Hypothyroidism prevalence among pregnant women is between 0.5 to 4% (Carney et al., 2014). Most studies look at the prolonged or severe reduction in thyroid hormone (TH) levels. We looked at how the reduced levels of TH during the third trimester of human gestation and the first weeks after birth in rodents impact the visual system. Additionally, we try to answer whether PTU treatment would affect neuronal plasticity in the visual cortex. We used the Visual Evoked Potential recordings to assess contrast sensitivity, spatial frequency acuity, and ocular dominance plasticity. In addition, we look into the expression of the photoreceptors in the retina. PTU exposure impacts the contrast sensitivity but not the spatial frequency acuity or ocular dominance plasticity. The expression level of the photoreceptor Opsin-M was also impacted. The reduced levels of the thyroid hormones during this crucial time have long-lasting consequences for the proper visual system processing.