Spatial distribution of macular birefringence associated with the Henle fibers

The spatial distribution of macular birefringence was modeled to examine the contribution from the foveal Henle fiber layer, particularly cone axons. The model was tested in 20 normal subjects, age 17–55 yr. Phase retardance due to Henle fibers was modeled for rings increasing in radius around the fovea, using a sinewave of two periods (2f). The 2f sinewave amplitude increased linearly with eccentricity for each individual, (p < 0.004) in 19 of 20 subjects. A good fit to linearity implies regular cone distribution and radial symmetry, and the uniformly excellent fits indicate no effect of age in our sample. The peak of the 2f sinewave amplitude varied across subjects from 1.06 to 2.46 deg. An increasingly eccentric peak with increasing age would indicate a relative decrease of cone axons in the central fovea, but the location of the peak was not associated with age for our sample, which did not include elderly subjects.