60M MemoryLens U940A MSF700/0 287 CeeOn722A CeeOn811C CeeOn811E SI40NB C31UB WS127 CeeOn911A CeeOn920 AQ2010V
HEMA ⫽ hydroxyethyl methacrylate; MMA ⫽ methyl methacrylate; PMMA ⫽ polymethyl methacrylate.
fects (such as stray light effects) could be avoided. The exit port of the sphere was covered with a standard Teflon (DuPont, Wilmington, DE) cup. A standardized lens power of 21 diopters was used for all lenses to avoid inconsistencies in light beam geometry and to ensure that all of the transmitted light reached the photomultiplier detector. The aperture mask was set at 1.5 mm (12⫻2 mm) to limit the standard beam geometry to the sample diameter and thereby also ensure the conformity of measurements. Effective ultraviolet radiation– blocking IOLs were defined as those lenses that transmitted no more than 10% of the incoming ultraviolet radiation, comparable to the ultraviolet radiation transmittance of the natural lens. A bar graph comparing the ultraviolet radiation cutoff wavelength of each lens model was compiled. The Varian Cary 5G UV/Vis/NIR spectrophotometer measured and recorded the transmittance of electromagnetic radiation of wavelength values between 200 and 800 nm, with a signal bandwidth of 1 nm, a stepwidth of 1 nm, and a signal average time of 0.1 seconds. A baseline scan without a mounted IOL was performed, through the 1.5-mm aperture, at wavelength values from 200 to 800 nm. Spectral transmittance curves plotted the percentage of ultraviolet radiation transmittance at different wavelengths within the ultraviolet radiation spectrum for each lens within a specific material group.
Materials and Methods The ultraviolet radiation absorption properties of 17 IOLs made by 13 different manufacturers were tested (Table 1). All lens types investigated were routinely implanted at our clinic. The IOLs were made of silicone (6 types), PMMA (6 types), hydrophobic and hydrophilic acrylic (4 types), and hydrogel (1 type). Three lenses of each type were tested. A high-performance computer-controlled spectrophotometer (Varian Cary 5G UV/Vis/NIR, Varian, Darmstadt, Germany) was used with a diffuse transmittance accessory (Ulbricht sphere) to determine the ultraviolet radiation absorbance of the lenses. The sample lenses were placed directly in front of the integrating Ulbricht sphere entrance port, between the aperture mask and the sphere (transmission position). In this position, unwanted ef-
Results All lenses showed nearly baseline ultraviolet radiation transmittance in the ultraviolet C (200 –280 nm) and ultraviolet B (280 – 320 nm) ranges (Figs 1– 4). With few exceptions, the IOLs also provided good filtering properties in the ultraviolet A range (wavelengths from 320 to 400 nm), transmitting ⬍10% of incoming ultraviolet radiation. Lenses of identical types showed no differences. Two of the 6 silicone lenses displayed an ultraviolet radiation wavelength cutoff between 340 nm and 350 nm, at which ⬎10% of ultraviolet radiation was transmitted (Fig 1). Three of 4 acrylic lenses, 1 hydrogel lens, and 1 PMMA lens revealed higher ultraviolet A transmittance at 375 nm (Figs 2– 4). Most lenses showed
Figure 1. Ultraviolet radiation transmittance curves of silicone intraocular lenses. UV-A ⫽ ultraviolet A; UV-B ⫽ ultraviolet B; UV-C ⫽ ultraviolet C.
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Ophthalmology Volume 111, Number 5, May 2004
Figure 2. Ultraviolet radiation transmittance curves of polymethyl methacrylate intraocular lenses. UV-A ⫽ ultraviolet A; UV-B ⫽ ultraviolet B; UV-C ⫽ ultraviolet C.
ⱖ90% transmittance in the visible light spectrum between 400 and 800 nm. Figure 5 compares the ultraviolet radiation cutoff wavelength of each lens model investigated. The order of cutoff wavelengths of 10% transmittance was not associated with the lens material. Both the highest and the lowest ultraviolet radiation cutoff wavelengths are reached by silicone IOLs. All lenses investigated prevent transmission of ultraviolet B and ultraviolet C radiation. Within the ultraviolet A spectrum the ultraviolet radiation cutoff wavelength of 10% ranges from approximately 350 to 400 nm (Fig 5). The best ultraviolet radiation protection is provided by 2 foldable lens types, the SI40NB silicone lens (Allergan, Irvine, CA) and the Acrysof hydrophobic acrylic lens MA60BM (Alcon, Inc., Fort Worth, TX) (Fig 5). These 2 lenses best approx-
imate the ultraviolet radiation– blocking capacity of the crystalline lens (Fig 6).
