A 50-year-old patient requires a +1.50 ADD. NRA/PRA at working distance yields NRA +1.75 and PRA -0.25. What is the new tentative add?

A 50-year-old patient requires a +1.50 ADD. NRA/PRA at working distance yields NRA +1.75 and PRA -0.25. What is the new tentative add?

• A. +1.50
• B. +2.25
• C. +3.00
• D. +2.00

Answer: (B)

The idea is to estimate a near addition by using the patient's accommodative reserve at the testing distance. NRA shows how much plus you can add to relax accommodation, and PRA shows how much minus you can add to stimulate it. The net accommodative range is NRA + PRA. To get a safe, comfortable tentative near add, you add half of that net range to the current distance add. Compute: NRA + PRA = +1.75 + (-0.25) = +1.50 D. Half of that is +0.75 D. Add to the existing near add of +1.50 D, giving +2.25 D. So the new tentative add is +2.25 D.

The idea is to estimate a near addition by using the patient's accommodative reserve at the testing distance. NRA shows how much plus you can add to relax accommodation, and PRA shows how much minus you can add to stimulate it. The net accommodative range is NRA + PRA. To get a safe, comfortable tentative near add, you add half of that net range to the current distance add.

Compute: NRA + PRA = +1.75 + (-0.25) = +1.50 D. Half of that is +0.75 D. Add to the existing near add of +1.50 D, giving +2.25 D.

So the new tentative add is +2.25 D.