The average amount of ocular diattenuation was studied using a double-pass polarimeter. This was directly computed from the central part of the elements of the first row of the Mueller matrix obtained from a series of 16 double-pass retinal images. For a 633 nm wavelength, the results show that the parameter is 0.10, on average. Axes of diattenuation are particular for each subject and differ from those associated with ocular birefringence. Moreover, polarization states providing maximum ocular intensity transmittance are in general elliptically polarized.