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

LENS PROTEIN BREAKDOWN OR LENS CAPSULE RUPTURE AND ITS SIGNIFICANCE IN INFLAMMATORY EYE DISEASE

Morphologic features suggesting pathologic lens capsule rupture (Fig. 10.13)

•Recoil or scrolling of the ends of the lens capsule is a feature that distinguishes pathologic rupture from artifact

•Entrapment or digestion of lens capsule at the site of rupture is a feature of pathologic rupture

•If the lens capsule remains intact, then there should be no cell type other than lens epithelial cells or metaplastic lens epithelial cells within the capsule

■Characteristic cells to look for, that suggest pathologic lens capsule rupture, include the following:

–Macrophage cells

–Neutrophils

–Red blood cells

–Fibroblasts and blood vessels.

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Phacolytic uveitis (lens-induced uveitis) (Fig. 10.14)

•Phacolytic uveitis occurs in response to the ‘broken down’ lens proteins that characterize cataract, particularly mature and hypermature cataract. These altered lens proteins are able to leak through an intact lens capsule into the aqueous inciting a mild to moderate inflammation

•There is a mild to moderate lymphoplasmacytic uveitis

•Subsequent formation of extensive posterior synechiae with iris bombé, or peripheral anterior synechiae, increases the risk of secondary glaucoma

•Apparent leakage of lens-related granular protein occurs in a small percentage of cats with idiopathic lymphoplasmacytic uveitis.

Phacoclastic uveitis

•In phacoclastic uveitis, inflammation occurs in response to the sudden release of relatively large quantities of lens protein after lens capsule rupture

•In our opinion, the true incidence of phacoclastic uveitis, not associated with pathologic organisms such as bacteria, is hard to determine because bacteria are often identified within ruptured lenses (see below)

•Lens rupture associated with rapidly progressive, intumescent diabetic cataract represents a special case, in which there is often a pronounced, macrophage-rich endophthalmitis associated with the explosive release of lens proteins

(Fig. 10.15).

Septic implantation syndrome (see Ch. 5) (Fig. 10.16)

•A penetrating ocular injury causing lens capsule rupture with implantation of bacteria or, more rarely fungi, into the lens is a common occurrence in both cats and dogs

•Although impossible to prove in every case, this syndrome is most frequently caused by a cat scratch

■There is often a latency period between the scratch and the onset of severe endophthalmitis

■Because of the time that elapses between the original cat scratch and the clinically apparent endophthalmitis, the morphologic features of the disease include evidence of chronicity, such as:

–Fibrosis and collagen deposition in association with the posterior synechiae

–Development of a collagenous cyclitic membrane

•There is suppurative and histiocytic inflammation within the posterior chamber and within the ruptured lens

•Bacterial colonies or fungal hyphae are seen away from the inflammatory infiltrate, implanted within the lens substance

•Endophthalmitis is centered around the lens.

Phacoclastic uveitis in rabbits associated with the microsporidium, Encephalitozoon cuniculi (Fig. 10.17)

•This syndrome is characterized by a white inflammatory nodule adherent to the lens at the site of a lens capsule break and extending into the anterior chamber and anterior uvea

•Dwarf rabbits are over-represented

•Histologic features of Encephalitozoon cuniculi-associated phacoclastic uveitis

■The inflammation is more confined and circumscribed than in septic implantation syndrome

■There is a more prominent granulomatous component to the inflammation

■Encephalitozoon cuniculi organisms may or may not be found. They are Gram-positive and a Gram-stain helps to demonstrate the organisms

•The mechanisms of disease transmission and pathogenesis have not been completely elucidated. Vertical transmission of the organism may be important in these cases, with lens infection occurring during lens development.

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Diseases of the Lens Chapter 10

Figure 10.16  Septic implantation syndrome. (A) Gross photograph of dog eye showing a suppurative exudate (arrow) plastered between the lens capsule and the posterior iris in septic implantation syndrome. (B) Low magnification photomicrograph showing the relationship between the ruptured lens capsule (white arrow), the iris (black arrow) and the crystalline lens. (C) Higher magnification showing the lens capsule rupture and the ragged edge of the capsule (arrow) infiltrated by neutrophils.

