Es. Macmillan et al., Loss of visual acuity is the main reason why reading addition increases after the age of sixty, OPT VIS SCI, 78(6), 2001, pp. 381-385
Purpose. To determine why the reading addition increases after the age of 5
5 to 60 years when accommodation is zero. Methods, Distance and near visual
acuities, arm length, habitual near working distance, reading addition, an
d pupil diameter were measured in 44 subjects aged >60 years (mean, 72.9 +/
- 5.7). Reading addition Values were attained using three techniques: least
-plus addition using both N-notation text and MN-READ text and the cross-cy
linder technique. Results. The mean dioptric working distance was 2.75 +/-
0.40 D. The reading addition found using N-notation text (+2.21 +/- 0.38 D)
was significantly lower than that measured using MN-READ text (+2.48 +/- 0
.49 D) or the cross-cylinder method (+2.53 +/- 0.44 D). The reading additio
n was positively correlated with the dioptric working distance (r = 0.47, p
< 0.01), and decreasing habitual working distance was associated with poor
er visual acuity (r = -0.42, p < 0.01). Conclusions. Our results suggest th
at decreases in near visual acuity after 60 years of age lead to a reductio
n in habitual working distance, which increases text angular subtense. In t
urn, the reduced working distance requires a greater reading addition. Incr
eases in depth of field associated with both suprathreshold text (N-notatio
n) and lower visual acuity lead to reading additions being less than the di
optric working distance.