Lenticular Optics Flashcards
The horizontal visible iris diameter, HVID
The horizontal corneal diameter
Vertical visible iris diameter (VVID)
Vertical corneal diameter
The anterior corneal curvature (ACC) relates to the ______ of the cornea
Shape of the front surface
Crystalline lens proved approximately ______ of the total static refractive power of the eye
1/3
What are the two purposes of the crystalline lens
- combines with cornea to form image on the retina
- mechanism for focusing at different distances
What kind of optical elements is the crystalline lens
Active
Crystalline lens is ______ in form
Biconvex
What is the diameter of the crystalline lens
9mm
What is the thickness of the lens when it is relaxed
3.6mm
How much bigger is the anterior surface radius of the lens than the posterior
1.7 times
Cornea is what kind of optical element
Static
What are the fundamental building block of the lens
Many lens fiber cells arranged in a hexagonal pattern
What do lens fibers cells do
Interdigitate to form sutures that make the lens very strong, and the suture is continuous through entire lens thickness
Lens growth throughout life
Grows constantly with new cells forming at the equator, then elongating as ‘fibers’ that wrap around the peripheral surface of the lens
What happens when the anatomy of the lens changes
The optical properties do to
What happens when the lens fibers are too coarse? *20microns)
Act as a diffraction grating
Close packing of the lens does what
Reduces light scatter at cell boundaries
How much light does the lens absorb
Very little due to no pigment
Lack of nutrients in the lens means what
These cells are metabolically inactive.
Why is the lack of nutrients and the fact that it is metaboclicalyl inactive goof
It is conducive for transmitting light, but cell damage cannot be reversed (cataract)
Anterior surface power of the crystalline lens
+5.1
Posterior surface power of the crystalline lens
+8.5D
What is the total lenticular power and why is it particular
+13.3D, it should be 21.35D and the difference is due to the different refractive indices in the lens