Abstract

A 24-year-old male California sea lion (Zalophus californianus) was housed as part of a performing pair of males at Busch Gardens Tampa, Florida. He had a long-standing history of bilateral mature cataracts, with the most developed cataract being on the left eye. Over the past several years, he had become blind, but was still able to see shadows and function in shows with routine behaviors. He cooperated well with vocal instructions from the training staff. His appetite and weight were unaffected by his visual loss.

A veterinary ophthalmologist visited twice yearly to monitor and assess the eyes. In 2001, this male began to experience excessive epiphora, intermittent pain and corneal edema, especially of the left eye. Initially, discomfort and edema could be managed well with gentocin ophthalmic drops (The Butler Company, Columbus, Ohio 43228, USA) and Muro 128 drops (Bausch & Lomb Pharmaceuticals, Inc., Tampa, Florida 33637, USA) three to four times daily for one to two weeks at a time. Periodically, during exams for the pain, a fluorescein dye test would be positive for punctate corneal ulcers. Increasing the frequency of the gentocin and Muro 128 to every two hours helped in the healing of these ulcers. During the periods of acute corneal ulcers, edema, and pain, he would not be used in the shows.

In the summer of 2001, this male again showed evidence of ocular pain by rubbing his face on the walls, holding his eye closed continually, and occasionally staying out of the water for hours at a time. Upon examination by the ophthalmologist, it was determined that the cornea contained several centrally located bullae. We speculated that the pain was generated as these bullae erupted and tried to heal. Conventional topical therapy, in addition to oral flunixin meglumine (Schering-Plough Animal Health Corporation, Union, New Jersey 07083, USA), controlled the pain temporarily, but the bullae did not resolve.

By September of 2001, a more aggressive therapy was attempted in an effort to eliminate the bullae and stimulate healing and epithelialization of the corneal area. Since this male was well trained for work with the eyes, the procedure was initially attempted with topical anesthetic alone. Proparacaine hydrochloride 0.5 percent topical anesthetic (The Butler Company, Columbus, Ohio, USA 43228) was applied to the surface of the left cornea to obtain surface anesthesia. When it was determined by corneal touch with a cotton tipped swab that anesthesia was adequate, the thermokeratoplasty procedure commenced. The heated ophthalmic fine-tipped cautery device (Aaron Medical Industries, Inc., 7100 30th Avenue North, St. Petersburg, Florida, USA 33710-2902) was applied for about one to two seconds onto a single bullae and this was repeated approximately 20 to 25 times arranged in a rectangular grid pattern. With magnification, the depth of each cauterized point was approximately 50 percent of the corneal thickness. The animal cooperated completely and the entire procedure was completed without the need for sedation or general anesthesia.

The eye was rechecked daily for the first week and every few days thereafter. There was evidence of discomfort for the first few days following the procedure. This was managed with topical Muro 128 drops four times a day and oral flunixin meglumine once daily for three days. Within the first week, there was evidence of neovascularization over the center of the left cornea. In the following weeks, the neovascularization increased rapidly and epithelialization became evident. Some bullae were still present on assessment several weeks later, but the overall appearance of the cornea and the pain induced by the bullae had greatly improved. The corneal thickness had decreased, and corneal clearing had increased. Neovascularization across the corneal surface incorporated the grid area of treatment. Except for initial discomfort, no complications were noted related to the thermokeratoplasty procedure.

In human ophthalmology, thermal keratoplasty is used to correct corneal conditions such as astigmatism and keratoconus. The temperature at the tip of the cautery probe can reach 70 to 85 degrees centigrade. This temperature will effectively coagulate corneal tissue and collagen fibers. This shrinks the collagen fibers, flattening the surface of the cornea. Ultimately, this promotes scarring of the cornea and neovascularization of the treated area to further promote healing and epithelialization of the corneal defect.¹

Due to this male's even temperament and many years of training and working with his eyes for exams and treatment, this procedure was accomplished with only topical anesthesia. In less cooperative animals, general anesthesia may be warranted. This technique gave us good results in this animal and helped to resolve the recurring bullous keratopathy that he was experiencing. No changes in vision were noted after the procedure, but this is likely due to the chronic nature of the corneal disease and advanced cataract. The procedure did provide satisfactory pain relief from the refractory corneal disease he was experiencing at that time. Thermokeratoplasty is a potential therapeutic option in other marine animals with chronic bullous keratopathy that does not response well to conventional topical therapies.

References

1.  Sporl E, U Genth, K Shmalfuss, T Seiler. 1996. Thermomechanical behavior of the cornea. Ger J Ophthalmol. Nov;5(6):322-7.