Eyes Flashcards
label the anatomy of the eye below
label the anatomy of the eyelids
label the anatomy of the third eyelid
label the anatomy of the anterior segment of the eye
label the anatomy of the posterior segment of the eye
what is Exopthalmos
abnormal protrusion of the eye from the orbit
- globe size remains normal
- globe position is protruding
- the eye itself appears normal
what is enopthalmos
abnormal recession of the eye within the orbit
- globe size remains normal
- globe position is sunken
- eye itself appears normal
what is hydropthalmos
enlargement of the globe
- globe size is enlarged
- globe position is normal
- eye itself appears abnormal
what is micropthalmos
congenitally abnormal (small) eye
- globe size is reduced
- globe position is normal
- eye(s) appear abnormal
what is the orbit
- the cavity within the skull that encloses the eye
- purpose is to protect the eye and separate it from the cranial cavity
contains foramina within the walls of the orbit to supply blood vessels and nerves to the eye
what types of orbit are there in domestic species
in domestic species the orbit is a bony cone with a soft tissue floor. there are 2 types:
- open/incomplete - has lateral orbital ligament (palpable as taut band in live animal) seen in CARNIVORES
- closed/complete - zygomatic and frontal bones are fused, seen in HERBIVORES
what is a brachycephalic skull and how does the shape impact the orbit
- relatively short skull
- shallow orbit with reduced protection offered to the eye
what is a mesocephalic skull and how does the shape impact the orbit
- medium length skull
- normal depth of the orbit
- moderate degree of protection offered to the eye
ex breeds: lab, GSD, Doberman, beagles etc.
what is a dolicephalic skull and how does it relate to the orbit
- long skulls
- deep orbit
- increased protection offered to the eye
example breed: dachshund, greyhound, great dane, poodle
what bones comprise of the orbital rim
- frontal
- lacrimal
- zygomatic bones
what bones and soft tissues comprise the wall of the orbit
- frontal bone (medial wall)
- frontal sinus bone (dorsal limit)
- zygomatic bone (orbital rim)
- maxillary bone (orbital rim)
- sphenoid bone (caudal limit)
- temporal muscles (dorsal limit)
- orbital ligament in dogs/cats (dorsal limit)
- masseter muscle (rostral and lateral limit)
- pterygoid muscles (ventral floor)
list the extraocular muscles and their innervation
- dorsal oblique mm (trochlear nn)
- dorsal rectus mm ( oculomotor nn)
- lateral rectus mm (oculomotor nn)
- medial rectus mm (oculomotor nn)
- retractor bulbi mm (abducens nn)
- ventral oblique mm (oculomotor nn)
- ventral rectus mm (abducens nn)
there are other structures that dont include muscles or bones in the orbit. what are they?
inside orbit:
- nasolacrimal duct
- base of nictitating membrane
- orbital fat cushion
outside the orbit:
- tooth roots
- zygomatic salivary glands
- paranasal sinuses
what are the 2 most important foramen in the orbit and what nerves/vessels pass through them
optic foramen:
- optic nerve, internal ophthalmic artery
Orbital fissure (dogs and cats)/orbital formaen (horses and ruminants):
- trochlear nerve, oculomotor nerve, abducens nerve, ophthalmic nerve
what is the major blood supply to the eye and what vessel is it derived from
the ophthalmic artery which is derived from the internal carotid artery
explain the venous drainage system of the eye and orbit
most venous drainage is through vortex veins and extensive orbital venous plexus. there is an alternative route through the ophthalmic vein.
all veins from the eye/orbit drain into the external jugular vein
what is anisocoria
unequal size of the pupils
what is miosis
excessive constriction of the pupil
what is mydriasis
dilation of the pupil
what is strabismus
cross eyed, inability to align both eyes simultaneously
what is nystagmus
condition of involuntary eye movement that may result in reduced or limited vision (eyes drift slowly away from lesion and flick rapidly back to centre)
how would you examine the orbit
- frontal and aerial view of the eyes from afar
- assess retropulsion ( should be equal and nonpainful) (limited in brachy breeds)
- oral exam (should have no pain on jaw movement, assess dental disease, ability to eat normally esp dry food?)
