Autonomic denervations influence ocular dimensions and intraocular pressure in chicks

Choroidal thickness and axial eye length in the chick undergo day/night flu ctuations that can also be modulated by visual experience. In the present s tudy, we tested the effect of parasympathetic and sympathetic denervations on both day/night and image dependent changes in ocular dimensions. We also correlated such changes with fluctuations in intraocular pressure. Parasym pathectomy influenced choroidal thickness and its day/night fluctuation, bu t had no effect on vision dependent choroidal thickness modulation. Parasym pathectomy also influenced-to a lesser extent-axial length and reduced the axial growth response to form vision deprivation. Sympathectomy had little effect on ocular dimensions, but reduced the day/night differences in intra ocular pressure. We conclude that (a) the parasympathetic nervous system in fluences both choroidal thickness and axial length and participates in the neural control mechanism leading to form deprivation myopia and, (b) the da y/night fluctuations of choroidal thickness and axial length are unlikely t o be explained by fluctuations in intraocular pressure. For the regulation of choroidal thickness, we hypothesize the existence of two independent mec hanisms. One involves the parasympathetic nervous system; it influences the day/night choroidal thickness fluctuation. The other uses a separate pathw ay and is driven by visual input. (C) 1999 Academic Press.