Eye Anatomy

What is the name of the tissues surrounding the eye?

Ocular adnexa

What is the purpose of the ocular adnexa?

Protect and support the eyeball

What structures form the ocular adnexa?

1. Orbit with orbital fat body 2. Orbital fasciae 3. Extrinsic eye muscles 4. Lacrimal apparatus 5. Vessels and nerves

What structures form the lateral orbital margin?

Frontal, lacrimal, maxillary, zygomatic bones and the orbital ligament

What bones form the medial wall of the orbit?

Frontal, presphenoid, and lacrimal bones

What structures form the ventral wall of the orbit?

The zygomatic salivary gland and pterygoideus muscles

What structure forms the dorsal wall of the orbit?

Temporalis muscle

What term is used to describe the eyelids?

Palpebra

What condition is the inability to close the eyelid completely?

Lagopthalmos

What condition is caused by the eyelid rolling inwards toward the eye?

Entropion

What condition is caused by the eyelid rolling outwards away from the eye?

Ectropion

What nerves innervate the eyelids?

Zygomatic nerve (branch of the maxillary nerve)- sensory function Facial nerve- motor function

What is the third eyelid?

Nictitating membrane

What is the function of the third eyelid?

1. Protection 2. Oxygenation 3. Nourishment

Rank species from most developed third eyelid to least developed

1. Cats 2. Dogs 3. Horses 4. Camelids 4. Pigs

In what species is the third eyelid absent?

Ruminants and rodents

What are the three methods of enucleation?

1. Transpalpebral: removes eye and accessory structures 2. Subconjunctival: removes only eye 3. Extenteration

What is the purpose of a tarsorrhaphy procedure?

Temporarily sutures eye closed to protect the cornea and promote healing

What is the action of the retractor bulbi muscle?

Retract the third eyelid

What are the structures of the third eyelid?

1. T-shaped cartilage 2. Nictitans gland

What species have harderian glands?

Rodents, birds, reptiles

What is the purpose of the harderian glands?

Produces lipids and pheromones

What does Haws syndrome cause?

Partial or complete third eyelid prolapse

What is the condition where the nictitans gland everts caused by defective or weak T-shaped cartilage?

Cherry eye

What is the origin of the levator palpebrae superioris muscle?

Apex of the orbit, extends over the dorsal rectus muscle

What is the insertion of the levator palpebrae superioris muscle?

Upper eyelid

What nerve innervates the levator palpebrae superioris muscle?

Oculomotor nerve (CN lll)

What is the action of the levator palpebrae superioris muscle?

Opening the eye

What glands line the inner aspect of the palpebra?

Meibomian glands (tarsal glands)

The fibrous plate that supports the margin of the eyelid?

Tarsal plate

What is the function of the tarsal glands?

1. Protection 2. Prevents excess evaporation

What conjunctiva lines the inner eyelid?

Palpebra conjunctiva

What conjunctiva lines the eyeball?

Bulbar conjunctiva

Which canthus of the eye is toward the nasal bone?

Medial canthus

Which canthus of the eye is towards the temporal bone?

Lateral canthus

What are the structures of the lacrimal apparatus?

1. Lacrimal gland 2. Lacrimal puncta 3. Lacrimal caniculi 4. Lacrimal sac 5. Nasolacrimal duct

What is the function of the lacrimal apparatus?

Enables tear production, distribution, and drainage

Which part of the lacrimal apparatus is embedded within bone?

Nasolacrimal duct

What percentage of tears are produced by the lacrimal and nictitans glands?

60% lacrimal gland 40% nictitans gland

Where is the tubuloalveolar gland located?

Beneath the orbital ligament of the upper eyelid

What type of gland is the tubuloalveolar gland?

Serous Mucoid in pigs

Where is the lacrimal gland located?

Inside the periorbita beneath the periorbital ligament, dorsolaterally to the eye

Where does the nasolacrimal duct open in horses?

Medial side of the nostril

Where does the nasolacrimal duct open in donkeys?

Lateral side of the nostrils, at the entrance to the "fake-nostril"

What structures form the lacrimal caruncle?

1. Third eyelid 2. Lacrimal puncta

Where is the lacrimal caruncle located?

A pink, triangular prominence at the medial canthus of the eye

What is the periorbita?

A cone-shaped sheath of connective tissue and smooth muscle enclosing the eye and its accessory structures

What is the insertion of extrinsic eye muscles?

