NRA indirectly tests PFV and PRA indirectly tests NFV. Which of the following statements is true?

NRA indirectly tests PFV and PRA indirectly tests NFV. Which of the following statements is true?

• A. NRA indirectly tests PFV and PRA indirectly tests NFV
• B. NRA indirectly tests NFV and PRA indirectly tests PFV
• C. NRA directly tests PFV
• D. PRA directly tests NFV

Answer: (A)

The key idea is how accommodation and vergence work together. NRA and PRA don’t measure PFV or NFV directly; they reveal how much the vergence system can compensate when accommodation demands shift. In the NRA test, you add plus lenses, which relaxes accommodation. Because less accommodation means less accommodative convergence, the eyes would tend to diverge in convergence unless PFV steps in to provide the needed convergence. If the patient can still maintain single vision as plus power increases, it shows a good PFV reserve. So NRA performance reflects PFV indirectly. In the PRA test, you add minus lenses, which increase accommodation demand and boost accommodative convergence. To stay aligned, the eyes must rely on NFV to diverge enough to offset that extra convergence. If fusion is maintained, it indicates a healthy NFV reserve. So PRA performance reflects NFV indirectly. Therefore, the true statement is that NRA indirectly tests PFV and PRA indirectly tests NFV.

The key idea is how accommodation and vergence work together. NRA and PRA don’t measure PFV or NFV directly; they reveal how much the vergence system can compensate when accommodation demands shift.

In the NRA test, you add plus lenses, which relaxes accommodation. Because less accommodation means less accommodative convergence, the eyes would tend to diverge in convergence unless PFV steps in to provide the needed convergence. If the patient can still maintain single vision as plus power increases, it shows a good PFV reserve. So NRA performance reflects PFV indirectly.

In the PRA test, you add minus lenses, which increase accommodation demand and boost accommodative convergence. To stay aligned, the eyes must rely on NFV to diverge enough to offset that extra convergence. If fusion is maintained, it indicates a healthy NFV reserve. So PRA performance reflects NFV indirectly.

Therefore, the true statement is that NRA indirectly tests PFV and PRA indirectly tests NFV.