Iol master

IOL Master

1. IOL Master
Moderator: Dr. A.Y.
Yakkundi
Presenter: Dr. Arushi
Prakash
4
th
March ‘15

2. History
•The optics of the eye
represents one of the oldest
fields in ophthalmology
•The history of IOL power
calculation began in 1949
when Sir Harold Ridley
implanted the first IOL.
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Department of Ophthalmology,
JNMC

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•He used the human lens as his model and
selected similar radii of curvature to create a
biconvex disc while using approximately half
the thickness and weight (∼5 mm thick and 230
mg for the human lens).
•One of his original lenses made by Rayner, a
23.00 diopter (D), was measured at 8.5 mm in
diameter and 2.4 mm thick, with a weight of
108 g
History
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4
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March 2015
Department of Ophthalmology,
JNMC

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•The Ridley lens was placed in the posterior
chamber after ECCE.
•The anterior capsulectomy of the day was very
large, and thus zonular support was poor. Some
Ridley lenses dislocated into the vitreous because
of poor zonular support,
and partially because of
their weight, which was
approximately eight
times that of
current IOLs.
History
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4
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March 2015
Department of Ophthalmology,
JNMC

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•Because of the difficulty with posterior chamber IOL
placement, pioneering surgeons spent the next two
decades trying to find a better place to fixate the IOL.
•The AC lens, pupil-fixated IOL, iris-fixated IOL, and
iridocapsular IOL were be placed in large numbers, only
to return to the posterior chamber in the 1970s.
History
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4
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March 2015
Department of Ophthalmology,
JNMC

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•A major breakthrough came in the late seventies with
Doctors Binkhorst and Worst in Europe and Dr. Shearing
in America
•They began putting their implants “in the bag”. Instead of
removing the entire cataract, they scooped out the inside
of the lens, leaving the capsule, the outer envelope of the
lens intact.
• They then implanted their lenses into this cavity which
gave the lens implant a natural support system. Success
dramatically improved.
History
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4
th
March 2015
Department of Ophthalmology,
JNMC

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•While this was going on, Dr. Charles Kelman, was
developing phacoemulsification, a radically new method
of removing cataracts.
•A small probe is passed into the eye, and ultrasonic
vibrations were used to break up the cataract into tiny
particles, easily removed through the small probe.
•This allowed the cataract to be removed through a small
opening. This left a problem: the opening was too small to
allow the insertion of the intraocular lens, so wound had to
be enlarged.
•Enter the foldable implant. First made of silicone, these
lenses could be folded in half, inserted through a small
opening, and then unfolded inside the eye to their original
shape, all this taking place “within the bag”.
History
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4
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March 2015
Department of Ophthalmology,
JNMC

8. •Implant materials and designs continued to improve
through the late 20th century and early 21st century.
Implants were developed that could be rolled instead of
just folded, allowing insertion through smaller and smaller
incisions.
•The next major leap forward was
the development of specialty lenses
with optics that could allow the
patient to see both distance and
near through the same lens.
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History
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4
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March 2015
Department of Ophthalmology,
JNMC

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•Some patients have a large amount of astigmatism.
• This defect can be optically corrected with proper glasses.
After cataract surgery, the shape of the cornea does not
change much.
• Therefore, patients with astigmatism will still need
glasses for distance and near to see clearly.
•Enter the toric implant. This implant is constructed with
astigmatism of various powers built in, and allows clear
vision, often without
glasses.
History
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4
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March 2015
Department of Ophthalmology,
JNMC

10. 4
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March 2015
Department of Ophthalmology,
JNMC 10
“Accurate and precise biometry is one of the key
factors in obtaining a good refractive outcome
after cataract surgery.”
An error of only 1.0 mm in
axial length will results in a
post-operative refractive
error of three dioptres
Ocular Biometry

11. Ophthalmic
Ultrasonography
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March 2015
Department of Ophthalmology,
JNMC 11
Non- invasive, efficient and inexpensive
diagnostic tool to detect and differentiate various
ocular and orbital pathologies
Indispensible tool for calculation of IOL power,
evaluation of posterior segment behind dense
cataract / vitreous haemorrhage, diagnosis of
complex vitreoretinal conditions and the
differentiation of ocular masses

