Reference Values of Schirmer Tear Tests and Intraocular Pressure in Mules

Determining the normal ranges for tear production and intraocular pressure (IOP) is crucial for the diagnosis and treatment of ocular disorders in animals. This study was carried out in clinically healthy mules to determine reference values for the intraocular pressure (IOP) and Schirmer tear tests (STT) for clinical application. Sixty clinically healthy adult mules (30 males and 30 females) were selected at random from a large variety of age groups: <5 years, 5–15 years, and >15 years old, with weights ranging from 200 to 400 kg. IOP was measured in each eye using a Tono-Pen Vet. Using a commercial STT strip, the STT I and STT II values were recorded in the eyes of all the mules. The mean ± SD of intraocular pressure measurements in the studied mules was as follows: in mule foals; the right eye was 25.65 ± 1.17 and the left eye was 25.23 ± 1.20, in immature mules; the right eye was 25.65 ± 1.07 and the left eye was 26.23 ± 1.10, and in mature mules; the right eye was 26.25 ± 1.08 and the left eye was 25.53 ± 1.06 mm Hg. The mean ± SD of STT I was as follows: in mule foals; the right eye was 26.33 ± 2.28 and the left eye was 26.43 ± 3.17, in immature mules; the right eye was 26.21 ± 2.31 and the left eye was 25.81 ± 2.09, in mature mules; the right eye was 26.66 ± 2.23 and the left eye was 24.51 ± 2.62 mm/min. The mean ± SD of STT II was as follows: in mule foals; the right eye was 26.73 ± 2.28 and the left eye was 26.13 ± 2.12, in immature mules; the right eye was 25.82 ± 2.20 and the left eye was 25.61 ± 1.90, in mature mules; the right eye was 25.26 ± 2.20 and the left eye was 24.41 ± 2.40 mm/min. The mean ± SD of IOP in mules was 25.90± 0.58, the mean ± SD of STT I in mules was 26.43± 0.23 and the mean ± SD of STT II in mules was 25.94± 0.74. The results of this study will aid veterinarians effectively in diagnosing and treating eye disorders in mules.