Which part first refracts incoming light as it enters the eye?

• A. Pupil
• B. Iris
• C. Cornea
• D. Vitreous humor

Answer: (C)

Light entering the eye is bent most at the cornea, the clear, curved outer surface. Because light moves from air into this different medium, the change in refractive index causes a strong bend there, making the cornea responsible for the majority of the eye’s focusing power. The iris and pupil merely regulate how much light enters; they do not bend it. The vitreous humor is the gel inside the eye that light travels through after passing the lens, not a surface that refracts at entry. After the cornea, light passes through the aqueous humor and the lens to fine-tune focus onto the retina.