what is the palpebral fissure
opening between the eyelids
what muscles/nerves control eyelid closing
orbicularis oculi mm supplied by facial verve (VII)
what muscles/nerves control eyelid opening
- levator palpebrae superioris supplied but oculomotor nerve
- muller mm (smooth mm) with sympathetic innervation
- several other mm with innervation from facial nerve (VII)
what nerves carry sensation from to the eyelids
branches of the ophthalmic and maxillary nerves from trigeminal nerve (V)
what are the meibomian glands
- white or yellow columnar structures at right angles to the eyelid margin - modified sebaceous glands
- usually 20-40 glands per eyelid
- produce meibum (lipid component of the tear film
what is the function of the eyelids
- eyelid closure protects the eye from trauma
- blinking which distributes tear film, drains tear film and removes debris from ocular surface
- contributes to tear film (mucin from palpebral conjunctiva and lipids from meibomian glands)
describe the anatomy of the third eyelid
- central T-shaped cartilage
- conjunctiva covering the bulbar and anterior faces
- stromal connective tissue
- lymphoid follicles on posterior surface
- nictitans gland at base
- cats contain smooth muscles to retract and allow to move across passively when blinking
what is the function of the third eyelid
- protection of ocular surface
- leading edge distributes tear film and removes debris from corneal surface
- gland contributes to tear film
- contains immunoglobulin secreting plasma cells - role in defence of ocular surface
label the anatomy of the conjunctiva
describe the anatomy of the conjunctiva
- sensory innervation by ophthalmic branch of trigeminal nerve
- superficial and deep layers of stroma have extensive lymphatic and vascular supplies
- bulbar conjunctiva overlies sclera: finer, branching conjunctival vessels overlie larger, straighter episcleral vessels
what is the function of the conjunctiva
- protects ocular surfaces while allowing free movement of ocular structures
- contributes to tear film: goblet cells produce mucin
- most exposed mucous membrane in the body: must respond rapidly to noxious stimuli
- everted lymph node - stroma contains CALT: conjunctival associated lymphoid tissue
many lymphocytes present, which form active follicles when stimulated by antigens
how do tears drain from the eye
through the nasolacrimal duct (duct connecting the eyes to the nasal cavity
what are you looking for in an examination of the eyelids
- blinking (menace response, palpebral reflex)
- blepharospasm (squinting) indicates ocular pain
- tear staining - excess lacrimation (pain), epiphora (non painful overflow)
- conformation and eyelid positioning
- skin diseases
- extra hairs, masses, swellings
how do you examine the third eyelid
- retropulse the globe to protrude the third eyelid
- look underneath the third eyelid
- note that there is variation in normal pigmentation of the third eyelid and this is normal
how do you examine the nasolacrimal system
- identify nasolacrimal puncta
- flush nasolacrimal ducts with cannula
- fluid should exit the other puncta if communicating with each other properly
- close off one puncta and flush, fluid should exit through nostril
how do you examine the conjunctiva
- examine the palpebral conjunctival surface and compare to bulbar conjunctiva
- assess colour (semi transparent, variable pigment. abnormal colour (jaundice, cyanosis, toxaemia)
- inflammation, ocular discharge
- petechiae/subconjunctival haemorrhage
what is entropion
inversion of all or parts of the eyelid margin (causes hairs to rub on eye and cause ulcers)
what is ectropion
eversion or outward turning of the eyelid
what is diamond eye
extra long eyelids (can cause rubbing on cornea)
what is distichiasis
extra eyelashes emerging from meibomian gland orfices
what is ectopic cilia
arise from follicle inside or near meibomian gland and emerge through conjunctival surface of eyelid
what is trichiasis
normally located but abnormally directed hair contacting ocular surfaces
what is happening in a “cherry eye”
prolapsed nictitans gland
what is scrolled cartilage
T-shaped cartilage gets too long and rolls (scrolls) outward or inward causing chronic conjunctivitis
what is chemosis
marked swelling of conjunctiva
what is epiphora
tear overflow
describe the structure of the tear film
L.A.M.E (outside to inside)
- lipids (limits evaporation)
- aqueous with soluble mucins (most of volume)
- mucin (aids spread and adherence of tear film)
- epithelial cells
7-8 micrometers thick
describe the origin of the layers of tear film
lipid layer: from meibomian glands
aqueous layer: from orbital gland (70%) and nicitans gland (30%)
mucin layer: conjunctival goblet cells
what is the function of the tear film
- provides nutrients and oxygen to the ocular surface
- protects ocular surface from desiccation and bacteria
- lubricates ocular surface
- provides smooth and transparent ocular surface
describe the anatomy of the sclera
- opaque
- largest portion of the outer coat of the eye
