Abstract
Cataracts are common in both free-ranging and captive phocids. Cataracts can severely affect visual acuity, making important tasks such as prey location and social interactions difficult. Surgical removal of cataracts is well described in many species of companion and zoo animals. However, previously published reports of cataract surgery in pinnipeds have demonstrated disappointing results due to poor wound healing, endothelial cell damage, and uveitis, all of which resulted in limited recovery of useful visual function. In addition, many clinicians have been hesitant to perform surgery on phocids due to the risk of anesthetic-related mortality in these animals. Recent advances in surgical technique and improved anesthetic support may increase the success of cataract surgery in phocids, providing better treatment options for the marine mammal clinician. To the best of our knowledge, this is the first report of a successful clear corneal cataract surgery performed on a northern elephant seal (Mirounga angustirostris).
A recently weaned male northern elephant seal (Mirounga angustirostris) pup that stranded along the central California coast on June 10, 2001 was brought to The Marine Mammal Center for rehabilitation. The seal was moderately underweight (47 kg), and did not appear to avoid obstacles or exhibit a menace response. The nictitating membrane of the right eye was inflamed, and there was moderate blepharospasm. Closer examination revealed bilateral cataracts. The seal was anesthetized with 38 mg of a 1:1 solution of tiletamine and zolazepam (TelazolTM) by intravenous (IV) injection into the epidural vein approximately 10 minutes after an intramuscular (IM) injection of 0.94 mg of atropine. An ophthalmic examination confirmed the bilateral mature cataracts. There was no pupillary light reflex in the right eye, but the left pupil reacted normally to light. The right cornea was clear, but approximately one-third of the left cornea was opaque. Ultrasonography revealed the vitreous of both eyes to be clear, and both retinas were attached. We recovered the animal and decided to attempt to remove the cataract in the left eye.
On July 7, the elephant seal was anesthetized again using Telazol IV after atropine IM. The seal was intubated with a nine mm diameter, cuffed endotracheal tube and maintained with 1.0 to 2.0 percent isoflurane in 100 percent oxygen. Assisted mechanical ventilation was provided at a rate of 10 breaths per minute and a volume of 600-800 ml per breath. Heart rate, oxygen saturation, respiratory rate, end-tidal carbon dioxide and temperature were monitored during the procedure.
The eye was dilated using a combination of 10 percent phenylephrine, 0.25 percent scopolamine, one percent cyclogyl, and one percent atropine. A retrobulbar nerve block consisting of 6.0 ml of a one percent lidocaine with epinephrine was then administered. The eye and peri-ocular area were cleaned and sterilized with a dilute povidone iodine solution. Two paracentesis sites were created in the cornea using a disposable AlconTM ophthalmic 22.5-degree eye knife. An air bubble was placed into the anterior chamber. Since the cataract was mature, visualization of the anterior capsule for capsulorhexis was extremely difficult. An intracameral injection of indocyanine green dye was given, staining the anterior capsule and allowing for visualization of the anterior lens capsule during the creation of a continuous curvilinear capsulorhexis.
The eye was then filled with ViscoatTM to maintain the anterior chamber during wound creation, and to protect the corneal endothelium during the phacoemulsification process. A beveled clear corneal incision was then made in the peripheral cornea, anterior to the corneal vascular arcade. An AlconTM 2.75 mm-angled slit knife was used for the corneal incision. A continuous curvilinear capsulorhexis was then created using a 1 1/2-inch 22-gauge needle. The nucleus was hydrodissected using BSS solution on a 27-gauge cannula. The cataract was then phacoemulsified within the capsular bag. The nucleus was noted to be dense, despite the young age of the animal. At the conclusion of the procedure, the wound was checked for water tightness, and found to be watertight. A subconjunctival injection of 25 mg of enrofloxacin and 1 mg dexamethasone was given. Ciprofloxacin ointment was then placed into the eye. Post operatively, the operated eye was sprayed four times a day with a combination of one percent prednisone and ciprofloxacin drops. Total surgical time was one hour and 16 minutes, time to recovery was 16 minutes, and total anesthetic time was two hours and three minutes.
The seal was placed in a pen without pool access for 24 hours following the procedure and then given access to a freshwater pool for four days after the surgery. The day after the surgery, marked edema and moderate blepharospasm of the left eye developed and continued for several days. On the fifth day after the surgery, the seal was placed in a saltwater pool and with the blepharospasm resolving after approximately three days. However, persisting corneal edema was noted. The seal showed no menace response.
Thirteen days after placement in the saltwater pool, the corneal opacification appeared to be diminishing, and the animal displayed a menace response. All medications were discontinued. The cornea continued to clear until only minimal corneal opacification remained at the incision sites, approximately 46 days after the cataract removal surgery. At this point, the elephant seal could avoid obstacles in its pen, displayed a menace response, watched other animals and people moving outside its pen, and could easily track and catch live fish. The elephant seal was released on September 6, 2001.
Clear corneal phacoemulsification cataract surgery successfully restored useful vision to our elephant seal, allowing the seal to be returned to the wild. The benefits of clear corneal cataract surgery in phocids include rapid wound healing, without the need for sutures, reduced inflammation and shorter surgical times. Utilization of modern cataract surgery techniques on marine mammals, coupled with improved anaesthetic support, should help to improve the success of cataract surgery in phocids in the future. It is likely that the seal also benefited from being placed in a saltwater pool post-operatively, and we recommend that saltwater pools with excellent water quality be made available for phocids following intra-ocular surgery.