Module 2 

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Module 2:

OVERVIEW

Estimated study time:  One hour.

Target Audience:  This module discusses advanced concepts.  It is appropriate for assistant,  technician, and technologist level personnel with A-scan experience.

Pre-requisites:  Module 1: Basic A-scan Biometry,  or the equivalent.

Date of original release:  February 2000

Section 1:

Description of content:  This section covers important factors to account for when performing an A-scan on a pseudophakic eye.  Evaluation of the pseudophakic scan is discussed.

Instructional  objectives:  Upon completion of  this section,  the student should be able to:

• Explain  why an pseudophakic scan may be needed

• Explain how an IOL may affect an A-scan

• Identify common IOL materials

• Choose the appropriate mode to use when performing an A-scan on a pseudophakic  eye

• Identify the characteristics of a pseudophakic scan

• Explain how an instrument may need to be adjusted in order to acquire an accurate pseudophakic measurement

Section 2:

Immersion Technique

Description of content:  This section discusses the problem of corneal compression and how the immersion technique eliminates this error source.  Equipment and procedure are discussed.

Instructional objectives:  Upon completion of this section,  the student should be able to:

• Explain why corneal compression is a problem and discuss options in handling this error source

• Identify acceptable substances for filling the immersion shell

• Describe how to determine the size of the Hansen shell

• List the steps in the immersion A-scan procedure 

• Identify the characteristics of a proper immersion scan graph

Section 3:

Description of content:  This section discusses similarities and differences in formulas used in the determination of the IOL power.  An example of a calculation using a regression formula is given.  Calculations for ammetropic results are discussed.  Methods for calculating the IOL power of post-RK patients are given.

Instructional objectives:  Upon  completion of this section,  the student should be able to:

• Explain the difference between a regression formula and a theoretical formula

• Identify current theoretical formulas and their most accurate ranges

• Name the variables of the regression formula

• Calculate the factor needed for a given ammetropic result

• List the information needed in order to calculate the IOL power for a post-RK patient

About the Author: Gary Gallimore is a certified ophthalmic technologist who assists with research at the Eye Foundation of Kansas City and works for a large multi-specialty ophthalmology practice in the metro area of Kansas City.    He has taught CE courses for many years on all subjects of ophthalmic technology. 

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