A Scans and IOL Basics

This course, for beginning, intermediate, and advanced levels, has been awarded 2 continuing education credits by the AOA/CPC. Covered topics: A-Scan measurements, IOL types, and IOL calculation formulas.

After completing this section the student should be able to do the following:

  • Define what biometry testing of the eye is
  • Define the following in terms of ultrasound: frequency, wavelength, velocity, amplitude
  • Define Hertz in terms of frequency
  • Describe reflectance
  • Identify the frequency of oscillation of most A Scan machines in Hertz
  • List the ocular structures that create peaks on an A Scan
  • Describe the 2 methods of testing axial length
  • Explain how corneal compression affects axial length
  • State the rule for error induced with corneal compression of .1 mm
  • Use the equation for finding axial length from velocity and time
  • Identify the ocular structure responsible for the main spikes in an A Scan (cornea, anterior and posterior lens, retina, sclera, orbital fat)
  • List 3 common mistakes that will result in lower spike levels
  • State what the average length of the following structures are: eye, anterior chamber, lens
  • Describe why longer than average eyes may need a lower power IOL
  • Describe why shorter than average eyes may need a higher power IOL
  • List the parts to the A Scan machine
  • Describe the steps to use to take an A Scan measurement
  • Describe how comparing anterior chamber depth can help with error tracking
  • Describe how evaluating spike height can help with error tracking
  • Describe the gain level and how it affects the A Scan graph
  • List 2 methods of performing non contact axial length measurements
  • Identify 2 types of scleral shells
  • Describe the spike pattern on an immersion A Scan
  • Explain how the double cornea spike is helpful in error tracking
  • List the steps to follow to perform immersion A Scan biometry
  • List 2 drawbacks to the IOL master
  • List 3 drawbacks when using immersion A Scans
  • Describe what the IOL Master does
  • List 3 advantages to measuring axial length with the IOL Master or Lenstar versus A Scan
  • Describe what optimization of the IOL Master and Lenstar does
  • List the measurements that are taken with the IOL Master and Lenstar
  • Describe what Keratometry, anterior chamber depth, and white to white are measurements of
  • Describe what special considerations need to be taken when measuring axial length of a pseudophakic eye
  • Describe what special considerations need to be taken when measuring axial length of a silicone oil eye
  • Describe how a posterior staphyloma can affect axial length measurement
  • List the 3 materials used to make IOLs
  • Describe what theoretical and regression IOL calculation formulas are
  • List 5 IOL calculation formula names
  • Describe what the following IOL types do: monofocal, Multifocal, toric
  • List 3 types of Multifocal IOLs
  • Describe how the Crystalens works
  • List 2 types of toric IOLs
  • Describe the 2 basic IOL shape designs

This course should take approximately two hours to complete. Successful completion of the post test is necessary to earn AOA/CPC credit. The link for the post-test is included in the course material. This course is not sponsored by the AOA/CPC; only reviewed for compliance with AOA/CPC standards and criteria and awarded continuing education credit accordingly.

This course was developed by our partners at Eye-Courses.