When deriving a near Rx from a distance Rx by adding +2.00 D, which statement is true?

When deriving a near Rx from a distance Rx by adding +2.00 D, which statement is true?

• A. Sphere power decreases toward more negative by ADD
• B. Sphere power moves toward zero by ADD
• C. Sphere power remains unchanged
• D. Sphere power moves toward more positive by ADD

Answer: (B)

Adding a plus add to a distance prescription changes the sphere by that amount. If the distance Rx is nearsighted (negative sphere), adding +2.00 D reduces the magnitude of the myopia, moving the sphere power closer to zero. For example, a distance Rx of -4.00 D becomes -2.00 D when you add +2.00 D. This is why the near Rx’s sphere power moves toward zero by the added plus. Note: if the original distance Rx were hyperopic or plano, adding +2.00 D would not move toward zero in the same way, but the scenario described—deriving a near Rx from a distance Rx by adding +2.00 D—typically applies to correcting myopia so the sphere shifts toward zero.

Adding a plus add to a distance prescription changes the sphere by that amount. If the distance Rx is nearsighted (negative sphere), adding +2.00 D reduces the magnitude of the myopia, moving the sphere power closer to zero. For example, a distance Rx of -4.00 D becomes -2.00 D when you add +2.00 D. This is why the near Rx’s sphere power moves toward zero by the added plus.

Note: if the original distance Rx were hyperopic or plano, adding +2.00 D would not move toward zero in the same way, but the scenario described—deriving a near Rx from a distance Rx by adding +2.00 D—typically applies to correcting myopia so the sphere shifts toward zero.