Ferret ophthalmology

Juvenile ocular abnormalities in a litter of black-footed ferrets

OBJECTIVE

To describe the clinical and histopathological features of ocular abnormalities noted in a litter of black-footed ferrets (Mustela nigripes), including corneal opacification, cataracts, persistent pupillary membranes, microphthalmia, symblepharon and anterior segment malformation.

ANIMALS STUDIED

A litter of eight black-footed ferrets examined at 10 weeks old with a history of ophthalmia neonatorum first noted at 7 days old and histopathological examination of three globes from three ferrets of the same litter between 5 and 7 months old following routine subconjunctival enucleation.

PROCEDURES

Due to the fractious nature of black-footed ferrets, slit-lamp biomicroscopic examination was performed under general isoflurane anesthesia at 10 weeks of age. Corneal opacification was noted in 9/16 eyes, cataracts in 4/16 eyes, and persistent pupillary membranes in 3/16 eyes, among other findings. Histopathology revealed persistent pupillary membranes and Descemet's membrane abnormalities consistent with congenital anterior segment malformation in all three globes. In one ferret, a posterior cortical cataract with posterior lenticular malformation and lens capsule discontinuity was noted. Purulent discharge was cultured at time of enucleation in one ferret with growth of E. coli.

CONCLUSIONS

A novel constellation of ocular malformations with primary congenital and secondary to ophthalmia neonatorum etiologies is described in black-footed ferrets. Due to endangered status of black-footed ferrets, small genetic pool and the requirement for adequate vision for wild-release, congenital ocular abnormalities such as anterior segment malformation and likely the cataracts described are of particular concern. Further investigation and monitoring are warranted to determine the heritability of these ocular abnormalities.

Eye Removal Surgeries in Exotic Pets

This article covers considerations and techniques of eye removal surgeries in exotic pets. After issues including surgical indications, anesthesia, patient preparation, and instrumentation are explored, surgical techniques are described. Enucleation/exenteration and modified evisceration are discussed, with species-specific nuances of small mammals, birds, reptiles, snakes, amphibians, and fish highlighted.

Evaluation of intraocular pressure in conscious Hermann's tortoises (Testudo hermanni) by means of rebound tonometry

OBJECTIVE

To determine intraocular pressure (IOP) in healthy Hermann's tortoises (Testudo hermanni).

ANIMALS

26 outdoor-housed Hermann's tortoises (13 males and 13 females); body weight ranged from 255 to 2,310 g, and age ranged from 4 to > 50 years.

PROCEDURES

After a preliminary ophthalmic evaluation was performed, IOP was measured by means of a rebound tonometer in both eyes of each tortoise. Three measurements were obtained for each eye; successive measurements were obtained from alternate eyes. Each measurement was based on the mean of 6 values automatically provided by the rebound tonometer. Statistical analysis was used to evaluate correlations between variables and to identify sex- or size-related IOP variations, and changes in IOP over multiple measurements.

RESULTS

Mean ± SEM IOP of the 52 eyes was 15.74 ± 0.20 mm Hg (range, 9 to 22 mm Hg). Results for t tests did not reveal significant differences in IOP between the right and left eyes or between males and females. A significant moderate negative correlation (r = -0.41; r(2) = 0.169) between IOP and body weight was detected. Results of repeated-measures ANOVA revealed a significant increase in IOP over multiple measurements.

CONCLUSIONS AND CLINICAL RELEVANCE

Rebound tonometry was a practical and rapid means of determining IOP in small- to medium-sized tortoises that required minimal manual restraint of the animals. Establishing IOP values in healthy Hermann's tortoises will provide a reference frame for use during complete ophthalmic examinations, thus allowing clinicians to diagnose a broader spectrum of ocular pathological conditions in tortoises.

Cryptococcus gattii chorioretinitis in a ferret

Bilateral exudative chorioretinitis was diagnosed in an 18-month-old male neutered ferret (Mustela putorius furo) with a generalized Cryptococcus gattii infection confirmed by PCR. The animal was referred to the Ophthalmology Service of the Autonomous University of Barcelona (VTH-UAB) for acute onset blindness. Complete ophthalmic examination revealed absent menace response and dazzle reflex in both eyes (OU), as well as subretinal edema located in the tapetal fundus. At that time, the clinical ophthalmologic diagnosis was bilateral exudative chorioretinitis. Treatment with prednisone (0.5 mg/kg PO q24 h) was instituted in addition to the ongoing treatment with fluconazole (10 mg/kg PO q24 h). The following rechecks revealed secondary cataracts with subsequent lens subluxation and panretinal degeneration OU. Despite being blind and the poor prognosis of disseminate cryptococcosis, the patient remained active and in good body condition during 6 months after the initial diagnosis. At that time, the ferret showed ataxia, incontinence, and generalized pain. A magnetic resonance imaging study revealed a mass affecting the spine. The owners declined further investigations and the ferret was humanely euthanized. The postmortem histopathology confirmed the initial diagnosis of cryptococcosis and the presence of intraretinal Cryptococcus spp. To the authors' knowledge, this is the first report of Cryptococcus spp. induced exudative chorioretinitis in a ferret.

Anatomic and physiological characteristics of the ferret lateral rectus muscle and abducens nucleus

The ferret has become a popular model for physiological and neurodevelopmental research in the visual system. We believed it important, therefore, to study extraocular whole muscle as well as single motor unit physiology in the ferret. Using extracellular stimulation, 62 individual motor units in the ferret abducens nucleus were evaluated for their contractile characteristics. Of these motor units, 56 innervated the lateral rectus (LR) muscle alone, while 6 were split between the LR and retractor bulbi (RB) muscle slips. In addition to individual motor units, the whole LR muscle was evaluated for twitch, tetanic peak force, and fatigue. The abducens nucleus motor units showed a twitch contraction time of 15.4 ms, a mean twitch tension of 30.2 mg, and an average fusion frequency of 154 Hz. Single-unit fatigue index averaged 0.634. Whole muscle twitch contraction time was 16.7 ms with a mean twitch tension of 3.32 g. The average fatigue index of whole muscle was 0.408. The abducens nucleus was examined with horseradish peroxidase conjugated with the subunit B of cholera toxin histochemistry and found to contain an average of 183 motoneurons. Samples of LR were found to contain an average of 4,687 fibers, indicating an LR innervation ratio of 25.6:1. Compared with cat and squirrel monkeys, the ferret LR motor units contract more slowly yet more powerfully. The functional visual requirements of the ferret may explain these fundamental differences.

Ocular disorders of pet ferrets

Ocular disorders in pet ferrets are becoming more widely recognized as the popularity of these animals as companions increases. Knowledge of the anatomy of ferrets and a thorough examination are critical to accurately diagnosing ocular disease. If recognized early, some conditions can be managed successfully. Veterinarians should continue to report ocular conditions that are encountered in this species to help increase knowledge about these disorders.

Ferrets. Examination and preventive medicine

As ferrets are anatomically and physiologically similar to dogs and cats, the basic elements of ferret examination, disease processes, and preventive health are familiar to small-animal practitioners. Like other domestic carnivores, ferrets are tolerant of handling and medical procedures, especially compared with rabbits, rodents, and most nondomestic mammals. These characteristics make ferrets amenable to many of the highly specialized diagnostic and therapeutic techniques that are now available in small-animal practice. Veterinarians who wish to add ferrets to their practices should be familiar with the ferret literature, but they should not forget to draw from the wealth of knowledge in canine and feline medicine when managing unusual or difficult ferret cases.