Ophthalmology Anatomy, Physiology, and Embryology Flashcards

1
Q

anatomy of the eye
- what are the sections? what structures are in each?

A

ANTERIOR SEGMENT
1. Anterior chamber
(in front of iris)
- cornea
- iris
- limbus
2. Posterior chamber
(behind iris)
- front of lens
- ciliary body
- sclera
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POSTERIOR SEGMENT
- back of lens
- sclera
- choroid
- tapetum
- retina
<><><><>
- optic nerve

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2
Q

bones of the orbit?
- what animals have complete vs incomplete?

A
  • 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)
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3
Q

nerves of the eye

A
  • optic, oculomotor, trochlear, trigeminal, abducens (CN II, III, IV, V, VI)
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4
Q

muscles of the eye, innervations

A

 Muscles attached to the globe via insertion into the sclera
 Function: move the globe via innervation with cranial nerves
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- 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

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5
Q

blood supply to the eye

A

maxillary > ophthalmic > ciliary artery and vein

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6
Q

Eyelids and nasolacrimal system anatomy

A

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

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7
Q

where is the fornix?

A
  • on the top, between bulbar and palpebral conjunctiva
  • on the bottom, between bulbar conjunctiva and bulbar side of the third eyelid
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8
Q

third eyelid structure and function

A

 Covered by bulbar conjunctiva on inner face (facing ocular globe)
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 Passive movement over cornea
o Function: protects eye
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 Contains cartilage and a lacrimal gland at its base
o Function: gland produces 30-40% of aqueous portion of tear film
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 Lymphoid nodules on bulbar conjunctiva
o Function: local immune system

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9
Q

Nasolacrimal system
- components of tears
- where they go

A

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

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10
Q

Anatomy: Episcleral and Scleral blood vessels appearance

A

Conjunctival blood vessels
* fine
* haphazard
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Scleral blood vessels
* robust
* ~straight

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11
Q

corneal epithelium structure and function

A

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

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12
Q

Corneal stroma structure and function

A
  • 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
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13
Q

corneal endothelium and Descemet’s membrane structure and function

A

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)

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14
Q

what is the uvea

A
  • the middle layer of the eye between the sclera part and the retina
  • It has 3 parts: Iris, Ciliary body, and choroid
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15
Q

iris structure and function

A

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

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16
Q

Iridocorneal angle - what is this, function?

A

iris connection to cornea (Descemet’s membrane)
o Contains trabecular meshwork
o Function: filters out aqueous humour into general circulation

17
Q

Ciliary body - structure and function

A
  • 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)
18
Q

Choroid structure and function

A

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

19
Q

Retina structure and function

A

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

20
Q

Optic nerve structure and function

A

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

21
Q

chambers of the eye and what they contain / do

A

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
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Posterior chamber:
Surrounds the lens
- Made of aqueous humor
* lens nutrition and waste removal
<><><><>
Vitreal chamber
- 98% water
- Collagen fibrils, GAG’s, hyalocytes

22
Q

aqueous humor functions

A

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

23
Q

consistency and function of vetrous humour

A

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

24
Q

lens anatomy

A

 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

25
Q

embyology - development of the eye

A
  • 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
26
Q

Coloboma - what is it

A

= congenital absence of a portion of tissue
- eg. iris coloboma, lens coloboma, optic nerve coloboma…

27
Q

somewhat common congenital defects of the eye

A
  • coloboma
  • eyelid agenesis
  • Persistent Pupillary Membranes (PPMs)
  • Cataracts (nuclear cataract, will be less relevant with age)
28
Q

Persistent Pupillary Membranes (PPMs)
- what is this?

A

Pupillary membrane
* Mesodermal tissue
* Covers pupil during development
* Normally regresses before birth
<><><><>
- dont cause problems for the dog, usually nothing to be concerned about