What effect does NRA have on accommodation?

What effect does NRA have on accommodation?

• A. Relax accommodation
• B. Stimulate accommodation
• C. Inhibit accommodation
• D. Have no effect

Answer: (A)

NRA measures how much the eyes can relax accommodation while maintaining clear, single vision at near. When testing, plus lenses are placed in front of the eyes, which lowers the accommodative demand of the near target (for example, at 40 cm the demand is about 2.5 diopters; adding plus reduces this required effort). As the demand decreases, the ciliary muscle can relax, and accommodation decreases until blur or loss of fusion occurs. So NRA reflects relaxation of accommodation, not stimulation or inhibition. Using minus lenses would instead increase accommodative demand to test how much you can stimulate accommodation. And there is clearly an effect—plus lenses cause accommodation to relax up to a point.

NRA measures how much the eyes can relax accommodation while maintaining clear, single vision at near. When testing, plus lenses are placed in front of the eyes, which lowers the accommodative demand of the near target (for example, at 40 cm the demand is about 2.5 diopters; adding plus reduces this required effort). As the demand decreases, the ciliary muscle can relax, and accommodation decreases until blur or loss of fusion occurs. So NRA reflects relaxation of accommodation, not stimulation or inhibition. Using minus lenses would instead increase accommodative demand to test how much you can stimulate accommodation. And there is clearly an effect—plus lenses cause accommodation to relax up to a point.