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The orbit and globe

image of The orbit and globe
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Abstract

Investigation of orbital disease is challenging and in many emergency situations rapid recognition of signs of orbital disease and instigation of appropriate management are critical to the final outcome for the patient. Familiarity with the anatomy and physiology of the region facilitates an understanding of the basic principles of orbital disease pathogenesis. This chapter considers anatomy and physiology; clinical signs; investigation of disease; canine and feline conditions; enucleation.

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Figures

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8.1 Dorsolateral view of the canine skull. The bones of the canine orbit. (b, Courtesy of Roser Tetas Pont)
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8.2 Soft tissue anatomy of the canine orbit. All structures within the periorbital fascia are termed intraconal, whilst those outside this plane are termed extraconal. The orbital septum is shown in cross-section: the septum extends from the bony orbit to the eyelids and encircles the globe. This structure is a critical barrier separating the more superficial adnexal structures such as the eyelids from the orbit. (Courtesy of Roser Tetas Pont)
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8.5 A 10-year-old Labrador Retriever presented with an acute history of bilateral blindness and right-sided exophthalmos. (a) The widened palpebral fissure and pronounced pupillary dilatation on the right side give the impression that the globe is enlarged. (b) When viewed from above, the anterior displacement of the right globe is readily appreciated. A 1-year-old English Springer Spaniel with glaucoma and hydrophthalmos of the right globe. (c) The widened palpebral fissure, pupillary dilatation and slightly increased scleral show could be mistaken for exophthalmos. (d) When viewed from above, the anterior displacement of the right globe is only marginal and is consistent with the degree of hydrophthalmos rather than exophthalmos.
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8.6 A false impression of right globe enlargement and/or exophthalmos can be created by differences in pupillary size, contralateral enophthalmos and asymmetry of the eyelid fissures. A 6-year-old male neutered Domestic Shorthaired cat with a fixed dilated right pupil due to an efferent pupil defect. A 9-year-old female neutered Domestic Shorthaired cat with Horner’s syndrome and enophthalmos affecting the left eye. An 8-year-old neutered Bulldog bitch with left-sided ptosis due to facial nerve paralysis.
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8.7 A 9-year-old entire Labrador Retriever bitch with an orbital tumour causing extreme dorsolateral strabismus of the right globe. The ventral limbus is just visible below the upper eyelid margin. MRI revealed a tumour in the ventromedial orbit.
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8.8 Pressure from an extraconal mass has led to indentation of the posterior aspect of the globe in a dog with orbital multilobular osteochondrosarcoma. Ophthalmoscopic appearance showing indentation of the fundus, deviation of the superficial retinal blood vessels and reduced tapetal reflectivity. B-mode ultrasonography confirms gross indentation of the posterior aspect of the globe. (Courtesy of the University of Wisconsin-Madison Comparative Ophthalmology Service)
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8.9 A 1-year-old Labrador Retriever with bilateral extraocular muscle myositis. The typical presentation is seen in this case, with signs of intraconal disease including bilateral exophthalmos without third eyelid protrusion, 360-degree scleral show and retraction of the upper eyelids.
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8.10 A 14-year-old crossbred dog with myxosarcoma affecting the left orbit. Signs of extraconal orbital disease include non-axial exophthalmos with the globe displaced dorsolaterally and third eyelid protrusion.
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8.11 Lateral oblique dental radiograph of a 10-year-old West Highland White Terrier with a history of recurrent orbital inflammation. There is an area of periapical lucency (arrowed) around the fourth premolar (carnassial) tooth consistent with a periapical tooth root abscess.
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8.12 A 3-month-old Great Dane with the merle coat colour. The ophthalmic abnormalities include microphthalmos, third eyelid protrusion (the third eyelid covered most of the globe and was retracted for ophthalmic examination), iris coloboma (note the localized absence of the iris from the 3–6 o’clock position), dyscoria, microphakia and cataract. Both eyes were similarly affected.
