1414 NAVC Conference 2016 ______

OCULAR DISEASE IN THE EXOTIC COMPANION enteration—removal of eye and all surrounding struc- MAMMAL: SEEING BEYOND THE EYES tures such as the lids, fat, glands, and muscles—is gen-erally reserved for cases of neoplasia or Natalie Antinoff, DVM, DABVP (Avian Practice) abscessation in which there is involvement (or potential Gulf Coast Veterinary Specialists involvement) of the surrounding tissues. Miscosurgical Houston, TX instruments are recommended for small rodents. Rabbits and some rodents have a venous sinus behind Peter G Fisher, DVM, DABVP the that may hemorrhage during enucleation. (Exotic Companion Mammal) Staying as close to the as possible minimizes this Pet Care Veterinary Hospital risk. It is not necessary to clamp or clip the Virginia Beach, VA and surrounding vessels, although this may be performed if the nerve is acces-sible. Use caution, GENERAL ADAPTATIONS AND CONSIDERATIONS however, and do not apply traction on the globe Ophthalmic examinations in exotic companion mam- because excessive traction can damage the nerve to mals can be performed as in other species but may be the contralateral eye. Pressure is generally ap-propriate more challenging due to the small patient size. Indirect to stop hemorrhage and can be applied via sterile ophthalmoscopy can be beneficial as it enlarges the cotton applicator, or a small piece of cellulose sponge view for the examiner. Normal values are reported for can be placed in the orbit before closing the lids. Schirmer tear test, but the strips are often too large to be used in most species, although they can be cut in Rabbit half lengthwise for smaller patients. A phenol red thread The eyes of the rabbit are laterally positioned, enab- test is preferred for these small patients. ling almost 360 degrees of vision. The large oc- Most of the patients discussed here are prey species cupies almost 30% of the globe. The is spherical. and have adaptations that may affect ocular evaluation. The is atapetal, and the fundus is merangiotic, Many of these animals will not have a menace where vessels are confined to a broad horizontal band response. Some have greater corneal thickness or (the larger of these vessels are readily visible macro- decreased cor-neal sensitivity than humans or other scopically) coincident with the area of dispersion of the mammals and so will not blink in response to small myelinated nerve fibers, which is unique among mam- fibers or fur on the corneal surface. Others, such as mals. are round, irises are heavily pigmented, rabbits, produce a thicker lipid component in their tears, and eyes are very prominent and relatively unprotected which reduces their blink frequency. Still others, such by the bony orbit. Rabbits have a prominent functional as rats, produce por-phyrin, so the production of red nic-titans and 4 orbital glands: the Harderian, orbital, tears is a normal finding. Understanding these lacri-mal, and gland of the nictitans. The lacrimal gland differences is essential to correct interpretation of the pro-duces clear secretions, and the gland of the third ophthalmic examination. produces milky secretions. Photoreceptors are When choosing medications for the exotic companion 95% rods and 5% cones. The prominence of the eyes mammal, it is important to consider potential drug makes them more susceptible to injury and trauma. The sensitivity. Ophthalmic preparations can be absorbed rabbit cornea is less sensitive than that of humans, and systemically in the diseased eye, and they also can be their tear film has a high lipid component so they blink groomed from the eye and ingested. Rabbits and infrequently. However, the intraocular inflammatory rodents can suffer severe dysbiosis, so antibiotics such cascade is rapid and there is greater aqueous fibrin as penicillins, cephalosporins, erythromycin, production than in humans following injury or lincomycin, tetracyclines, and macrolides should be perforation. There is a retro-bulbar venous plexus, avoided. Most of these animals are also highly sensitive which is important when consider-ing enucleation in to the adverse effects of steroids, which should be rabbits. The nasolacrimal duct has only 1 ventral avoided in almost all cases unless absolutely punctum, which is located approximately 3 to 4 mm necessary. Ferrets are the ex-ception, in which steroids medial to the eyelid. The duct has two bends prior to are well