- composed of collagen and fibroblasts
- 3 layers (lamina fusca. sclera proper/stroma, episclera)
- anterior portion covered by bulbar conjunctiva
what is the limbus
- where cornea, sclera and bulbar conjunctiva merge
- source of stem cells
what is tenons capsule
- connective tissue sheath
- connects bulbar conjunctiva to underlying sclera
what is the episclera
- dense, highly vascular fibrous layer
- binds tenons capsule to sclera
what are the 3 components of the cornea
- epithelium
- stroma
- endothelium
describe the structure of the cornea from outermost to innermost
- stratified epithelium and its basement membrane
- collagenous stroma
- descements membrane
- endothelium
describe the structure of the corneal epithelium
- stratified, squamous, non-keritinised epithelium
- 50-60 micrometers thick
- tight junctions between cells (permeability barrier)
- continual turnover of cells
- basement membrane 40-60 nm thick
describe the structure of the stromain the cornea
- 90% corneal thickness
- collagen fibrils in regularly spaced layers
- relatively dehydrated layer
describe the structure of the corneal epithelium
- one cell layer thick
- no turnover
- Na/K ATPase pump: pumps ions from stroma into the aqueous humour (keeps water out)
What factors contribute to corneal transparency
- smooth optical surface
- relatively dehydrated state
- very regular arrangement of collagen fibrils
- low cell density
- no keratin, blood vessels or melanin
what is the function of the cornea
- refract and transmit light - major refractive component of the eye
- tensile strength - lends rigidity to globe
- protection
how do you examine the tear film
- corneal reflection
- schirmer tear test to measure tear production
how do you examine the cornea and what abnormalities are you looking for
- light source +/- magnification
- darkened room
- looking for: irregularities, opacification, vascularization, pigmentation - should be clear and transparent if normal
- fluorescein staining
how does fluoroscein stain work
orange dye that turns green in alkaline tears.
- adheres to and stains hydrophilic tissues such as exposed corneal stroma
- extremely useful for diagnosis of corneal ulcers
what is keratoconjunctivitis sicca
- dry eye caused by inadequate tear production
- STT <15mm/min (norm=15-25)
- common esp in cocker Spaniels and toy breeds
- local immune-mediated destruction of orbital and nictitans lacrimal glands
- clinical signs include: conjunctivitis, thick mucoid discharge, blepharospasm, corneal ulceration, corneal vascularization and pigmentation, reduced vision
what is a corneal ulcer
break in the continuity of corneal epithelium with exposure of underlying stroma
- caused by: trauma, eyelid abnormalities, eyelash lesions, dystrophies/degeneration, infection, keratconjunctivitis sicca
what causes corneal ulcers
- truama (lacerations, abrasions, foreign body)
- eyelid abnormalities (entropion)
- eyelash lesions (ectopic cilium)
- dystrophies/degenerations
- infections e.g. IBK in cattle
- keratoconjunctivitis sicca
what are the different types of corneal ulcers
- superficial (involving epithelial layer)
- deep (stromal)
- descemetocoele (goes down to descemets membrane, bulges to surface - DESCEMET’S MEMBRANE DOES NOT TAKE UP STAIN!!!)
how does the epithelium of the eye heal
- proliferation of basal epithelial cells at limbus, movement of peripheral cells towards centre of cornea, epithelial cells lost form corneal surface into tear film
- faster if basement membrane remains intact
how does the stroma of the eye heal
- starts once re-epitherlialisation is complete
- fibroblasts migrate in and lay down new collagen
- requires vascularization (blood vessels budd off and move to area of injury)
results in scar tissue: remodelling over time
what does a blue corneal opacity indicate
oedema - where fluid enters the troma and disrupts the regular arrangements of collagen fibres caused by either an epithelial dysfunction (i.e. corneal ulcer) or endothelial dysfunction)
what does a red corneal opacity indicate
vacularisation
what does a white corneal opacity indicate
scarring, lipid, calcium, cellular infiltration
what does a dark coloured corneal opacity indicate
pigment
what are the 3 main anatomical components of the uveal tract
- iris (anterior uvea)
- ciliary body (anterior uvea)
- choroid (posterior uvea)
what are the gross anatomical components of the iris
- ciliary zone (peripheral)
- pupillary zone (central)
- collarette (transition)
describe the blood supply of the iris
- long posterior ciliary arteries
- anterior ciliary arteries
- incomplete major arterial circle
describe the anatomy of the iris
- stroma (most of the iris): composed of fibrous connective tissue, collagen bundles, pigmented and non-pigmented cells, blood vessels, iris sphincter muscle
- Anterior surface: modified stromal border layer (not epithelium)
- posterior surface: bilayered iris epithelium (includes iris dilator muscle within anterior layer
what is the function of the iris
