Anatomy Flashcards
what is the eyeball?
optical apparatus and is roughly 25mm in diameter
what is the shape of an eyeball?
• Spherical shape – comprised of 3 layers + fascial sheath
what are the 3 layers of the eyeball?
Fibrous layer (outer) Vascular layer (uvea) Retina (inner)
what two parts make up the outer fibrous layer of the eye?
cornea
sclera
(junction between corneal limbus)
what is the cornea of the eye?
o anterior 1/6, approx. 540microns thick, thickest peripherally, avascular
o transparent fibrous layer – epithelium, Bowmans membrane, stroma, Descemets membrane, endothelium
o 2/3 of refractive power
what is the sclera of the eye?
o Posterior 5/6, tough, opaque layer
o extraocular muscles attach to the outer sclera
o collagen, ground substance, coarse weave
what are the 3 parts of the uvea of the eye?
choroid
ciliary body
iris
what is the role of the uvea of the eye?
role in absorbing reflected light + provides nutritional support
what is the structure of the choroid of the eye?
o Dark brown layer between sclera + retina
o Larger vessels externally, finer vessels internally
o Avascular area of retina
what is the ciliary muscle of the eye?
Smooth muscle, ring overlying ciliary processes, posterior to corneoscleral junction
Provides attachment for the lens
Contraction and relaxation changes shape of lens, controlling focus
Connects choroid with circumference of iris
what are the 3 parts of the ciliary body of the eye?
ciliary muscle
ciliary process
pars plana
what is the ciliary process of the eye?
Ciliary epithelium secretes of aqueous humour and maintains ocular pressure
what is the iris of the eye?
o Contractible diaphragm with a central aperture, pupil
o Coloured part of the eye
o Separates the anterior and posterior chamber
what are the two muscles that make up the iris?
Sphincter pupillae
Dilator pupillae
what is the iridocorneal angle of the eye?
lies between the iris, the anterior tip of the ciliary body and the cornea. Site of aqueous drainage from the eye via the trabecular meshwork
what is the retina of the eye?
sensory neural layer
what are the 3 parts of the retina?
retina
macule
optic disc
what is the structure of the retina?
o Anterior continuation of the pigmented layer and a layer of supporting cells
o Extends over the ciliary body + posterior surface of iris – to the pupillary margin
what is the structure of the macule of the eye?
o Lateral to the optic disc
o Small oval area – made of cones (rods around the periphery)
o Yellow in colour
o Centre of the macule = Fovea – area of most acute vision – cones at highest density
what is the structure of the optic disc of the eye?
o Where sensory fibres + vessels conveyed by the optic nerve enter the eye – only point of entry/exit
o Contains no photoreceptors so insensitive to light = BLINDSPOT
what is the anterior segment of the eye?
in front of lens, divided into chambers
what is the anterior chamber of the anterior segment of the eye?
Between cornea + iris
Contains aqueous humour
what is the posterior chamber of the anterior segment of the eye?
Between iris + supporting ligaments
Contains aqueous humour
what is the posterior segment of the eye?
behind lens
2/3rds of eye
Contains vitreous humour
what are the 7 bones that make up the bony orbit?
o Frontal, zygomatic, sphenoid, ethmoid, lacrimal, maxilla + paletine
o Additional bone is nasal
what are the shapes of the bony orbit?
quadrangular pyramids
what is the structure of the apices of the bony orbit?
directed anterolaterally = optic canal
what is the structure of the bases of the bony orbit?
directed posterior laterally
Called orbital margins/rim
Superior (frontal), inferior (maxillary), lateral (zygomatic), medial (lacrimal + ethmoid – orbital plate)
what is the role of the eyelid?
offer mechanical protection to the globe, spread the tears over the conjunctiva and cornea with each blink
what are the layers of the eyelid?
Skin – orbicularis oculi (muscle) – orbital septum + ligaments + tarsus – conjunctiva
what is two parts of the orbicularis oculi?
