Ophthalmology Anatomy, Physiology, and Embryology Flashcards
anatomy of the eye
- what are the sections? what structures are in each?
ANTERIOR SEGMENT
1. Anterior chamber
(in front of iris)
- cornea
- iris
- limbus
2. Posterior chamber
(behind iris)
- front of lens
- ciliary body
- sclera
<><><><>
POSTERIOR SEGMENT
- back of lens
- sclera
- choroid
- tapetum
- retina
<><><><>
- optic nerve
bones of the orbit?
- what animals have complete vs incomplete?
- Frontal
- Maxillary
- Lacrimal
- Zygomatic
<><> - Pterygoid
- Palatine
- Sphenoid
> these 3 Hidden under the zygomatic arch
<><><><>
Incomplete orbit - orbital ligament
- dogs, cats, pigs
<><><><>
Complete orbit - temporal bone
- most grazing animals (horse, oxen, sheep, goat)
nerves of the eye
- optic, oculomotor, trochlear, trigeminal, abducens (CN II, III, IV, V, VI)
muscles of the eye, innervations
Muscles attached to the globe via insertion into the sclera
Function: move the globe via innervation with cranial nerves
<><>
- Recti: dorsal/ventral/medial/lateral/dorsal oblique/ventral oblique
> Dorsal, medial, ventral and ventral oblique recti: CNIII
> Lateral rectus: CN VI
> Dorsal oblique: CN IV
> Retrobulbar muscles (cone): CN VI
blood supply to the eye
maxillary > ophthalmic > ciliary artery and vein
Eyelids and nasolacrimal system anatomy
Upper/lower eyelid: Cilia on upper eyelid
Exterior covered by skin
Meibomian glands located on palpebral margin
o Function: secrete meibum (lipid)
Interior covered by palpebral conjunctiva
o Function: conjunctival goblet cells secretes mucin in tear film
Medial canthus: inner corner where upper and lower eyelid meet
Lateral cantus: outer corner where upper and lower eyelid meet
Closure: done by obicularis muscle and CN VII
Opening: done by levator palpebral superioris muscle and CN III
o Function: protect eye, distribute tear film, flush away debris
where is the fornix?
- on the top, between bulbar and palpebral conjunctiva
- on the bottom, between bulbar conjunctiva and bulbar side of the third eyelid
third eyelid structure and function
Covered by bulbar conjunctiva on inner face (facing ocular globe)
<><>
Passive movement over cornea
o Function: protects eye
<><>
Contains cartilage and a lacrimal gland at its base
o Function: gland produces 30-40% of aqueous portion of tear film
<><>
Lymphoid nodules on bulbar conjunctiva
o Function: local immune system
Nasolacrimal system
- components of tears
- where they go
Tears have 3 components:
o Meibum (top layer): neutral oils, phospholipids
> Function: prevents evaporation, increases tear film stability
o Aqueous (middle layer): water with inorganic salts
> Function: contains nutrients and immunoglobulins
o Mucin (bottom layer): glycoproteins rich in sialomucin
> Function: adheres tear film to corneal epithelial cells
<><>
Tears accumulate in lacrimal lake (medial canthal area cranial to third eyelid)
Nasolacrimal system: lacrimal punctum in upper and lower eyelids with their associated canaliculi join into the duct that terminates at the nasal punctum
o Function: filter tears into upper & lower lacrimal puncta by capillary flow into the canaliculi and duct to exit at nasal punctum
Anatomy: Episcleral and Scleral blood vessels appearance
Conjunctival blood vessels
* fine
* haphazard
<><>
Scleral blood vessels
* robust
* ~straight
corneal epithelium structure and function
Corneal Epithelium
* Non-keratinized stratified epithelium
* Non-pigmented, avascular
* Lipophilic layer
* Water barrier
* Renews itself in 7 days
* 8-15 cell layers thick
* Heavily innervated (CN Vo)
* Mechanical barrier
Corneal stroma structure and function
- Parallel and highly organized collagen fiber
bundles made from keratocytes - =~90% of corneal thickness
- Fewer nerves (CN V)
- Avascular
- Hydrophilic in nature
- Retains fluorescein stain
corneal endothelium and Descemet’s membrane structure and function
Descemet’s Membrane
* Basement membrane
* Elastic
* Does not retain fluorescein stain
* Barrier
<><><><>
Endothelium
* Monolayer
* No mitosis
* Active metabolic pump > pumps out aqueous humour (i.e.: keeps the cornea transparent by keeping aqueous out)
what is the uvea
- the middle layer of the eye between the sclera part and the retina
- It has 3 parts: Iris, Ciliary body, and choroid
iris structure and function
Iris: anterior uvea
o Open anterior margin: no epithelial coverage (tight junctions)
> Gateway for cells, protein, fibrin to enter anterior chamber
o Double epithelial layer on posterior margin
o Muscles: Dilator and Sphincter (smooth muscles)
o Colarette: middle section of iris
o Function: regulates amount of light entering the eye
Iridocorneal angle - what is this, function?
