Nuclear sclerosis increases the refractivity of the ocular crystalline lens
as animals get older. This increased refractivity causes the two pinpoint
lens reflections seen in the eyes of young adult dogs and cats to appear to
increase in size. Increasing refractivity also causes the clear lens nucle
us to develop a faint blue-gray appearance that becomes increasingly intens
e. When categorized, these changes can be used to divide life span into age
groups, thereby allowing the age of mature dogs and cats with unknown hist
ories to be determined more accurately than is possible using the dental me
thod of estimating ages.