Discussion The study results provide a basis for the practical comparison of ultraviolet radiation transmittance of commonly implanted IOLs. The ultraviolet radiation cutoff wavelengths of all 17 lenses documented in Figure 5 reveal that some lenses allow ⬎10% transmittance at wavelengths within the ultraviolet radiation spectral range. In the present
Figure 3. Ultraviolet radiation transmittance curves of acrylic intraocular lenses. UV-A ⫽ ultraviolet A; UV-B ⫽ ultraviolet B; UV-C ⫽ ultraviolet C.
882
Laube et al 䡠 Ultraviolet Radiation Absorption of IOLs
Figure 4. Ultraviolet radiation transmittance curves of hydrogel (Hydroview, Bausch & Lomb, Rochester, NY) and Memory (CIBA Vision Corp., Duluth, GA) intraocular lenses. UV-A ⫽ ultraviolet A; UV-B ⫽ ultraviolet B; UV-C ⫽ ultraviolet C.
study, a cutoff rate of 10% ultraviolet radiation transmittance was defined as a value that ensures efficient protection and allows differentiation of the measured transmission curves. The overall outcome shows that some of the currently
used IOLs provide less ultraviolet radiation protection than other lens types. The most striking absorption differences were noted within the near ultraviolet radiation wavelength (ultraviolet A) range (320 – 400 nm). The multiformity of the results implies that lenses produced by different manu-
Figure 5. Ultraviolet radiation cutoff wavelength of 10% transmittance for 21 diopters. UV-A ⫽ ultraviolet A; UV-B ⫽ ultraviolet B; UV-C ⫽ ultraviolet C.
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Ophthalmology Volume 111, Number 5, May 2004
Figure 6. Ultraviolet radiation transmittance curves of the eye. UV-A ⫽ ultraviolet A; UV-B ⫽ ultraviolet B; UV-C ⫽ ultraviolet C. Modified after Boettner EA, Wolter JR. Transmission of the ocular media. Invest Ophthalmol 1962;1:776 – 83.
facturers out of the same materials can have different basic properties. Some of the silicone lenses in particular showed very little ultraviolet radiation protection, particularly in the upper ultraviolet radiation spectrum. It is interesting to note that, of all IOLs under investigation, 2 foldable lenses provided the best ultraviolet radiation protection, thus approaching the ultraviolet radiation– blocking capacity of the crystalline lens given by Boettner and Wolter1 at best. Unlike the crystalline lens, which has a 10% cutoff rate at 400 nm, increases transmittance to 90% at 450 nm, then gradually transmits wavelengths between 450 and 800 nm, however, the tested IOLs revealed a steep rise in the transmittance of wavelengths beyond 400 nm. As the visible light spectrum ranges from 400 to 700 nm, progressing from high-energy blue light to green, yellow, and red light, this occurrence may account for the more intensive subjective sensitivity to blue. Wavelengths beyond 700 nm are perceived as heat (infrared) and not seen. The cornea, aqueous humor, and vitreous humor are largely transparent between 300 and 400 nm, allowing these spectra to pass freely into the eye, whereas the natural crystalline lens effectively absorbs the ultraviolet A range and shields the retina from the potentially toxic effects of these wavelengths (Fig 6).1 As both ultraviolet B radiation exposure and ultraviolet A radiation exposure have been implicated in retinal damage, it seems desirable for manufacturers and surgeons alike to seek optimal protection within the ultraviolet radiation range by using discretion in their choice of lenses and lens materials. Patients implanted with IOLs that are less effective ultraviolet radiation absorbers might consider the use of ultraviolet A–absorbing spectacle glasses.
