The substitution of glass for plastics progresses with functionalized plastic parts. Especially for optical applications as lenses and visual indicators high quality requirements are desired. Shrinkage and warpage impact on optical properties due to inaccuracies of surface shape consistency. The physical effects of shrinkage and warpage can be traced back to the order and distribution of molecular chains in the plastic material. These effects influence refractivity as well as transmission. Additionally, a gradient in the number of molecular chains correlates with different density values which cause residual stresses in the part. Negative impacts can be deflection and diffusion of light rays which have to be transmitted through the part. This research examines the processing, which effect mechanical and thermal stresses on molecular chains. This leads to a shortening or orientation pattern of molecular chains. To identify the main influences, i.e. injection velocity, melt and mold temperature, a parameter study has been carried out on an injection molding machine and compared with calculated properties such as shear strain in a FEM flow simulation. Correlating the transmittance of the test specimen with calculated stresses, a proposition for optical behavior of plastic parts can be determined. PMMA, PC and cyclical olefin types are compared. The temperature regime during cooling of these lenses show major influence on achievable optical properties. Higher melt temperature leads to higher transmittance through the material. This finding can be confirmed by subsequent heat treatment leading to lower residual stresses and better transmittance. Reduced injection speed also improves transmittance. A prediction of residual stresses in optical lenses is possible using FEM flow simulation, although variant cooling conditions lead to a difference of measured residual stresses and calculated shear stresses. Comparisons between calculated and measured results are presented.