Essentials of Veterinary Ophthalmology

By Kirk N. Gelatt

Essentials of Veterinary Ophthalmology, Third Edition offers an updated introduction to the diagnosis and clinical management of ocular conditions in veterinary patients, providing trusted information in a user-friendly format.  The content of the book is distilled from the fifth edition of the gold-standard reference Veterinary Ophthalmology, emphasizing the information most relevant to veterinary students and general practitioners.  Fully updated throughout, the Third Edition focuses more strongly on small animals and horses, with streamlined coverage of other species, and new chapters have been added on morphology, physiology, and pharmacology.

Carefully designed to be equally useful for learning and in practice, the book offers a streamlined, practical approach, with bolded terms to enhance comprehension.  High-quality color photographs provide visual depictions of the conditions discussed.  Essentials of Veterinary Ophthalmology, Third Edition is an indispensable resource for veterinary students or clinicians wishing to hone their ophthalmology knowledge and skills.

• Language: English
• Publisher: Wiley
• Release date: Aug 6, 2014
• ISBN: 9781118771877

Book preview

Table of Contents

Title page

Copyright page

Preface

Acknowledgments

About the Companion Website

Section 1: Basics for Clinical Veterinary Ophthalmology

Chapter 1: Development of the Eye

Gastrulation and Neurulation

Formation of the Optic Vesicle and Optic Cup

Lens Formation

Vascular Development

Development of the Cornea and Anterior Chamber

Development of the Iris, Ciliary Body, and Iridocorneal Angle

Retina and Optic Nerve Development

Sclera, Choroid, and Tapetum

Vitreous

Optic Nerve

Eyelids

Extraocular Muscles

Chapter 2: Ophthalmic Structures

Adnexa: Protective Apparatus

Upper and Lower Eyelids

Conjunctivae

Third Eyelid: Nictitating Membrane

Lacrimal and Nasolacrimal System

Globe

Cornea

Sclera

Uvea

Lens

Vitreous

Retina

Optic Nerve

Vasculature of the Eye and Orbit

Chapter 3: Physiology of the Eye

Anterior Segment of the Eye

Tear Production and Drainage

Cornea

Drug Transport Through the Cornea, Limbus, Bulbar Conjunctiva, and Sclera

Iris and Pupil

Nutrition of Intraocular Tissues

Ocular Circulation

Ocular Barriers

Aqueous Humor and Intraocular Pressure

Lens

Vitreous

Ocular Mobility

Chapter 4: Optics and Physiology of Vision

Light and Vision

Refractive Structures of the Eye

Visual Processing: From Photoreceptors to Cortex

Visual Perception

Chapter 5: Ocular Pharmacology and Therapeutics

Drug Delivery and Pharmacokinetics

Barriers to Ocular Drug Delivery

Topical Administration

Drug Disposition after Eye Drop Application

Systemic Absorption

Topical Drug Delivery to the Posterior Eye Segment

Drug Delivery Kinetics and Ocular Bioavailability

Periocular Administration

Intraocular Administration

Sustained Drug Delivery to Intraocular Tissues

Systemic Administration

Other Methods of Ocular Drug Delivery

Antimicrobial Agents

Antibacterial Agents

Antifungal Agents

Antiviral Agents

Anti-Inflammatory and Immunosuppressant Drugs

Anti-Inflammatory Agents

Nonsteroidal Anti-Inflammatory Drugs

Immunosuppressant Drugs

Mydriatics/Cycloplegics, Anesthetics, and Tear Substitutes and Stimulators

Mydriatics/Cycloplegics

Local Anesthetics

Tear Substitutes and Stimulators

Drugs That Affect Aqueous Humor Dynamics and Intraocular Pressure

Parasympathomimetics (or Cholinomimetics)

Drugs Acting on Adrenoceptors

Carbonic Anhydrase Inhibitors

Prostaglandin Analogues

Osmotic Agents

Section 2: Ophthalmic Examination and Imaging

Chapter 6: Eye Examination and Diagnostics

History

General (Basic and Advanced) Ocular Examination

Restraint

Eyelid Akinesia

Regional Anesthesia/Analgesia

Ophthalmic Examination in Ambient Lighting

Tear Tests

Close Examination of the Adnexa and Globe

Intraocular Pressure Measurement and Pupil Dilation

Anterior Segment Examination after Pupil Dilation: Lens Examination

Posterior Segment Examination

Ophthalmic Diagnostic Procedures

Basic Ophthalmic Diagnostics

Advanced Ophthalmic Diagnostics

Ocular Imaging: Basic and Advanced Diagnostics

Basic Imaging Systems

Advanced Imaging Systems

Ophthalmic Imaging by Ultrasonography

Physics and Basic Principles

Examination Technique

Standard (10–12 MHz) Ultrasonographic Imaging

Advanced Ultrasound Imaging (20–100 MHz)

Color Doppler Ultrasound

Electrodiagnostic Evaluation of Vision

Flash Electroretinogram

Equipment for Recording and Light Stimulation

Patient Preparation

Anesthetic Protocol

ERG Results

Section 3: Canine Ophthalmology

Chapter 7: Canine Orbit: Diseases and Surgery

Clinical Signs/Examination

Ancillary Diagnostic Tests

Congenital Anomalies of the Orbit and Globe

Exophthalmos

Acquired Orbital Diseases

Surgery of the Globe and the Orbit

Chapter 8: Canine Eyelids: Diseases And Surgery

Structure and Function

Diagnostic Tests for Eyelids

Principles of Eyelid Surgery

Congenital and Presumed Heredity Structural Abnormalities

Entropion

Lid Trauma

Inflammations

Other Eyelid Diseases

Reconstructive Blepharoplasty

Other Eyelid Procedures

Chapter 9: Canine Nasolacrimal Duct and Lacrimal Secretory Systems: Diseases and Surgery

Nasolacrimal Duct System

Embryology

Anatomy

Physiology

Clinical Manifestations of Nasolacrimal Disease

Diagnostic Procedures

Congenital Diseases

Developmental Disorders

Acquired Diseases

Lacrimal Secretory System

Formation and Dynamics of Tear Components

Pathogenesis of Tear Film Disease

Tear Deficiency

Qualitative Abnormalities

Treatment

Cysts and Neoplasms

Chapter 10: Canine Conjunctiva: Diseases and Surgery

Conjunctiva

Functional Anatomy and Physiology

Normal Bacterial and Fungal Flora

Conjunctival Cytology

General Response to Disease

Infectious Conjunctivitis

Noninfectious Conjunctivitis

Follicular Conjunctivitis

Conjunctivitis Associated with Tear Deficiencies

Ligneous Conjunctivitis

Conjunctival Neoplasia

Non-neoplastic Conjunctival Masses

Conjunctival Hemorrhages

Foreign Bodies

Orbital Disease

Anatomic Abnormalities

Conjunctival Manifestations of Systemic Disease

Effects of Radiation

Surgical Procedures

Nictitating Membrane

Anatomy, Histology, and Function

Anomalous, Congenital, and Developmental Disorders

Neoplasia

Inflammatory Conditions

Trauma, Reconstruction, and Foreign Bodies

Nictitating Membrane Surgery

Chapter 11: Canine Cornea: Diseases and Surgery

Cornea

Anatomy

Corneal Clarity

Corneal Wound Healing

Corneal Pigmentation

Corneal Edema

Corneal Vascularization

Developmental Abnormalities and Congenital Diseases

Inflammatory Keratopathies

Descemetoceles and Corneal Perforations

Full-Thickness Corneal Lacerations

Nonulcerative Keratitis

Noninflammatory Keratopathies

Corneoscleral Masses and Neoplasms

Scleral Diseases

Episcleritis

Nodular Granulomatous Episcleritis

Chapter 12: Canine Glaucomas

Epidemiology of the Glaucomas in the Dog versus Man

Classification of the Glaucomas

Diagnostics Tests

Provocative Tests

Clinical and Pathologic Effects of Elevated Intraocular Pressure

Primary and Breed-Predisposed Canine Glaucomas

Secondary Glaucomas

Congenital Glaucomas

Medical and Surgical Treatment of the Canine Glaucomas

Chapter 13: Canine Anterior Uvea: Diseases and Surgery

Developmental Conditions

Degenerative Iridal Changes

Uveal Inflammation

Uveal Manifestations of Selected Diseases

Ocular Manifestations of Miscellaneous Diseases

Uveal Trauma

Hyphema

Non-Neoplastic Iridal Proliferations

Anterior Uveal Tumors

Uveal Surgery

Chapter 14: Canine Lens: Cataract, Luxation, and Surgery

Congenital and Developmental Abnormalities

Cataract Formation

Classification of Canine Cataract

Nuclear or Lenticular Sclerosis

Clinical and Biomicroscopic Features of Canine Cataracts

Cataracts with a Heritable or Presumed Heritable Basis

Cataracts Associated with Systemic Diseases

Cataracts Associated with Medications or Other Toxic Substances

Dietary Deficiencies

Injury to the Lens

Age-Related Cataracts

Cataracts Resulting from Inflammations and Lens-Associated Inflammation

Nonsurgical Clinical Considerations for Canine Cataracts

Medical Treatment of Cataracts

Dislocation of the Crystalline Lens

Cataract Surgery

Chapter 15: Canine Posterior Segment: Diseases and Surgery

Diseases of the Vitreous

Development and Anatomy

Morphology

Diagnostic Procedures

Therapeutic Procedures

Vitreal Diseases

Vitreous in Relation to Other Ophthalmic Disorders

Diseases of the Canine Ocular Fundus

Methods of Examination

Structural Visualization of the Fundus

Functional Testing of the Retina

Normal Canine Ocular Fundus

Developmental Anomalies

Inherited Retinal Degenerations/Dystrophies

Late-Onset Photoreceptor Degenerations

Other Generalized Retinopathies/Retinal Dystrophies

Retinal Pigment Epithelial Autofluorescent Inclusion Epitheliopathy/Retinal Pigment Epithelial Dystrophy

