Moreover, if we compare the means for the extremes in the ages studied, namely, those under twenty-one and those over fifty years of age, we find that the older group definitely has a longer pupillary latency (0.273 sec.) than the younger group (0.238 sec.). Comparing the means of these two groups, a highly significantt value of 3.92 was found with 34 degrees of freedom. The probability that the two populations would have the same mean would be less than 1 in 1000.
If we compare the original pupil size and aging, we find that with aging, the pupil diameter decreases. Statistically, this may be expressed by a Pearsonian r of -0.55, a regression line y=0.36x+7.5, a chi-square of 11.20 (df=1; p<.001).
The average latency of response to original pupil size in darkness shows a negative relationship.
A possible relationship between latency of response and myopia with mydriasis has been brought to our attention in five cases which we have studied. In each instance, regardless of age, the latency period has been longer than 0.260 sec. Whether these longer latency periods have occurred by chance or not will have to be determined by further studies.
Longer latency period in pupillary constriction as a possible correlate of nerve conduction disease was introduced to us by a physician, who, himself, was the victim of Charcot-Marie-Tooth disease, a progressive disorder that symmetrically affects only the distal muscles of the legs and occasionally the arms. It is associated with pathologic changes in the anterior horn cells, peripheral neuromuscular units, posterior columns and frequently other tracts of the spinal cord including the pyramidal (Baker, 1962). Our patient showed, at the age of fifty-one, a pupillary latency period of 0.299 sec.
CONCLUSIONS
1) A method is described for measuring pupillary contraction latency period regardless of initial absolute pupil diameter.
2) Papillary contraction latency period increases with age. The data presented show that the normal pupil, as usually found in healthy young people, has a shorter latency than is found in older normal subjects.
