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Glaucoma

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Abstract

Glaucoma in domestic animals presents as a group of well recognized pathological changes involving the globe. These may result from one or more ocular disorders whose common endpoint is elevation of the intraocular pressure (IOP) above normal limits, leading to impairment or loss of vision. This chapter covers physiological control of intraocular pressure; investigation of disease; clinical signs; classification and causes of glaucoma; treatment; glaucoma in cats.

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Figures

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15.1 Aqueous humour is produced by the ciliary body and flows through the pupil into the anterior chamber. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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15.2 Drainage of aqueous occurs primarily through the pectinate ligament and trabecular meshwork into the aqueous plexus, and thence to the scleral venous circulation. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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15.3 Photomicrograph of the drainage structures in the eye of a cat. A = sclera; B = trabecular meshwork within ciliary cleft; C = anterior chamber; D = iris; E = ciliary body. (Courtesy of E Scurrell)
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15.4 The fibres of the pectinate ligament viewed from within the anterior chamber. (Courtesy of JRB Mould)
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15.6 A goniolens alters the refraction at the corneal surface, allowing light that would normally be internally reflected to travel from the drainage angle to the viewer’s eye.
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15.7 A Barkan goniolens applied to a topically anaesthetized cornea. This lens employs negative pressure, created by the column of saline within the attached silicone tubing, to maintain adherence of the lens to the globe. An improved view may be obtained by filling the chamber of the lens with artificial tears prior to placement on the cornea.
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15.8 A Koeppe goniolens in place. This lens is held in place by a combination of surface tension on the corneal surface and the presence of a flange on the margin of the lens, which engages under the eyelids.
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15.9 Gonioscopic view of normal pectinate fibres and ciliary cleft entrance in a Labrador Retriever.
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15.11 Acute-onset glaucoma secondary to endophthalmitis in a Greyhound. Marked corneal oedema was accompanied by signs of severe ocular discomfort in the right eye.
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15.12 Corneal oedema due to high IOP in a 2-year-old English Springer Spaniel. Secondary glaucoma developed following intraocular haemorrhage.
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15.13 Deep corneal vascularization in a Labrador Retriever with primary glaucoma associated with goniodysgenesis. The vessels have invaded the cornea through 360 degrees and exhibit a ‘brush-border’ appearance at the leading edge. Deep vessels (arrowed) cannot be seen to cross the limbus in dogs (compare with the superficial vessels in Figure 15.21 ).
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15.14 Mydriasis and moderate corneal oedema in a Basset Hound with acute-onset primary glaucoma associated with goniodysgenesis.
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15.15 Episcleral congestion. Large vessels, which do not move with the conjunctiva, are seen against the scleral background.
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15.20 Buphthalmos in a kitten with congenital glaucoma.
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15.21 Superficial vascularization in chronic glaucoma. The vessels (arrowed) are branching and can be seen to cross the limbus (compare with Figure 15.13 ).
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15.22 A Chow Chow with chronic glaucoma secondary to previous anterior uveitis. Descemet’s streaks (Haab’s striae) can be seen as blue-grey streaks across the cornea. They represent breaks in the Descemet’s membrane, which occurs as a result of stretching of the ocular tunics.
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15.23 Equatorial staphyloma. Occasionally, pressure-induced thinning of the sclera may cause a bluish swelling posterior to the limbus. In contrast to a neoplastic mass, a staphyloma can be transilluminated because of thinning of the tissues. (Courtesy of PGC Bedford)
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15.24 Primary open-angle glaucoma in a crossbred dog. The globe has enlarged, resulting in secondary lens luxation. The lens can be seen lying in the anterior chamber.
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15.25 Primary open-angle glaucoma in a collie cross, resulting in bilateral globe enlargement. Both lenses are suspended near the visual axes by the remaining zonular fibres. The refractile lens equator can be seen and adjacent to this is an aphakic crescent. The cornea shows signs of breaks in the Descemet’s membrane and corneal pigmentation has developed as a result of gross buphthalmos.
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15.26 Globe enlargement in a case of chronic glaucoma, which has caused secondary lens luxation and cataract development. Chronic superficial corneal vascularization is also present.
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15.28 Primary open-angle glaucoma in a crossbred dog. The optic disc is severely cupped. The retinal vessels drop down over the rim of the cup where they are lost to view when the focus is in the plane of the retina.
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15.29 Severely cupped optic nerve head. (Courtesy of E Scurrell)
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15.30 Histological section of a globe with chronic glaucomatous damage. The optic nerve head is cupped. The margins of the disc are denoted by the arrows. (Courtesy of JRB Mould)
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15.31 Sectoral retinal necrosis in a Basset Hound with primary glaucoma. The sharp demarcation between the hyper-reflective zone (indicative of retinal thinning) and the adjacent more normal area of reflectivity is known as a ‘watershed’ lesion.
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15.32 Chronic fundic changes in glaucoma due to goniodysgenesis in an English Springer Spaniel. The tapetal fundus shows generalized hyper-reflectivity and there is marked retinal vessel attenuation. The optic disc is severely cupped.
