['This study used dopamine D2 receptor (D2R) knockout (KO) mice to investigate the role of D2R activity in the development of form-deprivation myopia (FDM). Sulpiride, a D2R antagonist, was administered systemically into wild-type (WT) mice to validate the involvement of D2R in FDM development.', 'The D2R KO and WT C57BL/6 mice were subjected to FDM. Wild-type mice received daily intraperitoneal injections of sulpiride, 8 μg/g body weight, for a period of 4 weeks. The body weight, refraction, corneal radius of curvature, and ocular axial components were measured at week 4 of the experiment. Differences in all ocular parameters between the experimental and control groups were compared statistically.', 'Form-deprivation myopia in D2R KO mice (FD-KO) was significantly reduced compared with their WT littermates (interocular difference, -2.12 ± 0.91 diopter [D] in FD-KO versus -5.35 ± 0.83 D in FD-WT, P = 0.014), with a smaller vitreous chamber depth (0.008 ± 0.006 vs. 0.026 ± 0.006 mm, P = 0.044) and axial length (-0.001 ± 0.007 vs. 0.027 ± 0.008 mm, P = 0.007). Furthermore, FDM was attenuated in animals treated with sulpiride (-2.01 ± 0.31 D in FD-sulpiride versus -4.06 ± 0.30 D in FD-DMSO, P < 0.001) compared with those treated with vehicle, with a retardation in growth of vitreous chamber depth (-0.001 ± 0.006 vs. 0.022 ± 0.004 mm, P = 0.003) and axial length (-0.004 ± 0.007 vs. 0.027 ± 0.005 mm, P = 0.001).'] Is activation of dopamine D2 receptor critical for the development of form-deprivation myopia in the C57BL/6 mouse?