Determination of age in dogs and cats by use of changes in lens reflections and transparency

To develop and test a noninvasive technique for determining age in dogs and cats on the basis of changes in lens reflections and transparency.

85 dogs representing 5 breeds and 73 domestic shorthair cats.

While examining dilated eyes in a darkened room, using a penlight, 2 experienced examiners who were blinded to actual age of animals individually measured the diameter of reflections from the anterior (La) and posterior (Lb) surfaces of the lens and scored lens transparency (Ltr) from 1 (clear) to 5 (severe opacity). Models were developed to predict age on the basis of these measurements.

Aging models developed for dogs and cats were as follows: Age(dogs) = 2.197 - 0.070 x (La) + 1.361 x (Lb) + 1.193 x (Ltr) and Age(cats) = 1.988 + 1.024 x (La) + 2.220 x (Lb) + 1.019 x (Ltr), where age was expressed in years, and La and Lb were in millimeters. All variables, except La in dogs, contributed significantly to accuracy of the models. Correlation between predicted and actual ages, as measured by Pearson's product-moment correlation coefficient, was significant in both species (P < 0.0001). Significant differences were not found between examiners or between the first and second evaluations by the same examiner.

A noninvasive technique based on evaluation of lens reflections and transparency can provide clinically useful predictions of age in mature dogs and cats. This technique could be an important tool for veterinarians or humane shelters in determining differential diagnoses and assessing longevity and adoptability of mature animals of unknown age.