12. Physics of
Ultrasonography
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March 2015
Department of Ophthalmology,
JNMC 12
•Based on propagation, reflection and
attenuation of sound waves
•Ultrasound are high frequency sound waves
(> 20,000 kilohertz)
•Those used for diagnostic ophthalmic
ultrasound have a frequency of 7.5 to 12
megahertz

13. Physics of
Ultrasonography
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March 2015
Department of Ophthalmology,
JNMC 13
•Speed of ultrasound depends on medium through
which it passes
•As the ultrasound passes through tissues, part of
the wave may be reflected back towards the
probe, this reflected wave is referred to as an
echo.
•Echoes are produced at the junction of media
with different sound velocities
•Greater the difference in the sound velocites of
the media at the interface, stronger is the echo

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Department of Ophthalmology,
JNMC 14
Examiner dependent
Needs high level of skill and expertise
Dynamic test
A scan ultrasound biometry is a contact method
and is operator dependent. Experience has
shown that excessive corneal indentation
compresses the eye, in the anterior-toposterior
direction. This produces an artificially short eye,
producing the myopic refractive results
Limitation

15. Measurement of
Corneal Power
•Corneal power accounts for about 2/3
rd
s of
the total dioptric power of the eye and is an
important component of the ocular refractive
system.
•If the corneal power is inaccurate, it will
induce error propagation and have profound
consequences on the remaining steps in the
calculation of IOL power.
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4
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March 2015
Department of Ophthalmology,
JNMC

16. •Unfortunately calculation of corneal power is
not a straight forward process
•No keratometer measures corneal power
directly.
•What is measured is the size of the image
reflected from the convex mirror constituted
by the tear film of the corneal surface
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Measurement of
Corneal Power
4
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March 2015
Department of Ophthalmology,
JNMC

17. •A magnification is calculated from the image
size which is directly related to the radius of
curvature of the reflecting corneal surface.
•To do this, the cornea is normally assumed to
be a sperocylinder,
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Measurement of
Corneal Power
4
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March 2015
Department of Ophthalmology,
JNMC

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Measurement of
Corneal Power
Department of Ophthalmology,
JNMC

19. Measurement of
Axial Length
•Measurement of axial length remains one of
the most crucial steps in IOL power
calculation.
•As a 0.1 mm error is axial length is equivalent
to an error of abut 0.27 D in the spectacle
plane (assuming normal eye dimensions),
accuracy of within 0.1mm is necessary
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4
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March 2015
Department of Ophthalmology,
JNMC

20. Variable Error Refractive
Error
Corneal Radius1.0 mm 5.7 D
Axial Length1.0 mm 2.7 D
Postoperative
AC Depth
1.0 mm 1.5 D
IOL Power 1.0 D 0.67 D
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•Deviation from the mean values of different
variables and corresponding refraction errors
4
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March 2015
Department of Ophthalmology,
JNMC

21. a = cornea spike
b = anterior lens spike
c = posterior lens spike
d = retinal spike
e = orbital spike
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Acoustic
Biometry
•What is really
measured by
ultrasound is the
transit time taken
by the ultrasonic
beam to travel
through the ocular
media while it is
deflected from the
internal structures
of the eye.
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March 2015

22. 22
Acoustic
Biometry
•The best signal is obtained when the
ultrasonic beam strikes a surface at normal
incidence that gives rise to a steep spike on
the echogram
•With good alignment along the ocular axis,
it is possible to detect a corneal signal
(sometimes a double spike), the front and
back surfaces of the lens and the retina at
the same time
4
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March 2015
Department of Ophthalmology,
JNMC

23. •The ‘retinal’ spike is generally assumed to
arise at the internal limiting membrane of the
retina
•This may call for correction to account for
retinal thickness when the readings are to be
used in an IOL power formula.
•It is important to know the velocity of
ultrasound in order to calculate the distances
in question
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Acoustic
Biometry
4
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March 2015
Department of Ophthalmology,
JNMC

24. •For the normal phakic eye, velocity is
generally assumed to be 1532/second for the
anterior chamber and vitreous and
1641m/second for the lens (Jansson & Knock)
•In an average eye, this is equivalent to 1550
m/second for the whole eye.
•However, if we assume a constant lens
thickness, this average velocity is lower in a
long eye and higher in a short eye, and should
be corrected to obtain an unbiased prediction
in these unusual eyes
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25. The pitfalls of ultrasound measurements are
numerous
•Readings should be coaxial with the ocular axis
•This requires a steep spike from the retina as
well as good spikes from the anterior and
posterior surfaces of the lens
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Acoustic
Biometry
limitations

