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Adam Dubis, Jungtae Rha, Hitesh Tanna, Kimberly Stepien, Joseph Carroll; Examining foveal cone packing using SD-OCT — implications for foveal development. Journal of Vision 2008;8(17):52. doi: 10.1167/8.17.52.
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Spectral domain optical coherence tomography (SD-OCT) permits non-invasive assessment of the human retina. Previously, we developed objective measures of foveal morphology, finding significant variation among individuals with normal vision (Dubis et al, 2008). It is well known that there is significant variation in cone density among normals, and it has been hypothesized that pit morphology and the degree of cone packing are developmentally related - specifically that a deep foveal pit is associated with increased cone packing (Springer & Hendrickson, 2005). Previous work suggests that high myopes have decreased foveal cone packing, and more shallow foveal pits, consistent with this relationship. Here we further probed this relationship, in children (7 to 10 years old), adults (30–40 years old) and two subjects with albinism using SD-OCT. We assessed the relative degree of cone packing by measuring the height of the outer segment (OS) layer in the center of the fovea; defined as the distance between the IS/OS junction and the retinal pigment epithelium. We show a similar increase in OS height at the fovea in both “normal” groups, but in two patients with ocular albinism, we observed no thickening of the OS layer in the foveal center, presumably reflecting an absence of foveal cone packing. However, while we found significant variation in the height of the OS layer (about a factor of 2 across 16 normal subjects), there was no correlation between OS height (i.e., cone packing) and any of the foveal morphological characteristics (pit depth, diameter, or slope). Future work will incorporate adaptive optics imaging of the cone mosaic to investigate how accurately OS layer height represents the degree of cone photoreceptor packing.
DubisA. M.McAllisterJ. T. (2008). “Three-Dimensional Mapping of the Fovea in Normal and Diseased Retina. Investigative Ophthalmology & Visual Science, 49, ARVO E-Abstract 1835.
SpringerA. D.HendricksonA. E. (2005). Development of the primate area of high acuity. 3: Temporal relationships between pit formation, retinal elongation and cone packing. Visual Neuroscience, 22(2), 171–185.
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