Pathology of the and

Philippe Labelle, DVM, DACVP Antech Diagnostics 12th Biannual William Magrane Basic Science Course in Veterinary and Comparative Cornea

• Congenital/dystrophies/degenerations • Non-specific responses to injury • • Specific infections/conditions General Considerations

• Cornea has limited ways it responds to injury • Cornea has limited healing capacity (to maintain function) Dermoid

• Ectopic island of skin on cornea (or ) • Congenital choristoma • Has many or all features of normal skin • “Cutaneous ” is not analogous to a dermoid. Dermoid

Courtesy UC Davis VMTH Ophthalmology Service Dermoid

Courtesy of Dr. Chris Reilly Dermoid

Hair follicle Thick pigmented

Sebaceous glands

Courtesy of Dr. Chris Reilly and Degeneration

• Epithelial, stromal or endothelial • True dystrophy is bilateral and symmetric • Not associated with inflammatory or metabolic • Often breed-related/heritable • Degeneration: Lesions secondary to other , not true dystrophies Corneal Epithelial Dystrophy

• Shetland Sheepdogs; Longhaired Dachshunds • Superficial punctate corneal dystrophy • of basement membrane • Dyskeratosis and necrosis of epithelium • Unlikely to be biopsied Corneal Epithelial Dystrophy Corneal Epithelial Dystrophy

Epithelial dystrophy in a Basilisk lizard H&E Deposition of excessive irregular PAS-positive, basement membrane material both on PAS the basal aspect of the epithelium and in the epithelium

Courtesy of COPLOW Mineral/

• Deposition of mineral in the basement membrane of the and/or superficial stroma • Usually secondary (not a true dystrophy) • Inflammation and hypercalcemia are potential causes of secondary mineral deposition. • Horses (/ steroid and phosphate containing topical solutions) Mineral/Band Keratopathy

• Calcareous degeneration: affects both the basement membrane area and the deep stroma; may be present in the absence of any other ocular disease • von Kossa stain highlights the phosphorus of the calcium-phosphorus complex. Alizarine Red specifically stains calcium Band Keratopathy Band Keratopathy Band Keratopathy

Courtesy of Dr. Chris Reilly Stromal Lipid Dystrophy

• “Corneal dystrophy” • Bilateral and symmetrical with no association to metabolic disease • Accumulation of lipids within the stroma • Macrophages may border these foci • Acquired lipid keratopathy can be associated with corneal or adjacent disease, or metabolic disease; typically well-vascularized Stromal Lipid Dystrophy

• Lipids are dissolved during routine processing • Lipids appear as clear space/vacuoles/clefts • Cholesterol clefts angular or needle shaped clearings. It is one form of lipid accumulation • Special stains for lipid (Oil Red O, Sudan Black) can on be performed on fresh, frozen or fixed but unprocessed sections Lipid/Cholesterol Dystrophy Lipid dystrophy

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Oil Red O, Courtesy of COPLOW Lipid Dystrophy

Courtesy of Dr. Brian Stacy, UCDavis Endothelial Dystrophy

• Most often secondary (not true dystrophy) • Primary in Boston terrier, Chihuahua • Initially affects the temporal cornea • Leads to corneal edema +/- ulceration • Endothelial attenuation Endothelial Dystrophy

• Formalin fixation can cause artifactual vacuolation of the • Anterior uveitis, , surgery, anterior luxation, are possible causes of endothelial degeneration • Fibrometaplasia, retrocorneal membranes may be present with endothelial degeneration • The endothelium can slide but cannot replicate (post-miotic) with rare exceptions (rabbits +\- dogs). Endothelial Dystrophy Cornea

• Congenital/dystrophies/degenerations • Non-specific responses to injury • Keratitis • Specific infections/conditions Inclusion cysts, epithelial downgrowth

• Cysts • Congenital or traumatic • Often secondary to surgery

• Epithelial downgrowth • Trauma, ulceration Inclusion cyst Epithelial downgrowth

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Courtesy of Dr. Chris Reilly Epithelial Downgrowth Epithelial Downgrowth Descemet’s Duplication

• Double layer of basement membrane • Relatively common • Trauma, lens luxation, glaucoma, surgery are possible causes • May accompany breaks in Descemet’s membrane • There may be endothelium lining one or both layers • Unclear significance unless associated with extension on the or traumatic lesions elsewhere • Kafarnik et al. Vet Path 2009 Descemet’s Duplication

Courtesy of Dr. Chris Reilly Descemet’s Duplication Descemet’s Duplication Descemet’s Duplication Endothelial Pigment

• Secondary to release of uveal pigment • Neoplasia, inflammation, anterior , ruptured uveal cyst, iris-cornea PPM • Does not appear to affect function (not associated with corneal edema) Endothelial Pigment Cornea

