Chronic photodamage in the chicken retina using 650-nm semiconductor laser

摘要

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 1 mo 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 6 mo. We obtained data at 1, 3, and 6 mo, 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 1 mo, the MDA content in Group D was higher than that observed in Group A(P=0.019). At 3 mo the MDA content in Groups C and D was higher than that reported in Group A(P=0.026, 0.003). At 6 mo, 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 3 mo. The SOD activity in group D was significantly decreased at 6 mo(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 6 min per day over 6 mo do not cause photodamage. Similarly, a 3-month exposure of 30 min per day do not cause damage. However, irradiation for 6 mo 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.