The human eye is an organ of the sensory nervous system that reacts to visible light and allows the use of visual information for various purposes including seeing things, keeping balance, and maintaining circadian rhythm. Arizona Eye Model. "A" is accommodation in diopters. The eye can be considered as a living optical device. It is approximately spherical in shape, with its outer layers, such as
![Human eye - Wikipedia](https://cdn-ak-scissors.b.st-hatena.com/image/square/90189af451caf192e945703fe18ec1ae2dccaf72/height=288;version=1;width=512/https%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fthumb%2F0%2F08%2FHuman_eye%252C_anterior_view.jpg%2F1200px-Human_eye%252C_anterior_view.jpg)