Block 10 Flashcards
What is the most anterior portion of the uveal tract
Iris
What does the iris separate
Anterior and posterior chambers of the eye
What surrounds the iris
Aqueous
T/F the iris rests on the lens
True but lightly
How much is the iris magnified when viewed through the cornea
1/8th
T/F the iris increases depth of field
True
The pupil that is seen is what?
Magnified virtual virtual image of the real object
What is the thickness of the iris at the root?
About 500 microns
What is the average diameter of the iris
12 mm
Where is the pupil located in relation to the iris
Slightly nasal and inferior to iris center
What is a Decentered pupil?
What effect does it have
Ectopic
Degrade optical quality
How does aqueous humor flow
From posterior into anterior chamber through he pupil
T/f the pupil is in a constant dynamic fluctuation
True
What are some things that cause this fluctuation
Slide 5
What is the posterior portion of the iris dervied from
Neurepithelium
The shape of the pupil varies in animals, what is the shape in humans
Round
How has the largest eyes in animal kingdom
Squid
What are the layers of the posterior iris
Dilator
Sphincter
Post pigmented epithelium
What is the anterior iris derived from
Mesoderm
What are the layers of the anterior iris
Stroma
Vessels
Here’s
Chromatophores
What are teh r4 layers of the iris anterior or posterior
Anterior border layer
Stroma and sphincter muscle
Anterior epithelium and dilator
Posterior and dilator
What layer of the iris has both mesoderm and ectoderm
Stroma and sphincter
What are the functions of the iris
Regulate retinal illumination, glare, optical aberrations, depth of focus; non-verbal communication and social signaling, attraction/mate selection
Where are glare and aberrations seen
Larger pupils
What are the only parts of the iris that facilitate movement
Muscles
The other elements are made to adapt to movement
What happens in mitosis
The pupillary portion of the iris gathers into pleas
Ciliary portion smooths out
What happens in mydriasis
Stroma and pupillary zone flatten
Ciliary area contracts
Is blood flow impeded in miosis and mydriasis
NO
T/F the stroma and iris vessels are elastic
False
Describe the stroma of the iris
It is loose but orderly meshwork of collagen fibers with aqueous fluid.
Describe iris vessels
Thin walled layer of endothelium
Outer covering of collagen fibrils
What is the thickest portion of the iris
Stroma
what is the function of the iris stroma
No active part in movement
Acts as an anchor for sphincter muscle, dilator-post-epith plate, nerves, and vessels
adapts to constant movement
Folds and unfolds with minimal resistance to minimize energy usage
How does the iris stroma protect nerves and vessels
It protects against stretching and kinking
T/F ALL elements of the iris maintain their identity and characteristics across millions of iris movements over decades
True
What is the anterior border layer
Porous
Fibroblasts interlaced with melanocytes
More solid and dense layers in pigmented eyes
Can have nevi
What causes blue iris color
Light scatter
T/F newborns can be born with blue eyes that darker with age
True
What leads to darker eye colors
Development of anterior stromal melanocytes and production of pigment granules
How is eye color determined
Genetics
Dark: dominant
Light: recessive
Where is iris blood flow dervied from
Ophthalmic artery from 2 long posterior ciliary Artie’s and anterior ciliary arteries
Does the iris bleed when cut
No
Anterior ciliary arteries run along what
Rectors muscles
Each has 2 except the lateral rectus (it has 1)
What are perivascualr collagen sheaths
They are unique to iris vessles (nowhere else in the body)
Allows for little distention an folding of vessels during the constant movement of the iris
Do humans react to light stimulation of the iris?
