The average corneal curvature measures approximately how many diopters on the Keratometer?

• A. 40 D
• B. 44 D
• C. 48 D
• D. 46 D

Answer: (B)

The reading you get from a keratometer reflects the central refractive power of the cornea. On average, that central corneal power is about 44 diopters. This aligns with the typical central corneal radius of roughly 7.6–7.8 mm. Using the keratometer’s conversion (which uses the corneal index difference to translate radius into diopters), a radius near 7.7 mm yields about 44 D. So the mid-40s, around 44 diopters, is the normal, expected value.

If the cornea were flatter, the diopter value would be lower (for example, around 40 D corresponds to a flatter radius), while a steeper cornea would push the value higher (46–48 D). The average, and therefore the best answer here, is about 44 D.