Inflammation and Infections Affecting the Ocular Fundus

Retinal Toxicities

Retinopathies of Nutritional Causes

Vascular Disease Processes

Retinopathies with Immunologic Diseases

Secondary Retinal Degenerations

Retinal Detachments: Medical Considerations

Neoplastic and Proliferative Conditions

Surgery of the Canine Posterior Segment

Anatomic Considerations for Vitreoretinal Surgeries

Retinal Detachment Treated by Surgery

Surgical Procedures for Treatment of Retinal Detachments

Gene Therapy

Diseases of the Canine Optic Nerve

Intraocular Optic Nerve

Vascular Supply

Clinical Examination

Diagnostics for the Optic Nerve

Electroretinography

Acquired Optic Nerve Diseases

Section 4: Special Species

Chapter 16: Feline Ophthalmology

Diseases of the Eyelids

Diseases of the Nasolacrimal and Tear Systems

Diseases of the Third Eyelid

Diseases of the Conjunctiva

Normal Cornea

Diseases of the Cornea

Diseases of the Anterior Uvea

Glaucoma

Diseases of the Lens and Cataract Formation

Diseases of the Posterior Segment

Diseases of the Optic Nerve and Central Nervous System

Diseases of the Orbit

Chapter 17: Equine Ophthalmology

Ocular Examination

Special Ophthalmic Considerations in Specific Groups of Horses

Diseases of the Orbit

Diseases of the Adnexa

Diseases of the Cornea

Diseases of the Uvea

Glaucoma

Diseases of the Lens

Diseases of the Posterior Segment

Diseases of the Optic Nerve

Chapter 18: Food Animal Ophthalmology

Cattle

Orbit

Eyelids

Nasolacrimal System

Conjunctiva and Cornea

Uveal Tract

Lens

Ocular Fundus

Sheep and Goats

Eyelids

Conjunctiva and Cornea

Uveal Tract

Lens

Ocular Fundus

Pigs

Orbit and Globe

Eyelids

Conjunctiva and Cornea

Uveal Tract

Lens

Ocular Fundus

Chapter 19: Exotic Animals: Ophthalmic Diseases and Surgery

Camelids

Examination Techniques

Ocular Medications

Ocular Anatomy

Ocular Diseases

Laboratory Animals

Examination Techniques

Lacrimal Gland Biology

Retinal Vasculature

Ocular Diseases

Rabbits

Ocular Anatomy

Intraocular Pressure and Tear Measurements

Ocular Diseases

Exotic Animals

Examination Techniques

Fish

Amphibians

Reptiles

Birds

Mammals

Marine and Other Aquatic Mammals

Section 5: Ophthalmic and Systemic Diseases

Chapter 20: Comparative Neuro-Ophthalmology

Neuro-Ophthalmic Examination

Neuroanatomic Lesion Localization and Neuro-Ophthalmic Syndromes

Neuro-Ophthalmic Diseases

Chapter 21: Systemic Disease and the Eye

Dogs

Congenital Diseases

Developmental Diseases

Acquired Diseases

Cats

Congenital Diseases

Developmental Diseases

Acquired Diseases

Horses

Congenital Diseases

Developmental Diseases

Acquired Diseases

Food Animals

Congenital Diseases

Developmental Disorders

Acquired Diseases

Appendix A: Adrenergics in Veterinary Ophthalmology

Appendix B: Artificial Tear Substitutes for Veterinary Ophthalmology

Appendix C: Topical and Local/Injectable Anesthetics for Veterinary Ophthalmology

Topical

Local/Injectable

Appendix D: Topical and Subconjunctival Antibiotics for Veterinary Ophthalmology

A.  Available Topical Antibiotics

B.  Selection of Initial Antibiotics on the Basis of Smear Morphology

C.  Development of Bacterial Resistance

D.  Suggested Dosages of Subconjunctival Antibiotics

Appendix E: Antiviral Drugs for Veterinary Ophthalmology (To Treat FHV-1 Ocular Infections)

Appendix F: Antifungals for Veterinary Ophthalmology

A.  Antifungals

B.  Selected Topical Antifungals Agents for Equine Fungal Keratitis/Fungal Abscesses

Appendix G: Carbonic Anhydrase Inhibitors (CAIs) for the Dog and Cat

Systemic (mg/kg): Single-Dose Studies in Dogs

Topical: 2–3× Daily

Recommended Clinical Multidoses

Appendix H: Corticosteroids in Veterinary Ophthalmology

A.  Topical Corticosteroids

B.  Depot Glucocorticoids for Subconjunctival Administration

Appendix I: Nonsteroidal Anti-inflammatory Drugs (NSAIDS) in Veterinary Ophthalmology

Appendix J: Hyperosmotics for Veterinary Ophthalmology

Topical

Systemic

Appendix K: Miotics in the Dog and Cat

Appendix L: Mydriatics or Pupil-Dilating Agents for the Dog

Appendix M: Mydriatics or Pupil-Dilating Agents for the Cat

Appendix N: Mydriatics or Pupil-Dilating Agents for the Horse

Appendix O: Mydriatics or Pupil-Dilating Agents for the Cow

Appendix P: Available Pupil Dilating Agents for Selected Birds

Appendix Q: Topical Prostaglandins for the Dog

Appendix R: Other Drugs for Veterinary Ophthalmology

Appendix S: DNA Tests for Feline and Canine Eye Diseases

Appendix T: Inherited Eye Diseases in the Dog

Appendix U: Inherited Eye Diseases in the Cat

Appendix V: Inherited Eye Diseases in the Horse

Appendix W: Inherited Eye Diseases in Food Animals

Appendix X: Lysosomal Storage Diseases in the Dog, Cat, and Food Animals

Glossary

Common Ophthalmic Roots

Common Words

Index

End User License Agreement

List of Tables

Table 1.1.  Sequence of Ocular Development in the Human, Mouse, and Dog

Table 1.2.  Sequence of Ocular Development in the Cow

Table 1.3.  Embryonic Origins of Ocular Tissues

Table 2.1.  Ratios of the Dimensions of the Globes of Domestic Species

Table 2.2.  Width and Height (mm) of the Cornea Measured in a Straight Line

Table 3.1.  Eyelid Reflexes

Table 3.2.  Adrenergic Receptors in the Iris and Ciliary Body

Table 3.3.  Estimates of Aqueous Humor Dynamics in Selected Species

Table 3.4.  Intraocular Pressures (IOP) in Selected Animal Species

Table 4.1.  Refractive Values in Selected Animal Species

Table 4.2.  Snellen Acuity in Selected Animal Species

Table 5.1.  Recommended Ophthalmic Antibiotic Choices Based on In Vitro Susceptibility of Organisms Isolated from Clinical Bacterial Keratitis Cases. Antibiotic (# Resistant/Total # Isolates Evaluated, % Resistant in Reference Indicated). Patient eyes vary for each antibiotic tested

Table 5.2.  Selected Antifungal Medications Used to Treat Keratomycosis

Table 5.3.  Summary of Selected Topically Administered Antiviral Drugs for Treatment of Feline Herpesvirus

Table 5.4.  Commercially Available Corticosteroid Agents for Subconjunctival Injection

Table 5.5.  Reported Activities of Commonly Utilized Mydratics in Dog, Cats and Horses

Table 6.1.  Fundus Magnification with Direct Ophthalmoscopy in Animalsa

Table 6.2.  Light Beam Selections for Direct Ophthalmoscopy

Table 6.3.  Topical Stains for Veterinary Ophthalmology

Table 6.4.  Normal Intraocular Pressure (IOP) Reported in Animals

Table 7.1.  Differential Diagnoses for Exophthalmos in the Dog

Table 7.2.  Recommended Treatment and Prognosis for Traumatic Proptosis in the Dog

Table 8.1.  Methods to Treat Distichiasis in the Dog

Table 8.2.  Site of Entropion in Selected Breeds

Table 8.3.  Surgical Procedures for Canine Entropion

Table 8.4.  Histogenic Classification and Frequency of Eyelid Tumors in Dogs

Table 10.1.  Summary of Cytology in Conjunctivitis

Table 11.1.  Dynamics of Corneal Healing after Corneal Ulceration

Table 11.2.  Types of Corneal Ulcerations in the Dog

Table 11.3.  Antiproteolytic Agents for Topical Treatment of Melting Ulcers

Table 11.4.  Breed Predisposition to Chronic Superficial Keratitis (Pannus), with Age of Onset Given When Available

Table 12.1.  Clinical Effects of Elevated Intraocular Pressure (IOP)

