With time and age, how do Stimulus AC/A and Response AC/A change?

With time and age, how do Stimulus AC/A and Response AC/A change?

• A. Both stimulus and response AC/A increase with age.
• B. Stimulus AC/A stays constant or decreases while the response AC/A increases slightly.
• C. Stimulus AC/A increases while the response AC/A decreases.
• D. Both remain constant with age.

Answer: (B)

AC/A ratios describe how vergence responds to accommodation, but there are two ways to express the relationship. Stimulus AC/A uses the planned accommodative demand (the stimulus to accommodation) as the denominator, while Response AC/A uses the actual accommodative response (what the eye actually does) as the denominator. The vergence response itself can shift with age, but the key difference comes from how accommodation changes with aging. As people age, accommodation becomes less effective (presbyopia). The actual accommodative response to a given demand declines, so the denominator for the response AC/A gets smaller. The vergence response to that demand tends to decrease as well, but not as much as the accommodative response does. Because you’re dividing the same (or only slightly reduced) vergence by a smaller actual accommodation, the response AC/A ratio tends to rise, even if only slightly. In contrast, the stimulus AC/A depends on the vergence response relative to the imposed stimulus. Since the vergence response tends to decline with age (even if the stimulus is the same), the stimulus AC/A stays about the same or decreases. So, with time and age, stimulus AC/A stays constant or decreases, while response AC/A increases slightly.

AC/A ratios describe how vergence responds to accommodation, but there are two ways to express the relationship. Stimulus AC/A uses the planned accommodative demand (the stimulus to accommodation) as the denominator, while Response AC/A uses the actual accommodative response (what the eye actually does) as the denominator. The vergence response itself can shift with age, but the key difference comes from how accommodation changes with aging.

As people age, accommodation becomes less effective (presbyopia). The actual accommodative response to a given demand declines, so the denominator for the response AC/A gets smaller. The vergence response to that demand tends to decrease as well, but not as much as the accommodative response does. Because you’re dividing the same (or only slightly reduced) vergence by a smaller actual accommodation, the response AC/A ratio tends to rise, even if only slightly.

In contrast, the stimulus AC/A depends on the vergence response relative to the imposed stimulus. Since the vergence response tends to decline with age (even if the stimulus is the same), the stimulus AC/A stays about the same or decreases.

So, with time and age, stimulus AC/A stays constant or decreases, while response AC/A increases slightly.