Surgery of Exotic Animals. Группа авторов

species (Copeland and Brown 1976). An important consideration when performing an enucleation is the presence of scleral ossicles in the anterior part of the globe, as in teleosts, and scleral cartilage or scleral calcifications in the posterior part in elasmobranchs (Pilgri and Franz‐Odendaal 2009).

The pupillary light reflex is usually absent, except in elasmobranchs (Duke‐Elder 1958). They have a slow retinomotor reflex that takes up to two hours. During the day, retinal‐pigmented epithelium granules migrate apically in the retinal epithelial cells, cones contract and rods elongate (Burnside et al. 1983). This retinomotor reflex protects photoreceptors from bright light, but rapid exposure of anesthetized patients to a scialytic lamp may impair vision and some authors have recommended covering fish eyes with an opaque material during surgery (Wildgoose 2000).

Figure 5.11 Green spotted pufferfish (Tetraodon nigroviridis) before (a) and after incisor plate occlusal adjustment (b).

      Source: Photo courtesy: Companion Avian and Exotic Pet Medicine Service, University of California, Davis.

Figure 5.12 Fluorescein staining of a large corneal ulceration in a lookdown (Selene vomer) associated with repeated trauma on the walls of the exhibit.

      Source: Photo courtesy: Companion Avian and Exotic Pet Medicine Service, University of California, Davis.

Corneal ulcers can be highlighted by the use of fluoresceine dye (Figure 5.12). Repair corneal perforations with small diameter suture material and use periorbital tissue to cover peripheral corneal perforations, similar to a conjunctival flap.

      Idiopathic gaseous exophthalmia (i.e. not due to gas oversaturation of water) has been treated with pseudobranchectomy. The pseudobranch is located dorsally in the opercular cavity in most teleosts (Harms and Wildgoose 2001). Visually locate the pseudobranch and apply electrocautery on various points to cauterize it.

      Some fancy goldfish, such as oranda and lionheads, are bred to have a fleshy outgrowth on the dorsal aspect of the skull and bilaterally in the buccal area, which is called a crown or “wen.” This wen is a hyperplastic epidermal and mucous cell covering of adipose cell deposition in the hypodermis (Angelidis et al. 2006). The wen grows continuously, sometimes covering the eyes and impairing vision. Use a scalpel or electrocautery to excise the periocular tissue (Sladky and Clarke 2016).

      Cataract Surgery

Cataract surgeries have been performed in fish, either with complete lens removal (Whitaker 1999; Adamovicz et al. 2015) or with phacoemulsification of the lens content in specific cases (Adamovicz et al. 2015; Bakal et al. 2005). After applying topical proparacaine and atropine, fill the anterior chamber with viscoelastic material and incise the dorsal cornea with a 2.75 mm keratome (Adamovicz et al. 2015) or a 11# scalpel blade. The authors recommend a dorsal incision of the cornea as it allows easier access to the retractor lensis muscle located ventral and caudal to the lens (Gustavsen et al. 2018). To prevent collapse of the anterior chamber, incise the cornea perpendicular to its surface initially, then with a more acute angle. Extract the lens, which physiologically protrudes into the anterior chamber, “en masse” with a Graefe cataract spoon through the corneal incision (Whitaker 1999). Close the cornea with simple interrupted 5‐0 to 9‐0 sutures. Apply a cyanoacrylate ophthalmic tissue adhesive (optional) to ensure impermeability of the cornea during healing (Whitaker 1999). In most cases, complete phacoemulsification is not possible due to the hard texture of the lens nucleus so partial phacoemulsification is followed by enlargement of the corneal incision and extraction of the lens nucleus (Adamovicz et al. 2015). However, in the case of a sturgeon infected by intraocular digenean trematodes, complete phacoemulsification of the lens has been reported (Bakal et al. 2005). These trematodes can cause cataracts causing inflammation that can lead to softening of the lens (Adamovicz et al. 2015).

      Enucleation

Enucleation is performed to alleviate pain associated with nonresolvable ocular lesions (Figure 5.13) (da Silva et al. 2010; Lair et al. 2014) or severe injury. A prosthetic eye can be placed (Nadelstein et al. 1997), but keeping the prosthesis in place long‐term may be problematic (Harms and Wildgoose 2001).

After performing a local block with lidocaine, dissect and transect periorbital tissue, conjunctiva and oculomotor muscles off the globe with fine curved scissors. Branches of the trigeminal and facial nerves running along the caudolateral border of the orbit should not be transected (Wildgoose 2007b). If a hemostat is placed on the retro‐orbital pedicle, minimize traction on the optic nerve to prevent damage to the optic chiasm, which will result in blindness in the contralateral eye. Transect the pedicle, remove the globe, and ligate the retro‐orbital vessels. Supplement hemostasis by applying digital pressure and a hemostatic agent (Gelfoam^®, Pfizer, New York, NY). Suturing the periorbital tissue, with an H‐plasty if needed, enables one to close the orbit for esthetical purposes in some fish species such as cod (Gadus morhua) and saithe (Pollachius virens) (Figure 5.14). In fish where this is not possible, leave the orbit open to heal (Figure 5.15) and expect mild hemorrhagic discharge after recovery. Some authors recommended placing a waterproof paste containing pectin, gelatin, and methylcellulose (Orabase®, ConvaTec, Bridgewater Township, NJ) into the orbit over the next 24–72 hours (Harms and Wildgoose 2001).

Figure 5.13 Enucleation of a rockfish (Sebastes caurinus) with a retinal tumor.

      Source: Photo courtesy: Aquarium du Québec.

Figure 5.14 Suture of the periorbital tissue after an enucleation in a saithe (Pollachius virens).

      Source: Photo courtesy: Aquarium du Québec.

Figure 5.15 Enucleation of a sea horse (Hippocampus erectus) with a retro‐orbital abscess. The tube on the right of the image is used for anesthesia maintenance and Harmon–Bishop's forceps were used to elevate the globe from the orbit and allow section of the optic nerve and retro‐orbital pedicle. In this species, it is not possible