Lens Flashcards
what type of tissue is the lens
two types of specialized epithelial tissue: cuboidal and elongated fiber cells
what 3 things must the lens have in order to project an image onto the retina
transparent, higher refractive index than the medium its suspended in, and have flexible refractive surfaces with the proper curvature
what happens to the lens if there is disruption of precise organization or damage to the proteins
destroys the transparency of the lens and cataract formation
what type of tissue is the lens epithelium
a sheet of cubodial cells
what type of tissue is the bulk of the lens
elongated fiber cells
what secretes the lens capsule
the epithelial and superficial fiber cells
where is the germanitive zone
near the equatorial margin of the lens epithelium
when do the fibers stop elongating
when they reach the Y sutures
what are the lens sutures
junctions between the apical and basal ends of the cells from opposite ends of the lens
where do the mature lens fibers go
they get buried deeper as fibers elongate and differentiate
when does synthesis stop
just before the organelle degradation
how do the mature fiber cells compare to those in the rest of the body
the components of mature fiber cells are more stable
what are the zonules
the inelastic microfibrils that suspend the lens
where do the zonules originate and insert
in the NPE of the ciliary epithelium and insert into the lens capsule near the equator
what is responsible for changing the lens curvature during accommodation
the zonules
what contributes to the refractive nature of the lens
the high concentration of crystallins in the cells and the curvature of the surfaces
what is the concentration of crystallins in the lens compared to typical cells
3 times higher concentration
what causes refractive error is younger individuals
corneal curvature or the length of the globe (rarely by the lens)
what does the transparency of the lens depend on
minimizing light scattering and absorption
why does light pass smoothly through the lens
regular structure of lens fibers, absence of membrane-bound organelles and small /uniform extracellular space between fiber cells
what happens to the nearly colorless lens as we age
becomes more yellow- lens absorbs short wavelength light (blues)
what is aphakia
the absence of the natural crystalline lens from natural causes or removal
what is congenital aphakia
caused by Rubella infection in first 4 weeks of pregnancy (mutation in PAX-6 gene)
what is pseudophakia
substitution of the natural crystalline lens with a synthetic lens