Modified eye evisceration in a tropical screech owl (Megascops choliba)

Abstract

Background: An adult owl was presented with an injury to the right eye that rendered it blind in that eye. The left eye was normal. Removal of the right eye was recommended and a modified eye evisceration was performed. No complications were observed during or after surgery. The objective of this paper is to describe the modified eye evisceration technique that was successfully used in a tropical screech owl (Megascops choliba). Case: An adult owl was presented with an injury to the right eye that rendered it blind in that eye. Two previous surgical treatments have been carried out but have not been successful. Using a portable slit-lamp (Kowa SL-15®), both eyes were examined. The left eye was normal. Upon ophthalmic examination of the right eye, the owl demonstrated blepharospasm and large central corneal ulcer. Removal of the right eye was recommended. The bird received midazolam hydrochloride [Dormire® - 1 mg/kg, IM] and ketamine hydrochloride [Ketamina® - 5 mg/kg IM] as pre-anesthetic medications. Subsequently, the bird was anesthetized with isoflurane (Isoforine®) by facemask for induction, and then maintained with isoflurane vaporized in 100% oxygen through an endotracheal tube. With the aid of a surgical microscope and microsurgery materials, a modified eye evisceration was performed. Post-operatively, the owl received meloxicam [Maxicam® - 0.5 mg/kg, IM] and tramadol hydrochloride [Cronidor® - 15 mg/kg, orally for 4 days]. The day after surgery, the owl was comfortable and its usual appetite was regained. The patient remained hospitalized for 3 weeks and was evaluated daily. The skin sutures were removed 10 days after the surgical procedure and the surgical wound had healed normally. The patient was reintroduced into the wild after 2 months. During the 6 months post-release, the bird was evaluated once a month, and no complications were observed. Discussion: Severe eye trauma and complicated corneal ulcers are common causes of eyeball removal in birds. In birds, there is a high risk of complications during enucleation. The fragility of the orbital bones makes them susceptible to trauma during the surgery. Evisceration involves the removal of the inner contents of the eye while leaving the cornea and the sclera intact. In the current case, evisceration was chosen because the eye was blind, and maintaining a blind eye would be a source of pain and infection. In the modified evisceration technique, the risk of complications is minimal compared to enucleation, mainly because surgical manipulation is minimal. In our case, the total surgery time was 20 min. Another complication reported after enucleation in birds is the possibility of disfiguring the bird because the removal of the globe disturbs the natural head balance. To avoid these complications, the use of an intraocular prosthesis after evisceration in birds has been performed. However, owls have a tubular-shaped globe with scleral ossicles. These factors could hinder or even prevent the accommodation of a cylindrical silicone prosthesis. In the present case, an intraocular prosthesis implant was never considered due to the unavailability of the prosthesis and to avoid the risk of postoperative complications that have been reported from the literature in dogs. In this case, the owl recovered well from anesthesia without complications, and no postoperative hemorrhage was observed. No signs of pain were observed during the postoperative period and the owl had already shown an appetite and fed on the first postoperative day. The previously published reports using the modified evisceration technique also demonstrated an absence of pain signs during the postoperative period.