National Contact Lens Examiners (NCLE) Practice Exam

In the field of contact lenses, the base curve is critical for achieving a proper fit on the cornea. The base curve specified for a contact lens affects the lens's overall curvature and its relationship to the eye's surface curvature. When the base curve of a lens is changed, it can alter the lens's power.

In this case, the base curve ordered was 7.80mm, and the base curve received is 7.85mm. Since a larger base curve radius represents a flatter surface in comparison to a smaller base curve radius, the lens that was received (7.85mm) is indeed flatter than the lens that was ordered (7.80mm).

To determine the impact on lens power, adjustments in base curve can be related to diopters (D). A difference in base curve of 0.05mm typically indicates a change in refractive power of approximately 0.25 D. Therefore, moving from 7.80mm to 7.85mm results in a change of 0.25 D in the flatter direction.

This connection between the base curve measurement and lens power elucidates why the correct answer is that the lens received is 0.25 D flatter than what was originally ordered. Understanding the