• Congenital/dystrophies/degenerations • Non-specific responses to injury • Keratitis • Specific infections/conditions Keratitis, General Considerations

• Ulcerative vs non-ulcerative • Inflammatory cellular infiltrate • Acute = neutrophils • Chronic= lymphoplasmacytic • Corneal edema • Stromal neovascularization Corneal edema

• Loss of normal lamellar arrangement of the stroma • Must be differentiated from fixation artifact causing separation of lamellae Corneal edema

Edema Artifact

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• Begins 48-72 hours after injury • Progresses up to 1mm/24h. Keratitis/Stromal Neovascularization

Courtesy of Dr. Chris Reilly Ulcerative keratitis

• Ulcerative keratitis • SCCED • Ulcerative keratitis with (melting ulcers) Ulcerative keratitis

• Epithelial changes in the remaining epithelium include sliding, rounding of the epithelial edges, • Neutrophils predominate in acute cases • Lymphoplasmacytic infiltration, stromal fibrosis and neovascularization with chronicity Ulcerative keratitis Ulcerative keratitis Ulcerative keratitis Ulcerative keratitis Ulcerative keratitis Ulcerative Keratitis with Keratomalacia

• Melting ulcer • Horses, dogs (brachycephalic) +\- cats • Degeneration of stromal • Metalloproteinases, serine proteases • Endogenous (inflammation/neutrophils) • Exogenous (some and fungi produce proteases) Ulcerative Keratitis with Keratomalacia Ulcerative Keratitis with Keratomalacia

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Courtesy of Dr. Chris Reilly Chronic Keratitis (Nonspecific)

• “Chronic keratitis, superficial” • End result of a variety of corneal insults • It is not a disease, but a response pattern • , /, neurogenic disorders, lacrimal/Meibomian disorders (KCS), irritation from a mass or issue • Frequent in enucleated globes • Severe cases may mimic Chronic Superficial Keratitis/Pannus Chronic Keratitis (Nonspecific)

• Epithelial lesions (hyperplasia, pigmentation +\- keratinization) • Lymphoplasmacytic inflammation • Pigmentary incontinence (leakage of ) • Stromal fibrosis and neovascularization Chronic Keratitis (Nonspecific) Chronic Keratitis (Nonspecific) Chronic Keratitis (Nonspecific) Chronic Keratitis (Nonspecific) Cornea

• Congenital/dystrophies/degenerations • Non-specific responses to injury • Keratitis • Specific infections/conditions Chronic Superficial Keratitis (Pannus)

• Immune mediated • German shepherds and sighthounds • Chronic lichenoid lymphoplasmacytic inflammation • Stromal fibrosis and neovascularization • Epithelial lesions (hyperplasia, pigmentation +\- keratinization) • Unlikely to be biopsied Chronic Superficial Keratitis/Pannus Chronic Superficial Keratitis/Pannus Chronic Superficial Keratitis (Pannus)

Courtesy of Dr. Chris Reilly Spontaneous Chronic Corneal Epithelial Defects (SCCEDs) • Dogs (Boxers), cats, horses • Separation of the epithelium and stroma results in erosion/ulceration • Separated epithelium shows dysmaturation with loss of organized layering • Thin, acellular, hyalinized band in the superficial stroma

• Murphy et al, IOVS, 2001; Bentley et al, IOVS, 2002; Gosling et al, VO, 2013; Hempstead JE et al VO, 2014. SCCED

Courtesy of Dr. Chris Reilly SCCED

Courtesy of Dr. Chris Reilly SCCED

* Corneal Sequestrum

• Cats (Persians) +\- horses, dogs • Well-circumscribed area of stromal devitalization, often with pigmentation • Some are not overtly pigmented • Acellular/devitalized/necrosis • Inflammation and neovascularization only at the periphery • Ulceration Corneal Sequestrum

• Melanin? Iron? Porphyrins? • Association of feline herpesvirus in some studies, not in others

• Stiles et al, AJVR 1997 • Nassisse et al, AJVR 1998 • Ejima et al, Science 1993 • Featherstone et al, VO, 2004 • Cullen et al, VO 2005 • Newkirk et al, VO, 2011 Corneal Sequestrum Corneal Sequestrum

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Courtesy of COPLOW Corneal Sequestrum (dog) Florida Keratopathy

• Florida spots • No convincing histologic lesions • Material in the picture in G5 may be acid fast positive; not acid-fast bacteria • Sarfaty (ECVO 2008) suggests fire ants