Table 12.2.  Clinical Signs of the Primary Glaucomas in the Dog

Table 12.3.  Treatments for the Secondary Glaucomas in Dogs

Table 12.4.  Intraocular Pressure (IOP) Controla

Table 13.1.  Clinical Signs of Uveitis

Table 13.2.  Recommended Therapies for Anterior Uveitis in the Dog

Table 13.3.  Diagnosis and Treatment of the Systemic Mycoses and Uveitis in the Dog

Table 14.1.  Inherited Cataracts in the Dog

Table 14.2.  Classification of Canine Cataracts Based on Maturity

Table 15.1.  Ophthalmoscopic Findings in Collie Eye Anomaly

Table 15.2.  Ophthalmoscopic Findings in Canine Retinal Dysplasia

Table 15.3.  Breeds of Dogs Affected with Retinal Dysplasia (RD)

Table 15.4.  Ophthalmoscopic Changes in Progressive Retinal Atrophy (PRA)

Table 15.5.  Characteristics of the Canine Retinal Photoreceptor Dysplasias

Table 15.6.  Characteristics of Canine Retinal Photoreceptor Degenerations

Table 15.7.  Ophthalmoscopic Changes in Chorioretinitis

Table 15.8.  Ophthalmoscopic Localization of Vitreal and Retinal Hemorrhages

Table 16.1.  Reported Eyelid Neoplasms in the Cat

Table 16.2.  Laboratory Diagnosis of Feline Herpesvirus 1 (FHV-1) in Cats

Table 16.3.  Laboratory Tests for the Feline Anterior Uveitides

Table 16.4.  Therapy for the Feline Uveitides

Table 17.1.  Treatment for Periocular Sarcoids

Table 17.2.  Treatment for Periocular Squamous Cell Carcinoma

Table 17.3.  Clinical Classification of Cataracts

Table 20.1.  Neuroanatomic Localization of Horner's Syndrome

Table 20.2.  Cavernous Sinus Syndrome

Table 21.1.  Ocular Toxicities with Selected Systemic Drugs in the Dog

Table 21.2.  Ophthalmic Diseases Associated with FHV-1 in the Cat

Table 21.3.  Treatment of FHV-1 Ophthalmic Diseases in the Cat

Table 21.4.  Selected Toxic Plants Producing Systemic and Ocular Disease in the Horse

Table 21.5.  Ophthalmic Manifestations of Selected Infectious Diseases in Food Animals

Table 21.6.  Selected Systemic Toxicities in Food Animals with Ophthalmic Manifestations

List of Illustrations

Figure 1.1.  Development of the optic sulci, which are the first sign of eye development. Optic sulci on the inside of the forebrain vesicles consist of neural ectoderm (shaded cells). The optic sulci evaginate toward the surface ectoderm as the forebrain vesicles simultaneously rotate inward to fuse. (Source: Cook C, Sulik K, Wright K. Embryology. In: Wright KW and Spiegel PH, eds. Pediatric Ophthalmology and Strabismus. St. Louis: Mosby–Year Book, 2003:3–53. Reproduced with permission of Elsevier.)

Figure 1.2.  Formation of the lens vesicle and optic cup. Note that the optic fissure is present, because the optic cup is not yet fused inferiorly. (A) Formation of the lens vesicle and optic cup with inferior choroidal or optic fissure. Mesenchyme (M) surrounds the invaginating lens vesicle. (B) Surface ectoderm forms the lens vesicle with a hollow interior. Note that the optic cup and optic stalk are of surface ectoderm origin. RPE, retinal pigment epithelium. (Source: Cook C, Sulik K, Wright K. Embryology. In: Wright KW and Spiegel PH, eds. Pediatric Ophthalmology and Strabismus. St. Louis: Mosby–Year Book, 2003:3–53. Reproduced with permission of Elsevier.)

Figure 1.3.  Cross-section through optic cup and optic fissure. The lens vesicle is separated from the surface ectoderm. Mesenchyme (M) surrounds the developing lens vesicle, and the hyaloid artery is seen within the optic fissure. RPE, retinal pigment epithelium. (Source: Cook C, Sulik K, Wright K. Embryology. In: Wright KW and Spiegel PH, eds. Pediatric Ophthalmology and Strabismus. St. Louis: Mosby–Year Book, 2003:3–53. Reproduced with permission of Elsevier.)

Figure 1.4.  The hyaloid vascular system and tunica vasculosa lentis. M, mesenchyme. (Source: Cook C, Sulik K, Wright K. Embryology. In: Wright KW and Spiegel PH, eds. Pediatric Ophthalmology and Strabismus. St. Louis: Mosby–Year Book, 2003:3–53. Reproduced with permission of Elsevier.)

Figure 2.1.  Canine orbit. Bones of the orbit shown: F, frontal; L, lacrimal; M, maxilla; S, sphenoid; T, temporal; Z, zygomatic. Orbital formina shown: A, rostral alar; E, ethmoidal; Op, optic; Or, orbital fissure.

Figure 2.2.  Equine orbit. Bones of the orbit shown: F, frontal; L, lacrimal; S, sphenoid; T, temporal; Z, zygomatic. Orbit foramina shown: A, rostral alar; E, ethmoidal; Op, optic; Or, orbital fissure; So, supraorbital.

Figure 2.3.  Divisions of the orbital fascia. MF, muscle fascia; OS, orbital septum; P, periorbita; T, Tenon's capsule.

Figure 2.4.  Orbital apex of the base in the dog, illustrating structures passing through the optic foramen and orbital fissure as well as the extraocular muscle attachments. (Source: Modified from Evans H, Christensen G. Miller's Anatomy of the Dog, 2nd edn. Philadelphia: WB Saunders, 1979. Reproduced with permission of Elsevier.)

Figure 2.5.  Surface anatomy of the dog's eye and adnexa at rest. A, medial canthus; B, lateral canthus; C, cilia; D, free margin of nonpigmented membrana nicitans; E, ciliary zone of iris; F, pupillary zone of iris; G, pupillary ruff; H, collarette.

Figure 2.6.  Surface anatomy of the cat's eye and adnexa at rest. Arrows show major arterial circle in the ciliary zone of the iris. A, medial canthus; B, lateral canthus; C, cilia; D, free margin of membrana nicitans.

Figure 2.7.  Upper eyelid of the dog. CF, cilia follicle; HF, hair follicle; O, orbicularis oculi muscle fibers; PC, palpebral conjunctiva; S, skin; TG, tarsal gland. (Original magnification, 10×.)

Figure 2.8.  Lower eyelid of the dog. The meibomian glands (MG) line the deep surface of the lid. Ciliary and sebaceous (SG) glands are closely associated with hair follicles (HF). (Original magnification, 100×.)

Figure 2.9.  Palpebral conjunctiva of a canine eyelid is externally lined by a stratified to pseudostratified columnar epithelium possessing numerous goblet cells (GC) near the fornix. (Original magnification, 250×.)

Figure 2.10.  Drawing of a histologic section of the mammalian nictitating membrane. (Source: Modified from Evans H, Christensen G. Miller's Anatomy of the Dog, 2nd edn. Philadelphia: WB Saunders, 1979. Reproduced with permission of Elsevier.)

Figure 2.11.  Nictitating membrane of the horse contains both glandular (G) and lymphoid (L) tissues, with the latter being superficially located within the stroma next to the bulbar surface (BS). C, Cartilage. (Original magnification, 10×.)

Figure 2.12.  The nasolacrimal system. C, canaliculi; LD, lacrimal ducts; LG, lacrimal gland; LS, lacrimal sac; ND, nasolacrimal duct; P, lacrimal puncta.

Figure 2.13.  Lacrimal gland of the cat. (Original magnification, 10×.)

Figure 2.14.  Diagram of the three basic coats or tunics that comprise the mammalian globe. Outermost fibrous tunic (yellow and white), consisting of the cornea (Co) and sclera (S); the middle tunic called the uvea (black), consisting of the choroid (Ch), ciliary body (CB) and the iris (I); and the nervous tunic or coat (gray) consisting of the retina (R) and optic nerve (ON), and epithelial lining (*) of the ciliary body and iris.

Figure 2.15.  Histologic view of the canine cornea, revealing four layers: anterior epithelium (AE), stroma (S), Descemet's membrane (DM), and endothelium (E). (Original magnification, 100×.)

Figure 2.16.  Anterior epithelia of (A) canine and (B) ovine corneas. BC, basal cells; SC, squamous cells; WC, wing cells. (Original magnification, 400×.)

Figure 2.17.  Basement membrane (arrows) of the anterior epithelium of the canine cornea viewed light microscopically with the aid of (A) PAS stain and (B) ultrastructurally. AE, anterior epithelium; HD, hemidesmosomes. (Original magnification: A, 400×; B, 18 000×.)

Figure 2.18.  Posterior cornea of a horse. PE, posterior epithelium (corneal endothelium); PLM, posterior limiting membrane (Descemet's membrane); PS, posterior stroma. (Original magnification, 1200×.)

Figure 2.19.  As the cornea ages, the Descemet's membrane continues to expand in width, as seen when comparing (A) a 1-year-old dog with (B) a 6-year-old individual. (Original magnification, 400×.)

Figure 2.20.  SEM of a 4-year-old canine corneal endothelium reveals occasional variability in cell size (A) and the lateral surface interdigitations between cells (B, arrowheads). The most prominent feature of the endothelial cell in the adult cornea is the nucleus (N), which bulges slightly into the anterior chamber. (Original magnification: A, 960×; B, 3500×.)

