White light-emitting diodes (LEDs) at domestic lighting levels and retinal injury in a rat model

Abstract

Background: Light-emitting diodes (LEDs) deliver higher levels of blue light to the retina than do conventional domestic light sources. Chronic exposure to high-intensity light (2,000-10,000 lux) has previously been found to result in light-induced retinal injury, but chronic exposure to relatively low-intensity (750 lux) light has not been previously assessed with LEDs in a rodent model.

Objective: We examined LED-induced retinal neuronal cell damage in the Sprague-Dawley rat using functional, histological, and biochemical measurements.

Methods: We used blue LEDs (460 nm) and full-spectrum white LEDs, coupled with matching compact fluorescent lights, for exposures. Pathological examinations included electroretinogram, hematoxylin and eosin (H&E) staining, immunohistochemistry (IHC), and transmission electron microscopy (TEM). We also measured free radical production in the retina to determine the oxidative stress level.

Results: H&E staining and TEM revealed apoptosis and necrosis of photoreceptors, which indicated blue-light induced photochemical injury of the retina. Free radical production in the retina was increased in LED-exposed groups. IHC staining demonstrated that oxidative stress was associated with retinal injury. Although we found serious retinal light injury in LED groups, the compact fluorescent lamp (CFL) groups showed moderate to mild injury.

Conclusion: Our results raise questions about adverse effects on the retina from chronic exposure to LED light compared with other light sources that have less blue light. Thus, we suggest a precautionary approach with regard to the use of blue-rich "white" LEDs for general lighting.

Citation: Shang YM, Wang GS, Sliney D, Yang CH, Lee LL. 2014. White light-emitting diodes (LEDs) at domestic lighting levels and retinal injury in a rat model. Environ Health Perspect 122:269-276; http://dx.doi.org/10.1289/ehp.1307294.

Figure 1

Timeline and experimental design. Abbreviations: CFL, compact fluorescent lamp; ERG, electroretinography; H&E, hematoxylin and eosin staining; IHC, immunohistochemistry; ROS, reactive oxygen species; TEM, transmission electron microscopy; TUNEL, terminal deoxynucleotidyl transferase dUTP nick end labeling. After 14 days of dark maintenance, the rats were divided into four groups and exposed to different light sources (blue LED, white LED, white CFL, or yellow CFL). Specific analytical techniques were performed at the end of exposure periods.

Figure 2

Light source SPD curves for (A) blue LED, (B) white LED, (C) white CFL, and (D) yellow CFL. The single-wavelength blue LED light (A) peaked at 460 nm (power of near 0.1 W/nm). White LED light (B) exhibited a CCT of 6,500 K. The first peak, which appeared at 460 nm with power of 0.028 W/nm, shows blue content; the bell shape of the second peak indicates higher yellow content. The SPD curve of white CFL light (C), with a CCT of 6,500 K, shows several sharp peaks across the spectrum; the blue peak is relatively shorter than the yellow or red peaks, and the full width at half maximum (FWHM) is smaller than that in (A) or (B). The SPD curve of yellow CFL light (D) is similar to that of white CFL (C), but with a CCT of 3,000 K; the highest peak represents yellow light. Although all of the light sources tested contain blue light peaks, the area under the curve variation leads to a difference in total intensity. Note the different scales for each light source.

Figure 3

Representative ERG responses (A) and ERG b‑wave amplitude (B) in unexposed (control) rats or rats exposed to blue LED, white LED, white CFL, or yellow CFL at 0 (baseline), 9, or 28 days of light exposure. Values shown in (B) are mean ± SD (for each time point, n = 3 controls and 8 for each light-exposure group at each time point. **p < 0.01, and ^#p < 0.001, compared with the control group by ANOVA and Tukey post hoc test.

