Eyedocs anatomy Flashcards
1
Q
What is the space called in the centre of the hyaloideocapsular ligament (Weiger)?
A
Berger’s space
2
Q
Where does Cloquet’s canal travel from?
A
Courses from Berger’s space posteriorly through the central vitreous
3
Q
What structures pass through the foramen rotundum and foramen ovale?
A
Rotundum - CNV2
Ovale - CNV3, accessory meningeal artery
4
Q
What structures pass through the internal acoustic meatus?
A
CN7 and CN8
Vestibular ganglion and labyrinthine artery
5
Q
What structures pass through the jugular foramen? Nerves, Arteries, Sinuses
A
Nerves: CN9, CN10, CN11
Arteries: meningeal branches of occipital and ascending pharyngeal arteries
Sinuses: inferior petrosal sinus, sigmoid sinus,
6
Q
Where are the motor nuclei of the cranial nerves?
A
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
7
Q
How long is each optic nerve segment?
1. intraocular
2. orbital
3. intracanalicular
4. intracranial
A
- 1mm
- 25mm
- 4-10mm
- 10mm
8
Q
Where is the inner capillary plexus of the retina located in?
A
The ganglion cell layer
9
Q
What is the first order neuron of the sympathetic pathway of the pupil?
A
Hypothalamus along the brainstem to synapse in the ciliospinal centre of Budge
10
Q
What is the second order and third order neuron of sympathetic pathway of pupil?
A
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
11
Q
Where do they layers project to in the primary visual cortex?
A
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
12
Q
What is the afferent pathway of the light reflex?
A
Retina –> optic chiasm –> cross into pretectal nucleus near superior colliculus in midrain
13
Q
What is the centre of the light reflex? What is responsible for the consensual reflex
A
Fibres from both pretectal nuclei go and connect with the edinger westphal nucleus via INTERNUCIAL NEURONS
14
Q
What is the efferent pathway of the light reflex?
A
Parasympathetic fibres from edinger westphal nucleus –> via third cranial nerve –> ciliary ganglion –> via short ciliary nerve –> sphincter pupillae
15
Q
Sphincter pupillae - which NS?
Dilator pupillae - which NS?
A
SP - Parasympathetic
DP - Sympathetic
16
Q
What is the difference in structure and nerve supply of sphincter pupillae and dilator pupillae?
A
structure : SP spherical, DP radial
nervous: SP supplied by short ciliary nerves
nervous: DP supplied by long ciliary nerves
17
Q
What is the pathway from the Edinger Westphal nucleus to the Sphincter pupillae (the parasympethetic pathway)?
A
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%)
18
Q
What is the pathway of the sympathetic nerve supply of the pupil?
A
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
19
Q
what are the functions of the RPE
A
20
Q
What is the structure of rod cones from RPE to vitreous?
A
Outer segment (transductive) –> inner segment (region for maintenance of cellular homeostasis) –> nuclear region (outer nuclear layers) –> transmissive region (outer plexiform/synaptic layer)
21
Q
Which types of cells are present in the inner nuclear layer? (3)
A
(1) bipolar neurons
(2) horizontal cells
(3) amacrine cells
22
Q
What is the difference between the outer segments of rods and cones ? (2)
A
RODS: cylindrical and contain rhodopsin pigment, made up of vitamin A (night blindness)
CONES: conical and contain iodopsin pigment (colour blindness)
23
Q
What is the difference in numbers between rods and cones?
A
rods: 120 million
cones: 5 million
24
Q
what is the maximum spectral sensitivity of the rod cells?
A
496nm
25
Where is the lens located?
In a saucer shaped space in the patellar fossa
26
What is the hyalodo-capsular ligament (Weigert's ligament)
Connects the posterior pole of the lens to the patellar fossa
27
What is retrolental space? (Berger's space)
Space which exists between hyaloid face and lens within circular ligament
28
What is the function of the lens? (3)
1. Transmits and refracts light - 35% refractive power
2. Lens absorbs UV light < 350nm wavelength
3. It helps in accomodation
29
What is the radius of curvature of the anterior surface of the lens vs posterior surface of lens
1. Posterior surface is more curved and thinner , so it is 6mm vs 10mm anterior surface (thicker)
30
What is the equatorial diameter of the lens at birth vs adulthood
6.5mm at birth, 9-10mm
31
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)
32
How far is the anterior pole of the lens from the centre of the cornea?
