Ординатура / Офтальмология / Английские материалы / Veterinary Ocular Pathology A Comparative Review_Dubielzig, Ketring, McLellan_2010

Glaucoma in canine ocular melanosis (Figs 13.18, 13.19)

•Obstruction of aqueous outflow at the level of the irido-corneal angle and ciliary cleft occurs as a frequent complication in dogs with primary ocular melanosis, or so-called ‘pigmentary glaucoma’

•Ocular melanosis is diagnosed when the uveal tract is thickened and distorted by an excess of heavily pigmented tissue

(see Ch. 9)

•Ocular melanosis is often associated with secondary glaucoma

•Breeds with the highest incidence are:

■Cairn terrier (‘pigmentary glaucoma’)

–The most commonly affected breed, in which the disease has been most extensively studied

–Affected dogs usually show bilateral ocular involvement

–A dominant mode of inheritance has been proposed in this breed

■Labrador Retriever

■Boxer

■Dachshund

•There is a small, but documented risk of melanoma developing in eyes with ocular melanosis.

Multiple thin-walled iridociliary cysts, pigmentary uveitis in Golden Retrievers (Fig. 13.20) (see also Ch. 9)

•Although also documented in the Great Dane, thin-walled iridociliary cysts associated with glaucoma are rarely seen in breeds other than the Golden Retriever

•One-cell-thick cysts of ciliary or iridal epithelial origin fill the posterior chamber and become plastered against the lens equator or the anterior capsule. The cyst can pull the iris back to form a posterior synechia

•The disease is called ‘pigmentary uveitis’ by ophthalmologists because of the protein in the aqueous, the dispersion of pigmented cells and fragments of cysts, and because pigmented cyst remnants are plastered against the anterior lens capsule mimicking inflammatory posterior synechiae or ‘iris rests’

•Morphologically, inflammation is a minor process in affected globes

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•Focal retro-corneal membrane or Descemet’s changes are seen because fragments of cysts attach to the corneal endothelium

•The precise mechanism for glaucoma development in affected dogs is unclear:

■Multiple cysts within the posterior chamber can push the iris anteriorly, narrowing the opening to the ciliary cleft

■Posterior synechiae or iris bombé are frequently seen in globes removed because of secondary glaucoma

■Pre-iridal fibrovascular membranes are commonly encountered, often with concurrent peripheral anterior synechiae

■Intraocular hemorrhage is common.

Glaucoma associated with neoplasia in dogs

•Of 5722 cases of neoplasia in dogs in the COPLOW collection, 1516 cases (26%) have glaucoma as part of the syndrome

■57% melanoma

■21% iridociliary epithelial tumors

■5% metastatic tumors

■4.5% lymphoma.

Comparative Comments

Secondary open-angle glaucoma refers to a group of diseases characterized by elevated intraocular pressure occurring with a well-formed anterior chamber without peripheral anterior synechiae. There are a number of types of secondary open-angle glaucoma recognized in humans:

•Inflammatory disorders may cause a trabeculitis or may result in mechanical blockage of aqueous outflow by proteinaceous exudates

•The presence of blood products may produce open-angle glaucoma in several ways

–Red blood cells from hemophthalmos, or macrophages containing degenerated blood cells, may block aqueous outflow

–In the case of a vitreous hemorrhage, red blood cells are lysed progressively and the rigid degenerating cells (‘ghost cells’) may migrate into the anterior chamber and obstruct the trabecular spaces

Comparative Comments (continued)

–Liquefied cortex may leak from the lens and lead to an influx of swollen mononuclear cells, which may obstruct the outflow system (phacolytic glaucoma). Liquefaction of the lens cortex may also lead to the release of particulate material into the anterior chamber, which itself can block the trabecular meshwork

•In some patients, a dispersion of pigment from the iris pigmented epithelium may occur. Phagocytosis of melanosomes by the trabecular endothelial cells may lead to obstruction of aqueous outflow and glaucoma (pigmentary glaucoma)

•The pseudoexfoliation syndrome is a systemic disorder in

which there is a deposition of a fibrillary protein-like material on the lens capsule, zonular fibers, trabecular meshwork, iris, ciliary body, and other ocular structures, as well as in other connective tissues

