enucleation of exotic pets

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Topics in Medicine and SurgeryTopics in Medicine and Surgery
Enucleation of Exotic Pets
Bradford J. Holmberg, DVM, PhD, Dip. ACVO
the orbit
88
Abstract
Enucleation is often the final option when considering ocular treatment for an
exotic pet patient. There are many considerations when performing the surgical
procedure to remove the eye. It is incumbent on the surgeon to be familiar with the
anatomy of the individual species’ globe and orbit to reduce hemorrhage, optic
nerve trauma, and postsurgical complications. This review of enucleation proce-
dures will focus on ocular anatomical differences and techniques that should be
used to maximize surgical success. Copyright 2007 Elsevier Inc. All rights reserved.
Key words: exotic pets; small mammal; enucleation; ocular; avian
Enucleation involves the surgical removal of
the globe along with a short segment of the
optic nerve. The eyelids, third eyelid, conjunc-
tiva, and lacrimal gland(s) are also excised, except in
the rare instance in which an ocular prosthesis (such
as a corneoscleral shell) is fitted. Although cosmesis
is enhanced with a prosthesis, the availability, cost,
and necessity for frequent cleaning prohibit custom-
ary usage. In small mammals, normal grooming be-
havior would likely dislodge the prosthesis and allow
contamination of the orbit, especially because of
their usual habitat consisting of straw or shavings.
Therefore, removal of the globe and adnexa fol-
lowed by closure of the surgical wound are recom-
mended to prevent secondary complications.
Enucleation is usually reserved for cases in which
previous attempts to control an ocular pathologic
process with medical and/or surgical therapy have
failed. It is the treatment of choice for a permanently
blind, painful eye regardless of the cause. Indica-
tions for enucleation include intraocular neoplasia,
diffuse surface ocular neoplasia, perforating corneal
and scleral injuries resulting in loss of ocular con-
tents, intractable intraocular inflammation (e.g.,
uveitis, endophthalmitis, panophthalmitis), unman-
ageable glaucoma, and chronic ocular pain. An ad-
ditional indication is palliation for chronic exposure
secondary to severe exophthalmos. The small size of
and difficulty accessing the retrobulbar
Journal of
space make orbital surgery for these cases challeng-
ing. Removal of the eye not only provides comfort,
but also an avenue to address the orbital disease.
Before surgery, knowledge of the relevant ocular
and orbital anatomy is imperative. Ocular anatomy is
similar among species, with all having an outer fibrous
tunic (cornea and sclera), middle vascular tunic
(uvea), inner nervous tunic (retina), and internal op-
tical media (aqueous humor, lens, vitreous). The sclera
of birds and reptiles contains cartilage posterior to the
equator and ossicles in the ciliary region. These in-
crease structural rigidity and, in the bird, contribute to
the tubular shape of the eye. The avian eye fits snuggly
within the shallow orbit, making periocular dissection
difficult. This combination of scleral ossicles, tubular
shape, and shallow orbit in birds necessitates modifica-
tion of routine enucleation techniques. Another
unique feature found in many small mammals (e.g.,
rabbits, ferrets, chinchilla, rats, mice) is the presence of
a large vascular sinus or plexus within the orbit. In the
From the Veterinary Medical Teaching Hospital, University of
California, Davis, CA 95616 USA.
Address correspondence to: Bradford J. Holmberg, Veterinary
Referral Centre, 48 Notch Road, Little Falls, NJ 07424. E-mail:
dvm4eyes@yahoo.com
© 2007 Elsevier Inc. All rights reserved.
1557-5063/07/1602-$30.00
doi:10.1053/j.jepm.2007.03.011
Exotic Pet Medicine, Vol 16, No 2 (April), 2007: pp 88-94
Enucleation of Exotic Pets 89
rabbit, the venous sinus extends from the globe equa-
tor to the orbital apex and drains posteriorly to the
pterygoid and cavernous sinuses. Laceration of the
sinus during surgery results in significant hemorrhage
and may lead to exsanguination if adequate hemostasis
is not achieved.