iris connection to cornea (Descemet’s membrane)
o Contains trabecular meshwork
o Function: filters out aqueous humour into general circulation
Ciliary body - structure and function
- continuation of posterior iris epithelium from iris
o Ciliary body extremities has zonules for lens attachment
o Function: site of aqueous humour production
> Ciliary body muscles action on zonules modify lens shape for accommodation (near or far vision)
Choroid structure and function
continuation of ciliary body posteriorly (posterior uvea)
o Covered by tapetum in the dorsal region of globe
o Function: chorio-capillaries supply blood to photoreceptors
Retina structure and function
Neurosensory layer
<><>
Retina: 9 layers + retinal pigment epithelial layer (RPE)
o Photoreceptors: rods (black/white vision) and cones (colour vision)
o Ganglion cells are the cell bodies to the axons of the optic nerve
o Retinal blood vessels supply inner most layers of retina
o Firmly attached at periphery and around optic nerve
> Otherwise apposed to retinal pigment epithelium
o Function: gathers light photons to produce image
Optic nerve structure and function
CNII
Composed of axons from the ganglion cells
Perforates sclera at lamina cribosa ventral and lateral to posterior pole
Surrounded by Dura matter and small amount of CSF
Function: conduction of retinal impulses to the brain
chambers of the eye and what they contain / do
Anterior, posterior, vitreal
<><><><>
Anterior chamber:
- Filled with clear aqueous humor
* water (99.9%)
* electrolytes (Na, K, Cl)
* proteins (albumin, Ig’s)
* nutrients (glucose)
Made by the ciliary body
<><><><>
Posterior chamber:
Surrounds the lens
- Made of aqueous humor
* lens nutrition and waste removal
<><><><>
Vitreal chamber
- 98% water
- Collagen fibrils, GAG’s, hyalocytes
aqueous humor functions
aqueous humour is similar to water in consistency
o Clear media made by non-pigmented ciliary body epithelium
o Aqueous molecules are born in the posterior chamber, filter through the pupil and exit through the iridocorneal angle
o Aqueous has quick turnaround (24 hours)
o Function: transmits light
> Provides nutrition to corneal endothelium and lens
> Helps maintain pressure in the eye
consistency and function of vetrous humour
vitreous is similar to egg whites in consistency
o Vitreous is attached to posterior lens capsule and retina
o Vitreous is formed by retinal cells, hyalocytes and non-pigmented ciliary body epithelium
o Vitreous has slow turn around (weeks – 3 months)
o Function: transmits light
> Stabilizes retina and apposes it choroid
> Maintains shape of globe
lens anatomy
Attached by zonules from extremities of ciliary bodies > Lens shape is modified by action from zonules
Relaxed zonules will make lens more spherical for near vision
Contracted zonules will make lens more ovoid for far vision
Grows throughout life: central compression of lens fibers
> Nuclear sclerosis (7 years in dogs; 10 years in cats)
Nutrition from aqueous humour
Anterior capsule contains epithelial cells that proliferate at the lens’ equator
Well aligned lens fibres are transparent
Lens fibres are all equal length and attach at suture line
> Form an upright “Y” on the anterior surface and an upside down “Y” on the posterior surface
Function: refract/bend light photons onto retina
<><><><>
- Surface ectoderm
- Biconcave, refraction
- Lens fibers – perfectly organized for clarity
- Nucleus doesn’t grow after birth
- Cortex enlarges after birth by the addition of
fiber layers
embyology - development of the eye
- Optic vesicles grow out
- Optic vesicle > optic cup
- Hyaloid vascular system
- Invagination of the lens placode
- Optic fissure closes, to enclose the hyaloid vascular system
- Vitreal and anterior chambers form
Coloboma - what is it
= congenital absence of a portion of tissue
- eg. iris coloboma, lens coloboma, optic nerve coloboma…
somewhat common congenital defects of the eye
- coloboma
- eyelid agenesis
- Persistent Pupillary Membranes (PPMs)
- Cataracts (nuclear cataract, will be less relevant with age)
Persistent Pupillary Membranes (PPMs)
- what is this?
Pupillary membrane
* Mesodermal tissue
* Covers pupil during development
* Normally regresses before birth
<><><><>
- dont cause problems for the dog, usually nothing to be concerned about
