Small Animal Ophthalmic Atlas and Guide

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3 Small Animal Ophthalmic Atlas and Guide

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5 Small Animal Ophthalmic Atlas and Guide Christine C. Lim, DVM Diplomate of the American College of Veterinary Ophthalmologists Assistant professor of ophthalmology University of Minnesota College of Veterinary Medicine St Paul, MN, USA

6 This edition first published by John Wiley & Sons, Inc. Editorial Offices 1606 Golden Aspen Drive, Suites 103 and 104, Ames, Iowa , USA The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK 9600 Garsington Road, Oxford, OX4 2DQ, UK For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by Blackwell Publishing, provided that the base fee is paid directly to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA For those organizations that have been granted a photocopy license by CCC, a separate system of payments has been arranged. The fee codes for users of the Transactional Reporting Service are ISBN-13: /2015. Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book. The contents of this work are intended to further general scientific research, understanding, and discussion only and are not intended and should not be relied upon as recommending or promoting a specific method, diagnosis, or treatment by health science practitioners for any particular patient. The publisher and the author make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of fitness for a particular purpose. In view of ongoing research, equipment modifications, changes in governmental regulations, and the constant flow of information relating to the use of medicines, equipment, and devices, the reader is urged to review and evaluate the information provided in the package insert or instructions for each medicine, equipment, or device for, among other things, any changes in the instructions or indication of usage and for added warnings and precautions. Readers should consult with a specialist where appropriate. The fact that an organization or Website is referred to in this work as a citation and/or a potential source of further information does not mean that the author or the publisher endorses the information the organization or Website may provide or recommendations it may make. Further, readers should be aware that Internet Websites listed in this work may have changed or disappeared between when this work was written and when it is read. No warranty may be created or extended by any promotional statements for this work. Neither the publisher nor the author shall be liable for any damages arising herefrom. Library of Congress Cataloging-in-Publication Data applied for. A catalogue record for this book is available from the British Library. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. Set in 9.5/12pt Minion by SPi Publisher Services, Pondicherry, India

7 To those who made this book possible: my colleagues, mentors, students, patients, and of course my family.

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9 Contents Preface, x List of abbreviations, xi Glossary, xii Section I Atlas, 1 1 Orbit, 3 Clinical signs associated with orbital neoplasia, 3 Clinical signs associated with orbital cellulitis, 3 Enophthalmos, 4 Brachycephalic ocular syndrome, 4 Ventromedial entropion associated with brachycephalic ocular syndrome, 4 Clinical signs associated with Horner s syndrome, 5 Clinical signs associated with Horner s syndrome, 5 Appearance of Horner s syndrome following application of sympathomimetic drugs, 5 Clinical signs associated with orbital neoplasia, 6 Clinical signs associated with proptosis, 6 2 Eyelids, 7 Normal appearance of punctum, 7 Ectopic cilia, 7 Distichiae, 8 Distichiae, 8 Ectopic cilia and chalazion, 8 Lower eyelid entropion due to conformation, 9 Facial trichiasis, 9 Eyelid agenesis, 9 Appearance of entropion after temporary correction using tacking sutures, 10 Lower eyelid ectropion, 10 Meibomian adenoma, 10 Meibomian adenoma, 11 Eyelid melanocytoma, 11 Chalazion, 11 Blepharitis, 12 Blepharitis, 12 Blepharitis, 12 3 Third eyelid, nasolacrimal system, and precorneal tear film, 13 Pathologic changes to the third eyelid associated with pannus, 13 Scrolled third eyelid cartilage, 13 Prolapsed third eyelid gland ( cherry eye ), 14 Prolapsed third eyelid gland ( cherry eye ), 14 Superficial neoplasia of the third eyelid, 14 Neoplasia of the third eyelid gland, 15 Positive Jones test appearance of fluorescein in mouth, 15 Positive Jones test appearance of fluorescein at nostril, 15 4 Conjunctiva, 16 Normal appearance of the conjunctiva, 16 Conjunctival hyperemia, 16 Chemosis and conjunctival hyperemia, 17 Chemosis, 17 Conjunctival follicles, 17 Conjunctival thickening associated with infiltrative neoplasia, 18 Superficial conjunctival neoplasia, 18 Subconjunctival hemorrhage, 18 Conjunctival follicles, 19 Superficial conjunctival neoplasia, 19 Conjunctival neoplasia, 19 5 Cornea, 20 Superficial corneal vascularization associated with keratoconjunctivitis sicca, 20 Appearance of a dry cornea with concurrent anterior uveitis, 20 Typical appearance of superficial corneal vessels, 21 Typical appearance of deep corneal vessels, 21 Typical appearance of corneal edema, 21 Corneal melanosis, 22 Typical melanin distribution associated with pigmentary keratitis, 22 Typical appearance of corneal fibrosis with concurrent corneal vascularization, 22 Corneal white cell infiltrate with concurrent corneal vascularization and edema, 23 Corneal deposits associated with corneal dystrophy, 23 Corneal deposits associated with corneal dystrophy, 23 Corneal mineral deposits, 24 Typical changes associated with keratoconjunctivitis sicca, 24 vii

