POST TEST FOR MODULE 1: Basic A-scan Biometry         Catalog      Home

Including:
Section 1: Basic Concepts
Section 2: Scanning Procedure
Section 3: Instrumentation

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1. When performing A-scan biometry, a one diopter IOL power error
could result from an axial length error of:

A. .4 mm
B. .04 mm
C. 4 mm
D. 4 cm
E. 4 meters

2. If an ultrasound beam strikes a surface in a perpendicular fashion,  ______ will be produced.

A. a hole
B. no spike
C. a negative spike
D. a low spike
E. a high spike

3. Which A-scan factor can be controlled by adjusting a setting on the instrument?

A. perpendicularity
B. reflectivity
C. compression
D. gain
E. all of the above

4. The optical axis is the distance from the _____ to the ______ .

A. iris, lens
B. corneal apex,  fovea

C. anterior sclera, posterior sclera
D. nasal fornix, temporal fornix
E. check-out desk, optical shop

5. Corneal compression, caused by excessive pressure from the probe, will:

A. have no affect on the measurement
B. cause an artificial shortening of the axial length
C. cause an artificial lengthening of the axial length
D. distort the lens
E. damage the probe

6. An ultrasound beam will not travel through:

A. water
B. the retina
C. the iris
D. the cornea
E. air

7. The speed of ultrasound through vitreous is:

A. 153.2 m/s
B. 15.32 m/s
C. 1532 m/s
D. 15.32 cm/s
E. 153.2 mm/s

8. When measuring the axial length of an eye that has no lens, which
mode should be used?

A. pseudophakic
B. cataract
C. dense cataract
D. aphakic
E. phakic

9. When performing an IOL measurement, which step should be performed first?

A. axial length measurement
B. keratometry
C. instill a topical anesthetic
D. tell the patient what you will be doing

10. What should be done if a membrane type probe tip has been contaminated?

A. replace the tip
B. wipe the tip with alcohol
C. soak the tip in 3% hydrogen peroxide
D. soak the tip in a 1:10 bleach solution

11. An error due to corneal compression is most likely with which method or mode?

A. tonometer mount method
B. hand-held method
C. immersion method
D. automatic mode

12. A-scan alignment with the optical axis of the eye will be indicated by:

A. a tall anterior lens spike
B. a tall posterior lens spike
C. a tall retina spike
D. all of the above

13. Corneal compression can be monitored by comparing _____ readings between scans.

A. corneal thickness
B. iris thickness
C. lens thickness
D. anterior chamber depth
E. posterior chamber depth

14. Consecutive A-scans should have total length readings within ______ to be 
considered to have good reproducibility.

A. 20 mm
B. 2.0 mm
C. .20 mm
D. .02 mm
E. 2.0 cm

15. The audible signal on a A-scan instrument may be able to:

A. indicate contact with the cornea
B. indicate axial alignment
C. guarantee an accurate measurement
D. all except B
E. all except C