Surgical Preparation and Instruments
The planned surgical field should be prepared in a
fashion such that the normal bacterial flora are de-
creased without damaging the skin to reduce the risk
of postoperative infection. The hair or feathers should
be clipped or plucked at least 1 cm around the eyelid
margins. Because of the thin, fragile nature of the skin
of many small mammals, clipping must be done with
extreme care to prevent tears or lacerations. The eyelid
margins and conjunctival fornices are cleansed with
dilute betadine (1:50) solution (Betadine solution; The
Purdue Frederick Co., Stamford, CT USA). Dilute be-
tadine is safe for the ocular surface unlike chlorhexi-
dine (Nolvasan Solution; Fort Dodge/Wyeth, Madison,
NJ USA), which can cause severe corneal cell toxicity.1
Surgical preparation is facilitated by sterile, cotton-
tipped applicators and flushing with a 21-gauge can-
nula. After aseptic preparation of the site, the surgical
field is then draped. Clear plastic, adhesive drapes
(VSP Surgical Drapes; Veterinary Specialty Products,
Inc., Mission, KS USA) are preferred over cloth or
disposable 4-quarter drapes. These transparent drapes
are conforming, inexpensive, and disposable. More
importantly, with the small size of many exotic pets,
they allow the anesthetist to continue monitoring the
patient.2
The small eye of most exotic pets necessitates the
use of magnification and delicate surgical instru-
ments. Several methods of magnification are avail-
able. Loupes are most commonly used, and a mag-
nification of 3.5� is adequate for most ophthalmic
procedures. An operating microscope provides supe-
rior magnification, but with some reduction in depth
and size of the surgical field. It is only necessary for
surgery on eyes with a horizontal corneal diameter of
less than 5 mm. A typical microsurgical pack for
enucleation should include at least the following
instruments: Bishop-Harmon toothed tissue forceps,
Barraquer pediatric eyelid speculum, conjunctival
fixation forceps, Westcott tenotomy scissors, Stevens
tenotomy scissors, mosquito hemostatic forceps, #15
and #11 Bard-Parker scalpel blades and handle, mi-
crosurgical needle driver (Troutman or similar),
Derf needle driver (for rabbits and larger birds),
bulldog clamp or serrefine, and a silicon bulb sy-
ringe and cannula.
Because of the extensive vascular network within the
retrobulbar space of many small mammals and their
small total blood volume, hemostasis is critical during
surgery. Three useful sponges include cotton-tipped
applicators, Weck-cel sponges (Medtronic Solan, Jack-
sonville, FL USA), and dental sponges. These sponges
absorb up to 0.1, 0.3, and 3.0 mL of blood, respectively,
and should be counted and used for estimation of
blood loss. Other mechanisms to achieve hemostasis
include the use of handheld thermal cautery, bipolar
radiosurgery (Ellman, Inc., Oceanside, NY USA), and
carbon dioxide laser energy. However, these modalities
are not sufficient for hemostasis of the large-diameter
retrobulbar sinus of small mammals. If the sinus is
ruptured, it cannot be ligated. The orbit should be
packed with dental sponges, and direct pressure
should be applied for at least 5 minutes. Many times
this is not adequate, and hemorrhage continues. Pack-
ing the orbit with an absorbable gelatin sponge (Gel-
foam; Pharmacia & UpJohn Co., Kalamazoo, MI USA)
or oxidized regenerated cellulose (Surgicel; Biosense
Webster, Inc., Diamond Bar, CA USA) may aid in
hemostasis. Some surgeons will wrap a piece of throm-
bin-soaked Gelfoam with Surgicel (a “hemostatic
taco”) to promote hemostasis.2 These agents can be left
in the orbit and not only promote clot formation but
also provide a matrix to which the clot can adhere.
Rapid and tight closure of the subcutaneous tissue and
orbital fascia will also aid in hemostasis.
Appropriate suture for closure of an enucleation
site in exotic pets should be minimally reactive, dis-
couragebacterial binding, and have good tensile
strength.3 Monofilament suture, such as poligleca-
prone 25 (Monocryl; Novartis Animal Health, Inc.,
Basel, Switzerland), is well tolerated, has good han-
dling characteristics, and maintains 65% of its tensile
strength for 1 week. Braided or multifilament suture
is contraindicated for subcutaneous closure of the
enucleation site because it may prolong and pro-
mote inflammation while also serving as a potential
nidus for bacterial growth.