3mm from the cornea
33
What is the refractive index of the lens? What is the refractive power of the lens?
index - 1.39
power - 16-17D
34
What material surrounds the lens?
1. hyaline collagenous membrane that surrounds lens, elastic but contains no elastic fibres
35
What is the structure of the anterior lens epithelium?
Cubiodal nucleated epithelium
36
Where is the most metabolically active part of the lens?
Anterior lens epithelium (cuboidal nucleated epithelium)
37
What is the epithelium in the equatorial region of the lens?
columnar cells --> they actively divide
38
What is the difference in shape between the central, peripheral and equatorial epithelial cells
central: cuboidal
peripheral: smaller and cynlindrical
equatorial: columnar
39
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)
40
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
41
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.
42
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)
43
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
44
What are the 3 types of conjunctiva? Subtypes?
1. Palpebral (inner eyelid) - marginal, tarsal, orbital
2. Bulbar (anterior eyeball) - scleral, limbal
3. Forniceal (in between both)
45
Where is the conjunctiva firmly adherent to? Where is the conjunctiva loosly attached to?
1. Adherent to lids over tarsal plates (upper > lower)
2. Loosely attached to fornices and over globe (except limbus)
46
1. What is the sulcus subtarsalis?
2. How far is it away from lid margin?
3. When is the subtarsalis scarred?
1. Groove 2mm away from lid margin
2. 2mm - common site for foreign body lodging
3. Trachoma - Arlt's line
47
What are the different structures in the palpebral conjunctiva?
1. Marginal conjunctiva (anterior - posterior lid margin)
2. Sulcus Subtarsalis
3. Tarsal Conjunctiva (covers tarsal plate)
4. Orbital Conjunctiva (between tarsal plate and fornix, over muller's muscle)
48
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
49
What is the difference between forniceal conjunctiva and tarsal conjunctiva?
Thicker conjunctiva and is loosely present to allow movement of globe
50
How much tear fluid is present in the conjunctival sac?
7 microlitres, can hold up to 30 microlitres
51
Where is the bulbar conjunctiva firmly adherent ?
1. 3mm zone near limbus
2. Insertion of rectus muscles
52
What type of epithelium is conjunctiva?
1. Stratified non keratinized epithelium
53
How many layers of epithelium are over the forniceal conjunctiva?
2 layers
54
What happens to the conjunctival epithelium when goes from fornices to the limbus?
Becomes thicker
55
How many layers of epithelium in the bulbar conjunctiva? Type of epithelium
10 layers of STRATIFIED SQUAMOUS EPITHELIUM
56
What is the pathological mechanism of squamous metaplasia of the conjunctiva?
transition of squamous, moist non-keratinised to become dry, keratinised epithelium
57
What is the function of the goblet cells ? (2) Where are they located (1)
1. Secrete 2.2ml of mucin
2. Ensure stability of tear film by decreasing surface tension
3. Located throughout the conjunctival epithelium and arise from basal layer
58
What are the structures within the adenoid/lymphoid layer of conjunctiva? (3)
1. Lymphoid tissue (follicles are formed)
2. Mast cells (6000 per mm cubed)
3. Plasma cells, lymphocytes, neutrophils (CALT - conjunctival associated lymphoid tissue)
59
When does the lymphoid/adenoid layer of the conjunctiva arise?
From 3-4 months old
60
What is the structure of the fibrous layer of the conjunctiva?
1. Connective tissue which attaches to tarsal plate - contributes to papillae
61
Where are the Popov glands located?
Located within the substance of the caruncle
62
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
63
Where are Krause and Wolfring glands located?
Krause - stroma of conjunctival fornix
Wolfring - upper border of tarsus
64
What are the accessory lacrimal glands? What is their role?
1. Krause, Wolfring, Popov
2. Contribute 10% of lacrimal secretions
3. Contribute to basal tear secretion, no contribution to reflex tear secretion
65
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)
66
What does the conjunctiva drain into ? What does the limbus drain into?
1. Superior and inferior ophthalmc veins from eyelid plexus
2. Limbus --> anterior ciliary vein
67
What is the nerve supply of the conjunctiva?
