This ppt is about IOL master machine

1. Shagufta Kadri
B.Sc (Optom) 3rd year
Aditya Jyot Institute of Optometry

3. Optical Biometry
 The IOL master is a combined Biometry
device for measurements of Human eye
required for the pre- operative
computation of IOL power.
 It uses Optical Low Coherence
Reflectometry a similar technology that
is used in OCT devices.

4. History
 Albert Michelson (1852 – 1931) the first
American scientist to win the Noble Prize,
invented the Optical interferometer.
 The Michleson Interferometry has been
widely used for over a century to make
precise measurements of wavelength and
distance

5. Principle
 Based on Partial coherence intereferometry
(PCI): Diode laser (780nm) measures echo
delay and intensity of infrared light reflected
back from tissue interfaces – cornea and
RPE.
 The Interference produces dark and light band
pattern which is detected by a photo detector.
 The signals are amplified, filtered and
recorded as a function of the position of the
interferometer mirror

6. Principle
 An optical encoder is used to convert the
measurements into axial length
measurements.

8. Optical Biometry
1) Joystick
2) Display
3) Canthus alignment
4) Instrument lock knob
5) Connector panel
6) Mouse connector
7) Keyboard connector
8) Keyboard optional:
printer

9. Intended use of the device
 Axial length measurement
 Corneal curvature
 Anterior Chamber depth
 White to white dot
 Calculation of the required IOL

10. Optical Biometry
 ALM: It is based on patented interference
optical method known as partial coherence
interferometry.
 Corneal curvature: It is determined by
measuring the distance between reflected light
images projected onto the cornea.
 ACD: It is determined as the distance between
the optic sections of the crystalline lens and
the cornea produced by lateral slit illumination.
 White to white dot: It is determined from the
image of the iris

11. Axial Length Measurement
 ALM: The IOL master requires 5
measurements to be taken. The meassage
measure again will appear.
 With stronger lens opacities,it may be
advisable to defocus the device. Defocusing
and shifting the reflection within the circle will
have no effect on the result, because
interferometric axial length is completely
independent of the distance.
 AL<22mm (indicates short ocular axis)
 AL >25mm (indicates long ocular axis)

12. Axial Length measurement
 When both eyes have been measured, the
difference in AL between right and left is also
checked.If the latter exceeds 0.3mm a
message appears to check the reading again
 ALM modes:
 Phakic
 Psuedophakic
 Aphakic
 Silicone filled eyed

13. Keratometry Reading
 Corneal curvature: The IOL master
requires 3 K’metry reading.
 The IOL master reflex 6 points of light,
arranged in 2.3 mm diameter hexagonal
pattern (measured by digital callipers) from
the air/tear film interface.
 The seperation of opposite pairs of lights is
measured objectively by the instruments
internal software and the toroidal surface
curvatures calculated

14. K’metry reading
 In some cases Eg: (
Keratoconus,Keratoglobus, corneal lesions
etc) it may not be possible to reach the green
traffic light for optimum measurement.
 The following possibilities may come out:
 R >8.4mm Very flat corneal curvature
 R <7.2mm Very steep corneal curvature
 (R1 - R2) – 0.5mm High Astigmatism
 If the difference in the Keratometry readings
between two eyes exceeds 0.2mm or 1D, you
have to check the readings.

15. K’metry reading
 If the last 3 readings differ by more than
0.5D or if the tolerance of the mean radius
of the last three readings of 0.08 to
0.01mm is exceeded the evaluation has to
be checked.

16. ACD measurement
 The lateral slit lamp is automatically turned
on.This illumination subjectively appears to be
very bright to the patients.
 The ACD may only be measured on phakic
eyes!
 ACD measurements on pseudophakic eyes
resulting in measuring errors and/or incorrect
readings. The readings for pseudophakic eyes
do not reflect the anterior chamber depth.
 Five ACD readings will be taken,togther with
the calculated mean.

17. White to White dot measurement
 Ask the patient to look at the fixation point.
 Focus on the iris not on the spot light
 The validity of the WTW determination
depends on this check of correct
recognition of the iris edge.
 The WTW is the horizontal diameter of the
iris.In addition of the wtw value,the
deviation of the visual axis from the centre
of the iris (X,Y) will also be displayed.

18. IOL calculation
 Once all the measurements have been taken
(depending on the IOL calculation
formula)options can be generate for IOL to be
implanted.
 Click on the appropriate tab to select the
desired formula.
 The IOL Haigis , HofferQ, Holladay, SRK 2 and
SRKT formulas are implanted as standard.
 After Refractive corneal surgery the Haigis-L
formulae may be selected.

19. Optical Biometry
 SNR (Signal to Noise) ratio
 RED indicates incorrect value
 Yellow indicates Uncertain
value/Borderline
 Green indicates good value

20. Screen Layouts

21. Screen layouts
 ALM

22. Screen layouts
 Keratometry reading

23. Screen Layouts (white to white dot)

24. Advantages
 Learned very quickly
 Extensive integrated safety features
 Non contact measurements
 It gives the true refractive length than
anatomical axial length.
 Accuracy of IOL master is 0.02um wich
is operator dependent.

25. Advantages
 It is upright non contact, ultra high
resolution biometry.
 Highly ametropic patient can wear glasses
while sitting on the IOL master which aids
in fixation.
 It has the advantage of measuring fovea in
case of posterior staphyloma.

26. Limitations
 Cannot measure AL in media opacities like
corneal opacities, dense cataract, NS IV
grade, posterior polar cataract.
 Cannot measure axial length in case of
vitreous haemorrhage.
 Difficulty in measuring axial length in
Infants, small children and mentally
handicapped patients.
 Patients with poor fixation.