Evaluation of Intraocular Pressure (IOP) Regarding Circadian Rhythm, Age, Sex and Eye Side in Awassi Sheep

Abstract

Measurement of intraocular pressure (IOP) in domestic animals has become a part of routine eye examination with advent of applanation tonometer. Delayed control of high IOP may lead to permanent blindness due to retinal ganglion cells dysfunction and optic nerve degeneration. This study aimed at evaluating IOP of Awassi sheep with respect to circadian rhythm, age, sex and eye sides and finally to establish a reference (baseline, normal) IOP value for this particular species. A total of 24 healthy sheep with different ages and sexes were used. The animals were divided into 2 equal groups, <1 (6 male, 6 female, n = 12) and ≥1 (6 male, 6 female, n = 12) years old. IOP measurements were performed twice, in the morning (6:00 a.m.) and in the evening (8:00 p.m.) with Tono-pen Vet® applanation tonometer. Mean IOP in the animals decreased from 16.21 mmHg in the morning to 12.65 mmHg in the evening with an approximately rate of 22% (P <0.0001). Comparison of mean IOP values of right eyes (n=12) to the left (n=12), male (n=48) to female (n=48), and ages < 1 (n=48) to ≥ 1 (n=48) showed no difference (P >0.05). The reference IOP for this animal was calculated as 14.43±2.72 mmHg notwithstanding any variable. It was concluded that in this breed IOP values can vary significantly as far as circadian rhythm is concerned and Tono-pen Vet® can be used for sheep IOP measurement as an alternative to other applanation tonometry.

Determination of intraocular pressure and Schirmer tear test and the comparison between the applanation tonometer (Tono‐Pen AVIA®) and the rebound tonometer (TonoVet Plus®) in mini lionhead rabbits

“…In some species, different IOP values were observed in healthy animals throughout the day. Possibly this fact stems from the influence of the circadian and adrenergic systems on the formation and regulation of aqueous humor 18,38,41 . In this study, significantly different IOP values were observed throughout the day, with both the rebound and applanation tonometers.…”

“…Possibly this fact stems from the influence of the circadian and adrenergic systems on the formation and regulation of aqueous humor. 18,38,41 In this study, significantly different IOP values were observed throughout the day, with both the rebound and applanation tonometers. IOP values were higher at the beginning of the day (6:00 a.m.), decreasing from 9:00 a.m. and increasing again at 6:00 p.m., as previously described for New Zealand rabbits.…”

“…21 Differences in IOP values obtained among studies that used the basic principles of rebound and applanation may also be related to the calibration of different types of tonometers, examiner experience, species or breeds studied, age, time of day when the measurement was performed, containment method, and prior anesthesia. 6,18,37,38 In order to minimize the influence of these factors, the IOP readings in rabbits investigated in this study were performed by a single evaluator and at fixed times, anesthesia and sedation were not used, neck compression was prevented, the eyelids were gently opened, and stress related to containment was avoided. In addition, the composition of the tear film and the corneal flexibility also influenced the results of the tonometry in New Zealand rabbits.…”

Circadian Rhythms in Murine Ocular Tissues including Sclera are affected by Neurobasal A Medium Preincubation, Mouse Strain, but not Sex

“…Several lines of evidence suggested that ocular rhythms may differ between sexes. The diurnal variation of intraocular pressure and tear production was shown to vary between sexes 29, 30 . Androgen, estrogen and progesterone receptor mRNA was found in a variety of ocular tissues 31, 32 .…”

TonoVet Plus®: Higher reliability and repeatability compared with Tono‐Pen XL™ and TonoVet® in rabbits

“…To minimize factors that are known to alter IOP, the evaluations were performed by a single examiner, 7 using the same devices, 21 and under the same conditions of animal containment and environment 6,32 . Disruptions in IOP values related to circadian rhythm 33 were not considered in this study, given that the measurements were performed at the same time on both evaluation days. Nevertheless, although some variables can be controlled by a consistent technique, not all interference can be completely mitigated 7 …”