by Noelle La Croix, DVM, Dip. ACVO
Enucleation refers to the surgical removal of the entire eye. This procedure is indicated for relatively few conditions that you and your client may face. One cannot underestimate the attachment of an owner to the eye of their pet. However, when necessary, enucleation can relieve suffering and prevent future maladies.
Common indications for enucleation include blinding painful glaucoma, severe trauma, and intraocular malignancy. The procedure, prosthetic options, and cosmetic effects should be well explained to the client. Pictures of other enucleated animals can help relieve client stress. Clients should understand that the entire eye will be removed. The option of replacing the enucleated globe with a silicone orbital conformer should be discussed. These conformers prevent the skin from sinking into the orbit, generating a more cosmetically pleasing result. With or without a conformer, the eyelids are permanently sutured shut. Complications of enucleation include infection and conformer rejection.
Blinding painful glaucoma can often be surgically corrected by the introduction of an intraocular prosthesis. This procedure preserves the globe and relieves pain. However, enucleation should be considered when the health of the cornea is at risk. In cases of corneal infection and/or loss of the corneal stroma, enucleation is preferable. Enucleation should also be considered when future corneal health may be jeopardized by low tear production or facial nerve paralysis.
Enucleation should be performed on proptosed eyes in which more than 3 extraocular muscles have been torn. Such trauma often involves destruction of the optic nerve and/or other cranial nerves resulting in blindness and future corneal deterioration.
Large primary intraocular tumors that cause blindness and/or glaucoma are best removed by enucleation. Enucleation is also indicated in severe cases of endophthalmitis and panophthalmitis. Enucleated globes should be submitted for histopathology to reveal any underlying disease.
The two most common enucleation procedures are subconjunctival and transpalpebral. In subconjunctival enucleation the globe is removed first, followed by the eyelid margins, 3rd eyelid, and conjunctiva. In transpalpebral enucleation, the eyelid margins are sutured together first, and then the eyelid margins, conjunctiva, 3rd eyelid, and globe are removed enbloc. The transpalpebral procedure has the advantage of ensuring complete removal of the conjunctiva. Remaining secretory conjunctiva may form orbital cysts that will need to be removed later. The transpalpebral approach also reduces the risk of orbital contamination in cases of corneal and/or conjunctival infection.
In either enucleation procedure, extraocular muscles should be approached beneath Tenon’s capsule. Intraperiorbital adipose tissue is diffusely located about the muscles of the globe and optic nerve. Adipose tissue is very difficult to promote hemostasis within, so it is best left surgically untouched. To minimize bleeding, each extraocular and retractor bulbi muscle should be excised at its tendon attachment to the globe. When cutting these, minimal tension should be placed on the optic nerve and globe. Excessive tension can cause reflexive bradycardia. In cats, excessive tension on the optic nerve can also damage the optic chiasm causing blindness in the contralateral eye.
The primary source of bleeding during enucleation is from long posterior ciliary arteries which extend along the optic nerve. A tonsil snare cautery can be used to cut the nerve and the associated arteries to minimize bleeding. Alternatively, the optic nerve and associated arteries can be clamped for 5 minutes, with a curved hemostatic forceps, and then cut. The optic nerve and associated arteries can also be tied with a sliding knot prior to excision to reduce bleeding.
After cutting the optic nerve, bleeding and retraction may conceal the posterior ciliary arteries within the intraperiorbital adipose tissue. Packing the orbit for 5 minutes may reduce this. Dilute 1:100,000 epinephrine and Gel foam can also be used. The orbit should not be closed until bleeding is controlled. A majority of post-operative swelling and pain is caused by arterial bleeding in a prematurely closed orbit. However, bleeding will eventually stop as the orbit fills and presses against the closed eyelids. The orbit should be sutured closed in four independent layers: the orbital cone, the periorbital fascia, the subcutaneous tissue, and then the outer skin.
A post-operative Elizabethan collar will prevent the patient from traumatizing the enucleation site. Oral antibiotics and pain medications are also recommended. Skin sutures should be removed 10-14 days post-operatively. The removal of a painful eye can bring about positive changes in an animal’s behavior that your clients will surely appreciate (Figure 1).
Noelle La Croix, DVM, Dip. ACVO
Veterinary Medical Center of Long Island
75 Sunrise Highway
West Islip, New York 11795
(631) 587-0800; fax (631) 587-2006
Figure 1: “Coco” seemed ready to play ball the day after her enucleation, but this activity was not recommended so soon after surgery.