Block10 Flashcards
The pupil that is seen is actually a
Magnified virtual image of the real object pupil
Separates AC and PC
Iris
How much is the iris magnified by when viewed through the cornea
1/8th
Average iris diameter
12 mm
Thinnest point of the iris is
At the iris root - 500 microns
Where is normal pupil center
Slightly inferionasal
Abnormal decentered pupil
Ectopic
Which area of the iris is broader in humans
Temporal iris
Largest eyes in animal kingdom
Giant squid
Largest eyes relative to body size
Tarsier
Posterior iris is derived from
Neuroepithelium
What structures of the iris are derived from neuroepithlium
Dilator muscle
Sphincter muscle
Posterior pigmented epithelium
Anterior portion of the iris is derived from
Mesoderm
What iris structures are derived from mesoderm
Stroma
Vessels
Nerves
Chromatophores
4 layers of the iris (anterior to posterior)
Anterior border layer
Stroma
Anterior epithelium and dilator muscle
Posterior pigmented epithelium
Which layer contains both mesoderm and ectoderm
Stroma and sphincter muscle
3 main functions of the pupil
Control of retinal illumination
Reduction in optical aberrations
Depth of focus
Functions of the iris (6)
Regulate retinal illumation Regulate glare Regulates optical aberrations Regulates depth of focus Provides nonverbal communication and social signaling Attraction/mate selection
Pupillary portion of iris gathers into pleats while ciliary portion smooths out: miosis or mydriasis
Miosis
Stromal pulls flat while contraction furrow appear in ciliary area: miosis or mydriasis
Mydriasis
Thickest portion of iris
Stroma
Function of stroma
Anchor for
- sphincter muscle
- dilator-posterior-epithelial plate
- iris nerves
- iris vessels
Is the iris considered porous
Yes
Newborns typically have what colored iris? Can it change?
Blue; yes
What causes iris to change colors
Development of anterior stromal melanocytes and production of pigment granules
What colored iris are more dominant
Darker colors
Blood flow to iris is derived from
Ophthalmic artery and 2 long posterior ciliary arteries and anterior ciliary arteries
Anterior ciliary arteries run along
Recti muscles
How many anterior ciliary arteries run along each recti muscle
2, except LR only has 1
Unique to the iris vessels and found nowhere else in the body
Perivascular collagen sheaths
Is the light reflex more telling of the iris or the retina
Retina
Pupil size changes most in which light intensity
Mesopic
in dark adapted eyes, pupillary reactions occur at what intensities
Those below photopic range (rods)
- parafovea and peripheral more sensitive
In normal light adapted eyes, which area of retina is more reactive
Fovea
- Threshold is much higher
Does pupillary contraction speed change with light intensity
No, always constant
Pupils gradually return in what time
3-15 seconds
If the stimulus is very short, will the pupil still contract
Only if the stimulus is long enough to allow the retinal to register it
When light covers a greater area, what happens to the pupil
Constricts more
Pupil sums afferent impulses, regardless of
Station distribution (rods and cones)
Greater spatial frequency, the ____ the pupil contracts
Less
Why may hyperopes have a slightly smaller pupil
They have to accommodate more
Pupil size resulting in image degradation and glare
Larger pupils
If pupils are too _____, diffraction limit and reduced illumination can effect visual performance
Too small
Optimal pupil size
2mm
Pupil size does what with age
Decreases
Pupillary diameter range
2-8mm
Near vision traid
Convergence, miosis, accommodation
3rd nerve nucleus
Eddinger-westphal
Iris muscles are derived from
Neural ectoderm
Which iris muscle innervated by parasympathetic
Iris sphincter
Which iris muscle is innervated by sympathetic
Iris dilator
Which iris muscle is thicker
Dilator - 3-5 layers thick
Sensory, emotional, or mental stimuli elicit
Dilation
Pupil size during sleep and after death
Smaller
Stimuli become less arousing over time –> les pupillary reaction
Sensitization
High levels of IR
Burn bc of deep penetration
What happens to the sphincter when it is stimulated by heat
Contracts
If iritis ensues, what may be a feature
Long-lasting miosis
Structures of the angles from anterior to posterior
Schwalbe’s line
Trabecular meshwork
Scleral spur
Ciliary body
What type of muscle is the ciliary muscle
