Safe dose of 650 nm low-power semiconductor laser irradiation in chicken retina / 中华实验眼科杂志

ABSTRACT

Objective:To observe whether there was a chronic light damage after the irradiation of 650 nm semiconductor laser (power 2 mW) in chicken cone-rich-retina and discuss the safety of this laser for retina.Methods:Sixty 1-month-old chicken reared under natural light were divided into a normal control group, an irradiation 3-min group, an irradiation 6-min group and an irradiation 30-min group by using a random number table and 15 for each group.The chicken eyes were irradiated with 650 nm laser for different duration according to a grouping.Relative retina area was measured with optical coherence tomography (OCT) at 1 month (2-month-old chicken), 3 months (4-month-old chicken) and 6 months (7-month-old chicken) after laser irradiation.Chickens were sacrificed by overdose anesthesia and the histopathology of chiken retina was examined by hematoxylin-eosin staining.The apoptosis of the retinal cells was evaluated by TUNEL staining.Chicken retinal homogenate was prepared, and the content of malondialdehyde and activity of superoxide dismutase (SOD) in the retina were detected by TBA method and NBT method, respectively.Western blot was employed to detect the expression of L/M opsin and rhodopsin in the retina.The use and care of the animals complied with Regulations for the Administration of Affair Concerning Experimental Animals by State Science and Technology Commission.Results:In 2-month-old chicken, the molar concentration of malondialdehyde in retina was significantly higher in the irradiation 30-min group compared with the normal control group ( P<0.05). In 4-month-old chicken, the molar concentration of malondialdehyde was statistically higher in the irradiation 6-min group and the irradiation 30-min group in comparison with the normal control group ( P=0.026, 0.003). In 7-month-old chicken, the concentrations of retinal malondialdehyde in the irradiation 3-min group, irradiation 6-min group and irradiation 30-min group were statistically higher than those of the normal control group( P=0.038, 0.032, <0.01). In 7-month-old chicken, the SOD activity and the relative expression of rhodopsin in the retina of the irradiation 30-min group were statistically reduced incomparison with the normal control group (SOD [140.20±5.99][nmol/s·mg] vs.[160.57±3.13][nmol/s·mg]); Rhodopsin 0.392±0.065 vs.0.566±0.072) (both at P<0.05). OCT showed that there was no significant difference in relative retinal area within 6 months among the four groups.Histopathological examination showed that the thickness of the retina in each irradiation group was close to the normal control group.TUNEL staining showed that the retinal cells were regularly arranged, and no TUNEL positive staining cells were found in all of the groups. Conclusions:Irradiation of a 650 nm semiconductor laser (2 mW) in chicken's eyes for 6 minutes is safe for retina within 6 months.The lasser irradiation 30 minutes for 6 months results in an increase of free radical content in the retina and a decrease in rhodopsin, suggesting the presence of photo damage.