Sclera of the eyeball (corneoscleral junction)

What are the extrinsic muscles of the eye?

1. Dorsal rectus muscle 2. Dorsal oblique muscle 3. Medial rectus muscle 4. Ventral rectus muscle 5. Ventral oblique muscle 6. Lateral rectus muscle 7. Retractor bulbi muscle

What is the action of the ventral oblique muscle?

Medial movement, ventral rotation

What is the action of the dorsal oblique muscle?

Medial movement, dorsal rotation

Which extrinsic eye muscles surround the optic nerve?

Retractor bulbi muscle

What is the action of the dorsal rectus muscle?

Upward movement

What is the action of the medial rectus muscle?

Adduction

What is the action of the ventral rectus muscle?

Downward movement

What is the action of the lateral rectus muscle?

Abduction

What nerve innervates the dorsal rectus, medial rectus, ventral rectus, and ventral oblique muscles?

Oculomotor nerve (CN lll)

What nerve innervates the lateral rectus and retractor bulbi muscles?

Abducens muscle (CN Vl)

What nerve innervates the dorsal oblique muscle?

Trochlear nerve (CN lV)

What are the pathways for the arteries supplying the eye?

Internal carotid artery-> optic canal-> internal opthalmic artery External carotid artery-> maxillary artery-> orbital fissure-> external opthalmic artery

What is the position of the optic nerve relative to the eye?

Caudoventral

What are the tunics of the eye?

1. Fibrous tunic 2. Vascular tunic (uvea) 3. Nervous tunic

What are the two components of the fibrous tunic?

1. Sclera (opaque) 2. Cornea (transparent)

What is the junction where the sclera and cornea meet?

The corneoscleral junction

Where is the sclera located?

Encloses the posterior 3/4's of the eye

Where is the cornea located?

Covers the anterior portion of the eye

What is the function of the sclera?

1. Forms the framework of the eyeball 2. Protection 3. Helps maintain pressure

What is the function of the cornea?

1. Allows the passage of light 2. Refracts light into the eye

Which structure covers the sclera anteriorly?

Bulbar conjunctiva

What structure forms the border between the sclera and cornea?

Limbus

What are the 5 epithelial layers of the cornea?

1. Anterior epithelium 2. Anterior limiting lamina 3. Substantia propria 4. Posterior limiting lamina 5. Posterior epithelium

What is the highest point of the cornea?

Vertex

What shape is the cornea in carnivores?

Rounded

What shape is the cornea in ungulates?

Oval

What are the structures of the vascular tunic?

1. Ciliary body 2. Iris 4. Choroid

What are the 4/5 layers of the choroid?

1. Suprachoroidal layer 2. Vascular layer 3. Tapetum lucidum (not present in all species) 4. Choroidopapillary layer 5. Basal lamina

What is the function of the tapetum lucidum?

Highly reflective, helps with night vision

What species lack a tapetum lucidum?

Humans and pigs

What color is the tapetum lucidum in cats?

Yellow

What color is the tapetum lucidum in dogs?

Green

What color is the tapetum lucidum in bovine and equine?

Blue-green

What is the function of the ciliary body?

1. Smooth muscle, alter shape of the lens 2. Aqueous humor production 3. Anchor zonular fibers to the lens (ciliary process)

Where is the iris located?

Surrounds the pupil

What is the function of the iris?

Pupillary constriction and dilation

Which muscles of the iris cause pupillary dilation under sympathetic stimulation?

Dilator (radiating) muscles

Which muscles of the iris cause pupillary constriction under parasympathetic stimulation?

Sphincter (circular) muscles

What is the condition of permanent constriction of the pupil?

Miosis

What is the condition of permanent dilation of the pupil

Mydriasis

What causes the color of the iris?

Melanin pigments (varies between individuals)

What species have an oval pupil shape?

Ungulates and cats

What is the shape of a dogs pupil?

Round

What is the junction between the cornea and iris?

Iridocorneal angle

What is the function of the retina?

Image formation

What are the 3 neuronal layers of the retina?

1. Photoreceptors (rods and cones) 2. Bipolar neurons 3. Ganglion neurons

What is the function of rod cells?

Light and shade perception

What is the function of cone cells?

Color and sharpness perception

What is the blind spot of the eye?

The optic disc (where optic nerve exits retina)

What shape is the lens?

Biconvex

What is the function of the lens?

Transmit and focus light on the retina

Which structures of the eye are avascular?

Cornea and lens