No, we react to stimulation of the retina
This can occur in some animals though
What is the light reflex important for
Testing the integrity of the retina, optic nerves, chiasm, and optic tracts
What variables affect the pupil
Light intensity Light Adaptation Temporal frequency Stimulus duration Retinal area Retinal location Stimulus wavelength Spatial frequency Motion
What affect to bright (photopic) lights have on the pupil
Pupil constricts
What affect ones the dark (scotopic) have on the pupil
Dilation
Where does the pupil start to reduce in size
In the mesopic range of light
What occurs in dark adapted eyes
Pupillary reactions occur at intensities below photopic range (due to rods)
Parafovea and peripheral more sensitive than fovea
T/f the pupil contracts at the same rate
True
If the pupil stimulus is too short what happens
There isn’t enough time for it to react
T/f the pupil is more constricted when light covers a greater area when light is equally bright
True
The pupil sums afferent impulses regardless of spatial distribution
True
Spectral sensitives math well with pupillary reactions
Yes
Look at slide 51 spatial freq
Read it
Does the pupil react to motion
Yes
Myopes have larger pupils than hyperopes
Not really, there is a 1% difference
What is the optimal pupil size
2 mm
What effect do large pupils have
Image degradation and glare
Does pupil size change with age
Yes it decreases
What range of diameters can he human eye vary in
2-8 mm
Does the pupil play a large role in regulating light levels
No, it is minimal
What is the near vision triad
Convergence
Miosis
Accommodation
What is the 3rd nerve nucleus
Eddinger-Westphal
Near vision pupillary contraction amplitude for young people is equal to what
Contraction from bright light
What are the sphincter and dilator muscle derived from
Neural ectoderm
What innervates the iris sphincter
PNS
What innervates the iris dilator
SNS
What causes Horner Syndrome
Interference with blood supply from carotid artery
When are pupils smaller
During sleep and after death
When are pupils larger
During waking hours and when frightened (Jill)
Drugs/disease that treat the CNS often have what effects
Pupil effects
Alphagan alphagan in a tree
This sucks and I’m sleepy
We’re not tested on this
As stimulus become less arousing what effect does that have on pupillary reaction
Less reaction
When stimuli become more infuriating over time what effect does it have on pupillary reaction
Greater reaction
What are some theories for reduction in pupil size
Reduced strength of dilator
Greater resistance of stroma
Iris fatigue
CNS fatigue
Pupils are round and smooth with ______ age
Advanced
Light reflex is brisk in _____
Middle age
Reduction in pupil size is what process
Linear
Does the thickness of the dilator muscle change with age
No
When does pupil size decrease begin
Healthy eyes
What is the cocaine test used for
Horner’s syndrome check
The pupil will dilate less than the normal pupil
What effect does apraclonidine have in Horners
Increased dilation in affected side
What effects does IR radiation have on pupil
High levels can burn ocular structures
Posterior Iris absorbs heat
Iris sphincter contracts when heated
Have iritis
What are the functions of the ciliary body?
Aqueous production
Aqueous outflow
Accommodation
Why is the ciliary muscle atypical for smooth muscles
Rapid contraction speed
Large motor neurons
Distance between muscle and motor neurons
Structure of ciliary M resembles skeletal M
What are the 4 layers of ciliary angle (in order)
Schwalbes line
Trabecular meshwork
Scleral spur
Ciliary body
What provides a large surface area of ciliary body
Finest rated capillaries and the number and shape of the processes
How is aqueous humor made
- Diffusion
- Ultrafiltration (negligible)
- Active secretion (80-90%)
Movement of what drives secretion in the posterior chamber
Na and Cl
What ion has an indirect role in moderating Cl flux
Bicarb
Where does aqueous production occur
In the ciliary processes
What is the purpose of aqueous production
Provide nutrients to cornea Prevents oxidative damage Prevents light scatter (low protein) Carries wastes from cornea and lens High lactate concentration from lens and cornea
What is the rat of aqueous production
2.5 uL/min
What is the purpose of zonular fibers
Stabilize lens
70-80 nm diameter
Allows flow from posterior to vitreous chamber
Superficial attachment to lens
T/F accommodation declines gradually until it is completely lost at age 50
True
What is accommodation
Contraction of the longitudinal fibers of the ciliary muscle pills the choroid forward, contraction of the circular fibers draws the ciliary body closer to the lens
Decreases the diameter of the ring formed by the ciliary body
Releases tension on the zonular fibers and allows the lens to become more spherical (more powerful)
What is the lens enclosed in
Lens capsule
Where do the zoules attach to the lens
At the equator
What is happening during far vision
Ciliary is relaxed
Zonular fibers are in tension
When the ciliary muscle contracts what is happening to the zonules
They relax, increases the power of lens
T/F changes in illumination do not alter pupil diameter
False, it does
Accommodation and convergence stimulate what
Miosis
Pupil constriction aids in clarity due to
Larger depth of field
Accommodative amplitude increases/decreases with age
Decreases
Contractile strength shows reduction with increasing age?