• Horses +\- dogs, rarely cats • Neutrophils +\- keratomalacia +\- stromal abscess • Ulceration • Fungal hyphae may be numerous or rare • Fungal hyphae are mostly in the deep stroma • Fungal hyphae may invade Descemet’s membrane • Aspergillus spp, Fusarium spp. • Opportunistic fungal colinization of injured will be only superficial Fungal Keratitis Equine Fungal Keratitis

Malacic stroma

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Courtesy of Dr. Chris Reilly Equine Fungal Keratitis Equine Fungal Keratitis Fungal Keratitis Fungal Keratitis Fungal Keratitis Protozoal Keratitis/

• Dogs, rare • Mass effect in the cornea +/- conjunctiva • Granulomatous/pyogranulomatous inflammation • Preexisting ocular surface disease, typically KCS • Immunomodulatory therapy • Amoeba, T. gondii, Leishmania (Beckwith-Cohen B et al. VO, 2016; Swinger RL et al. VO 2009) • + Sarcocytis Protozoal Keratitis/Conjunctivitis

Right (a) and left (b) at the time the Right 2 months after protozoal conjunctivitis was diagnosed tacrolimus was discontinued and clindamycin initiated

Veterinary Ophthalmology Volume 19, Issue 3, pages 206-213, 3 JUN 2015 DOI: 10.1111/vop.12285 http://onlinelibrary.wiley.com/doi/10.1111/vop.12285/full#vop12285-fig-0002 Protozoal Keratitis/Conjunctivitis Protozoal Keratitis/Conjunctivitis

Sarcocystis sp. Feline Eosinophilic Keratitis/ • Proliferative keratitis • Proliferative gross appearance • Eosinophils are a component of the inflammation • Eosinophils may not be the predominant cell type (lymphoplasmacytic) • Herpesvirus infection, Mycoplasma, Chlamydophila • Typically unilateral • Typical cases unlikely to be biopsied Feline Eosinophilic Keratitis/Keratoconjunctivitis Feline Eosinophilic Keratitis/Keratoconjunctivitis Feline Eosinophilic Keratitis/Keratoconjunctivitis Feline Eosinophilic Keratitis/Keratoconjunctivitis Feline Eosinophilic Keratitis/Keratoconjunctivitis Acute Bullous Keratopathy

• Cats • Severe corneal edema • Rupture of Descemet’s membrane • The cause is not known • An association with systemic anti- inflammatory/immunosuppressive drugs has been proposed • Pierce ke et al. VO 2016 Epub; Pederson Sl et al. VO 2016 Epub Acute Bullous Keratopathy Acute Bullous Keratopathy Acute Bullous Keratopathy Malignant Catarrhal Fever

• Bovine • Alcelaphine herpesvirus 1, ovine herpesvirus 2 • Endotheliitis Malignant Catarrhal Fever

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• Infection or some vaccines • Adenovirus type 1-2 • Endothelial necrosis +\- inclusions • Results in severe corneal edema, “blue eye” Canine Adenovirus

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Adenoviral inclusion

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• Full or partial thickness scleral (or corneal) defect lined by protruding • Congenital or acquired (glaucoma, ) • Some cases with staphyloma present as a suspicion of neoplasia (melanocytic neoplasia) Staphyloma

Courtesy of Dr. Carol Naranjo Staphyloma

Courtesy of Dr. Chris Reilly Granulomatous

• Severe granulomatous inflammation centered on the sclera • The term “necrotizing” causes confusion as it has been used in reference to cases with collagen degeneration/lysis or cases with neutrophils • Can extend in the uveal tract • No association with immune-mediated diseases affecting other sites (except 1 dog). • Denk et al, VO, 2012; Day et al. VO, 2008. Granulomatous Scleritis

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Courtesy of Dr. Chris Reilly Granulomatous Scleritis

Courtesy of Dr. Chris Reilly Granulomatous Scleritis

Courtesy of Dr. Chris Reilly Granulomatous Scleritis

Courtesy of Dr. Chris Reilly Scleral Mineralization/Metaplasia

• Horses (mineralization) • Age associated change

• Sheep (, dorsal sclera) • Unclear significance; Smith et al, Vet Path, 2011

• (cartilage +/- , typically dorsal or near ON) • Unclear significance; Tusler CA et al. VO 2016 Epub.

• Fisher rats (bone +/- cartilage, dorsal sclera) • Age associated change Scleral Mineralization/Metaplasia Scleral Mineralization/MetaplasiaFigure 1. Sclera; sheep No. 1.

Alcian blue Type II collagen IHC J. D. Smith et al. Vet Pathol 2010;48:827-829

Copyright © by American College of Veterinary Pathologists Scleral Mineralization/Metaplasia

Tusler CA et al. VO 2016 Epub Scleral Mineralization/Metaplasia

Tusler CA et al. VO 2016 Epub