1. Superior Palpebral and forniceal - V1 (frontal and lacrimal branches)
2. Inferior palpebral and forniceal - V1 and V2 (lacrimal branches and infraorbital nerve)
3. Bulbar : long ciliary nerve (nasociliary nerve - V1)
68
What is the function of the conjunctiva? (4)
1. Tear production (mucin by goblet cells, aqueous by accessory lacrimal glands
2. Supply of oxygen directly to cornea when eye is open
3. Wash off debris and maintain smooth ocular surface
4. Protection of eye by defense mechanisms - secretory IgA, mucin clumping, mast cell outpouring, intact epithelial barrier, lacrimation
69
Where are the goblet cells most abundant?
Fornices and plica semilunaris
70
Which nutrients are the most essential for health of conjunctival epithelium and goblet cells?
retinoids and vitamin A
71
Where do the lymphatics drain laterally and medially?
Laterally : superficial parotid nodes
Medially: submandibular nodes
72
Epithelial basement membrane of the conjunctiva is composed of which type of collagen?
Type IV
73
The lateral fornix of the conjunctiva extends how far from the limbus to the equator?
14mm
74
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
75
Where does the lateral canthus lie in relation to the lateral orbital margin?
5-7mm
76
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
77
What is the difference between the gland of zeiss and the gland of moll in terms of
1. Location
2. Lobularity
3. Function
1. Zeiss : margin of the eyelid,
Moll: between cilia (eyelash) and anterior lid margin
2. Zeiss: unilobular
Moll: unbranched spiral shape
3. Zeiss: modified sebaceous gland that produces sebum to prevent eyelashes from becoming dry and brittle
Moll: apocrine sweat gland
78
What is the horizontal and vertical measurement of the palpebral fissure?
horizontal - 30mm
vertical - 9-11mm
79
What is a mongoloid slant? Which strabismus pattern does it exhibit
1. Elevation of lateral canthus > 2mm
2. Pseudo A pattern strabismus
80
What conditions have mongoloid slant?
1. Down's syndrome
2. Noonan's syndrome
81
What conditions have Anti-mongoloid slant? What strabismus pattern?
1. Treacher collin syndrome
2. Coffin lowry syndrome
3. Zygomatic maxillary complex fracture
Pseudo V pattern strabismus
82
What are the 7 layers of the eyelid from outside to inside?
1. Skin - v thin loosely adhered to muscle
2. Subcutaneous areolar tissue - only fat
3. Striated muscle layer (orbicularis + LPS)
4. Submuscular areolar tissue
5. Fibrous layer (tarsal plate and orbital septum
6. Non-striated muscle layer - Muller's muscle
7. Conjunctiva
83
What are the two parts of the orbicularis muscle? What is their function?
1. Orbital part - forced closure of eyelid
2. Palpebral part - gentle closure of eyelid
84
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
85
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
86
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
87
What is the tarsal plate?
Dense fibrous tissue of the eyelid giving strength and firmness, has meibomian glands embedded within it
88
What is the upper and lower tarsal height
Upper : 10mm
Lower: 4-5mm
89
How many meibomian glands are there?
20-30 on each lid
90
What do meibomian glands produce?
Sebaceous glands (like Zeiss glands) Produce lipids (meibum) that forms the outer layer of tear film to stop evaporation
91
What is attached to the superior tarsal border? (2)
What structure is attached below the superior tarsal border?
1.Orbital septum and muller's muscle
2. LPS aponeurosis attaches 3-4mm below,
92
What is attached to the inferior tarsal border? (3)
Orbital septum, capsulopalpebral fascia, inferior palpebral/tarsal muscle (lockwood ligament) which connects to the inferior rectus
93
What are the lateral ends of the tarsus attached to?
What are the medial ends of the tarsus attached to?
Lateral: whitnal tubercle by lateral palpebral ligament
Medial: attach to anterior lacrimal crest and frontal process of maxillla by medial palpebral ligament
94
What is the muller's muscle and inferior palpebral muscle supplied by?
sympathetic nerve fibres -- irritation leads to retraction of lids --> paralysis leads to horner's syndrome
95
Which nerve is not covered by the neurilemma? What is this nerve covered by?
optic nerve, covered by the meninges
96
How many parts of the optic nerve are there? (4) How long is each part?
1. Intraocular part : 1mm
2. Intraorbital part: 25-30mm
3. Intracanalicular part: 6-9mm
4. Intracranial part - 16mm
Total - 50mm
97
What is the average diameter of the optic nerve head? What happens at level of the sclera?
1.5mm. At the level of sclera it doubles to 3mm as there is now myelination of the fibres
98
What are the 4 subregions of the intraocular part of the optic nerve? What is their blood supply?
