Optics: Crystalline Lens Flashcards
The crystalline lens provides approx. _____ of total static refractive power of the eye
1/3
What are the two purposes of the lens
-Combine with cornea to form image on the retina
-provides a mechanism for focusing at different distances
The Lens is ______ in form, with a diameter of ____ mm
Biconvex, 9mm
For a relaxed lens, the thickness is ___mm.
3.6
The anterior surface radius of lens is about ___ times that of the posterior surface.
1.7
The lens is shaped like a ____ spheroid
Oblate
The lens consists of what three parts
Capsule, epithelium, and fiber cells
The lens capsule is..
A thin acellular membrane that envelops the lens
What role does the lens capsule play in accommodation
Distributes the force produced by normal zonular tension across the lens surface
The lens capsule is thicker at the ____ than the ____ lens capsule
Anterior, posterior
Does age increase or decrease the thickness of the lens?
INCREASE
Lens epithelium is located
Beneath the capsule in the anterior and equator
Lens epithelium is not present on which part of the lens
Posterior
Lens fiber cells are arranged in a ____ pattern
Hexagonal
Lens fibers cells ____ to form sutures that make the lens very strong
Interdigitate (picture dr. Martin interlocking his fingers)
The suture is ____ through entire lens thickness
Continuous
As the anatomy of the lens changes so does the _____ properties
Optical
The lens grows through out life with new cells forming at the
Equator, then elongating to peripheral
Lens fibers are too ____ to act as diffraction grating
Coarse
The close packing of the fiber cells reduces ___ ____ at cell boundaries
Light scattering— lens absorbs little light(no pigment and a vascular)
The lack of nutrients of the lens means that the cells are _________ inactive.
Metabolically
Being metabolically inactive is conductive fro transmitting light but it also means that the lens cannot
Reverse cell damage e.g cataract
Because the refractive index of the crystalline lens varies from center to edge, it is called
Gradient index lens or GRIN
The missing 8 diopters for the lens to add up to about 21D is due to what?
The change in refractive index throughout the lens
Are GRIN lenses commonly made commercially?
Nope, its very hard to make them but the lenses are common in nature
If using the equivalent refractive index, it needs to be ___ compared with the maximum value of the gradient lens of about 1.406
1.42
Refraction occurs at ______, ______, and _______ on the crystalline lens
Anterior, posterior, and within
The combined refraction produces ____ D
21.35
At accommodated state, lens refraction is ___ D.
31.85
Does lens thickness increase with accommodation?
YES
Does curvature increase with accommodation?
YEAH
The distance between the far and near points is called
Accommodation range
What is amplitude of accommodation
The difference between the vergence of the far and near points
How can you estimate your AA using your age
15-(1/4)age
Aging Eye: transmittance of UV and visible wavelengths
Decrease
Aging Eye: scattering of light for both forward and backward direction
Increases, after 40years old
Aging Eye: lens axial thickness
Increase at 13 microns per year
Aging Eye: Lens axial thickness increases so ___ ____ depth decreases
Anterior chamber depth
Aging Eye:anterior radius of curvature
Reduces
16mm @ 8yrs
8.3mm @ 82yrs
Aging Eye: posterior radius of curvature
Reduces slightly
Equatorial diameter of the unaccommodated lens
Increases
All possible shape changes _____ in the lens as we age
Decrease
A cataract is any disturbance in the optical ______ of the lens such as …
Homogeneity
Fluid filled pools and opaque spots that scatter light
Phakic eye
Contains the natural lens
Aphakic eye
Is without the natural lens
Pseudophakic eye
Contains an intraocular lens
What are the three options for aphakic eyes? Which is most common?
1.spectacles
2.contact lens
3. Intraocular lenses(best and most common)