Figure 2.21.  Canine limbus. Overall view shows merging of the irregular connective tissue of the sclera (s) with the highly organized connective tissue of the cornea (c). (Original magnification, 400×.)

Figure 2.22.  The intrascleral plexus (ISP) of a dog is located within the midsclera (S), being interconnected to the angular aqueous plexus (AAP) by aqueous veins (AV) that are sometimes prominent in size. ESV, episcleral veins. (Original magnification, 125×.)

Figure 2.23.  Scleral ossicles (SO) in birds vary somewhat in size and shape, (A) being well developed with large interosseal spaces in owls (screech owl) (original magnification, 40×) and (B) comparatively thin in the chicken, with considerable overlap between adjacent ossicles (original magnification, 100×). CM, ciliary body musculature (Crampton's muscle); TM, trabecular meshwork.

Figure 2.24.  SEM of the canine anterior uvea. C, cornea; CM, ciliary body musculature; CP, ciliary processes; I, iris; S, sclera. (Original magnification, 25×.)

Figure 2.25.  Iris (I) and anterior ciliary body (CB) of the goat. The arrow points to the granular iridica, which extends posteriorly along the posterior pigment epithelium. C, cornea.

Figure 2.26.  In many canine irides, melanocytes are concentrated in a wide band anterior to the dilator muscle (DM), as seen in the lower half of this iris. MAC, major arterial circle. (Original magnification, 100×.)

Figure 2.27.  Sphincter muscle (SM) is located more posteriorly within the stroma of the iris in (A) the dog than (B) in the horse. The sphincter muscle in the young horse is capped by the granula iridica (GI), which is a proliferation of the posterior epithelium (PE). (Original magnification: A, 200×; B, 200×.)

Figure 2.28.  The canine iridal dilator muscle (DM) consists of a single layer of overlapping smooth muscle fibers. Apically, the nucleus (arrowheads) of each cell is partially surrounded by pigment granules. PE, posterior epithelium. (Plastic section; original magnification, 1000×.)

Figure 2.29.  Inner surface of the ciliary body of a dog previously treated with α-chymotrypsin to remove the lenticular zonules possesses thin ciliary processes (CP), which posteriorly give rise to smaller secondary folds (arrowheads). These folds flatten and disappear in the region called the pars plana (PP), which ends posteriorly at the adjoining retina, forming a line known as the ora ciliaris retinae (arrows). (Original magnification, 18×.)

Figure 2.30.  The ciliary epithelium that lines the processes and intervening valleys is bilayered. The outer layer is pigmented; the inner layer is nonpigmented. (A) Cross-section of a canine ciliary process. The bilayered epithelium, which is cuboidal, lines blood vessels (BV), which together form a blood–aqueous barrier. (Plastic section; original magnification, 250×.) (B) Longitudinal section of an equine ciliary epithelium at the base of a process. Both layers are considerably more columnar than those in the dog. (Original magnification, 400×.)

Figure 2.31.  The ciliary body muscle fibers (CM) are mostly oriented along the meridional plane in the dog. These fibers are interspersed with a variable amount of pigmentation. CP, ciliary process; S, sclera. (Original magnification, 40×.)

Figure 2.32.  Frontal-view SEM of the canine iridocorneal angle. Fibrous pillars that attach the iris (I) to the limbus form the pectinate ligament (PL). Arrowheads indicate smaller fibrous connections between these pillars and the uveal trabeculae located behind the pectinate ligament. (Original magnification, 160×.)

Figure 2.33.  The corneoscleral trabecular meshwork (CM) and adjacent angular aqueous plexus (AAP) in the dog. Asterisks indicate intertrabecular spaces. S, sclera. (Original magnification, 400×.)

Figure 2.34.  The canine choroid consists of the suprachoroidea (1), stroma with large blood vessels (2), stroma with medium-sized vessels and tapetum (3), and choriocapillaris (4). A, artery; R, retina; V, vein. (Original magnification, 40×.)

Figure 2.35.  The carnivorous tapetum lucidum consists of layers of cells, called iridocytes, which vary in number, size, and composition. (A) The dog. (B) The cat. (Original magnification: Both, 200×.)

Figure 2.36.  (A) Young horse lens near the equator. Anterior lens capsule (*). Arrows delineate the formation of the lens bow by the nuclei of the newly formed fibers. Open arrow points rostrally. (Original magnification, 500×.) (B) Newly formed canine secondary lens fibers are evenly hexagonal in cross-section. They form small ball-and-socket junctions (arrows) along their six angular edges. SEM. (Original magnification, 6600×.)

Figure 2.37.  The ringwulst, or annular pad (AP), of a screech owl's lens consists of radially arranged cells (arrows) that can withstand direct pressure placed on them. (Original magnification, ×200.) Insert, Overview of the annular pad. I, iris. (Original magnification, 20×.)

Figure 2.38.  Caudal-view SEM of ciliary processes and zonular attachments to the lens in a cat. Note the zonular fibers extending from the valleys and producing a cluster of fibers at their lenticular insertion with gaps between bundles. A, Posterior lens; B, ciliary process; C, posterior zonular fibers; D, anterior zonular fibers. (Original magnification, 40×.)

Figure 2.39.  The sensory retina consists of nine discrete layers and a supportive pigmented epithelium that forms an outer, tenth layer, as demonstrated by (A) the SEM in the pig and (B) the plastic section in the dog. The canine retina is rod dominant, being sparsely populated with cones (arrowheads and arrows). The porcine retina, compared to the dog, has a large population of cones and a smaller ratio of rods to cones. A, amacrine cell nuclei; B, bipolar cell nuclei; C, cone nuclei; G, ganglion cell nuclei; H, horizontal cell nuclei; M, Müller cell nuclei; 1, retinal pigment epithelium; 2, layer of rods' and cones' outer (OS) and inner segments (IS); 3, outer limiting membrane; 4, outer nuclear layer; 5, outer plexiform layer; 6, inner nuclear layer; 7, inner plexiform layer; 8, ganglion cell layer; 9, nerve fiber layer; 10, inner limiting membrane. (Original magnification: Both 250×.)

Figure 2.40.  The visual cell layer of the pig contains many cones (C) among the rods (R) within the area centralis, making this animal well suited for day vision. (Original magnification, 400×.)

Figure 2.41.  (A) The avian pecten, as seen here in the chicken, consists of a pleated vascular plexus that lies vitreally atop the optic nerve head (ON). (Original magnification, ×50.) (B) Close-up of the base of the pecten as it internally lines the nerve fibers (NF) that form the optic nerve head. BV, blood vessels of the pecten. (Original magnification, 250×.)

Figure 2.42.  The optic nerve head and optic nerve of a dog. Arrows indicate lamina cribosa; note the number of astrocytes anterior to it. C, choroid; CMK, central meniscus of Kuhnt (accumulation of astrocytes in physiologic cup); CRV, central retinal vein; PS, pial septa; RV, retinal veins; S, sclera. (Original magnification, 720×.)

Figure 3.1.  The precorneal film, as proposed by Butovich, Millar and Ham, demonstrates the very close interaction of lipid-binding proteins within the precorneal film and especially in its outer lipid component. (Source: Modified from Butovich, Millar and Ham. Understanding and analyzing meibomian lipids – a review. Current Eye Research 2008;33:405–420.)

Figure 3.2.  Pupillomotor pathways. 1, A descending, excitatory multisynaptic pathway leaving the hypothalamus and projecting through the sympathetic nervous system. 2, A descending, inhibitory multisynaptic pathway leaving the hypothalamus and projecting to the Edinger–Westphal nucleus. 3, An ascending, inhibitory system leaving the reticular formation and projecting to the Edinger–Westphal nucleus. 4, An ascending, inhibitory system leaving the dorsal horn and projecting to the Edinger–Westphal nucleus. Ant median N, anterior median nucleus; DL, dorsal cochlear nucleus; Ex cun N, external cuneate nucleus; Inf Ol, inferior olivary nucleus; IP, interpeduncular nucleus; Ped, cerebral peduncle; Pyr Tr, pyramidal tract; Red N, red nucleus; Sup col, superior colliculus; Sub nig, substantia nigra. (Source: Modified from Loewy AD, Araujo JC, Kerr FW. Pupillodilator pathways in the brain stem of the cat: anatomical and electrophysiological identification of a central autonomic pathway. Brain Res 1973;60:65. Reproduced with permission of Elsevier.)

Figure 3.3.  Chemical composition of the aqueous humor and lens. Water and protein are expressed as percentages of lens weight. Na+, Cl−, K+, and Ca²+ ions are expressed in μEq/mL of lens water. Other compounds are expressed in μmol/g of lens weight or μmol/mL of aqueous humor. AA, amino acids; RNA, ribonucleic acid.

Figure 4.1.  Refraction of light through various lenses. (A) A spherical convex lens with a power of 10 D focuses parallel light rays at a distance of 0.1 m. (B) A flatter, spherical convex lens with a power of 5 D focuses parallel rays at a distance of 0.2 m. (C) Parallel rays passing through a concave spherical lens diverge. A virtual image is formed by tracing back (dashed lines) the diverging rays.