1. Surface nerve fibre layer - nerve fibres (95%) plus astrocytes (5%)
--> branches of central retinal artery
2. Prelaminar region: higher number of astrocytes and neurons
--> short posterior ciliary artery
3. Laminar region : passing through lamina cribrosa through fenestrations
--> short posterior ciliary artery + arterial circle of zinn
4. Retrolaminar region: astrocytes decrease and oligodendrocytes increase to form myelin
--> pile plexus (centripetal branches) + centrifugal branches
99
When does the central retinal artery and vein enter the intraorbital part of the nerve?
About 10mm from the eyeball and passes inferomedially.
100
Where is the internal carotid artery in relation to the intracranial part of the optic nerve
Runs inferiorly and laterally to the optic nerve
101
What defect produces a junctional scotoma defect?
Defect in optic nerve near optic chiasm at wilbrands knee --> nasal fibres decussate and bend upwards towards opposte optic and get affected
102
What field is produced with a central optic chiasm defect?
Leads to bitemporal hemianopia (both nasal fibres are affected)
Bitemporal hemianoic paralysis of the pupillary response
103
What is the visual pathway? (7)
1. Retina
2. Optic nerve
3. Optic chiasm
4. Optic tract
5. Lateral geniculate body
6.. Optic radiations
7. Visual cortex
104
What are the causes of a central optic chiasm lesion (5)
1. Craniopharyngioma
2. Pituitary tumor
3. Suprasellar aneurysm
4. Supresellar meningioma
5. Third ventricular dilatation due to hydrocephalus
105
What is the outcome of a lateral optic chiasm defect
Affects temporal fibres of optic chiasm --> nasal defect
Binasal hemianopia
Binasal hemianopic paralysis of pupillary reflex
106
What happens following an optic tract lesion to the fibres? What visual defect?
uncrossed temporal fibres lead to nasal defect in ipsilateral eye and crossed nasal fibres lead to temporal defect in opposite eye - homonymous hemianopia
Can cause a third nerve palsy and ipsilateral hemiplegia
107
What are the main causes of optic tract lesions? (5)
1. Thalamus tumours
2. Syphilitic meningitis
3. TB
4. Posterior cerebral artery aneurysm
5. Superior cerebellar artery aneurysm
108
What visual defect is produced with a lateral geniculate body lesions? Pupillary response is present or absent?
Homonymous hemianopia with sparing of pupillary reflex as the pupillary fibres have already left the optic tract at the superior folliculus
109
What visual defect is produced from a lesion in Meyer's loop (inferior retinal fibres in optic radiation travelling in temporal lobe)
Homonymous superior temporal quadrantinopia (pie in the sky)
110
What visual field defect is produced from a lesion in superior retinal fibres from optic radiations?
Homonymous inferior temporal quadrantinopia (pie in the floor)
--> fibres pass through parietal lobe
111
What is the blood supply of the visual cortex?
1. Posterior cerebral artery
2. Middle cerebral artery
112
What visual field lesion is seen in a visual cortex lesion (PCA /MCA stroke)
1. Congruous Homonymous hemianopia with macular sparing (macular spared as receives dual supply from PCA or MCA
113
The anterior surface of the cornea is ..... shaped whereas posterior surface of the cornea is ..... shaped
1. eliptical
2. spherical
114
What is the horizontal diameter of the cornea?
What is the vertical diameter of the cornea?
What is the average diameter of the cornea?
1. 11.7mm
2. 11mm
3. 11.5mm
115
What is the radius of the curvature of the cornea?
What is the radius of curvature of the sclera?
1. 7.8mm
2. 12mm.
116
What is the average central corneal thickness?
What is the average peripheral corneal thickness?
1. 520 micrometers
2. 670 micrometers
117
What is the refractive power of the cornea?
What is the refractive power of the lens?
1. +45 D
2. +15 D
118
What is the refractive index for these structures?
1. Air
2. Cornea
3. Anterior Chamber
4. Lens
5. Vitreous
1. Air - 1
2. Cornea - 1.37
3. AC -1.33
4. Lens - 1.42
5. Vitreous - 1.33
119
Where are the corneal layers derived from?
Epithelium - surface ectoderm
Stroma - mesoderm
Descemet's membrane - mesoderm
Endothelium - mesoderm
120
What type of epithelium is the cornea?
Stratified (5-6 layers)
Squamous (superficial cells flattened)
Non keratinised (nucleated, no keratin)
Epithelium
121
How long does it take for entire cornea epithelium to be replaced?
