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 controls were done (n=7). 8-14 d later, axial dimensions were measured with ultrasonography at 4-hr intervals over 24 hrs. Rhythm parameters were assessed using a "best fit" function, and growth rates measured. Both types of lesion resulted in ultradian (>1 cycle/24 hr) rhythms in choroidal thickness and axial length, and increased vitreous chamber growth (Expfellow: double: 69 μm; triple: 104 μm; 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 sham surgery controls (axial: 107 vs 54 μm; choroid: 124 vs 29 μm, p<0.05). These findings provide evidence for the involvement of abnormal ocular rhythms in the growth stimulation underlying myopia development.

Relationship Between Autonomic Nervous System Activity and Axial Length in Children

“…In addition, Schmid et al reported that sympathectomy had an effect on ocular dimensions, and parasympathectomy could significantly influence AL, CT, and choroidal day-night fluctuation rhythm [ 49 ]. After parasympathectomy, AL and the fluctuation of CT increase, indicating that the parasympathetic nervous system influences CT and participates in the neural control mechanism of axial elongation [ 25 , 49 ]. Previous studies also indicate that the autonomic nervous system may play an important role in the development of myopia [ 27 – 29 ].…”

“…Thus, no effective treatment has been established to control axial elongation or prevent the progression of myopia. Previous studies have reported that the autonomic nervous system innervates the iris, ciliary muscle, and choroid of the eye, and regulates accommodation, choroidal thickness (CT), choroidal rhythm, and pupillary responses, which are closely related to the development of myopia [23][24][25][26]. By regulating the choroid and sclera, the autonomic nervous system plays an important role in the development of myopia [27][28][29][30].…”