Surgical Technique
The 3 surgical techniques described for enucleation
are the transconjunctival, transpalpebral, and lateral
approach.4 The transpalpebral and lateral ap-
proaches are associated with a reduced chance of
leaving neoplastic or infectious material from the
globe or adnexa within the orbit. However, because
of the inherent risks of hemorrhage in exotic pets,
the transconjunctival enucleation is usually pre-
ferred. The unique anatomy of the bird eye requires
ous ti
90 Holmberg
modifications of this technique and will be described
separately.
An eyelid speculum is placed in all animals with
palpebral fissures large enough to accommodate
one. In animals whose palpebral fissure is less than
10 mm (measured from the medial to lateral can-
thus), a horizontal mattress suture with 6-0 silk can
be placed in the upper and lower eyelids. The free
ends of the suture are clamped with a Dieffenbach
serrefine or bulldog clamp and can be used to re-
tract the eyelids. A lateral canthotomy is then per-
formed to increase visualization of the globe (Fig
1-1). A mosquito hemostatic forcep is clamped along
the lateral canthus before performing the incision.
The forcep is removed, and a #15 scalpel blade is
used to incise within the crushed area. The globe is
grasped with conjunctival fixation forceps next to
the limbus, and a 360° peritomy (circumferential
incision through the conjunctival attachment to the
limbus) is performed approximately 2 mm caudal to
the limbus with either Westcott or Stevens tenotomy
scissors (Fig 1-2). The 2-mm rim of bulbar conjunc-
tiva is intentionally left to provide an area to grasp
the globe and manipulate it during further dissec-
tion. Blunt dissection with tenotomy scissors is then
performed through Tenon’s fascia to the level of
sclera and caudal to the insertion of the extraocular
muscles. To incise the extraocular muscles, the teno-
Figure 1. Transconjunctival enucleation technique in a rabbit. (1) A
A peritomy is performed with tenotomy scissors. (3) The extraocula
After transection of all extraocular muscle attachments, the optic n
The eyelids are removed by cutting from the lateral canthus toward
Note that the third eyelid is still in place. Closure of the subcutane
tomy scissors should be opened, the lower jaw slid
under the muscle, and gentle anterior pressure ap-
plied (Figs 1-3). This ensures the incision is made
through the muscle insertion, not the muscle belly,
thereby decreasing intraoperative hemorrhage. The
globe can be rotated to facilitate transection of all
rectii and oblique muscles. The retractor bulbi mus-
cles are then transected in a similar fashion, at their
attachment close to the sclera. Once all muscle at-
tachments are released, the globe should rotate
freely in the orbit. The globe is then rotated medially
to facilitate access to the optic nerve from the lateral
side. Clamping blood vessels coursing with the optic
nerve (ciliary arteries, branches of the external oph-
thalmic artery) must be done carefully, because an-
terior traction of the nerve can lead to pressure at
the optic chiasm and permanent damage to the
contralateral nerve. A mosquito hemostatic forcep
can be used in larger exotic species such as rabbits
(Fig 1-4). In most other species, a dedicated pair of
lockable microsurgical needle drivers can be used.
The optic nerve is incised with tenotomy scissors
proximal to the clamp, and the globe is removed.
Care must be taken not to cut the posterior sclera,
especially in animals with septic endophthalmitis or
an intraocular tumor, because this can permit con-
tamination of the orbit. If the posterior sclera is
ruptured, the orbit should be copiously lavaged with
lid speculum is placed, and a lateral canthotomy is performed. (2)
cle attachments are transected at their insertions to the sclera. (4)
nd associated vessels are clamped, and the globe is removed. (5)
edial canthus. (6) The eyelids and conjunctiva have been removed.
ssue/orbital fascia is begun before removal of the third eyelid.
n eye
r mus
erve a
the m
dilute (1:50) betadine solution. Because of the
Enucleation of Exotic Pets 91
threat of significant hemorrhage, the clamp is left in
place during the removal of the adnexa.
