The part of the human eye that controls the size of the pupil is the iris. The iris is the colored part of the eye that surrounds the pupil and regulates the amount of light that enters the eye by adjusting the size of the pupil. The size of the pupil can change in response to different lighting conditions and stimulation. In bright light, the iris contracts to make the pupil smaller in order to reduce the amount of light entering the eye. This helps to protect the sensitive structures inside the eye from damage caused by excessive light. On the other hand, in dim light, the iris expands to make the pupil larger, allowing more light to enter the eye to improve visibility. The ability of the iris to regulate the size of the pupil is controlled by a complex network of muscles and nerves. These muscles work together to adjust the diameter of the pupil in a process known as pupillary light reflex. This reflex is automatic and helps to maintain optimal visual acuity in various lighting conditions. Understanding how the iris controls the size of the pupil is important for maintaining good eye health and vision. If you experience any changes in pupil size or have concerns about your eye health, it is essential to consult with an eye care professional for a comprehensive eye examination. To learn more about the anatomy and function of the human eye, you can visit websites such as [www.aao.org/eye-health/anatomy](www.aao.org/eye-health/anatomy) or [www.nei.nih.gov/learn-about-eye](www.nei.nih.gov/learn-about-eye). These resources provide valuable information on the different parts of the eye, including the iris and pupil, and how they work together to help you see clearly. In conclusion, the iris is the part of the human eye that controls the size of the pupil. By adjusting the diameter of the pupil in response to changing lighting conditions, the iris plays a crucial role in maintaining optimal vision and eye health. If you have any concerns about your eye health, don't hesitate to seek professional advice from an eye care specialist.

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