Orbital – thicker, redder colour, fibres form complete ellipse, used for tightly closing
Palpebral – thin, pale, arises rom medial palpebral ligament, used for lightly closing
what are the two tarsus of the eye?
o Superior tarsus – supports upper eye lid
o Inferior tarsus – supports lower eye lid
what is the structure of the tarsus?
dense bands of connective tissue
what are the ligaments of the of the eyelid?
o lateral palpebral ligament – connects tarsus to lateral margin
o medial palpebral ligament – connects tarsi to medial margin of orbit, orbicularis oculi originates + insert
what is the leviator palebrae superiors?
o tendon attaches to superior tarsus
o responsible for opening eye/lifting eyelid superiorly
what is the orbital septum?
o sheet of fascia – spans tarsi to margins of orbit
o Helps prevent spread of infection from superficial to deep
what are the two types of eye conjunctiva?
Palpebral
Bulbar
what is the palpebral conjunctiva?
inner surface of eyelids
more vascular than bulbar
contains follicles and papillae
what is the bulbar conjunctiva?
lines eyeball
less bascular
what does conjunctiva contain?
goblet cells which secrete part of tear film
what are the parts of the lacrimal apparatus?
lacrimal glands - excretory ducts - lacrimal canaliculi - nasocrimal ducts - accessory lacrimal glands
what is the role of the lacrimal glands?
Secretes lacrimal fluid (saline containing bactericidal enzyme lysozyme)
o Moistens + lubricates conjunctiva + cornea
o Also provides nutrients and oxygen
what is the role of the excretory ducts?
transfer lacrimal fluid lacrimal glands – conjunctival sac
what are the parts of the lacrimal canaliculi?
o Canals
o Lacrimal punctum (openings) on lacrimal papilla – lacrimal lake – lacrimal sac
what is the role of the nasocrimal ducts?
conveys fluid to inferior nasal meatus
what is the role of the tear film?
Has antimicrobial properties due to the action of lyzoyme
what is the structure of the tear film?
o Lipid Phase 0.2μm o queus Phase 3-4μm o Mucous Phase 1μm o Microvilli o Epithelium
what is the arterial blood supply of the eye?
internal carotid - ophthalmic artery
ophthalmic - central artery of the retina - end artery
ophthalmic - posterior ciliary arteries (8) - short posterior ciliary arteries (6) + long posterior ciliary arteries
ophthalmic - muscular branches - anterior ciliary arteries
what is the venous supply of the eye?
central vein of retina - superior ophthalmic vein
vorticose veins + central vein of the retina - inferior ophthalmic vein - pterygoid venous plexus + cavernous sinus
what are the retinal layers of the eye?
- Retinal Pigment Epithelium
- The Photoreceptors (rods and cones)
- Bipolar Nerve Layer (+ amacrine and horizontal nerve cells)
- The ganglion cells
- The axons of the ganglion cells lie anterior to the ganglion cells
what is phototransduction?
retinol (II-cis retina) changes to all-trans retinal
transducin breaks away from rhodopsin
binds to cGMP PDE (breaks down cGMP to GMP_
decreased cGMP causes sodium channels to close - hyperpolarisation occurs sending a signal
what is the range of visible light we see?
750nm – 350nm
what is the structure of photoreceptors?
o Outer segment – optic discs stacked up
o Inner segment
o Cell body
o Synaptic terminal
what are the two types of photoreceptor?
rods and cones
what are the features of rods?
- Achromatic
- Peripheral retina
- High convergence
- High light sensitivity
- Low visual acuity
- 120 million
- Slow recovery
what are the features of cones?
- Chromatic
- Central retina
- Low convergence
- Low light sensitivity
- High visual acuity
- 6 million
- High recovery
how is light from visual fields process?
o Light from objects in the right visual field is processed by left primary visual cortex
o Light from objects in the lower visual field is processed by the upper primary visual cortex
for what visual field does the retina cross over?
