Lecture Notes: Negative and Positive Relative Accommodation Tests

Introduction

• Purpose: Perform Negative Relative Accommodation (NRA) and Positive Relative Accommodation (PRA) tests.
• Pre-requisites:
  • Patient must be fully corrected for refractive error.
  • Distance for both tests: 40 cm.
  • Target: One line above the best-corrected visual acuity.

Negative Relative Accommodation (NRA)

• Visual Acuity Example: If visual acuity is N6, use N8 as the target.
• Procedure:
  • Patient should try to keep the target clear.
  • Report when sustained blur is achieved.
  • Use plus lenses to gradually increase power.
  • Ensure the next lens is placed before removing the previous lens.
• Expected Values:
  • Normal NRA: +2.50 diopters.
  • Higher NRA (> +2.50) indicates:
    • Uncorrected hyperopia or overcorrected myopia.
    • Example: NRA = +3.5 indicates 1 diopter undercorrected hyperopia or 1 diopter overcorrected myopia.
  • Lower NRA (< +2.50) indicates:
    • Undercorrected myopia or overcorrected hyperopia.
    • Example: NRA = +1.0 indicates 1.5 diopters undercorrected myopia or 1.5 diopters overcorrected hyperopia.
• Defogging Process:
  • Reverse the process by reducing lens power.

Positive Relative Accommodation (PRA)

• Procedure:
  • Start with minus lenses.
  • Increase power until blur is reported.
  • Remove the current lens before placing the next stronger lens.
  • Example sequence: Start with -0.25, increase to -0.50, and continue.
• Expected Values:
  • Normal PRA: -2.50 diopters.
  • Higher PRA (> -2.50) is possible.
  • Lower PRA (< -2.50) may indicate binocular vision anomalies, especially vergence or accommodative problems.
• Reduction Practice:
  • Reverse lens power from -2.5 down to 0 by removing higher power lenses first.

Conclusion

• Both NRA and PRA tests assess visual accommodation and help in identifying refractive errors or anomalies in binocular vision.