Histologic Basis of Ocular Disease in Animals

Foreword xiii

Acknowledgements xv

1 Fixation and processing of ocular tissues 1

Fixatives 1

Fixation and sectioning artifacts 2

Fixation techniques 3

Trimming the fixed globe 5

Electron microscopy 13

References 14

2 General pathology of the eye 15

Adaptations characterized by changes in cell size, number, or appearance 15

Neoplasia 19

Nomenclature 23

Distinguishing benign from malignant 25

Prognostication 27

Unsuccessful adaptation: cellular degeneration, necrosis, and apoptosis 27

Calcification, pigmentation, and cystic change 30

Ocular inflammation 32

Ocular manifestations of acute inflammation 34

Chronic inflammation 39

Ocular manifestations of chronic inflammation 39

Immune privilege 41

Lymphocytic–plasmacytic endophthalmitis 42

The sequelae of intraocular inflammation and other injuries 43

Limited regenerative ability 43

Susceptibility to scarring 43

Further reading 46

3 Congenital anomalies 49

Introduction 49

Defective organogenesis 50

Defective early organogenesis 50

Anophthalmos and cystic globe 53

Anophthalmos and microphthalmos 54

Cyclopia and synophthalmos 56

Congenital anomalies of lens 56

Congenital retinal nonattachment 63

Aniridia – iridal hypoplasia or aplasia 63

Coloboma 63

Defective later organogenesis 64

Neurectodermal defects 64

Multifocal retinopathies 71

Multiple ocular anomalies (MOA) in Rocky Mountain horses 71

Anomalies of surface ectodermal origin that develop during later organogenesis 73

Congenital adnexal cysts 73

Dermoids 73

Defects of neural crest migration and mesenchymal differentiation that develop in later organogenesis 73

Congenital corneal disease 73

Congenital disorders of neurocrest and mesenchymal tissues that manifest in the uvea during later organogenesis 74

Persistent pupillary membranes (PPMs) 74

Congenital glaucoma 75

Uveal hypoplasia 78

Collie eye anomaly (CEA) and related defects 78

Persistence of embryonic vasculature 81

References 83

4 Histopathology of ocular trauma 89

Perforating and penetrating wounds of the globe and ocular tissues 89

Perforating wounds of the globe 89

Traumatic intraocular hemorrhage 89

Expulsive subchoroidal hemorrhage 90

Sequelae of intraocular hemorrhage 90

Posttraumatic inflammation 95

Phacoclastic endophthalmitis and traumatic cataract 95

Infectious endophthalmitis 95

Trauma to individual ocular tissues 95

Orbit and optic nerve 95

Cornea/sclera 95

Uvea 100

Lens 101

Vitreous and retina 101

Globe as a whole 101

Reaction to foreign materials 101

Complications of ocular surgery 102

Chemical and thermal burns 102

Effects of radiant energy 103

References 103

5 Diseases of the eyelid, conjunctiva, lacrimal, and nasolacrimal systems 105

Eyelids 105

Structural disorders 105

Dermoids 105

Hamartomas 105

Subconjunctival fat prolapse 105

Entropion, ectropion, and medial canthal pocket syndrome 105

Distichiasis, districhiasis, and ectopic cilia 106

Inflammatory disease 108

Pyogranulomatous (granulomatous) blepharitis 108

Juvenile sterile granulomatous dermatitis and lymphadenitis (juvenile cellulitis) 110

Chalazion 110

Medial canthal erosion syndrome 111

Proliferative pox virus blepharitis in birds 111

Parasitic eyelid disorders 111

Demodicosis 111

Cnemidocoptes pilae (scaly beak) infestation of avian species 113

Eyelid tumors and neoplasms 113

Cystic apocrine hyperplasia (hidrocystomas, sudoriferous cysts, and apocrine cysts) 113

