Structural and Functional Change in Albino Rat Retina Induced by Various Visible Light Wavelengths

Abstract

The effects of visible light, from short to long wavelengths, on the retina were investigated functionally and histologically. The left eyes of Sprague-Dawley albino rats (6-weeks old, n = 6 for each wavelength) were exposed to seven narrow-band wavelengths (central wavelengths, 421, 441, 459, 501, 541, 581, and 615 nm) with bandwidths of 16 to 29 nm (half bandwidth, ±8-14.5 nm) using a xenon lamp source with bandpass filters at the retinal radiant exposures of 340 and 680 J/cm². The right unexposed eyes served as controls. Seven days after exposure, flash electroretinograms (ERGs) were recorded, and the outer nuclear layer (ONL) thickness was measured. Compared to the unexposed eyes, significant reductions in the a- and b-wave ERG amplitudes were seen in eyes exposed to 460-nm or shorter wavelengths of light. The ONL thickness near the optic nerve head also tended to decrease with exposure to shorter wavelengths. The decreased ERG amplitudes and ONL thicknesses were most prominent in eyes exposed to 420-nm light at both radiant exposures. When the wavelengths were the same, the higher the amount of radiant exposure and the stronger the damage. Compared to the unexposed eyes, the a- and b-waves did not decrease significantly in eyes exposed to 500-nm or longer wavelength light. The results indicate that the retinal damage induced by visible light observed in albino rats depends on the wavelength and energy level of the exposed light.

Keywords: electroretinograms; outer nuclear layer; retinal degeneration; visible light.

Figure 1

Measurement of retinal function by electroretinography. Data were expressed as mean ± SD. (a) The a-wave amplitude (% of the amplitude in normal control right eyes) for unexposed right eyes. (b) The b-wave amplitude (% of the amplitude in normal control right eyes) for unexposed right eyes. (c) The a-wave amplitude (% of the amplitude in unexposed right eyes) for eyes exposed to 340 J/cm² light. (d) The b-wave amplitude (% of the amplitude in unexposed right eyes) for eyes exposed to 340 J/cm² light. (e) The a-wave amplitude (% of the amplitude in unexposed right eyes) for eyes exposed to 680 J/cm² light. (f) The b-wave amplitude (% of the amplitude in the unexposed right eyes) for eyes exposed to 680 J/cm² light. Both eyes were compared using the paired t-test, and between-group comparisons were performed using the unpaired t-test. * p < 0.05, ** p < 0.01, *** p < 0.001. n = 6 in each group.

Figure 2

ONL thicknesses in normal controls and those exposed to light. (a) ONL thickness of normal control retinas. (b–h) ONL thicknesses of light-exposed retinas (left eye) are compared with those of unexposed retinas (right eye) at the following wavelengths: 420 nm, 440 nm, 460 nm, 500 nm, 540 nm, 580 nm, and 615 nm. The data are expressed as the mean ± SD (n = 6 in each group). Comparisons between groups were performed using the unpaired t-test. * p < 0.05 and ** p < 0.01 vs. unexposed eyes.

Figure 3

ONL area. (a) ONL area of normal retina (right eye) and opposite retina exposed to 340 J/cm² (right eye). (b) ONL area of normal retina (right eye) and opposite retina exposed to 680 J/cm² (right eye). (c) ONL area of normal retina (left eye) and retina exposed to 340 J/cm² (left eye). (d) ONL area of normal retina (left eye) and retina exposed to 680 J/cm² (left eye). L, left eye; R, right eye. The data are expressed as mean ± SD (n = 6 in each group). Both eyes were compared using the paired t-test, and between-group comparisons were performed using the unpaired t-test. * p < 0.05 and *** p < 0.001 vs. normal control eyes and ^§ p < 0.05, ^§§ p < 0.01, and ^§§§ p < 0.001 vs. unexposed eyes.

Figure 4

H&E of the retina 500–1000 µm superior the optic nerve. (a) Normal control retinas. (b–h) Light-exposed retinas exposed to following wavelengths: 420 nm, 440 nm, 460 nm, 500 nm, 540 nm, 580 nm, and 615 nm. GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer; RIS, rod inner segments; ROS, rod outer segments; RPE, retinal pigment epithelium. Bar = 50 µm.

Figure 5

Spectral distributions of white fluorescent light from a xenon lamp and rats exposed to light. (a) Spectral distribution of white fluorescent light. (b) Spectral distribution of light from a xenon lamp source. (c) Rats exposed to light of different wavelengths. Arrow indicates the direction of the exposed visible light.

Figure 6

Spectral transmittance of the rat corneas and lenses. Values calculated from the transmittance of the corneas [41] and lenses [42].