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Ophthalmology

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Abstract

This chapter covers the ocular and orbital anatomy of rabbits and clinical examination. It then goes on to review the common disorders, including systemic disease, neuro-ophthalmological disease, lacrimal and nasolacrimal disease, eyelid disease, and more.

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Figures

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16.1 The rabbit pupil is a vertical ovoid when half dilated; the accompanying arrangement of pupillary muscle fibres allows more rapid and complete dilation than a circular pupillary motor arrangement. The lateral upper eyelashes and the more medial lower eyelashes overlap when the lids close; this may help to protect the eye from dirt during burrowing. Note the pigmented nodules on the leading edge of the third eyelid; these are a normal finding of uncertain significance.
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16.2 Repetitive 30-degree lateral movements of the head in the alert standing rabbit can produce a near total hemispherical survey of the environment, and this behaviour can be observed in the wild rabbit in response to auditory or visual stimuli.
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16.3 Lateral visual fields in the rabbit, illustrating the effect of ear elevation and exophthalmos .
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16.5 The globe is aspherical, with an anterior–posterior length some 15% less than the globe diameter. Note the large cornea, which covers approximately 75% of the globe.
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16.6 Normal globe. Note the large cornea, shallow anterior chamber, marked anterior bowing of the iris, very large lens (43% of axial lens length), the dorsally located optic nerve head and the adjacent horizontal myelination and superficial retinal vessels. Normal albinotic rabbit globe. Note the absence of pigment throughout the uveal tract. (Courtesy of John Mould)
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16.7 The dorsal rectus muscle is normally visible through the dorsal bulbar conjunctiva.
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16.8 The bilobed Harderian gland. Both the white and pink lobes produce a mixture of protein, lipid and carbohydrate. The function of the Harderian glands is believed to be complex, including ocular lubrication, pheromone production and immune modulation. (Courtesy of R Dubeilzig)
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16.10 Normal lower eyelid and nictitating membrane. Note the tight adherence of the anterior nictitans to the lower lid. H&E stain. (Courtesy of R Dubeilzig)
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16.11 The position of the globe and third eyelid should be assessed with the head: in the neutral position; and lowered beneath the level of the heart.
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16.12 Normal fundus of a pigmented wild rabbit (). Note the visible choroidal vasculature. (Retinal images photographed using iPhone 4S using technique described by ). Normal merangiotic optic nerve head with prominent lateral nerve fibre layer and physiological nerve head cupping.
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16.13 Wild rabbit () with right-sided facial paralysis following peripheral facial trauma (dog bite). Note the obvious change in ear carriage but the normal palpebral aperture and very subtle position change of the right-sided naris. No blink could be induced by touching the medial or lateral canthus (negative palpebral reflex) and the right naris was paralysed.
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16.14 Retrobulbar abscess in the left eye. Drawing a line between the pupils illustrates the marked dorsal displacement of the globe. Note partial third eye lid prolapse caused by a retrobulbar mass and the ventromedial scleral show caused by dorsolateral displacement of the globe, localizing the mass to the ventromedial orbit.
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16.15 Glaucoma causing marked globe enlargement (buphthalmos) in the right eye. Note the absence of nictitans prolapse and the circumferential visible sclera.
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16.17 Presumed retrobulbar adenitis. This rabbit was clinically well, with no evidence of dental disease, but presented with sudden-onset bilateral exophthalmos. Bilateral multilobular masses were identified on ocular ultrasonography. Resolution with no recurrence was seen following 7 days’ treatment with systemic meloxicam and enrofloxacin.
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16.18 Chronic bilateral vascular exophthalmos due to abnormal venous drainage. Engorged vessels visible subconjunctivally caudal to the prolapsed third eyelid. Magnetic resonance image: transverse slice showing bizarre vascular pattern in dewlap. These vessels were contiguous with the vena cava; congenital or post-traumatic lesions were suspected. (Images courtesy of Kevin Eatwell)
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16.19 Mature cataract and glaucoma (IOP 84 mmHg) prior to evisceration. Note the circumferential scleral show and normal nictitans position. Intrascleral silicone implant placed following removal of all globe contents (evisceration) via a dorsolateral scleral incision parallel to the limbus; immediate postoperative photo.
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16.20 Dacryocystitis with secondary blepharoconjunctivitis. Dacryocystitis: massaging pus from the lacrimal sac.
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16.21 Contrast computed tomographic dacryocystogram. Cross-sectional CT view of the head, showing overgrowth of all the molar tooth roots, particularly the right maxillary molar teeth (blue arrow). Disruption of the tooth-root architecture and mild osteolytic changes the bony tooth sockets are seen. Proximity of the nasolacrimal duct (seen as a pool of bright white contrast material) to the maxillary, molar tooth roots can be appreciated (purple arrow). (Courtesy of Vim Katarunga)
