A 46-year-old woman has an amplitude of accommodation of 3.00 D in each eye. She wishes to read comfortably at 40 cm, keeping at least half her amplitude in reserve. What near addition should be prescribed over her distance correction?

• A +0.75 D
• B +2.50 D
• C +1.50 D
• D +1.00 D ✓

Explanation

Reading at 40 cm demands 2.50 B of accommodation. To keep half the amplitude, 1.50 B, in reserve, she can comfortably use only the remaining 1.50 B. The shortfall of 1.00 B must be supplied by a near addition, so +1.00 B is added over the distance prescription. Prescribing the full 2.50 B demand as an addition would leave zero reserve and cause asthenopic fatigue, while +1.50 B would leave her holding more than half in reserve than needed.

Reference: Parsons' Diseases of the Eye, 23rd ed.

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