7 days
122
What is the function of the microvilli in the cornea?
Are present with glycocalyx and help in adhesion and stability of the tear film to prevent tear film evaporation and subsequent dry eye.
123
Where are the corneal epithelium stem cells found?
In the limbal basal epithelium at the palisades of Vogt
124
What is the thickness of Bowman's membrane?
8-14 micrometers
125
What is Bowman's membrane composed of?
randomly arranged collagen fibres generally resistant to trauma - cannot be regenerated
126
What are the main components of the corneal stroma (3)
1. Uniform Collagen fibrils (arranged in flat bundles called laminae - 300 laminae present)
2. keratocytes which secrete collagen
3. Extracellular ground substances
127
What is responsible for the transparence of the cornea?
The highly uniform collagen fibres in the stroma (25-35micrometers) and distance between two corneal fibres is uniform (41.5nm)
128
What are the reasons for corneal transparency? (5)
1. Optically smooth tear film
2. Role of corneal epithelium
3. Arrangement of stromal fibres
4. Avascularity of the cornea
5. Absence of myelination in corneal nerves
129
What is the thickness of descemets membrane at birth and in adulthood?
1. 3 micrometers
2. 10 micrometers
130
What is descemets membrane formed from?
secreted by endothelial cells
131
Descemet's membrane is ..... attached to the stroma and is ...... to ezyme degradation by phacotyes and toxisn
1. weakly
2. resistant
132
What is the main shape of the corneal endothelium?
How are they conneted together?
1. hexagonal forming continuous mosaic pattern
2. Various juncional complexes (1) zonula occcludans (2) macula occludans (3) macula adherens
133
What do the corneal endothelial pumps do?
Sets osmotic gradient that causes fluid to move from stroma to the aqueous to maintain 70% corneal hydration to keep cornea transparent
134
What are the 3 different endothelial pumps?
1. Na/K --> 3 Na exit to AH, 2 K+ enter
2. Na/H --> 1 Na enters, 1 H+ exits
3. Na/HCO3 --> Na exits to AH, bicarb exits
135
What endothelial cell density leads to corneal decompensation?
800 cells / mm2
136
What is the blood supply of the cornea?
No blood supply
Anterior ciliary artery (ophthalmic artery) forms arcade in limbal region
137
What is the nerve supply to the cornea?
Long posterior ciliary nerve --> Nasocilliary nerve --> V1
138
What is the borders of the anterior chamber?
posterior cornea anteriorly
anterior iris posteriorly
139
How deep is the anterior chamber?
Is it shallower in hypermetropes or myopes?
1. 3mm
2. Shallower in hypermetropic eyes (axial length is smaller)
140
How much aqueous humor is present in the anterior chamber?
0.25ml
141
What are the structures of the angle of the anterior chamber? (6)
1. Schwalbe's line
2. Anterior Trabecular meshwork
3. Posterior trabecular meshwork
4. Scleral Spur
5. Ciliary body band
6. Root of iris
142
What is the scleral spur
At the junction of the limbus, internally there is a groove/indendation called the scleral sulcus.
A projection posteriorfrom this area and is called the scleral spur
143
What is the ciliary body band?
Ciliary body is attached to scleral spur - a space exists here called the supraciliary space bewteen the ciliary body and sclera
Iris inserts into anterior side of ciliary body, and part of the ciliary body between iris and scleral spur is ciliary band, which is seen on gonioscopy
144
What is Schlemm's canal
Continuation of trabecular meshwork as a canal - it is oval in shape and is lined by endothelium
It is perforated by aqueous collector channels which branch into intrascleral and deep scleral plexi
145
What is Schwalbe's line
Trabecular meshwork inerts into the periphery of the cornea at a ridge, known as Schwalbe's line - makes the end of Descemet's membrane of the cornea
Most anterior structure of gonioscopy
146
What is posterior embryotoxon?
Anterior displacement of Schwalbe's line which is prominent on external exmination - associated with eisenfeld riger syndrome
147
What is Sampaoelsi's line?
Pigmented Schwalbe's line seen in PXF and pigment dispersion syndrome
148
What are the layers of the Posterior trabecular meshwork? (3)
1. Uveoscleral
2. Corneoscleral
3. Juxtacanalicular
149
What are the main age related changes seen in the trabecular meshwork? (5)
1. Increased pigmentation
2. Increased debris accumulation
3. Increased glycosaminoglycan deposition in extracellular space
4. Thickened basement membrane
5. Reduced endothelial cells
150
What is the root of the iris?
