Free CPO Keratometry and Corneal Topography Questions and Answers 1 — Questions and Answers
Question 1: A keratometer is an instrument used to measure the:
- Intraocular pressure
- Curvature of the central cornea (Correct answer)
- Axial length of the eye
- Thickness of the cornea
Correct answer: Curvature of the central cornea
The keratometer, or ophthalmometer, is specifically designed to measure the curvature of the anterior surface of the cornea. These measurements, known as K-readings, are crucial for contact lens fitting and calculating the power of intraocular lenses for cataract surgery.
Question 2: In 'with-the-rule' astigmatism, the steepest corneal meridian is located at or near:
- 180 degrees (horizontal)
- 45 degrees (oblique)
- 90 degrees (vertical) (Correct answer)
- 135 degrees (oblique)
Correct answer: 90 degrees (vertical)
'With-the-rule' astigmatism is the most common form, where the vertical meridian is steeper than the horizontal meridian. This is similar to the shape of a football lying on its side.
Question 3: What is the primary advantage of corneal topography over standard keratometry?
- It is faster to perform.
- It provides a detailed map of the entire corneal surface. (Correct answer)
- It can also measure intraocular pressure.
- It does not require the patient to fixate on a target.
Correct answer: It provides a detailed map of the entire corneal surface.
While a keratometer measures only a few central points on the cornea, a corneal topographer maps the curvature of the entire corneal surface. This provides a much more detailed view, which is essential for detecting irregular astigmatism, keratoconus, and for planning refractive surgery.
Question 4: A patient's K-readings are 43.50 @ 180 / 45.00 @ 090. What is the amount of corneal astigmatism?
- 0.50 D
- 1.00 D
- 44.25 D
- 1.50 D (Correct answer)
Correct answer: 1.50 D
Corneal astigmatism is calculated by finding the difference between the two principal meridians. In this case, the difference between 45.00 D and 43.50 D is 1.50 D.
Question 5: On a standard corneal topography map, 'hot' colors such as red and orange typically represent areas that are:
- Steeper in curvature (Correct answer)
- Flatter in curvature
- Thinner than average
- Affected by scarring
Correct answer: Steeper in curvature
Topography maps use a color scale to represent corneal power, which is related to curvature. Hot colors (reds, oranges) indicate steeper areas with higher power, while cool colors (blues, greens) indicate flatter areas with lower power.
Question 6: If the keratometer mires are blurry and cannot be brought into focus, the most likely cause is:
- Incorrect instrument calibration
- High intraocular pressure
- A poor or unstable tear film (Correct answer)
- A small pupil size
Correct answer: A poor or unstable tear film
The most common reason for an inability to focus the mires is an unstable or poor-quality tear film, which disrupts the reflection from the corneal surface. Other causes can include corneal irregularities or patient movement, but a poor tear film is the most frequent issue.
Free CPO Keratometry and Corneal Topography Questions and Answers 1
A keratometer is an instrument used to measure the: