The pupil literally plays a central role in vision: it is the opening in the middle of the eye that regulates how much light falls on the retina. If it is dark, the pupil becomes large and lets a lot ...

Pupils naturally dilate in low light to allow more light into the eye, and also due to emotional or mental stimuli. Other causes of dilated pupils include medications given during an eye exam, various ...

A person’s pupils may be of different sizes (anisocoria) for several reasons, including physical trauma, response to light, and infection. The condition may also be present from birth. Pupils, or the ...

Why do the eyes of some animals, including goats, have horizontal-shaped pupils, while others, such as rattlesnakes and domestic cats, have vertical slits? It is a question that has longed intrigued ...

It is commonly known that pupil size fluctuates in response to brightness and darkness during wakefulness. What is less commonly known is that pupil size is also regulated by the autonomic nervous ...