Chapter 56 - Surgery of the Globe and orbit Flashcards
Figure 56-1. A normal skull, demonstrating the complete anterior bony
orbital rim of the horse. The pertinent bones that form the orbit of the
horse are labeled. LAC, Lacrimal bone; OF, orbital foramina including
ethmoid, optic, orbital fissure, and rostral alar; S, sphenoid bone; SF,
supraorbital foramen; T, temporal bone; Z, zygomatic bone; ZPF, zygomatic
process of the frontal bone; ZPT, zygomatic process of the temporal bone.
Note that part of the coronoid process of the mandible is missing.
What is the primary function of the orbits?
To protect the eye and its associated structures.
What are the average dimensions of the equine orbit?
62 mm in width, 59 mm in height, and 98 mm in depth.
Which bones compose the orbital rim in horses?
The frontal, lacrimal, and zygomatic bones.
At what angle are the axes of the eyes and orbits directed?
Laterally at 80 degrees off the midline.
How wide is the average equine eye globe?
48 mm in widt and 47 mm height
What forms the lateral border of the equine orbit?
The descending zygomatic process of the frontal bone, the ascending frontal process of the zygomatic bone, and the zygomatic process of the temporal bone.
What does the lacrimal sac contain?
The lacrimal fossa, which is an indentation in the lacrimal bone.
Where is the supraorbital foramen located?
Dorsolaterally within the zygomatic process of the frontal bone.
What structure disrupts normal tear flow when affected?
The lacrimal bone.
Which bones form the medial wall of the orbit?
The lacrimal, sphenoid, and palatine bones.
What is the risk during surgical manipulation of the orbital floor?
Potential for extensive hemorrhage and nerve damage.
What foramina are found at the orbital apex?
Ethmoidal foramen, optic foramen, orbital fissure, and rostral alar foramen.
Which nerve passes through the optic foramen?
the optic nerve (CN II).
Which muscle does the trochlear nerve (CN IV) innervate?
The dorsal oblique muscle.
What does the oculomotor nerve innervate?
Several extraocular muscles, including the levator palpebrae superioris and the iris sphincter.
What does the ophthalmic branch of the trigeminal nerve (CN V) provide?
Sensation to the cornea, conjunctiva, and dorsal eyelid.
What muscles are responsible for globe movement?
The extraocular muscles: dorsal, ventral, medial, and lateral rectus, as well as the oblique muscles.
What is the role of orbital fascia?
It supports the globe and maintains anatomic relationships.
How is the periorbita related to the orbital bones?
It is a periosteal layer that lines the orbital bones and is continuous with the dural sheath of the optic nerve.
What connects the periorbita with the eyelids?
The orbital septum.
Where is the lacrimal gland located?
Dorsolateral to the globe within the periorbita.
What is Tenon’s capsule?
The connective tissue layer between the bulbar conjunctiva and the sclera.
How many ducts release secretions from the lacrimal gland?
12 to 16 ducts.
What is the function of the nictitating membrane?
It elevates passively as the globe retracts.
What structure surrounds the base of the T-shaped cartilage in the third eyelid?
The gland of the nictitans.
What type of cancer frequently affects the third eyelid?
Squamous cell carcinoma.
Which sinus is located medial and ventral to the orbit?
The sphenopalatine sinus.
What is the conchofrontal sinus composed of?
Frontal and dorsal conchal portions.
Where are the maxillary sinuses located in relation to the orbit?
Ventral and axial to the orbit.
What is a risk associated with trephination near the orbit?
Damage to the nasolacrimal duct.
What is the role of orbital fat?
To cushion the globe and fill dead space.
What is the significance of the orbital fissure?
It allows passage of important nerves and vessels, including the abducens nerve.
What structure provides the majority of the orbital blood supply?
The external ophthalmic artery.
What muscle retracts the globe?
The retractor bulbi muscle (VI abducens n)
What anatomical feature facilitates precise globe movements?
the orbital fascia (thin tough connective tissue envelope (the orbital fascia)
How does the superior oblique muscle affect the globe?
It rotates the dorsal aspect of the globe ventrad and mediad.
Which structure is responsible for cushioning the globe within the orbit?
Orbital fat.
the orbital fascia is divided into
periorbita
extraoxular muscle fascia
episcleral fascia (Tenon’s capsul
Figure 56-17. (A) Enucleation by the transpalpebral method involves closure of the lids. (B) An incision around the eyelid margin is performed. (C) Blunt dissection posteriorly without breaking into the conjunctival sac follows. The arrows highlight the dashed lines denoting transection of the extraocular muscles near their insertions on the globe. (D) Transection of the optic nerve. (E) The subconjunctival enucleation technique involves incising the conjunctiva and continuing the subconjunctival dissection posteriorly (F).