884
References 1. Boettner EA, Wolter JR. Transmission of the ocular media. Invest Ophthalmol 1962;1:776 – 83. 2. Bergmanson JP, Sheldon TM. Ultraviolet radiation revisited. CLAO J 1997;23:196 –204. 3. Clarke SM, Doughty MJ, Cullen AP. Acute effects of ultraviolet-B irradiation on the corneal surface of the pigmented rabbit studied by quantitative scanning electron microscopy. Acta Ophthalmol (Copenh) 1990;68:639 –50. 4. Cullen AP, Chou BR, Hall MG, Jany SE. Ultraviolet-B damages corneal endothelium. Am J Optom Physiol Opt 1984;61: 473– 8. 5. Pitts DG, Cullen AP, Hacker PD. Ocular effects of ultraviolet radiation from 295 to 365 nm. Invest Ophthalmol Vis Sci 1977;16:932–9. 6. Hiller R, Giacometti L, Yuen K. Sunlight and cataract: an epidemiologic investigation. Am J Epidemiol 1977;105: 450 –9. 7. Katoh N, Jonasson F, Sasaki H, et al, Reykjavik Eye Study Group. Cortical lens opacification in Iceland. Risk factors analysis—Reykjavik Eye Study. Acta Ophthalmol Scand 2001;79:154 –9. 8. Klein BE, Klein R, Linton KL. Prevalence of age-related lens opacities in a population. The Beaver Dam Eye Study. Ophthalmology 1992;99:546 –52. 9. West S. Ocular ultraviolet B exposure and lens opacities: a review. J Epidemiol 1999;9(suppl):S97–101. 10. Taylor HR. Ocular effects of UV-B exposure. Doc Ophthalmol 1995;88:285–93. 11. Lindstrom RL, Doddi N. Ultraviolet light absorption in intraocular lenses. J Cataract Refract Surg 1986;12:285–9. 12. Hickson-Curran SB, Nason RJ, Becherer PD, et al. Clinical evaluation of Acuvue contact lenses with UV blocking characteristics. Optom Vis Sci 1997;74:632– 8. 13. Clausen M, Meyer C. Wie gut schu¨tzen Sonnenbrillen vor scha¨dlichen UV-Strahlen? [How well do sunglasses protect
Laube et al 䡠 Ultraviolet Radiation Absorption of IOLs
14. 15. 16. 17.
18. 19. 20.
from damaging UV rays?]. Klin Monatsbl Augenheilkd 1998; 212:aA9 –13. Cruickshanks KJ, Klein R, Klein BE, Nondahl DM. Sunlight and the 5-year incidence of early age-related maculopathy: the Beaver Dam Eye Study. Arch Ophthalmol 2001;119:246 –50. Kraff MC, Sanders DR, Jampol LM, Lieberman HL. Effect of an ultraviolet-filtering intraocular lens on cystoid macular edema. Ophthalmology 1985;92:366 –9. Pitts DG, Bergmanson JP. The UV problem: have the rules changed? J Am Optom Assoc 1989;60:420 – 4. Rapp LM, Fisher PL, Dhinsda HS. Reduced rate of rod outer segment disk synthesis in photoreceptor cells recovering from UVA light damage. Invest Ophthalmol Vis Sci 1994;35: 3540 – 8. Taylor HR, West S, Mun˜oz B, et al. The long-term effects of visible light on the eye. Arch Ophthalmol 1992;110:99 –104. Zuclich JA. Ultraviolet-induced photochemical damage in ocular tissues. Health Phys 1989;56:671– 82. Roberts JE. Ocular phototoxicity. J Photochem Photobiol B 2001;64:136 – 43.
21. Ellerin BE, Nisce LZ, Roberts CW, et al. The effect of ionizing radiation on intraocular lenses. Int J Radiat Oncol Biol Phys 2001;51:184 –208. 22. Francese JE, Pham L, Christ FR. Accelerated hydrolytic and ultraviolet aging studies on SI-18NB and SI-20NB silicone lenses. J Cataract Refract Surg 1992;18:402–5. 23. Schmidbauer JM, Werner L, Apple DJ, et al. Postoperative ¨ bersicht [PostTru¨bung von Hinterkammerlinsen— eine U operative opacification of posterior chamber intraocular lenses—a review]. Klin Monatsbl Augenheilkd 2001;218: 586 –94. 24. Yang S, Makker H, Christ FR. Accelerated ultraviolet aging of intraocular lens optic materials: a 50 year simulation. J Cataract Refract Surg 1997;23:940 –7. 25. Vola JL, Petrakian JP, Mardrus R. Phototoxicite´ des ultraviolets sur le cristallin et la re´tine. Etude de la transmission optique d’implants traite´s et non traite´s anti-U.V. [Phototoxicity of ultraviolet rays on crystalline lens and retina. Study of the optic transmission of implants with or without anti-UV treatment]. J Fr Ophtalmol 1988;11:277– 83.
