The AC/A ratio, age and presbyopia

Previous reports concerning the effect of age on the AC/A ratio have been equivocal. Therefore, the present study investigated both the stimulus (AC/As) and response (AC/Ar) ratios using a subjective haploscopeoptometer in a relatively large sample of subjects (n= 42) over a wide range of ages (22–65 years). The AC/As showed a small but significant decrease with age (∼0.04 Δ/D/year). When the older subjects (>45 years of age) were excluded, however, there was no systematic age effect. The AC/Ar exhibited a small but significant increase with age (∼ 0.08 Δ/D/year) for subjects under 45 years of age. However, when the older pre‐presbyopes and younger presbyopes (35–44 years of age) were excluded, there was no systematic age effect. In subjects 45 years of age and older, the AC/Ar could not be reliably assessed. This was attributed to physiological and instrumentation noise as a result of the minimal change in accommodative response, In the mid‐aged subjects (35–44 years of age), the apparent increase in AC/Ar with age was speculated to be due to neural adaptation of the crosslink gain from the accommodative to the vergence system and/or slight intrusion into the upper non‐linear response region of accommodation with the measurements. The finding of AC/Ar constancy with age when mid‐aged pre‐presbyopes and early presbyopes were excluded supports the non‐linearity hypothesis, and thus there appears to be no real change in AC/Ar with increased age. The results support the Hess‐Gullstrand theory of presbyopia.