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8.13 A 6-month-old Domestic Shorthaired cat with a history of hydrophthalmos affecting the right eye since kittenhood. Globe enlargement can be dramatic in young animals, especially cats, in which the fibrous tunic of the eye is more elastic. Note the dark appearance of the sclera. This is due to advanced scleral thinning exposing the underlying darkly pigmented choroid.
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8.14 A 12-year-old neutered Jack Russell Terrier bitch with phthisis bulbi affecting the left eye. The eye is severely shrunken with a small grey cornea. The eyelids have been actively retracted to allow visualization of the globe. Although lower lateral entropion is present, the globe is usually completely covered by the third eyelid and the dog was asymptomatic.
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8.15 An 8-year-old Border Collie with an orbital abscess. Ophthalmic findings included a non-axial exophthalmos with a dorsolateral strabismus, swelling, protrusion, exposure, desiccation and ulceration of the third eyelid, lagophthalmos and corneal desiccation and ulceration. Surgical drainage of the abscess located in the ventral extraconal space. Haemostats are inserted through the surgical wound in the pterygopalatine fossa. Blunt dissection is carefully advanced towards the orbit until drainage of the abscess is achieved. The surgical wound is left open to permit continued drainage. (c, Courtesy of Roser Tetas Pont)
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8.16 B-mode ultrasonogram of a 9-month-old entire Labrador Retriever bitch with bilateral extraocular polymyositis. The enlarged hypoechoic lateral and medial rectus muscles are denoted by the callipers.
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8.17 A 1-year-old Bull Mastiff with progressive bilateral medial strabismus associated with fibrosing extraocular muscle myositis. Note that the medial strabismus is more severe on the right side.
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8.19 An 11-year-old Labrador Retriever presented with an acute history of blindness and exophthalmos affecting the right eye. The T2-weighted dorsal MR image revealed an extensive orbital tumour (*) with invasion through the calvarium into the brain (black arrows) and nasal cavity (white arrow).
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8.20 A 2-year-old male neutered Shih Tzu with lateral strabismus of the left eye following traumatic proptosis. Other ophthalmic findings in the left eye included blindness, loss of direct and consensual pupillary light responses, reduced corneal sensation, lagophthalmos and corneal ulceration.
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8.21 Temporary tarsorrhaphy technique. Partial thickness horizontal mattress sutures are placed using 4/0–5/0 (1.5–1.0 metric) non-absorbable suture material (e.g. polyamide) on a reverse cutting or micropoint needle. If eyelid swelling is severe, placement of the suture through a stent (see Chapter 12) may help to prevent pressure necrosis. The suture should pass through the anterior eyelid margin (anterior to the meibomian gland openings) to reduce the chance of corneal contact. The medial aspect of the palpebral fissure (over the third eyelid) may be left open to facilitate administration of topical medication. (Courtesy of Roser Tetas Pont)
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8.22 A 3-year-old Cavalier King Charles Spaniel with a salivary mucocele. Oral examination revealed a painless fluctuant swelling in the pterygopalatine fossa. T2-weighted sagittal MR image showing a complex fluid-filled cavity in the right orbit. Note the ventral extension of the mucocele towards the oral cavity, which presented as the swelling in the pterygopalatine fossa. T2-weighted transverse MR image showing the left and right zygomatic salivary glands (arrowed). Serial transverse MR images demonstrated a direct communication between the right zygomatic salivary gland and the mucocele (*).
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8.23 Drainage of a salivary mucocele (same dog as in Figure 8.22 ). A large-gauge needle is inserted into the mucocele through the pterygopalatine fossa. Approximately 20 ml of blood-stained saliva was removed from the mucocele.
