Purchase this article with an account.
Alan D Springer; Reverse engineering of foveal cone packing and stacking in three primate species. Invest. Ophthalmol. Vis. Sci. 2017;58(8):342.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Foveal cone nuclei in primates are arranged, initially, as a monolayer close to the outer limiting membrane (OLM). This monolayer persists until after the pit forms. The monolayer then transforms into a compact mound of nuclei. This transformation is often interpreted as the cone nuclei migrating actively, centripetally and axially (inwardly) to create a stack of nuclei. The topography within the nuclear stack is uncertain. One suggestion is that the oldest nuclei are innermost and the youngest are outermost, close to the OLM. Such topography implies that the nuclei are arranged in a tangential laminated fashion as are the other retinal laminae. These assumptions, and alternatives, were evaluated using image analysis methods.
Sections through the foveas of humans, Macaque and marmoset monkeys of varying ages were evaluated quantitatively to determine whether foveal cone nuclei were oriented more parallel or orthogonal to the OLM (i.e., horizontal (H) vs. vertical (V)). Images were analyzed using both H and V line filter kernels. These filters led to elongated nuclear profiles (blobs) that encompassed 1-8 nuclei. The angles formed by the major axis of the blobs with respect to the OLM were quantified as to how many degrees they deviated from being vertical.
Mean angular deviation from V was 15° using a V filter and 27° using a H filter for humans (n=6), 13° and 27° for Macaque (n=9) and 13° and 24° for marmosets (n=9). Paired t-tests found the V-H differences to be significant for each group (Ps=0.005, Power >0.95). These data indicate that there are columns of cone nuclei that are more V than H oriented at the fovea of all three species. Perfectly vertical nuclear columns were not expected because inner retinal cell displacements tilts cone columns centrifugally.
These results led to an “inchworm model” of foveal packing and stacking (see Fig.). The cone nuclei in the monolayer undergo variable distance nucleokinesis in the axial/inward direction. As the cones pack, the tangential compression of the resulting sinusoidal array of nuclei preserves the parallel arrangement of the outer segments, inner segments, outer fibers and Henle axons. Also maintained are the nearest neighbor nuclear contiguities that existed in the nuclear monolayer. Moreover, the model is consistent with cone packing beginning at the edge of the pure cone array and progressing toward the center of the array.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
This PDF is available to Subscribers Only