885
The different tissues of the eye absorb incoming ultraviolet radiation at varying degrees.1 Although ultraviolet C rays (200 –280 nm) are normally blocked by stratospheric ozone, holes that have formed in the protective ozone layer allow increased levels of ultraviolet C radiation to reach the earth’s surface, in addition to ultraviolet B (280 –315 nm) and ultraviolet A (315– 400 nm) radiation.2 A large portion of the ultraviolet B rays that enter the eye is absorbed by the cornea and has been shown to elicit structural damage to the corneal epithelial surface and stromal cells.3–5 Although the cornea, vitreous, and aqueous humor transmit wavelengths of 300 nm, the crystalline lens absorbs a large portion of the ultraviolet B and ultraviolet A spectra, up to 390 nm for the young eye and up to 400 nm in a 63-year-old lens.1 Chronic ultraviolet B exposure to the crystalline lens is well known to be associated with cortical cataract formation.6 –10 Numerous studies support these theories and advocate the further use of tinted contact lenses, sunglasses, or intraocular lenses (IOLs) with chromophore components to block Originally received: January 7, 2003. Accepted: August 25, 2003.
Manuscript no. 230015.
1
Department of Ophthalmology, Essen University, Essen, Germany. 2 Varian GmbH, Darmstadt, Germany. 3 Klinik Dardenne, Bonn-Bad Godesberg, Germany. First results partly presented as a poster at: American Academy of Ophthalmology Annual Meeting, October 26 –29, 1997; San Francisco. Drs Laube and Koch have no financial interest in any product mentioned in this article. Dr Apel was a collaborator with Varian GmbH until 2001. Correspondence to Thomas Laube, MD, Department of Ophthalmology, University of Essen, Hufelandstr. 55, 45147 Essen, Germany. E-mail: [email protected].
880
© 2004 by the American Academy of Ophthalmology Published by Elsevier Inc.
out damaging ultraviolet rays, especially when considering the state of reduced ozone protection, longer life expectancies (i.e., longer ultraviolet radiation exposure), and increased lifestyle-associated sun exposure.2,11–13 When the natural lens is removed and replaced by an IOL, however, the absorptive characteristics of an artificial lens may not be enough to block reliably the potentially harmful ultraviolet rays from reaching the retina. Although the precise effect of ultraviolet radiation on the retina is a subject of much debate, most would agree that the risk of ultraviolet radiation damage to the aphakic eye is dramatically increased. Both older and more recent investigations of chronic ultraviolet radiation exposure show evidence of reduced photoreceptor sensitivity and an association with cystoid macular edema and age-related macular degeneration.14 –20 Most authors therefore would agree that lenses with maximal ultraviolet radiation absorption should be implanted to protect this sensitive ocular layer. Although a number of investigations have substantiated the photostability of certain IOL materials and the integrity of the ultraviolet radiation–absorptive capacities of specific IOLs,15,21–25 a more comprehensive overview is lacking. The present comparative study was designed to illustrate the differences and similarities in the ultraviolet radiation absorption properties of IOLs of different compositions and to allow surgeons to contrast ultraviolet radiation transmission percentages of lenses made of like substances from different lens manufacturers. The lenses studied include currently used silicone, polymethyl methacrylate (PMMA), hydrophobic and hydrophilic acrylic, and hydrogel IOLs. ISSN 0161-6420/04/$–see front matter doi:10.1016/j.ophtha.2003.08.031
Laube et al 䡠 Ultraviolet Radiation Absorption of IOLs Table 1. Intraocular Lens (IOL) Manufacturers Manufacturer
Material
Name of Lens
Alcon IOLTECH Tomey Corneal Storz Mentor Dr. Schmidt Ophtec Pharmacia Pharmacia Pharmacia Allergan Chiron IOVISION Pharmacia Pharmacia Staar
Acrylic Acrylic Acrylic Acrylic Hydrogel HEMA/MMA PMMA PMMA PMMA PMMA ⫹ heparin PMMA Silicone Silicone Silicone Silicone Silicone Silicone
Acrysof MA60BM Acrystal Eyecryl HD Acrygel ACR6D Hydroview H60M MemoryLens U940A MSF700/0 287 CeeOn722A CeeOn811C CeeOn811E SI40NB C31UB WS127 CeeOn911A CeeOn920 AQ2010V
HEMA ⫽ hydroxyethyl methacrylate; MMA ⫽ methyl methacrylate; PMMA ⫽ polymethyl methacrylate.
