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Tonometry was performed to estimate intraocular pressure (IOP) in 12 Nubian ibexes (Capra ibex nubiana), 10 Grant zebras (Equus burchelli ) and five Arabian oryxes (Oryx leucoryx), using both applanation (Tono-Pen) and/or indentation (Schiotz) tonometers. Animals were anesthetized with a mixture of etorphine hydrochloride and acepromazine maleate. Mean (+/- SD) IOP in the ibex was 17.95 +/- 4.78 mmHg (24 eyes, indentation tonometry). In the zebra, indentation tonometry (20 eyes) yielded a mean IOP of 25.30 +/- 3.06 mmHg, and applanation tonometry (six eyes) yielded a mean IOP of 29.47 +/- 3.43 mmHg. In the oryx, indentation tonometry (five eyes) yielded a mean IOP of 22.68 +/- 8.15 mmHg, and applanation tonometry (10 eyes) yielded a mean IOP of 11.76 +/- 3.43 mmHg. There were no significant effects of gender, age, weight, side or reading number on the IOP measured in any of the three species. No significant differences were found between the IOP of the three species, nor between the readings of the two instruments, although some of the P-values were close to the significance level.

The intraocular pressure and rate of tear production were measured in 18 addax antelopes (Addax nasomaculatus), four impalas (Aepyceros melampus), 11 wide-lipped rhinoceroses (Ceratotherium simum), 10 white-tailed wildebeests (Connochaetes gnou) and seven scimitar-horned oryxes (Oryx dammah). The animals were anaesthetised with an intramuscular injection of etorphine hydrochloride and acepromazine maleate, and the Schirmer tear test I was used to evaluate tear production, and applanation tonometry was used to evaluate the intraocular pressure. The mean (sd) rate of tear production ranged from 17.6 (3.1) mm/minute in the rhinoceros to 28.8 (8.3) mm/minute in the addax. The intraocular pressure ranged from 8.0 (1.2) mmHg in the impala to 32.1 (10.4) mmHg in the rhinoceros. The rate of tear production in the addax and the intraocular pressure in the rhinoceros appear to be the highest values of these variables to have been reported in any species.

Applanation tonometry was used to estimate intraocular pressure (IOP) and Schirmer tear test (STT) I was used to estimate tear production in both eyes of 12 juvenile elands (Taurotragus oryx) and one eye each of 15 Asian fallow deer (Dama mesopotamica). Mean (Ϯ standard deviation) IOP was 14.6 Ϯ 4.0 mm Hg in the eland and 11.9 Ϯ 3.3 mm Hg in the deer. Mean tear production was 18.7 Ϯ 5.9 mm/min in the eland and 10.5 Ϯ 6.5 mm/ min in the deer. The large variation in IOP between two members of the family Bovidae, the elands reported here and the Thomson gazelle (Gazella thomsoni) for which we previously reported a mean pressure of 7.6 mm Hg, illustrates the need to establish reference values for each species. Tear production may be influenced by the species' natural habitat.

The Schirmer tear test (STT) I was performed to evaluate tear production in 12 captive Nubian ibex (Capra ibex nubiana), 10 captive Burchell's zebras (Equus burchelli) and five Arabian oryx (Oryx leucoryx) at the TelAviv Ramat-Gan Zoological Center (Israel). Mean (Ϯstandard deviation) STT values were 13.2 Ϯ 5.1 mm/min in the ibex, 23.4 Ϯ 3.4 mm/ min in the zebra and 12.7 Ϯ 4.8 mm/min in the oryx. There were no significant effects of gender, age, weight, or side of the eye. There were no significant differences in STT values between ibex and oryx, but tear production in both species was significantly lower than in zebras. Knowledge of normal tear production values is important for the differential diagnosis of conjunctivitis and keratitis in these species.

Phenol red thread test and STT are both valid methods to measure tear production; however, a separate baseline must be determined for each species using these methods, as the results of one method cannot be extrapolated to the other. Due to significant differences observed within diurnal and nocturnal species, it appears that a more intricate division should be used when comparing these parameters for raptors, and the classification of diurnal or nocturnal holds little significance in the baseline of these data.

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