26. •Some eyes do not have perfectly parallel
structures, however,
•readings can be difficult to obtain in eyes with
dense cataracts
•and eyes with posterior staphyloma.
•Care should be taken not to indent the cornea
if contact measurements are used .
•For this reason immersion readings are
generally considered more accurate than
contact measurements
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Acoustic
Biometry
limitations
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March 2015

27. 27
Optical
Biometry
4
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March 2015
Department of Ophthalmology,
JNMC

28. •The introduction of optical biometry using
partial coherence interferometry significantly
improved the accuracy with which axial
length can be measured.
•The fact that the retinal pigment epithelium is
the end– point of an optical measurement,
whereas the interface between the vitreous
and the neuro retina is the endpoint of an
ultrasonic measurement, makes measurements
by PCLI longer than those taken with
ultrasound
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29. OPTICAL
BIOMETRY
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•However, just as distance measurements taken
with ultrasound are dependent on the assumed
ultrasound velocity, optical biometry is
dependent on the assumed group refractive
indices of the phakic eye.
•The indices used by the Zeiss IOL Master
were estimated by Haigis and were partly
based on extrapolated data.
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March 2015

30. 30
Optical Biometry –
Uses Optical Low-Coherence Reflectometry,
a similar technology that is used in OCT
devices. This technology results in highly
accurate measurements of the eye using
light in comparison to sound. The added
benefit is that this technology is also non
contact and can be performed with the
patient sitting comfortably in a chair without
the need for any topical anaesthesia, and
without the risk of damage to the cornea.
4
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March 2015
Department of Ophthalmology,
JNMC

31. Principle of Michelson
Interferometer
Xiaoyu Ding
Albert Michelson (1852~1931)
the first American scientist to
receive a Nobel prize, invented
the optical interferometer.
The Michelson interferometer has
been widely used for over a
century to make precise
measurements of wavelengths
and distances.
Albert Michelson
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32. Principle of Michelson
Interferometer
A Michelson Interferometer for use on an optical table
Xiaoyu Ding
1)Separation
2)Recombination
3)Interference
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4
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March 2015
Department of Ophthalmology,
JNMC

33. 33
IOL master employs the principle of optical
coherence biometry (OCB)
It uses partially coherent infrared light beams of
780nm diode laser light emitted is split up into two
beams in a Michelson interferometer one mirror of
the interferometer is fixed and the other is moved at
constant speed making one beam out of phase with
the other. Both beams are projected in the ye and get
reflected at cornea and retina .
The light reflected from the cornea interferes with
that reflected by the retina as the optical paths of
both the beams are equal
4
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March 2015
Department of Ophthalmology,
JNMC

34. 34
This interference produces a light and dark 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.
An optical encoder is used to convert the
measurements into axial length measurements
In interferometer, the eye needs to be absolutely
stable so as not to disturb interference patterns
4
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March 2015
Department of Ophthalmology,
JNMC

35. The Down Side
Since optical Biometry uses light
there is a higher probability of the
“scatter” effect. Meaning that if the
light beam is reflected prior to the
RPE then the signal returning to the
device sensor will be very weak if
detected at all. This will result in low
SNR. Patients with Dense PSC,
Extreme Corneal Abnormalities, or
White Cataracts are very tough to
measure.
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4
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March 2015
Department of Ophthalmology,
JNMC

36. IOL Master (Carl Zeiss)
Lenstar LS 900 (Haag-Streit)
Manufacturers
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4
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March 2015
Department of Ophthalmology,
JNMC

37. IOL Master
A combined biometry instrument. It measures
parameters of the human eye needed for
intraocular lens calculation.
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March 2015
Department of Ophthalmology,
JNMC

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March 2015
Department of Ophthalmology,
JNMC 38

1.Joystick with
release button
2.Display
3.Red eye
level marks
4.Lock knob
5.Connector
panel
6.Mouse
connector
7.Keyboard
connector
8.keyboard
PAR
TS
Department of Ophthalmology,
JNMC

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March 2015
Department of Ophthalmology,
JNMC 39

1.DVD Drive
2.Adjustment
of headrest
3.Chin rest
4.Holding
pins for paper
pads
5.Forehead
rest
6. aperture
for diode
laser
7. device
control
connector
PAR
TS
Department of Ophthalmology,
JNMC