fects (such as stray light effects) could be avoided. The exit port of the sphere was covered with a standard Teflon (DuPont, Wilmington, DE) cup. A standardized lens power of 21 diopters was used for all lenses to avoid inconsistencies in light beam geometry and to ensure that all of the transmitted light reached the photomultiplier detector. The aperture mask was set at 1.5 mm (12⫻2 mm) to limit the standard beam geometry to the sample diameter and thereby also ensure the conformity of measurements. Effective ultraviolet radiation– blocking IOLs were defined as those lenses that transmitted no more than 10% of the incoming ultraviolet radiation, comparable to the ultraviolet radiation transmittance of the natural lens. A bar graph comparing the ultraviolet radiation cutoff wavelength of each lens model was compiled. The Varian Cary 5G UV/Vis/NIR spectrophotometer measured and recorded the transmittance of electromagnetic radiation of wavelength values between 200 and 800 nm, with a signal bandwidth of 1 nm, a stepwidth of 1 nm, and a signal average time of 0.1 seconds. A baseline scan without a mounted IOL was performed, through the 1.5-mm aperture, at wavelength values from 200 to 800 nm. Spectral transmittance curves plotted the percentage of ultraviolet radiation transmittance at different wavelengths within the ultraviolet radiation spectrum for each lens within a specific material group.
Materials and Methods The ultraviolet radiation absorption properties of 17 IOLs made by 13 different manufacturers were tested (Table 1). All lens types investigated were routinely implanted at our clinic. The IOLs were made of silicone (6 types), PMMA (6 types), hydrophobic and hydrophilic acrylic (4 types), and hydrogel (1 type). Three lenses of each type were tested. A high-performance computer-controlled spectrophotometer (Varian Cary 5G UV/Vis/NIR, Varian, Darmstadt, Germany) was used with a diffuse transmittance accessory (Ulbricht sphere) to determine the ultraviolet radiation absorbance of the lenses. The sample lenses were placed directly in front of the integrating Ulbricht sphere entrance port, between the aperture mask and the sphere (transmission position). In this position, unwanted ef-
Results All lenses showed nearly baseline ultraviolet radiation transmittance in the ultraviolet C (200 –280 nm) and ultraviolet B (280 – 320 nm) ranges (Figs 1– 4). With few exceptions, the IOLs also provided good filtering properties in the ultraviolet A range (wavelengths from 320 to 400 nm), transmitting ⬍10% of incoming ultraviolet radiation. Lenses of identical types showed no differences. Two of the 6 silicone lenses displayed an ultraviolet radiation wavelength cutoff between 340 nm and 350 nm, at which ⬎10% of ultraviolet radiation was transmitted (Fig 1). Three of 4 acrylic lenses, 1 hydrogel lens, and 1 PMMA lens revealed higher ultraviolet A transmittance at 375 nm (Figs 2– 4). Most lenses showed
Figure 1. Ultraviolet radiation transmittance curves of silicone intraocular lenses. UV-A ⫽ ultraviolet A; UV-B ⫽ ultraviolet B; UV-C ⫽ ultraviolet C.
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Ophthalmology Volume 111, Number 5, May 2004
Figure 2. Ultraviolet radiation transmittance curves of polymethyl methacrylate intraocular lenses. UV-A ⫽ ultraviolet A; UV-B ⫽ ultraviolet B; UV-C ⫽ ultraviolet C.
ⱖ90% transmittance in the visible light spectrum between 400 and 800 nm. Figure 5 compares the ultraviolet radiation cutoff wavelength of each lens model investigated. The order of cutoff wavelengths of 10% transmittance was not associated with the lens material. Both the highest and the lowest ultraviolet radiation cutoff wavelengths are reached by silicone IOLs. All lenses investigated prevent transmission of ultraviolet B and ultraviolet C radiation. Within the ultraviolet A spectrum the ultraviolet radiation cutoff wavelength of 10% ranges from approximately 350 to 400 nm (Fig 5). The best ultraviolet radiation protection is provided by 2 foldable lens types, the SI40NB silicone lens (Allergan, Irvine, CA) and the Acrysof hydrophobic acrylic lens MA60BM (Alcon, Inc., Fort Worth, TX) (Fig 5). These 2 lenses best approx-
imate the ultraviolet radiation– blocking capacity of the crystalline lens (Fig 6).