- controls the amount of light entering the eye
- forms part of blood ocular barrier
describe the anatomy of the ciliary body
- continuation of posterior aspect of iris
- comprised of smooth muscle, connective tissue blood vessels and nerves
- forms uveal part of the iridocorneal drainage angle
- double layer of epithelium
- pars plicata (=folded part of ciliary processes) and pars plana (=flat)
what are the zonular fibres
support the lens
originate within the tips and valleys of ciliary processes
what is the function of the ciliary body
- production and drainage of aqueous humour
- maintains intraocular pressure
- provides nutrition to lens and inner cornea
- anchors lens zonules and provides accommodation (focussing)
- constitutes blood-aqueous barrier
- provides blood and nerve supply to anterior segment
how is aqueous humour produced and drained
- produced by ciliary processes, diffusion, ultrafiltration and active secretion
- drained mostly by uveal trabecular meshwork
describe the function of the aqueous humour
- supplies nutrients and remove waste from avascular tissues of the eye (cornea, trabecular meshwork, lens, anterior vitreous)
- maintains optical clarity of the eye
- composed of 98% water, proteins (albumin, igG), ascorbate, lactate, glucose, amino acids, oxygen
label the anatomy of the choroid
what is the function of the choroid
- blood supply of the retina
- part of blood-ocular barrier
- includes tapetum: reflecting light back into the retina to improve vision in dim light
what is the purpose of the blood-ocular barrier
to supply blood to the eye without compromising vision/clarity of the eye
what is uveitis
inflammation of the uvea caused by:
- increased blood supply
- increased permeability of vessels
- white blood cell migration
clinical signs:
- pain
- red eye
- miosis
- inflammation
- corneal oedema
- low intraocular pressure
what is glaucoma
- intraocular pressure depends on volume of aqueous present and ocular rigidity
- constant production and drainage of aqueous by ciliary body
- reduced drainage
- raised intraocular pressure
blinding, painful, treatment is challenging
can be caused by other optical conditions (uveitis, lens luxation, tumours)
- pain, red eye, corneal oedema, fixed dilated pupil, vision loss, globe enlargement, corneal changes, lens luxation, cataracts, permanent blindness
IOP of over 25 mmHg in dog/cat = abnormal
over 20 in rabbit = abnormal
difference of >8mmHg between eyes = abnormal
what methods are there to measure intraoccular pressure
-schioz tonometry
- tonopen
- tonovet
describe the anatomy of the lens
- see-through m&m (transparent, avascular, convex body)
- sits in hyaloid fossa posteriorly
- supports iris anteriorly
- supported by lens zonules
- has a lens cpasule and anterior lens epithelium
- lens fibres have tick centres and tapered ends
- fibres cannot meet in a single point (not enough space) and instead meet in a Y shaped pattern (right side up anteriorly and upside down posteriorly)
describe lens development as the animal ages
- secondary lens fibres continue to form throughout life
- concentric growth (like bone)
- new lens fibres form from anterior epithelium at the lens equator and wrap around embryonic nucleus
- older fibres denser and less transparent than younger fibres in cortex: nuclear sclerosis
explain the difference between how the fetal lens and adult lens receive nutrition
Fetus:
- tunica vasculosa lentis (regresses away w/in 2 weeks of birth in dogs/cats BEFORE eyes open)
- anteriorly: pupillary membrane (no pupila in developing eye)
- posteriorly: primary vitreous (hyaloid artery main blood vessel)
Adult:
- aqueous humour: oxygen and glucose enter mainly by diffusion
- no blood vessels and no nerves
describe the composition of the lens and why is composition important
- 35% protein (soluble =85%, rest insoluble)
- 65% water
- stable composition of the lens is vital to maintain transparency
- if amount and type if proteins changes, cataract develops
what is the function of the lens
- 30-35% refractive power of the eye (focusing of light onto retina)
- accommodation
- blocking UV light from retina
Describe the anatomy of the vitreous humour
- gel between lens and retina
- largest ocular structure
- transparent
- avascular and nerve free
- 99% water, 1% protein/cells
what is the function of the vitreous humour
- shock absorber
- removes waste products
- maintains intraocular anatomy
what are some developmental abnormalities of the uveal tract blood supply
- persistent pupillary membranes (failure of regression of anterior portion of tunica vasculosa lentis
- persistent hyaloid artery
what is the oldest part of the lens
the embyronic nucleus
what is nuclear sclerosis
- secondary lens fibres continue to form throughout life: from anterior epithelium at lens equator, and wrap around embryonic nucleus
- finite space within the eue = pregressive compression of the nucleus
- older fibres denser and less transparent than younger cortical fibres
- nucleus becomes sclerotic (hardened)
