What is the normal pupil diameter?

As the saying goes, eyes are the windows to the soul. Obviously, eyes are very important to a person's spiritual expression. When people talk about eye size, they are usually referring to the size of a person's pupils. So does it mean that larger pupils mean better-looking eyes and a more beautiful mind? Does it mean that if the pupil is small, the eyes will definitely be small?

The pupil is the small round hole in the center of the iris in the eye, which is what we call the pupil, also called the "pupil", which is the channel for light to enter the eye. The contraction and expansion of the smooth muscles on the iris can shrink or expand the diameter of the pupil, thereby controlling the amount of light entering the pupil. There are two kinds of tiny smooth muscles on the iris. One is called the sphincter pupillae, which surrounds the pupil and is less than 1 mm wide. It is responsible for the constriction of the pupil and is controlled by the parasympathetic nerves in the oculomotor nerve. The other is called the dilator pupillae, which is arranged radially in the iris and is responsible for the dilation of the pupil and is controlled by the sympathetic nerves. These two muscles coordinate and restrict each other, expanding and contracting to adapt to various different environments.

The pupil diameter of an adult is generally 2-4mm, in a perfect circle, equal in size on both sides, with a difference of no more than 0.25mm. However, if the pupil diameters of both eyes differ by 0.25-0.5mm, and there are no abnormalities in pupil reactions or drug experiments, it can be considered physiological anisocoria. The range of pupil variation can be very large. When extremely contracted, the diameter of the human pupil can be less than 1 mm, and when extremely dilated, it can be greater than 9 mm. This is because the iris sphincter can shrink to 87% of its length, which is almost impossible for other smooth muscles or striated muscles in the human body to achieve. In addition to changing with the intensity of light, the size of the pupil is also related to factors such as age, refraction, and physiological condition. Generally speaking, the pupils of older people are smaller, while those of infants to adults are larger, especially during adolescence when the pupils are largest. People with myopia have larger pupils than people with hyperopia. The pupils will dilate when you are nervous or excited, and will shrink when you take deep breaths, do mental work, or sleep. In addition, the pupils may dilate or contract when certain diseases occur or certain medications are used. When the pupil is exposed to light, the aperture becomes smaller, which is called direct light reflex. If light is shone on the other eye, the pupil of the non-illuminated eye will shrink, which is called indirect light reflex. When looking at close objects, the pupil shrinks due to accommodation and convergence, which is called the pupil near reflex, which is the coordination of the cerebral cortex.

From the above analysis and discussion, it can be seen that the diameter of the pupil is not a fixed value. The pupil diameters of different people are different; for the same person, the size of his pupils also varies with certain conditions and situations. Therefore, the normal value of pupil diameter is dynamic for everyone. As long as you are healthy, there is no need to worry.