After removal of the globe, the eyelids, conjunc-
tiva, and third eyelid are removed. Failure to com-
pletely remove these structures and their associated
glands can result in cyst formation postoperatively. A
mosquito hemostatic forcep is placed 2 mm caudal
to the upper and lower eyelid margins and clamped
for 15 seconds to aid in hemostasis. The eyelids are
then incised with Metezenbaum or Mayo scissors
from the lateral aspect toward the medial canthus
(Fig 1-5). The incisions are joined at the medial
canthus with a #15 scalpel blade, being careful not to
incise the medial angular vein that courses superfi-
cial and medial to the orbital rim. Most of the pal-
pebral conjunctiva will also be excised during this
part of the procedure. However, careful inspection
of the remaining orbital tissue should be performed,
and any remaining conjunctiva should be excised
(Fig 1-6).
In this author’s experience, significant hemor-
rhage can commonly be encountered during re-
moval of the third eyelid. Therefore, before remov-
ing the third eyelid and its associated glands (gland
of the third eyelid and Harderian gland), closure of
the surgical wound is begun. This permits more
rapid closure of the surgical wound and aids hemo-
stasis. Remaining Tenon’s fascia, orbital septum, and
extraocular muscles are apposed in a simple contin-
uous pattern with 5-0 to 6-0 absorbable monofila-
ment sutures. The medial aspect is left open to allow
access to the third eyelid. The third eyelid is then
grasped, anteriorly displaced, and removed by care-
ful dissection with tenotomy scissors, sometimes aug-
mented with thermal cautery. Use of a carbon diox-
ide laser has not achieved the desired vessel coagu-
lation and has resulted in significant hemorrhage.
After removal of the third eyelid, any hemorrhage is
controlled by means of direct pressure with dental
sponges or cotton-tipped applicators. However, if
the orbital sinus has been lacerated, direct pressure
will not be sufficient to achieve hemostasis, and pack-
ing the orbit with the hemostatic aids mentioned
above will be necessary to decrease hemorrhage and
provide a matrix to allow clot formation. Suturing is
then completed. Because skin sutures are not always
well tolerated in exotic pets, the skin should be
apposed with an intradermal/subcuticular pattern,
making sure the knots are buried (Fig 2).
Two techniques have been described for the enu-
cleation of birds.5 Raptors with an extensive external
ear opening, such as owls, can be enucleated with a
transaural approach.5 With this technique, the globe
can be removed intact, which aids histological anal-
ysis. In birds without this anatomic configuration,
the transaural technique is not appropriate, and a
globe-collapsing technique is recommended to facil-
itate globe removal (Fig 3) . Unfortunately, this tech-
nique somewhat compromises histological examina-
tion.
The globe-collapsing technique for enucleation
of birds is similar to the subconjunctival enucleation
of small mammals. After aseptic preparation of the
surgery site, a wire eyelid speculum (or stay sutures,
depending on the size of the globe) is placed under
the eyelids and third eyelid to increase exposure. A
lateral canthotomy and peritomy are performed as
described above (Figs 3-1 and 2). Blunt dissection isthen performed to the level of the sclera, caudal to
the limbus 360° around the globe. Insertions of the
extraocular muscles are transected as they are en-
countered. Because of the tubular shape of the
globe, the presence of scleral ossicles, and the fact
that anterior traction on the globe should be
avoided, further caudal dissection is often not possi-
ble. Therefore, a full-thickness limbal incision is
made throughout the dorsal 180° of the globe (Fig
3-3). Manipulation of the globe is facilitated by
placement of a stay suture through the cornea at the
12 o’clock position. Aqueous humor will egress
through this limbal incision. Globe collapse is fur-
ther enhanced by making an incision through the
sclera, perpendicular to the limbus and parallel to
the scleral ossicles (Fig 3-4). The ossicles are then
Figure 2. Postoperative appearance after enucleation of the left eye
of a rabbit. Notice the lack of skin sutures.
incised with Metezenbaum scissors. To prevent sig-
nd th
92 Holmberg
nificant hemorrhage, only the sclera and ossicles are
incised; the uvea should be left intact. This incision
allows the surgeon to overlap the ossicles and in-
crease visualization of the posterior globe (Fig 3-5).
