Topography of the human Henle Fiber Layer (HFL) as revealed by imaging and histology

Purpose To create a model of the topography of the Henle Fibers (HF) connecting photoreceptor cell bodies of the human fovea to the inner retina based on information available in recent imaging and histological studies. Detailed knowledge of the HF is of importance for analysis of connectivity between the outer and inner retina and for evaluation of radial displacement of retinal neurons from their synaptically connected photoreceptors. Methods Reported data of the Henle Fiber Layer (HFL) thickness (HFLt) at different eccentricities along the horizontal meridian of the human fovea from studies with optical coherence tomography (OCT) and histology was used. The radial displacement caused by HF was calculated from data of total displacement within the retina, corrected by data of other displacements obtained from Sjostrand et al( unpublished). Results A comparison of OCT and histology data showed a similar profile of HFLt vs eccentricity and similar HF topography. The angle of the Henle fibers vs. the external limiting membrane (ELM) was low centrally ranging from a few degrees (deg) to approximately 6 deg at a cone eccentricity of 0.9 mm.Thereafter the angle slowly increased with increasing eccentricity to an angle of 9-10 deg at cone eccentricity of 1.8 mm . The locations of the maxima of HFLt and projected HF length were at a cone eccentricity of approximately 0.5 mm. A model was constructed displaying the characteristics of the topography of HFL. Conclusion Published data of the topography of HFL fits with a model where the the maximal HFLt is attained at a cone eccentricity where the fiber angle vs ELM still is of low degree and the HF length reaches a maximum.