The document discusses biometry in the context of cataract surgery, focusing on the measurement of living tissue and the calculation of intraocular lens (IOL) power through sound wave dynamics. It includes details about different tissues' acoustic properties and the functioning of ultrasound machines, especially in obtaining a-scans. Key issues such as immersion errors and lens power calculation are highlighted.

1. BIOMETRY
1
Measurement
of living tissue.
Preoperative
assessment of
cataract
surgery.
Calculate
power of IOL

2. Wave change velocity as they pass through different
densities
• Cornea
• Aqueous/ Vitreous
• Lens
• Silicone oil
• Aphakia
• Phakia
• 1641
• 1532
• 1641
• 980 – 1040
• 1532
• 1550

3. MECHANISM• Probe const sound
wave
Reflected echoes
(vary in ampl. & freq)
Echoes generate
Current
Quartz crystal
(piezoelectric effect)
Computed into display
by U.S machiene

6. Contact A-scans.

7. Immersion A-scans.

8. Gain settings
-Electronic amplification of sound waves
• Higher the gain lower the resolution
Low resolution

9. A hand-held probe mounted on a holder at the slit
lamp

10. IMMERSION SHELL

13.  Corneal echo seen as a tall
single spike
 Aqueous chamber does not
produce any echo
 Antr. & post. lens capsule
produce tall echoes
 Vitreous cavity- few to no
echoes
 Retina tall sharp rising echo
 Orbital fat medium to low
echoes
CHARACTERISTICS OF A GOOD SCAN
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14. Issues
11/29/2019PEDIATRIC BIOMETRY 14
Not perpendicular to
retina
Immersion
Error
Applanation

21. Intraocular Lens Power Calculations