Insertion of the iris to the ciliary body and it is thinnest here.
151
What is irdodialysis?
At the thinnest point, root of the iris becomes detached and causes a D shaped pupil
152
What is the diameter of the iris?
What is the diameter of the pupil
1. 12mm
2. 3-4mm
153
What is the thickness of the iris?
0.5mm
154
What is the collarette of the iris?
2mm from pupillary margin is a zig zag line which divides anterior iris into 2 zones (ciliary and pupillary zone) and represents attachment of pupillary membrane
155
What are the important structures of the ciliary zone/outer zone of the iris (2)
1. Radial streaks correspond to radial streaks and become wavy when pupil is dilated
2. Contraction furrows are faint lines parallel to colarratte
3. Crypts : absent anterior layers
156
What are the layers of the iris (4)
1. Anterior limiting membrane
2. Stroma
3. Anterior pigmented epithelium
4. Posterior pigmented epithelium
157
What is contained in the anterior limiting layer?
Consists of melanocytes and fibroblasts - decides the colour of the iris.
---> thin/few melanocytes - blue iris
----> thick/many melanocytes - brown/black iris
This layer is absent in crypts and thin in furrows
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What can pass through the anterior limiting layer of the iris?
Aqueous can penetrate through this layer into the stroma as it is not a true epithelium
159
What happens in iris heterochromia / Fuch's uveitis? (2)
Progressive atrophy of the anterior layer and stroma of iris --> loss of iris colour
1. Transillumination defects
2. Blurring of iris crypts (darker individuals)
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What is contained within the iris stroma ? (6)
1. Network collagen
2. Ground substance
3. Sphincter Pupillae
4. Dilator Pupillae
5. Vessels and nerves
6. Pigment
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Where is sphincter pupillae derived from?
Where is dilator pupillae derived from?
Sphincter - ectoderm
Dilator - myoepithelium
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What is the nerve supply of the sphincter and dilator pupillae?
1. Sphincter - parasympathetic post-ganglionic fibres of third nerve via short ciliary nerve
2. Dilator - sympathetic cervical chain via long ciliary nerve
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Where is the sphincter pupillae located?
Where is the dilator pupillae located?
Sphincter - pupillary zone (inner zone)
Dilator - Ciliary zone near iris root
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What are the main vessels of the iris? What characteristics do they have?
Radial branches of major arterial circle, responsible for formation of radial furrows
1. Lack internal elastic lamina
2. Have non fenestrated endothelium
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What type of cells are present in the iris stroma? (5)
1. Melanocytes - melanosomes and branching filaments
2. Clump cells - round in shape without branching filaments
3. Fibroblasts
4. Macrophages
5. Lymphocytes
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What is contained within the anterior epithelium of the iris?
Pigmented layer containing origin of dilator pupillae muscle
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What is contained within the posterior pigmented epithelium of the iris
At pupillary margin, forms the pupillary frill and meets anterior epithelium
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What is the difference between seclusio pupillae and occlusio pupillae?
Seclusio - 360 degrees synechiae
Occlusio - 360 degrees synechiae with lens not visible (fibrin formation)
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What are the layers of the ciliary body? (5)
1. Internal Limiting Membrane (AC - inside)
2. Non Pigmented Inner Epithelium
3. Pigmented outer epithelium
4. Stroma of Ciliary body
5. Supraciliary Lamina (sclera - outside)
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What is contained in the stroma of the ciliary body (2)
1. Connective tissue and Collagen
2. Ciliaris Muscles
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What is main structural features of the ciliaris muscle?
Non striated involuntary muscle triangular in shape
1. Longitudinal muscle fibres - attachment to scleral spur and assist drainage of aqueous
2. Circular muscle fibres - accomodation
3. Radial muscle fibres
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What is the action of the ciliary muscle in accomodation?
Contraction of ciliary muscle towards lens --> slackening/loosening of zonules ---> increase in anterior curvature of the lens --> accomodation
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What is the nerve supply of the ciliary muscle?
Parasympathetic innovation from 3rd nerve postganglionnic fibres
Ciliary ganglion --> short ciliary nerve to supply the ciliary muscle and sphincter pupillae
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What is contained in the stroma of the ciliary body?