Nerve fibres from the nasal half of each retina cross over at the optic chiasm.
where is does the visual process terminate?
Striate Complex
where is the visual field mapped?
retina, LGN, superior colliculus & cortex
what is the origin of the levitator palpebrae superioris?
Lesser wing of sphenoid bone, superior and anterior to optic canal
what is the origin of the superior oblique?
Body of sphenoid
what is the origin of the inferior oblique?
Anterior part of floor of orbit
what is the origin of the superior rectus?
Common tendinous ring
what is the origin of the inferior rectus?
Common tendinous ring
what is the origin of the medial rectus?
Common tendinous ring
what is the origin of the lateral rectus?
Common tendinous ring
what is the insertion point of the levitator palpebrae superioris?
Superior tarsus and skin of superior eyelid
what is the insertion point of the superior oblique?
Its tendon passes through a fibrous ring or trochlea, changes its direction and inserts into sclera deep to superior rectus muscle
what is the insertion point of the inferior oblique?
Sclera deep to lateral rectus muscle
what is the insertion point of the superior rectus?
Sclera just posterior to corneoscleral junction
what is the insertion point of the inferior rectus?
Sclera just posterior to corneoscleral junction
what is the insertion point of the medial rectus?
Sclera just posterior to corneoscleral junction
what is the insertion point of the lateral rectus?
Sclera just posterior to corneoscleral junction
what is the innervation of the levitator palpebrae superioris?
CN3
what is the innervation of the superior oblique?
CN4
what is the innervation of the inferior oblique?
CN3
what is the innervation of the superior rectus?
CN3
what is the innervation of the inferior rectus?
CN3
what is the innervation of the medial rectus?
CN3
what is the innervation of the lateral rectus?
CN6
what is the action of the levitator palpebrae superioris?
Elevates superior eyelid
what is the action of the superior oblique?
Abducts, depresses and medially rotates eyeball
what is the action of the inferior oblique?
Abducts, elevates and laterally rotates eyeball
what is the action of the superior rectus?
Elevates, adducts and rotates eyeball medially
what is the action of the lateral rectus?
Depresses, adducts and roatates eyeball laterally
what is the action of the medial rectus?
Adducts eyeball
what is the action of the lateral rectus?
Abducts eyeball
sensory innervation of the eye comes from which nerve?
trigeminal
what is the sensory afferent of the blink reflex?
Action potentials conducted from cornea via CNV1 branches (nasocillary) - To trigeminal ganglion then along CN V - to pons - Central CNS Connections between CN V + CNVII - Motor Efferent Limb Action potentials conducted via CNVII - eye lid part of orbicularis occuli
where to the presynaptic axons form CNS for the eye arise?
o Exit spinal cord in T1 spinal nerve
o Ascend within
o Synapse in superior cervical sympathetic ganglion
what is the route of post synaptic sympathetic innervation?
o Eneter internal + exteral xarotid nerves
o Pass onto the surface of internal + external arteries
o Carried to the organs of the head of the surface of the brnaces of these arteries
o Oprhalmic artery carries sympathetic axons into the orbit
what is the route of the oculomotor nerve?
- Connects with CNS at junction between midline and pons
- Passes through the cavernous sinus, exits via superior orbital fissure
- Divides into the inferior and superior branch as it enters the orbit through the orbit fissure
what are the long ciliary nerves?
o Branches of CNV1 (nasocillary branch)
o Pass to the eyeball, by passing the ciliary ganglion, convey post synaptic fibres to dilator pupillae and afferent fibres from the iris and cornea
o Sympathetic and osmatic sensory
what are the short ciliary nerves?
o Branches of CNV1
o Parasympathetic + sympathetic to ciliary body + iris
o Postsynaptic parasympathetic fibres originating in the ciliary ganglion, afferent fibres from nasociliary nerve that pass through the ganglion and post synaptic sympathetic fibres
what is the role of the ciliary nerves?
