How is gradient AC/A measured?

How is gradient AC/A measured?

• A. By comparing near phoria with normal viewing to near phoria while wearing ±1.00 D lenses and calculating Δvergence/Δaccommodation
• B. By measuring the change in vergence as accommodation is changed with lenses
• C. By comparing far phoria with near phoria under different lighting
• D. By assessing vergence facility at near

Answer: (A)

Gradient AC/A measures how much vergence is driven by a change in accommodation when you intentionally alter the accommodative demand with lenses while keeping the viewing distance fixed. The idea is to compare how the near vergence (or near phoria) changes when the eye’s need to accommodate is shifted by a known amount. In practice, you fix the target at a near distance (for example around 40 cm) and first measure the near phoria under normal viewing. Then you place lenses of known power (commonly ±1.00 diopter) in front of the eyes and re-measure the near phoria. The difference in vergence required between the two conditions is Δvergence, and the change in accommodation is the lens power you added (Δaccommodation, typically 1.00 D). The gradient AC/A ratio is computed as Δvergence divided by Δaccommodation (in prism diopters per diopter). This approach isolates accommodative convergence by changing only the stimulus to accommodation and holding the viewing distance constant.

Gradient AC/A measures how much vergence is driven by a change in accommodation when you intentionally alter the accommodative demand with lenses while keeping the viewing distance fixed. The idea is to compare how the near vergence (or near phoria) changes when the eye’s need to accommodate is shifted by a known amount. In practice, you fix the target at a near distance (for example around 40 cm) and first measure the near phoria under normal viewing. Then you place lenses of known power (commonly ±1.00 diopter) in front of the eyes and re-measure the near phoria. The difference in vergence required between the two conditions is Δvergence, and the change in accommodation is the lens power you added (Δaccommodation, typically 1.00 D). The gradient AC/A ratio is computed as Δvergence divided by Δaccommodation (in prism diopters per diopter). This approach isolates accommodative convergence by changing only the stimulus to accommodation and holding the viewing distance constant.