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18 Cards in this Set
- Front
- Back
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Which is steeper, anterior lens surface or posterior?
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Posterior
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What is the thickness of the unaccomodating lens and how much does it increase each year?
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3.5-5 mm thick, increasing 0.02mm each year
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What is thediameter of the lens as a baby and adult?
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baby- 6.5mm
After age 9- 9mm |
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What is the refractive power of the lens?
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about 20D, with 2-14D more from accomodation. Best accomodation is aroud 8-12 years of age.
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What is the function and composition of the lens capsule?
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surrounds lens, thinnest at poles and thicker near equator. Composed of collagen w/ acellular basement membrane. Function is to mold lens shape, prefering spherical, and to block large proteins from getting through
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Which direct is the basal and apical anterior lens epithelium?
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Basal is directed towards the lens capsule, apical is directed toward the posterior pole.
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What is the function of the lens epithelium?
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pass nutrients and waste products.
Secrete the lens capsule |
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What's the deal with the posterior lens epithelium?
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It is only present from 2wks to 2mo of prenatal development
It forms the embryonic nucleus. |
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What is the function of the germinal zone and what orientation are the cells?
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Function: mitosis- forms secondary lens fibers
Basal portion grows toward posterior pole Apical portion grows toward anterior pole |
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What is the EFI?
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Epithelium-fiber interface.
It allows nutrients to pass through the epithelium into the lens fibers. Pinocytosis is the prevalent mechanism |
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What forms the embryonic nucleus and when?
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formed by primary lens fibers. 2wks-2mo prenatal development
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What forms the fetal nucleus and when?
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formed by secondary lens fibers. From 3mo-birth. Contains anterior/posterior Y-sutures
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What forms the adult nucleus and when?
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formed by secondary lens fibers from birth to sexual maturation. Contains stellate sutures
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What forms the lens cortex and when?
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formed by secondary lens fibers from sexual matuation to death. Contains stellate sutures. The basal aspect of the newest fromed fibers secret posterior lens capsule
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What is lens shagreen?
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orange peel like appearance of anterior surface
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What do the zonule fibers attach to?
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They arise from BM of Non-pigmented ciliary epithelium in pars plana in valleys between the processes. attach near lens equator(some pre-equatorial, some post equatorial)
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What did Young, Purkinge, Graves, and Helmholtz have to do with accomodation?
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Young- theorized that the eyeball lengthened to see near.
Purkinge- described reflections from refracting media Helmholtz- found that lens balled up a bit Graves- changes in tension of lens capsule contributes to lens change in shape |
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What is the composition of the crystalline lens?
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2/3 water, about half binding to proteins.
1/3 protein, most 'cystallins' which are water soluble. water insoluble proteins collect with age |
