Detailed presentation on Ultrasound immersion, contact A scan and Optical a scan

1. A scan biometry
Presenter: Dr. Kshama K
IOL FELLOW
RJ SANKARA EYE HOSPITAL,
NEW PANVEL

2. Ocular Biometry
• Word meaning of biometry: measurement of tissues
• Components of ocular biometry include
• Measurement of axial length
• Measurement of corneal dioptric power
• IOL formulae and IOL power calculations
• The key issue faced in selecting an accurate power IOL is obtaining
accurate measurements and selection of optimal IOL calculation
formula.

3. Axial length measurements
• Different methods to measure the axial length of the eye ball
• Ultrasound
• A scan : applanation and immersion a scan
• B scan
• Optical Biometer

4. Ultrasound A scan
• One dimensional scan in which echoes are represented as vertical
spikes from baseline
• 1mm error in AXL – 2.35D error
• Axial length has to be repeated if difference between 2 eyes is 0.3
mm or if there is difference of 0.2 mm in consequtive readings

5. • Time required for sound pulse to travel from probe to interface is
noted
• Velocity of sound in different medium is known
• 1620 m/s in cornea
• 1641 m/s in lens
• 1629 in dense cataract
• 1630 m/s sclera
• 1532 m/s in aqueous and vitreous
• 986 m/s in silicone oil
• 2718 m/s PMMA
• Knowing time and velocity distance between two spikes gives the
length / AXL

6. Ultrasound waves have frequency greater than
20khz (20,000 oscillations/sec),inaudible to
human ears.
Audible Sound Waves : 20-20,000 Hz

7. • Diagnostic ophthalmology utilizes frequency of 8-10 Mhz
(1Mhz=1,000,000 cycles/sec)
• High frequencies produces short wavelength <0.2mm, which allows
resolution of minute ocular structure.
• Lower frequency produce longer wavelength

8. Principles of Ultrasound
• Reflectivity
• When sound wave travels part of the sound is reflected from the interfaces
into the probe -echo.
• Greater the density difference at the interface, stronger the echo
• stronger echo : higher the spike in A-scan and brighter the dots in B-scan.

9. • Velocity
• Angle of incidence
perpendicular
angle of incidence will be equal to the angle of
reflection
oblique
part of the echo is reflected away from the p
tip
weaker echo than the perpendicular sound
incidence
Less energy is returned
displayed image is compromised.

10. Probes
• first generation of contact biometers: water-filled probes with a soft
membranous tip.
• filled with distilled water,
• small air bubbles trapped : erroneous AEL
• Newer biometers : solid probes
• Applanation/ contact vs immersion probes
• 10-12 MHz
• Focused vs non focused beam

12. Applanation probe

13. Instrumentation

14. Instrument Settings
• (1) measurement mode,
• (2) eye type,
• (3) position of electronic gates or cursors, and
• (4) gain.

15. Measurement Mode (Automatic vs. Manual)
Automatic Measurement Mode
In automatic continuous measurement mode the software uses standard settings for gain, gates and
detection threshold.
Beep is heard after each reading. Beep indicates valid scan , and momentarily freezes the scan pattern
on the screen.
Rapid
10 reading are taken continuously .
Used for most of the cooperative patients with normal cataract eyes.

16. Manual Measurement Mode
The A-scan will recognise the valid pattern
freeze the amplitude pattern for 2 seconds after which the screen is reset.
if the biometrist decides to retain the reading, press the freeze button.

17. Eye type ( Sound velocity)
• velocity setting on the instrument should
always be checked prior to beginning the
examination.
• phakic eye:
• Avg sound velocity setting : 1550 m/s
• Assumes constant relationship btwn lens thickness and
the depth of the anterior chamber.
• sufficient for measuring the normal phakic eye , small
errors in thick and thin lenses, long or short eyes
• Measure components separately and add the AXL
• VELOCITY CONVERSION EQUATION can be
used if uncorrect velocity is used

18. Gates
• Electronic calipers that
measure between two points
• Auto mode : gate position
decided by the machine
• Manual mode : gate position
decided by operator

19. Gain setting
• degree of echo amplification in an ultrasound system.
• beginning of an examination, the gain must be high – align grossly
along the visual axis to see overall appearance of echo gram
• Reduce gain to medium level – improve resolution of spikes
• High gain – artefact spike is tall and confused with Retinal spike –
short AXL
• Low gain – small retinal spike – adjacent scleral spike might be
misread as retinal spike – longer AXL