40. IOL Master
4
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March 2015
Department of Ophthalmology,
JNMC 40
It measures quickly and precisely :

1. Axial length
2. Corneal curvature
3. Anterior chamber depth (ACD)
4. White-To-White (optional)
5. IOL power

41. It measures quickly and precisely
Axial length : Based on partial coherence interferometry
( Michelson interferometer)
Corneal curvature is determined by measuring the distance
between reflected light images.
ACD : as the distance between the optical sections of the
crystalline lens and the cornea produced by lateral slit
illumination.
White to white is determined from the image of the iris.
IOL power calculation : by software incorporating
internationally accepted calculation formulae.
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42. How do we operate
IOLmaster ?
After switching on the device, patient manager screen will
appear
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43. Screen layout
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44. Axial length
measurement(alm)
Activate the axial length measurement mode by clicking on
ALM icon.
Switching to ALM mode will automatically change the
magnification ratio: a smaller section of the eye becomes
visible with the reflection of the alignment light and a
vertical line.
The patient should look at the red fixation point in the
center . A crosshair with a circle in the middle will appear
on the display.
Fine align the device so that the reflection of the alignment
light appears within the circle.
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4
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March 2015
Department of Ophthalmology,
JNMC

45. Note : The patient should be asked if he or she sees the
fixation point. If the patient fails to fixate properly, the visual
axis will not be correctly recognized, which may result in
measuring errors.
In the case of poor visual acuity/high ametropia (> 4 D) it is
advisable to measure through the spectacles. If the
procedure is followed correctly, no measuring errors will be
produced. Measurements should not be taken while a
patient is wearing contact lenses, as this will result in
measuring errors.
The corresponding display field next to the video image will
show the measured axial length.
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Axial length
measurement
4
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March 2015
Department of Ophthalmology,
JNMC

46. The IOL Master requires five measurements to be taken.
The message Measure again will thus appear. Only then
will the composite signal be calculated and displayed as a
blue measurement curve following the red individual
measuring signal.
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 measurement is completely
independent of distance.
46
Axial length
measurement
4
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March 2015
Department of Ophthalmology,
JNMC

47. Axial Length Modes
1.Phakic
2.Pseudophakic
3.Aphakic
4.Silicone filled eyes
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Axial length
measurement
4
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March 2015
Department of Ophthalmology,
JNMC

48.  IOLMaster produces a primary maxima (narrow, well-defined,
centered peak identified by a circle above it), secondary
maxima (discrete lower peaks, sometimes disappearing into
the baseline), and a baseline (which is low and even, but may
become high and uneven with decreasing signal-to-noise ratio
(SNR)).
Triple peak
curve

49. SNR categories :SNR is a measure of accuracy and
decreases with increasing cataract density.
The SNR is automatically analyzed while the system is
internally calculating the axial length from the interference
signal.
SNR display at GREEN  reading is valid.
SNR display at YELLOW  reading is uncertain
SNR display at RED reading should not be used
49
Axial length
measurement
4
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March 2015
Department of Ophthalmology,
JNMC

50. Keratometric
measurement
Ask the patient to relax and look at the fixation
light. If the patient cannot see the fixation light,
he or she should look straight ahead into the
device.
When adjusting the device, make sure that all 6
peripheral points are visible and located in the
field between the two auxiliary circles, as
closely as possible to the center of the display.
The images of the measuring marks on the
display must be optimally focused by varying
the distance between patient and device.
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4
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March 2015
Department of Ophthalmology,
JNMC

51. Focus points
51
The IOLMaster
reflects six points of
light, arranged in a 2.3
mm diameter
hexagonal pattern
(measured by digital
callipers), from the
air/tear film interface.
The separation of
opposite pairs of lights
is measured
objectively by the
instrument’s internal
software and the
toroidal surface
curvatures calculated
from three fixed
meridians
Keratometric
measurement
Department of Ophthalmology,
JNMC

52. Acd measurement
Ask the patient to relax and look at the fixation
light. If the patient cannot see the fixation light, he
or she should look straight ahead into the device.
When the anterior chamber depth mode is turned
on, the system automatically activates the lateral
slit illumination. The illumination always originates
from a temporal direction.
An image similar to that of a slit lamp (optical
section through the anterior segment of the eye) is
visible on the display. Align the device to the
patient’s eye by lateral adjustment using the
joystick until:
 The image of the fixation point appears optimally
focused in the green square on the display.
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53. The image of the anterior crystalline lens is visible in the
pupil.
The image of the fixation point may not lie in the image of
the lens or cornea.
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Acd measurement
4
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March 2015
Department of Ophthalmology,
JNMC