Major arterial circle formed by long posterior ciliary arteries and anterior ciliary arteries
175
What is the continuation of the pigmented epithelium of ciliary body (outer epithelium towards sclera)
Anteriorly continuation anterior epithelium of iris
Posterior continuation of RPE of retina
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What is the continuation of the non pigmented inner epithelium of the ciliary body?
Continues anteriorly with posterior pigmented epithelium of iris
Continues posteriorly with the neurosensory retina
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What is the length of the ciliary process ? How many are there?
Which part of the ciliary body has this
finger like projections 2mm in length, about 70-80 in number in the pars plicata
178
What is the ultrastructure of the ciliary process?
Epithelium contains fenestrations which facilitates ultrafiltration of water, ions and large proteins in to the adjacent stroma
High oncotic pressure in ciliary process stroma --> aqueous humor secretion
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What type of epithelium is present in the ciliary body/ciliary process? WHere is it from embryologically?
1. Bilayered epithelium - pigmented outer and non-pigmented inner epithelium
2. Neuroectodermal origin - anterior end of the optic cup
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What is the difference between pigmented outer epithelium and non-pigmented inner epithelium of the ciliairy body (4)
1.
Outer pigmented - low cuboidal cells
Inner non-pigmented - columnar cells
2.
Outer pigmented - melanin granules separated from stroma by atypical basement membrane (continuation of Bruch's)
Inner non-pigmented - mitochondria and endoplasmic reticulum separated with typical basement membrane with tight junctions on apical surfaces
3. Separated by low resistance gap junctions to faciliate ion transport between epithelial layers crucial for aqueous humor secretion
4. Each layer connected to each other by tight junctions which forms blood-aqueous barrier
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What are the structures that form the blood aqueous barrier? (3)
1. tight junctions between cells of non-pigmented inner epithelium of ciliary body
2. tight junctions between outer pigmented epithelium of ciliary body
3. Non-fenestrated iris vessels
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What is the choroidal thickness posteriorly? What is the choroidal thickness anteriorly?
1. posterior - 0.22mm
2. anterior - 0.1mm
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What are the layers of the choroid from outside to inside? (4)
1. Suprachoroidal lamina (lamina fusca)
2. Choroidal stroma (Haller's and Sattlers)
3. Choriocapillaries layer (Ruysch)
4. Bruch's membrane --> RPE
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What is the lamina fusca? What is it connected to anteriorly? What space is in this layer? (3)
1. Thin condensed membrane of choroidal stroma
2. Continuous anteriorly with supraciliary lamina of the ciliary body
3. Space between here and sclera is the suprachoroidal space - useful for drug delivery
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What does the choroidal stroma consist of? (3)
1. Framework of collagen, elastin and reticular tissue with pigment cells and other cells
2. Outer Hallers layer - large diameter vessels
3. Inner Satler layer - intermediate size vessels
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What type of endothelium does the choriocapillaries have? What is it surrounded by?
1. Fenestrated endothelium
2. Basement membrane and pericytes
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Where is the highest density of the choriocapillaries?
Highest in the macular area - thickesst here at 10um
188
How much ocular blood flow does the choriocapillaries receive? How much oxygen extraction?
How much ocular blood flow does retina receive? How much oxygen extraction?
1. 65-70% of ocular bloodflow - 3% of oxgen
2. 5% of ocular blood flow - 38% of oxygen extraction
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What are the reasons of slower blood flow in the choriocapillaries (5 times slower)
(3)
1. Large lumina of the choriocapillaries
2. Large blood volume in choroid
3. Lobular configuation of the choriocapillaries
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What are the 5 layers of the Bruch's membrane? Inner to outside
1. Basement membrane of RPE
2. Inner Collagenous layer
3. Elastic Layer - anti-angiogenic property
4. Outer collagenous layer
5. Basement membrane of choriocapillaries
191
What are the structures involved in the outer blood retinal barrier?
1. Bruch's membrane
2. Tight junctions of RPE
Prevent leakage of fluid from choroid into the retina
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What are the functions of the uvea? (6)
1. Source of blood flow to outer 4 layers of retina (outer plexiform layer, outer nuclear layer, IS/OS zone and RPE)
2. Source of aqueous humor production
3. Ciliary muscle helps as accomodation
4. Acts as thermal sink of the eye (choriocapillaris, sattler's, hattlers)
5. Production of eicosanoids of eye
5. Anti-oxidant properties
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Which hole does the internal carotid artery go through?