Figure 4.2.  (A) In emmetropia, parallel light rays are focused on the retina. (B) In a far sighted (hypermetropic or hyperopic) eye, light rays are focused behind the retina. (C) In a near sighted, or myopic, eye, the light is focused in front of the retina.

Figure 4.3.  Spherical aberrations occur when light passes through the (A) lens and (B) cornea. In both cases, peripheral rays are refracted (bent) more than central rays. Therefore, the focal point of the peripheral rays is closer to the lens/cornea, while the focal point of the central rays is closer to the retina. The result is a blurred image. The distance between the two focal points is called spherical aberration and is measured in diopters.

Figure 4.4.  Photoreceptor pathways. In the fovea or area centralis region, each cone synapses with a single midget bipolar cell. This nonconvergent pathway provides for the high resolution vision which is characteristic of the cone pathway in the central retina (top right panel). In the more peripheral retina, several cones converge their output on a single diffuse bipolar, resulting in lower visual resolution (bottom right panel). The rod pathway is more complex, with a large number of rods converging on a single rod bipolar cell (RBC) (left panel). Its output is modulated by A17 and AII amacrine cells. DCB and HCB are depolarizing and hyperpolarizing cone bipolar cells, respectively, that output to ganglion cells (GC). Their input and output are modulated by horizontal cells (HC) and AII amacrine cells, respectively. (Source: Goldstein, E. B. (2005) Blackwell Handbook of Sensation and Perception, 2nd edn, Blackwell Publishing, Malden, MA. Reproduced with permission of John Wiley & Sons Ltd.)

Figure 4.5.  Dorsal view of the left hemisphere of the canine brain. The solid arrow points to the location of the cortical area of central vision in Beagles. The hollow arrow points to the location of the cortical area of central vision in Greyhounds. The vertical axis represents distance (cm) anterior (positive values) and posterior (negative values) to the interaural plane (IAP); the horizontal axis represents distance (cm) lateral to the midline. A, marginal sulcus; B, marginal gyrus; C, endomarginal sulcus; D, endomarginal gyrus. (Source: Ofri R, Dawson WW, Samuelson DA. Mapping of the cortical area of central vision in two dog breeds. Vet Comp Ophthalmol 1994;4:172–178.)

Figure 5.1.  Disposition of drugs instilled in the eye.

Figure 5.2.  Differences in kinetic profiles of drugs applied as eye drops or as a sustained-release delivery system. Following application of eye drops, a maximum drug concentration is achieved locally, and then drug levels exponentially decline (first-order kinetics) to subtherapeutic tissue concentrations until the next dose. With sustained-release drug delivery systems (i.e., ophthalmic insert or implant), a plateau level of drug distribution is achieved (zero-order kinetics), allowing constant drug release over time.

Figure 5.3.  Effect on intraocular pressure (IOP) of 0.005% latanoprost in the Beagle with primary open-angle glaucoma after (A) evening and (B) q12 h dosing.

Figure 6.1.  Horse skull depicting sites for the auriculopalpebral (a and b), palpebral (c), frontal/supraorbital (d), lacrimal (e), zygomatic (f), and infratrochear (g) nerve blocks.

Figure 6.2.  Corneal reflex: Corneal sensation is tested by means of a wisp of cotton wool contacting the peripheral cornea.

Figure 6.3.  (A) To obtain a conjunctival sample, for either microbiology or cytology, the swab is gently rolled in the lower conjunctival sac anterior to the third eyelid. This is facilitated by retropulsion to protrude the third eyelid. Care must be taken to ensure that the swab touches only the area of interest to avoid contamination from nearby structures, e.g. eyelids. (B) Instruments for corneoconjunctival cytology include the Kimura spatula (top), cytobrush (middle), and scalpel blade (bottom).

Figure 6.4.  Optics of direct ophthalmoscopy. The direct ophthalmoscope allows alignment of the observer's visual axis with a light beam, which is reflected via a mirror to illuminate the patient's fundus. Light rays emanating from the patient's eye form a real image on the observer's retina.

Figure 6.5.  Close direct ophthalmoscopy. The examiner must be as close as possible to obtain an optimal image with direct ophthalmoscopy. To achieve this, the examiner ideally should use the right eye to examine the patient's right eye and vice versa.

Figure 6.6.  Direct ophthalmoscope head. (A) Observer's side with viewing aperture, lens dial, quick lens switch, and diopter indicator. (B) Patient side with viewing hole and switches/dials allowing selection of beam size and shape, as well as light filters.

Figure 6.7.  (A) Fluorescein dye is available as a sterile impregnated paper strip and can be made into a solution by mixing with sterile water, saline, or eyewash. (B) Fluorescein dye stains the exposed hydrophilic corneal stroma in a large superficial corneal ulcer in a cat.

Figure 6.8.  Application of fluorescein dye. The fluorescein impregnated strip is moistened with, for example, sterile saline or eyewash, and then gently touched once on the dorsal bulbar conjunctiva, with the upper lid retracted. The eyelids are then closed or the animal allowed to blink to distribute the fluorescein across the ocular surface.

Figure 6.9.  Jones test (fluorescein dye passage test) in a 1-year-old Labrador Retriever with a swelling ventral to the medial canthus of the right eye. (A) Fluorescein dye flows onto the skin at the medial canthus of the right eye. (B) As viewed at the nostrils, the right nasolacrimal apparatus is occluded but the left nasolacrimal system is patent.

Figure 6.10.  A positive Jones result at the right nostril in a horse.

Figure 6.11.  Aqueous tear production accessed by the Schirmer tear test 1. The short folded end of the paper strip is placed in the lateral half of the lower conjunctival sac in order to measure both basal and reflex tear production.

Figure 6.12.  Corneal sensation can be assessed quantitatively by a Cochet–Bonnet esthesiometer. (Source: Courtesy of UW Madison Ophthalmology Service, Madison, WI, USA.)

Figure 6.13.  Positive Seidel test depicts a leaking corneal wound at 12 o'clock.

Figure 6.14.  Gonioscopy lenses can be divided into direct and indirect. (A) Direct gonioscopy lenses allow examination of the iridocorneal angle (ICA) opposite to the viewing position of the examiner, and create a real image. (B) Indirect goniolenses form a virtual image, which the observer examines from a frontal position.

Figure 6.15.  Koeppe lens in situ. The lens is retained by suction on the corneal surface, freeing the examiner's hands.

Figure 6.16.  Normal iridocorneal angle in a Flat Coated Retriever. (Source: Courtesy of Stuart Ellis, Riverbank Veterinary Centre, Ashton, Preston, Lancashire, UK.)

Figure 6.17.  Binocular indirect ophthalmoscopy with the Keeler Vantage head-mounted indirect ophthalmoscope in the dog. In this technique, the observer does not only have sterosis, but also one hand free to hold the patient's head and eyelids. (Source: Courtesy of Franck J. Ollivier.)

Figure 6.18.  Comparison of direct (A,D), panoptic (B,E), and indirect ophthalmoscopy (C,F). These photographs illustrate the different appearances in terms of magnification and orientation of the canine and equine ocular fundus with each of the three methods of ophthalmoscopy.

Figure 6.19.  The optics of binocular indirect ophthalmoscope allow the light from the indirect ophthalmoscope to illuminate the patient's ocular fundus. The image is split with a prism into both examiner's eyes, permitting stereopsis. The patient's fundus image is virtual and inverted.

Figure 6.20.  Monocular indirect ophthalmoscopy. The technique can be carried out with minimal equipment but stereopsis is lost and the observer relies on the help of an assistant to stabilize the patient's head.

Figure 6.21.  The panoptic ophthalmoscope is a good compromise between the direct and indirect methods of ophthalmoscopy proving a real image (neither inverted or reversed) and is intermediate in magnifications between the two. (Source: Courtesy of Franck J. Ollivier, Centre Veterinaire DMV, Montreal QC, Canada.)

Figure 6.22.  Selection of plastic and metal lacrimal cannulas suitable for performing a nasolacrimal flush in a small animal, e.g., dog and cat. Entry into the lacrimal puncta can be facilitated by cutting the end short and at an oblique angle.

Figure 6.23.  Nasolacrimal flush in a dog. With a 2–5 mL syringe of sterile saline or eyewash attached to the cannula, and the upper lid everted to expose the upper punctum, the cannula is inserted into the dorsal punctum in a ventromedial direction, following the line of the upper canaliculus.

Figure 6.24.  Paracentesis. (A) Aqueous paracentesis. The hypodermic needle is inserted (bevel up) through the clear cornea immediately adjacent to the limbus or the subconjunctival limbus. A tunneling motion faciliates passage through the sclera or cornea. The needle must enter the anterior chamber anterior to the iris and be directed parallel with the iris. (B) Vitreous paracentesis. The hypodermic needle is inserted posterior to the limbus (5–7 mm in the dog and 10–12 mm in the horse) and firmly tunneled through the sclera and pars plana of the ciliary body. The needle must be directed toward the posterior pole to avoid the lens. (Source: Courtesy of Simon Scurrell, Willow Referral Service, Shirley, West Midlands, UK.)

Figure 6.25.  Retinoscopy carried out in a dog. Note the working distance of 67 cm between examiner and patient. The skiascopy bar or rack is positioned in front of the dog's eye; it contains a series of plus and minus spherical lenses in increments of 0.5–1.0D to quantify the eye's refractive error.

