Tear production in canine neonates--evaluation using a modified Schirmer tear test

The ability of human newborns to produce tears has been a subject of controversy in the literature since the mid-20th century, and there has been considerable debate as to whether they are able to produce tears. Recently, it was established that total tear secretion (reflex + basal) in full-term infants is similar to those of adults whereas both reflex and basal tear production is reduced in premature babies. The objectives of this study were to assess whether newborn dogs have measurable aqueous tear production at the fourth week of life and to evaluate a modified Schirmer tear test (mSTT) as a useful method for measuring neonatal tear production in dogs.

Thirty four-week-old healthy puppies from six litters were evaluated. A control group was composed of 10 normal adult dogs. The mSTT strips were obtained by cutting a 5 mm-wide strip in half (making two 2.5 mm-wide strips). The mSTT1 was performed in puppies and adult dogs. Values were compared using t-tests.

In neonates, the average value for the mSTT1 was 13.6 ± 3.07 (range = 7-19 mm/min), which was significantly lower in neonates than in adult dogs (23.25 ± 3.5, range = 17-30 mm/min, P < 0.0001).

Canine neonates do produce tears by the fourth week of life, which can be successfully measured with the mSTT. This report established for the first time that canine neonates have significantly reduced total (reflex + basal) tear secretion compared to adults.