The objective of the proposed research is to study the central nervous control of accommodation. The nucleus of Edinger-Westphal (EW), via its projection to the ciliary ganglion, is involved in the mediation of three clinically important visual functions: accommodation, pupilloconstriction, and choroidal blood flow. EW in birds is much more clearly delineated in its cytoarchitecture than in mammals, and two morphologically distinct subpopulations of neurons (i.e., choroid and ciliary) have been described in the avian ciliary ganglion. Our previous studies of the central control of the pupillary light reflex and choroidal blood flow have identified two bisynaptic retinofugal pathways projecting to different subdivisions of EW. A third subdivision of EW may be involved in the control of accommodation. The major goals of the present proposed studies are to determine: (1) the central pathways controlling accommodation, (2) the differential projection of the three subdivisions of EW on the two cell types in the ciliary ganglion, and (3) the pupillary subdivision of EW in the cat and rabbit, important mammalian models for visual studies. Anatomical methods will be used, including: microstimulation in conjunction with discrete lesions, conventional pathway tracing techniques (i.e., autoradiography, HRP and immunohistochemistry), and transsynaptic transport methods. In order to help establish the visual function(s) of specific pathways, both pupillometry and retinoscopy will be used to measure changes in pupil size and accommodative state fo the eye during microstimulation of selected neuronal structures. More anatomical knowledge of the central control of accommodation may provide critically needed experimental models for the future investigation of the role of over-accommodation in the development of myopia.
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