Eyedocs anatomy Flashcards
What is the space called in the centre of the hyaloideocapsular ligament (Weiger)?
Berger’s space
Where does Cloquet’s canal travel from?
Courses from Berger’s space posteriorly through the central vitreous
What structures pass through the foramen rotundum and foramen ovale?
Rotundum - CNV2
Ovale - CNV3, accessory meningeal artery
What structures pass through the internal acoustic meatus?
CN7 and CN8
Vestibular ganglion and labyrinthine artery
What structures pass through the jugular foramen? Nerves, Arteries, Sinuses
Nerves: CN9, CN10, CN11
Arteries: meningeal branches of occipital and ascending pharyngeal arteries
Sinuses: inferior petrosal sinus, sigmoid sinus,
Where are the motor nuclei of the cranial nerves?
CN I - no nucleus, originals from olfactory bulb
CN II - no nucleus, originates from retina
CN III - upper part of midbrain at level of superior colliculus
CN IV - lower part of midbrain at level of inferior colliculus
CN V - upper dorsal part of the pons
CN VI - lower pons, deep to facial colliculus in floor of fourth ventricle
CN VII - lower part of pontine tegmentum
CN IX, X, XI nucleus ambiguus in the medulla.
CN XII - below hypoglossal trigone in floor of fourth ventricle of upper medulla
How long is each optic nerve segment?
1. intraocular
2. orbital
3. intracanalicular
4. intracranial
- 1mm
- 25mm
- 4-10mm
- 10mm
Where is the inner capillary plexus of the retina located in?
The ganglion cell layer
What is the first order neuron of the sympathetic pathway of the pupil?
Hypothalamus along the brainstem to synapse in the ciliospinal centre of Budge
What is the second order and third order neuron of sympathetic pathway of pupil?
Second: Centre of Budge to superior cervical ganglion
Third: Superior cervical ganglion, travels along carotid plexus, branches join ophthalmic division of trigeminal nerve and pass through ciliary ganglion to nasociliary and short ciliary nerves
Where do they layers project to in the primary visual cortex?
Layer II/III: project to secondary visual cortex
Layer IV: receives fibres from macula
Layer V: projects to superior colliculus
Layer VI: Projects to LGN
What is the afferent pathway of the light reflex?
Retina –> optic chiasm –> cross into pretectal nucleus near superior colliculus in midrain
What is the centre of the light reflex? What is responsible for the consensual reflex
Fibres from both pretectal nuclei go and connect with the edinger westphal nucleus via INTERNUCIAL NEURONS
What is the efferent pathway of the light reflex?
Parasympathetic fibres from edinger westphal nucleus –> via third cranial nerve –> ciliary ganglion –> via short ciliary nerve –> sphincter pupillae
Sphincter pupillae - which NS?
Dilator pupillae - which NS?
SP - Parasympathetic
DP - Sympathetic
What is the difference in structure and nerve supply of sphincter pupillae and dilator pupillae?
structure : SP spherical, DP radial
nervous: SP supplied by short ciliary nerves
nervous: DP supplied by long ciliary nerves
What is the pathway from the Edinger Westphal nucleus to the Sphincter pupillae (the parasympethetic pathway)?
Edinger westphal –> third cranial nerve through cavernous sinus –> third CN splits into superior and inferior divisions –> inferior division supplies IR, IO, MR and synapses with ciliary ganglion. Post-ganglionic fibres (posterior short ciliary nerves) pierce sclera and enter eyeball and supply ciliary muscle (95%) and sphincter pupillae (5%)
What is the pathway of the sympathetic nerve supply of the pupil?
1) hypothalamic centre causes inhibition of edinger westphal nucleus
2) hypothalamic centre sends nerves to spinal centre of budge (C8, T1, T2, T3, T4) –> leave through sympathetic cervical chain to the superior cervical ganglion (SCG)
3) Post ganglionic fibres from SCG enter skull and coil around the internal carotid artery (carotid plexus) into the cavernous sinus
4) sympathetic fibres pass over the trigeminal ganglion and pass into V1 in cavernous sinus.