–Between 10% and 23% of patients with pseudoexfoliation syndrome develop glaucoma

–The trabecular meshwork in pseudoexfoliation syndrome also contains an excessive amount of pigment

•Siderosis, from retained ocular foreign bodies, can cause open-angle glaucoma

•Blunt trauma to the ocular anterior segment can damage the trabecular meshwork and the base of the iris, and produce subsequent scarring in the trabecular meshwork or posterior proliferation of the peripheral corneal endothelium over the angle structures. This can lead to increased intraocular pressure and the development of glaucoma

•Additional forms of secondary open-angle glaucoma are anterior chamber epithelialization and anterior chamber endothelialization

Secondary angle-closure glaucoma is seen in four circumstances in human eyes:

•Neovascular glaucoma

–Enucleated eyes with neovascular glaucoma are commonly seen in human eye pathology laboratories. Neovascular membranes occur as a complication of diabetic retinopathy, central retinal vein occlusion, intraocular neoplasia, and long-standing retinal detachment. A common feature in all of these is the formation of angiogenic factors acting on the iris vessels. New vessel production and subsequent contraction of the fibroblastic component of the membrane can draw the iris pigment epithelium through the pupil onto the front of the iris, as well as causing peripheral anterior synechiae and angle closure

•Tumors

–In secondary angle-closure glaucoma due to tumor, there is mechanical displacement of the iris and lens by tumors of the ciliary body, choroid, or retina, which leads to pupillary blockage

•Uveitis

–In cases of uveitis, the sticky fibrinous exudate is

responsible for the formation of peripheral anterior and central posterior synechiae, which cause secondary angle closure and glaucoma. With severe or prolonged inflammation, neovascularization will also contribute to the rise in intraocular pressure

•Trauma

–Following surgical or nonsurgical trauma, because of perforation of the cornea or limbus, hypotony and reactionary fibrosis may lead to peripheral anterior synechiae compromising the chamber angle.

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THE FELINE GLAUCOMAS

Some general features of feline glaucoma compared to canine glaucoma

•Glaucoma is relatively uncommon in the cat compared to the dog, although it is possible that many feline cases go unrecognized. In contrast to the situation in dogs, feline glaucoma is often an insidious, gradually progressive disease. Moderate elevations in IOP are associated with few overt clinical signs and cats are frequently not presented for evaluation until late in the disease process

•Sudden, fulminant onset of disease is not typical of the feline glaucomas, which makes it difficult to determine the progressive steps that occur early in the disease process

•In one recent retrospective study, 73% of glaucomatous cats were blind at the time of initial presentation. However, some vision may be preserved in chronically glaucomatous cats despite gross buphthalmos

•The optic nerve is often more gliotic and atrophic, rather than necrotic

•There is typically a loss of retinal ganglion cells but the outer retina does not progressively degenerate unless there are other factors in play, such as trauma.

The majority of cases of feline glaucoma are secondary to other ocular disease

•Intraocular inflammation, particularly chronic lymphoplasmacytic uveitis (see below), is a frequently reported cause of glaucoma in cats and may lead to elevation of IOP through a number of different pathogenic mechanisms

•Intraocular hemorrhage, particularly related to high blood pressure in elderly cats may also result in secondary glaucoma

•Intraocular neoplasia is another important cause of glaucoma in cats

•Lens-associated glaucoma in cats

■May occur secondary to phacoclastic uveitis resulting from lens trauma

■In contrast to dogs, lens luxation in cats is often secondary to glaucoma or uveitis and seldom directly results in glaucoma.

Lymphoplasmacytic uveitis (Fig. 13.21)

•Lymphoplasmacytic uveitis is one of the most common causes of feline glaucoma, and is second to diffuse iris melanoma as the most common cause of feline glaucoma resulting in enucleation. Of the total number of feline submissions to COPLOW, 10% are lymphoplasmacytic uveitis with glaucoma

•Globes submitted to the pathology lab are enucleated because of vision loss and blindness due to glaucoma

•While lymphoplasmacytic uveitis does not invariably lead to glaucoma, globes with concurrent glaucoma are more likely to be submitted for histopathologic evaluation