Granular cell tumor 113

Meibomian (tarsal gland) adenoma 115

Melanocytoma and melanoma 115

Histiocytoma 118

Mast cell tumor 118

Peripheral nerve sheath tumors 118

Equine sarcoid 121

Squamous cell carcinoma 122

Diseases of the conjunctiva 123

General pathology of the conjunctiva 124

Congenital conjunctival abnormalities 124

Infectious conjunctivitis 126

Herpesvirus 126

Chlamydophila (chlamydia) 126

Rickettsia rickettsi 126

Moraxella bovis 126

Parasitic conjunctivitis 126

Noninfectious inflammatory disease 127

Episclerokerataconjunctivitis 127

Lipogranulomatous conjunctivitis of cats 127

Eosinophilic conjunctivitis 128

Miscellaneous conjunctival disorders 128

Conjunctival overgrowth in rabbits (pseudopterygium) 128

Membranous (ligneous) conjunctivitis 129

Conjunctival neoplasms 129

Conjunctival lymphoma 129

Conjunctival mast cell tumors 130

Conjunctival melanoma and melanocytoma 130

Viral papillomas 133

Conjunctiva squamous papilloma 133

Conjunctival squamous cell carcinoma 133

Conjunctival vascular neoplasia 133

Miscellaneous neoplasms of the third eyelid 133

Lacrimal and nasolacrimal disorders 136

Neoplasms of the gland of the third eyelid 136

Prolapsed gland of the third eyelid 138

Keratoconjunctivitis sicca (KCS) 138

Dacryops and canaliculops 138

References 138

6 Diseases of the cornea 143

Corneal wound healing 143

Epithelial wound healing 143

Stromal wound healing 147

Endothelial wound healing 149

Epithelial and fibrous ingrowth 151

Healing of corneal grafts 152

Nonspecific corneal responses to insult 152

Corneal vascularization 152

Corneal pigmentation 154

Corneal edema 154

Keratitis 154

Epithelial alterations of keratitis 154

Stromal alterations of keratitis 156

Endothelialitis 158

Specific inflammatory corneal disease 159

Immune‐mediated nonulcerative keratitis 159

Immune‐mediated ulcerative keratitis 159

Superficial punctate keratitis (punctate erosive corneal dystrophy) 159

Chronic superficial keratitis (pannus) 159

Eosinophilic keratitis 161

Miscellaneous corneal disorders: corneal sequestrum, indolent corneal ulceration, corneal dystrophy, corneal lipid infiltrates, and corneal degeneration 161

Corneal sequestrum 161

Indolent ulceration (boxer ulcer, spontaneous corneal epithelial defects) 164

Corneal dystrophies, corneal lipid infiltrates, and corneal calcific/lipid degeneration 165

Miscellaneous corneal disease 167

Corneal neoplasia 172

References 177

7 Diseases of the episclera and sclera 181

Primary episcleral and scleral inflammatory disorders: a brief introduction 181

Secondary scleritis 181

Scleral neoplasia 182

Limbal melanocytoma 184

Episcleritis (episclerokeratitis, episclerokeratoconjunctivitis) 185

Scleritis and necrotizing scleritis a continuum or separate conditions? 189

Non‐necrotizing scleritis 193

Necrotizing scleritis 195

Parasitic episcleral disease (onchocerca vulpis/lienalis) 195

References 196

8 Histologic manifestations of disorders of the uvea 197

Normal aging changes 203

Degenerative diseases of the uvea 205

Uveal atrophy 205

Uveal cysts 205

Cystoid degeneration of the pars plana ciliary epithelium 205

Pre‐iridal fibrovascular membranes (PIFMs) 208

Heterotopic bony metaplasia of the ciliary body in guinea pigs 208

Uveitis 210

The nomenclature of uveitis 210

The intraocular events of uveitis 210

The etiologic implications of inflammatory exudates 216

Immune privilege 218

Consequences of uveitis 218

Histologic basis of the common infectious, idiopathic, and immune‐mediated uveitis syndromes in domestic animals 221

