Choroid Ciliary Body Iris Flashcards
What are the strands which suspend the lens in place
Zonules, suspensory ligaments
What re the zonule fibres composed of
Non collagenous and composed of FIBRILLIN for elasticity
Where do the zonules attach to
They run through the ciliary processes of pars plicata and pars plana and join on dentures along the ora serrata
What structure anchors the zonules on the floor between the ciliary processes
Tension fibres; they allow the zonules to change direction 90 degrees
What is accommodation
Accommodation is the ability for the eye to rapidly increase its refractive power to bring near objects into focus, I.e. converging image on the retina from behind
Describe the ways how humans accommodate
Changing its lens power
Elongating the size of the eyeball
Change corneal curvature
Making lens multifocal
Moving lens along the axis
Which way do humans tend to accommodate
Through altering the power of the lens, changing refractive power
What are the biomechanics when there is contraction of longitudinal and circular ciliary muscles
Lens has a wider axial length
Anterior portion of lens is more curved and bulbous
Zonules fibres are lax
What controls the ciliary muscle
The autonomic nervous system , parasympathetic branch
How is accommodation controlled
Edinger westphal nucleus, which contains preganglionic parasympathetic neurones innervated by oculamotor nerve, synapsing in ciliary ganglion, causing ciliary muscle to contract
How does the body know how much accommodation is required
The edinger westphal nucleus receives information from the supraoculomoter area which received direct input from the visual cortex
The visual cortex uses cues to determine how much accommodation is needed
Near triad system of the edinger westphal nucleus
Accommodation, increasing refractive power
Pupil constriction, increasing the depth of field
Convergence, to ensure the second focal point lies on the fovea
What is the diameter and depth of the anterior chamber
11.3-12.4mm in diameter and 3 mm in depth
What is the aqueous humour responsible for
Nutrition of the avascular lens and cornea, as well as removing metabolic waste products
Describe the pathway of the aqueous humour from production to drainage
It is produced by the unpigmented epithlium of the pars plicata, travelling from the posterior to the anterior chamber supplying lens and cornea with nutrients, then drained at the iridocorneal angle at the a canal of schlemm
Describe briefly the mechanism of aqueous production
Ions are actively transported from the Stroma to the pigmented epithelium, then via gap junctions to the Non pigmented epithelium, the actively transported to the posterior chamber
What is the role of adenylate cyclase in regulation of aqueous production
Adenylate cyclase is what causes the catalytic conversion of ATP to cyclic AMP, alpha agonists activate AC, and hence reducing the IOP, whereas beta agonists, inhibit action of AC, increasing IOP
Is the uveoscleral pathway pressure independent or depend
Pressure independent, meaning that even if the IOP is low, in some cases, drainage will still occur, I.e. if metabolic waste products need to be eliminated
What is the step a of the iris composed of
Loose areolar connective tissue, allowing the iris to easily change shape controlling pupil size
Which segment of the iris contains the highest vascular system
Stroma
Function of clump cells
Ingesting melanocytes and debris from epithelial cell death, clean up to keep aqueous free of debris
Name the two muscles in the iris
Sphincter and dilator
Function of dilator muscle
To increase size of pupil, pupil dilates as the radial dilator muscles contract
Why does the iris contain tight and gap junctions
This is due to the fact that the length of each muscle spindle isn’t long enough to span from the iris root to pupil margin
Function of the iris sphincter
This is to constrict the size of the pupil, miosis, as the circular sphincter muscles contract, they cause the pupil to shorten, in bright light especially
Is the main blood supply for the iris
Major iridic circle
Which part of the brain innervates pupil constriction
Edinger westphal nucleus of the midbrain via oculamotor nerve
Where does the outer retina receive its bloody supply and nutrients from
The choroid, choriocapillaris
What is drusen and its consequences
Drusen essentially are a set of debris composed of proteins and lipids, its function is to push the photoreceptor layer away from the choriocapillaris, hence starving the photoreceptors of essential nutrients
Linked with AMD
