Biometry, A-Scan, Lenstar

1. 9.30 am to 9.45 am
Biometry Immersion/Optical
-Helpful tips & key points
BOS 7-6-2015
Dr.Anand Sudhalkar
Dr. Shubhangi Puntambekar
Mrs. Angela Macwan

2. Why Biometry?
 Achieve “Desired “ refractive status
post operatively.
 “Better than before”

3. Common Procedures done
1984…….
Keratometry
Ultrasonography

5. Keratometry
3.2mm

6. Steep and Flat meridian

7. Axial Length
Cornea to ILM
Contact and Immersion

8. Simple formula
 SRK I:
 P = A - 0.9 K - 2.5 L(1)
 P: IOL power for emmetropia
 K: corneal refractive power (K-reading)
 L: axial length
 A: A-constant of IOL

12. Areas of Refractive Surprises

13. Effective Lens Position

14. Effective Lens Position

15. IOL A-constant
 Optimised for Biometry
 Personalised by surgeon

16. Optical Coherence Biometry

17. Ultrasound v/s Optical A-Scan
Ultrasound
 Sound Wave 10MHz
 Topical Anesth, contact
probe
 Corneal compression
 Anatomical axis length
 Keratometry, CCT
separate
 Modern formulas absent
Optical
 780um light (9X faster)
 Non Contact
 No compression
 Visual – Refractive Axial
length
 All measurements (9) in
one go, along same axis
 More measurements for
4th Generation formulas

18. Keratometry
The Lenstar,, measures at two zones (2.3 mm and 1.65 mm).
In addition to its 32 points of measurements, each scan captures 128 points
of measurements, such that five sets of readings captures 640 points of measurements
In clinical studies this has been proven that the keratometry on the Lenstar is equivalent
to the gold standard manual keratometry.

19. CCT
Range 300 to 800u

20. ACD
Range 1.5 to 5.5mm

21. Lens Thickness
Range: 0.5 to 6.5mm

22. Axial Length
14 to 32mm,
Repeatability +- 0.035mm