Accommodation

When the eye is relaxed and the interior lens is the least rounded, the lens has its maximum focal length for distant viewing . As the muscle tension around the ring of muscle is increased and the supporting fibers are thereby loosened, the interior lens rounds out to its minimum focal length..

Modeling Accommodation

To model the accommodation of the eye, the scale model eye was used with the cornea through the front surface of the lens held constant at the model values. The matrix for that part of the eye was calculated and then the thickness d and back surface power P were varied. 为模拟眼睛的调节功能，使用了标尺模型眼睛，其中角膜通过透镜的前表面保持在模型值不变。该部分眼睛的矩阵已被计算，然后厚度d和后表面功率P被进行变化。

Ciliary Muscle and Fibers

When the ciliary muscles contract, they loosen the ciliary fibers which are attached to the envelope of the crystalline lens. Because the lens is pliable, it relaxes into a more curves shape, increasing it's refractive power to accommodate for closer viewing. The iris serves as the aperture stop for the eye, closing to about 2mm in diameter in bright light and opening to a maximum of about 8mm in dim light. 当睫状肌收缩时，它们会放松附着在晶状体包膜上的睫状纤维。由于晶状体具有可塑性，它会放松成一个更弯曲的形状，从而增加其折射力，以适应近距离观察。虹膜作为眼睛的光圈限制装置，在强光下收缩到约2毫米直径，弱光下则扩张到最大约8毫米直径。

Accommodation in Animal Eyes

Many animals can see clearly both in water and on land. Some have extraordinary accommodation ranges, and others have developed other strategies. Cormorants and dippers can vary the refractive power of their lenses by 40-50 diopters, compared to about 16 diopters for an average adolescent human. The increased accommodation is due largely to highly developed sphincter muscles which vary the curvature of the front of the lens. Turtles and otters also have very strong sphincter muscles. Variations in lens geometries are used in various species of birds and fish. The short article by James and Laura White opens some fascinating possibilities .