21. EXAMINATION PROCEDURES FOR A-SCAN
BIOMETRY
• history and explaining the examination to the patient.
• Patient Positioning
• Applanation : chin rest
• Hand held contact : sitting/reclining
• Immersion : supine / recliner/ supine with chin elevation
• Silicone filled eyes : sitting with no head tilting back
• instrument settings adjusted
• both eyes measured whenever possible
• Actual measurement

22. Contact Technique
• probe placed gently on the center of the cornea
• no ointment or excess fluid : erroneously high AXL
• Steps to minimise corneal compression
• If manual mode :
• measurement taken as soon as the probe touches cornea.
• Probe is removed before taking subsequent measurements: intermittent probe contact
• Pt asked to blink
• Each reading to see ACD
• 3 high quality readings

23. Applanation method.
• Pressure sensitive probe can be used
• Joystick is retracted as far away as possible
• joystick is then advanced until the probe gently touches the center of
thecornea.

24. Handheld method
• cornea is more easily compressed with
this technique than with the
applanation method.
• When a pressure sensitive sleeve is not
employed, the patient should be
reclined.
• When pt seated upright , examiner
should observe cornea from side to
minimise compression

25. Immersion Technique
• employs a small water bath – hence corneal compression avoided
• separate corneal spike (not present in the contact method) -facilitate
alignment of the sound beam along visual axis.
• Avoid air bubbles
Ossoinig Hansen

26. Immersion a scan

27. Prager shell
An advantage of this shell is that it allows the immersion ex- amination
to be performed with the patient sitting upright rather than reclined.

28. • examiner immerses the probe into the fluid just until an echogram si
displayed.
• tip located approximately 3⁄8inch from the bottom of the shell.
• balanced salt solution
• double-peaked corneal spike and single-peaked spikes from the
anterior and posterior lens surfaces, retina, and sclera.
• 3 high quality reading

29. fluid for immersion
• If Hansen scleral shells are used : CMC 1%
• If prager shell: BSS (slightly hypotonic) or CMC 0.5%
• goniosol: hypromellose 40ml
• Dacriose: 60ml
• Isotonic, Buffered Solution of Purified Water, Sodium
Phosphate, Potassium Chloride, Sodium Hydroxide, Edetate
Disodium and Sodium Chloride, Preserved with Benzalkonium
Chloride 0.1 mg/ml.

30. Measurement of Phakic Eye
• Phakic setting is used
• Phakic setting works in 3 way depending on the instrument
• In extremely dense cataracts :
• Sound attenuation : weakening of retinal spike – prolonged measuring time
• Manual mode / dense cataract mode to be used

31. Measurement of Phakic Eye
• 3WAYS
• 2 gates
• between initial spike and retinal spike
• Preset avg sound velocity – 1550 m/sec
• 4 gates
• AC depth measured using 1532 m/s
• LENS thickness using 1641 m/s
• vitreous cavity using 1532 m/s
• ACD+LT+VL = AXL
• Aphakic sound velocity setting of 1532 m/s
• Uses 2 gates
• AXL measured + CALF (0.32 mm)CALF depends on the lens thickness for the age
• CALF changes with density of cataract
• Avg CALF value for most cataract pts is 0.32

32. Multiple signals
• Between ant n posterior lens capsule
• due to interfaces within a cataractous lens
• In vitreous baseline (reverberations) :
• These decrease with decrease in gain
• caution should be exercised in using the automatic mode when
multiple signals are present: the instrument may place one or more
gates on the wrong spikes, resulting in erroneous measurement

34. A scan of a moderately dense Cataract:. Spikes between anterior and
posterior Lens capsule spikes are seen.

35. Multiple signals in vitreous baseline

37. Measurement of Aphakic Eye
• The aphakic echogram consists of
• initial spike
• spike from iris/posterior lens capsule/anterior vitreous face spike
• spike from retina and sclera.
• aphakic type (1532m/sec) is used for measurement
• two gates,
• three gates

38. Measurement of Pseudophakic Eye
• Manual mode
• Aphakic velocity
• pseudophakic echogram
: IOL reverberations
• Reverberations of PMMA
vs. Acrylic into the
vitreous cavity. Longer chain of
reverberation :
PMMA
Shorter chain
chain of
reverberation :
acrylic

