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Carl F. Marfurt, Miracle Anokwute, Kaleigh Fetcko; Comparative Anatomy Of The Corneal Subbasal Nerve Plexus. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1797.
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The mechanisms that regulate pattern formation of the mammalian corneal subbasal nerve plexus are unclear but may include physical pressures from centripetally migrating corneal epithelial cells, chemotropic guidance, and shearing forces exerted by eyelid movements. The purpose of the current study was to describe in detail the directional orientation of the subbasal nerve plexus in seven mammals that differ substantially in corneal surface area, radius of curvature, and presence or absence of a third eyelid.
Corneal nerves in four species possessing a nictitating membrane (rabbit, dog, cow, and pig) and three species lacking a nictitating membrane (human, rat, and guinea pig) were stained immunohistochemically with antiserum directed against neurotubulin. The subbasal nerve plexuses were reconstructed onto large-scale corneal maps using a drawing tube attached to a light microscope.
Subbasal nerve fibers in humans, rats, guinea pigs and dogs radiate centrally from the corneoscleral limbus in a whorl-like pattern whose center of convergence, or vortex, is located either inferonasal or inferotemporal to the corneal apex. Subbasal nerve fibers in rabbit and bovine corneas do not form spiral patterns and instead course horizontally across the ocular surface in the direction of the nasal or inferonasal limbus. Subbasal nerve fibers in the pig cornea differ markedly from all other species examined in this study and radiate centrifugally in all directions from a focal point, or hub, located approximately equidistant between the corneal apex and the superior pole.
The results of the present study have revealed the existence of three distinct architectural patterns of subbasal nerve plexus organization in mammalian corneas. The patterns do not correlate in any meaningful way with interspecies differences in corneal surface area, radius of curvature, or the presence of a third eyelid. The mechanisms that regulate subbasal nerve fiber pattern formation in the mammalian eye, both developmentally and during corneal nerve regeneration, remain incompletely understood and warrant additional investigation.
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