5 - Crystalline Lens Flashcards
Which region is the lens located in the eye?
Posterior Chamber
What is the eye suspended by?
Zonular Fibers of the Ciliary Body
What is the posterior part of the lens attached to?
Anterior Vitreous face by the Hyaloid Capsular Ligament
What is the basic shape of the lens?
Convex
Note: The posterior part of the lens more steeper than the anterior
What are the centers of the lens called?
Poles
What is the normal thickness of the unaccommodated lens?
3.5 to 5 mm
Note: It increases 0.02 mm each year in life
What is the refractive power of the unaccomodative eye?
20D
True or False. The index of refraction increases as you go from anterior to posterior.
True
Note: The index of refraction changes due to increase amount of protein found in the lens
What is the embryological composition of lens made of?
Epithelial cells
What structure of the lens, during embryology, form the primary lens fibers?
Posterior cells
Note: This is why there is no posterior epithelium
Where does cell division occur throughout life?
Germinative zone
What part of the lens capsule becomes the thickest over time?
Anterior pole
Note: Posterior lens capsule changes very little over a period of age
What is the lens capsule primarily made of?
Collagen fibers
Note: There are no elastic fibers but is highly elastic due to lamellar arrangement of the fibers
What is the name of the superficial zone of the lens capsule, where zonular fibers are attached to?
Zonular Lamella
What structure prevents large molecules to pass through the anterior of the lens?
Lens capsule
Lens Epithelium
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Since 80 to 90% of lens proteins are water soluble (alpha, beta, and gamma crystallins) which are packed in the CYTOPLASM of lens fiber cells, what can threaten the optical transparency of the lens?
UV Radiation
What type of crystalline protein is considered the molecular chaperone?
Alpha crystalline
Note: Offers resistance to the degradation of gamma and beta crystalline
True or False. The lens is more basic in pH compared to the Aqueous humor?
False.
Lens pH = 6.9
AH = 7.6
Plasma = 7.4
Since, the crystallin concentration varies among the lens, where is the refractive index gradient highest?
Nucleus = 1.41
Outer Cortical Surface = 1.38
Note: The VH n=1.336
As you know the lens is avascular and has the largest percent of protein in the body. Where does it get its nutrients from and what type of proteins does it require?
From the Aqueous and receives glucose and oxygen and maintains 2 functions:
1)Production of NEW LENS FIBERS and PROTEIN SYNTHESIS
2) Maintenance of Na/K pump.
- The lens is constantly pumping out water to create the correct constituents optically. Note: ATP is required to maintain a dehydrated lens
True or False. Since there is ANAEROBIC GLYCOLYSIS, occuring in the lens epithlium, it has a higher concentration of lactic acid than blood plasma?
True.
