In each of the 3 visual functions examined at baseline there were signs of decline from
approximately 40 years of age. However, this needs qualification as data presented are not
displayed with age as a linear variable. In the tritan axis, baseline colour contrast sensitivity
increased significantly over about 40 years compared to younger subjects by maximum of
47% and an average of around 20% (Figure 1A, p ≤ 0.0001).
Over the total group spanning 28-68 years of age there was a significant improvement in
tritan thresholds after exposure to 670nm by 14% (p ≤ 0.01) represented by lower values.
However, when the total group was divided into younger and older, the improved thresholds
were clearly the result of positive shifts in those over the age of 38 where there was a 22%
improvement (p ≤ 0.001), while younger individuals showed no change (Figure 1B, p >
0.05). Hence, 670nm treatment in older subjects improved tritan thresholds bringing them
towards levels found in younger individuals. However, significant differences remained
between the younger baseline and older treated (p ≤ 0.01). Protan thresholds showed no
change after 670nm exposure in the younger group (Figure 1C, p > 0.05), but it did improve
by approximately 10% in the older subjects, although this did not reach statistical
significance (Figure 1D, p > 0.05).
Scotopic thresholds were measured in decibels (dB) where improved sensitivity results in
increased numerical values. Improved sensitivity was found in 8 of the 12 subjects, 3 of
which were under the age of 40 (Figure 1E). But there was no statistically significant changes
in the younger group (p > 0.05). However, in line with the group tested for tritan thresholds,
older individuals showed significant improvement (Figure 1F, p ≤ 0.05). While significant
improvements in photoreceptors function were found for both rods and cones, subjects did
not report any subjective changes in their vision.
Page 6 of 15Journal of Gerontology: Biological Sciences