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55. Measuring errors
The "Error" message may have two basic
causes:
• The results of the five internal individual
measurements vary by more than 0.15 mm (very
rare), or
• The images produced (optical sections) do not
contain relevant structures (normally without the
edge of the crystalline lens) or disturbances are
preventing their detection.
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Acd measurement
4
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March 2015
Department of Ophthalmology,
JNMC

56. Ask the patient to relax and look at the fixation light.
Focus on the iris, not on the light spots.
After the image has been taken, the operator should check
if the software has correctly detected the edge of the iris. If
the circle segments drawn in the image do not define the
iris correctly, the result must be discarded.
56
WTW
measurement
4
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March 2015
Department of Ophthalmology,
JNMC

57. 57
4
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March 2015
Department of Ophthalmology,
JNMC

58. Once all measurements have been taken (depending on
the IOL calculation formula), options can be generated for
intraocular lenses to be implanted.
Start the calculation by: clicking on IOL
Click on the appropriate tab to select the desired formula.
The IOL Haigis, HofferQ, Holladay, SRK II, and SRK®/T
formulae are implemented as standards.
After refractive corneal surgery the Haigis-L formulae may
be selected.

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IOL
CALCULATION
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60. result
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61. Measuring ranges Axial length : 14 – 40 mm
Corneal radii : 5 – 10 mm
Depth of anterior chamber : 1.5 – 6.5 mm
White-to-white : 8 – 16 mm
formulas SRK® II, SRK®/T, Holladay, Hoffer Q, Haigis
Haigis-L for IOL calculation for eyes after
myopic/hyperopic LASIK/PRK/LASEK
Optimization of IOL constants
Line voltage 100 – 240 V +/– 10% (self sensing)
Line frequency 50 – 60 Hz
Power consumption max. 90 VA
Technical data
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4
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Department of Ophthalmology,
JNMC

62. 62
Biometry Formulas
4
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March 2015
Department of Ophthalmology,
JNMC

63. IOL Formulas
1
st
Generation – The first theoretical formula
(based on Geometric Optics as applied to
schematic eye models) was developed in 1967.
These formulas were very primitive and usually
resulted in large amounts of post-cataract surgery
refractive errors. (Regression)
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4
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March 2015
Department of Ophthalmology,
JNMC

64. IOL formulas
1
st
generation
•Most are based on regression formula developed
by Sander ,Retzlaff & Kraff
•Known as SRK formula.
•P = A - 2.5(L) - 0.9(K)
•P=lens implant power for emetropia
•L= Axial length (mm)
•K=average keratometric reading (diopters)
•A= lens constant
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4
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March 2015
Department of Ophthalmology,
JNMC

65. IOL formulas
2
nd
Generation – With an extreme need for
increased IOL Calculation, the second generation
formulas (Hoffer, SRK II) listed manual
correction factors for long or short eyes. (These
formulas are now considered obsolete.)
(Regression)
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4
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March 2015
Department of Ophthalmology,
JNMC

66. IOL formulas
•IOL FORMULA 2
nd
generation
•SRK II formula
• modification of SRK
• works on ELP
• P = A1 – 2.5L – 0.9K
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4
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March 2015
Department of Ophthalmology,
JNMC

67. IOL formulas
3
rd
Generation – In 1988 Dr. Holladay published
a formula (Holladay I)that predicted the AC
Depth on the basis of K Height and the distance
from the iris plane to the IOL optical plane called
the “Surgeon Factor”. This change in the physics
greatly increased the visual outcomes for Cataract
Surgery. This generation also includes the
SRK/T and Hoffer Q.
4
th
Generation – Consist of Holladay II as well as
the modern post-refractive formulas
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68. IOL formulas
•IOL FORMULA 3
rd
generation
•Third generation formulas-
•SRK/T -very long eyes >26mm
•Holladay I -long eyes 24-26 mm
•HofferQ -Short eyes<22mm
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4
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March 2015
Department of Ophthalmology,
JNMC

