Steepening the GP base curve by 0.2 mm results in approximately how much change in lens power (magnitude)?

Steepening the GP base curve by 0.2 mm results in approximately how much change in lens power (magnitude)?

• A. +0.25 D
• B. +0.50 D
• C. +1.00 D
• D. +1.50 D

Answer: (C)

In GP lens fitting, small changes to the posterior curvature (base curve) of the lens noticeably affect the eye’s effective refractive power. The reason is that the base curve, together with the tear layer between the lens and cornea, determines the optical surface that the pupil uses. A common practical rule is that about 0.5 diopters of power change occur for each 0.1 mm change in base-curve radius. So steepening the base curve by 0.2 mm tightens the lens fit and increases the effective curvature by roughly twice that amount, giving an approximate 1.0 D change in lens power. This is an approximate figure used in clinic because the exact change depends on lens diameter, tear film, and fit, but 0.2 mm steepening reliably yields around 1 diopter of power shift.

In GP lens fitting, small changes to the posterior curvature (base curve) of the lens noticeably affect the eye’s effective refractive power. The reason is that the base curve, together with the tear layer between the lens and cornea, determines the optical surface that the pupil uses. A common practical rule is that about 0.5 diopters of power change occur for each 0.1 mm change in base-curve radius. So steepening the base curve by 0.2 mm tightens the lens fit and increases the effective curvature by roughly twice that amount, giving an approximate 1.0 D change in lens power. This is an approximate figure used in clinic because the exact change depends on lens diameter, tear film, and fit, but 0.2 mm steepening reliably yields around 1 diopter of power shift.