2020–2021 BCSC Basic and Clinical Science Course™
3 Clinical Optics
Chapter 6: Intraocular Lenses
Chapter Exercises
Questions
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6.1. Error in sound velocity. An ophthalmologist discovers that a measured axial length (AL) was taken using an incorrect AL. What should be the next course of action?
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The patient should be scheduled for a return visit and the ultrasound repeated using the correct sound velocity.
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A simple correction factor can be added algebraically to the incorrect-measure AL value.
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The incorrect AL is likely due to an incorrect velocity. The incorrect AL can be corrected by dividing the AL by the incorrect velocity and multiplying by the correct velocity.
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The sound velocity is so negligible that it does not need to be corrected.
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6.2. The optical performance of monofocal, bifocal, and extended depth of focus (EDOF) IOLs necessarily differ in which way?
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the acuities they produce at distance
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the chromatic aberration induced
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the contrast degradation induced at distance
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the degree of accommodation each exhibits (ELP)
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6.3. Which statement is the most characteristic of multifocal IOLs?
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They offer increased image clarity and contrast for both near and far viewing.
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They are independent of pupil size if they are well centered.
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They offer a trade-off between decreased image quality and increased depth of focus.
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They are indicated for all patients.
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6.4. Which statement applies to piggyback IOLs?
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Piggyback IOLs modify the vergence of light entering the eye after it exits the incorrectly powered primary IOL.
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Piggyback IOLs can be used in a second operation only if the original IOL power was too low and additional dioptric strength is indicated.
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A piggyback IOL may be useful after removal of an incorrectly powered IOL.
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Piggyback IOLs may be less necessary as standard IOL power ranges increase.
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6.5. What is the most relevant statement with respect to biometric formulas for IOL calculation?
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The AL is the least important factor in the formula.
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The refractive error resulting from an error in AL measurement is more consequential in long eyes than in short eyes.
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Accuracy in AL measurement is relatively more important in short eyes than in long eyes.
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During ultrasonic measurement of AL (A-scan), sound travels faster through the aqueous and vitreous than through the crystalline lens and cornea. Therefore, there is a need to make adjustment to the AL “measurement” by correcting for the incorrect velocity of sound.
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The velocity of sound in an aphakic eye varies significantly between short and long eyes.
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.