69. IOL formulas
•IOL FORMULA 4
th
generation
•Holladay II
•Haigis formula-
• d = a0 + (a1 * ACD) + (a2 * AL)
•ACD is the measured anterior chamber depth
•AL is the axial length of the eye
•The a0, a1 and a2 constants are set by optimizing
•a set of surgeon- and IOL-specific outcomes for a wide
•range of ALs and ACDs.
•SRK/T formula — uses "A-constant“
•Holladay 1 formula — uses "Surgeon Factor“
•Holladay 2 formula — uses "Anterior Chamber Depth“
•Hoffer Q formula — uses "Anterior Chamber Depth"
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4
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March 2015
Department of Ophthalmology,
JNMC

70. IOL formulas
•When capsular tear does not allow bag
placement of the lens → change IOL
power for sulcus placement
•>=28.5 D Decrease by 1.5 D
•+17 To 28 D Decrease by 1.0 D
•+9 To 17 D Decrease by 0.5 D
•<+ 9 D
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4
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March 2015
Department of Ophthalmology,
JNMC

71. Lens Constants
A-Constants are used with all IOL formulas, and
are determined by the anticipated position within
the eye.
Surgeon Factor – is used with the first Holladay
formula, and is determined by the distance from
the Iris plane to the Optical plane of the implant.
Effective Lens Position (ELP) is used for the
Holladay II formula, and is based on the depth of
the AC following Cataract surgery with the new
IOL in place.
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72. Types of Formulas
Regression formulas are based upon mathematical
analysis of a large sampling of post-operative results. 
The most familiar regression formula is the SRK
formula. The basic SRK formula  works well for eyes in
the "average" measurement range; 22.5 to 25.0 mm in
axial length, with certain combinations of K readings. 
The formula does not work well for "long" (>25 mm) or
"short" (<22.5 mm) eyes. 
Advantage - relatively simple to calculate.  A factor
can be added to a simple regression formula to
compensate for a long or a short eye
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73. Types of Formulas
Theoretical formulas are optical formulas based on the
optical properties of the eye.  They do a better job of
predicting post-op outcomes for long and short eyes.
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4
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March 2015
Department of Ophthalmology,
JNMC

74. Formula Requirements
HaigisHoffer QSRK/2 SRK/T HOLLADAY 1 HOLLADAY 2 Olsen
Axial Length YES YES YES YES YES YES YES
ACD YES NO NO NO NO YES* YES
Keratometry YES YES YES YES YES YES YES
Lens Thickness NO NO NO NO NO YES YES
Corneal Thickness NO NO NO NO NO NO NO
White to White NO NO NO NO NO YES YES
Pupil Size NO NO NO NO NO NO NO
Visual Axis NO NO NO NO NO NO NO

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75. Formula Preferences
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Short Eyes (<22.0mm)Hoffer Q / Holladay 2
Average Eyes (22.1-
24.4mm)
Hoffer Q /

Holladay I / SRK/T
Medium-Long Eyes
(24.5-25.9mm
Holladay I / Hoffer Q
Long Eyes (25.0mm +)SRK/T / Holladay I
(Holladay II All eye
lengths.)
(Haigis All eye lengths
w/o optimization)

76. Post-Refractive Surgery Patient
One of the most challenging problems facing modern
Cataract Surgery is the Post-Refractive patient. Following
refractive surgery (RK, PRK, LASIK, ect) accurate K
readings cannot be obtained from topography, automated
or manual keratometry because the central cornea has
been flattened causing the mires of the measuring device
to measure roughly 4.5mm versus 3.0mm for which they
were designed. This causes erroneous K readings
compromising the effectiveness of all modern IOL
formulas.
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Department of Ophthalmology,
JNMC

77. Post Refractive Formulas
Haigis L - The Haigis-L formula offers predictable outcomes
after laser refractive surgery for myopia based only on current
measurements without refractive history.)
Masket Method - The Masket Method of post-LASIK corneal
power estimation is a postoperative regression method developed
by Samuel Masket and Clinical History Method – Is usable when
both the pre-op and post-op Keratometry values are known.
Contact Lens Method - The Contact Lens Method, originally
outlined by Dr. Holladay is considered a helpful way to estimate
the average central corneal power following radial keratotomy.
This technique required a special PMMA contact lens, of a known
base curve and power.
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78. Shammas – Used when no pre-op data is available such as
refraction and keratometry.
Double K SRK/T – Utilizes pre-op refraction and keratometry
Post Refractive Formulas
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Department of Ophthalmology,
JNMC