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8.24 Transconjunctival enucleation technique. A lateral canthotomy is performed to improve exposure of the globe and an eyelid speculum is then inserted. Using tenotomy scissors, an incision is made through the bulbar conjunctiva and Tenon’s capsule to the level of the sclera, approximately 5 mm posterior to the limbus (this allows haemostats or Allis tissue forceps to be attached to the remaining conjunctiva at the limbus and the globe to be manipulated into the desired position to assist the surgeon). Blunt dissection is continued caudally on this scleral plane to identify the insertion of the superior rectus muscle, which is transected close to the sclera, minimizing haemorrhage. Dissection is continued around the globe through 360 degrees in the scleral plane in order to identify and transect the other rectus and oblique muscles at their insertions on the sclera. Once all the rectus muscle and superior and inferior oblique muscle insertions have been sectioned, the globe should be rotated medially in order to identify the retractor bulbi muscles, which surround the optic nerve (direct observation of the optic nerve is usually not possible owing to their presence). Medial rotation of the globe is preferable to placing forward traction on the globe. The optic nerve and retractor bulbi muscles are transected with fine curved Metzenbaum scissors (with or without prior clamping). Exposure and ligation of the optic nerve is not recommended because this may place excessive traction on the optic nerve and chiasm, which could lead to damage of the contralateral optic nerve fibres. This is particularly important in cats, in which the globe occupies most of the orbital space and therefore forward traction on the globe carries a greater risk of a blinding tractional injury to the optic chiasm. Once the globe has been removed, the orbit is packed with gauze sponges to control any haemorrhage from the extraocular muscles and orbital vasculature: typically packing the orbit for 5 minutes will control bleeding. The third eyelid, third eyelid gland and associated conjunctiva are excised. The eyelids are removed using large Mayo scissors. The excision should extend approximately 7 mm from the lateral eyelid margins to ensure removal of the meibomian glands. The margin of the excision should taper towards the medial canthus, where only about 3–4 mm of skin should be removed. Dissection of the medial canthal skin and medial caruncle tissue is performed using tenotomy scissors: staying close to the medial canthus reduces the chance of transecting the angularis oculi vein, which can be associated with significant haemorrhage. Any remaining conjunctival tissue is dissected and removed. The lacrimal gland, which lies deep to the orbital ligament, can be identified and dissected from the orbit (although this is not typically performed). After removal of the gauze packing from the orbit, most of the haemorrhage is controlled, but specific bleeding vessels may need to be ligated or cauterized. Haemorrhage from some eyelid vessels can be more significant and require ligation or cautery. Closure of the deep surgical wound should be in two layers: closure of the deep fascia over the orbital opening followed by closure of the subcutaneous layer using a continuous 4/0 (1.5 metric) absorbable suture. The dead space caused by removal of the globe will fill with serosanguineous material, and closure of the deeper layer will prevent the extensive subcutaneous haematoma and swelling often seen post enucleation. The eyelid skin is closed in a simple interrupted pattern with 4/0 (1.5 metric) non-absorbable monofilament suture material. (Courtesy of Roser Tetas Pont)
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8.25 Transpalpebral enucleation technique. The eyelids may be sutured together using a large-gauge non-absorbable monofilament suture such as 2/0 (3 metric) nylon, or they may be held together using Allis tissue forceps to allow an assistant to provide traction on the eyelids in an appropriate direction depending on the area of surgical dissection. Two curved skin incisions are made in the periocular skin of the upper and lower eyelids approximately 7 mm away from the eyelid margin and joined near the medial and lateral canthi. At the medial canthus, the incisions should meet approximately 3–4 mm from the medial canthal margin. Blunt dissection is performed towards the globe, taking care not to penetrate the conjunctival sac, until the sclera is identified. Sectioning of the lateral canthal ligament aids exposure, and digital palpation helps guide the blunt dissection and facilitates finding the appropriate plane of dissection. Once the sclera is exposed, this plane of dissection should be maintained around the superior, temporal and inferior aspects of the globe. The extraocular muscles should be identified as transected (as described for the transconjunctival enucleation technique). Medially, the dissection continues on the outer surface of the third eyelid. Sectioning the short medial canthal ligament facilitates exposure and freeing of the outer surface of the third eyelid. As with the transconjunctival enucleation technique, rotation of the globe medially to expose and allow transection of the retrobulbar muscles and optic nerve is recommended, rather than direct forward traction on the globe. Wound closure and aftercare are as described for the transconjunctival enucleation technique. (Courtesy of Roser Tetas Pont)

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