Birefringence of the human foveal area assessed in vivo with Mueller-matrix ellipsometry.

We have assessed retinal birefringence in the foveal and parafoveal regions by applying Mueller matrix ellipsometry on the human eye in vivo. Basically, a light beam passed the ocular media twice and was scattered at the fundus intermediately. Keeping the entry and exit positions on the cornea constant and varying the retinal location along a circle around the foveal center enabled us to separate the corneal and retinal components of the measured retardation. We conclude that the retina within the outer margin of the parafovea behaves as a uniaxial crystal, with its slow axis radially oriented from the fovea and a retardation of about 16 deg (to 70 deg in the corneal center). We believe that Henle's fiber layer causes retardation in this specific configuration of entrance and exit beams. The outer segments of the photoreceptors, although birefringent, have their optic axes aligned with these beams.