Figure 56-19. In both methods of enucleation (see Figure 56-17), the extraocular muscles are transected and the optic nerve is subsequently clamped (A and B). A three-layer closure is performed (C).
Figure 56-20. This methyl methacrylate cosmetic shell (right) was custom made to fit anterior to an orbital silicone implant in a horse. The impression tray (left) was used to make the initial mold for the shell.
Figure 56-21. The surgical techniques for evisceration (A), enucleation (B), and exenteration (C).
Figure 56-23. Diagrammatic orbitotomy technique involving zygomatic arch transection to remove orbital masses. (A) The positions where the zygomatic arch and zygomatic process of the frontal bone are drilled before transection of the arch. (B) The extraocular muscle cone is exposed after removal of the zygomatic arch and temporal muscle. a, Zygomatic process of frontal bone; b, zygomatic arch; c, zygomatic process of temporal bone; d, scutular muscles; e, temporal muscle; f, retrobulbar muscle cone; g, lacrimal gland; h, supraorbital nerve. (Technique modified
What is the main challenge in diagnosing lesions in the orbit using radiography?
The superimposition of complex anatomic structures complicates accurate diagnoses.
What types of lesions warrant skull radiography?
Orbital and facial bone fractures, invasive neoplasia, gas-forming abscesses, exophthalmos, and metallic foreign bodies.
What is a Flieringa ring used for in ocular radiography?
To identify the globe within the orbit.
How does ultrasonography assist in ocular examination?
It evaluates exophthalmic globes, retrobulbar masses, cysts, and foreign bodies noninvasively.
What imaging mode is most commonly used in ultrasonography for clinical examination?
Brightness mode (B-scan).
What distinguishes neoplasms on ultrasound from other orbital structures?
hey usually appear more hyperechoic.
What frequency range of ultrasound probes provides the best resolution for orbital imaging?
6 to 10 MHz.
What type of appearance do abscesses typically have on ultrasound?
Variably hypoechoic areas.
What imaging technique provides superior soft tissue detail of orbital structures?
Magnetic resonance imaging (MRI).
How are MRI images generated?
By radio waves emitted from hydrogen protons returning to equilibrium in a magnetic field.
What are the disadvantages of MRI compared to CT?
Longer acquisition times, poorer spatial resolution, and limited ability to detect cortical bone defects.
What can significantly reduce eye movement during ocular surgery?
The use of an anesthetic gas analyzer.
What preoperative medication is recommended for horses undergoing ocular surgery?
Flunixin meglumine (1.1 mg/kg IV).
What are potential complications of retrobulbar blocks?
Orbital abscess formation, optic nerve damage, retrobulbar hemorrhage, and elicitation of the oculocardiac reflex.
What is the general approach for performing a retrobulbar nerve block?
Insert a spinal needle into the supraorbital fossa, aiming for the retrobulbar muscle cone.
What is the purpose of using an evisceration spoon during ocular surgery?
To separate the uvea from the sclera during evisceration.
What should occur when the needle passes through the muscle cone during a retrobulbar block?
A slight dorsal movement of the eye or a “popping” sensation.
What is the surgical goal of evisceration?
To remove the uveal tract, lens, vitreous, and retina while leaving the fibrous tunic intact.
What type of eyes is evisceration inappropriate for?
Eyes with septic endophthalmitis, intraocular neoplasia, or marked phthisis bulbi.
What suture pattern is typically used to close the scleral incision?
A simple-interrupted pattern with 6-0 absorbable suture.
What type of incision is made to access the sclera during evisceration?
A full-thickness incision about 4 to 5 mm from the limbus.
What postoperative care is essential after ocular surgery?
Topical and systemic antibiotics and nonsteroidal antiinflammatories.
What is the purpose of a temporary tarsorrhaphy?
o protect the cornea from exposure during healing.
What is the typical healing time following ocular surgery?
6 to 8 weeks.
What role does the methylcellulose coupling agent play in ultrasonography?
It facilitates contact between the ultrasound probe and the eyelids for better imaging.
How is the scleral incision extended during evisceration?
With scissors to create a 180-degree opening.
Why is careful handling of the corneal endothelium critical during evisceration?
To prevent damage and potential complications during the procedure.
What are some common postoperative complications following orbital surgery?
Complications include corneal ulceration, endophthalmitis, and surgical site dehiscence.
What is the consequence of corneal perforation or incisional dehiscence?
It can lead to the extrusion of the implant, necessitating enucleation.