Foramen lacerum
194
Where does the ophthalmic artery arise and start from?
Arises from medial aspect of ICA and starts medial to anterior clinoid process
195
Where does the central retinal artery arise from? When does it change course?
1. FIrst branch of ophthalmic artery
2. Changes course 10-15mm inferiorly optic tract, pierces the optic nerve sheaths superiorly (dura, arachnoid pia) and travels within optic nerve and reaches retina
196
What is the course of the extraocular part of the central retinal artery?
Enters retina through lamina cribrosa and opening of sclera into optic cup.
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What does the central retinal artery supply?
The inner 6 layers of the retina
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What are the structures lateral to the ophthalmic artery as it enters the lateral component of the orbit? (4) What branch does it give here?
1. Ciliary Ganglion
2. III nerve
3. VI nerve
4. Lateral rectus
Gives a lacrimal branch --> lacrimal artery
Lacrimal artery gives branch lateral palpebral artery which supplies lateral side of eyelids
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What branches does the ophthalmic artery give in the lateral compartment of the orbit? (2)
Gives a lacrimal branch --> lacrimal artery
Lacrimal artery gives branch lateral palpebral artery which supplies lateral side of eyelids
Recurrent meningeal artery --> travels in lateral SOF and anastamoses with middle meningeal artery (branch of external carotid artery)
200
What structures accompany the ophthalmic artery as it travels above the optic nerve in the medial compartment of the orbit? (2)
1. Superior ophthalmic vein
2. Nasociliary nerve
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What branches does the ophthalmic artery give off in the medial compartment of the orbit?
Posterior ciliary artery --> divides into lateral and medial posterior ciliary arteries.
the long posterior ciliary arteries travel in the suprachoroidal space and reach ciliary body and form the major anastamosis
202
Where do the posterior ciliary arteries arise from?
1. Arise as two trunks from ophthalmic artery and divide into 10-20 branches
203
What do the short posterior ciliary arteries do?
1. Pierce sclera and supply choroid in segmental manner
2. Some branches form anastamotic ring around optic disc --> circle of Zinn-Haller
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Which branch of the ophthalmic artery travels above the optic nerve and just superior to the LPS and superior rectus just below orbital roof and exits at the supraorbital notch?
Supraorbital artery (accompanied with supraorbital nerve)
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Which branches of the supraorbital artery branch off just superior to optic nerve?
MUSCULAR ARTERIES
1. Medial muscular artery - MR, IR, IO
2. Lateral muscular artery - SR, LPS, LR, SO
These further subdivide into anterior ciliary arteries -
206
How many anterior ciliary arteries are there? Where do they arise from?
1. 7 in number, 2 for each recti, one for LR
2. Muscular branches of the ophthalmic artery
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What arteries are involved in the major arterial circle? Where do they start?
1. Anterior ciliary artery (70%) and long posterior ciliary artery (30%)
2. Pierces sclera 4mm from limbus
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What happens at the major arterial circle?
1. Several branches run radially into the iris as iris vessels which anastamose at the pupillary margin which This forms the minor arterial circle
209
What arterial branches are formed from the ophthalmic artery at the medial compartment of the orbit?
1. Anterior ethmodial artery --> anterior ethmoidal foramen ----> nose
2. Posterior ethmoidal artery --> posterior ethmoidal foramen ----> nose
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What are the terminal branches at the level of the superior oblique of the ophthalmic artery?
1. Dorsal Nasal - gives off medial palpebral artery (anastamoses with lateral palpebral artery from lacrimal artery ---> superior and inferior marginal archade)
2. Supratrochlear -
211
Where are the ampullae of the vortex veins vissible?
8-9mm from the ora serrata
212
Where is the uvea firmly attached to the sclera?
1. Scleral Sulcus
2. Ampulla of vortex veins
213
Where do the vortex veins drain into?
1. Superior vortex - superior ophthalmic vein
2. Inferior vortex - inferior ophthalmic vein
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What are the main actions of the inferior rectus?
1. Depression --> greatest in ABduction.
2. Adduction
3. Extorsion
215
What is the anterior portion of the optic radiation supplied by?
anterior choroidal artery
216
What are the main differences between rods and cones? (4)
1. Rod discs are enclosed with a cell membrane
2. Rod concentration higher in periphery
3. Ratio of rod:cone is 20:1
4. Peak sensitivity of rods is 496nm, cones is 420 (S), 530 (M) and 560 (L)
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