- normal ageing process
- appears greyish blue haze
- causes presbyopia (age related reduced ability to focus on near objects) but no major effect on vision in animals
how to tell the difference between nuclear sclerosis and cataracts
- using distant direct ophthalmoscopy
- 0 dioptres setting in a dark room
- observe from arms length and look at tapetal reflection
- mature cataract blocks tapetal reflex
- nuclear sclerosis does NOT block tapetal reflex
what is a cataract
- any opactiy of the lens or its capsule
- part or all lens loses normal transparency and becomes white
- change in ratio of normal lens proteins
- causes: hereditary, senile, metabolic (diabetes), trauma, other intraocular diseases
why is an anterior lens luxation a more serious condition than posterior luxation
- when the lens luxates anteriorly, the ens blocks the flow of aqueous humour
- pressure inside the eye increases rapidly causing acute secondary glaucoma (emergency)
label the layers of histology of the posterior segment of the eye
list the layers of the retina from posterior to anterior
- internal limiting layer
- nerve fibre layer
- ganglion cell layer
- inner plexiform layer
- inner nuclear layer
- outer plexiform layer
- outer nuclear layer
- external limiting membrane
- photoreceptor layer
- retinal pigment epithelium
OR more simply:
- retinal pigment epithelium (most anterior)
- neurosensory layer (the rest)
describe the retinal pigment epithelium
- outermost layer, single layer of cells
- lies in front of the tapetum
- despite its name, RPE is both pigmented and non-pigmented (pigmented in ventral fundus where tapetum is absent and non-pigmented in dorsal fundus where tapetum is present to allow tapetum to be seen
- essential for retinal integrity nd function
- photoreceptors are therefore embedded within the RPE
what is the function of retinal pigment epithelium
support system for seurosensory retina above
- recycles “used” photopigments
- phagocytosing and renewing photoreceptor outer segments
- stores vitamin A
- melanin pigments (in non-tapetal areas only) to absorb stray light and scarvenge free radicals
- forms part of blood-retinal barrier
- phagocytic role in retinal infalmmation
what are rods and cones
- cells where light energy is convertd to a nerve impulse
- cones = colour visional and visual acuity
- rods = night vision
simplify the steps of phototransduction
- light absorbed
- hyperpolarisation of photoreceptor cell
- nerve impulse sent to optic nerve
what is the function of the retina
- absorbs light rays and converts light energy into electrical energy which travels as nerve impulse up optic nerve to visual cortex
what is the lamina cribosa
- sieve like area at posterior pole of the globe which the optic nerve passes through
- a weak point that is sensitive to increased intraocular pressure
- may be either myelinated (dogs) or non-myelinated (cats), affecting appearance of optic disc
what is the fundus
the portion of the posterior sement of the eye that is viewed with the ophthalmoscope
what animal is this
dog
why? myelinated = white/pink optic disk
what animal is this
cat
why? non myelinated = grey optic disk
what animal is this? is it normal?
this is a dog (probably a golden retreiver)
this is normal. some dog breeds have pronounced myelination (making the optic disc look “fluffy”)
outline the blood supply to the retina
the retina has a high metabolic rate and therefore has dual blood supply
- inner retina: retinal blood vessels
- outer retina: choroidal blood vessels
- different species have different arrangement of blood vessels which affects the appearance of the fundus
what does the term holangiotic mean
retinal blood vessels supply the whole retina (dogs, cats, cows, sheep, goats)
what does the term paurangiotic mean
retinal blood vessels supply a small focal area of retina (horse)
what is the tapetum
- part of the choroid, lies behind the retina
- retina is translucent, like tissue paper, so tapetum can be seen underneath
- shiny reflective layer like a mirror - causes the eye shine at night/ when looking with bright light
- only in the dorsal fundus
what is the function of the tapetum
reflect light rays so retina receives light twice
what colour is the tapetum in cats, dogs and yound animals
cats: yellow
dogs: green/blue
young animals: blue/turqoise
can be normal fundus variations depending on breed, merle collies for example have no pigment in the fundus and therefore no tapetum
if the retina has thinned, would you expect the tapetum to appear more or less reflective on ophthalmoscopy
more reflective
what are some clinically relevant conditions of the retina
- gPRA (hyper reflective)
- retinal detachement (sudden blindness)
- retinal haemorrhage
- chorioretinitis
what is hyphaema
blood in anterior chamber of eye
what is hypopyon
pus in anterior chamber of eye
what is corpora nigra/granula iridica and whats the difference
black masses at dorsal edge of pupil in horses/ruminants
norpora nigra = horses
granula iridica = ruminants