tolerated in topical and systemic form. exiting the nasal ostium; this increases potential for Most surgical procedures performed on dogs and blockage by debris or exudate. cats can also be performed on exotic companion The lateral location of the eyes, along with the mammals. The most common procedures performed merangiotic fundus, is believed to provide the ability to are tarsor-rhapy and enucleation. Tarsorrhapy can be visualize the horizon; vision is monocular laterally but modified to use small pieces of red rubber tubing as binocular directly in front of the face and probably stents, or in some animals stents can be avoided above and behind. One study suggested that rabbits completely if the can be opposed without are near-sighted when using directly tension. In most of these animals a single suture will forward but farsighted when looking laterally. The suffice for tarsorrhaphy. majority of cones are green/blue sensitive, which is Enucleation, which is removal of the eye leaving the believed to enable them to detect predator movement surrounding structures intact, can be performed via in grass and sky. either a transpalpebral or transconjunctival approach. Normal rabbit intraocular pressure (IOP) is 15 to 25 Regardless of the technique used, it is essential to mm Hg. Normal Schirmer tear test values are 5.30 +/- remove the globe, , and any glands that are 2.96 mm/min (range, 0–11.22 mm/min). Phenol red present in order to prevent dehiscence or drainage. Ex- Small Animal – Exotic Companion Mammals 1415 ______

thread test values are 20.88 mm/15 sec (range, 15–17 Rods are the predominant characteristic of the retina +/- 2.90 mm/15 sec). and also have an area centralis (area of increased Atropinesterase is present in about 40% of rabbits, so photoreceptor density). The ferret has less visual acuity atropine may be ineffective at dilation. than the cat or human but has a lower light threshold, Tropicamide can be used in these cases. enabling improved vision at lower light. IOP via rebound tonometry is 14.07 +/- 0.35 mm Hg, similar to values Guinea Pig obtained by applanation tonometry (14.5 +/- 3.27 mm Guinea pigs have small eyes with rudimentary Hg). Normal Schirmer tear test values are 5.31 +/- 1.32 nictitans and a round pupil. The guinea pig eye has an mm/min. atapetal retina with a paurangiotic fundus in which the retinal blood vessels are minute and restricted to the Hedgehog direct neighborhood of the optic disk. Normal Schirmer Hedgehogs have very small but prominent eyes that tear test values for guinea pigs are 3 mm/min (range, are unprotected by the bony orbit. Normal hedgehog 0–12 mm/min). Normal phenol red thread values are 21 eyes are mildly exophthalmic with . Visual +/-4.2 mm/15 sec. Guinea pigs have a large intraorbital acuity is fair, although other senses are primarily used lacrimal gland and a prominent zygomatic salivary for navigation. Hedgehogs have monochromatic vision gland. They are a precocious species and eyelids are and lack cones, although some of the rods contain opened at birth. are less sensitive than in cone-type nuclei. Mean Schirmer tear test values are other species. 1.7 +/- 1.2 mm/min (range, 0–4 mm/min), and IOP is 20.1 +/- 4 mm Hg (range, 11.5–26.5 mm Hg). Chinchilla The fundus of chinchillas is anangiotic (lacks blood Sugar Glider vessels). The pupil is a vertical slit, and the nictitans is Sugar gliders are nocturnal and have large prominent rudimentary. Chinchillas are precocious and have eye- eyes with round pupils. They have a lacrimal gland, and lids open at birth. IOP is 17.71 +/- 4.17 mm Hg for the retina is avascular. A tapetum lucidum is present, applanation tonometry, although values may be much and the predominant photoreceptors are rods. lower using a Tonopen or rebound tonometry. DISEASES AND CLINICAL PRESENTATION Rat/Mouse/Hamster/Gerbil Rabbit Rats and mice have small eyes, round pupils, and Bacterial in rabbits has commonly thin corneas. Hamsters and gerbils have larger eyes been associated with Staphylococcus spp and relative to body size, and hamsters have shallower Pasteurella multocida, but other infectious agents may orbits among the small rodents (and thus are more be involved. and reddened eyelid margins are predisposed to proptosis). The fundus of all these the most common clinical signs, and infected rabbits rodents is holangiotic, with vessels radiating from the often present with a clear to milky aqueous