Figure 4

H&E staining of representative retinal tissue sections from control rats (A) and from rats exposed to white LED for 28 days (B) or to blue LED (C), white LED (D), white CFL (E), or yellow CFL (F) for 9 days. (G) ONL thickness (mean ± SD) measured in retinas (n = 3 controls, n = 8 for each light-exposure group at either time point). Abbreviations: GCL, ganglion cell layer; INL, inner nuclear layer; IS, inner segment; ONL, outer nuclear layer; OS, outer segment; RPE, retinal pigment epithelium (usually next to the OS layer but is detached and cannot be found within this scope). (A) Control tissue shows normal retinal layers. (B) After exposure to white LED for 28 days, retinal injury included pyknotic photo­receptor nuclei (arrow), swelling of the inner segment (arrow head), a dis­organized outer segment with no visable RPE [asterisk (*)], and INL degeneration. Photoreceptors were not present in retinals from rats exposed to blue LED (C) or white LED (D) light; the white CFL group (E) exhibited distortion of the OS and ONL, and the yellow CFL group (F) exhibited less movement in each layer. In (A–F), bar = 50 μm. (G) ONL thickness was significantly decreased in the LED groups at days 9 and 28, whereas the ONL thickness in white and yellow CFL groups was not significantly altered at day 9. **p < 0.01, compared with the control group by ANOVA and the Tukey post hoc test.

Figure 5

Retinal cell apoptosis detected by TUNEL labeling (damaged retinal cells show positive labeling). (A) Representative images of retinal cell apoptosis in control rats and in rats exposed to blue LED, white LED, white CFL, or yellow CFL for 9 days (bar = 50 μm); more apoptotic cells (arrows) appear in the retina of LED-exposed groups than that of CFL-exposed groups. Abbreviations: GCL, ganglion cell layer; INL, inner nuclear layer; ONL, outer nuclear layer; RPE, retinal pigment epithelium. (B) Fluorescence intensity of apoptosis in light exposure groups shown as the mean ± SD fold of the control value (n = 3 controls and 8 for each exposure group). The LED-exposed groups exhibit higher fluorescence intensity than that of CFL-exposed groups. **p < 0.01, and ^#p < 0.001, compared with the control group by ANOVA and the Tukey post hoc test.

Figure 6

Representative TEM photomicrographs showing retinal cellular injury of the ONL nucleolus (A–F) and photo­receptors (G–L) in control rats (A,G) and those exposed to white LED light (B–F, H–L) at day 9. Abbreviations: INL, inner nuclear layer; IS, inner segment; ONL, outer nuclear layer; OS, outer segment; RPE, retinal pigment epithelium. ONL nuclear deformations (arrows) were observed in (A) control ONL nucleus and as (B) nucleolus condensation, (C) karyolysis, (D,E) pyknosis, and (F) karyorrhexis. (G–L) Normal photo­receptor, IS, and OS from a control rat (G); photo­receptor deformations showing minor disruption (H,I); and IS disappearance followed by OS shrinkage and the formation of several small round shapes (J,K,L). For (A–F) and (I,J,L), bar = 1 μm; for (G,H,K), bar = 2 μm. Each photomicrograph is from a different sample.

Figure 7

Retinal light injury shown by IHC staining for acrolein to detect lipid adducts on macro­molecules (A), 8-OHdG to detect DNA adducts (B), and nitro­tyrosine to recognize protein adducts (C) in the retina of unxexposed rats or rats exposed to blue LED, white LED, white CFL, or yellow CFL for 9 days. Abbreviations: B, blue; W, white; Y, yellow. Left, representative photo­micrographs (bar = 50 μm). Right, mean ± SD fluorescence of protein-positive cells relative to the control group (n = 3 controls, n = 8 for each light-exposure group). LED-exposed groups exhibited higher fluorescence intensity on ONL, and the CFL groups had lower fluorescence intensity. *p < 0.05, **p < 0.01, and ^#p < 0.001, compared with the control group by ANOVA and the Tukey post hoc test.

Figure 8

ROS assay performed in control rats and rats exposed to blue LED, white LED, white CFL, or yellow CFL for 3 days (A) or 9 days (B). Values are presented as mean ± SD chemiluminescence (CL) intensity. Abbreviations: B, blue; W, white; Y, yellow. (A) After 3 days of exposure to blue LED light, lucigenin-stimulated O₂^•– exceeded 60,000 in total count, the white LED group had a high total count near 40,000, and the CFL groups had total counts of 20,000–30,000; At this time point, control rats exhibited a count of approximately 1,000. n = 3 controls, and n = 3 for each exposure group. (B) After 9 days of exposure, the O₂^•– total count for the blue LED light group decreased to 8,000, that for the white LED light group decreased to 18,000, and that for both fluorescent light groups remained at the same level. n = 3 controls, and n = 8 for each exposure group. **p < 0.01, and ^#p < 0.001, compared with the control group by ANOVA and the Tukey post hoc test.