Basics of Biometry for power calculation of intraocular lens in cataract surgery

1. Dr. Md. Rezwanul Hasan
Jr. Consultant
Deep Eye Care Foundation

2. Biometry is the process of measuring the
power of the cornea ( keratometry) and the
axial length of the eye, by using the data to
determine the ideal intraocular lens (IOL)
power.

3. Biometry essentially includes:
 Measurement of axial length (AL)
 Keratometry (K- reading), i.e. measurement
of corneal power and
 Effective IOL position

8. Average eye 2.50D
Short eye 1.75D
Long eye 3.75D

9.  Used to measure the corneal curvature
 1D error results 1D error in IOL power
calculation
 Types of keratometer
1. Mannual
2. Auto keratometer, keratometer
incorporated with IOL Master and Lenster
3.Topography- Placido disc based or
elevation based topography

11.  Depending upon the basis of their derivation
1. THEORETICAL : these are derived
from geometrical optics
2. REGRESSION FORMULAE : Actual
postoperative refractive results of many lens
implantations are used to predict IOL power
Grouped into various GENERATIONS

12. 1st Generation
SRK I, Hoffer
2nd Generation
Binkhorst, SRK II
3rd Generation
Holladay-1, Hoffer-Q, SRK/T
4th Generation
Holladay-2, Haigis

22. Coming up next…

23.  Aphakic eye
 Keratoconus eye
 Inadequate pt. fixation such as nystagmus,
blepharospasm,strabismus etc.
 Post. Staphyloma
 Silicon oil filled eye
 Macular leisions such as RD,Macular oedema,
tumour, vit. hge.
 Dense Cataract

24.  Corneal refractive surgery such as LASIK, PRK
 Piggyback IOL
 Eye with high myopia
 Paediatric IOL

25. That’s all for today…
ALLAH HAFIZ..