5) V1 subdivides into lacrimal branch, frontal branch, nasociliary branch –> long ciliary nerve.
6) long ciliary nerves pierce sclera and supply dilator pupillae to cause dilatation of pupil
what are the functions of the RPE
What is the structure of rod cones from RPE to vitreous?
Outer segment (transductive) –> inner segment (region for maintenance of cellular homeostasis) –> nuclear region (outer nuclear layers) –> transmissive region (outer plexiform/synaptic layer)
Which types of cells are present in the inner nuclear layer? (3)
(1) bipolar neurons
(2) horizontal cells
(3) amacrine cells
What is the difference between the outer segments of rods and cones ? (2)
RODS: cylindrical and contain rhodopsin pigment, made up of vitamin A (night blindness)
CONES: conical and contain iodopsin pigment (colour blindness)
What is the difference in numbers between rods and cones?
rods: 120 million
cones: 5 million
what is the maximum spectral sensitivity of the rod cells?
496nm
Where is the lens located?
In a saucer shaped space in the patellar fossa
What is the hyalodo-capsular ligament (Weigert’s ligament)
Connects the posterior pole of the lens to the patellar fossa
What is retrolental space? (Berger’s space)
Space which exists between hyaloid face and lens within circular ligament
What is the function of the lens? (3)
- Transmits and refracts light - 35% refractive power
- Lens absorbs UV light < 350nm wavelength
- It helps in accomodation
What is the radius of curvature of the anterior surface of the lens vs posterior surface of lens
- Posterior surface is more curved and thinner , so it is 6mm vs 10mm anterior surface (thicker)
What is the equatorial diameter of the lens at birth vs adulthood
6.5mm at birth, 9-10mm
What is the lens thickness at birth and at extreme adulthood (what is average rate of growth)
3.5mm at birth, 5.5mm extreme adult life (0.2mm each year)
How far is the anterior pole of the lens from the centre of the cornea?
3mm from the cornea
What is the refractive index of the lens? What is the refractive power of the lens?
index - 1.39
power - 16-17D
What material surrounds the lens?
- hyaline collagenous membrane that surrounds lens, elastic but contains no elastic fibres
What is the structure of the anterior lens epithelium?
Cubiodal nucleated epithelium
Where is the most metabolically active part of the lens?
Anterior lens epithelium (cuboidal nucleated epithelium)
What is the epithelium in the equatorial region of the lens?
columnar cells –> they actively divide
What is the difference in shape between the central, peripheral and equatorial epithelial cells
central: cuboidal
peripheral: smaller and cynlindrical
equatorial: columnar
Which lens epithelial cells undergo mitosis?
central epithelial cells: undergo metaplasia in shield cataract –> glaucomfleken
peripheral zone epithelial cells: rarely undero mitosis
equatorial zone: actively mitose, and migrate posteriorly to form new lens fibres –> dysplasia of these cells called posterior subcapsular cataract (myotonic dystrophy, radiation, neurofibromitosis 2)
What is the bow region of the lens?
The newly laid lens fibres from migratory cells of equatorial zone ELONGATE so that their nuclei are more anterior to the nuclei of the older, more superficial cells
What is the difference between Elschnig’s pearls and Soemmering’s rings?
POSTERIOR CAPSULAR OPACIFICATION: Residual epithelial cells migrate posteriorly and differentiate into a balloon like wedl cell –> Elschnig pearl
If become a doughnut shape configuration - Soemmering’s rings.
What is the structure of the nuclear zone lens fibres?
Primary lens fibres : develop from posterior epithelium before 3 months of age (oldest cells are in the centre)
Secondary lens fibres: develop from the equatorial zone (youngest cells are in the periphery)
Where do the zonules of zinn arise from and where do they insert?
