Donders push-up method tends to overestimate accommodative amplitude by about 2.00 D due to what cause?

Donders push-up method tends to overestimate accommodative amplitude by about 2.00 D due to what cause?

• A. Relative distance magnification
• B. Measurement noise in the device
• C. Pupil dilation effects
• D. Overestimation by observers

Answer: (A)

The key idea is that the Donders push-up method introduces a systematic bias because the stimulus for accommodation isn’t just the object’s physical distance. As the target is moved closer, it subtends a larger retinal angle, so size cues amplify the accommodative drive beyond what the actual dioptric distance would predict. This relative distance magnification makes the near point appear closer than its true optical distance, so when you compute amplitude as the reciprocal of that near point, you get an amplitude larger by about 2 diopters. The result is a consistent overestimation of accommodative amplitude with this method. Other factors like random measurement noise, pupil dilation effects, or observer bias can affect measurements, but they don’t produce the characteristic ~2 D bias explained by relative distance magnification.

The key idea is that the Donders push-up method introduces a systematic bias because the stimulus for accommodation isn’t just the object’s physical distance. As the target is moved closer, it subtends a larger retinal angle, so size cues amplify the accommodative drive beyond what the actual dioptric distance would predict. This relative distance magnification makes the near point appear closer than its true optical distance, so when you compute amplitude as the reciprocal of that near point, you get an amplitude larger by about 2 diopters. The result is a consistent overestimation of accommodative amplitude with this method. Other factors like random measurement noise, pupil dilation effects, or observer bias can affect measurements, but they don’t produce the characteristic ~2 D bias explained by relative distance magnification.