39. • IOL can be made from PMMA, Silicone or acrylic lenses.
• true AEL is determined by adding appropriate correction factor for
the IOL composition

40. Potential sources of error with contact
technique
• corneal compression
• fluid meniscus
• misalignment of the sound beam.
• Improper gate position

41. Potential sources of error with contact
technique
• small air bubbles within the fluid
• improper gate position,
• selection of an inappropriate eye type (sound velocity) setting

42. TROUBLESHOOTING
• Inadequate Patient Fixation
• Incorrect Sound Velocity Settings
• Intraocular Lesions
• Posterior Staphyloma
• Macular Lesions
• Retinal D e t a c h m e n t
• Vitreous Lesions
• Silicone Oil
• Dense Cataract
• Post Trab

43. Inadequate patient fixation
• Re explaining the procedure to patient
• Patch other eye to eliminate distraction or if there is strabismus
• Fix at a target with another eye
• If fixation near primary gaze cannot be achieved – examination from
unconventional side position
• Nystagmus and blepharospasm – immersion is preferred

44. Incorrect Sound Velocity Settings
• Velocity Conversion Equation
• correct measurement when an inappropriate sound velocity is used
during the examination.
• correct value = (Vc/Vm) X measurement
• For example, an aphakic eye was measured using in correct velocity -
1,550 m/see rather than aphakic velocity
• The erroneous axial length reading obtained was 25.0 mm. To
determine the correct (true) axial length measurement:
• 1.532/1.550 m/sec × 25.0 mm= 24.71 mm

45. Intra ocular lesions
• Patients history
• high myopia
• previous cataract or
vitreoretinal surger
• DR
• ARMD
• B-scan examination – detect
any abnormalities that
affects AXL
• rule of thumb : if no view
during ophthalmoscopy – b
scan prior to biometry

46. Posterior Staphyloma
• posterior staphyloma is suggested:
• distinct, high retinal spike is difficult to display
• AXL readings : long and inconsistent
• fi a distinct retinal spike and consistent measurements are obtained but the
probe appears to be directed eccentric to the macula (e.g., nasally)
• Immersion a scan is preferred
• Vector Ascan/Bsacan
• Horizontal axial B-scan echogram

48. Macular lesions
• suspected if
• Difficulty in displaying a steeply rising, retinal spike
• Distance between retinal and scleral spike is more
• If macular lesions are temporary
• Measure macular thickness on OCT/ Bscan and add the thickness to AL
• OR DISTANCE BETWEEN RETINAL AND SCLERAL SPIKE

49. Retinal Detatchment ( macula off)
• suspected when
• wider than normal distance between the retinal and scleral spikes
• B scan is indicated
• Other eye AXL If no refractive error difference between both eyes
• User adjusted AXL*
• both optical and US biometry is performed
• In optical scans: posterior spike considered
• SNR 2dB or more
• If on optical biometry: multiple spikes – posterior peak correlating to AL is
guided by fellow Eye AL or ipsilateral Ultrasound AL
Rahman, R. et al. (2016) “Accuracy of user-adjusted axial length measurements with optical biometry in eyes having combined phacovitrectomy for
macular-off Rhegmatogenous Retinal Detachment,” Journal of Cataract and Refractive Surgery, 42(7), pp. 1009–1014. Available at:
https://doi.org/10.1016/j.jcrs.2016.04.030.

50. Silicone Oil
• Cataract surgery after silicone oil injection or combined cataract
surgery and oil removal
• Pre oil inj biometry
• Conversion factor
• 0.64 if 1000 cs silicone used
• 0.71 if 1300 cs silicone used
• Conversion factor can be obtained by : Velocity (oil)/ velocity ( vitreous)
• Silicone oil in eye over estimates AXL so conversion factor is needed
• If above methods not possible
• Other eye biometry if no ref error difference
Biometry of the silicone oil-filled eye1999 Jun;13 ( Pt 3a):319-24. doi: 10.1038/eye.1999.82

51. • There are presently 2 viscosity of silicon oil in use:
• 1000mPas : 980 m/s
• 5000mPas: 1040 m/s
• If an optical bio meter is not available, the next best approach is
• prior biometry before silicon oil injection
• Or first remove silicon oil and then in place IOL

52. Post trab*
• AL reduction postoperatively, which became stable nearly 3 months
after the surgery.
• the amount of reduction in AL measured by optical devices is less
than that measured by ultrasonic tools
• Changes in ACD are of small amount and short lived : doesn’t affect
IOL power calculation
• reported changes in AL and keratometry are of sufficient magnitude
to affect refractive prediction of cataract surgery

53. • better to delay cataract surgery and lens implantation if possible until
AL and keratometry changes stabilize
• preferable to measure biometric parameters using non‐contact
optical biometry method instead of contact ultrasound biometry for
IOL power calculation in such cases.
Esfandiari, H. et al. (2016) “Ocular biometric changes after
trabeculectomy,” Journal of Ophthalmic and Vision Research, 11(3), p. 296.
Available at: https://doi.org/10.4103/2008-322x.188399.