10 viii Contents Predominantly melanotic corneal changes associated with pannus, 24 Predominantly fibrovascular corneal changes associated with pannus, 25 Corneal changes associated with pannus, mixture of melanosis and fibrovascular changes, 25 Superficial corneal ulcer, 25 Indolent corneal ulcer with fluorescein stain applied, 26 Indolent corneal ulcer prior to fluorescein stain, 26 Indolent corneal ulcer after fluorescein stain, 26 Deep corneal ulcer, 27 Descemetocele after application of fluorescein stain, 27 Descemetocele after application of fluorescein stain, viewed with cobalt blue light, 27 Corneal perforation with iris prolapse, 28 Corneal perforation with iris prolapse and hyphema, 28 Corneal perforation with large iris prolapse, 28 Melting corneal ulcer, 29 Perforated melting corneal ulcer, 29 Dendritic corneal ulcers, 29 Eosinophilic keratoconjunctivitis, 30 Eosinophilic keratoconjunctivitis, 30 Eosinophilic keratoconjunctivitis, 30 Corneal sequestrum; light brown, with minimal keratitis, 31 Corneal sequestrum; dark brown, with moderate keratoconjunctivitis, 31 Corneal sequestrum; dark brown, with significant keratoconjunctivitis, 31 6 Anterior uvea, 32 Iris-to-cornea persistent pupillary membranes, 32 Iris-to-iris persistent pupillary membranes, 32 Posterior synechiae, 33 Anterior chamber uveal cysts, 33 Anterior chamber uveal cysts, 33 Transillumination of posterior chamber uveal cysts, 34 Iris atrophy, 34 Iris atrophy, 34 Severe iris atrophy, 35 Focal iris hyperpigmentation, 35 Feline diffuse iris melanoma, 35 Feline diffuse iris melanoma, 36 Canine melanocytoma, 36 Canine melanocytoma, 36 Canine ciliary body adenoma, 37 Clinical signs of uveitis: chemosis, episcleral congestion, deep corneal vascularization, and diffuse corneal edema, 37 Aqueous flare, 37 Keratic precipitates, 38 Hypopyon with concurrent corneal ulceration, 38 Hyphema, 38 Rubeosis iridis, 39 Iris thickening, 39 Posterior synechia, 39 Iris bombé, 40 7 Lens, 41 Nuclear sclerosis, 41 Nuclear sclerosis, 41 Incipient cataract, 42 Incipient cataract, 42 Incomplete cataract, 42 Incomplete cataract, 43 Incomplete cataract, 43 Complete cataract, 43 Complete, resorbing cataract, 44 Incomplete resorbing cataract, 44 Lens subluxation, 44 Lens subluxation, 45 Anterior lens luxation, 45 Posterior lens luxation, 45 8 Posterior segment, 46 Normal canine fundus, 46 Normal canine fundus, 46 Normal feline fundus, 47 Subalbinotic, atapetal canine fundus, 47 Subalbinotic feline fundus, 47 Tapetal hyperreflectivity and retinal vascular attenuation in a cat, 48 Tapetal hyperreflectivity and retinal vascular attenuation in a dog, 48 Focal retinal degeneration/chorioretinal scar, 48 Focal retinal degeneration/chorioretinal scar, 49 Tapetal hyporeflectivity due to hypertensive retinopathy, 49 Tapetal hyporeflectivity, 49 Tapetal hyporeflectivity, 50 Fluid and white cell infiltrate in the nontapetal fundus (chorioretinitis), 50 Focal white cell infiltrate (chorioretinitis) and retinal degeneration in the nontapetal fundus, 50 Multifocal retinal degeneration in the nontapetal fundus, 51 Hemorrhage in the nontapetal fundus, 51 Hemorrhage in the tapetal fundus, 51 Serous retinal detachment and retinal hemorrhage due to hypertensive retinopathy, 52 External view of serous retinal detachment, 52 Serous retinal detachment, 52 Rhegmatogenous retinal detachment, 53 Optic nerve atrophy/degeneration - mild, 53 Optic nerve atrophy/degeneration - severe, 53 Optic disc cupping in an atapetal fundus, 54 Optic disc cupping, 54 Optic neuritis, 54 Optic neuritis, 55 Asteroid hyalosis, 55

