Ophthalmic Examination Findings in A Captive Colony of Western Gray Kangaroos (Macropus fuliginosus)

Successful bilateral phacoemulsification and vitrectomy in a Bennett's wallaby (Macropus rufogriseus)

CASE DESCRIPTION

A 7-month-old hand-reared female Bennett's wallaby (Macropus rufogriseus) was evaluated for bilateral ocular opacity of 3 months' duration.

CLINICAL FINDINGS

On physical examination, the wallaby was in good overall condition. An ophthalmic examination revealed mature cataracts in both eyes (OU). The cataracts were suspected to have a nutritional origin as it has been described in hand-reared macropods. Results of tonometry were normal OU. Results of CBC and serum biochemistry were unremarkable. The wallaby was premedicated with medetomidine and ketamine hydrochloride. Ocular ultrasonography performed while the wallaby was anesthetized revealed a thickened and opaque lens, mildly heterogeneous vitreous humor, and no sign of retinal detachment OU. An electroretinogram confirmed functional retinae OU.

TREATMENT AND OUTCOME

Surgery was considered necessary for welfare reasons. Phacoemulsification and vitrectomy were performed without intraoperative complication. The wallaby recovered uneventfully, and systemic NSAID, topical corticosteroid, and systemic and topical antimicrobial therapy were prescribed. One year later, the animal had vision OU. Physical examination did not show any vision-threatening postoperative complications.

CLINICAL RELEVANCE

The etiology of nutritional cataracts is not fully understood in macropods, but this condition is rather common in these species. To our knowledge, this is the first detailed report of a successful bilateral phacoemulsification and vitrectomy in a Bennett's wallaby.

The eye of the giant anteater (Myrmecophaga tridactyla): Ophthalmic examination findings and diagnostic tests

OBJECTIVE

To describe ophthalmic examination and diagnostic values for Schirmer tear test (STT), intraocular pressure (IOP), corneal horizontal diameter (CHD), palpebral fissure length (PFL), fundoscopy, and palpebral conjunctiva microbiota from healthy giant anteaters.

ANIMALS STUDIED

Twelve giant anteaters (Myrmecophaga tridactyla), 11 adults and one juvenile, five males and seven females.

PROCEDURES

The animals were submitted to general anesthesia and ophthalmic evaluation with portable slit-lamp biomicroscope, Finoff transilluminator, and fundoscopy, as well as STT, bacterial culture from palpebral conjunctiva, rebound tonometry IOP, and measurement of PFL and CHD. Data compiled were analyzed with ANOVA and Tukey tests.

RESULTS

The results (mean ± standard deviation) were as follows: STT 8.04 ± 6.21 mm/min; IOP 10.92 ± 2.45 mmHg; PFL 0.75 ± 0.11 cm; CHD 0.96 ± 0.10 cm. Out of the 24 eyes swab samples for bacterial culture, 17 were positive, with three genera of Gram-positive bacteria identified Staphylococcus spp., Bacillus sp., and Corynebacterium sp. Gram-negative bacteria were not isolated from any of the samples.

CONCLUSIONS

As conservation work in this vulnerable species continues, this report on basic ophthalmic examination and diagnostic parameters will be helpful improve their treatment and care. More ophthalmic studies are encouraged in animals within the Pilosa order.

OCULAR ANATOMY AND PATHOLOGY IN LUMHOLTZ'S TREE-KANGAROO (DENDROLAGUS LUMHOLTZI)

Lumholtz's tree-kangaroo (Dendrolagus lumholtzi) is one of two species of tree-kangaroos found in Queensland, Australia. There is little information about ocular anatomy and pathology in any species of tree-kangaroo, and there are claims of blindness from unknown causes in free-ranging Lumholtz's tree-kangaroos. This study investigated ocular anatomy and pathology in 80 individuals, using examination of 31 live animals and histopathologic examination of eyes from 49 carcasses. Tree-kangaroos were found to have a typical vertebrate eye with immuno-histochemical evidence for dichromatic color vision. Only 5.4% of animals had evidence of pathology from traumatic injury, infection, or a variety of nonspecific lesions. Toxoplasmosis was implicated in ocular lesions in three animals. This study did not find evidence of widespread blindness in free-ranging animals nor evidence of toxic optic neuropathy. Examinations of live animals highlighted the need to establish normal ocular examination parameters and vision testing protocols suitable for use in tree-kangaroos and the need for more comprehensive examination and testing of animals thought to have vision loss of unknown origin.

Clinical ophthalmological diagnostic description of 10 healthy sugar gliders (Petaurus breviceps) and prevalence of ocular-related presentations in a larger hospital population

OBJECTIVE

To provide reference values for ocular examination and diagnostics in ophthalmologically normal sugar gliders (Petaurus breviceps). To retrospectively determine the prevalence of ocular diseases in sugar gliders presenting to a single institution.

ANIMALS

Ten client owned and 106 previously evaluated sugar gliders.

PROCEDURE

A descriptive study evaluated sugar gliders presented to Colorado State University's Avian, Exotics, and Zoological Medicine Service (CSU-AEZ) from August-2019 to January-2020. A complete ophthalmic examination including Schirmer tear test II (STT II), phenol red threat test (PRTT), intraocular pressure (IOP) via rebound tonometry, fluorescein, and rose bengal stain was performed under anesthesia. Conjunctival aerobic culture swabs and cytology were collected prior to ophthalmic evaluation. A retrospective review of medical records of sugar gliders presented to CSU-AEZ from 2008 to 2018 for ocular disease was performed.

RESULTS

Mean values ± standard deviation for selected diagnostics included the following: STT II: 2.2 ± 6.7 mm/min; PRTT: 0 ± 0 mm/15 s; IOP: 12 ± 2.6 mm Hg. Fluorescein and rose bengal staining highlighted corneal abrasions secondary to tear testing. The three most common conjunctival bacterial isolates cultured were Staphylococcus spp. (3/20, 15%), Coryneform spp. (3/20, 15%), and unidentified Gram-positive cocci (3/20, 15%). Retrospective analysis revealed ocular diseases to be the third most common abnormality resulting in sugar glider presentations (13/106, 12.3%).

CONCLUSION

This descriptive study gives reference values for IOP, conjunctival microbiology, and cytology for sugar gliders. STT II and PRTT provide little clinical value in sugar gliders. The retrospective study revealed that ocular abnormalities, often secondary to dental disease, are a common reason for presentation.

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.

Bilateral lens luxation and intracapsular lens extractions in a Matshchie's tree kangaroo

An adult, female, captive, Matshchie's tree kangaroo was diagnosed with an anterior lens luxation in the right eye and a lens subluxation in the left eye. Both eyes were treated surgically with intracapsular lens extractions. A 360° rhegmatogenous retinal detachment was diagnosed 6 months postoperatively in the left eye. Aphakic vision was maintained in the right eye 9 months postoperatively. Based on family history and the lack of antecedent ocular disease, the lens luxations were presumed to be inherited and veterinarians should be aware of this condition within the captive tree kangaroo population.