OCULAR HEALTH ASSESSMENT, TEAR PRODUCTION, AND INTRAOCULAR PRESSURE IN THE ANDROS ISLAND IGUANA ( CYCLURA CYCHLURA CYCHLURA )

CLINICAL OPHTHALMIC PARAMETERS OF THE TEXAS TORTOISE (GOPHERUS BERLANDIERI)

Ophthalmic studies of the Texas tortoise (Gopherus berlandieri) established normal ophthalmic parameters for select diagnostic tests in captive tortoises and assessment of differences among individuals of differing size and health status. Sixty-one tortoises of varying weight, shell size, Mycoplasma seroprevalence, and herpesvirus exposure were included. Complete ophthalmic examinations, including neuro-ophthalmic reflexes, phenol red thread test, rebound tonometry, fluorescein staining, palpebral fissure length measurement, slit lamp biomicroscopy, indirect fundoscopy, and ocular ultrasound measurements of axial globe length, anterior chamber depth, lens thickness, and vitreous length, were recorded. All tortoises had negative dazzle and pupillary light reflexes, inconsistent menace responses, and positive palpebral reflexes. Mean ± SD tear production and intraocular pressure (IOP) were 14.2 ± 5.6 mm/15 sec and 13.8 ± 2.4 mm Hg in healthy tortoises, respectively. Mycoplasma-seropositive tortoises (with or without herpesvirus exposure) had significantly increased tear production (20.2 ± 8.1 and 19.9 ± 8.9 mm/15 sec, respectively) compared with healthy seronegative tortoises (14.2 ± 5.6 mm/15 sec; P = 0.02). As body size decreased, so too did palpebral fissure length and ocular ultrasound measurements, while IOP increased. Overall, palpebral fissure length appeared relatively small, and tear production relatively increased compared with other chelonian species, likely on the basis of the relatively arid native habitat. Further work is recommended to establish baseline values in related species, as well as comparison in aquatic versus terrestrial chelonians. The authors further suggest that the finding of relatively increased tear production in tortoises may indicate the need to rule out mycoplasmosis as a cause of upper respiratory tract disease.

OPHTHALMIC EXAMINATION FINDINGS AND INTRAOCULAR PRESSURE MEASUREMENTS IN SIX SPECIES OF ANURA

A complete ophthalmic exam, including intraocular pressure (IOP) measurement, is key to diagnosing ocular diseases such as uveitis and glaucoma in frogs. We performed complete ophthalmic anterior segment examinations and IOP rebound tonometry measurements using two different settings (other "p" and canine "d") for six anuran species. The objectives were to describe common ocular abnormalities found in these species, to compare IOP values between different tonometer settings, and to compare IOPs between species. Examinations revealed abnormalities including cataracts (11/98 total eyes), lenticular sclerosis (10/98) and lipid keratopathy (9/98). IOP was measured with the TonoVet^® and the ranges (oculus uterque, OU mm Hg other "p" setting, canine "d" setting) were giant waxy monkey tree frogs (Phyllomedusa bicolor) (3.5-7.6; 6.5-11.7; n = 5), mission golden-eyed tree frogs (Trachycephalus resinifictrix) (7.0-9.7, 13.2-15.7; n = 6), boreal toads (Bufo boreas boreas) (0.8-5.5, 5.7-10.5; n = 13), Mexican giant tree frogs (Pachymedusa dacnicolor) (3.8-5.0, 8.3-11.8; n = 3), Lake Titicaca frogs (Telmatobius culeus) (8.8-10.5, 14.0-17.2; n = 8), and mossy tree frogs (Theloderma corticale) (9.7-11.0, 15.7-17.0; n = 5). The TonoVet canine "d" setting IOP measurements were statistically higher (P = 0.01) than the other "p" setting measurements for all species except the giant waxy monkey tree frogs. IOP was significantly lower for giant waxy monkey tree frog eyes with cataracts (P < 0.05) with the other "p" setting. IOP did not statistically differ in eyes with lenticular sclerosis. IOP can be measured by rebound tonometer in anurans, but more research is needed for species-specific references using consistent settings.

Ocular findings in a group of healthy captive leopard geckos

OBJECTIVE

Leopard Geckos (Eublepharis macularius) are popular pets and can be affected by a range of ocular disorders. Our objective was to report ocular findings in a group of healthy captive leopard geckos and to establish reference ranges for commonly performed ocular diagnostic tests.

ANIMALS STUDIED

Twenty-six healthy male geckos aged 1 year old (n = 4) and >2 years old (n = 22).

PROCEDURES

All animals underwent ophthalmic examination, corneal esthesiometry, modified Schirmer tear test (mSTT), rebound tonometry, conjunctival bacterial aerobic and fungal culture, and measurement of ocular dimensions. Student's t test was used to compare values of corneal esthesiometry, tonometry and mSTT between groups. Multiple correlations were assessed by Pearson correlation coefficient.