NO
What is presbyopia
Loss of ability to accommodate
Normal age related change
What changes occur/do not occur with presbyopia
Ciliary muscle contractive power increases UNTIL presbyopia
No change in zonular length
T/F the limiting factor for accommodation is the ciliary muscle
False, it is the movement and shape of the lens
T/F ciliary muscle contraction can change the configuration of the trabecular meshwork
True
What is he ciliary muscle derived from
Mesoderm
What is teh Tyndall phenomenon
Breakdown of blood-aqueous barrier
Cells and flares are visible Aqueous is invisible Leukocytes Whitefish Can form hypopyon
What is hyphema
Trauma to head or whiplash can tear the iris
Break blood vessels entering the major arterial circle of iris
Blood settles inferiorly
What is aqueous humor
Clear, colorless fluid that fills the anterior and posterior chamber of the eye
What is the function of the aqueous humor
It supplies nutrients and oxygen/removes wastes from the anterior tissues
Inflates the eye and creates IOP
Transport ascorbic acid into the anterior segment where it is antioxidative
Facilitates the local immune responses during inflammation and infection
What is the primary site of aqueous humor formation
Pars plicata
What tissue forms aqueous humor
Non-pigmented ciliary epithelium
How much aqueous humor is there
250-300 uL
What is the refractive index of aqueous
1.333
What is the pH of aqueous
7.2
Aqueous is hyperosmotic or hypoosmotic
Hyperosmotic
What is the rate of aqueous formation
- 75 uL/min (day)
1. 08 uL/min (night)
What is higher in ascorbic acid AH or BP
AH
What is higher in proteins AH or BP
BP
How is aqueous produced
- Blood flows to vascular bed of ciliary stroma
- Loading of solute from stroma into PE cells
- Translocation of solute through gap junctions into NPE cells
- Exclusion of solute from NPE to posterior chamber
- Osmotic gradient made by the solutes facilitates the passive flow of water
What are the mechanisms of solutes across the CE
Diffusion (passive movement due to concentration difference)
Ultrafiltration (passive movement due to pressure)
Active transport (energy consuming process, moves against gradient)
What is the major mechanism of solutes moving across the CE
Active transport
What enzyme is responsible for the production of HCO3
Carbonic anhydrase
What affect does carbonic anhydrase inhibitor have
Reduces AH formation
What does vasopressin do?
Supports active transport of Na ions across CE and increases AH
What do A2 agonists do
Decrease AH formation
What do B2 agonists do?
Increase AH formation
What is the blood aqueous barrier
Barrier to the movement of intermediate and high molecular weight substances (protein)
Protects the eyes from entry of toxic substances and maintains homeostatic control
What explains how drugs that are taken orally or IV can barely reach therapeutic levels in intraocular tissues
Blood aqueous barrier
What is the BAB made up of
- Tight junctions are present on NPCE
- Endothelial of inner schlemms canal are joined tightly to prevent retrograde movement of solutes and fluid
- Tight jxns are at iridologist vascular endothelium as well as between iris epithelia
Where are tight jxns present?