11 Contents ix Choroidal hypoplasia (collie eye anomaly), 55 Posterior polar coloboma and choroidal hypoplasia (collie eye anomaly) in a subalbinotic fundus, 56 9 Glaucoma, 57 Typical appearance of acute glaucoma, 57 Haab s striae, 57 Section II Guide, Orbit, 61 Diseases of the orbit, 62 Brachycephalic ocular syndrome, 62 Horner s syndrome, 63 Orbital cellulitis and abscess, 65 Orbital neoplasia, 67 Proptosis, 68 Further reading, 70 References, Eyelids, 71 Diseases of the eyelid, 72 Distichiasis, 72 Ectopic cilia, 73 Trichiasis, 73 Eyelid agenesis, 75 Entropion, 75 Ectropion, 77 Eyelid neoplasia, 78 Chalazion, 79 Blepharitis, 80 Eyelid laceration, 81 Further reading, 82 References, The third eyelid, nasolacrimal system, and precorneal tear film, 83 Diseases of the third eyelid and lacrimal system, 84 Third eyelid gland prolapse ( cherry eye ), 84 Third eyelid neoplasia, 85 Nasolacrimal duct obstruction, 87 Tear film disorders KCS, 88 Qualitative tear film abnormality, 88 References, Conjunctiva, 91 Diseases of conjunctiva, 91 Canine conjunctivitis, 91 Feline conjunctivitis, 93 Conjunctival neoplasia, 95 Further reading, 96 References, Cornea, 98 Corneal diseases, 99 Corneal dystrophy, 99 Canine keratitis, 100 Keratoconjunctivitis sicca (KCS), 101 Pigmentary keratitis, 103 Pannus/chronic superficial keratitis, 104 Corneal ulceration, 105 Simple corneal ulceration, 105 Indolent corneal ulceration, 106 Deep and perforating corneal ulceration, 108 Melting corneal ulceration, 110 Feline keratitis, nonulcerative and ulcerative, 111 Feline eosinophilic keratoconjunctivitis (EK), 112 Corneal sequestrum, 113 Further reading, 114 References, Anterior uvea, 116 Anterior uveal diseases, 116 Persistent pupillary membranes (PPMs), 116 Uveal cysts, 117 Iris atrophy, 118 Feline diffuse iris melanoma, 118 Canine anterior uveal melanocytic neoplasia, 119 Iridociliary neoplasia, 120 Anterior uveitis, 121 Further reading, 124 References, Lens, 125 Diseases of the lens, 125 Nuclear sclerosis, 125 Cataract, 126 Lens subluxation and luxation, 128 Further reading, 129 References, Posterior segment, 131 Diseases of the posterior segment, 133 Asteroid hyalosis, 133 Collie eye anomaly, 133 Progressive retinal atrophy (PRA), 134 Sudden acquired retinal degeneration syndrome (SARDS), 135 Retinal degeneration (excluding PRA and SARDS), 136 Chorioretinitis, 137 Retinal detachment, 138 Hypertensive retinopathy, 140 Optic neuritis, 141 Further reading, 142 References, Glaucoma, 144 Glaucoma, 144 Further reading, 148 References, 148 Index, 149