discharge center, and lacks a tapetum lucidum. There are three that causes matting and crusting of the facial fur near orbital glands in rats: intraorbital, extraorbital, and the medial canthus. Initial treatment involves topical Harderian. The Harderian gland is associated with the antibiotic ophthalmics such as ciprofloxacin. If the third eyelid and produces porphyrin, resulting in patient does not respond, then porphyrin-stained tears. Porphyrin production by the (inflammation of the lac-rimal sac) or dacryosolenitis Harderian gland is controlled by parasympathetic (inflammation of the naso-lacrimal duct) should be innervation, so factors such as disease or stress may considered. With disease pro-gression, white threads of increase porphyrin production as well as the mucus or pus appear at the medial canthus or in the appearance of red tears. Rats have a retro-orbital ventral conjunctival sac. The nasolacrimal drainage venous plexus, whereas mice and hamsters have an system provides a conduit for tears from the lacrimal orbital venous plexus. lake to the nasal cavity. In rab-bits, a single ventral Rats and mice have predominantly rods, and they lacrimal punctum can be found 3 to 4 mm from the have mainly ultraviolet green and blue vision, which is medial canthus lid margin. Facial derma-titis as a result believed to be beneficial during dawn and dusk. They of chronic epiphora secondary to dacryocystitis is not have very poor visual acuity but a wide field of view. uncommon in rabbits and may result from thick Schirmer tear test values for the rat are 10.2 +/- 1.6 inflammatory discharge or in association with an mm/min. IOP in rats is 15 to 30 mm Hg when measured elongated incisor or third or fourth upper cheek tooth via TonoPen and 13.0 +/- 1.2 mm Hg using rebound reserve crown, both of which may result in blockage of tonometry. IOP in mice is 10 to 20 mm Hg. the nasolacrimal system. If lacrimation is excessive and nasolacrimal obstruction is suspected, fluorescein stain Ferrets can be used to assess nasolacrimal duct patency. If Ferrets have a small globe and laterally located, obstruction is suspected, a topical ophthalmic prominent eyes with a large spherical lens. The anesthetic can be applied and in the sedated patient nictitans is prominent. The pupillary opening is elliptical using a 23-gauge (0.64-mm) lacrimal cannula, or an along the horizontal axis. They have a holangiotic appropriately sized IV catheter (with the stylet removed) fundus in which the retina contains a compact plexus of can be used as an irrigating cannula to enter and flush blood vessels located in the major part of the light- (with 0.9% saline or eyewash solution) the proximal sensitive portion of the retina and a tapetum lucidum. nasolacrimal duct via the punctum lacrimale, which is 1416 NAVC Conference 2016 ______

located in the ventral lid margin several millimeters from been advocated depending on the underlying cause the medial canthus. This will help remove purulent and severity of disease. debris and pos-sibly relieve any blockage. Samples can Spontaneous chronic corneal epithelial defects be collected for cytology and culture. A retrospective (SCCED), also known as indolent ulcers, have been study looking at the results of bacterial culture and well described in dogs.4,5 However, these chronic, sensitivity from naso-lacrimal duct flushes in rabbits superficial, nonhealing corneal ulcers have not been with ocular and/or nasal discharge showed a well described in rabbits. The authors have seen prevalence of P. multocida, Entero-bacter cloacae, several cases in rabbits that present with Bordetella bronchiseptica, Moraxella spp, blepharospasm, conjunctival hyperemia, corneal Pseudomonas spp, and Staphylococcus spp.1 The edema and neovascularization, and ocular pain cannulation technique can be used to infuse iodine- associated with these nonhealing ulcers. In dogs, based contrast medium in order to perform a contrast classic histopathologic features include nonad-herent, study to confirm more severe and permanent blockage, dysplastic epithelium adjacent to the ulcerated region, possibly the result of underlying dental disease, and loss of basement membrane, the presence of a aids in prognosis and long-term management. hyalinized, acellular zone in the superficial stroma, and Viral conjunctivitis resulting from herpes simplex an abnormal nerve plexus in the anterior stroma sur- virus has been