Aim: To investigate the occurrence of chronic photodamage in the cone-based retina, following long-term exposure to a 650-nm semiconductor laser (power: 2 mW).
Methods: Chickens fed for 1mo under natural light after hatching were irradiated with 650-nm laser light at different times each day. Fifteen animals were included in each group. Group A was a control group, irradiated with natural light during the entire study. Group B was irradiated with laser for 3 min/d. Group C was irradiated with laser for 6 min/d. Group D was irradiated with laser for 30 min/d. The duration of the light experiment was 6mo. We obtained data at 1, 3, and 6mo, including measuring the retinal thickness in vivo using optical coherence tomography, hematoxylin and eosin staining, TUNEL assay, apoptosis staining, malondialdehyde (MDA) content, superoxide dismutase (SOD) activity, and Western blotting to detect changes in L/M opsins and rhodopsin.
Results: At 1mo, the MDA content in Group D was higher than that observed in Group A (P=0.019). At 3mo the MDA content in Groups C and D was higher than that reported in Group A (P=0.026, 0.003). At 6mo, the MDA content in Groups B, C, and D was higher than that observed in Group A (P=0.038, 0.032, 0.000, respectively). There was no difference in SOD activity, and L/M opsin and rhodopsin content between the groups at 1 and 3mo. The SOD activity in group D was significantly decreased at 6mo (P=0.000), as was the content of rhodopsin. There was no significant reduction observed in retinal thickness, abnormal cell arrangement, and positive staining of TUNEL in the groups during the 6-month study period.
Conclusion: Irradiation using a 650 nm semiconductor laser (power: 2 mW) for 6min per day over 6mo do not cause photodamage. Similarly, a 3-month exposure of 30min per day do not cause damage. However, irradiation for 6mo resulted in a significant increase in the content of free radicals and a decrease in the content of rhodopsin in the retina, suggesting the presence of photodamage.
Keywords: apoptosis; chicken retina; light/adverse effects; oxidative stress; red light.