(D) High magnification photomicrograph showing Gram-positive bacterial cocci embedded in the lens away from the suppurative exudates, typical of septic implantation syndrome (Gram stain). (E) High magnification showing long filamentous bacteria in a cat with septic implantation syndrome.

Comparative Comments

Phacolytic uveitis, generally referred to in humans as phacoantigenic endophthalmitis, or lens-related uveitis, is a similar pathologic entity to that described in other species and is seen commonly in phakic eyes with sympathetic ophthalmia.

THE LENS EPITHELIUM AND ITS ROLE IN DISEASE AFTER LENS CAPSULE RUPTURE (Fig. 10.18)

Following spontaneous lens capsule rupture, chronic cataract, or following cataract surgery, remaining lens epithelial cells undergo a predictable series of changes which can lead to serious complications.

•Spindle cell metaplasia, forming cells that express smooth muscle actin that are typical of myofibroblastic mesenchymal cells

•Proliferation of remaining epithelial cells and migration of metaplastic cells within the lens capsule

■In humans, the migration of lens epithelial cells is confined to the lens capsule, but this is not the case in dogs and cats

■Together with mesenchymal transformation, this is a major cause of posterior capsular opacification following cataract surgery in humans and animals. Complications of cataract surgery are discussed in detail in Chapter 4

•Migration of metaplastic lens epithelial cells to cover the inner aspect of the uvea, lining the globe

•Potential, vision-threatening consequences of the migration of metaplastic lens epithelial cells out of the lens capsule include:

■Synechiae formation

■Traction leading to retinal detachment

■Glaucoma due to angle closure or pupillary block

■Proliferative membranes in the posterior segment

•Malignant transformation causing spindle cell variant post-traumatic ocular sarcoma in cats (see Ch. 5) (Fig. 10.19)

■After a latency period which averages 7 years following traumatic lens capsule rupture, lens epithelial cells may undergo transformation into malignant spindle cells

■The malignant cells extend around the interior of the globe and may infiltrate into the sclera, optic nerve, and peripheral nerve tissue

■Malignant cells often continue to secrete a thick, lens capsule-like basement membrane and may also continue to express alpha A crystallin protein.

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LENS LUXATION

•Lens luxation is the separation of the lens from its zonular ligament moorings (Figs 10.20, 10.21)

•The position of a highly mobile luxated lens can change rapidly, before the observer’s eye.

Subluxation

Partial dislocation of the lens which, although somewhat displaced, remains within the patella fossa on the anterior vitreous face.

•Morphologic features of lens luxation apparent on the gross examination of the globe include:

■Lens out of position and free within the globe

■Liquid vitreous body, often with strands across the front or attached to the free lens

•Morphologic features of lens luxation apparent on histopathology include:

■An angular, posterior bend in the profile of the iris (‘dogleg’ iris)

■Atrophy of the pars plicata of the ciliary body

■Attenuation of the corneal endothelium secondary to touch by the luxated lens.

Anterior luxation

The dislocated lens lies partly or entirely within the anterior chamber.

Posterior luxation

The dislocated lens falls back into the vitreous, implying degeneration or disruption of the anterior vitreous.

Detecting pre-existing lens luxation in the enucleated globe

•Detecting lens luxation can be problematic because the lens is commonly displaced artifactually during cutting and processing of the globe

•The best way to detect a pathological lens luxation is to read the history carefully because the ophthalmologic exam is most likely to be accurate

Vision-threatening consequences of lens luxation (Fig. 10.22)

•Physical contact between the luxated lens and the corneal endothelial cells results in attenuation of the endothelium or formation of a retro-corneal membrane

■Loss of function of the central or paraxial corneal endothelium may result in corneal edema

■Corneal edema, in turn, may lead to:

–Bullous keratopathy and corneal ulceration

–Secondary infectious keratitis

–Collagenolysis with corneal perforation

•Entrapment of the lens in the anterior chamber causing angle closure and/or pupillary block with secondary glaucoma

•Posterior synechiae leading to pupil block, iris bombé and glaucoma

•Anterior vitreous prolapse contributing to retinal detachment or pupil-block and secondary glaucoma.

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