Dissection medial to the globe can damage the frag-
ile interorbital bony septum. The optic nerve and
associated vessels are then clamped, and the globe is
removed. Access to the retrobulbar space is en-
hanced with the globe-collapsing procedure, and
clamping or possible ligation of the optic nerve and
vessels is feasible. The anesthetist should be alerted
before clamping the optic nerve and vessels because
profound bradycardia may occur because of the ocu-
Figure 3. Globe-collapsing procedure for enucleation. (1) An eyelid
exposure. A peritomy is performed to the level of sclera. (2) A full-th
to facilitate manipulation of the globe. (3) Further caudal dissection
The sclera and its associated ossicles are transected, sparing the un
sclera ossicles, increasing visualization of the posterior aspect of th
After globe removal, the conjunctiva and third eyelid are removed a
locardiac reflex. After removal of the globe, the
conjunctiva, third eyelid, and eyelids are removed in
a similar fashion as is used in small mammals. Clo-
sure of the wound is usually performed in 2 layers, a
deep subcutaneous layer and a skin layer (Fig 3-6, Fig
4). Unlike small mammals, birds infrequently dis-
turb their skin sutures.2
Complications
Complications infrequently occur after enucleation.
The most common intraoperative and immediate
postoperative complication is hemorrhage, espe-
ulum is placed and a lateral canthotomy is performed to increase
s, 180° limbal incision is made dorsally and a stay suture is placed
rformed, and insertions of extraocular muscles are transected. (4)
ing uvea. (5) Forceps are used to collapse the globe and overlap the
be to permit further dissection and clamping of the optic nerve. (6)
e skin is closed. Reprinted with permission.5
spec
icknes
is pe
derly
e glo
cially in species with a large venous sinus or plexus.
Enucleation of Exotic Pets 93
Meticulous surgical technique and attention to he-
mostasis usually prevent this from being a life-threat-
ening complication. Additional complications in-
clude orbital infection, suture line abscesses, wound
dehiscence, and orbital cyst formation. Infection of
the orbit may be secondary to intraoperative rupture
of a septic globe, failure to follow aseptic technique,
or due to systemic septicemia. Prophylactic periop-
erative and postoperative therapy with a broad-spec-
trum antibiotic may decrease the prevalence of or-
bital infection after enucleation. Dehiscence of the
wound is usually secondary to a local inflammatory
reaction associated with infection or excessive
grooming by the animal. Closure in 3 layers may
prevent the likelihood of dehiscence. Likewise, su-
ture line abscesses usually occur with the use of
braided suture or contamination of the suture line
by environmental factors. Cyst formation within the
orbit has been noted secondary to continued secre-
tions from the conjunctival epithelium and/or lacri-
mal glands (orbital lacrimal gland, gland of the third
eyelid, Harderian gland). Cyst formation is mini-
mized by careful inspection of the surgery site before
closure to ensure all conjunctival epithelium and
glandular tissue have been removed.
Rare complications include orbital emphysema
and contralateral blindness. If the nasolacrimal duct
remains patent after surgery, air may be forced
through the duct and into the orbit because of in-
creased intranasal air pressure resulting in accumu-
lation of air within the orbit.6 Treatment involves
opening the surgical incision, locating the opening
to the nasolacrimal duct, and closing it with either
suture or thermal cautery. Although extremely rare,
enucleation may result in blindness of the contralat-
Figure 4. Postoperative appearance after enucleation of the right
eye of a bird. Notice the presence of skin sutures.
eral eye. Excessive manipulation of the globe during
surgery may result in tractional forces on the optic
chiasm, damaging chiasmal axons. This is most com-
mon in animals with a small orbit and a short dis-
tance between the posterior globe and chiasm. In
these animals, a hemostat should not be placed pos-
terior to the globe before removing the eye because
this can cause enough anterior traction to injure the
chiasm. Either no clamp or a smaller clamp such as
a lockable microsurgical needle driver should be
used.
