Specialty testing in CL Fitting

Question 1

In a ____________ cornea, there is gradual flattening from center to periphery

Answer 1

prolate

Question 2

When do we see an oblate cornea?

Answer 2

post surgery (flatter centrally, steeper peripherally)

Question 3

What is eccentricity?

Answer 3

amount of flattening

Question 4

What is the E value for a prolate cornea? An Oblate Cornea?

Answer 4

Prolate: between 0-1; Oblate <0

Question 5

What is the average E value?

Answer 5

0.50 (range 0.3-0.7)

Question 6

What is Asphericity (Q)?

Answer 6

The rate of change of curvature from apex to periphery

Question 7

What type of cornea has a (-) Q?

Answer 7

prolate

Question 8

What is the average Q?

Answer 8

-0.26

Question 9

What type of keratometry is the Oculus Pentacam?

Answer 9

Projection/ slit scanning

Question 10

What is the axial map used for?

Answer 10

showing overall shape, following progression, power change (assumes center of curvature is the center of cornea)

Question 11

What is the tangential map used for?

Answer 11

local curvature; keratoconus, orthoK centration

Question 12

What is the elevation map used for?

Answer 12

interpreting NaFl patterns in corneal GPs

Question 13

What are the 5 parameters given in the Belin/ Ambrosio Enhanced Ectasia Display?

Answer 13

• Df: changes in anterior elevation from standard to enhanced reference surface
• Db: changes in posterior elevation
• Dt: corneal thickness at the thinnest point
• Da: thinnest point displacement
• Dp: pachymetric progression

Question 14

How is Final D calculated in the BAD?

Answer 14

considers all 5 parameters and performs a linear regression against a standard database of normal and KC corneas

Question 15

What is the index of vertical asymmetry?

Answer 15

Mean difference between superior and inferior corneal curvature by assessing the level of curvature symmetry with respect to the horizontal meridian as the axis of reflection

Question 16

Is the IVA or BAD better at predicting KCN?

Answer 16

BAD

Question 17

What measurement is KCN staging based on?

Answer 17

posterior curvature and thickness measurements based on the thinnest point, not the apical measurement

Question 18

Which instrument has the best repeatability for min/ max K readings?

Answer 18

IOLMaster

Question 19

What is the gold standard for CCT?

Answer 19

Ultrasound pachymetry

Question 20

When is CCT helpful?

Answer 20

keratorefractive procedures; glaucoma

Question 21

When is ECC helpful?

Answer 21

early stages of dystrophic endothelial disease

Question 22

When considering corneal grafts, is a higher or lower ECC associated with a higher chance of rejection?

Answer 22

lower ECC

Question 23

What happens to the cornea when the Na/K ATP pumps become less effective?

Answer 23

stromal swelling

Question 24

How does endothelial cell density change throughout life?

Answer 24

decreases (children: 3,000-4,000 cells/ mm ²; 80 year olds: 2300 cells/ mm²)

Question 25

what does a lower CD value mean?

Answer 25

endothelium depleting faster than normal

Question 26

What is the average adult axial length?

Answer 26

24 mm

Question 27

What change in axial length do we see in children with progressive myopia?

Answer 27

1D of myopia = ~0.50 mm AXL

Question 28

What are the uses for axial length measurements?

Answer 28

cataract surgery; myopia control progression

Question 29

How does the lens compensate for the initial increase in AXL?

Answer 29

thins until it reaches physiological limit, then myopia begins

Question 30

What age is the peak incidence of myopia?

Answer 30

8-10 years old

Question 31

When does myopia usually stabilize?

Answer 31

by 16 years old

Question 32

What are the goals for myopia control?

Answer 32

keep myopia < 6.00 D and axial length <26 mm

Question 33

What are uses of Anterior Seg OCT?

Answer 33

glaucoma, retina, cornea; scleral lens fitting