Ocular Anatomy

Orbit

eye socket

Globe

Eyeball

Adnexa

Everything except the globe: orbti, muscles, eyelids, conjuctiva, nictitating membrane, lacrimal system

Anterior segment

cornea, anterior chamber, iris, irodocorneal angle, ciliary body, lens

Posterior Segment

1. vitreous humor

2. retina

3. choroid

4. optic nerve

5. posterior sclera

Orbit in carnivores

Eye socket has incomplete bony rim

Orbit in herbivores

Complete bony rim eye socket

More trauma to break

Bony socket

lined with fascia,

wraped in conjunctiva, nictitans (third eyelid), fat, extraocular muscles, muscles of mastication, blood vessles, glands, cranial nerves 2-8, autonomic nerves

What does Ramus do?

Ramus of mandible contacts floor of orbit so can cause pain when opening mouth if infected.

Extraocular Muscles

1. move globe in orbit

2. Muscle cone anchored in back of orbit

3. Rectus uscles

4. oblique muscles (rotate globe)

5. retractor bulbi (pulls globe back in orbit

What do oblique muscles of extraocular muscles do?

Rotate globe

• dorsal/superior

• ventral/ interior

What do retractor bulbi do?

Pulls globe back in orbit; third eyelid comes up

What are eyelids made of?

skin, hair, mucocutaneous junction, conjucntiva, glands, musclesE

Eyelid skin is thin…

not much subcutaneous tissue near margin, elastic, but elasticity with vary with species and breed

Cilia in eyes

eyelashes, varies among species, originate outside Meibomian gland opening

Meibomian glands

Row of sebacious glands are eyelid margin

What is gray line on eyelid?

Ducts open at mucocutaneous junction

Secrete lipid layer of tear film

Tarsus of eye

Tarsal plate gives toughness and support

• extends 3-4 mm from eyelid margin

• muscle attachment

Three types of eyelid muscles

Constrict palpebral fissure

depress lower lid

elevate upper lid

Leveator palpebrae

elevate upper eyelid

Orbicularis oculi

surrounds margins and closes upper and eyelids

Innervation of eyelid

5: sensory

3 + 7: motor

autonomic-0 sympathetic nerve

What is purpose of sphincter muscle setup?

Helps spread tears and clear debris

Mueller’s Muscle

Smooth muscle,

Sympathetic tone

Tone to the tarsus

Medial and lateral canthal ligaments

Ligament bands anchor medial and lateral

Muscle transect during enuclation

Vascular supply of eyelids

Well vascularized by longitudinal vessels

heal quickly and are rare to get infected

Palpebral

lines eyelids

Bulbar

lines exposed surfaces of globe

Fornix

cul-de-ac formed by reflections of conjunctiva at transition from lid to globe

Nictitans

covers palebral and bulbar surfaces of the nictitating membrane

What is conjunctiva?

Mobile, elastic membrane

What does normal conjunctiva look like?

Pale, pink non-pigmented in most species, some pigment is normal

What is conjunctiva covered in?

Non-keratinized stratified squamous epithelium

Where are Goblet cells and why are they important?

Between epithelial cells that secrete mucous

Substantia propria

loose CT, fenestrated (leaky) capillaires, lymphoid tissue

Subconjiunctival space

Between conjucntiva and space

Purpose of conjucntiva

1. Smooth gliding of nictitans and eyelid

2. muycus layer of tear film (goblet cells)

3. Immune protection

   1. lymphoid tissue, immunoglobulins

4. corneal repair (graft)

Where does nictitans sit?

Medial fornix/canthus

leading edge is usually pigmented (but not always)

Function of nictitans

1. moves dorsolaterally as globe retracted

2. spread tear film

3. protect globe

4. removes particulate matter (squige)

How does nictitans function?

T shape cartialge squigee

gland of nictans produces water

What is retropulsion?

retract third eyelid by gently pressing on the globe; check for cancer

Cherry eye

gland is prolapsed and not anchored

Tear layer films

Lipid layer: outer

Aqueous: middle

Mucin: inner

What are lipid layer produced by?

Meibomian

What is aqueous layer produced by?

lacrimal gland

What is mucin layer produce by?

Goblet cells

Lacrimal outflow apparatus

drains the tears from the eyelids to the nose

Steps for lacrimal outflow

1. Ocular puncta (in eyelids, conjunctiva)

2. canaliculi

3. lacrimal sac in medial canthus

4. nasolacrimal duct

5. nasal puncta

Anterior parts of eye

1. Sclera

2. Iris

3. Pupil

4. Limbus

5. Cornea

Inside anterior globe

3 concentric tunics of globe

1. fibrous (conrea, sclera)

2. vascular (iris, ciliary body, chorid)

3. nervous (retina, optic nerve)

What are fibrous tunics made of?