Discussion The study results provide a basis for the practical comparison of ultraviolet radiation transmittance of commonly implanted IOLs. The ultraviolet radiation cutoff wavelengths of all 17 lenses documented in Figure 5 reveal that some lenses allow ⬎10% transmittance at wavelengths within the ultraviolet radiation spectral range. In the present
Figure 3. Ultraviolet radiation transmittance curves of acrylic intraocular lenses. UV-A ⫽ ultraviolet A; UV-B ⫽ ultraviolet B; UV-C ⫽ ultraviolet C.
882
Laube et al 䡠 Ultraviolet Radiation Absorption of IOLs
Figure 4. Ultraviolet radiation transmittance curves of hydrogel (Hydroview, Bausch & Lomb, Rochester, NY) and Memory (CIBA Vision Corp., Duluth, GA) intraocular lenses. UV-A ⫽ ultraviolet A; UV-B ⫽ ultraviolet B; UV-C ⫽ ultraviolet C.
study, a cutoff rate of 10% ultraviolet radiation transmittance was defined as a value that ensures efficient protection and allows differentiation of the measured transmission curves. The overall outcome shows that some of the currently
used IOLs provide less ultraviolet radiation protection than other lens types. The most striking absorption differences were noted within the near ultraviolet radiation wavelength (ultraviolet A) range (320 – 400 nm). The multiformity of the results implies that lenses produced by different manu-
Figure 5. Ultraviolet radiation cutoff wavelength of 10% transmittance for 21 diopters. UV-A ⫽ ultraviolet A; UV-B ⫽ ultraviolet B; UV-C ⫽ ultraviolet C.
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Ophthalmology Volume 111, Number 5, May 2004
Figure 6. Ultraviolet radiation transmittance curves of the eye. UV-A ⫽ ultraviolet A; UV-B ⫽ ultraviolet B; UV-C ⫽ ultraviolet C. Modified after Boettner EA, Wolter JR. Transmission of the ocular media. Invest Ophthalmol 1962;1:776 – 83.
facturers out of the same materials can have different basic properties. Some of the silicone lenses in particular showed very little ultraviolet radiation protection, particularly in the upper ultraviolet radiation spectrum. It is interesting to note that, of all IOLs under investigation, 2 foldable lenses provided the best ultraviolet radiation protection, thus approaching the ultraviolet radiation– blocking capacity of the crystalline lens given by Boettner and Wolter1 at best. Unlike the crystalline lens, which has a 10% cutoff rate at 400 nm, increases transmittance to 90% at 450 nm, then gradually transmits wavelengths between 450 and 800 nm, however, the tested IOLs revealed a steep rise in the transmittance of wavelengths beyond 400 nm. As the visible light spectrum ranges from 400 to 700 nm, progressing from high-energy blue light to green, yellow, and red light, this occurrence may account for the more intensive subjective sensitivity to blue. Wavelengths beyond 700 nm are perceived as heat (infrared) and not seen. The cornea, aqueous humor, and vitreous humor are largely transparent between 300 and 400 nm, allowing these spectra to pass freely into the eye, whereas the natural crystalline lens effectively absorbs the ultraviolet A range and shields the retina from the potentially toxic effects of these wavelengths (Fig 6).1 As both ultraviolet B radiation exposure and ultraviolet A radiation exposure have been implicated in retinal damage, it seems desirable for manufacturers and surgeons alike to seek optimal protection within the ultraviolet radiation range by using discretion in their choice of lenses and lens materials. Patients implanted with IOLs that are less effective ultraviolet radiation absorbers might consider the use of ultraviolet A–absorbing spectacle glasses.
