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Carl F. Marfurt; Subbasal Nerve Plexus Architecture In Mammals With And Without A Nictitating Membrane. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4193.
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The mechanisms that regulate pattern formation of the corneal subbasal nerve plexus are unclear but may be related in part to eyelid movements during spontaneous blinking. The purpose of this study is to test the hypothesis that subbasal nerve plexus architecture differs between mammals with or without a nictitating membrane.
Corneal nerves in three species with a nictitating membrane (rabbit, porcine, and cow) and three species without a nictitating membrane (human, rat, and guinea pig) were stained immunohistochemically with a neurotubulin antibody. Subbasal nerve plexuses in whole corneas were reconstructed onto series of large-scale corneal maps using a drawing tube attached to a light microscope.
Subbasal nerve fibers (snfs) in species without a nictitating membrane radiated centrally from all corneal regions to form a whorl-like pattern whose center of convergence, or vortex, was located approximately 0.5-1.0mm (rats and guinea pigs) or 2.5mm (humans) inferior or inferonasal to the corneal apex. Snfs in rabbit and bovine corneas swept collectively over the corneal surface towards the inferonasal limbus; however, the nerves did not form a spiral or vortex. The area of limbus towards which the fibers converged was equidistant between the nasal and inferior poles in bovine corneas, but closer (about 2.0mm inferior) to the nasal pole in rabbits. The architectural pattern of the subbasal nerve plexus in porcine corneas was drastically different than that of any other species. Porcine snfs radiated centrifugally in all directions from an imaginary center located in the superior cornea close to the vertical meridian and slightly greater than half the distance from the corneal apex to the limbus.
The results of the present study have demonstrated substantial interspecies differences in subbasal nerve plexus architecture; however, a meaningful relationship between snf pattern and the presence of a nictitating membrane was not shown. Subbasal nerve fibers in rabbit and bovine corneas radiated uniformly in an inferonasal direction towards the nictitating membrane; however porcine snfs radiated, unexpectedly, centrifugally in all directions from a superior focal point. The mechanisms that regulate snf elongation and pattern development remain elusive and warrant additional investigation.
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