BIOMETRY-OPTOMETRY Special Thanx to Shimna Shiyas(2010-14 optometry batch Alsalama College Of Optometry,Perinthalmanna)

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
11/29/2019 13

14. Issues
11/29/2019PEDIATRIC BIOMETRY 14
Not perpendicular to
retina
Immersion
Error
Applanation

21. Intraocular Lens Power Calculations