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15.34 Gonioscopic view of goniodysgenesis in a Great Dane. The pectinate ligament comprises a sheet of tissue with only intermittent flow holes (arrowed) (compare with Figure 15.9 ).
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15.35 Gonioscopic view showing extreme narrowing of the entrance to the ciliary cleft (arrowed).
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15.36 Histological section showing goniodysgenesis. The trabecular meshwork and other normal structures of the ciliary cleft (see Figure 15.3 ) are collapsed or not apparent. (Courtesy of E Scurrell)
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15.38 Iris bombé results when 360-degree posterior synechiae prevent flow of aqueous through the pupil.
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15.39 A Labrador Retriever was hit in the right eye by a golf ball 2 weeks previously. Glaucoma has developed as a result of uveitis and there has been considerable iris bombé formation. A cataract is also present and a small amount of haemorrhage can be seen in the pupil. The side view shows the iris bulging forward.
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15.40 Extensive fibrin deposition within the pupil and anterior chamber as a result of blunt ocular trauma in a Persian cat.
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15.41 Gonioscopic view of fibrovascular membranes overlying the pectinate ligament and occluding the entrance to the ciliary cleft in a crossbred dog with uveitis.
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15.42 Histological section showing a pre-iridal fibrovascular membrane (arrowed) overlying the anterior face of the iris and extending across the entrance to the secondarily collapsed ciliary cleft. The iris is characteristically shortened and distorted by the membrane. (Courtesy of E Scurrell)
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15.43 An 8-year-old Staffordshire Bull Terrier with a history of right ocular pain and discoloration. The iris is dark and swollen dorsomedially, and the pupil is distorted. Corneal oedema is present. The diagnosis was one of glaucoma secondary to anterior uveal melanoma. The cross-section of the globe shows that the bulk of the melanoma lies in the dorsal iris and ciliary body, but there is ‘ring’ spread to involve the entire anterior uvea. (b, Courtesy of JRB Mould)
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15.44 The left eye of an Anatolian Karabash bitch presenting with bilateral glaucoma secondary to metastatic carcinoma. The bitch had a history of recent mammary carcinoma resection. Thoracic radiography revealed the presence of multiple pulmonary metastases. The left eye shows the presence of mild globe enlargement, corneal oedema, corneal vascularization and intraocular haemorrhage. Similar changes were evident in the right eye. The section of the left globe shows evidence of invasion of the uveal tract by metastatic carcinoma (arrowed). The anterior chamber appears yellowish-white as a result of the post-mortem effect of the glutaraldehyde fixative in the presence of high protein levels, which have resulted from the ante-mortem breakdown of the blood–aqueous barrier.
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15.46 Ocular melanosis in a Cairn Terrier. Heavy pigment deposition is evident within the sclera and at the limbus. The iris is dark and thickened. Histologically, the iris, drainage angle and areas of the sclera are shown to be heavily infiltrated with pigmented cells, the majority of which are melanocytes. (b, Courtesy of E Scurrell)
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15.47 A Great Dane with a cataract, lens-induced uveitis, retinal detachment and pre-iridal fibrovascular membrane formation, which in turn has caused glaucoma. Corneal oedema and corneal vascularization are present. Note also the obscured view of the cataract. Post-enucleation specimen showing evidence of globe enlargement and total retinal detachment. The iris (arrowed) is shortened as a result of the pre-iridal fibrovascular membrane. (b, Courtesy of JRB Mould)
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15.51 A diode laser unit suitable for trans-scleral cyclophotocoagulation.
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15.52 Trans-scleral laser cyclophotocoagulation in progress. The globe has been rotated so that the 9 o’clock position is away from the laser beam.
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15.53 Endoscopic laser cyclophotocoagulation. The ciliary processes can be visualized during the procedure. Note that the processes have turned white at the photocoagulated sites. (Courtesy of D Wilkie)
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15.55 A Joseph implant being placed in the left eye of a Flat-coated Retriever with primary glaucoma due to goniodysgenesis. The strap is passed under the rectus muscles and sutured to the sclera. The Joseph implant tubing can be seen in the anterior chamber at the end of the procedure.
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15.56 Diffuse iris melanoma in a Persian cat with secondary glaucoma. The iris is thickened, discoloured and distorted. A section of the affected eye. (b, Courtesy of E Scurrell)
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15.57 Glaucoma secondary to lymphoma in a Domestic Shorthaired cat with feline leukaemia virus. The eye shows signs of conjunctival swelling and hyperaemia, corneal oedema and neovascularization. The iris is largely obscured due to the presence of fibrin, cellular effusion and haemorrhage in the anterior chamber. The cross-section of the globe shows that the iris and ciliary body are heavily infiltrated by lymphoma tissue (arrowed). The aqueous appears opaque owing to the effect of fixative in the presence of high protein levels. (b, Courtesy of JRB Mould)
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15.58 Lymphocytic-plasmacytic uveitis and secondary glaucoma in a cat. Focal accumulations of inflammatory cells (‘iris nodules’), iris neovascularization, keratic precipitates and a secondary cataract can be seen. The gross section of the globe shows the cell infiltrates within the iris and obliterating the drainage angle. The lens has been removed. Photomicrograph showing heavy infiltration of the iris and ciliary cleft by inflammatory cells. (b–c, Courtesy of E Scurrell)
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15.59 A 1-year-old Domestic Shorthaired cat with bilateral glaucoma secondary to uveitis caused by feline infectious peritonitis. The left eye is grossly enlarged and shows signs of a haemorrhagic inflammatory deposit on the corneal endothelium.

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