Postoperative Care
The goal of postoperative care is to ensure patient
comfort and prevent potential complications. Post-
operatively, animals should be placed in a warm,
quiet, dim, nonstressful environment with easy ac-
cess to both food and water.7 Sufficient ventilation
and proper sanitation are necessary, with particular
attention to environmental temperature and humid-
ity (specifics depend on species). The animal’s hab-
itat may also need to be changed to prevent second-
ary contamination of the surgical wound. For in-
stance, rodents may be housed on artificial turf after
enucleation instead of shavings.
Determination of the degree of surgical pain in
exotic pets is difficult. Some indications of pain in-
clude anorexia, decreased grooming/preening activ-
ity, and alterations in normal behaviors (explora-
tion, social interactions, and so forth).8,9 Analgesia
for both small mammals and birds should start be-
fore surgery, so-called preemptive analgesia. Treat-
ing before a noxious stimulus prevents hypersensiti-
zation of pain receptors and may reduce the amount
of inhalant anesthesia necessary to maintain a surgi-
cal plane.8 Multimodal analgesia involving the use of
several classes of medications is more effective at
controlling postoperative pain. Butorphanol (1-3
mg/kg intramuscularly, Torbugesic-SA; Fort Dodge
Animal Health, Fort Dodge, IA USA) is a good an-
algesic for birds, because they have a greater popu-
lation of � versus � opioid receptors.9 Long-term
analgesia can be accomplished with oral nonsteroi-
dal antiinflammatory drugs such as meloxicam (0.1
mg/kg by mouth every 24 hours, Metacam; Boehr-
inger Inglelheim Vetmedica, Inc., St. Joseph, MO
USA) or carprofen (2-4 mg/kg by mouth twice per
day, Rimadyl; Pfizer Animal Health, New York, NY
USA).9 The response of small mammals to both
opiates and nonsteroidal antiinflammatory drugs
varies among species, with some animals such as
ferrets more sensitive to their effects. Doses for these
drugs are available in the literature8,9 and should be
researched before surgery.
94 Holmberg
Conclusion
Enucleation is the most commonly performed oph-
thalmic procedure in veterinary medicine. In exotic
pets, a transconjunctival approach is recommended
to enhance visualization and prevent secondary com-
plications. This technique is modified in birds to
account for the presence of scleral ossicles, tubular
shape of the eye, and tight fit of the globe in the
orbit. Complications are rare, especiallyif intraoper-
ative hemorrhage is limited.
References
1. Green K, Livingston V, Bowman K, et al: Chlorhexi-
dine effects on corneal epithelium and endothelium.
Arch Ophthalmol 98:1273, 1980
2. Bennett RA: Preparation and equipment useful for
surgery in small exotic pets. Vet Clin North Am (Ex-
otic Anim Pract) 3:563-585, 2000
3. Mullen HS: Nonreproductive surgery in small mam-
mals. Vet Clin North Am (Exotic Anim Pract) 3:629-
645, 2000
4. Ramsey DT, Fox DB: Surgery of the orbit. Vet Clin
North Am (Sm Anim Pract) 27:1215-1264, 1997
5. Murphy CJ, Brooks DE, Kern TJ, et al: Enucleation in
birds of prey. J Am Vet Med Assoc 183:1234-1237, 1983
6. Martin CL: A complication of ocular enucleation in
the dog: orbital emphysema. Vet Med Small Anim
Clin 66:986-989, 1971
7. Pollock C: Postoperative management of the exotic
animal patient. Vet Clin North Am (Exotic Anim
Pract) 5:183-212, 2002
8. Flecknell PA: Analgesia of small mammals. Vet Clin
North Am (Exotic Anim Pract) 4:47-56, 2001
9. Paul-Murphy J, Ludders JW: Avian analgesia. Vet Clin
North Am (Exotic Anim Pract) 4:35-46, 2001
	Enucleation of Exotic Pets
	Surgical Preparation and Instruments
	Surgical Technique
	Complications
	Postoperative Care
	Conclusion
	References