Topo

Question 1

area of greatest corneal curvature? Normally centered, but where when decentered?

Answer 1

corneal APEX; I-T (Inf-Temp)

Question 2

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?

Answer 2

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

Question 3

Eccentricity of central cornea? What shape does it assume?

Answer 3

0.50D; ellipse

Question 4

What are “orthogonal” meridians?

Answer 4

synonymous w/ “regular” corneas - principle meridians @ 90 deg from each other

Question 5

T/F; Sag affects CL fitting. If so, how?

Answer 5

true; greater sag requires larger LD or Steeper lens (BC)

Question 6

Most common corneal-scleral jx type?

Answer 6

gradual/tangential - #2

Other options:
-gradual/convex, -marked/convex, -marked/tangential, -concave/convex (rare)

Question 7

Four techniques for measuring corneal topo:[POPO]

Answer 7

Placido disk
Orbscan
Pentacam
OCT

Question 8

Placido disk - concentric ___ mapping instantaneous ____ of curvature

example?

Answer 8

rings - mapping thousands of radii of curvature

Humphrey-Zeiss Atlas

Question 9

Orbscan - a series of __ __ beams compiled across the cornea

• T/F: thickness map can be created
• T/F: Surface irregularities can be mapped

Answer 9

slit lamp beams

• true
• true

Question 10

Pentacam - rotating S____ camera

-what can it measure?

Answer 10

Scheimpflug

• topo, thickness, AC depth, LENS curvature
• a LOT it’s a 3D pic of whole ant. seg.

Question 11

OCT - based on reflecting light

• results in one __D image
• can map __ seg, combine w/ P___ disk to map surface

Answer 11

one, 3D image (multiple scans/series of images)

-anterior seg mapping, topo w/ Placido disk (Visante Omni)

Question 12

Computer-assisted Videokeratography (topo) disadvantages:

Answer 12

• accuracy of Placido disk?
• UNABLE to measure limbus/sclera
• cost (8,000-60K)

Question 13

AXIAL (general) maps: ___ reference spheres

• maps w/ respect to ___ ___
• curvatures relate to patient’s actual r___ p___
• LIMIT: d___

Answer 13

ONE reference sph

• respects patient’s visual axis
• refractive power
• DETAIL

Question 14

TANGENTIAL (more data) maps: ___ ref. sphs

• respects the n___ at each point
• better visualization of surface d___
• LIMIT: relation to patient’s actual r____

Answer 14

multiple ref sph

• normal - each point has its OWN ref sph
• details: measures size/shape anomalies
• refraction-limited

Question 15

Axial maps - ____-limited

Tangential maps - ___-limited

Answer 15

axial - DETAIL limited

tangential - REFRACTION limited

Question 16

Which color scales are not comparable to one another unless the scales are identical?

Answer 16

relative (vs absolute)

-the most COMMON display type

Question 17

Compare: absolute vs. relative color scales

Answer 17

Absolute: same colors for same values - consistent

Relative: always changing based on high/low values (red = steep, blue = flat)

Question 18

Name the four topo pattern types: [ROBI]

-what does each signify refractively/about what percentage of people have this pattern?

Answer 18

round: spherical, ~23%
oval: low astigmatism, ~20%
bow-tie - asymm (32%), OR symm (18%)
irregular - ~7%

Question 19

Most common refractive pattern type? What percent of people?

Answer 19

Asymmetrical Bow-Tie - ~32%

Question 20

Irregular pattern types:

• inferior steep zone –> _____
• flat central zone –> ____
• butterfly wing pattern –> ____

Answer 20

• Kconus
• refractive surgery
• PMD - pellucid marginal degeneration
• butterfly pattern - usually inferior (where PMD corneal ectasia occurs)

Question 21

elevation maps use how many ref. spheres?

• relative to the mean r___ of the cornea
• significance red/blue?
• patterns you may find

Answer 21

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

Question 22

difference maps - uses two maps to compare c___, p___, or e___ differences

-good for monitoring corneal c____

Answer 22

curvature, power, elevation differences

-corneal changes (Kconus, pre/post surg)

Question 23

KConus detection - watch for changes >__D between superior/inferior halves

Answer 23

> 2D - watch out!

-also watch for steeper curvature, HIGHER e-values, greater surface irregularity