What do they do
Between NPCE
Constitute an effective barrier to intermediate and high molecular weight substances (proteins)
What happens when the BAB breaks down
Aqueous becomes cloudy due to leakage of plasma proteins into the posterior and anterior chamber
Inflammatory cells may also be present
What are some causes of BAB breakdown
Ocular injuries (trauma, inflammation, disorders, tumor)
Ocular hypotony (IOP of 5mmHG or less)
What are the mechanisms of BAB breakdown due to injury/inflammation
Release of cytokines and growth factor
Activation of immune response
Breakdown
What are the mechanisms of BAB breakdown due to hypotony
Opening of non-penetrated endothelial layer of iris capillaries and tight jxns of ciliary epithelium
Increases episcleral venous pressure
Breakdown
What is the vitreous humor
Clear gel in the posterior chamber
Where is vitreous located
Between crystalline lens and retina (80% of the volume of the eyeball)
What is primary vitreous
3-4 gestational age
Optic cup filled by a system of fibrillation material (secreted by embryonic retinal cells)
VEGF released by lens induces vasculogenesis
Hyaloid artery penetration
What is secondary vitreous (6 weeks gestation)
Increasing size of vitreous cavity
Anti-angiogenesis factor present, regression of hyaloid artery and it leaves a Cloquets canal surrounded by 2ndary vitreous
Vitreous gel formed
What is tertiary vitreous
Controversial
Secreted by NPCE of pars plana and persists in adult as suspensory ligament of lens (zonular fibers)
What is Bergmeisters Papillae?
Center of optic disc
Small tuft of fibrous tissue that is a remnant of fetal hyaloid artery
What is Mittendorfs dot:
Small circular opacity on posterior lens capsule (nasal)
Anterior attachment of hyaloid artery
What is Cloquets canal
Tubular structure continuing remnant of primary vitreous
Located at posterior aspect of lens and the retina (in vicinity of optic disc)
Vitreous cortex:
Outer surface (hyaloid surface)
Center zone:
Cloquets canal
Intermediate zone
Inner to cortex and surrounds the center canal
What is the uvea
Middle layer of the eye
What are the regions of the uvea
Iris
Ciliary body
Choroid
Where is the choroid located
Extends from ora serrata to optic nerve
Between sclera and retina
What absorbs excess light
Darkly pigmented choroid
What is the function of the vascular choroid
It provides nutrients to and removes waste from the outer retina
What is so different about the macula
It is avascular
No vessels
What supplies blood to the macula
Choriocapillaries
What arteries supply/pass the choroid
Long posterior ciliary (2)
Short posterior ciliary (20)
Ciliary artery
Ophthalmic A
What nerves supply/pass the choroid
Long ciliary and short ciliary nerves
Where are the nerves and vessels that supply the choroid held
Suprachoroid space
Long ciliary nerve carry what info
Sensory
Sympathetic
Short ciliary nerves carry what info
Sympathetic
Parasympathetic
T/F the choroid can rapidly change its thickness, and the vary the location of the retina and the state of focus of the eye
True
What are the functions of the choroid (4)
- Provide nutrients and remove wastes from outer retina
- Passage of nerves and vessels
- Absorb excess light
- Regulate emmetropization
What changes occur in the iris
Loss of pigmentation
Dilator muscle atrophic
Sphincter muscle sclerotic
What changes occur in the ciliary body with age
- Elasticity decreased due to amount of connective tissue increased in the ciliary body
- Formation of aqueous humor decreases with age
At age 80 with the production of aqueous compared to younger
25%
What changes occur to the choroid with aging
- Choriocapillaries decrease in density and diameter, choroidal blood flow decreases
- Bruchs membrane thickens
- Various substances and particles accumulate in Bruchs
What is Bruchs membrane
Nutrient from choriocapillaries and waste product from retina must pass though Bruchs membrane
What is Drusen
Calcification and ellow deposits in teh inner collagenous layer of Bruchs layer
Made of the remaining damaged cells from oxidative stress
What is Lipfuscin
Yellow-brown pigment granules composed of lipid-containing residues from oxidative stress
What does accumulation of drusen do?
Makes Bruchs membrane hypdrophobic
Barrier to water movement
Inhibits passage of metabolites
Accumulation of water between Bruchs and RPE can cause what
Detachment
What serious condition is associated with drusen
AMD
What are some stimulus types that can cause dilation
Sensory
Emotional
Mental