12 Preface Small animal general practice is a high-paced profession that requires the veterinarian to arrive at a diagnosis and formulate diagnostic and therapeutic plans within a 15- to 20-minute appointment window. As a general practitioner, I often found myself in this position. When I did, I wished for a reference where I could find a photograph similar to what I observed in the patient, along with enough information to implement a plan for treatment. Such scenarios provided the idea for this book. The Small Animal Ophthalmic Atlas and Guide is designed as a handy reference for the busy general practitioner. The book s goals are to (i) provide an extensive collection of images that practitioners can use to obtain a diagnosis during an outpatient appointment, and (ii) provide just enough information about each disease, relevant diagnostic tests, and treatment to allow for development of a medically sound management plan. The majority of ophthalmic conditions selected for inclusion in this book are those that present frequently in general practice. A smaller number of less common conditions are also included because of their significant impact on vision and/or overall health of the eye. The purpose of this book is not to describe every known small animal ophthalmic disease, nor is it intended to be an exhaustive review of the diseases included in the book. Because this is intended to be a quick reference, each chapter includes only enough background information to facilitate discussion of each ocular disease, most of the information is designed to support immediate management, and only select procedures are detailed step-by-step. (For example, detailed directions for ocular surgeries should be sought from other texts.) As a guide for those who wish to delve more deeply into specific ophthalmic conditions, each chapter contains a list of suggestions for further reading. Of course, no reference book can be a substitute for up-to-date education, sound clinical judgment, and the practitioner s individual knowledge of a particular patient. Readers of this book should always think critically about the cases presenting to them, seek advice from and make referrals to veterinary ophthalmologists when expert care is warranted, and verify that new research or information from manufacturers has not eclipsed the information in this text. My hope is that this book will make it easier for practitioners to handle ophthalmic cases in their daily practice. Christine C. Lim x

13 List of abbreviations CBC CsA CT DNA DSH ERG FeLV FIP FHV-1 FIV IOP IV complete blood count cyclosporine A computed tomography deoxyribonucleic acid domestic shorthair electroretinogram feline leukemia virus feline infectious peritonitis feline herpesvirus feline immunodeficiency virus intraocular pressure intravenous KCS LIU MRI NSAID PLR PO PPM PRA RPE SARDS STT keratoconjunctivitis sicca lens-induced uveitis magnetic resonance imaging nonsteroidal anti-inflammatory drug pupillary light reflex by mouth persistent pupillary membrane progressive retinal atrophy retinal pigmented epithelium sudden acquired retinal degeneration syndrome Schirmer tear test xi

