Topo Flashcards
area of greatest corneal curvature? Normally centered, but where when decentered?
corneal APEX; I-T (Inf-Temp)
What is meant by “asphericity” of the cornea-What is always changing?
What term describes the rate of change from central to periphery?
Is “e” larger/smaller toward periphery?
radius of curvature! Usually steepest central and flattens out peripherally
eccentricity - HPEC - hyperbola, parabola, ellipse, circle (central)
“e” is LARGER toward periphery (curvature changes faster) - range from ~0.50-0.99
Eccentricity of central cornea? What shape does it assume?
0.50D; ellipse
What are “orthogonal” meridians?
synonymous w/ “regular” corneas - principle meridians @ 90 deg from each other
T/F; Sag affects CL fitting. If so, how?
true; greater sag requires larger LD or Steeper lens (BC)
Most common corneal-scleral jx type?
gradual/tangential - #2
Other options:
-gradual/convex, -marked/convex, -marked/tangential, -concave/convex (rare)
Four techniques for measuring corneal topo:[POPO]
Placido disk
Orbscan
Pentacam
OCT
Placido disk - concentric ___ mapping instantaneous ____ of curvature
example?
rings - mapping thousands of radii of curvature
Humphrey-Zeiss Atlas
Orbscan - a series of __ __ beams compiled across the cornea
- T/F: thickness map can be created
- T/F: Surface irregularities can be mapped
slit lamp beams
- true
- true
Pentacam - rotating S____ camera
-what can it measure?
Scheimpflug
- topo, thickness, AC depth, LENS curvature
- a LOT it’s a 3D pic of whole ant. seg.
OCT - based on reflecting light
- results in one __D image
- can map __ seg, combine w/ P___ disk to map surface
one, 3D image (multiple scans/series of images)
-anterior seg mapping, topo w/ Placido disk (Visante Omni)
Computer-assisted Videokeratography (topo) disadvantages:
- accuracy of Placido disk?
- UNABLE to measure limbus/sclera
- cost (8,000-60K)
AXIAL (general) maps: ___ reference spheres
- maps w/ respect to ___ ___
- curvatures relate to patient’s actual r___ p___
- LIMIT: d___
ONE reference sph
- respects patient’s visual axis
- refractive power
- DETAIL
TANGENTIAL (more data) maps: ___ ref. sphs
- respects the n___ at each point
- better visualization of surface d___
- LIMIT: relation to patient’s actual r____
multiple ref sph
- normal - each point has its OWN ref sph
- details: measures size/shape anomalies
- refraction-limited
Axial maps - ____-limited
Tangential maps - ___-limited
axial - DETAIL limited
tangential - REFRACTION limited
Which color scales are not comparable to one another unless the scales are identical?
relative (vs absolute)
-the most COMMON display type
Compare: absolute vs. relative color scales
Absolute: same colors for same values - consistent
Relative: always changing based on high/low values (red = steep, blue = flat)
Name the four topo pattern types: [ROBI]
-what does each signify refractively/about what percentage of people have this pattern?
round: spherical, ~23%
oval: low astigmatism, ~20%
bow-tie - asymm (32%), OR symm (18%)
irregular - ~7%
Most common refractive pattern type? What percent of people?
Asymmetrical Bow-Tie - ~32%
Irregular pattern types:
- inferior steep zone –> _____
- flat central zone –> ____
- butterfly wing pattern –> ____
- Kconus
- refractive surgery
- PMD - pellucid marginal degeneration
- butterfly pattern - usually inferior (where PMD corneal ectasia occurs)
elevation maps use how many ref. spheres?
- relative to the mean r___ of the cornea
- significance red/blue?
- patterns you may find
ONE ref. sphere, relative to mean RADIUS of cornea
- red - higher than ref sph, blue = lower
- normal, KConus, refractive surgery/ortho-K
- can predict staining patterns based off this
difference maps - uses two maps to compare c___, p___, or e___ differences
-good for monitoring corneal c____
curvature, power, elevation differences
-corneal changes (Kconus, pre/post surg)
KConus detection - watch for changes >__D between superior/inferior halves
> 2D - watch out!
-also watch for steeper curvature, HIGHER e-values, greater surface irregularity
