A cat’s eyes are different not only in the early morning and late evening, but also at noon compared to morning and evening. There is a Chinese folk saying about the three daily changes of a cat’s eyes: “In the hours of Yin, Mao, Shen, and You, they are like a date pit; in the hours of Chen, Si, Wu, and Wei, they are like a line; in the hours of Zi, Chou, Xu, and Hai, they are like a full moon.” This saying vividly describes the changes in a cat’s eyes.
Why do a cat’s eyes change three times a day? We just need to carefully study the structure of its eyeballs to understand the reason.
It turns out that a cat’s pupils are very large, and the contraction ability of the pupil sphincter muscle is particularly strong. When humans look at the sun, their pupils will shrink, but after shrinking to a certain extent, they will no longer shrink. Therefore, after a long time, the eyes will feel uncomfortable. Similarly, looking in excessively dim places for too long can cause dizziness. However, cats can adapt well to different lighting conditions: in the intense sunlight at noon, their pupils can shrink very small, like a line; in the dim conditions of the night, their pupils can open as wide as a full moon; in the medium light of the morning, their pupils can take the shape of a date pit. Because their pupils have a greater ability to contract than humans, their response to light is more sensitive. Thus, despite very strong or very weak light conditions, cats can still see things clearly.