reported in rabbits in association with rounding the erosion. Reported surgical therapies in- close contact between affected rabbits and humans clude debridement, anterior stromal puncture with herpes labialis.2 In addition to bilateral techniques (grid keratotomy, multiple punctate conjunctivitis, infected rabbits show hypersalivation and keratotomy), third eyelid flaps, temporary tarsorrhaphy, severe signs of central nervous system dysfunction, application of cyanoacrylate tissue adhesives, thermal including incoor-dination, intermittent myoclonic cautery, and superficial keratectomy. More recently, the seizures, and opistho-tonos resulting from herpesvirus- use of a handheld device (Algerbrush) for diamond burr associated nonsup-purative meningoencephalitis of mecha-nized debridement of the cornea in cases of cerebral grey matter. SCCED has been described.5 The burr is passed over Pseudopterygium or corneal occlusion syndrome the bed in multiple circular or wave-like is a rare condition in rabbits in which the conjunctiva passes, removing nonadherent epithelial tissue until grows over, but does not adhere to, the cornea, even- stable epithelium is encountered. This technique has tually leaving a small opening in the center before been used by the author (PGF) for successful progression stops. The condition is acquired but the resolution of a rabbit SCCED. Ophthalmologists have exact cause is unknown; however, this sudden growth suggested that the diamond burr creates micro- of tissue could reflect an acquired inflammatory erosions of the base-ment membrane that contribute to reaction or a hyperplastic response to changes in an alteration of corneal topography, which aids in the corneal sensiti-vity.3 Veterinarians have reported adhesion of new epithelial cells, and that the technique treating any underlying pathology and leaving the may contribute to fibrosis and improved epithelial corneal membrane undis-turbed. The rabbits are pain adhesion strength. free and remain unchanged on annual physical may be seen in mature rabbits as part of examinations. Surgical removal of the precorneal the lens aging process, but they have also been membrane has also been documented, but a high rate associated with Encephalitzoon cuniculi, a microspori- of recurrence is reported. Postoperative application of dial obligate intracellular parasite. As the lens has no topical cyclosporine may be effective in preventing independent blood supply, it is theorized that E. cuniculi recurrence. infection of the lens occurs in utero. The granulomatous Ulcerative is relatively common in pet inflammation associated with E. cuniculi may result in rabbits, with the normal lateral positioning of the rabbit lens rupture leading to phacoclastic . Topical eye predisposing to traumatic injury. Typical clinical ophthalmic corticosteroids may be indicated, along with signs include epiphora, conjunctivitis, blepharospasm, benzimadazole therapy if phacoclastic uveitis is and corneal edema. A defect in the corneal epithelium suspect-ed. However, other authors dispute the use of and stroma may be observed, and application of fluore- steroids in any case and prefer flurbiprofen. scein dye is recommended to visualize the extent and can occur in rabbits due to ocular, depth. Signs of anterior uveitis such as and periocular, or systemic disease. Ocular and periocular aqueous flare may also be present. Eyelid diseases disease results in unilateral exophthalmos, with the dif- such as and distichiasis have been ferential diagnosis including retrobulbar abscess (most reported as causes of corneal trauma and ulceration often secondary to dental infection), neoplasia, salivary and may be more common in giant breeds. Chronic mucocele, and trauma. Bilateral exophthalmos can dacryocystitis, sicca, and orbital occur secondary to engorgement of the orbital sinus disease resulting in exophthalmos and exposure (retro-bulbar venous plexus located behind the globe), keratitis are also possible underlying causes. Treatment which is most often the result of cranial thoracic involves determining and treating the underlying cause disease (eg, thymoma, lymphoma, abscess) causing along with treatment of secondary infection and support pressure on the vena cava. of corneal health. Broad-spectrum ophthalmic antibiotic can also occur in rabbits, usually associ- solutions, artificial tears, immune-modulating preps, ated with buphthalmos. This is reported in rabbits and it autologous serum, and anti-inflammatories have all is important to differentiate from exophthalmos. In many rabbits glaucoma is attributed to a recessive gene Small Animal – Exotic Companion Mammals 1417 ______