54. Limitations of Immersion A scan
• After a single immersion A scan , 18-34 samples (53%) grew
organisms from probe/ shell or tubing
• Positive cultures in 32% of immersion shell/probe (11 of 34) and in
31% of infusion tubing samples (10 of 32)
• Shell/ probe should be soaked in alcohol or hydrogen peroxide for at
least 5 min. immersion shell should be allowed to dry completely and
flushed with BSS
VELAZQUEZESTADES, L. et al. (2005) “Microbial contamination of immersion biometry ultrasound equipment,” Ophthalmology, 112(5). Available at:
https://doi.org/10.1016/j.ophtha.2005.01.030.

55. Method of disinfection
• Following each biometry remove the tubing Kit from the Prager Shell
and discard.
• soak both shell and probe in
• 70% isopropanol or
• solution of 3% hydrogen peroxide for a minimum of 5 minutes.
• Follow CDC Guidelines avoid viral and bacterial patient cross-
contamination.
• CDC Guidelines. wiped clean and then disinfected by:
• (a) a 5- to 10-minute exposure to a fresh solution of 3% hydrogen
peroxide; or (
• (b) a fresh solution containing 5,000 parts per million (mg/L) free available
chlorine--a 1/10 dilution of common household bleach (sodium
hypochlorite);
• (c) 70% ethanol; or
• (d) 70% isopropanol.
• The device should be thoroughly rinsed and dried before patient use.

56. Good A scan
• Corneal echo seen as tall single spike
• No echoes from aqueous humour
• Ant and post lens capsule produce tall echoes
• Retina – tall sharp rising – no stair casing at origin
• Orbital fat medium to low echoes
• If retinal spike is not followed by multiple small spikes – one is hitting
the optic nerve

57. • Adequate gain
• ACD : maximum ACD
• 8-10 measurements
• SD < 0.06 ( here we take < 0.03)

59. AXL length measurement instruments in our
hospital
• Ascan :
• Biomedix echorule pro
• Applanation and immersion
BIOMEDIX ECHORULE 2 BIOMEDIX ECHORULE PRO

60. Optical biometry
• Optical biometry is highly accurate, noninvasive automated method
for measuring anatomical details of eye.
• First optical biometer – IOL Master 500 – 1999
• Biometric measurements provided
• AL, K, ACD, LT, CCT, PS, WTW

61. partial coherence interferometry
(PCI) biometry was first created by
Austrian physicists Fercher and Roth
in 1986
1986
In 1999, Carl Zeiss released the IOL
master 500 ( first commercially
accessible optical biometer.)
1999

62. Currently available optical biometers
• Today’s optical biometers employ one of the following technologies:
• PCI
• OLCR
• Swept-source optical coherence tomography (SS-OCT).

63. PCI
• Uses 780 nm wavelength IR light wave
• light is reflected by tissue surfaces with different refractive indices
• The ocular distances are then measured using interferometric
techniques.
• Dual Co axial beam interferometer is used

64. • Example
• IOL master 500
• AL scan
• Pentacam AXL

65. OLCR
• Video
• A detector detects the interference pattern generated by the
coaxially travelling emitted and reflected light.
• Scanning the reference beam determines the precise spot from
which the light was reflected from within the eye.

67. • Example
• Lenstar LS900 (Haag-Streit),
• Aladdin (Topcon),
• Galilei G6 (Zeimer).