Figure 6.26.  Use of a handheld slit-lamp biomicroscope in a dog.

Figure 6.27.  Indentation tonometry. (A) Schiotz tonometer with 7.5 and 10.0 g weights. (B) Schiotz tonometer use in a cat.

Figure 6.28.  Applanation tonometry. (A) TonoPen-Vet. (B) The footplate contains a central pressure-sensitive tip that protrudes from and is surrounded by an insensitive ring. (C) The tip is covered by a disposable latex membrane that protects the sensitive plunger and prevents disease transmission. (D) TonoPen-Vet use in a dog.

Figure 6.29.  Rebound tonometry with the TonoVet in a dog.

Figure 6.30.  Reformatted sagittal CT images of a normal feline globe seen in the soft tissue window (W 426, L 55). (Source: Courtesy of Paul Mahoney, Willows Veterinary Centre & Referral Service, Solihull, UK.)

Figure 6.31.  (A) Dacryocystorhinogram of the normal nasolacrimal duct system of a 9-year-old West Highland white terrier. The cannula placed via the upper punctum into the lacrimal sac is visible (small arrow). Contrast medium is present at the nares and refluxing into the nasal cavity (large arrow). Note that the metallic pulse oximetry device is superimposed over the rostral nares and maxillary region. (B) Dacryocystorhinogram of a 3-year-old Labrador Retriever with chronic dacryocystitis affecting the right side. Obstruction of contrast is evident at the level of the third upper premolar tooth (arrow). Proximal to the obstruction there is an irregular cystic dilation of the duct. No contrast is visible distal (rostral) to the obstruction.

Figure 6.32.  The appearance of the normal canine globe and orbit on (A) dorsal T1- and (B) T2-weighted MRI. (A) The dorsal T1 image shows hyperintense retrobulbar fat, lens capsule, iris, and ciliary body. The aqueous humor and vitreous humor have a slightly lower signal when compared with muscle, and the normal lens has low signal characteristics. (Source: Courtesy of Paul Mahoney, Willows Veterinary Centre & Referral Service, Solihull, UK.)

Figure 6.33.  (A) Noncontact specular microscopy being undertaken on an anesthetized Beagle cross-bred dog. (B) Specular microscopy image of the central corneal endothelium of a normal 9-month-old cross-bred dog. (Source: Courtesy of Matthew Chandler, Animal Eye Clinic of North Florida, Jacksonville, FL, USA.)

Figure 6.34.  Optical coherence tomography (OCT) with 3D reconstruction images of the fundus of a normal, 15-week-old domestic shorthair kitten fundus. (Source: Courtesy of Laurence Occelli and Simon Petersen-Jones, Michigan State University, East Lansing, MI, USA.)

Figure 6.35.  Normal equine fluorescent antibody image with maximal fluorescence (retinal arterial and venous phase). (Source: Molleda J.M., Cervantes I., Galan A., et al. (2008) Fluorangiographic study of the ocular fundus in normal horses. Veterinary Ophthalmology.11(1), 2–7. Reproduced with permission of John Wiley & Sons Ltd.)

Figure 6.36.  (A) Standardized diagnostic A-mode probe with tissue model for calibration. (B) Ocular ultrasound probes. Top: Diagnostic 10-MHz probe. The white marker on the probe designates the upper portion of the echogram. Middle: High-frequency (20 MHz) B-mode probe. Bottom: Standardized diagnostic 8-MHz A-mode probe.

Figure 6.37.  Vertical axial scan. The white marker on the probe points dorsally.

Figure 6.38.  Normal B-mode/vector A-scan echogram of the canine eye. The integrated vector A-scan is displayed in the bottom half of the echogram. Echoes appear as bright lines or dots of different intensity on B-mode, and as vertical spikes from a horizontal baseline on the A-scan vector. In axial vertical direction (white marker points dorsally), the posterior lens capsule produces a strong echo A-mode and B-mode (arrows). The strong posterior eye wall echo contrasts against the acoustically empty vitreous.

Figure 6.39.  Ciliary body tumor (T) invading the vitreous and causing a lens subluxation (arrow).

Figure 6.40.  B-mode ultrasound of a long-standing retinal detachment, which appears as a T-shaped membrane (closed funnel).

Figure 6.41.  B-mode/vector A-scan echogram of a retrobulbar abscess in a Miniature Schnauzer. The abscess (A) is anechoic in the center and surrounded by a thick, highly reflective wall. It can be clearly distinguished from the surrounding orbital tissues. The corresponding vector A-scan shows the low echogenicity within the cystic abscess and the high posterior wall echo (arrows).

Figure 6.42.  Ultrasound biomicroscopy (50 MHz) of the iridocorneal angle (ICA) of a dog. A, cornea; B, sclera; C, basal iris; D, pectinate ligaments; and E, ciliary cleft.

Figure 6.43.  Color Doppler images (top) and pulse waves (bottom) of the short posterior ciliary arteries (SPCA; arrows) of a normal (A) and (B) glaucomatous Beagle. Comparisons of the normal to the glaucomatous Beagle's SPCA Doppler blood flow parameter indicated decreased end-diastolic velocities (EDV) and increased resistive indexes compared to the normal dogs. (Source: Courtesy of Kathleen Gelatt-Nickolson, North Florida Radiology, Gainesville, FL, USA.)

Figure 6.44.  A dark-adapted canine electroretinogram (ERG) in response to a brief, bright flash. Both rod and cone photoreceptors drive this response. OP, oscillatory potential.

Figure 6.45.  (A) The corkscrew, needle, and button-type electrodes are reliable and easy to use as reference and ground electrodes, as well as active electrodes for visual evoked potentials (VEPs) in animals. The JET electrode is a monopolar corneal contact lens electrode that can be used in many species, such as the cat and dog. (B) The gold-foil electrode can be used as an active electrode for recording the equine electroretinogram (ERG). The plastic foil is bent over the rim of the lower eyelid so the gold-coated side touches the corneal surface.

Figure 6.46.  Two types of stimulators for flash electroretinograms (FERGs) and flash visual evoked potentials (FVEPs). (A) Both the stimulus and background light intensities need to be measured to ensure that a known amount of light is delivered to the patient's eye. The detector of the photometer is positioned at the level of the eye of a patient. A xenon flash and a halogen bulb, used for steady adapting light, are built into the aluminum housing on top of this full-field (Ganzfeld) stimulator. (B) A handheld stimulator (mini-Ganzfeld) is easy and convenient to use in large animals, but can be also used in small animals. The stimulator should be held close to the eye without disturbing the corneal electrode.

Figure 6.47.  Four electroretinogram (ERG) responses from a normal dog. (A) A mixed, dark-adapted rod–cone response. The small positive deflection just below the letter is a stimulus artifact, which shows when a brief, white flash (3.0 cd/m²/s) is delivered. The response has a conspicuous, negative a-wave followed by the large, positive b-wave. Superimposed on the ascending limb are a few OPs (open arrow). The peak of the b-wave is bipartite where the later peak reflects the slower rod b-wave (black arrow). (B) A dark-adapted, mainly rod-driven ERG in response to a dim white flash (0.03 cd/m²/s). Note that there is no obvious a-wave and that the implicit time of the b-wave is similar to the rod-driven peak in A. (C) A cone response to a bright, white flash (3.0 cd/m²/s) presented on a rod-saturating background (40 cd/m²). The amplitude is considerably smaller than that of the dark-adapted responses, but both an a- and a b-wave can be seen. (D) A cone-driven response to a bright, white flickering stimulus (30 Hz) in the presence of the steady, adapting light.

Figure 7.1.  Canine skull demonstrating the lack of an osseous orbital floor, rendering the orbital contents susceptible to penetrating trauma through the roof of the mouth.

Figure 7.2.  Ultrasonography of an orbital neoplasm (meningioma) in a 10-year-old Collie. There is marked indentation of the caudonasal globe.

Figure 7.3.  Ultrasound probe placement for a transoral approach to the orbit.

Figure 7.4.  Orbital foreign body in a 6-year-old dog. (A) Dog at initial presentation with chronic purulent discharge of the right eye. (B) Fistulous tract in the dorsal conjunctival fornix.

Figure 7.5.  Transoral abscess drainage technique.

Figure 7.6.  Distended excretory duct resulting from adenitis of the zygomatic salivary gland.

Figure 7.7.  Masticatory muscle myositis in a German Shepherd. There is marked swelling of the masticatory muscles and bilateral exophthalmos, which is more marked in the left eye. (Source: Courtesy of Ingo Walde, Faculty of Veterinary Medicine, Vienna, Austria.)

Figure 7.8.  Bilateral extraocular polymyositis in an 8-month-old Golden Retriever.

Figure 7.9.  A 12-year-old Rough Collie with nictitans protrusion, exophthalmos, and dorsolateral displacement of the globe. Orbital lymphoma was suspected based on an ultrasound-guided fine-needle aspirate (FNA). A polymerase chain reaction (PCR) assay for antigen receptor rearrangement (PARR) confirmed the diagnosis of lymphoma.

Figure 7.10.  Proptosis of the right globe in a young Golden Retriever. There is entrapment of the eyelids as well as severe swelling and hyperemia of the bulbar conjunctiva. The cornea has already been protected with an ointment.

