Glasser A, Troilo D, Howland H C
Section of Physiology, Cornell University, Ithaca, NY 14853.
Vision Res. 1994 Jun;34(12):1549-66. doi: 10.1016/0042-6989(94)90112-0.
Corneal accommodation can account for up to 9 D of accommodation in a freely behaving chick. We have explored the possibility that changes in corneal curvature are due to changes in intraocular pressure (IOP) during accommodation. In an in vitro preparation we demonstrate that increasing the pressure will tend to flatten the cornea. We have used electrical stimulation of the Edinger-Westphal (EW) nucleus to further test the pressure hypothesis in vivo by recording IOP changes in the eye during EW-stimulated accommodation and by artificially modulating the IOP to assess the effects on corneal curvature. During EW stimulation there is an increase in IOP on the order of 1-3 mmHg which tends to flatten the curvature of the cornea, thus eliminating changes in IOP as a possible mechanism of corneal accommodation. Slit-lamp observations of accommodative changes at the corneo-scleral margin and electrical stimulation of dissected eyes in vitro indicate that corneal accommodation is mediated by a contraction of the ciliary muscles, which exerts a pull on the inner lamella of the cornea, flattening the peripheral cornea and increasing the curvature of the central cornea. Histological examination of the ciliary region of the eye confirms the appropriate positioning of the ciliary muscles. We conclude that corneal accommodation in the chick eye is accomplished by a ciliary muscle-mediated mechanism.
在自由活动的雏鸡中，角膜调节可提供高达9 D的调节力。我们探讨了调节过程中角膜曲率变化是否是由于眼内压（IOP）变化所致的可能性。在体外实验中，我们证明增加压力会使角膜趋于变平。我们通过记录电刺激动眼神经核（EW）引起的眼内压变化，并人为调节眼内压以评估其对角膜曲率的影响，进一步在体内验证压力假说。在电刺激EW期间，眼内压升高约1 - 3 mmHg，这会使角膜曲率变平，因此排除了眼内压变化作为角膜调节可能机制的可能性。裂隙灯观察角膜巩膜缘的调节变化以及体外对离体眼的电刺激表明，角膜调节是由睫状肌收缩介导的，睫状肌收缩会对角膜内层施加拉力，使周边角膜变平，中央角膜曲率增加。对眼部睫状区的组织学检查证实了睫状肌的正确定位。我们得出结论，雏鸡眼角膜调节是通过睫状肌介导的机制完成的。
