Chapter 6 - Keratometry

Question 1

The average power of the human cornea is:
a) 30 to 32 D
b) 35 to 36 D
c) 43 to 44 D
d) 45 to 47 D

Answer 1

C- 43 to 44 D

Question 2

Average thickness of the central cornea is:
a) 0.8 mm
b) 0.5 mm
c) 0.2 mm
d) 1.0 cm

Answer 2

B- 0.5 mm

Question 3

Which of the following is an example of oblique astigmatism?
a) −2.00 + 1.25 × 093
b) −0.75 − 1.25 × 003
c) −4.25 + 2.75 × 046
d) Plano

Answer 3

C) -4.25+ 2.75 x 046

Question 4

Of the following, which patient is most likely to have irregular astigmatism?
a) postoperative cataract
b) aphakic
c) surface ocular trauma
d) postoperative LASIK

Answer 4

C- surface ocular trauma

Question 5

The steepest part of the cornea is the: a) periphery
b) inferior one-fourth
c) stroma
d) center

Answer 5

D- center

Question 6

The diameter of the cornea’s optic zone, or cap, measures:
a) 4.0 mm
b) 0.5 mm
c) 20 mm
d) 3.06 µm

Answer 6

A- 4.0 mm

Question 7

Manual keratometry would not be the most appropriate method for reliable measurements in which of the following cases?
a) fitting contact lenses
b) monitoring keratoconus
c) calculating intraocular lens (IOL) power
d) evaluating after cataract surgery

Answer 7

B- monitoring keratoconus

Question 8

You are attempting a K reading and do not see both horizontal plus signs. This might be due to:
a) a drooped upper lid
b) the patient closing his or her eye
c) a keratometer occluder in the way d) improper focusing

Answer 8

C- a keratometer occluder in the way

Question 9

K readings in a contact lens-wearing patient may be used to evaluate all of the following except:
a) progressive corneal steepening
b) lens fit
c) lens coverage
d) corneal warpage

Answer 9

C- lens coverage

Question 10

Which of the following types of astigmatism is not obvious when measuring with the keratometer?
a) astigmatism at 180 degrees
b) irregular astigmatism
c) lenticular astigmatism
d) oblique astigmatism

Answer 10

C- lenticular astigmatism

Question 11

You have taken a K reading by extending the instrument’s range. To get the correct value, you can:
a) use a conversion chart
b) subtract the power of the extending lens
c) add the power of the extending lens d) simply record the drum reading

Answer 11

A- use a conversion chart

Question 12

You are adjusting the keratometer eye piece by looking at the occluder through the ocular. The mires are distorted. You should:
a) calibrate with metal balls
b) spray cleaner into the instrument
c) clean the instrument with compressed air
d) return to the manufacturer for cleaning

Answer 12

D- return to the manufacturer for cleaning