17 This chapter focuses on small exotic pets rather the large zoo species. Among exotic pets, the domestic rabbit seems the most popular; however, rodents and reptiles are frequently encountered. While there are many ophthalmic diseases in exotic pets, this chapter is devoted to those ophthalmic diseases that are the most often presented to the veterinarian. Snakes lack mobile eyelids, having instead evolved with a clear spectacle that covers the corneas for their protection. The outer aspects of the spectacle of snakes are normally shed during each ecdysis, as eyelid skin would be. It becomes cloudy with the thickening of its layers and accumulation of fluid between the old and new layers just before ecdysis. Retained spectacles are associated with dry environments, generalized integumentary diseases, local injury of the spectacle, systemic illnesses, and mite and tick infestations (Figure 17.1). Semi‐translucent to opaque spectacle can cause a snake to become irritable, aggressive, and unable or unwilling to eat. Figure 17.1 (A) Retained/opaque spectacle in a snake. Note the spectacle nearly obstructs the cornea, pupil, and vision. (B) Retained spectacle in another snake. (C) Subspectacular infection in an Indigo snake. Note the infection has affected the entire spectacle. (D) Exophthalmos, spectacular inflammation, and opacity and uveitis in a septic albino Burmese python. Conservative treatment is recommended initially, and consists of misting or soaking the snake and facilitating a natural shed for the next cycle. Topical acetylcysteine may soften and loosen the spectacle and permit careful removal with thumb forceps. Damage to the deeper aspects of the spectacle and the cornea should be avoided. Closely related but more serious, subspectacular infections and abscesses can potentially damage the cornea. Infection can enter the subspectacular space from penetrating injuries, systemic infections, or ascending through the nasolacrimal duct. Clinical signs include an enlarged bulging spectacle (often confused with glaucoma, i.e., pseudobuphthalmia) with subspectacular exudate. Bacteria recovered include Pseudomonas and Proteus spp., and Providencia rettgeri. Treatment typically includes excision of a 30° wedge of the spectacle, taking care not to damage the underlying cornea, irrigation of the subspectacular space, and antibiotics. Trauma is the most common cause of ophthalmic disease in raptors and other birds of prey (Figure 17.2). Damage is to the eyelids, nictitating membrane, cornea, lens, or posterior segment. Intraocular hemorrhage, retinal tears and detachments are often present. Prognosis and treatment depend on the amount of ocular damage present and the secondary inflammation. Treatment is generally directed at controlling the corneal and intraocular inflammation, and preventing or treating infection. Figure 17.2 Raptors are frequently presented with ophthalmic trauma (blunt and penetrating). (A) In this Bald Eagle a lead pellet has penetrated the cornea and lodged in the anterior chamber. Secondary iridocyclitis with considerable iridal swelling and fibrin are present. (B) Trauma to the eye of a Golden Eagle. Behind a corneal defect, fibrin, clotted hyphema, and secondary iridocyclitis can be appreciated. (C) Chorioretinal scars and damaged pectin with hemorrhage in a Barred Owl secondary to trauma and inflammation. (D) Traumatic globe rupture in a Screech Owl resulting in globe hypotension, loss of the anterior chamber, and deflation.(E) Traumatic uveitis in a Barred Owl has resulted in posterior segment hemorrhage, anterior chamber fibrin, and an axial cataract. (F) Sealed corneal perforation in a Great Horned Owl with anterior synechia, anterior lens capsule rupture, and cataract. The rabbit is among the most common exotic pets and can suffer from a wide variety of ophthalmic diseases. The rabbit has a very prominent eye that is positioned laterally which permits a nearly 360° visual field. The retrobulbar space in rabbits has a very large venous plexus, which presents challenges to orbital surgery and enucleation procedures because there is considerable risk of hemorrhage. The nasolacrimal system has only one lacrimal punctum (lower) which is close to the molar and incisor teeth roots. Because of this close proximity, abscesses of the tooth roots can affect the nasolacrimal system. In these instances, dacryocystorhinography can be valuable in outlying the entire nasolacrimal system. The rabbit’s pupil is round, and in albino rabbits the iris is pink. The rabbit has an atapetal fundus that is variably pigmented. The optic nerve head is oriented horizontally with myelinated nerve fibers and retinal blood vessels extending both laterally and medially from the disc. The rabbit’s ocular fundus has a visual streak and the estimated visual acuity is 22/200 (based on pattern‐evoked cortical potentials). Color vision appears limited to the blue (425 nm) and green (520 nm) wavelengths. Orbital abscessation is the most common cause of exophthalmia in rabbits and usually results from an infection associated with a tooth root (Figure 17.3). The exophthalmia is often rapidly progressive with resultant exposure keratitis and strabismus. Orbital imaging is valuable to demonstrate the site and extent of the abscess and image the orbital tissue contents. Enucleation can be attempted but postoperative infections of the surgical site are common. Figure 17.3 (A) Exophthalmos in a rabbit with orbital and tooth root abscess. Culture revealed Pasteurella sp. If enucleation is performed, the retrobulbar infection may remain. Prognosis is guarded. (B) Advanced exophthalmos and retrobulbar abscess. Entropion occurring in rabbits can be treated surgically as in dogs and cats. In very young rabbits (kits), tacking of the eyelids can be used to prevent secondary severe corneal damage until adult size is reached (Figure 17.4).
Ophthalmology in Exotic Pets
Diseases of the Snake Spectacle
Ophthalmic Disease in Raptors
Trauma
Ophthalmic Disease in Rabbits
Orbital Abscessation
Entropion
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