What are the indications for performing an enucleation?
Indications include blind painful globes, severe infections, intraocular neoplasia, and traumatized globes.
What are the two surgical approaches for enucleation?
The two approaches are transpalpebral and subconjunctival.
What is the purpose of placing an orbital prosthesis during enucleation?
To improve the cosmetic appearance of the eye.
What is a major advantage of the subconjunctival enucleation technique?
It is quicker and associated with less hemorrhage compared to the transpalpebral approach.
What complication can occur if the orbital implant is too small?
It will result in a cosmetically unacceptable eye.
What should be done if a visual eye must be removed?
An opaque mask or full cup blinker should be placed preoperatively.
What postoperative care is recommended for all enucleated globes?
Submit the globes for histologic evaluation.
What technique can be employed to prevent mucocele formation post-surgery?
Complete excision of remaining conjunctiva.
What may be required if orbital tissues are to be removed during an exenteration?
Adjunctive treatments such as cryotherapy or radiotherapy may be warranted.
What is a common cause of orbital fractures in horses?
v
What materials can be used to stabilize bone fragments during orbital fracture repair?
Monofilament stainless steel wire, cerclage wire, and orthopedic bone plates.
How can an incomplete excision of neoplastic tissue post-surgery affect the outcome?
It can lead to recurrence of the disease or complications like excessive swelling.
What should be done if severe intraoperative hemorrhage occurs during surgery?
Wet-field cautery or manual tamponade should be applied to restore hemostasis.
What does an exenteration involve?
The complete removal of all orbital tissues.
What is the potential complication of placing an intraorbital prosthesis?
An 8.6% complication rate for intraorbital infection and implant extrusion has been reported.
What should be done immediately postoperatively to assist with hemostasis?
A pressure bandage should be placed.
What surgical approach helps maintain eyelid margins during enucleation?
The subconjunctival approach preserves eyelid margins.
How can orbital fractures impact the globe’s integrity?
They can cause displacement, impingement, or laceration of the globe.
What are the signs of orbital fractures in horses?
igns include facial asymmetry, epistaxis, and exophthalmos.
What method can be used to assist with hemostasis in case of severe contamination during surgery?
Placement of a drain may be necessary.
what does an evisceration involve?
An evisceration involves the surgical removal of the uveal tract, lens, vitreous, and retina from the fibrous tunic (cornea and sclera), which remains intact
Evisceration is indicated to which type of condition?
Evisceration is a cosmetic surgical procedure for blind and painful eyes
Not appropriate for septic endophthalmitis, intraocular neoplasia and marked phthisis bulbi
describe evisceration procedure
lateral canthotomy should be performed to improve exposure of the surgical field. Using tenotomy scissors, the conjunctiva should be incised parallel to and 6 to 8 mm posterior to the limbus to create a 180-degree peritomy (Figure 56-14).92 The sclera should be exposed by bluntly undermining the conjunctiva, taking care not to undermine the insertions of the extraocular muscles (Figure 56-15). A No. 15 scalpel blade or No. 64 microsurgical blade can be used to make a 1.5-cm full-thickness incision in the sclera 4 to 5 mm from the limbus. Suction and cautery should be used to control extensive hemorrhage and visualize the incision. An evisceration spoon is then inserted into the suprachoroidal space to separate the uvea from the sclera. The scleral incision should then be extended to 180 degrees with scissors. The uveal tract should be grasped crosswise with a pair of blunt-tipped forceps and gentle traction applied with a rocking motion to deliver the uvea, retina, and vitreous. The lens can be removed with the evisceration spoon or a lens loop. Care should be taken to avoid scraping the corneal endothelium. The intraocular contents should be submitted for histopathologic examination if neoplasia is suspected. A suitably sized silicone implant (usually 34–44 mm in diameter) should be inserted into the sclera. A sphere introducer will facilitate implantation. The scleral incision should be apposed without undue tension. Implant insertion simple-interrupted pattern of 6-0 absorbable suture is placed in the sclera and a simple-continuous pattern of 6-0 absorbable suture in the conjunctiva. The lateral canthotomy is closed routinely.
what does invole enucleation?
Enucleation involves the surgical removal of the palpebral margins, nictitans, conjunctiva, and globe
transpalpebral enucleation is ideal for which situations?
it prevents contamination of the orbit if neoplasia or severe ocular infection is present
what is the % of implant complication rate?