68. SS OCT
examples
The IOL Master
700 (Carl Zeiss),
Argos (Movu),
O.A 2000
(Tomey)
Eyestar 900
(Haag-Streit).
Rapid-cycle tunable wavelength laser
source is used

69. COMPANY PRINCIPLE SOURCE OF LIGHT METHOD OF
MEASURING K
VALUE
IOL MASTER S00 Carl Zeiss, Meditec
AG, Jena , Germany
PCI 780 nm IR laser Reflection based
AL SCAN (NIDEK) Nidek PCI 830 nm diode laser Reflection based
PENTACAM AXL OCULUS
Optikgeräte
GmbH, Germany
PCI 475 nm
monochromatic slit
of blue light
Dual Scheimpflug
rotating camera
with placido disc
imaging

70. Scanning in opaque
media
Parameters Special features Limitations
IOL MASTER S00 New version 5.0 can
scan in opaque
media
AL, K ACD, WTC GOLD STD
BIOMETER*
Old version can
scan opaque media
AL SCAN (NIDEK) No AL, K ACD, WTW,
pupil size, CCT, ACD
( CCT and ACD
scheimpflug
principles)
3D auto tracking,
auto shoot,
aberrations, torrid
lens assist software
Attached US AXL
and patchy for
dense opacities
Cannot scan in
opaque media
PENTACAM AXL Acquisition success
rate is less **
AL, K ACD, WTW,
pupil size, CCT, ACD
The Gold Standard in
anterior eye segment
tomography
Toric IOL, IOL after LVC,
cataract density grading,
wavefront analysis
Acquisition rate in
denser cataracts is
less
BhattAB,ScheflerAC,FeuerWJ,YooSH,MurrayTG.Comparisonof predictions made by intraocular lens master and ultrasound biometry. Arch Ophthalmol
2008;126:929‐33.
**Henriquez, M.A. et al. (2020) “Effectiveness and agreement of 3 optical biometers in measuring axial length in the eyes of patients with mature
cataracts,” Journal of Cataract and Refractive Surgery, 46(9), pp. 1222–1228. Available at: https://doi.org/10.1097/j.jcrs.0000000000000237.

71. COMPANY PRINCIPLE SOURCE OF LIGHT METHOD OF
MEASURING K
VALUE
LENSTAR LS 900 HAAG-STREIT AG,
Switzerland
OLCR 820 nm
superluminescent
diode
Placido disc +
optical T module
ALLADIN HW 3.0 TOPCON OLCR 850 nm laser –
penetration in
dense cataracts
Placido disc
GALILEI G6 System vision,
Greece
OLCR 880nm Dual Scheimpflug
and Placido disc

72. Scanning in opaque
media
Parameters Special features Limitations
LENSTAR LS 900 Poor when
compared to IOL
master 500
AL, K ACD, WTC EYE SUITE IOL:
Comprehensive set
of premium IOL
calculat formulae
Automated
positioning- allows
dynamic eye
tracking of patients.
Poor acquisitions in
dense cataract
ALLADIN HW 3.0 Good AL, K ACD, WTW,
pupil size, CCT, ACD,
LT
Zernicke wavefront
analysis for higher
order aberrations
Mesopic, photo pic
and dynamic
pupillometry
Posterior corneal
surface not
measured
GALILEI G6 System vision,
Greece
AL, K ACD, WTW,
pupil size, CCT, ACD,
LT
3D AC analysis, refractive
surgery,
Ray tracing IOL formulae
Scheimpflug + OCT helpful
in post LVC
Newer IOL formulae
IOL formulae
available are less
compared to
pentacam axl

73. COMPANY PRINCIPLE SOURCE OF LIGHT METHOD OF
MEASURING K
VALUE
IOL master 700 Carl Zeiss, Meditec
AG, Jena , Germany
SS OCT ( first to use
ss oct)
rapidly tuned laser
with longer
wavelength (1310
nm)
SS OCT with placido
pattern
Argos SS OCT 1060nm From OCT image +
2.2 diameter ring
OA 2000 TOMEY GmbH ,
Nagoya, Japan )
SS OCT Placido disc based
EYE STAR 900 HAAG-STREIT AG,
Switzerland
SSOCT OCT based with
placido pattern

74. Scanning in opaque
media
Parameters Special features Limitations
IOL master 700 Good K, CCT, ACD, LT,
WTW, PS, AXL,
Telecentric
keratometry
Good in media
opacities
Crystalline lens tilt
or decentration
Fixation check
OA 2000 Fair AL, ACD, LT, CCT,
WTW,
K 3 , 5.5 mm
OA 4000: hAndheld
ultrasound AL,CCT
Scan acquisition
not there in mature
catarcts
EYESTAR 900 Under trial Eye suite software
3D pics of anterior
segment and lens
Hill RBF 3.0

