Use of imaging techniques to reveal connectivity within the human fovea and to predict consequences of lesions.

Abstract

Purpose A knowledge of connectivity from the central photoreceptors and their axons, via the bipolar cells to the retinal ganglion cells (RGC), is required to understand the consequences of lesions in different locations of the human fovea. The purpose was to create a model of the connectivity within the fovea based on information available in recent non‐invasive studies of the normal fovea with optical coherence tomography (OCT) and adaptive optics (AO). Methods OCT data from the study by Lujan et al. (2011) of the thickness of the Henle fiber layer (HFL) at various eccentricities was used in combination with data of cone density and visual resolution obtained from AO studies. An angle of 6 degrees was assumed between the cone axons and the external limiting membrane, at eccentricities between 0.2 and 1 mm, to calculate the lateral displacement from the cone photoreceptor cell body to the cone pedicle. Cone density and visual resolution was obtained from published AO studies (Wolfing et al., 2006; Rossi & Roorda, 2010). Results The thickness (HFLt) versus eccentricity along the horizontal meridian was derived from Lujan et al. (2011) and used to calculate the lateral displacement of cone pedicles. Zones in the cone pedicle layer and RGC layer connected to corresponding regions of the cone mosaic (0‐0.2 mm, 0.2‐0.4 mm, 0.4‐0.6 mm) were calculated and related to AO estimates of visual resolution. Conclusion Our model may be useful to visualize functional connectivity and to predict the effect of lesions within the fovea. A maximal effect of lesions in the bipolar and RGC layers, due to the displacement caused by the cone axons, may be anticipated at an eccentricity of about 0.5 mm or 2 degrees.