Development of tear production and intraocular pressure in healthy canine neonates

The aim of this study was to investigate the development of aqueous tear production and intraocular pressure in healthy canine neonates between 2 and 12 weeks of age.

One litter, consisting of 8 healthy Beagle dogs--four males and four females-was used.

Between the age of 2 and 12 weeks, tear production and intraocular pressure were measured weekly in both eyes. Tear production was measured by Schirmer tear test, before (STT1) and after (STT2) topical anesthesia and drying of the conjunctival sac. Intraocular pressure (IOP) was measured using a rebound tonometer. As no significant differences existed between left and right eye measurements (STT1, STT2, and IOP) at all time points, only right eye measurements were further analyzed.

STT1, STT2, and IOP values increased significantly until the age of 9 weeks for STT1, until the age of 10 weeks for STT2, and until the age of 6 weeks and again between 10 and 11 weeks of age for IOP. IOP decreased significantly between 11 and 12 weeks of age. There were no significant differences in STT1, STT2, and IOP between males and females, except for IOP at 10 and 12 weeks of age. No significant correlation was demonstrated between body weight and STT1 or STT2.

STT1, STT2, and IOP values increased significantly in the first weeks after birth. The results of this study indicate that separate reference values for tear production and intraocular pressure need to be established for neonatal dogs.