What is the formula for calculated AC/A?

What is the formula for calculated AC/A?

• A. PD (cm) + Near fixation distance (m) (Near phoria- Distance phoria)
• B. PD (cm) - Near fixation distance (m) (Near phoria- Distance phoria)
• C. PD (mm) + Near fixation distance (m) (Near phoria- Distance phoria)
• D. PD (cm) + Near fixation distance (m) (Distance phoria- Near phoria)

Answer: (A)

The main thing being tested is how to calculate the AC/A ratio using a standard relationship: it combines the vergence generated by accommodation with the baseline vergence from eye separation. The amount of convergence caused when looking at a near target is captured by how much the phoria changes from distance to near (near phoria minus distance phoria). The interpupillary distance, expressed in centimeters, represents the base vergence required just from the eyes being apart. Adding these two pieces gives the calculated AC/A value: PD in centimeters plus (near phoria minus distance phoria). So the formula PD (cm) + (Near phoria – Distance phoria) correctly expresses calculated AC/A.

The main thing being tested is how to calculate the AC/A ratio using a standard relationship: it combines the vergence generated by accommodation with the baseline vergence from eye separation. The amount of convergence caused when looking at a near target is captured by how much the phoria changes from distance to near (near phoria minus distance phoria). The interpupillary distance, expressed in centimeters, represents the base vergence required just from the eyes being apart. Adding these two pieces gives the calculated AC/A value: PD in centimeters plus (near phoria minus distance phoria). So the formula PD (cm) + (Near phoria – Distance phoria) correctly expresses calculated AC/A.