8.6%
describe the transpalpebral enucleation
The eyelids should be sutured together with 2-0 to 3-0 nonabsorbable sutures in a continuous pattern (Figure 56-17, A to D). An elliptical, full-thickness skin incision should be created around and 5 mm posterior to the eyelid margins using a No. 15 scalpel blade. Using Metzenbaum scissors, blunt and sharp subcutaneous dissection is performed posteriorly, taking care to avoid incising the conjunctival sac. The firm medial and lateral canthal ligaments are transected with heavy-gauge scissors. Care should be taken to avoid the angularis oculi vein at the medial canthus. Blunt dissection is continued along the sclera with transection of the extraocular muscles at their tendinous insertions, thus minimizing hemorrhage. The retractor bulbi muscle is blindly transected using curved, serrated Mayo scissors. Clamping of the optic nerve with either a Rochester-Carmalt forceps or Satinsky vascular clamp is optional. Curved, serrated Mayo scissors are used to transect the optic nerve while avoiding incising the globe. Also, one should avoid excess tension on the optic nerve, which could traumatize the optic chiasm and result in vision loss in the
contralateral eye.
At this point, a silicone implant (equine conforming intraorbital implant) (Figure 56-18), polymethylmethacrylate sphere (34–40 mm in diameter), or suture meshwork can be placed within the orbit to improve postoperative cosmesis.91,92,97
describe subconjunctival enucleation
The bulbar conjunctiva is incised 5 mm posterior to the limbus using blunt-tipped Stevens tenotomy scissors and a 360-degree peritomy is performed (see Figure 56-17, E and F). All four quadrants should be undermined posteriorly between the Tenon’s capsule and the sclera with tenotomy scissors and Bishop-Harmon forceps. The extraocular muscles are isolated and transected at their tendinous insertions on the globe. The retractor bulbi muscle and optic nerve are transected as described earlier (Figure 56-19). The orbit can be temporarily packed with sterile gauze to provide hemostasis. The third eyelid, gland, and associated conjunctiva are completely excised with scissors, along with 3 to 5 mm of the lid margin and associated meibomian glands. The remaining conjunctiva should be excised to prevent mucocele formation. Placement of pressure bandage can also assist with hemostasis and diminish trauma to the surgical site during recovery
advantages of subconjunctival enucleation
The subconjunctival approach is quicker, is associated with less hemorrhage, and removes less orbital tissue.
what are te sclerar shell prosthesis options
scleral shell or conformer of hydroxyapatite (HA), porcelain, or methyl methacrylate
what are the contraindications of placement of corneoscleral prosthesis?
Contraindications to placement of a corneoscleral prosthesis include poorly developed conjunctival fornices, intraorbital infection, intraorbital neoplasia, and a horse that is difficult to treat.
what does involve exeneration?
Exenteration involves removing all orbital tissues (Figure 56-21).
what are the indications of exenteration?
intraocular neoplasia
can you lace orbital implant followin exenteration?
no, it is contraindicated
orbitotomy is used when?
Lesions necessitating orbital exploration include parasitic cysts or granulomas, encapsulated orbital abscesses, foreign bodies, circumscribed neoplasia, repair of some orbital fractures, and cystic dilation of the nasolacrimal or salivary system.
describe obitotomy
A dorsal orbitotomy is used for lesions in the dorsal orbit and supraorbital fossa. A curvilinear skin incision is made over the dorsal orbital region just lateral to the external sagittal crest of the parietal and frontal bones, curving laterally caudal to the zygomatic process of the frontal bone. Lateral retraction of the frontoscutularis, interscutularis, and temporal muscles exposes the extraocular muscle cone deep within the orbit.
In an alternative dorsal approach, an S-shaped skin incision can be made parallel to the zygomatic process of the frontal bone. The surgeon must avoid transecting the neurovascular bundle within the supraorbital foramen and nerve fibers entering the orbicularis oculi laterally. The periosteum is incised anteriorly, reflected off the bone, and preserved for later closure. The zygomatic process of the frontal bone is resected in section after predrilling 20-gauge holes within the bone for reattachment (Figure 56-23). Performing a lateral canthotomy may increase exposure. At closure, the zygomatic process is replaced and fixed with 20-gauge stainless steel surgical wire. The periosteum is closed in a simple-interrupted pattern with 4-0 or 5-0 absorbable suture material. The subcutaneous tissue and skin are subsequently closed. A lateral approach has also been described. A horizontal lateral canthal incision is extended caudally 5 mm through the skin, followed by dissection through the levator anguli oculi muscle. Two centimeters of the zygomatic process of the temporal bone and its ventrolateral aspect are resected after predrilling. Closure is performed as described earlier.
when should periorbital fractures repaires?
Periorbital fractures should be repaired quickly before callus forms at 10 to 14 days, which makes manipulation difficult