14 Glossary Accommodation the process by which the eye changes its focus (e.g., from near objects to far objects, or vice versa). Anisocoria unequal pupil size between eyes. Anterior uvea iris and ciliary body. Anterior uveitis inflammation of the iris and ciliary body. Aphakic crescent this describes the crescent-shaped area of pupil that is visible when the lens is subluxated or luxated. It is an area of pupil that no longer has a lens in it (due to the dislocation). The borders of the aphakic crescent are the pupillary margin and the equator of the lens. Blepharitis inflammation of the eyelids. Blepharospasm squinting. This is due to spasm of the orbicularis oculi muscle. Marked blepharospasm can cause the eyelids to roll inward (referred to as entropion). Blood-aqueous barrier tight junctions within the anterior uvea, which limit the entrance of blood-borne substances into the eye. For example, systemically administered medications may not penetrate into the eye when the blood-aqueous barrier is intact. In the presence of uveitis, the blood-aqueous barrier is compromised. In addition to the blood-aqueous barrier anteriorly, and the blood-retina barrier functions similarly posteriorly. Brachycephalic ocular syndrome a set of conformational abnormalities most commonly seen in brachycephalic dogs. These abnormalities include bilateral exophthalmos, bilateral macropalpebral fissure, and bilateral medial trichiasis. Buphthalmos enlargement of the eye as a result of increased intraocular pressure. Cataract an opacity of the lens. The size of the opacity can range from small and focal to encompassing the entire lens. Chalazion retention of inspissated Meibomian gland secretions within the eyelid, usually accompanied by eyelid inflammation. Chemosis edema of the conjunctiva. Cherry eye this term is used to describe prolapse of the gland of the third eyelid. Chorioretinitis inflammation of the choroid and retina, also referred to as posterior uveitis. Choroid the posterior portion of the vascular tunic of the eye, also known as the posterior uvea. Ciliary body a portion of the anterior uvea. The ciliary body is not visible on ophthalmic examination because it is posterior to the iris. Functions of the ciliary body include aqueous humor production and accommodation, and it also forms a part of the blood-aqueous barrier. Coloboma congenital absence of tissue. For example, an optic nerve coloboma refers to an area of the optic nerve where it is missing tissue. Conjunctivitis inflammation of the conjunctiva. Cyclitis inflammation of the ciliary body. Cyclophotocoagulation destruction of the ciliary body with laser energy. This procedure is performed in patients with glaucoma. The goal of this procedure is to decrease aqueous humor production (thereby lowering intraocular pressure). Cycloplegia paralysis of the ciliary body. Dacryocystitis inflammation of the nasolacrimal canaliculi and lacrimal sac, usually due to nasolacrimal duct obstruction. Distichia an aberrant hair that arises from a Meibomian gland and emerges from the Meibomian gland openings. Dyscoria abnormal shape of the pupil. Ectopic cilium an aberrant hair that arises from a Meibomian gland and emerges through the palpebral conjunctiva. Because the ectopic cilium emerges through the palpebral conjunctiva, it is in constant contact with the ocular surface. Ectropion outward rolling of the eyelids. Electroretingram (ERG) this is a test that measures the response of the retina to light; that is, it is a test of retinal function. Enophthalmos refers to position of the globe when it is set more posteriorly than normal within the orbit. Entropion inward rolling of the eyelids that results in eyelid hairs directly rubbing against the cornea. Enucleation surgical removal of the eye, third eyelid, conjunctiva, and eyelid margins. Epiphora spillage of tears onto the face. Exenteration surgical removal of all orbital contents (i.e., removal of all other orbital soft tissues in addition to enucleation). This is usually performed to remove ocular or orbital neoplasia. Exophthalmos refers to position of the globe when it is set more anteriorly than normal within the orbit. Fundus the image obtained when the posterior segment is viewed through the pupil with an ophthalmoscope. The image is created by a superimposition of the retina and optic nerve upon the choroid (which includes the tapetum) and sclera. Glaucoma optic nerve damage as a result of increased intraocular pressure (intraocular pressure greater than 25 mm Hg). Goniodysgenesis congenital malformation of the iridocorneal angle. Also referred to as pectinate ligament dysplasia. Gonioscopy visual examination of the iridocorneal angle. This test is performed by a veterinary ophthalmologist. It is most often used to determine if glaucoma is primary or secondary. Hyphema blood in the anterior chamber. Presence of hyphema indicates anterior uveitis. Hypopyon pus in the anterior chamber. Presence of hypopyon indicates anterior uveitis. Hypotony decreased intraocular pressure. This is often a symptom of anterior uveitis. Iridocorneal angle the angle created by the iris and the cornea. This is the main exit pathway for aqueous humor from the eye. This aqueous outflow pathway is referred to as the conventional pathway. Iridocyclitis inflammation of the iris and ciliary body. Iridodonesis visible movement of the iris seen as a result of zonular breakdown (indicates lens instability). Keratectomy surgical removal of a portion of the cornea. xii