Lens‐induced uveitis 221

Phacolytic uveitis 223

Phacoclastic uveitis 224

Equine recurrent uveitis 227

Feline lymphocytic–plasmacytic uveitis 231

Pigmentary uveitis/pigmentary glaucoma of dogs 231

Equine heterochromic iridocyclitis with secondary keratitis 233

Vogt–Koyanagi–Harada‐like or uveodermatologic syndrome in dogs 233

Uveal xanthogranuloma in miniature schnauzers 235

Uveitis associated with specific infectious agents 235

Viruses 235

Feline infectious peritonitis 235

Canine adenovirus‐associated uveitis 238

Canine distemper virus‐associated uveitis 239

Bovine malignant catarrhal fever (MCF)‐associated uveitis 239

Bovine viral diarrhea mucosal disease‐associated uveitis 239

Ovine bluetongue 239

Equine viral arteritis (EVA)‐associated uveitis 239

West Nile‐associated avian uveitis 239

Hog cholera 239

Bacteria 240

Fungi 241

Other infectious causes for endophthalmitis 245

Algal endophthalmitis 246

Protozoan endophthalmitis 246

Metazoan parasitic uveitis 246

References 250

9 Histologic basis of glaucoma 255

Introduction 255

The gross, subgross, and histologic lesions of elevated IOP 255

Retinal changes 257

Optic nerve changes 262

Classification of canine glaucoma and introduction to open and closed angles 266

Congenital glaucoma 267

Primary glaucoma 270

Open angle glaucoma of beagle dogs 274

Primary (congenital) glaucoma in New Zealand white rabbit 274

Secondary glaucoma 274

Pre‐iridal Fibrovascular Membrane 274

Posterior Synechia with Pupillary Block 275

Vitreous degeneration, syneresis, and anterior chamber prolapse 275

Trabecular obstruction by tumor 278

Other causes of secondary glaucoma in dogs 278

Glaucoma in cats 283

Glaucoma in horses 284

References 286

10 Histologic manifestations of acquired and inherited diseases of the lens 289

Embryology and anatomy of the lens 289

Physiology of the lens 292

Pathology of the lens 292

Aging changes 294

Cataract 294

The classification of cataracts 294

The histopathology of cataract 294

The pathogenesis of cataracts 299

Etiologies of cataract 299

Lens luxation 302

Inherited lens zonular dysplasia 303

References 305

11 Acquired diseases of the vitreous 307

Primary disorders of the vitreous 310

Vitreous degeneration 310

Asteroid hyalosis 315

Posterior vitreous detachment 315

Synchisis scintillans 315

Uveal and neuroectodermal pigment and cysts within the vitreous and incidental parasitic encounters 317

Neovascularization 317

Conditions with secondary vitreous involvement 317

Vitritis 317

Vitreous hemorrhage 319

References 322

12 Histologic manifestations of retinal disease 325

Introduction 325

Retinal diseases by histologic pattern 328

Retinal atrophy 329

Inner retinal atrophies 329

The pathogenesis of retinal degeneration secondary to glaucoma 329

Retinal atrophy secondary to non‐glaucomatous optic nerve injury and vascular disease 335

Optic nerve hypoplasia/aplasia 336

Outer retinal (photoreceptor) atrophies 336

Inherited photoreceptor dysplasias and degenerations 336

Retinal detachment 340

Toxic and nutritional retinopathies 346

Fluoroquinolone‐induced retinal degeneration 346

Vitamin A deficiency 347

Vitamin E deficiency 347

Taurine deficiency 347

Light‐induced retinal degeneration 347

Sudden acquired retinal degeneration (SARD) and immune mediated retinopathy (IMR) of dogs 352

Diseases targeting the retinal pigment epithelium 352

Retinal pigment epithelial dystrophy (central progressive retinal atrophy) 352

Hereditary retinal pigment epithelial disorders (congenital stationary night blindness of briard dogs, multifocal retinopathies) 352

