Lens and Cataracts Flashcards
(117 cards)
the lens is a ____ structure located within the ____
transparent, biconvex;
posterior chamber
the lens is suspended in the posterior chamber via ____
zonules (suspensory ligaments)
the lens focuses ____
light rays to a point source on the retina
the lens contributes ____ of total refractive power of the eye
13-17 D
the lens has a ____ refractive index (____)
high; 1.3-1.4
the lens is composed of ____ and is divided into ____
epithelial cells with a basement membrane;
the embryonic nucleus, fetal nucleus, adult nucleus, cortex, and capsule
during gestation, a single layer of _____ forms a hollow sphere, called the _____
epithelial cells; lens vesicle
_____ cells of the lens vesicle elongate to become primary lens fibers; they fill the lens vesicle and form the ____
posterior;
embryonic nucleus
_____ cells of the lens vesicle near the equator divide to produce new epithelial cells; these cells elongate to become secondary lens fibers and form the ____, which surrounds the ____
cell elongation continues until ____; form ____, allowing cells to remain tightly connected during accommodation
as cells reach the sutures, ____; cells consist of ____
anterior;
fetal nucleus;
embryonic nucleus
nasal and temporal cells meet (suture); interlocking ball-and-socket and tongue-and-groove junctions
nuclei and organelles are degraded; only a cell membrane, cytoskeleton, and crystallins (proteins)
the anterior suture appears as ____, while the posterior suture appears as ____
an upright Y;
an inverted Y
after birth, _____ cells continue to divide and elongate;
secondary lens fibers produced after birth form the ____, which surrounds the ____
newly produced secondary lens fibers are located in the ____
new fibers continue to surround older more central fibers; growth results in concentric layers of _____;
_____ cells are removed from the lens; cells in the center of the lens are ____
anterior;
adult nucleus;
fetal nucleus
cortex
secondary lens fibers;
no;
the oldest cells in the body
the basement membrane of the outer epithelial cells is called the _____; it surrounds ____
lens capsule;
the entire lens
the lens capsule is composed of _____; arrangement makes the lens capsule ____
primarily type IV collagen and GAGs;
highly elastic
____ lens capsule thickens throughout life; lens capsule components are secreted by _____; becomes the ____ BM in the body
anterior;
anterior epithelial cells;
thickest
____ lens capsule remains the same thickness throughout life; no _____ to secrete the lens capsule components
posterior;
posterior epithelial cells
the lens absorbs _____
ultraviolet light
_____ in the lens absorb most of UV-A (320-400 nm) radiation to prevent it from _____; absorption of UV radiation leads to production of ____
chromophores (yellow pigment);
reaching the retina;
free radicals –> DNA damage and protein aggregation
the lens refracts _____
visible light (400-700 nm)
refractive power of the lens changes with ____
contraction of the ciliary muscle
What happens with contraction of the ciliary muscle?
zonules relax –> lens thickness increases –> lens equatorial diameter decreases –> anterior lens radius of curvature decreases (anterior surface curvature steepens) –> lens refractive power increases (> 20D) = accommodation
with age, ability for the lens to change its curvature is ____; ciliary body moves progressively ____; lens _____; lens rigidity ____; nucleus becomes ____ than the cortex
impaired (presbyopia); inward toward the lens; thickens; increases; stiffer
the lens transmits ____
visible light (400-700 nm)
for optimal light transmission, the lens must be ____
transparent
the ____ are the only transparent tissues in the body
lens, cornea, vitreous
