Which structure contributes the most refractive power?

Which structure contributes the most refractive power?

• A. The cornea
• B. The lens
• C. The iris
• D. The sclera

Answer: (A)

The cornea provides the most refractive power because it is the first and strongest bending surface light encounters as it enters the eye. The interface from air (low refractive index) to corneal tissue (higher index) is steeply curved, which creates a large change in light direction—roughly about 40 diopters of power. The lens inside the eye adds further focusing but contributes much less, around 20 diopters, and it can adjust its shape for near or far vision. The iris and sclera don’t contribute meaningful refractive power; the iris mainly controls light entering the eye, and the sclera is largely a structural, non-refracting layer. So, the cornea accounts for the majority of the eye’s optical power.

The cornea provides the most refractive power because it is the first and strongest bending surface light encounters as it enters the eye. The interface from air (low refractive index) to corneal tissue (higher index) is steeply curved, which creates a large change in light direction—roughly about 40 diopters of power. The lens inside the eye adds further focusing but contributes much less, around 20 diopters, and it can adjust its shape for near or far vision. The iris and sclera don’t contribute meaningful refractive power; the iris mainly controls light entering the eye, and the sclera is largely a structural, non-refracting layer. So, the cornea accounts for the majority of the eye’s optical power.