Competency 3.1.1

Question 1

What Part of the Cornea Does Keratometry Assess?

Answer 1

• The a 3mm zone in the central cornea
• Corneal topography is able to assess the entire cornea

Question 2

Uses of a Keratometer

Answer 2

• Determining degree of corneal astigmatism present
• Obtaining location of astigmatic meridians (WTC or ATR)
• Radii of curvature for contact lens fitting
• Assessing CL fit
• Detection of corneal pathology

Question 3

Determining Degree of Astigmatism from K Readings

Answer 3

• For each 0.05mm of difference this equates to approx 0.25DC of corneal astigmatism
• Any residual astigmatism in the prescription is lenticular

Question 4

Flat and Steep K Readings

Answer 4

• Flatter cornea’s have larger numerical values and are less dioptriclally powerful
• A steeper cornea has a smaller numerical value and are more dioptric value

Question 5

With the Rule or Against the Rule Astigmatism

Answer 5

• In WTR the flatter K is located along the horizontal meridian
• In ATR the flatter K is located along the vertical meridian
• Oblique astigmatism doesn’t fall into either of these categories

Question 6

Where is WTR and ATR Astigmatism More Common

Answer 6

• WTR is more common in young and myopic eyes
• ATR is more common in older eyes with cataract

Question 7

How to Obtain SCL BOZR from K Readings

Answer 7

• Take flattest K and add 0.7 or multiply by 1.1

Question 8

How to Obtain RGP BOZR from K Readings

Answer 8

• Use formula and round answer to nearest 0.05mm
• FlatK- ([FlatK-SteepK]/3)
• It gives a slightly flatter fit than the flattest K

Question 9

Keratometer in Assessing SCL Fit

Answer 9

• Bausch and Lomb Keratometer only
• A good fitting lens will show clear mires before and after a blink
• A tight fitting lens will show distorted mires which clear up after a blink
• A flat fitting lens will show clear mires which distort right after blink

Question 10

Keratometry in Detection of Pathology

Answer 10

Keratoconus will show as:
- Minification of mires due to high myopia
- Oval mires due to significant astigmatism
- Wavy and irregular mires seen in advanced keratoconus

Question 11

Principle of Keratometry

Answer 11

Based on that principle that:
- Cornea acts as a mirror which produces images of the mires
- The size of these images is dependent upon the radius of curvature of the corneal surface
- Image size can then be used to determine K values

Question 12

Bausch and Lomb Keratometer Design

Answer 12

• One position keratometer
• Works on principle of constant object size and varying image size

Question 13

Javal- Schiotz Keratometer Design

Answer 13

• Two position keratometer
• Works on principle of varying image size and constant image size

Question 14

Bausch and Lomb Keratometer Pros and Cons

Answer 14

Advantages
- Measures both meridians at same time
- Quick and easy to use
- Can be used for other purposes e.g. SCL fitting and keratoconus assessment

Disadvantages
- Inaccurate in presence of irregular astigmatism
- Less accurate due to shortened working distance

Question 15

Javal-Schiotz Keratometer Pros and Cons

Answer 15

Advantages
- Can be used to measure irregular astigmatism
- More accurate due to longer working distance

Disadvantages
- Need to move to second position