American Board of Ophthalmology (ABO) Practice Exam

When transposing a prescription, how does the add power change?

1. Increases

2. Decreases

3. Stays the same

4. Varies based on lens type

The correct answer is: Stays the same

When transposing a prescription, the add power remains the same. This is because the add power specifically refers to the additional lens power required for near vision tasks, such as reading. The process of transposing involves changing the form of a prescription by converting between plus and minus cylinder formats, but it does not affect the addition for near vision. In practical terms, when practitioners transpose a prescription, they adjust the sphere and cylinder values while adhering to the original add power. Therefore, the add remains stable irrespective of whether the prescription is expressed in the minus or plus cylinder form. This consistency is crucial for ensuring that the patient receives the correct level of near vision correction they require, regardless of the adjustments made during the transposition process. Understanding this principle is key for both prescribing accurate glasses and ensuring patient satisfaction in visual tasks that require multifocal lenses.