See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/342702678 Photobiology – Presentation of a blue light hazard in vivo experiment on the rat Article in Light and Engineering · January 2015 CITATIONS READS 0 6 6 authors , including: Christophe Martinsons Samuel Carré Centre Scientifique et Technique du Bâtiment Centre Scientifique et Technique du Bâtiment 82 PUBLICATIONS 408 CITATIONS 33 PUBLICATIONS 189 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: Inverse Problems and Parameter Estimation in Engineering View project baseline estimation View project All content following this page was uploaded by Christophe Martinsons on 20 March 2020. The user has requested enhancement of the downloaded file.
Boulenguez, P. et al. PHOTOBIOLOGY – PRESENTATION OF A BLUE LIGHT HAZARD IN VIVO EXPERIMENT ON THE RAT PHOTOBIOLOGY – PRESENTATION OF A BLUE LIGHT HAZARD IN VIVO EXPERIMENT ON THE RAT Boulenguez P. 1 , Jaadane I. 2 , Martinsons C. 1 , Carré S. 1 , Chahory S. 3 , Torriglia A. 2 1 Centre Scientifique et Technique du Bâtiment, Grenoble, FRANCE, 2 Institut National de la Santé et de la Recherche Médicale, Paris, FRANCE, 3 Ecole Nationale Vétérinaire d’Alfort, Alfort, FRANCE, Pierre.Boulenguez@cstb.fr Abstract This paper presents an in vivo experiment designed to gain a better understanding of the mechanisms underlying blue-light retinal toxicity. Groups of Wistar rats were exposed to light from four types of LEDs. The eyes were analyzed using Western Blot, immunofluorescence, Terminal transferase dUTP nick end labelling (TUNEL), and transmission electron microscopy. Dosimetry and illumination device are discussed in detail. Keywords : Blue Light Hazard, Exposure Limit Values, Wistar Rat, Dosimetry. 1 Introduction Blue Light Hazard Blue light hazard (BLH) is an incompletely understood phenomenon by which radiations in the blue-end of the visible spectrum induce lesions in the retinal pigment epithelium (RPE) and photoreceptors layer. Effects of rapid onset following high-dose exposure (retinal dose > 20 J/cm2) have long been observed, but low-dose chronic exposition is also suspected to play a role in age-related macular degeneration (AMD) since seminal studies [Ham76]. No epidemiological study demonstrated it so far yet; it is now known that A2E (a constituent of lipofuscin, which is involved in the formation of drusen, the hallmark of AMD) is an initiator of blue light-induced apoptosis of RPE cells. Solid State Lighting Figure 1 InGaN LED and BLH action spectra. The regain of interest for the BLH owes to the emergence of light-emitting diodes (LEDs) as general lighting service (GLS) sources. LEDs have excellent luminous efficacy and durability,
Boulenguez, P. et al. PHOTOBIOLOGY – PRESENTATION OF A BLUE LIGHT HAZARD IN VIVO EXPERIMENT ON THE RAT but the ubiquitous indium gallium nitride (InGaN) “white - light” LED emits significantly more blue- light per lumen than the lamps it intends to replace ( cf. Figure 1). Exposure Limit Values The BLH action spectrum in Figure 1 was established through animal experiment. In a recent survey [NORREN11], the following animal models were identified: rats (9), macaques (7), rabbits (2), and squirrel (1). These studies moreover form the basis of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) exposure limit values (ELVs) [ICNIRP13]. It is noteworthy that a threshold safe-dose of BLH-weighted retinal irradiance was taken at 2,2 J/cm2 (considering that deleterious effects were observed for doses of the order of 20 to 30 J/cm2 [ICNIRP05]). This dose was converted to spatially-averaged BLH-weighted radiance (of sources) by accounting, notably, for human vision physiology. These ELVs are the foundation of the classification of lamps and lamp systems into photobiological risk groups by the Illuminating Engineering Society of North America (IESNA), the International Commission on Illumination (CIE), and the International Electrotechnical Commission (IEC) [CIES009]. 2 In Vivo Experiment This paper presents an animal experiment aiming at a better understanding of the biological mechanisms underlying blue-light retinal toxicity. Animal Model Figure 2 Outbred albino Wistar rat. Wistar rat ( cf. Figure 2) is widely considered as the golden standard general multipurpose model organism. The strain has been used in ophthalmological studies since its inception [1] yet the translation of the model to human being remains to this day a matter of debate. All procedures were conducted in compliance with the animal use and care committee of the veterinary school of Maison Alfort (ENVA).