Smooth (resembles skeletal)
3 functions of ciliary body
Aqueous production
Aqueous outflow
Accommodation
What accounts for 80-90% of aqueous production
Active secretion
What is higher in the aqueous than in the blood
Ascorbate (ascorbic acid)
What is higher in the blood than in the aqueous
Protein
Rate of aqueous production
2.5 microL/min
What time of day is there more aqueous production
During the day
How much does aqueous production rate decrease at night
50%
Diameter of zonular fibers
70-80nm
Purpose of zonular fibers
Stabilize lens
Allow fluid to flow from PC to AC
At what age is accommodation typically completely lost
50
Why are some presbyopia still able to read, even though they cannot accommodate
Pupil constriction (miosis)
Zonular fibers during accommodation
Relaxes, less tension
When using distance vision, is the ciliary muscle relaxed or contracted
Relaxes
When using distance vision, are the zonular fibers relaxed or is their tension
Tension
During accommodation, is the ciliary muscle relaxed or contracted
Contracted
Why are dark iris’s less effected by dilating drops
Pigmented epi and ciliary body bind with pharmaceutical agents
What is the cause of the decreased accommodation with age: lens or ciliary muscle
Thickening and stiffening of lens
When is there more aqueous outflow, during distance or near stimulation and why
Near bc the ciliary muscle contracts, opening the TM to allow aqueous to flow
Iris sphincter muscle is derived from
Neural ectoderm
Ciliary muscle is derived from
Mesoderm
Cells and flare visible in AH
Tyndall phenomenon
What is the Tyndall phenomenon due to
Breakdown of BAB
White collection at bottom of iris
Hypopyon
Blood settling in inferior iris from trauma
Hyphema
Which arterial circle is located in the iris
Major circle of iris
Clear, colorless fluid that fills the AC and PC
AH
Main function of AH
Inflate the globe and create IOP for normal optical functioning
Primary site of AH formation
Pars Plicata of ciliary processes
Which layer of epithelium forms AH
NPCE
Average rate of AH formation during the day
2.75microL/min
Average rate of AH formation at night
1.08 microL/min
What is 99.9% of normal AH
Water
Transport of blood to AH steps (5)
- Blood to ciliary stroma
- Solute from stroma in PCE cells
- Thru GJ into NPCE
- From NPCE to Post chamber (PC)
- Osmotic gradient created facilitates the passive flow of water into the PC
3 mechanisms that solutes can move across the ciliary epithelium
Diffusion
Ultrafiltration
Active transport
Passive moment of solutes across ciliary epithelium due to a concentration gradient
Diffusion
Passive movement of water and water soluble substances across ciliary epithelium due to hydrostatic and oncotic pressure
Ultrafiltration
Energy consuming process against concentration gradient
Active transport
Major mechanism of transportation across ciliary epithelium
Active transport
What enzyme plays a key role in AH formation
Carbonic anhydrase
What would a carbonic anhydrase inhibitor do
Reduce AH formation
What would an alpha2 agonist do to AH formation
Reduce AH formation
What would a beta2 agonist do to AH formation
Increase AH formation
What could a beta antagonist do to AH formation
Decrease AH formation
Barrier to movement of intermediate and high molecular weight substances (like protein)
BAB
Protects eye from entry of toxic substances and maintains homeostatic control
BAB
Reason why drugs administered orally or IV hardly ever reach therapeutic levels in intraocular tissues
BAB
Type of connections between NPCE cells
Tight junctions
Type of connection between PCE and NPCE
Gap junctions
Which type of connection creates an effective barrier to proteins
tight junctions
What happens to the AH as the BAB breaks down
Becomes cloudy due to leakage of plasma proteins
2 major causes of BAB breakdown
Ocular injuries
Ocular hypotonic
What is ocular hypotony
IOP of less than or equal to 5mmHg
Clear gel in posterior compartment of eye
VH
Makes up 80% of globe volume
VH
Located between lens and retina
VH
3 stages of vitreous development: 3-4 weeks gestation
Primary vitreous
3 stages of vitreous development: VEGF released by lens inducing vasculogensis; hyaloid artery penetration
Primary vitreous
3 stages of vitreous development: 6th gestation week
Secondary vitreous
3 stages of vitreous development: increasing size of vitreous cavity
