Effects of autonomic denervations on the rhythms in axial length and choroidal thickness in chicks.

Abstract

In chicks, axial length and choroidal thickness undergo circadian oscillations. The choroid is innervated by both branches of the autonomic nervous system, but their contribution(s) to these rhythms is unknown. We used two combination lesions to test this. For parasympathectomy, nerve VII was sectioned presynaptic to the pterygopalatine ganglia, and the ciliary post-ganglionics were cut (double lesion; n = 8). Triple lesions excised the sympathetic superior cervical ganglion as well (n = 8). Sham surgery was done in controls (n = 7). 8-14days later, axial dimensions were measured with ultrasonography at 4-h intervals over 24h. Rhythm parameters were assessed using a "best fit" function, and growth rates measured. Both types of lesions resulted in ultradian (> 1 cycle/24h) rhythms in choroidal thickness and axial length, and increased vitreous chamber growth (Exp-fellow: double: 69µm; triple: 104µm; p < 0.05). For double lesions, the frequency was 1.5 cycles/day for both rhythms; for triples the choroidal rhythm was 1.5 cycles/day, and the axial was 3 cycles/day. For double lesions, the amplitudes of both rhythms were larger than those ofsham surgery controls (axial: 107 vs 54µm; choroid: 124 vs 29µm, p < 0.05). These findings provide evidence for the involvement of abnormal ocular rhythms in the growth stimulation underlying myopia development.