CL 2-2a: Lab: Corneal Topography

Question 1

Topography:

1. What does it give us?
2. Measures what 2 things?
3. Useful in what 4 things?

Answer 1

1. Geographic map of the cornea
2. Corneal Shape and Power
3. CL fitting; Surgery; Monitoring Corneal Disorders; Diagnosis of Corneal Conditions

Question 2

Alternative for Topography

1. Keratometry: What 3 things?

Answer 2

1. SCL; Normal Cornea GP Fitting; Screening for Irregularity

Question 3

Keratometry

1. Measures where?
2. Number of meridians?
3. Data Analysis?
4. Accuracy to what?
5. Tear Film Stability?

Answer 3

1. Central 3 mm
2. 2 Meridians
3. None
4. to 0.12 D
5. Tear film stability is Critical

Question 4

Topography

1. Measures where?
2. Number of meridians?
3. Data Analysis?
4. Accuracy to what?
5. Tear Film Stability?

Answer 4

1. Limbus to Limbus
2. All Meridians
3. Extensive Data Analysis
4. to 0.01 D
5. is Critical

Question 5

Astigmatism

1. Manifest Astigmatism is MADE up of 2 Components: What are they?

Answer 5

1. Corneal Astigmatism (topography and keratometry)

2. Internal Astigmatism (not measured clinically)

Question 6

Placido’s Disc

1. Diameter of Disc?
2. What is it?
3. What do you do?
4. how is it interpreted?

Answer 6

1. 20 cm diameter disc w/handles
2. Concentric Black/white rings w/a Central Lens
3. Look thru lens and view reflection of Placido’s Disc in the Cornea
4. Assess ring separation: CLOSER TOGETHER (STEEPER)

and

Further Apart (FLATTER)

Question 7

Axial Map

1. AKA?
2. Avg power measured how?
3. Type of effect?
4. Accuracy in periphery?
5. Is it beneficial for detecting small abnormalities?
6. USES?

Answer 7

1. Sagittal Map
2. radially out from the Center
3. Smoothing effect
4. LESS ACCURATE
5. No
6. Screening; Location of Astigmatism (Central vs. Limbus-to-limbus)

Question 8

Tangential Map

1. AKA?
2. Gives us what kind of curvature?
3. More sensitive to what?
4. Accurate where?
5. Useful in what kind of cornea?

Answer 8

1. Instantaneous Map
2. TRUE Curvature
3. to Local or Immediate Change and More detailed
   * LESS Reproducible
4. in the Periphery as well as central
5. Irregular Cornea

Question 9

Difference Map

1. Useful in what 2 situations?

Answer 9

1. Ortho-K or Refractive Surgery

Question 10

Topography

1. Type of Image?
2. Map or Section?
3. Characterizes what surface?
4. Example?

Answer 10

1. 2-D Image
2. MAP
3. Anterior Corneal Surface
4. Placido’s disc imaging

Question 11

Tomography

1. Type of Image?
2. Map or Section?
3. Characterizes what surface?
4. Example?

Answer 11

1. 3-D image
2. Section
3. Anterior and Posterior Corneal Surface
4. Slit Scanning, Sheimflug Imaging, Very High Frequency Ultrasound (VHFU) or Optical Coherence Tomography (OCT)

Question 12

Other Functions of Topographers

Aberrometry

1. Lower Order Aberrations (LOA)
2. Higher Order Aberrations (HOA)

Answer 12

1. Hyperopia, Myopia, Astigmatism

2. Coma, Trefoil, Spherical Aberration, etc.

Question 13

Concept: Eccentricity

1. What does it DESCRIBE?
2. Denotes how a Cornea deviates from what?
3. E Value
   a. Positive
   b. Zero
   c. Negative

d. Avg?
e. Think pathology when?

Answer 13

1. Corneal Shape
2. from a Perfect Sphere
3. a. Steeper centrally, Flatter Peripherally
   b. Perfect Sphere
   c. Flatter Centrally, Steeper Peripherally
   d. 0.45
   e. When e-value is > 0.7

Question 14

Reimbursement

1. Most insurance companies WILL NOT REIMBURSE what?
2. What do you need for reimbursement?

Answer 14

1. 378.21 (regular astigmatism)

2. Medical Diagnosis: Irregular Astigmatism; Keratoconus