Axial Eye Length Measurements (A-scan Biometry)

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Author:
zimmerk
ID:
218545
Filename:
Axial Eye Length Measurements (A-scan Biometry)
Updated:
2013-05-10 10:49:24
Tags:
eye ultrasound
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Description:
Ch. 10 - Axial Eye Length Measurements (A-scan Biometry)
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  1. What is the average Axial Length for a normal eye & what is the normal range?
    Average length 23.6mm; Average range for most individuals 22.0mm ‐ 24.5mm
  2. In most individuals what is the average difference between both eyes
    within 0.3mm
  3. What is the average Axial length for children of different ages?
    Newborn to 120days is 17.02mm ‐ 19.43mm; 5months to 18months is 20.09mm ‐ 20.14mm; 19months to 10years is 22.01mm ‐ 23.12mm
  4. What are the average values for the corneal thickness, anterior chamber depth & thickness of the crystalline lens?
    Corneal thickness=0.55mm; Anterior chamber depth=3.24mm; Crystalline Lens=4.63mm
  5. What is the Sound Velocity of the Cornea?
    1,641 m/sec
  6. What is the Sound Velocity of the Aqueous/vitreous?
    1,532 m/sec
  7. Wha is the Sound Velocity of a Crystalline Lens?
    1,641 m/sec (this value may decrease with age)
  8. What is the Sound Velocity of Solid Tissue?
    1,550 m/sec
  9. What is the Sound velocity of an IOL Implant?
    • PMMA - 2,720 m/sec; correction factor of +0.4mm
    • Silicone - 980 m/sec; correction factor of -0.8mm
    • Silicone - 1,090 m/sec; correction factor of -0.6mm
    • Acrylic - 1,900 m/sec; correction factor of +0.3mm
    • Acrylic - 2,120 m/sec; correction factor of +0.2mm
  10. What is the Sound Velocity of Silicone Oil?
    980-1,040 m/sec
  11. What is the Sound Velocity of an Aphakic Eye?
    1,532 m/sec
  12. What is the Sound Velocity of a Phakic eye (average)?
    1,550 m/sec
  13. What is the Sound Velocity of a Pseudophakic Eye?
    • 1,532 m/sec +/- correction factor
    • PMMA - correction factor of +0.4mm
    • Silicone - correction factor of -0.8mm
    • Silicone - correction factor of -0.6mm
    • Acrylic - correction factor of +0.3mm
    • Acrylic - correction factor of +0.2mm
  14. What are some possible causes of an Erroneously SHORT AEL Measurement?
    • Corneal compressions (contact-method),
    • Sound velocity too slow,
    • Corneal gate to right of corneal spike,
    • Retinal gate incorrectly positioned at spike in vitreous cavity,
    • Gain set too high,
    • Lens measured too thin,
    • Macular thickening/detachment,
    • Misalignment of the sound beam
  15. What are some possible causes of an Erroneously LONG AEL Measurement?
    • Air bubble in fluid bath (immersion method),
    • Fluid bridge (contact method),
    • Sound velocity too fast,
    • Retinal gate to right of retinal spike,
    • Gain set too low,
    • Lens measured too thick,
    • Posterior staphyloma eccentric to macula,
    • Misalignment of the sound beam

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