Arise from the posterior end pars plana of ciliary body (up to 1.5mm from ora serrata) and insert into the equator of the lens
What are the 3 types of conjunctiva? Subtypes?
- Palpebral (inner eyelid) - marginal, tarsal, orbital
- Bulbar (anterior eyeball) - scleral, limbal
- Forniceal (in between both)
Where is the conjunctiva firmly adherent to? Where is the conjunctiva loosly attached to?
- Adherent to lids over tarsal plates (upper > lower)
- Loosely attached to fornices and over globe (except limbus)
- What is the sulcus subtarsalis?
- How far is it away from lid margin?
- When is the subtarsalis scarred?
- Groove 2mm away from lid margin
- 2mm - common site for foreign body lodging
- Trachoma - Arlt’s line
What are the different structures in the palpebral conjunctiva?
- Marginal conjunctiva (anterior - posterior lid margin)
- Sulcus Subtarsalis
- Tarsal Conjunctiva (covers tarsal plate)
- Orbital Conjunctiva (between tarsal plate and fornix, over muller’s muscle)
What are the types of epithelium in the palpebral conjunctiva? How many layers of epithelium?
- Marginal - transition zone between skin and conjunctiva - stratified epithelium - 5 layers of STRATIFIED SQUAMOUS EPITHELIUM
- Tarsal - 2 layers of STRATIFIED CUBOIDAL EPITHELIUM
- Orbital - idk
What is the difference between forniceal conjunctiva and tarsal conjunctiva?
Thicker conjunctiva and is loosely present to allow movement of globe
How much tear fluid is present in the conjunctival sac?
7 microlitres, can hold up to 30 microlitres
Where is the bulbar conjunctiva firmly adherent ?
- 3mm zone near limbus
- Insertion of rectus muscles
What type of epithelium is conjunctiva?
- Stratified non keratinized epithelium
How many layers of epithelium are over the forniceal conjunctiva?
2 layers
What happens to the conjunctival epithelium when goes from fornices to the limbus?
Becomes thicker
How many layers of epithelium in the bulbar conjunctiva? Type of epithelium
10 layers of STRATIFIED SQUAMOUS EPITHELIUM
What is the pathological mechanism of squamous metaplasia of the conjunctiva?
transition of squamous, moist non-keratinised to become dry, keratinised epithelium
What is the function of the goblet cells ? (2) Where are they located (1)
- Secrete 2.2ml of mucin
- Ensure stability of tear film by decreasing surface tension
- Located throughout the conjunctival epithelium and arise from basal layer
What are the structures within the adenoid/lymphoid layer of conjunctiva? (3)
- Lymphoid tissue (follicles are formed)
- Mast cells (6000 per mm cubed)
- Plasma cells, lymphocytes, neutrophils (CALT - conjunctival associated lymphoid tissue)
When does the lymphoid/adenoid layer of the conjunctiva arise?
From 3-4 months old
What is the structure of the fibrous layer of the conjunctiva?
- Connective tissue which attaches to tarsal plate - contributes to papillae
Where are the Popov glands located?
Located within the substance of the caruncle
How many Krause /Wolfring glands are there?
Krause - 20-40 in upper fornix, 6-8 in lower fornix
Wolfring - 2-5 located along superior tarsal border
Where are Krause and Wolfring glands located?
Krause - stroma of conjunctival fornix
Wolfring - upper border of tarsus
What are the accessory lacrimal glands? What is their role?
- Krause, Wolfring, Popov
- Contribute 10% of lacrimal secretions
- Contribute to basal tear secretion, no contribution to reflex tear secretion
What supplies the palpebral conjunctiva? What supplies the bulbar conjunctiva?
Palpebral : marginal arcade (marginal) and peripheral arcade (forniceal + orbital + tarsal)
Bulbar: anterior conjunctival artery (branch of anterior ciliary for limbus) and posterior conjunctival artery (branch of peripheral arcade)
What does the conjunctiva drain into ? What does the limbus drain into?