•This is an idiopathic uveitis characterized by a lymphoplasmacytic infiltrate in the iris and ciliary body

■The formation of lymphoid follicles is a distinctive feature commonly seen in affected globes

•Other morphologic features often seen in feline lymphoplasmacytic uveitis are described in Chapter 9

•Pathogenesis of glaucoma in feline lymphoplasmacytic uveitis

■The most frequently cited mechanism is the inflammatory infiltration with obliteration of the aqueous outflow structures

–In many affected globes, the extent of the inflammatory infiltrate within the irido-corneal angle and ciliary cleft is minimal, and these drainage angle structures remain intact

■Other factors that might contribute to the pathogenesis of glaucoma in lymphoplasmacytic uveitis include:

–Lens luxation

–Vitreous prolapse

–Neovascular membranes (rarely seen)

–Synechiae.

submissions, 53% have neoplasia. 11% are diagnosed as melanoma with glaucoma. Of the total feline submissions, 26% have feline diffuse iris melanoma (see also Ch. 9).

Aqueous humor misdirection syndrome (malignant glaucoma) (Fig. 13.24)

Unlike melanoma, this syndrome is vastly under-represented in the COPLOW collection. There are a total of 10 cases in the COPLOW collection.

•Although loss of vision is common, these eyes are not characteristically red or painful

•The disease has an insidious onset in older cats.

Glaucoma associated with feline diffuse iris melanoma (Figs 13.22, 13.23)

•In the COPLOW collection, this appears to be over-represented relative to clinical incidence of the syndrome. Of the total feline

Clinical features of aqueous humor misdirection syndrome

•Dilation of the pupil with associated anisocoria, as the disease is frequently unilateral at the time of initial presentation

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A B

C D

•Uniformly shallow anterior chamber associated with anterior displacement of the iris and lens

•Decreased pupillary light reflex

•Decreased menace response

•Subtle, glaucomatous abnormalities of the optic nerve head

•Ocular ultrasonography reveals thickening of the anterior vitreous face, anterior displacement of the iris and lens, and clear spaces in the vitreous cavity.

Morphologic features of the aqueous misdirection syndrome

•These globes are very quiet and the changes are easily missed

•Grossly the vitreous may be partially liquid, or irregular in viscosity

•The anterior face of the vitreous is thickened because of excess mucinous deposition with or without a spindle cell component

•The anterior vitreous is pushed forward, crowding into the posterior chamber, yet the anterior face of the vitreous remains well defined

•The changes seen in the optic nerve and retina are as expected with other kinds of glaucoma in cats

It has been postulated that aqueous humor is misdirected posteriorly, becoming trapped within ‘pools’ in the vitreous cavity

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Figure 13.22  Glaucoma associated

with feline diffuse iris melanoma, clinical.

(A) DSH, 6 years old: Chronic glaucoma resulted in a buphthalmic globe. Iris detail cannot be seen in this photograph.

(B) DSH, 9 years old: the iris is irregularly thickened with pale elevated masses (arrow). (C) DSH, 13 years old: the iris is heavily pigmented, resulting in dyscoria. Ectropion uvea or neoplastic infiltrate accounts for the dark area along the pupil margin. (D) DSH, 14 years old: the iris is heavily pigmented with a ragged pupil margin. Pigmented cells are present on the anterior lens capsule.

•Subsequently, anteriorly displaced vitreal elements become condensed, compressed and juxtaposed against the lens and ciliary processes.

•This juxtaposition is responsible for so-called ‘cilio-vitreal- lenticular block’, with elevation in IOP, collapse of the ciliary cleft and narrowing of the irido-corneal angle.

Angle recession (contusion) glaucoma (Fig. 13.25)

•The defining feature of angle recession is the posterior position of the irido-corneal angle

•This change is usually seen in conjunction with lymphoplasmacytic uveitis and there is seldom a history of trauma

•The existence of a distinct entity of angle recession glaucoma in cats (and more rarely in dogs) is subject to debate for the following reasons:

■The structures of the normal feline irido-corneal angle are widely spaced, and clearly defined criteria that indicate pathologic angle recession are lacking

■This change is usually seen in eyes with concurrent lymphoplasmacytic uveitis, which can be responsible for glaucoma independent of the presence of angle recession