Cornea and sclera

Cornea function

avascular

.5-1mm thick

Transmit and refract light

protect internal contents

thin windshield

cornea innervation

Opthalmic branch of trigeminal nerve 5:

anterior 1/3 of cornea (superficial layer)

4 layers of cornea

1. epithelium

2. stroma

3. descemets membrane

4. endothelium

Corneal epithelium

1. non-keratnized, nonpigmented squmous cells

2. wing cells

3. basal cells

4. basement membrane

Cornea epithelium turnover rate

about 7 days

cornea stroma is made of

collagen (regularly arranged)

keratocytes

glycosaminoglycans

water (78%)

NO blood vessles

Corneal Stroma

hydrophillic; will swell if there is a break in epithelial or endothelial barriers

Needs to maintain deturgescence (deydration)

Deturgescence

relative dehydration to remain clear

ulceration

focal corneal edema

Diffuse corneal edema is likely damage to…

endothelium (innermost layer of cornea)

Descemets membrane

basement membrane of corneal endothelium

Endothelium

monolayer of hexagonal cell

activley pump fluid out of cornea to maintian deturgescence

mechanical barrier

Do endothelium undergo mitosis?

Only in young animals

What happens when there aren’t enough endothelial cells?

Corneal endothelial degeneration; does not have enough to maintain deturgence

What is gunderson flap?

Corneal endothelial degeneration with flap

Limbus

zone of transition from regularly arranged collagen and straight basement membrane

Sclera tissue

irregularly arranged, densley packed collage fibrils

Vascularized

opaque

Zone of transition in eyes

Point of weakness,

Blunt trauma can rupture

Sclera has opening for what?

posterior opening for optic nerve which is a point of weakenss

Lamina cribosa

Collage sieve supports axons of optic nerve (site of weakness)

Uvea parts

Middle tunic of the eye

1. Iris

2. Ciliary body

3. Choroid

Iris

Most anterior portion

What does the iris/pupil do?

Regulate amount of light entering posterior portions fo the eye

Blood aqueous barrier

keeps cells protein, in blood vessels to keep fluid clear and protect eye from damage

Maintians clarity

Parts of Iris

1. sphinctor muscle (encircles pupil)

2. stroma

3. dilator muscle (backside fo iris longitudinally)

4. Posterior pigmenged epithelium

Iris stroma makeup

1. nerves, muscles, melanocytes, fibroblasts, vessels

What can inflamation do to pupil?

constrict them

Pupil shape is related to what?

Sphinctor muscle distribution

Iris color

related to melanin and other pigments

can be related to coat/skin color

Heterocrhomia

iris color variation

Dog vs cats iris color

dogs have dark brown round melanin

cats: golden brown pigment or linear shape

Iris color in albino rat

no melanin so iris will appear red because all you see is stromal tissue with lots of blood vessels

Iridocorneal angle

junction of iris at base via pectinate ligaments (collagen)

Site of drainage of aqueous humor through trabecular meshwork

Gonioscopy lens

looks right at iridocornela angle acros iris to drainage tissue

Ciliary body

posteior to iris

Oriented 3 directions

1. longitudenal

2. circumferential

3. radial

Pars plicata

ciliary process

Pars plana

flat protion where retina inserts

Accomodation

fine focusing with ciliary body smooth muscle

Dogs and horses accomodation

dont have developed accomodation because retina is not developed so cillary muscle is not developed

Ciliary body epithelium

1. pigmented epithelium

2. non-pigmented epithelium

Aqueous humor produced by

non-pigmented epithelium in the posterior chamber and flows through Iridocorneal angle (ICA)

Aqueous prouduction outflow

ciliary epthelium

2. between iris and lens

3. pupil into anterior chamber

4. iridocorneal angle

5. trabecular meshwork

6. Sceleral Venous Pleus

Glaucoma

primary or secondary closure of iridocorneal angle (breed, inflammation)

Glaucoma

Obstruction of aqueous humor through the iridocorneal angle increase intraocular pressure. (overfilling water balloon)

Won’t burst but will create globe enlargement

How to address glaucoma:

laser surgery of endothelium?

Lens anatomy

1. non-vascularized

2. non-innervated

3. 355 crystaline protein, 65% water

4. capsule of basement membrane

5. lens epithelium

6. lens fibers

7. zonules attachements

Lens capsule:

Anterior lens epithelial cells

equatorial lens

antiorr/posterior (choclate of mm)

nuclesu (nut in center of mm)

Lens fiber formation

lens fibers elongate and are move internally which is created by new fibers that push them

Central lens fibers compressed to form fetal and adult nuceleus