What is the equation for Stimulus to Accommodation?

What is the equation for Stimulus to Accommodation?

• A. SAcc = Vcornea + RE
• B. SAcc = RE - Vcornea
• C. SAcc = 1 / (Vcornea + RE)
• D. SAcc = Vcornea - RE

Answer: (A)

Stimulus to accommodation is the dioptric demand the eye must meet to bring a near target into focus. In this simple model, that demand comes from two additive factors: the cornea’s contribution to vergence (Vcornea) and the eye’s refractive error (RE). Put together, they determine the total accommodative need, so the stimulus to accommodation is the sum of those two terms. For example, if the near target requires 2.5 diopters of vergence at the cornea and the eye has a hyperopic error of +1 D, the stimulus to accommodate would be 3.5 D. If the eye is myopic by 1 D, the stimulus would be 1.5 D. The other forms would mix distance (reciprocal) or differencing the components, which does not represent the actual dioptric demand driving accommodation.

Stimulus to accommodation is the dioptric demand the eye must meet to bring a near target into focus. In this simple model, that demand comes from two additive factors: the cornea’s contribution to vergence (Vcornea) and the eye’s refractive error (RE). Put together, they determine the total accommodative need, so the stimulus to accommodation is the sum of those two terms. For example, if the near target requires 2.5 diopters of vergence at the cornea and the eye has a hyperopic error of +1 D, the stimulus to accommodate would be 3.5 D. If the eye is myopic by 1 D, the stimulus would be 1.5 D. The other forms would mix distance (reciprocal) or differencing the components, which does not represent the actual dioptric demand driving accommodation.