Canine multifocal retinopathy 354

Retinal pigment epithelial dysplasia in the royal college of surgeons rat 354

Localized chorioretinal atrophy in rats 354

Retinitis 354

Bystander retinitis 356

Retinitis as a manifestation of neurologic disease 356

Histophilus somni (formerly Hemophilus somnus) infection in cattle 356

Canine distemper 356

Retinal lesions reflecting noninfectious systemic disease 357

Retinal lesions of systemic hypertension 357

Retinal lesions resulting from inborn errors in the intermediary metabolism (lysosomal storage diseases and others) 357

Retinal injury from thermal energy 358

Retinal neoplasms 358

Medullopitheliomas 360

Retinoblastoma 360

References 360

13 Acquired diseases of the optic nerve 367

Intraocular disorders with associated optic neuropathy 367

Glaucomatous optic neuropathy 367

Endophthalmitis and ascending optic neuritis 372

Canine distemper optic neuritis 372

Orbital disorders that affect the optic nerve 372

Proptotic optic neuropathy 372

Orbital cellulitis/abscess with optic nerve sepsis 372

CNS conditions that affect the optic nerve 372

Optic nerve disorders 376

Granulomatous meningoencephalitis 376

Unilateral granulomatous optic neuritis 376

Optic neuropathy in horses 376

Feline optic neuropathies 376

Other causes of optic neuritis 378

Toxic optic neuropathy 378

Vitamin A deficiency 379

Primary optic nerve neoplasms 381

Meningioma 381

Optic nerve gliomas 382

Peripapillary medulloepitheliomas 382

Lymphosarcoma and other metastatic neoplasms 382

References 384

14 Acquired diseases of the orbit 387

Introduction 387

Inflammatory disease 387

Extraocular myositis 388

Lacrimal adenitis 389

Orbital trauma/hematoma 390

Zygomatic sialocoele 391

Orbital cysts and post‐enucleation orbital mucocoeles 393

Parasitic orbital disease 396

Orbital neoplasia 396

Multilobular tumor of bone (multilobular osteochondroma) 398

Primary orbital osteoma and osteosarcoma 402

Lacrimal adenoma and adenocarcinoma 404

Harderian gland adenomas and adenocarcinomas 404

Rhabdomyosarcoma 404

Orbital myofibroblastic sarcoma 404

Vascular anomalies 406

References 406

15 Intraocular neoplasia 409

Non‐neoplastic hyperpigmented lesions 410

Benign melanocytic neoplasia 410

Uveal melanocytoma 410

Uveal melanocytosis (melanosis) 415

Malignant uveal melanomas 415

Canine and feline uveal malignant melanoma 415

Diffuse iris melanoma of cats 417

Iris and ciliary epithelial neoplasia 422

Medulloepithelioma and retinoblastoma (primitive neuroectodermal tumors) 426

Primary ocular sarcomas of cats and rabbits 428

Schwannomas of blue eyed dogs 430

Osteosarcoma and chondrosarcoma 430

Miscellaneous primary intraocular tumors 432

Metastatic uveal neoplasia 433

Lymphosarcoma 433

Secondary intraocular neoplastic extension from primary nasal and orbital and adnexal neoplasms 435

References 436

Index 443

Bruce Grahn, DVM, Diplomate ACVO, ABVP, is Professor Emeritus of Veterinary Ophthalmology at the Western College of Veterinary Medicine, Prairie Ocular Pathology Service, University of Saskatchewan in Saskatoon, Saskatchewan, Canada.

Robert Peiffer, DVM, PhD, Diplomate ACVO, is Professor Emeritus of Ophthalmology and Pathology, School of Medicine at the University of North Carolina in Chapel Hill, North Carolina, USA.

Brian Wilcock, DVM, PhD, Honorary Diplomate ACVO, is Professor Emeritus of Pathology, Ontario Veterinary College at the University of Guelph and Owner of Histovet Surgical Pathology in Guelph, Ontario, Canada.