What is the primary refractive element of the eye?

What is the primary refractive element of the eye?

• A. The cornea, with a power of +43 D
• B. The lens, with variable power
• C. The retina
• D. The iris

Answer: (A)

The main idea is that the cornea does the majority of the eye’s focusing. Because light passes from air into the curved, highly refractive front surface of the eye, it experiences the largest bend there. The cornea contributes about +40 to +43 diopters of optical power, which is the bulk of the eye’s focusing ability. The lens sits behind the cornea and can change shape to adjust focus for near vs. far tasks, adding a smaller, variable amount of power (roughly a few to about twenty diopters when accommodating). But this power change is secondary to the cornea’s fixed, dominant contribution. The eye’s total refractive power is around +60 diopters, with the cornea providing the major share. The retina is simply the image plane, and the iris is involved in controlling the amount of light entering the eye; neither accounts for focusing. That’s why the cornea, with about +43 diopters, is the best answer for the primary refractive element.

The main idea is that the cornea does the majority of the eye’s focusing. Because light passes from air into the curved, highly refractive front surface of the eye, it experiences the largest bend there. The cornea contributes about +40 to +43 diopters of optical power, which is the bulk of the eye’s focusing ability. The lens sits behind the cornea and can change shape to adjust focus for near vs. far tasks, adding a smaller, variable amount of power (roughly a few to about twenty diopters when accommodating). But this power change is secondary to the cornea’s fixed, dominant contribution. The eye’s total refractive power is around +60 diopters, with the cornea providing the major share.

The retina is simply the image plane, and the iris is involved in controlling the amount of light entering the eye; neither accounts for focusing. That’s why the cornea, with about +43 diopters, is the best answer for the primary refractive element.