Secondary vitreous
3 stages of vitreous development: hyaloid artery disappears leaving a tube of primary vitreous
Secondary vitreous
Tube of primary vitreous surrounded by secondary vitreous
Cloquet’s canal
3 stages of vitreous development: secreted by NPCE of pars plana
Tertiary vitreous
Arises from center of optic disc; remnant of hyaloid artery
Bergmeister’s papillae
Small opacity on posterior lens from the anterior attachment of hyaloid arter
Mittendorf’s dot
Typically, where on the posterior lens is mittendorf’s dot located
Nasally
Contains remnants of primary vitrous
Cloquet’s canal
What can pass to the posterior chamber: ions, water, or protein
Ions and water
Can uveitis cause breakdown of BAB
Yes
Can diabetes cause breakdown of BAB
Yes
Can moderate dry eye cause BAB to breakdown
No
3 stages of vitreous development: zonular fibers
Tertiary vitreous
Outermost zone of vitreous
Vitreous cortex
Area of VH that is inner to the cortex and surrounds cloquet’s canal
Intermediate zone
Middle layer of the eye
Uvea
The regions of the uvea from ant to post
Iris
Ciliary body
Choroid
From what 2 structures does the choroid extend from
Ora serrata to optic nerve
Layer between sclera and retina
Choroid
4 main layers of choroid (from sclera to retina)
Suprachoroid
Stroma
Choriocapillaris
Bruch’s membrane
Single layer of fenestrated capillaries of the choroid
Choriocapillaris
Thin, pigmented, connective tissue layer of choroid
Suprachoroid
Layers of the choroid: Pigmented, vascularized, containing melanocytes, fibroblasts, macrophages, lymphocytes, mast cells
Stroma
Layer of the choroid that fuses with the retina
Bruch’s membrane
What absorbs excess light in the choroid
Darkly pigmented choroid
Vascular choroid provides nutrient and removes wast from which layers of retina
Outer retina
Area of the macula devoid of vessels
Fovea avascular zone
Sole blood supply to foveal avascular zone
Choriocapillaries
What provides a path for the posterior vessels that supply the anterior segment
Suprachoroidal space of choroid
Arteries that supply the choroid
Ophthlamic a. –> ciliary a. –> 20 short post and 2 long posterior ciliary a.
Fibers carried by long ciliary nerves
Sensory and sympathetic fibers
Fibers carried by short ciliary nerves
Sympathetic and parasympathetic fibers
Provides a path for the nerves that supply the anterior segment
Suprachoroidal space of choroid
In hyperopic defocus, what happens the the thickness of the choroid
Thins
In hyperopic defocus, does choroidal growth increase or decrease
Increase
Myopic defocus, what happens to the thickness of choroid
Thickens
Myopic defocus causes the growth of choroid to what
Decrease
Can rapidly modulate its thickness, vary position of the retina and the state of focus
Choroid
4 main functions of the choroid
- provide nutrients and remove waste from outer retina
- passage of nerves and vessels
- absorption of excess light
- regulate emmetropization
3 aging changes in iris
- loss of pigmentation
- dilator becomes atrophic
- sphincter becomes sclerotic
Aging changes in ciliary body
Formation of aqueous humor decreases
By 80 years, 25% of what it was
3 aging changes in choroid
- choriocapillaries decreases in density and diameter –> choroidal blood flow decreases
- bruch’s membrane increases in thickness
- accumulations in bruch’s membrane
5 layers of bruch’s membrane from inner to outer
Basement membrane of RPE cells Inner collagenous zone Elastic layer Outer collagenous zone Interrupted basement membrane
Drusen accumulates in which layer of bruch’s membrane
Inner collagenous layer
What is drusen made of
Lipofuscin
Yellow-brown pigment granules composed of lipid-containing residues from oxidative stress
Lipofusion
Difference between wet and dry AMD
Wet has neovascularization
Accumulation of water between RPE and Bruch’s membrane can cause
Detachment
Accumulation of drusen makes Bruch’s
Hydrophobic
Which layer is multilaminated sheet and fuses with RPE
Bruch’s membrane
What provides blood to fovea region
Choriocapillaries
Which part of retina receives blood supply from choroid
Outer retina
Which layer of choroid proves a pathway for the vessels and nerves that supply the anterior segment
Suprachoroidal space
What happens to bruch’s membrane with aging
Thickness increases
Which layer of bruch’s membrane does drusen deposit
Inner collagenous zone
