To investigate the efficacy and safety of the adrenergic α-receptor blocker tolazoline in the treatment of experimental myopia in chicks, and explore its mechanism.

In this experimental study, totally 61 6-day-old White Lehorn chickens were randomly divided into form deprivation control group (FDM), tolazoline treatment group after form deprivation (FDM+T100), tolazoline combined with NOS inhibitor L-NAME group after form deprivation (FDM+T100+L-NAME), lens induction control group (LIM), tolazoline treatment group after lens induction (LIM+T100), and tolazoline combined with NOS inhibitor L-NAME group after lens induction (LIM+T100+L-NAME) for efficacy study. Chickens were also divided into blank control group (Blank) and tolazoline treatment group (Blank+T100) for safety study. The experimental intervention was performed on the right eyes of all chicks. Eyes requiring tolazoline (T100) treatment were injected with 12.5 μL tolazoline, eyes requiring tolazoline combined L-NAME (T100+L-NAME) were injected with equal equivalent tolazoline and L-NAME, and the control group was injected with normal saline for 6 days. The diopter and eye biological parameters of each group before and after treatment were recorded and analyzed statistically. In the safety study, ERG examinations were performed on blank group and blank+T100 group. After sacrificing the chicks, the eyeballs were fixed and sliced for TUNEL staining to observe retinal damage. The experimental group and the control group in different myopia model were compared in pairs in this study. The independent samples t-test was used for diopter, vitreous depth, choroid thickness, and axial length which satisfy the normal distribution, and the Mann-Whitney U test was used for the electroretinogram ratio results which did not meet the normal distribution.

After 6 days of treatment, in the form deprivation model, the FDM+T100 group had reduced refractive myopia (t=-16.16, P<0.001), reduced amount of axial length growth (t=12.41, P<0.001), and reduced amount of choroidal thickness thinning (t=-2.46, P=0.031) compared to the FDM group. Compared to the FDM+T100 group, the FDM+T100+L-NAME group had increased refractive myopia (t=4.20, P=0.001 ), increased amount of axial length growth (t=-2.33, P=0.033). In the lens induction model, when compared with the LIM group, the refractive diopter was reduced in the LIM+T100 group (t=-5.77, P<0.001), axial length growth was reduced (t=4.19, P<0.001). When compared with the LIM+T100 group, the refractive diopter was increased in the LIM+T100+L-NAME group (t=3.74, P=0.001), and increased amount of axial length growth (t=-3.20, P=0.005). In the safety study, there was no significant difference in the diopter, the changes of eyeball biological parameters and ERG right/left eye ratio between the blank control group and the simple tolazoline treatment group. No significant apoptosis was found among the groups in TUNEL staining.

Tolazoline can effectively delay the diopter and axial progression of experimental myopia in chicks. But this effect was weakened by NOS inhibitor L-NAME. It is suggested that nitric oxide (NO) may also play an important role in the dilation of choroidal blood vessels by tolazoline.

myopia; tolazoline; chicks; experimental myopia; choroid