884
References 1. Boettner EA, Wolter JR. Transmission of the ocular media. Invest Ophthalmol 1962;1:776 – 83. 2. Bergmanson JP, Sheldon TM. Ultraviolet radiation revisited. CLAO J 1997;23:196 –204. 3. Clarke SM, Doughty MJ, Cullen AP. Acute effects of ultraviolet-B irradiation on the corneal surface of the pigmented rabbit studied by quantitative scanning electron microscopy. Acta Ophthalmol (Copenh) 1990;68:639 –50. 4. Cullen AP, Chou BR, Hall MG, Jany SE. Ultraviolet-B damages corneal endothelium. Am J Optom Physiol Opt 1984;61: 473– 8. 5. Pitts DG, Cullen AP, Hacker PD. Ocular effects of ultraviolet radiation from 295 to 365 nm. Invest Ophthalmol Vis Sci 1977;16:932–9. 6. Hiller R, Giacometti L, Yuen K. Sunlight and cataract: an epidemiologic investigation. Am J Epidemiol 1977;105: 450 –9. 7. Katoh N, Jonasson F, Sasaki H, et al, Reykjavik Eye Study Group. Cortical lens opacification in Iceland. Risk factors analysis—Reykjavik Eye Study. Acta Ophthalmol Scand 2001;79:154 –9. 8. Klein BE, Klein R, Linton KL. Prevalence of age-related lens opacities in a population. The Beaver Dam Eye Study. Ophthalmology 1992;99:546 –52. 9. West S. Ocular ultraviolet B exposure and lens opacities: a review. J Epidemiol 1999;9(suppl):S97–101. 10. Taylor HR. Ocular effects of UV-B exposure. Doc Ophthalmol 1995;88:285–93. 11. Lindstrom RL, Doddi N. Ultraviolet light absorption in intraocular lenses. J Cataract Refract Surg 1986;12:285–9. 12. Hickson-Curran SB, Nason RJ, Becherer PD, et al. Clinical evaluation of Acuvue contact lenses with UV blocking characteristics. Optom Vis Sci 1997;74:632– 8. 13. Clausen M, Meyer C. Wie gut schu¨tzen Sonnenbrillen vor scha¨dlichen UV-Strahlen? [How well do sunglasses protect
Laube et al 䡠 Ultraviolet Radiation Absorption of IOLs
14. 15. 16. 17.
18. 19. 20.
from damaging UV rays?]. Klin Monatsbl Augenheilkd 1998; 212:aA9 –13. Cruickshanks KJ, Klein R, Klein BE, Nondahl DM. Sunlight and the 5-year incidence of early age-related maculopathy: the Beaver Dam Eye Study. Arch Ophthalmol 2001;119:246 –50. Kraff MC, Sanders DR, Jampol LM, Lieberman HL. Effect of an ultraviolet-filtering intraocular lens on cystoid macular edema. Ophthalmology 1985;92:366 –9. Pitts DG, Bergmanson JP. The UV problem: have the rules changed? J Am Optom Assoc 1989;60:420 – 4. Rapp LM, Fisher PL, Dhinsda HS. Reduced rate of rod outer segment disk synthesis in photoreceptor cells recovering from UVA light damage. Invest Ophthalmol Vis Sci 1994;35: 3540 – 8. Taylor HR, West S, Mun˜oz B, et al. The long-term effects of visible light on the eye. Arch Ophthalmol 1992;110:99 –104. Zuclich JA. Ultraviolet-induced photochemical damage in ocular tissues. Health Phys 1989;56:671– 82. Roberts JE. Ocular phototoxicity. J Photochem Photobiol B 2001;64:136 – 43.
21. Ellerin BE, Nisce LZ, Roberts CW, et al. The effect of ionizing radiation on intraocular lenses. Int J Radiat Oncol Biol Phys 2001;51:184 –208. 22. Francese JE, Pham L, Christ FR. Accelerated hydrolytic and ultraviolet aging studies on SI-18NB and SI-20NB silicone lenses. J Cataract Refract Surg 1992;18:402–5. 23. Schmidbauer JM, Werner L, Apple DJ, et al. Postoperative ¨ bersicht [PostTru¨bung von Hinterkammerlinsen— eine U operative opacification of posterior chamber intraocular lenses—a review]. Klin Monatsbl Augenheilkd 2001;218: 586 –94. 24. Yang S, Makker H, Christ FR. Accelerated ultraviolet aging of intraocular lens optic materials: a 50 year simulation. J Cataract Refract Surg 1997;23:940 –7. 25. Vola JL, Petrakian JP, Mardrus R. Phototoxicite´ des ultraviolets sur le cristallin et la re´tine. Etude de la transmission optique d’implants traite´s et non traite´s anti-U.V. [Phototoxicity of ultraviolet rays on crystalline lens and retina. Study of the optic transmission of implants with or without anti-UV treatment]. J Fr Ophtalmol 1988;11:277– 83.
885