NRA, PRA, and binocular facility are what in relation to accommodation and vergence?

• A. They measure vergence directly and accommodation indirectly.
• B. They are direct measures of accommodation and indirect measures of vergence.
• C. They are not related to accommodation.
• D. They only measure accommodation and not vergence.

Answer: (B)

These tests focus on how the eye’s focusing system responds when demands change and how the eyes work together to keep vision single. NRA and PRA quantify how much the accommodative system can relax or intensify its focus by adding plus or minus lenses while the target remains clear and single. That gives a direct readout of accommodation in diopters. Vergence isn’t measured directly here—the tests rely on maintaining fusion while accommodation shifts, so any vergence response is inferred rather than explicitly quantified. Binocular facility assesses how readily the system can switch focus and maintain single vision under binocular viewing, which again emphasizes the ability to change accommodation, with vergence changes occurring as needed but not measured directly. So together, they are direct measures of accommodation with indirect indications of vergence.