known as the bu gene (for buphthalmos), which may be infectious conjunctivitis from Pseudomonas spp, more prevalent in New Zealand white rabbits but may Staphylococcus spp, and Corynebacterium; and dental occur in any breed. Diagnosis is via measurement of disease, most commonly elongation of the maxillary IOP; the unaffected eye can be used for comparison. molar reserve crowns. Manage-ment is similar to other species. Rat/Mouse/Hamster/Gerbil Guinea Pig In rodents the Harderian gland, a lacrimal structure Chlamydial conjunctivitis associated with located posterior to the globe in the orbit, contains por- Chlamydo-phila caviae is the most common cause of phyrin, a red-brown pigment. As a result, overflow of infectious conjunctivitis in guinea pigs. Spread is via tears (epiphora) resulting from ocular irritation, naso- direct contact or aerosol. Common in guinea pigs 4 to 8 lacrimal duct inflammation, and inflammation of the sali- weeks old, clinical disease most often results in vary or lacrimal glands is often associated with red tear inflammatory con-junctivitis (mild to severe) along with staining of the face. signs of rhinitis (sneezing, clear to mucopurulent nasal , inflammation of the lacrimal system discharge). Polymerase chain reaction testing is the and, most importantly, the Harderian gland, is usually most reliable method of diagnosis. Antichlamydial associated with sialodacryoadenitis virus, a therapy with sys-temic tetracyclines and ophthalmic coronavirus that is readily transmitted between rats by ciprofloxacin are the treatments of choice, although direct contact, aerosol, or fomites. Rhinitis resulting in tetracyclines can cause bacterial gastrointestinal sniffling is usually followed in several days by unilateral dysbiosis. Concurrent bacterial infections may worsen or bilateral blepharospasm and . Interman- clinical signs and can lead to development of uveitis or dibular swelling resulting from involvement of the sali- a corneal stromal abscess characterized by a focal vary glands is also frequently seen. Other secondary corneal stromal infiltrate (yellow or white) that varies in conditions include keratitis, conjunctivitis, uveitis, size and can affect any stromal to endothelial level of exoph-thalmia, and possible multifocal retinal the cornea. Samples for cytology and culture and degeneration. sensitivity can be obtained by scraping the lesion. Mycoplasmosis is a primary cause of conjunctivitis Aggressive systemic and topical antibiotic therapy is in rats and mice and may also cause dacryoadenitis. indicated. Keratectomy and conjunctival graft Tetracyclines are the treatment of choice. Other placement should be considered with corneal bacteria implicated in rat conjunctivitis include abscesses that do not respond to medical therapy. Pseudomonas spp, Salmonella spp, Streptococcus Pea eye, a permanent protrusion of the conjunctival spp, and Coryne-bacterium. Treatment is based on sac, is considered an inherited trait in guinea pigs and results of culture and sensitivity testing. may be associated with fat deposition. In general, Microphthalmos is seen periodically as an incidental affected guinea pigs do not seem uncomfortable and congenital finding in rats and mice. can thrive without treatment. Alternatively, surgery may Cataracts, both congenital and due to aging, may be performed to remove these conjunctival protrusions. occur spontaneously in rats. Prolapse of the infraorbital gland of the third eyelid Corneal dystrophies, characterized by punctate (cherry eye) can look similar to pea eye and is treated white opacities observed in the interpalpebral fissure, surgically by returning the prolapsed gland to a deeper are common in both rats and mice. The opacities are position with suture techniques employed as for the often present shortly after birth and do not tend to same condition in the dog. progress. Elevated cage ammonia levels resulting from Heterotropic bone formation (formerly osseus poor en-closure hygiene and its effect on the cornea choristoma), an ossification of tissue at the has been proposed as one potential underlying cause. iridocorneal angle, may appear as a ring of irregular Treatment is not