Figure 7.11.  Severe proptosis with avulsion of the optic nerve and several extraocular muscles in a Cocker Spaniel. Despite the clear and intact anterior segment, enucleation was inevitable.

Figure 7.12.  Enucleation: subconjunctival approach. (A) Incision of the bulbar conjunctiva. (B) After transection of the extraocular muscles close to their scleral attachments, the optic nerve is clamped and severed. (C) The orbit is packed with a gauze sponge and the nictitating membrane resected. (D) Excision of the lid margins. (E,F) Closure of the periorbital and deep fascial layers with a continuous suture pattern, after removal of the gauze sponge. Skin closure with simple interrupted or continuous sutures.

Figure 7.13.  (A) Dog with intrascleral prostheses in both eyes. (B) Close-up of right eye showing mild corneal neovascularization, pigmentation, and fibrosis of the cornea.

Figure 8.1.  Cross-section through the canine lid. 1, Eyelash-like hair on the lateral part of the upper lid; 2, Zeis/Moll glands; 3, meibomian gland; 4, mucus cells conjunctiva; 5, fornix; 6, scleral conjunctiva; 7, nictitating membrane gland; 8, orbicularis oculi muscle; 9, tarsal plate.

Figure 8.2.  Muscles of the lids of the left eye of the dog. 1, Orbicularis oculi muscle; 2, lateral palpebral ligament or retractor anguli oculi lateralis; 3, medial palpebral ligament; 4, malaris muscle; 5, levator palpebrae muscle; 6, levator anguli oculi medialis muscle.

Figure 8.3.  The ends of the upper lid or lateral canthus sutures can be caught or linked together in an outer-placed suture to prevent irritation of the cornea.

Figure 8.4.  Pathologic ankyloblepharon. Delayed eyelid opening in a puppy has resulted in ophthalmic neonatorum with pus extruding from the medial canthus.

Figure 8.5.  Distichiasis (hairs in or on the lid margin) emerging from the meibomian (1), Zeis, or Moll (2) gland openings. 3, Tear film; 4, cornea.

Figure 8.6.  Cryodestruction of multiple distichiae in the conjunctiva–tarsal plate in a dog.

Figure 8.7.  Entropion correction by retraction sutures (tacking). The sutures can be maintained for at least 2–3 weeks. The scar tissue tube formed around the suture material will result in moderate permanent correction. (A) Simple, interrupted sutures. (B) U-figure suture, with the disadvantage that the needle points in the direction of the cornea during suturing.

Figure 8.8.  Celsus–Hotz procedure for the correction of severe lower lid entropion with corneal ulceration. (A) The skin is incised at about 2.5 mm (as near as possible to the margin for better prediction of the entropion correction, but with enough space for skin suturing) from and parallel to the lid margin (B). (C) The skin plus orbicularis muscle are excised [not deeper: canaliculus and (sub)conjunctival tissues should not be damaged]. The lid margin should no longer show spontaneous intention of inward rolling. (D) The skin is sutured with material not exceeding 5-0 (e.g., nonabsorbable silk or absorbable, especially in difficult-to-handle animals, mono- or poly-filament), using a fine, round-body needle with or without a micropoint. Continuous sutures alone are not used because of the risk of rupture of the suture material when rubbed, resulting in dehiscence of the entire wound. The first sutures are placed at the medial and lateral ends, and the rest of the wound is closed by halving the intervals in the following order 1, 2, 3, 4, and so on. The distance between sutures is 2–2.5 mm. Alternatively, the intervals of the simple interrupted sutures can be made at about 4 mm and thereafter the remaining wound intervals closed by a continuous suture. (E) Secondary upper eyelid trichiasis to the lower, caused by postoperative lower lid conjunctival swelling, can be prevented by tacking of the upper lid (5).

Figure 8.9.  Pronounced macroblepharon–ectropion (diamond-shaped fissure) in a Blood Hound. The stretched fissure length was 48 mm. There is also some medial and lateral entropion, and a notch or kink in the lower lid margin. Note that the lower lid hangs in the middle, about 15 mm away from the third eyelid–cornea and is not really everted in an ectropion position. This results in chronic exposure and secondary conjunctivitis.

Figure 8.10.  Kuhnt–Szymanowski procedure, modified by Blaskovics and further by Fox and Smith for ectropion–macroblepharon to avoid splitting the lid margin. Use in the dog was first described by Munger–Carter. (A,B) The skin incision is 2–2.5 mm below the eyelid margin and extends 5–10 mm beyond the lateral canthus. The skin flap is dissected from its deeper muscle layers. All bleeding has to be arrested. (C,D) Equal-sized wedges, one of the lid margin conjunctiva and one of the skin are excised with scissors. The lid margin is apposed by a figure-of-eight or figure-U 5-0 to 6-0 suture. If desired, the conjunctival wound can be sutured by a subconjunctival, simple, continuous, 8-0 absorbable suture. The skin defect is apposed by simple, interrupted, 5-0 to 6-0 sutures. Advantage: staggering wound, less damaging to the lid margin. Disadvantage: shortens only the lower lid.

Figure 8.11.  The Roberts–Jensen pocket method for lid fissure length reduction by permanent medial or lateral tarsorrhaphy. (A) The procedure starts with the removal of the outside lid margin and the inside margin plus meibomian glands. If performed in the medial canthus, the upper lacrimal punctum is incised in the procedure. (B) Flap of upper conjunctiva is pulled downward into the pocket in the lower lid between the conjunctiva and muscle–skin layers, and anchored through the muscle–skin with a simple, interrupted, 5-0 suture. (C) Apposition of the new lateral or medial canthus by a figure-of-eight, 5-0 to 6-0 suture, and further closure by simple interrupted sutures.

Figure 8.12.  For the treatment of nasal fold trichiasis, the nasal folds can be excised. (A) The nasal folds are clamped and carefully excised with curved Mayo scissors. (B) The wound edges are apposed with simple, interrupted, 5-0 to 6-0 sutures. The first sutures are placed at the upper and lower ends and at the medial canthus; then, the rest of the wound is closed by halving the intervals.

Figure 8.13.  Chronic staphylococcal blepharitis in an adult dog. (Source: Courtesy KN Gelatt.)

Figure 8.14.  Eyelid pyogranulomas of the upper lid and lateral canthus in a Miniature Poodle. (Source: Courtesy of KN Gelatt.)

Figure 8.15.  Immune-mediated medial canthal blepharitis in an adult mongrel German hunting dog. The dog also has bilateral chronic superficial keratitis.

Figure 8.16.  Preoperative (A) and postoperative (B) appearance of an adenoma in the lateral upper eyelid in a 9-year-old Dalmatian.

Figure 8.17.  Temporary tarsorrhaphy. After, for example, a canthotomy and repositioning of a luxated or proptosed globe, a temporary tarsorrhaphy can be performed. The lid fissure is closed by two or three U-figure sutures, and these are prevented from cutting into the skin by, for example, infusion tubing.

Figure 9.1.  Strategy and procedures for diagnosis and treatment of nasolacrimal (drainage) disease. (Character of the ocular discharge is mainly serous or seromucus. If the ocular discharge is mucopurulent or purulent, see Chapter 10.)

Figure 9.2.  Embryologic development of the canine nasolacrimal system. (A) Note the nasolacrimal groove between the lateral nasal fold and the maxillary process at approximately day 21 of gestation in the dog. (B) The lateral nasal fold fuses with the maxillary process between days 22 and 26. This fusion buries the surface ectoderm cells, which will grow and form the nasolacrimal duct system. (C) The ectodermal cells form a cord with two proximal processes that extend toward the medial upper and lower eyelid, whereas the distal end grows toward the nostril. This ectodermal cord canalizes and becomes a duct and canaliculi shortly after birth.

Figure 9.3.  Gross anatomy of the canine nasolacrimal duct system. Note the relationship of the eyelids, puncta, canaliculi, lacrimal sac, nasolacrimal duct, and nasal puncta.

Figure 9.4.  12-week-old Papillion puppy with bilateral inferior punctal atresia, resulting in marked epiphora.

Figure 9.5.  Ventral punctual atresia. Note the ballooning of the conjunctiva over the aplastic punctum (A) during a normograde nasolacrimal flush through the superior punctum. The ballooning conjunctiva is excised with scissors (B) to create a new punctum.

Figure 9.6.  Anomalies of the medial canthus of the small-breed of dogs that predispose to epiphora and pigmentary keratitis. Note the caruncular trichiasis, the tight medial canthal ligaments that create a medial canthal trough, and the medial ventral entropion that compress the ventral lacrimal punctum and canaliculus.

Figure 9.7.  A superior punctual and canalicular foreign body that was causing darcyocystitis in a 2-year-old Lhasa Apso. Note the mucopurulent ocular discharge and conjunctivitis.

Figure 9.8.  Scanning electron micrograph of the bulbar surface of the canine third eyelid (nictitating membrane). A nictitans ductile opening onto the posterocentral surface of the third eyelid is well visualized. (Original magnification, 800×).

Figure 9.9.  Acute-onset keratoconjunctivitis sicca in a 5-year-old female Pug with mucopurulent discharge, hyperemic conjunctiva, and an infected axial corneal ulcer, stromal malacia, diffuse corneal edema, and ciliary flush.