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16.22 Prolapse of the deep gland of the orbit.
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16.23 Acute marginal blepharitis. There is marginal lid folding, in this case secondary to blepharoconjunctivitis. Dacryocystitis was the underlying pathology in this dwarf-breed rabbit. Chronic marginal blepharitis in a case of long-standing corneal abscessation. Note the multiple lid margin folds; these remained after the corneal disease had been treated successfully.
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16.24 Incidental finding of chalazia in a rabbit with active chronic dacryocystitis. The lid swelling can be seen in the upper lateral lid. Everting the lid is an important part of the examination and reveals the grossly abnormal meibomian glands laterally. Multiple chalazia identified incidentally in another rabbit following a history of dacryocystitis.
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16.25 Acute myxomatosis. Ulcerative, oedematous blepharitis with markedly purulent conjunctivitis in a wild rabbit. Ulcerative keratitis is a common sequel. Severe ulcerative blepharitis and a secondary bacterial keratoconjunctivitis in a domestic rabbit.
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16.26 Eyelid margin myxoma in a vaccinated rabbit. Note the dorsal keratitis present. This lesion resolved uneventfully, the keratitis was treated with ocular lubricants and a full recovery was seen.
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16.27 Chronic myxoma formation on the eyelid and nose of a vaccinated rabbit. Both lesions sloughed and the rabbit made an uneventful recovery. (Courtesy of David Nutbrown-Hughes)
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16.28 blepharitis in a domestic rabbit. Crusting skin lesions were present on the nares, pinna, feet and vulval regions. Lesions often become more extensive and ulcerative.
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16.29 Lid overlength leading to combined entropion and ectropion in a giant-breed rabbit. Note the upper lid notch and the striking marginal folding of the lower lid due to secondary marginal blepharitis.
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16.30 Eyelid melanoma. Upper medial lid, middle-aged Dwarf Lop. Resected and closed in two layers using 0.7 metric (6/0 USP) polyglycolic acid.
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16.31 Lid margin repair with secondary superficial ulcer. Note the vertical pattern of ulceration.
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16.32 A large well circumscribed pink fleshy mass arising from the ventrolateral limbus. Perilesional corneal oedema, corneal vascularization, and moderate conjunctival hyperaemia are present. (Reproduced from with the permission of Wiley)
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16.33 Ectopic cilium visible as a black dot on the conjunctival lid margin surface at the base of the tarsal plate. Visualization is often difficult, requiring high magnification. Ectopic cilium removal. The lid margin is stabilized with a chalazion clamp and the hair removed together with a section of overlying conjunctiva. Removal of all hair follicles is essential, making magnification mandatory.
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16.37 Indolent ulcer prior to debridement; a rim of non-adherent epithelium is present. The same ulcer following debridement with a sterile cotton bud, revealing the true area of corneal abnormality. Phenol has been applied sparingly to the exposed corneal stroma where coagulated corneal stromal protein can be seen as a white plaque. Healed indolent ulcer, day 10 after phenol cautery.
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16.38 Descemetocele: note the white colour of the exposed stroma. Conjunctival pedicle graft in place, repairing the stromal deficit. Appearance on day 45 after surgery: rapid corneal remodelling and a transparent conjunctival graft are seen.
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16.39 Lipid keratopathy in a dwarf-breed rabbit. Note the linear central distribution matching the cooler regions of the cornea, where lipids precipitate in the anterior corneal stroma. (Courtesy of Vim Katarunga)
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16.40 Posterior capsular and subcapsular cataract associated with a persistent hyaloid remnant.
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16.41 Epinuclear cataract in a 3-year-old domestic rabbit. The epinuclear region of the lens develops at or around birth; thus lens opacities in this position are thought to reflect metabolic insults to the lens at this time.
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16.42 Aphakic eye immediately following cataract removal by phacoemulsification for -associated lens rupture and lens-induced uveitis. The edge of the posterior rhexis is just visible. Corneal neovascularization is present, associated with a pre-existing chronic lens-induced uveitis.
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16.43 Chronic glaucoma of unknown cause. Gonioscopic view of the iridocorneal drainage angle shows haemorrhage in the drainage angle consistent with anterior uveitis.
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16.44 Chronic glaucoma. Secondary lens luxation due to progressive globe enlargement.
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16.45 Chronic glaucoma with marked optic nerve head cupping and complete vascular attenuation.
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16.46 Rabbit following bilateral enucleation, playing ‘tug-of-war’ with a sighted companion.

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