The present estimates of displacement within the human central fovea offer the possibility of analysis of quantitative relations between cones and retinal ganglion cells. Our data provide predictive guidance by establishing that vitreo-retinal procedures causing damage to retinal ganglion cells up to 1 mm from the foveal centre could have implications for loss of information generated within the fovea.
Purpose To create a time‐line model of developmental events during normal maturation of the inner and outer foveal layers based on imaging and histological studies. Methods Data from recently published imaging studies using hand‐held OCT during the period following premature birth (Dubis et al. 2012; Maldonado et al., 2012; Vajkovic et al., 2012) and histology of normal donor eyes (Dubis et al., 2012; Hendrickson et al. 2012; Vajkovic et al., 2012) was used to establish the timing of foveal developmental events from the time of mid‐gestation to early childhood. A model of the onset and maturation of the following foveal developmental events was constructed: Pit formation, extrusion of inner retinal layers, widening of the outer nuclear layer, separation of the hyperreflective inner segment layer from the RPE, and lengthening of the outer segment. Developmental events were graded as incipient, intermediate or mature. Results The normal developmental events within the central fovea are depicted along a logarithmic time‐line. The developmental models based on OCT or histology of the inner and outer retina show a close correspondence. The structural elements of the inner retina all reach near full to full maturity at term birth. At this time the outer retinal structures are immature and the maturation of the photoreceptor layers starts at an age of some postnatal weeks and reach near full to full maturity at one to three years of age. Conclusion The inner and outer foveal layers reach maturity within different time frames; the inner layers during the late part of gestation, and the outer layers during the first postnatal years. Our model is of importance when evaluating abnormalities in e.g. prematurity or albinism.
Purpose To present a model useful for analysis of images of central retina based on functional connectivity between outer retina with its photoreceptors and retinal ganglion cells (RGC) of the inner retina. In addition, to evaluate the nomenclature and to propose clinically relevant definitions of the fovea and surrounding zones based on neural connectivity, function and development. Methods Published measurements of radial displacement of inner retina relative to outer retina were used to determine the area of RGC corresponding to central photoreceptors. A model of central retina with displaced outer and inner retinal zones was constructed based on data from histological reports and data from recent studies with non‐invasive imaging studies, the convention of the ETDRS study, and psychophysical studies. Results A model is presented where functional relationships within the retina are based on neural connectivity, i.e the radial displacement of RGC and synaptically connected cones. The statement by S. Polyak (1941) that "the entire inner foveal excavation corresponds to a small central region" of photoreceptors is confirmed. The model indicates that the template for analysis should be separate for outer and inner retina in order to mirror corresponding areas and functional relationships. Based on the model we propose a template relevant for clinical analysis of images of the outer retina mainly based on anatomical nomenclature and partly adapted according to the ETDRS convention. Conclusion A model of the central retina based on neural connectivity is recommended as a frame for analysis of corresponding but displaced zones of the central retina.Templates for analysis of zones of cones and RGC are proposed.
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.
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 Sjöstrand 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.
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