A very low PRA may indicate which of the following?

A very low PRA may indicate which of the following?

• A. Near Eso and/or NRV Values
• B. Hyperopia
• C. Large PFV Reserve
• D. High Exophoria at Distance

Answer: (A)

PRA shows how much you can increase accommodation (stimulate near focus) by adding minus lenses while keeping single binocular vision. A very low PRA means there isn’t much room to ramp up accommodation without breaking fusion, which points to limitations in the vergence system that support accommodation, especially Negative Relative Vergence (NRV). When you demand more accommodation, you also need more convergence. If NRV reserves are reduced or the near alignment is already biased toward esophoria, the ocular motor system can’t supply the extra vergence needed, so fusion is lost sooner and PRA drops. That’s why near esophoria and/or NRV deficiencies best explain a very low PRA. Larger PFV reserves would help maintain fusion under increased accommodation, and high exophoria at distance doesn’t directly drive PRA down. Hyperopia can influence overall accommodative demands, but its effect is more on related measures of accommodation and vergence balance than on PRA itself.

PRA shows how much you can increase accommodation (stimulate near focus) by adding minus lenses while keeping single binocular vision. A very low PRA means there isn’t much room to ramp up accommodation without breaking fusion, which points to limitations in the vergence system that support accommodation, especially Negative Relative Vergence (NRV). When you demand more accommodation, you also need more convergence. If NRV reserves are reduced or the near alignment is already biased toward esophoria, the ocular motor system can’t supply the extra vergence needed, so fusion is lost sooner and PRA drops. That’s why near esophoria and/or NRV deficiencies best explain a very low PRA. Larger PFV reserves would help maintain fusion under increased accommodation, and high exophoria at distance doesn’t directly drive PRA down. Hyperopia can influence overall accommodative demands, but its effect is more on related measures of accommodation and vergence balance than on PRA itself.