79. Advantages
#  Learned very quickly (User Friendly)
#  Extensive integrated safety features
# Non-contact measurements.
# It gives the true refractive length than anatomical
axial length
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Department of Ophthalmology,
JNMC

80. Advantages
#Accuracy of IOL Master is 0.02 µm which is
operator independent
#It is upright, non contact, ultra high resiltuion
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 cases
of posterior staphyloma
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Department of Ophthalmology,
JNMC

81. Limitations
# Cannot measure axial length in media
opacities like corneal opacities, dense
cataract, nuclear sclerosis grade IV, posterior
Polar Cataract
#Cannot measure axial length in cases of
vitreous haemmorrhage
#Difficulty in measuring axial lengths in
infants, small children and mentally
handicapped patients
#Patients with poor fixation
81
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Department of Ophthalmology,
JNMC

82. Do not throw away old ultrasound
machine
Immersion
ultrasound
IOL
master
Posterior staphyloma
Silicone oil
Pseudophakia
4++brunescent lens
Central PSC plaque
Vitreous hemorrhage
Central corneal scar
Difficult
Difficult
Variable
•Yes
•Yes
•Yes
•Yes
•Yes
•Yes
•Yes
No
No
No
No

83. Lenstar 900
4th March 2015 Department of Ophthalmology,
JNMC
83
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84. Lenstar 900
Lenstar features a unique dual zone keratometer with a
total of 32 marker points on two concentric rings of 1.65
and 2.3 mm in diameter for improved refractive
outcomes with toric lense.
84
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85. Lenstar 900
It has been complemented with
an optional T-Cone topography
add-on and an optional toric
surgery planning platform.
The T-Cone enables the Lenstar
to provide true Placido
topograph of the central 6 mm
optical zone.
The toric surgery planning
platform allows planning and
optimization of the surgical
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86. Lenstar 900
•The toric planner shows the implantation axis, the
incision location and user-defined guiding meridians in
the real patient image.
•Incision optimization tools allow for precise placement
of the incision to minimize the residual astigmatism
based on the surgically induced astigmatism.
•Planning of the operation on real eye images allows the
user to define recognizable, additional guiding lines to
anatomical landmarks in the intraoperative view.
•They either serve as a base line point for the
intraoperative orientation or as a fallback strategy if
external marking is not successful.
•The planning sketch can easily be printed and hung near
the microscope
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87. •The LENSTAR LS 900 ® measures:
·· Axial eye length
·· Corneal thickness
·· Anterior chamber depth
·· Aqueous depth
·· Lens thickness
·· Radii of curvature of flat and
steep meridian
·· Axis of the flat meridian
··White-to-white distance
·· Pupil diameter
4th March 2015 Department of Ophthalmology,
JNMC
87
Lenstar 900
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88. 88
Olsen formula
calculates the postoperative lens
position as a fraction of the
crystalline lens thickness and the
ACD.
This approach allows accurate
calculation of the lens position
independent of the corneal status
of the eye.
The lens position is then used to
calculate the IOL power based
on ray tracing, the same
technology that physicists use to
design telescopes and camera
lenses. 88
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89. Post -refractive IOL
calculation
4th March 2015 Department of Ophthalmology,
JNMC
89
•Shammas No-History and Masket – for
premium results
•The Lenstar EyeSuite software provides
the user with a comprehensive set of
cutting-edge IOL calculation formulae
for normal eyes. IOL Power calculation
in patients with prior LASIK or PRK,
presenting with no history, is easily
achieved with the on-board Shammas
No-History method.
•If the change in refraction is known, then
the Masket and modified Masket
formulae may also be used.
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90. Optical Biometer Properties
90
Feature Device
IOL Master Lenstar
Axial Length X X
White to White X X
Keratometry X X
ACD X X
Pachymetry X
Lens Thickness X
Retinal
Thickness
X
Pupillometry X
Visual Axis X

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91. Summary
With state of the art technology
and modern IOL calculation
formulas, excellent refractive
outcomes can be achieved after
IOL implantation in challenging
eyes, that approach the
benchmarks postulated for
normal eyes.
91
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Department of Ophthalmology,
JNMC

92. 08/22/15 01:46 PM Dept. of Ophthalmology, JNMC 92