What is the dark opening in the center of the eye that lets light in?
AnswerPupil
The pupil is an opening that widens in dim light and narrows in bright light.
Science · Facts & stats
Eye facts & stats
7 fact-checked facts about the human eye and vision, each with the reason behind it. 5 more are in today's round and join this page after it closes.
The basics
What is the tough white outer layer of the eyeball called?
AnswerSclera
The sclera is the white, protective outer coat of the eyeball.
Going deeper
Which cells in the retina are mainly responsible for color vision?
AnswerCones
Cone cells detect color and fine detail in bright light; rods work best in dim light.
How is the image formed on the retina oriented?
AnswerUpside down
The lens projects an inverted image onto the retina, and the brain interprets it upright.
What is the common medical term for nearsightedness?
AnswerMyopia
Myopia means distant objects look blurry while close objects are clear.
Expert level
How many types of cone cells do most humans have?
Answer3
Most people have three cone types, sensitive roughly to short, medium and long wavelengths of light.
The light-sensitive pigment in rod cells is built from a molecule derived from which vitamin?
AnswerVitamin A
Rhodopsin in rods uses retinal, a form of vitamin A, to detect light.
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