Crystalline Lens Flashcards
what is the crystalline lens
all cells, transparent, biconvex structure
what is the posterior curvature
5-8mm radius of curvature
what is the anterior curvature
8-14mm
which side, anterior or posterior of the lens is steeper
the posterior side
how far away from the pars plicata is the lens equator
about 0.5mm away from the ciliary processes
what are the dimensions of an adult lens (unaccommodated)
10mm in diameter and 4mm thick
what changes as we age, the diameter or thickness of the lens
the thickness, increases about 0.02mm per year
what keeps the lens in place on the posterior surface to the anterior surface of the vitreous
the hyaloid capsular ligament
how much of the total power of the eye is the lens power
about 15 to 20 D (the cornea accounts for the rest)
what are the 3 parts to the lens
an elastic capsule, lens epithelium, and lens fibers
what is the thickest basement in the body
the elastic capsule of the lens
where is the thickest part of the lens
just anterior and posterior to the equator
where is the lens the thinest
at the posterior pole
does the posterior side have an epithelium
no
how is the lens capsule secreted anteriorly
by the anterior lens epithelium
how is the lens capsule secreted posteriorly
by the superficial lens fibers
which side of the lens capsule thickens with age, posterior or anterior
the anterior side does
what are the two functions of the lens capsule
act as a diffusion barrier that is freely permeable to low-molecular weight compounds and to make the lens more pliable in response to the pull of the zonular fibers during accommodation
where do the zonules attach to the lens capsule
between the equator and the poles
why is there no posterior epihelium
it was used to form the primary lens fibers during embryonic development
where do cells proliferate
the pre-equatorial (germanative zone) near the equator
what happens to the cell after it is created
it transitions into an elongated columnar shape and arranged in meridional rows and will become secondary lens fibers
do any of the fibers die off as we age
no, they become compacted and make the lens less pliable
how does the lens receive nutrients
the central anterior epithelium is involved in the transport of substances from the aqueous humor (the lens is avascular)
what is the bulk of the lens
the secondary fibers
where is the nucleus located in the secondary lens fibers
it is anterior, it gradually disintergrates and the fiber will lose contact with the basement membrane
what are lens Y sutrures
the place where anterior and posterior end of fibers meet
how long and what shape are the lens fibers
they are 10mm long and U-shaped to fit in the lens (4-5mm thick)
which side, anterior or posterior is the Y suture upright
the anterior side
how are the lens fibers held together
by interlocking adjacent plasma membranes (ball and socket)
what type of junction is present in the fibers
gap junctions to permit the deeper fibers with nutrients from the aqueous humor
besides suppling nutrition what else to the gap junctions aid with
helping the lens to act like a single cell
what is the epithelium-fiber interface
the border of the apical portion of the anterior epithelium and the apical portion of the secondary lens fiber
after the nuecli are lost in the fibers, what happens to them
they become specialized to form crystallins (alpha and beta): the bulk of the lens fiber 40%
why is the lens so refractive
due to the specialization of the fibers forming crystallins
what is the earliest fiber mass called
the embryonic nucleus (center of lens)
when is the embryonic nucleus formed
first 2 months of embryonic development (doesn’t increase in size)
what fibers are formed before birth that have the Y sutures
the fetal nucleus
what nucleus has the fibers formed between birth and sexual maturation, that increases throughout life
the adult nucleus
is there blood supply to the crystalline lens
not after embryologic development
