Henle Fibers Are Organized in Bundles Consistent Between Individuals and Conserved in Primates

Purpose: To test the hypothesis that Henle fiber bundles are similar in number between individuals. Methods: Adeno-associated virus (AAV) using a cone-specific promoter to drive enhanced green fluorescent protein (EGFP) was administered to the rhesus macaque macula to visualize Henle fibers (individual cone axons) in vivo. Directional optical coherence tomography (OCT) was performed on a patient with a macular star to determine the site of lipid deposition in relation to the Henle fiber layer (HFL). Publicly available images of macular star retinopathy from 18 eyes were analyzed to determine the number of radial lines as a surrogate for bundles of Henle fibers. Results: AAV-mediated expression of EGFP in macular cones in nonhuman primates revealed a macular star pattern in cone axons of Henle fibers in vivo. Directional OCT highlighting hyperreflective exudates confirmed the presence of lipid at the level of the HFL. This suggests that the macular star likely delineates bundles of Henle fibers through lipid deposition. The number of lines was 30.0 ± 2.2 SEM when measured proximal (0.5 mm) and was 60.3 ± 2.5 SEM distal (1.25 mm) to the foveal center. Conclusions: High similarity in the number of radial lines between eyes suggests that Henle fiber bundle counts are consistent between individuals. Furthermore, the number of distal lines is approximately double the number of proximal lines, suggesting that Henle fiber bundles may converge as they approach the foveal center.