• Ciliary nerves supply autonomic axons to control diameter of iris & refractive shape of lens
what are the autonomic reflexes of eye?
- Maximal eyelid elevation/wide opening of fight or flight
- Pupillary dilation/constriction adjusting light entry pupillary light/reflex
- Focusing lens far & near vision: accommodation reflex
- Lacrimation reflex tear production
how do pupils dilate?
sympathetic
Dilator pupillae fibres are radically arranged around external circumference of iris
When radial fibres contract, pull muscle to pull pupil
how do pupils constrict?
parasympathetic
Sphincter pupillae fibres encircle pupil – around the internal circumference of iris
what is the light reflex?
o Direct light reflex occurs in the stimulated ee
o A consensual light reflex occurs in non-stimulated
what is the 4 neurone chain of light reflex chain?
1st Neurone – retinal ganglion cells, pass via ipsilateral optic nerve, decussate in optic chiasm, synapses in pretectal nucleus in midbrain
2nd Neurone – located entirely within midbrain & connect pretectal nucleus to next sunapse in Edinger-Westphal Nucleus (location of cell bodies of parasympathetic axons of CN III)
3rd Neurone- pass from EW nucleus, via CN3 then its inferior division to synapse in ciliary ganglion
4th Neurone – course in short ciliary nerves to sphincter pupillae
what apparatus is involved in focusing the lens
ciliary body
how does the lens change for far vision?
o Sympathetic stimulation
o Muscle ring is relaxed, diameter of muscle ring becomes larger
o Lens suspended is under tension as periphery is stretched
o Ligament tightens and lens flattens to focus on object in distance – less convex
how does the lens change for near vision?
o Parasympathetic
o Muscle is contracted, ring becomes smaller
o Lens tension is reduced, ligament relaxes & lens becomes spherical – more convex
what is the accommodation reflex?
o Active process of changing the shape of lens for near vision
how does the accommodation reflex occur?
Bilateral pupillary constriction, parasympahteic constriction of sphincter – CNIII
Bilateral convergence of both eyes towards midline, medial recrys CNIII
Bilateral relaxation of the lens, lens become spherical due to contraction CNIII
what are the different types of tears?
reflex
emotional
basal
what is the process of reflex tears?
parasympathetics CNVII (muscles of facial expression) → CNVII (stylomastoid foramen) → CNVII (internal acoustic meatus) → CNVII (branch containing parasympathetic axons for lacrimal) → V2 → V1 → Lacrimal Gland
what is the innate immune system of the eye?
- Physical Barrier – no skin transparent + exposed
- Commensal bacteria – not many
- Chemical agents – yes
- Cells – yes
what are the alternative methods of eye immune system?
- Blink reflex and physical properties
- Chemical Properties of eye surface
- Immune cells in eyes – tears
how do tears act in the eyes immune system?
• Tears – physical, flushing, mucus layer – anti adhesive
what are the chemical properties of the eye surface?
- Tears – chemical
- Lysozyme – gram -ve bacteria, fungi (destroy cell walls)
- Lactoferrin and transferrin – gram +ve bacteria
- Tear lipids – antibacterial to cell membranes/scavenger of bacterial products
- Angiogenin – antimicrobial effect
- Secretory IgA – revents attachment
- Complement
- IL-6, IL-8, MIP – antimicrobial molecules that recruit leukocytes
what are the immune cells in the eyes?
(neutrophils, macrophages, conjunctival mast cells)
what is the adaptive immune system of the eye?
- Antigen Presenting Cells – APC = dendritic cells, B cells, macrophages
- Lymphatic Drainage to lymphnode
- Variety of effector cells – CD4+ T cells, CD8+ T cells, B cells
what are Langerhan cells?
- Principle APC for external eye
- Rick n class II MHC molecules
- Abundant at corneo-scleral limbus, less in peripheral cornea, absent from central 1/3rd of cornea
