Accommodation (F) Flashcards
What innervates the ciliary muscles? 1. What are the receptors found (along with their actions)? 2
- parasympathetic and sympathetic systems
- Para = M3 receptors (contraction)
Sym = β2-adrenergic receptors (relaxation)
Which ciliary muscle fibers may trigger slightly before the others?
longitudinal
Embryonically, what is smooth muscle derived from? 1. What are ciliary muscle fibers derived from? 2
- mesoderm
2. ectoderm
What do longitudinal fibers have fewer of than smooth muscle? 1. More of? 2. Do longitudinal fibers have a smaller or larger nucleus? 3
- mitochondria
- myofibrils
- larger
What is the action of anterior portion of ciliary muscle fibers? 1. Action of posterior portion? 2
- applies force to the scleral spur and opens trabecular meshwork
- applies force to pars plana moving it anteriorly
What is the action of anterior portion of ciliary muscle fibers? 1. Action of posterior portion? 2
- applies force to the scleral spur and opens trabecular meshwork
- applies force to pars plana moving it anteriorly
Do the circular ciliary muscle fibers increase or decrease thickness during contraction? 1. Longitudinal fibers? 2 Radial fibers? 3
- increase
- decrease
- decrease
During relaxation, what is the reason the ciliary is returned to its unaccommodated configuration?
elasticity of the choroid pulling it back into place and posterior ciliary zonules
What are the functions of the ciliary zonules?
- Hold lens in place
- Transmit tensile forces for accommodative shape change of the lens
- Form fibril structures that allow fluid to pass
Where do the anterior zonules originate? 1. Where do they attach? 2
- pars plana and valleys of Kuhnt
2. anterior capsule
Where do the posterior zonules originate? 1. Where do they attach? 2
- near ora serrata and valleys of Kuhnt
2. posterior capsule (at ligament of Weiger) and vitreous membrane
Where do the equatorial zonules originate? 1. Where do they attach? 2
- valleys of Kuhnt
2. equatorial capsule
Where do the equatorial zonules originate? 1. Where do they attach? 2
- valleys of Kuhnt
2. equatorial capsule
What is the function of interciliary zonules or tensor fibrils? 1. Where do these occur? 2
- anchor the ciliary zonules passing through the pars plicata
- zonular plexus (valley of Kuhnt)
What synthesizes zonules?
non-pigmented ciliary epithelium
What is the percentage of people Marfans that have dislocated lens?
60%
What are zonules made out of? 1. What are the subcategories of these? 2
- glycoproteins
2. Fibrillin (make beads and string) and MAGP-1 (Microfibril-associated glycoprotein 1) (make beads)
How much collagen are in zonules? 1. Elastin? 2
- none
2. none
What are large cysteine-rich multidomain glycoprotein that polymerize in the extracellular space in a head-to-tail manner to form microfibrils?
fibrillins
What is the thin transparent elastic membrane around the lens? 1. What is it secreted by? 2. Where is it the thickest and the thinnest? 3
- lens capsule
- lens epithelial and fiber cells
- Thickest just anterior and posterior to equatorial region, thinnest posteriorly
What is the lens capsule composed of?
- Collagen IV
- Laminin
- Heparin sulfate proteoglycans (Perlecan, Nidogen, Collagen XVIII)
What is the lens capsule composed of?
- Collagen IV
- Laminin
- Heparin sulfate proteoglycans (Perlecan, Nidogen, Collagen XVIII)
What is the function of the lens capsule?
serves as a force distributor, evenly applying stored elastic energy over the surface of the lens
What is the rate of decline of accommodation?
2.5D/10 years
What is the inability to accommodate with age mostly due to?
increase in stiffness of lens
How thick is the capsule at birth? 1. At age 60? 2. How does the elasticity change? 3
- 11 microns
- 20 microns
- 50% decrease
What increases the stiffness of the lens capsule?
Non-enzymatic glycation of collagen
What increases the stiffness of the lens capsule?
Non-enzymatic glycation of collagen
What is the covalent bonding of proteins (collagen) with a sugar molecule (glucose/fructose)?
glycation
What is the change in elasticity of zonule fibers with age?
none
How does the Equatorial zonule insertion shift with age?
anterior to equator
How does the contractile force of ciliary fibers change with age?
doe not change
How does the contractile force of ciliary fibers change with age?
does not change
What residues of collagen in the capsule has non-enzymatic, random intra/inter-molecular and interfibrillar cross-linking occur with age?
lysine and arginine
What is the accommodative triad?
1) Ciliary muscle contraction
2) Pupil Constriction
3) Convergence
What are the major excitatory neurons of the sphincter muscle? 1. Minor inhibitory neurons? 2
- parasympathetic (Mediated by acetylcholine and muscarinic receptors)
- sympathetic
What are the major excitatory neurons of the dilator muscle? 1. Minor inhibitory neurons? 2
- sympathetic (Mediated by norepinephrine and α1 receptors)
2. parasympathetic
What is a neurological disorder characterized by a tonically dilated pupil that reacts slowly to light and accommodation? 1. What is the cause of the pupil affect? 2
- Holmes-Adie syndrome
2. viral or bacterial infection damaging neurons in ciliary ganglion or lesion there
What provides sensory innervation to the iris?
ophthalmic division of the trigeminal nerve (CN V)
What provides sensory innervation to the iris?
ophthalmic division of the trigeminal nerve (CN V)
What are the major functions of the pupil?
1) Control of retinal illumination
2) Reduction of optical aberrations
3) Improve depth of focus/field
What causes the pupillary response?
- Light induced
2. Near-response (accommodation)
What is the efferent pathway to control the pupillary response for light induced? 1. For near-response? 2
- Parasympathetic control of iris sphincter
2. Parasympathetic control of iris sphincter
What is the pupillary light response mediated by?
projections to LGN and OPN from Intrinsically photosensitive retinal ganglion cells (ipRGC ), rods and cones
How do ipRGCs sense light?
photosensitive pigment (melanopsin)
Where do interneurons from the OPN project to?
Edinger-Westphal nucleus
Where do interneurons from the OPN project to?
Edinger-Westphal nucleus
Where does input from accommodative pupillary response come from?
cortical areas surrounding the visual cortex and from cortical areas within the frontal eye fields
What does supranuclear neuronal input from near visual tasks stimulate?
parasympathetic neurons in Edinger-Westphal nucleus and stimulates ciliary muscle neurons
How does pupillary dilation occur neuronally?
- Supranuclear inhibition of the Edinger-Westphal nucleus (sympathetic innervation, inhibiting para)
- Stimulation of sympathetic nerves in dilator muscle (not required)
How can dilation occur humorally?
Circulating catecholamines in blood may act directly on iris dilator muscle via bloodstream
What is a condition characterized by an unequal size of the pupils? 1. What does this indicate? 2
- Anisocoria
- damage has occurred to either iris sphincter or dilator muscle, Innervation is interrupted, or External pharmacologic factors influencing pupils
What is a condition characterized by an unequal size of the pupils? 1. What does this indicate? 2
- Anisocoria
- damage has occurred to either iris sphincter or dilator muscle, Innervation is interrupted, or External pharmacologic factors influencing pupils
What is the simultaneous movement of both eyes in opposite directions to obtain or maintain single binocular vision?
vergence
Where is accommodative esotropia commonly found?
hyperopes