15 Glossary xiii Keratitis inflammation of the cornea. Keratoconjunctivitis inflammation of the cornea and conjunctiva. Keratoconjunctivitis sicca inflammation of the cornea and conjunctiva due to insufficient production of the aqueous component of the precorneal tear film. This is diagnosed when the tear production is less than 15 mm/min as measured by the Schirmer tear test. Keratotomy incision into the cornea without removal of tissue. Lacrimomimetic tear film substitute (artificial tears). Lagophthalmos incomplete blink. Lagophthalmos causes exposure and drying of the cornea (usually the central cornea). This is a common finding in exophthalmic eyes. Luxation complete dislocation of a structure. In ophthalmology, the term luxation is most often used in reference to the lens; lens luxation means that the lens has completely dislocated from its normal position. Macroblepharon abnormally large eyelid openings. This is often seen in dogs with brachycephalic ocular syndrome. Also referred to as macropalpebral fissure. Macropalpebral fissure abnormally large eyelid openings. This is often seen in dogs with brachycephalic ocular syndrome. Also referred to as macroblepharon. Miosis small pupil due to constriction of the pupillary sphincter muscle. Miosis occurs as a normal response to light. It also occurs in the presence of uveitis or in response to certain drugs. Mucinomimetic having properties similar to precorneal tear film mucin. This term is used to describe how closely artificial tears approximate tears made by the body. Mucinomimetic properties are desired when there is a deficiency of mucin in the precorneal tear film (a qualitative tear film abnormality). Mydriasis pupil dilation, as a result of constriction of the iris dilator muscle. Mydriasis occurs as a normal response to decreased ambient light. It also occurs as a result of retina and optic nerve disease or in response to certain medications (most notably, atropine). Nictitans the third eyelid. Also referred to as the nictitating membrane. Optic neuritis inflammation of the optic nerve. Pannus also referred to as chronic superficial keratitis. This is immune-mediated inflammation that can involve the conjunctiva, cornea, and third eyelid. It is commonly seen in German shepherds and related breeds. Pectinate ligament dysplasia congenital malformation of the iridocorneal angle. Also referred to as goniodysgenesis. Peripapillary refers to the region of the fundus immediately surrounding the optic nerve. Phacodonesis visible movement of the lens seen as a result of zonular breakdown (indicates lens instability). Phthisis bulbi an atrophied eye. This eye is smaller than normal and is no longer functional. Phthisis bulbi occurs as a sequela to chronic inflammation and chronic glaucoma. Pigmentary keratitis this describes a syndrome of corneal melanosis and vascularization that preferentially affects the medial and central cornea. It most commonly affects dogs with brachycephalic ocular syndrome. Posterior uveitis inflammation of the choroid. Since inflammation of the retina usually occurs in the presence of choroidal inflammation, posterior uveitis usually refers to inflammation of both the choroid and the retina. This is also referred to as chorioretinitis. Ptosis drooping of the upper eyelid. This is one abnormality consistently found in Horner s syndrome. Qualitative tear film abnormality deficiency of the lipid or mucin portion of the tears. Quantitative tear film abnormality deficiency of the aqueous portion of the tears (keratoconjunctivitis sicca). Retropulsion this refers to gentle, posteriorly directed pressure placed onto the eyes. It is used to assess orbital disease. Retropulsion is performed by placing the index and/or middle fingers over the eyes, through closed eyelids. Gentle pressure is then used to push the eyes in the posterior direction (into the orbit). The amount of resistance by the eyes should feel equal on both sides. In the presence of orbital disease, the resistance noted by this action could be increased or decreased compared to normal. Unilateral orbital disease will show asymmetric resistance to retropulsion. Schirmer tear test (STT) this is a measurement of tear production. The test is performed by placing an STT strip (commercially available adsorbent paper strip) into the ventrolateral conjunctival sac and leaving it in place for 1 minute. During this minute, tears are taken up by the test strip. After 1 minute, the strip is removed from the conjunctival sac and the length of wet strip is measured. Tear production is expressed in the units of millimeter per minute. Normal STT values are above 15 mm/min in the dog. Schirmer tear test values are extremely variable in the cat. Sequestrum usually used to describe a corneal sequestrum, which is necrotic corneal tissue resulting from chronic irritation. This condition is most commonly seen in cats. It rarely occurs in dogs. Strabismus misalignment of the eyes relative to one another. Strabismus can be a congenital condition or an acquired condition. For example, following traumatic avulsion of the medial rectus muscle (e.g., following traumatic proptosis), there is unopposed action of the lateral rectus muscle. This causes the direction of gaze of the affected eye to become deviated laterally. Subluxation partial dislocation of a structure. In ophthalmology, the term subluxation is most often used in reference to the lens; lens subluxation means that the lens has partially dislocated from its normal position. Synechia adhesion of the iris to an adjacent ocular structure, resulting from inflammation. Anterior synechia refers to an adhesion between the iris and the cornea. Posterior synechia refers to an adhesion between the iris and the lens. Tapetum reflective layer that is part of the choroid. The tapetum is found in the innermost layer of the dorsal half of the choroid. Tarsorrhaphy a procedure that partially or completely closes the palpebral fissure by suturing the upper and lower eyelids to each other. Tear film break up time (TFBUT) this measures the amount of the time the precorneal tear film remains as a stable film over the corneal surface. Therefore, it is a measure of tear film stability, with shorter TFBUTs indicating less stability of the tear film (earlier evaporation of the tears). The TFBUT is considered an indirect measure of the mucin content of the tears. Normal TFBUTs in the cat fall between 12 and 21 seconds, while normal values in the dog fall between 15 and 25 seconds. Tonometry measurement of intraocular pressure. Transillumination the act of shining light through a structure during the ophthalmic examination. Uvea the vascular tunic of the eye. This can be divided into the anterior uvea (which is made up of the iris and ciliary body) and the posterior uvea (which is made up of the choroid). Uveitis inflammation of all or part of the uveal tract. See anterior uveitis, cyclitis, iridocyclitis, chorioretinitis, posterior uveitis. Zonule a thin ligament that runs radially between the ciliary body and the lens. Zonules hold the lens in correct position. Breakdown of the zonules results in lens subluxation or luxation.

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17 Section I Atlas