The effects of choroidal or ciliary nerve transection on myopic eye growth induced by goggles

Abstract

Purpose: To determine the role of the choroidal and ciliary nerves and the functions they control, choroidal blood flow (CBF) and accommodation-pupil diameter, respectively, in myopia induced by form-vision deprivation.

Methods: Three groups of chicks were studied: chicks with choroidal nerves cut in the right eye, chicks with ciliary nerves cut in the right eye, and sham control chicks that received the same surgical preparation but no nerve cuts. A plastic, dome-shaped goggle was glued over the right eye of birds in all three groups after orbital surgery, and, 2 weeks later, CBF was measured using laser Doppler flowmetry. Refractive status was then measured using streak retinoscopy, and axial, nasotemporal, and dorsoventral lengths were measured using vernier calipers after enucleation. The eyes were also weighed.

Results: In the sham control birds, considerable ocular enlargement in all dimensions and a high degree of myopia (-14.68 diopters) was observed in the goggled eye, and CBF in the goggled eye was 66% of that in the nongoggled eye. In birds with choroidal nerve cuts, the degree of enlargement of the goggled eye was less in all dimensions, and the myopia in the goggled eye (-4.74 D) was attenuated compared to that observed in the sham controls. CBF in the goggled eye was 21% of that in nongoggled eye. Finally, in the birds with ciliary nerve cuts, nasotemporal and dorsoventral enlargement of the goggled eye were similar to that in the shams, but the axial elongation and the degree of myopia (-9.57 D) were less than observed in sham control eyes. As in the shams, CBF in the goggled eye was reduced to 59% of that in the nongoggled eye.

Conclusions: These results show that although elimination of accommodation and severe reductions in CBF do affect eye growth (the latter more so), they do not prevent form-vision deprivation-induced myopia. Thus, either the mechanism of visual deprivation-induced myopia is different from that in idiopathic human myopia, or CBF levels and accommodation do not play a major role in either.