2 Corneal Optics Flashcards
What’s the optical power of the tear film?
48D
Tear film stability primarily refers to ____________ rate
Evaporation
Irregularities in the TF over a period of time improves the retinal image quality. T or F
FALSE. Degrades retinal image quality
List the layers of the cornea from superficial to deep:
1. 2. 3. 4. 5.
Epithelium Bowman's layer Stroma Descemet's membrane Endothelium
Cornea has a ______ optical power. It has about 2/3 of the total power of the eye. It’s around __D and a refractive index of 1.377.
The refractive index of the _____ dominates the other corneal layers. Corneal diameter is about __mm in size.
Does CCT decrease with age due to decrease in keratocytes?
African Americans have thinner CCT than other races. T or F
FIXED; 42D
Stroma; 12mm
0.5mm
It does!
T thinner
What’s the anterior surface power of the cornea?
N=1
N’=1.377
Ra=7.68mm
Fa=(n-n’)/Ra
What about posterior surface? N=1 N'=1.336 Rp=5.81mm Fp=(n-n')/Ra
Total corneal power?
- 09D
- 7.06D - 03D
BUT cornea is NOT spherical surface
The cornea is regarded as a ________, and the ________ is ellipsoidal.
When light passes through a spherical lens F=__mm.
When light passes through an aspheric lens F= ___mm. This nullifies Spherical aberrations.
Conicoid, conicoid
50mm
100mm
When Q= 0 you have a ______ lens
0 >Q> -1 you have an ________ lens
Sphere
Ellipsoid
The cornea _______ away from the vertex because the Q (anterior corneal asphericity) values are usually NEGATIVE.
This is significant because:
- To ________ spherical aberration. Q required -0.528 to eliminate.
- To make ______ join with the main globe of eye. Shapes the eye
Flattens.
- Reduce
- Smooth
What are the three factors in the cornea that affect vision?
Corneal diameter (CD)
Anterior corneal curvature (ACC)
Central corneal thickness (CCT)
Corneal diameter is from the _______ to limbus (white of the eye). Accurate measurement of CD helps:
To ensure _______ lens diameter is sufficient.
To produce right size anterior chamber of IOLs
To diagnose some diseases
Horizontal diameter is __mm in adults while the Vertical diameter is __mm in adults.
Does CD decrease slightly with age?
Males or females have wider horizontal diameter?
Asians CD is _______ than the Caucasians
Limbus
Contact
11mm, 12mm
YES, can increase chances of glaucoma with narrowing of anterior chamber
Males significantly wider
Smaller
The anterior corneal curvature (ACC) exhibit _______. You can collect this data from what three things? (K.I.T.)
Cornea is _______ in both radius of curvature and asphericity.
If the refractive surface, pupil diameter, and asphericity are constant, the spherical aberration will:
________ If the corneal surface flattens and will ________ as the cornea becomes steeper.
Hyperopes are _______ than myopic eyes.
400th of a mm correlates to 0.25D
Toricity
- Keratometer
- IOL master
- Topographer
Asymmetric
Decrease, increase
Flatter
A cornea too _____ leads to a condition called keraticonus.
A cornea too ____ leads to a condition called cornea plana.
WTR astigmatism occurs when the _______ meridian of the cornea is steepest. ATR astigmatism is when the _________ meridian is steepest.
Corneal curvature becomes ________ as age increases due to elasticity of cornea. Females had significantly ________ corneal curvature.
Curved
Flat
Vertical, horizontal
Steeper, steeper
The CCT is about 0.5mm. A ____ cornea leads to underestimation of intraocular pressure. A _____ corneal leads to overestimation of IOP
Thin
Thick
For a conicoid surface, the radius of curvature at off-axis points depends upon two things:
The distance from the ______. And on the _______ at that point.
Vertex. Meridian