- Superior and inferior ophthalmc veins from eyelid plexus
- Limbus –> anterior ciliary vein
What is the nerve supply of the conjunctiva?
- Superior Palpebral and forniceal - V1 (frontal and lacrimal branches)
- Inferior palpebral and forniceal - V1 and V2 (lacrimal branches and infraorbital nerve)
- Bulbar : long ciliary nerve (nasociliary nerve - V1)
What is the function of the conjunctiva? (4)
- Tear production (mucin by goblet cells, aqueous by accessory lacrimal glands
- Supply of oxygen directly to cornea when eye is open
- Wash off debris and maintain smooth ocular surface
- Protection of eye by defense mechanisms - secretory IgA, mucin clumping, mast cell outpouring, intact epithelial barrier, lacrimation
Where are the goblet cells most abundant?
Fornices and plica semilunaris
Which nutrients are the most essential for health of conjunctival epithelium and goblet cells?
retinoids and vitamin A
Where do the lymphatics drain laterally and medially?
Laterally : superficial parotid nodes
Medially: submandibular nodes
Epithelial basement membrane of the conjunctiva is composed of which type of collagen?
Type IV
The lateral fornix of the conjunctiva extends how far from the limbus to the equator?
14mm
In primary gaze position, where does the upper lid and lower lid cover in relation to the cornea?
upper lid : covers 1/6th of cornea
lower lid: covers inferior limbus
Where does the lateral canthus lie in relation to the lateral orbital margin?
5-7mm
What is the grey line of the eyelid? What does it divide?
Gray line divides the eyelid margin into the anterior lamina and posterior lamina
What is the difference between the gland of zeiss and the gland of moll in terms of
1. Location
2. Lobularity
3. Function
- Zeiss : margin of the eyelid,
Moll: between cilia (eyelash) and anterior lid margin - Zeiss: unilobular
Moll: unbranched spiral shape - Zeiss: modified sebaceous gland that produces sebum to prevent eyelashes from becoming dry and brittle
Moll: apocrine sweat gland
What is the horizontal and vertical measurement of the palpebral fissure?
horizontal - 30mm
vertical - 9-11mm
What is a mongoloid slant? Which strabismus pattern does it exhibit
- Elevation of lateral canthus > 2mm
- Pseudo A pattern strabismus
What conditions have mongoloid slant?
- Down’s syndrome
- Noonan’s syndrome
What conditions have Anti-mongoloid slant? What strabismus pattern?
- Treacher collin syndrome
- Coffin lowry syndrome
- Zygomatic maxillary complex fracture
Pseudo V pattern strabismus
What are the 7 layers of the eyelid from outside to inside?
- Skin - v thin loosely adhered to muscle
- Subcutaneous areolar tissue - only fat
- Striated muscle layer (orbicularis + LPS)
- Submuscular areolar tissue
- Fibrous layer (tarsal plate and orbital septum
- Non-striated muscle layer - Muller’s muscle
- Conjunctiva
What are the two parts of the orbicularis muscle? What is their function?
- Orbital part - forced closure of eyelid
- Palpebral part - gentle closure of eyelid
What happens upon contraction of Horner muscle in orbicularis oculi?
Acts as lacrimal pump:
Draws the eyelid medially and posteriorly upon blinking which creates a negative pressure in lacrimal sac –> which draws tears into the sac from the canaliculus
What is the origin and insertion of the LPS
Origin: lesser wing of sphenoid
Insertion: levator aponeurosis divided into anterior and posterior portions
anterior fibres - insert into the skin to form skin crease
posterior fibres - anterior surface of tarsus
Which layer consists of the nerves and vessels of the eyelid? What does this layer connect with?
Submuscular areolar tissue
Communicates with striatum of scalp - dangerous area of scalp and can act as communication for pus/blood between two areas