Figure 9.10.  A 4-year-old Boston Terrier with early keratoconjunctivitis sicca. Note the mucoid ocular discharge, moderate conjunctival hyperemia, and mild chemosis. This eye had a Schirmer tear test 1 of 8 mm wetting/min.

Figure 9.11.  Dog with early keratoconjunctivitis sicca. Note the intense conjunctival hyperemia, thick mucopurulent discharge, and chronic keratitis characteristic of a subacute or chronic tear deficiency.

Figure 9.12.  A 6-year-old male castrated, mixed-breed dog with chronic keratoconjunctivitis sicca. Note the marked conjunctival hyperemia, lackluster appearance to the corneal surface, and superficial corneal neovascularization.

Figure 9.13.  Tear film break-up time(TBUT) test can be performed in the dog with some difficulty. Immediately after instillation of one drop of topical fluorescein stain, the eyelids are digitally held open, and the dispersion of fluorescein is observed with a portable slit-lamp biomicroscope using a cobalt blue filter. The TBUT is the mean time for the development of dark (dry) spots in the precorneal film.

Figure 9.14.  (A) A 10-year-old male castrated Shih Tzu with chronic keratoconjunctivitis sicca. The condition had been treated intermittently with topical antibiotics and corticosteroids and twice-daily topical cyclosporine therapy for 4 years. (B) Same dog after substituting topical 0.02% tacrolimus ointment for the cyclosporine therapy. Patient exhibited marked improvement with less mucopurulent ocular discharge and ocular comfort.

Figure 9.15.  A 7-year-old female spayed Yorkshire Terrier 3 months after parotid duct transposition, showing precipitates on the ocular surface and eyelids.

Figure 10.1.  Clinical strategy for the diagnosis and treatment of conjunctivitis of the dog.

Figure 10.2.  Neutrophils, cocci, and conjunctival epithelial cells in a cytologic specimen from a dog with bacterial conjunctivitis. (Diff Quik; original magnification, 33×.)

Figure 10.3.  Dog with experimentally-induced recurrent canine herpesvirus-1 conjunctivitis in a dog. (Source: Courtesy of Eric Ledbetter, Cornell University, Ithaca, NY, USA.)

Figure 10.4.  Chemosis in a dog associated with a bee sting.

Figure 10.5.  Follicular conjunctivitis involving the bulbar conjunctiva of the nictitating membrane.

Figure 10.6.  Multiple papillomas on the skin and bulbar conjunctiva. (Source: Courtesy of Nancy McLean, VCA Veterinary Care Animal Hospital and Referral Center, Albuquerque, NM, USA.)

Figure 10.7.  Nodular fasciitis on the temporal aspect of the globe. An immature cataract is also present.

Figure 10.8.  Conjunctival dermoid with hair at the temporal aspect of the globe.

Figure 10.9.  Onchocerca granuloma in the ventral bulbar conjunctiva. (Source: Courtesy of Nancy McLean, VCA Veterinary Care Animal Hospital and Referral Center, Albuquerque, NM, USA.)

Figure 10.10.  Conjunctival hemorrhage secondary to trauma in a dog. Note the miosis indicating anterior uveitis, which is also a result of the trauma.

Figure 10.11.  Severe conjunctivitis associated with systemic and retrobulbar blastomycosis.

Figure 10.12.  Petechial and ecchymotic hemorrhages are present on the conjunctiva of the nictitating membrane in a dog with thrombocytopenia.

Figure 10.13.  Pedicle bulbar conjunctival graft. A viable conjunctival graft 2 weeks post surgery. Multiple vessels are seen extending to the edges of the graft. The polyglactin 910 sutures are still present.

Figure 10.14.  Completely encircling nictitating membrane in an American Cocker Spaniel.

Figure 10.15.  Eversion of the cartilage of the nictitating membrane in a Great Dane.

Figure 10.16.  Prolapse of the gland of the nictitating membrane (cherry eye) in an English Bulldog.

Figure 10.17.  Strategy for diagnosis and treatment of protrusion of the nictitating membrane.

Figure 10.18.  Adenoma of the gland of the nictitating membrane.

Figure 10.19.  Plasma cell infiltration of the nictitating membrane, plasmoma, in a German Shepherd.

Figure 11.1.  The canine cornea.

Figure 11.2.  Keratomalacia in a dog with bacterial keratitis.

Figure 11.3.  Superficial corneal pigment in a Pug with chronic pigmentary keratitis.

Figure 11.4.  Pigment deposits on the endothelial surface of the cornea resulting from the rupture of uveal cysts. Several intact uveal cysts remain in the anterior chamber and adjacent to the corneal endothelium.

Figure 11.5.  Afghan Hound with diffuse corneal edema after CA-1 vaccination.

Figure 11.6.  Dermoid, or choristoma, at the temporal limbus in a young dog.

Figure 11.7.  Complete incision superficial keratectomy. (A) The initial corneal incision, which may be round, square, or triangular, should completely surround the lesion to be removed and can be made using a corneal trephine, diamond knife, or microsurgical blade. (B,C) After the initial incision is made, the edge of the tissue to be removed is grasped by a forceps, and a corneal dissector (e.g., Martinez corneal dissector, Beaver #64 microsurgical blade, iris spatula) is introduced and held parallel to the cornea. The dissector is used to separate the corneal lamella without penetrating deeper than the original incision. The cornea is then separated until the opposite incision line, or limbus, is reached. (D) Scissors may be needed to connect the dissection to the opposite incision or to remove the corneal tissue from the limbus.

Figure 11.8.  Dog with persistent pupillary membranes adherent to the posterior cornea, resulting in a focal corneal opacity.

Figure 11.9.  Canine herpesvirus-1 dendritic ulcerative keratitis in a dog receiving systemic immunosuppressive therapy (cornea stained with fluorescein).

Figure 11.10.  Chemical burn or keratitis after mace exposure in a dog.

Figure 11.11.  A corneal ulcer is diagnosed on the basis of retention of topically applied fluorescein dye by the corneal stroma, as observed in this superficial corneal ulcer.

Figure 11.12.  A large nonvascularized spontaneous chronic corneal epithelial defect (SCCED) in a 9-year-old Boxer. Note the axial location, ring of loose epithelium, and the decrease in intensity of the fluorescein staining as it migrates under the loose epithelium surrounding the defect.

Figure 11.13.  Epithelial debridement of a spontaneous chronic corneal epithelial defect (SCCED) in a 9-year-old Golden Retriever. One cotton-tipped applicator is used to remove loose epithelium, while a second is used to prevent prolapse of the third eyelid.

Figure 11.14.  Central, deep stromal corneal ulcer in a brachycephalic dog.

Figure 11.15.  Bridge or bipedicle conjunctival graft. (A) The conjunctiva is excised from the limbus for approximately 180° both adjacent and parallel to the linear corneal lesion. This area is extensively undermined, and the underlying fibrous tissue is removed. A second conjunctival incision is made 5–8 mm peripheral and parallel to the original conjunctival incision, thus creating a bridge of conjunctiva. (B,C) The bridge is advanced over the lesion and then sutured, using simple, interrupted sutures into the cornea around the lesion. (D) The original graft-harvesting site is closed by opposing the remaining conjunctiva with a simple, continuous suture.

Figure 11.16.  Pedicle conjunctival graft. (A) The base of the pedicle flap should be directed toward the area of the limbus nearest to the lesion. Once the location of the base is determined, a site 1.0–1.5 cm temporal to the base is located, at which the flap will be initiated. Through a small slit in the conjunctiva, the entire conjunctival flap site is undermined using blunt dissection. Two parallel cuts are then made to create a strip of conjunctiva. (B) The strip of conjunctiva is rotated to cover the corneal lesion. The flap is sutured to the cornea with simple, interrupted sutures of 7-0 to 9-0 polyglactin 910 or nylon. (C) The sutures are placed first at the distal end of the flap and then 1.0–1.5 mm apart.

Figure 11.17.  (A) After the corneal ulcer is healed, the blood supply to the conjunctival graft can be trimmed. (B) After applying topical anesthetic, scissors can be placed under the pedicle portion of the graft, which is not adhered to the underlying normal corneal epithelium.

Figure 11.18.  Central corneal descemetocele in a dog with chronic corneal disease.

Figure 11.19.  Penetrating keratoplasty using fresh tissue in a dog with diffuse corneal edema, (A) immediately after surgery and (B) 3 years later. Frozen cornea can also be used for perforations, but a clear cornea, as observed here, should not be expected. (Source: Courtesy of Bob English, Animal Eye Care Veterinary Ophthalmology Practice, Cary, NC, USA.)

Figure 11.20.  Horizontal full-thickness corneal laceration with uveal prolapse and hyphema in a dog.

Figure 11.21.  (A) Mild and (B) severe chronic superficial keratitis in German Shepherd dogs.

Figure 11.22.  Dachshund with superficial punctate keratitis.

Figure 11.23.  Crystalline corneal dystrophy in a Siberian Husky.

Figure 11.24.  (A) Dog with Cushing's disease with focal lipid keratopathy. (B) Dog with perilimbal lipid keratopathy.

Figure 11.25.  (A) Dog with focal corneal degeneration with lipid infiltration and vascularization. (B) Diffuse corneal degeneration with a dense white plaque and vascularization.

Figure 11.26.  Diffuse corneal edema in a Boston Terrier with advanced corneal endothelial