Lecture 2- Corneal Optics Flashcards
Cornea has a fixed ________
optical power
Cornea has about ____of the total power of the eye (Relaxed).
2/3
Corneal Power is calculated as
~42 D
Cornea has a refractive index of _______
refractive Index of _________dominates the other corneal layers
1.377
stroma
Corneal diameter of about ______ in size
12 mm
The central corneal thickness (CCT) is about ________
0.5mm
Aspherity:
the cornea is regarded as a ________and the _____ is ____________
conicoid
conicoid
ellipsoidal
The Anterior corneal asphericity (Q) values are usually ______ which indicates that cornea ___________the vertex.
negative
flattens
away from
The significance of the corneal flattening away from the vertex or center is:
2 things-
- To reduce spherical aberration. .
2. To make smooth join with the main globe of the eye
__________ is limbus to limbus, (the
white of the eye)
Corneal diameter
Accurate measurement of CD helps,
• To ensure contact lens diameter is________________________
• To produce _______________________
• To diagnose diseases such as __________________
sufficient
to maintain full coverage of the cornea.
right size anterior chamber IOLs.
microcornea,
megalocornea, relative microphthalmos,
and corneal dystrophies.
• Horizontal diameter of the cornea on average is _______ in infants and ________ in adults
10 mm
11 mm
Vertical diameter of the cornea on average is______ in infants and_____in adults.
11 mm
12 mm
Age: Studies show that corneal diameter (CD) _________ slightly with age due to:
decreases
the age related narrowing of anterior chamber increasing the chances of glaucoma.
• Gender: Males have significantly ______horizontal corneal diameter than their female
counterparts (in 130 eyes).
wider
Race: A study comparing corneal diameter of asian eyes (125) and Caucasian eyes (81)
shows that _______ CD is smaller than the _________. T
Asians
Caucasians
Radius of curvature: Anterior corneal curvature (ACC) exhibit _______
toricity.
There are two principal meridians:
• the tangential meridian, which lies along
_____________and
• the sagittal meridian, which is______________
the radius line from the vertex,
perpendicular to the tangential meridian.
Cornea is significantly _______ in both radius of curvature and asphericity
asymmetric
If the refractive index, pupil diameter and asphericity are considered constant, the spherical
aberration will
• _______ if the corneal surface flattens and
• ________ as the cornea becomes steeper.
decrease
increase
Hyperopes tend to be _______ than the myopic eyes (more –ve Q values for hyperopes than myopes).
flatter
Cornea too curved leads to a condition called
___________.
Keratoconus
Cornea too flat leads to a condition called
_________
Cornea plana.
The average cornea curvature has a smaller radius in the_______meridian
compared to the __________meridian, which contributes to the ‘with-the-rule
astigmatism’ in young adults.
vertical
horizontal
- “__________” astigmatism occurs when the vertical meridian of the cornea is steepest
With-the-rule
- “_____________” astigmatism occurs when the horizontal meridian of the cornea is steepest
Against-the-rule
_________ becomes steeper with increasing age due to the
changes in the elasticity of the cornea.
Corneal curvature
Gender: __________had significantly steeper average corneal curvature than
____________
females
males
The central corneal thickness (CCT) is
about________
0.5mm.
Race: Studies show that _______________ have
thinner CCT than other races.
African Americans and other African descent
Age: Several studies report that reduction of CCT with age due to the decrease
in ‘_________ with age
keratocytes
For a conicoid surface, the radius of
curvature at off-axis points depends
upon 2 things:
the distance from the vertex,
• on the meridian at that point.
