Retinal image quality measurements (double-pass and Hartmann-Shack) using spatially coherent light sources like lasers or super-luminescent diodes suffer from the presence of speckle in the final images. This well-known phenomenon diminishes the performance of those systems. Although solutions to this problem have been proposed, there still exist room to implement effective methods to face this challenge. We evaluate the influence of changing the polarization states of a laser beam in a double-pass system in order to reduce the speckle noise. By rotating the linear polarization state during the exposure time of the camera the speckle changes and partially averages out. We use the speckle contrast metric to evaluate the performance of the proposed method over experimental results