Boulenguez, P. et al. PHOTOBIOLOGY – PRESENTATION OF A BLUE LIGHT HAZARD IN VIVO EXPERIMENT ON THE RAT Experimental Set-Up Figure 3 Illumination device: the cage was placed below a plane emitting diffuse light. Six weeks old males moving freely in a cage were exposed to blue-light for eighteen hours. The illumination device, presented on Figure 3 and 4, was designed to maximize irradiance uniformity in the plane of the eyes. Figure 4 Illumination device: assembling of sources. Four different sources were used ( cf. Table 1) in order to study the impact of spectral distribution (a group of rats was exposed to a single source). Table 1 Four types of LEDs were used. XP-E Blue XP-E Royal Blue NCSE119A NCSB119 LED LED LED LED Type Cree Cree Nichia Nichia Brand 473 449 507 473 Dominant wavelength (nm)
Boulenguez, P. et al. PHOTOBIOLOGY – PRESENTATION OF A BLUE LIGHT HAZARD IN VIVO EXPERIMENT ON THE RAT Dosimetry Figure 5 Dosimetry software (Python). Dosimetry was based on in situ measurements (section 2.3.1), and on a theoretical model linking retinal spectral irradiance (section 2.3.2) to retinal dose (section 2.3.3). A software was developed to ease interpretation of results ( cf. Figure 5). Spectrophotometric Measurements Spectral irradiance was measured within the cages using a fibre spectrophotometer (with a 𝐹 𝑛𝑗𝑜 diffusing head). Irradiance uniformity (given by the ratio 𝐹 𝑏𝑤𝑓 ) was about 0,7 for all sources. Retinal Spectral Irradiance Table 2 Parameters used for the Wistar rat eye model. Focal length 𝒈 Ocular transmission 𝝊 Pupil diameter 𝒆 𝒒 5mm 2,4mm 100% Retinal spectral irradiance of a rat was dependent upon his head glaze. For overall dose estimation, it was considered that, on average, a rat keeps his head aligned with his body. Following the arguments in [NORREN11], the eye was approached as a globe. As only the upper plane was emitting light ( cf. Figure 3), average corneal spectral irradiance was estimated as: 𝐹 𝜇 𝐹 𝜇,𝑑𝑝𝑠 = 2 [W/nm.m 2 ], and the average retinal spectral irradiance was approached as: 𝐵 𝑑𝑝𝑠 𝐹 𝜇,𝑠𝑓𝑢 = 𝜐𝐹 𝜇,𝑑𝑝𝑠 𝐵 𝑠𝑓𝑢 [W/nm.m 2 ], where 𝜐 is the transmittance of the ocular media, 𝐵 𝑑𝑝𝑠 is the effective area of the illuminated cornea, and 𝐵 𝑠𝑓𝑢 the area of the illuminated retina. The corneal area 𝐵 𝑑𝑝𝑠 was estimated as: 2 𝜌𝑒 𝑞 𝐵 𝑑𝑝𝑠 = 4 [m 2 ], where 𝑒 𝑞 is the diameter of the pupil. The retinal area 𝐵 𝑠𝑓𝑢 was approached as half that of the ocular globe: 𝐵 𝑠𝑓𝑢 = 2𝜌𝑔 2 [m 2 ], where 𝑔 is the focal length (the diameter of the ocular globe for an eye focused at infinity). The average spectral retinal irradiance was thus: 2 𝑒 𝑞 𝐹 𝜇,𝑠𝑓𝑢 = 𝜐𝐹 𝜇 16𝑔 2 [W/nm.m 2 ]. Parameters in the model are given in Table 2.
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