RESULTS

All animals had a normal ocular examination. Tear production as measured with a mSTT (mean ± SD) technique was 3.1 ± 1.3 mm/min and tonometry values (mean ± SD) were 8.2 ± 1.7 mm Hg. Corneal touch threshold (median, range) was 4.4 cm, 2.5-5.0. Younger animals had a significantly increased corneal sensitivity compared to older animals (P = .0383). Results of culture showed no growth for fungal organism in any animals. Conjunctival bacterial isolation rates were low, with only 7/26 samples positive for nine bacterial species.

CONCLUSIONS

Leopard geckos are amenable to ophthalmic examination and ocular diagnostic database testing with minimal manual restraint.

Modified Schirmer tear test and rebound tonometry in blue-fronted Amazon parrot (Amazona aestiva)

ABSTRACT: The aim of this study was to describe the modified Schirmer tear test (mSTT), intraocular pressure (IOP) by rebound tonometry and palpebral fissure length (PFL) in blue-fronted Amazon parrots (Amazona aestiva). Thirty-five healthy adult animals from a conservation breeding center in Brazil were used in this study. Modified Schirmer tear test, rebound tonometry and PFL measurements were performed in both eyes, with birds under physical restraint. Mean mSTT was 6.2±0.1mm/min and mean IOP was 6.4±0.1mmHg, while PFL was 10.1±0.1mm. A moderate correlation was seen between mSTT and PFL for OD (ρ=0.14) and OS (ρ=0.20). The results provide ophthalmic tests reference values for A. aestiva.

MEASURING INTRAOCULAR PRESSURE IN WHITE'S TREE FROGS (LITORIA CAERULEA) BY REBOUND TONOMETRY: COMPARING DEVICE, TIME OF DAY, AND MANUAL VERSUS CHEMICAL RESTRAINT METHODS

Ocular diseases reported in frogs include uveitis and glaucoma, which are associated with changes in intraocular pressure (IOP). The objectives of this study were to characterize the normal IOP for White's tree frogs ( Litoria caerulea ) using two types of rebound tonometers, and to assess whether time of day or method of restraint affected IOP. Eighteen conscious, unrestrained, ophthalmologically normal frogs were used to measure IOP using TonoVet® and TonoLab® tonometers, at three time points during the day. In a subset of 12 frogs, IOP was measured while under manual restraint using the TonoVet. Anesthesia was induced in 9 frogs using two different concentrations of MS-222 (0.5 g/L and 2 g/L) in order to evaluate for changes in IOP with the TonoVet. Mean (± SD) IOP values for the TonoLab (16.8 ± 3.9 mm Hg) were significantly higher than TonoVet values (14.7 ± 1.6 mm Hg; P < 0.01). TonoVet IOP values did not significantly change with time of day. TonoLab values were significantly lower in the evening (1600-1800; 14.5 ± 3.1 mm Hg), compared with morning and midday measurements (0800-1000 and 1200-1400; 18.0 ± 3.8 mm Hg; P < 0.01). Manually restrained frogs had significantly lower IOP (13.4 ± 1.5 mm Hg) compared with unrestrained frogs (15.3 ± 1.2 mm Hg; P < 0.01). Chemical restraint did not cause significant changes in IOP. Intraocular pressure can be measured with both types of rebound tonometers in White's tree frogs, but time of day and manual restraint can affect IOP values.

Allometry and Scaling of the Intraocular Pressure and Aqueous Humour Flow Rate in Vertebrate Eyes

In vertebrates, intraocular pressure (IOP) is required to maintain the eye into a shape allowing it to function as an optical instrument. It is sustained by the balance between the production of aqueous humour by the ciliary body and the resistance to its outflow from the eye. Dysregulation of the IOP is often pathological to vision. High IOP may lead to glaucoma, which is in man the second most prevalent cause of blindness. Here, we examine the importance of the IOP and rate of formation of aqueous humour in the development of vertebrate eyes by performing allometric and scaling analyses of the forces acting on the eye during head movement and the energy demands of the cornea, and testing the predictions of the models against a list of measurements in vertebrates collated through a systematic review. We show that the IOP has a weak dependence on body mass, and that in order to maintain the focal length of the eye, it needs to be an order of magnitude greater than the pressure drop across the eye resulting from gravity or head movement. This constitutes an evolutionary constraint that is common to all vertebrates. In animals with cornea-based optics, this constraint also represents a condition to maintain visual acuity. Estimated IOPs were found to increase with the evolution of terrestrial animals. The rate of formation of aqueous humour was found to be adjusted to the metabolic requirements of the cornea, scaling as Vac(0.67), where Vac is the volume of the anterior chamber. The present work highlights an interdependence between IOP and aqueous flow rate crucial to ocular function that must be considered to understand the evolution of the dioptric apparatus. It should also be taken into consideration in the prevention and treatment of glaucoma.

Intraocular pressure in free-ranging anuran species in Oklahoma

Ocular disease appears to be a common issue in anurans. Intraocular pressures were measured for six species of free-ranging anurans in central Oklahoma. No significant differences were identified between left or right eyes. There was a significant negative relationship between the weight of the anuran and intraocular pressure. The intraocular pressure range for the six species was 3-10 mm Hg. Tonometry values in anurans are, to the authors' knowledge, previously unreported and this study provides initial information on intraocular pressure measurement in anurans.