The development of the refractive state in the newborn Thomson gazelle.

Changes in refractive error during the first 3 months of life were studied retinoscopically in six Thomson gazelles ( Gazella thomsoni). Animals were hand-raised to allow repeat testing over time without chemical restraint. Refraction results were correlated with ultrasound measurements of intraocular dimensions, and with values in adult gazelles. Gazelles are born hyperopic with a mean refractive error of 3.44+/-0.31 D. By day 50, the animals are virtually emmetropic (0.13+/-0.21 D) and remain so in adulthood (0.03+/-0.09 D). The refractive error is highly correlated with the axial length ( r(2)=0.96) and with the vitreous chamber depth ( r(2)=0.83), but not with anterior chamber depth. Significant with-the-rule astigmatism was recorded ( P<0.001).

Intraocular pressure and tear production in five herbivorous wildlife species.

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.

Development of the refractive state in eyes of ostrich chicks (Struthio camelus).

OBJECTIVE: To follow the development of the refractive error in the eyes of ostrich chicks from age 0 to day 37 after hatching. ANIMALS: 35 ostrich chicks. PROCEDURES: Spot retinoscopy was conducted to assess refractive error in ostrich chicks. Seventy eyes of 35 ostrich chicks were examined. Of these, 18 chicks were followed over time. At least 4 serial measurements (at 2- to 7- day intervals) were conducted in each of these chicks from day 1 to 37 after hatching. Seventeen additional chicks were examined on days 0, 3, 12, and 19 after hatching. RESULTS: Ostrich chicks were myopic at hatching, with a mean +/- SD refractive error of -4.47 +/- 0.15 diopters (D). The refractive error rapidly decreased during the first week of life, and by day 7 after hatching, chicks were slightly hyperopic, with a mean refractive error of 0.42 +/- 0.12 D. After day 7, there were no significant differences in the mean refractive error. CONCLUSIONS: The development of optics in the ostrich eye appears to be unique among animals and is characterized by myopia at hatching, rapid onset of emmetropia, and minimal variation in refractive error among chicks.

How low can we get? Tonometry in the Thomson gazelle (Gazella thomsoni).

PURPOSE: To establish a normal reference range of intraocular pressure estimates in Thomson gazelles (Gazella thomsoni). MATERIALS AND METHODS: Applanation tonometry was conducted in 22 eyes of 11 gazelles anesthetized for transportation purposes with a mixture of etorphine hydrochloride and acepromazine maleate. Five sequential readings using a Tono-Pen XL (Mentor Ophthalmics, Inc., Norwell, MA) were obtained from each eye. Results were analyzed for the effect of age, weight, gender, side, and replicate readings and were compared with estimates in other species. RESULTS: Mean (+/- standard deviation) intraocular pressure estimate in 22 eyes of 11 gazelles was 7.6 +/- 1.6 mm Hg. None of the variables tested had a significant effect on the results. CONCLUSIONS: To date, the intraocular pressure estimates in the Thomson gazelle are the lowest reported in any species.

The effect of elevated progesterone levels on intraocular pressure in lions (Panthera leo).

Recently, we reported that intraocular pressure (IOP) in juvenile male lions (Panthera leo) is significantly higher than in juvenile lionesses. Whilst we could not ascertain the basis for this gender-related difference, we suspected that they were the result of fluctuations in levels of sex hormones. Because 19 of the 22 lions described in our previous report had to be re-anaesthetized, we repeated tonometry in these animals, to try and correlate between IOP and the levels of progesterone, oestrogen and/or testosterone. Based on elevated (>5 ng ml(-1)) levels of progesterone, lionesses were divided into a luteal (n = 8) and a non-luteal (n = 13) group. In the luteal group, mean IOP was 27.07+/-2.15 mm Hg, significantly (P = 0.001) higher than in the non-luteal group (21.61+/-2.70 mm Hg). Oestrogen, testosterone, anesthesia and age had no significant effect on IOP. It is suggested that elevated progesterone levels associated with the luteal phase in lionesses cause increased resistance to aqueous humor outflow, leading to IOP elevation. Similar ocular hypertension has been observed in rabbits following exogenous progesterone application, but this is the first report on the hypertensive effect of endogenous progesterone on IOP.

Arnold-Chiari malformation in a captive African lion cub.

Progressive ataxia, delayed growth, dementia and tremors were noted in a female African lion (Panthera leo) cub at the Tel-Aviv Ramat-Gan Zoological Center (Israel). The lioness was 3-mo-old when clinical signs were first noticed. Repeated neurological evaluations and blood tests were conducted in an attempt to establish a diagnosis. A congenital abnormality was suspected and the lioness died 6 molater. Post mortem examination revealed an Arnold-Chiari malformation. The abnormality was classified as a Chiari type 2 malformation, based on the herniation of the cerebellar vermis and paravermis and the slight caudal displacement of the medulla, combined with lack of displacement in other parts of the brainstem.

Tonometry in three herbivorous wildlife species.

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.