necessary. opaque material. The is the most common site of choristoma development and is often an Ferret incidental finding in clini-cally normal guinea pigs. The Ferret infectious conjunctivitis has been reported exact cause is unknown, but the concentration of in association canine distemper virus, human influenza plasma ascorbic acid into the aqueous humor and its virus, systemic salmonellosis, and mycobacteriosis. promotion of ciliary body ossifi-cation has been With canine distemper, ocular signs are often the first proposed. No treatment is indicated, but monitoring for signs of this nearly 100% fatal disease. At 7 to 9 days signs of glaucoma is recommended. postex-posure a moderate to severe conjunctivitis with Dermoid, a congenital area of normal skin muco-purulent ocular and nasal discharge becomes component tissues, may be found involving the cornea apparent. As the disease progresses, so do the or conjunct-tiva in both guinea pigs and rabbits. associated ocular signs, which may include , Keratectomy of the abnormal tissue is the treatment of corneal ulceration, keratoconjunctivitis sicca, and choice. (partial or complete fusion of the eyelids). Ferrets are suscep-tible to several strains of Chinchilla human influenza virus, and early clinical ocular signs Ocular disease is uncommon in chinchillas, with epi- (most commonly conjunctivitis) can mimic early canine phora and cataracts being the most commonly reported distemper. However, with influ-enza the conjunctivitis clinical complaints. Epiphora has been associated with does not progress and responds to topical antibiotic environmental irritants (eg, dust bath material); ophthalmic therapy. Mycobacterium genavense 1418 NAVC Conference 2016 ______infection has been diagnosed in ferrets, with cases of REFERENCES disseminated mycobacteriosis showing gener-alized 1. Quinton JF, Lennox A, Guillon L, et al. Results of peripheral lymph node enlargement along with a bac-terial culture and sensitivity testing from proliferative lesion of the conjunctiva and nictitating nasolacrimal duct flushes in one hundred and three membranes resulting in serous ocular discharge. both healthy and clinically ill pet rabbits (Oryctolagus Defini-tive diagnosis is based on histopathology and cuniculus). Int J Appl Res Vet Med. 2014;12(2):107- sequence analysis of 16S rRNA amplicons from 120. formalin-fixed, paraffin-embedded tissue. Infected 2. Muller K, et al. Encephalitis in a rabbit caused by ferrets have been treated successfully using rifampicin. human herpesvirus-1. JAVMA. 2009;235(1):66-69. Spontaneous cataracts, of congenital, hereditary, or 3. Dupont C, Carrier M, Gauvin J. Bilateral precorneal acquired origin, have been reported in ferrets. membranous occlusion in a dwarf rabbit. J Small Cataracts in ferrets usually involve both the cortex and Exotic Anim Med. 1995;3(2):41-44. nucleus of the lens, with the exact cause unknown. 4. Gosling AA, Labelle AL, Breaux CB. Management of Inherited, genetic, and nutritional causes have all been spontaneous chronic corneal epithelial defects postulated. (SCCEDs) in dogs with diamond burr debridement Zygomatic salivary gland mucocele and malignant and placement of a bandage contact lens. Vet lymphoma involving the orbit have both been reported Ophthalmol. 2013;16(2):83-88. in ferrets and may lead to exophthalmos and 5. Sila HH, Morreale RJ, Lorimer DW, et al. A retro- subsequent exposure keratitis. spective evaluation of the diamond burr superficial Ophthalmia neonatorium is seen in kits aged 3 keratectomy in the treatment of spontaneous chronic days to several weeks. Bacterial infection involving the corneal epithelial defects in dogs from 2006 to 2008. conjunctival mucous membranes results in exudate Proc Coll Vet Ophthalmol Annu Mtg. 2009;40:404. accumulation behind the closed lids and is clinically 6. Williams DL. of Exotic Pets. West recognized by unilateral or bilateral swelling of the Sussex, UK: Wiley Blackwell; 2013. sealed eyes. Treatment involves surgically separating 7. Harkness JE, Turner PT, VendeWoud S, Wheler C. the natural suture line between the eyelids and flushing Harkenss and Wagner’s Biology and Medicine of away the purulent debris, followed by application of a Rabbits and Rodents, 5th ed. Sussex, UK: Wiley broad-spectrum ophthalmic ointment for several days. Blackwell; 2010. Warm compresses and gentle manipulation of the lid margins may be used to prevent recurrence.