76. Purpose: To systematically compare and rank
ocular measurements with optical and
ultrasound biometers based on big data.
methods
129 studies
17,181 eyes
12 optical biometers and two ultrasound
biometers (with both contact and
immersion techniques)

77. • AL and ACD measurements : statistically significant differences
existed btwn contact ultrasound biometry and optical biometers.
• There were no statistically significant differences among 4 ( SS-OCT)
based devices (IOLMaster 700, OA-2000, Argos and ANTERION).
• Ks, Km and CD, statistically significant differences : pentacam AXL was
compared with the IOLMaster 700 and IOLMaster 500.
• There were statistically significant differences for CCT when the OA-
2000 was compared to Pentacam AXL, IOLMaster 700, Lenstar, AL-
Scan and Galilei G6.

78. • AL and ACD, contact ultrasound biometry obtained lower values
compared to all optical biometers.
• Lowest CCT : OA 2000; highest CCT : Galilei G6
• In relation to Kf, ACD, CCT and CD measurements, results indicate
that there is too much heterogeneity to draw reliable conclusions.

79. J Cataract Refract Surg 2021; 47:802–814
Copyright © 2021 The Author(s). Published by
Wolters Kluwer Health, Inc. on behalf of ASCRS
and ESCRS

80. • Purpose: updated review of the repeatability and re- producibility of
optical biometers based on SS-OCT and their agreement for ocular
dimensions necessary for cat- aract surgery,
• repeatability, reproducibility, and agreement between devices were
analyzed.
• conclusion:
• Differences obtained between some parameters in different studies
has to be analysed and validated to use these values interchangeably

81. Agreement between Two Swept-Source Optical
Coherence Tomography Biometers and a Partial
Coherence Interferometer

82. • Purpose :
• agreement between anterion and OA 2000 AND IOL master 500
• Methods
• 51 eyes
• Flat and steep K, ACD, AXL
• Predicted IOL power of each device was compared ( srk/t, Haigis, Barrett
universal 2 and Kane formulas)

83. Results:
• K values : anterion flatter than other instruments,
but more agreeable with OA 2000
• ACD of anterion and OA 2000 was interchangeable
• Axl high agreement btwn devices
• Iol powers were not interchangeable
ONLY AXL SHOWED GOOD AGREEMENT
BETWEEN THESE DEVICES

85. Purpose: agreement btwn OA2000 and IOL master
700
103 eyes considered
Except CCT, WTW and PD, IOLMaster 700 and OA-
2000 have excellent agreement on AXL, ACD and
astigmatism power vectors

86. Intra op wavefront aberrometry
• It uses a system which produces a fringe pattern as wave fronts.
Based on the pattern formed after diffraction through media, sphere,
cylinder and axis is determined
• WaveTec vision systems, Inc : ORAnge , ORA
• Later - Alcon

87. • Aphakic and pseudophakic measurements
• Confirm and update IOL power, optimise lens postion, corneal
arucate incisions
• Incorporation of AnalyzOR, compares pre-, intra-, and post-op data
and allows surgeons to fine-tune their calculations to improve
outcomes.

88. • HOLOS
• HOLOS IntraOp by Clarity is the newest available product.
• rapidly rotating micro electro-mechanical system (MEMS) mirror and
quad detector
• measure the magnitude of wavefront displacement.

89. • 90 measurements per second and has a range from -5D to +16 D
• It attaches to operating microscope
• Advantage is that surgeon doesn’t have change the focus as it has
inbuilt auto focus

90. Currently available optical biometers
Turczynowska, M. et al. (2016) “Effective ocular biometry and intraocular lens power calculation,” European Ophthalmic Review, 10(02), p. 94. Available
at: https://doi.org/10.17925/eor.2016.10.02.94.

91. Haigis, W. et al. (2000) “Comparison of immersion ultrasound biometry and partial
coherence interferometry for intraocular lens calculation according to
Haigis,” Graefe's Archive for Clinical and Experimental Ophthalmology, 238(9), pp.
765–773. Available at: https://doi.org/10.1007/s004170000188.
OPTICAL BIOMETER US A SCAN
From corneal vertex to RPE From corneal vertex to ILM
IR Light rays used Ultrasound used
Non contact Contact procedure
Difficult in axial opacities Can be done in axial opacities
Easier in posterior staphylomas ( fovea
may lie along the slope of staphyloma)
Erroneously measured as long axial
length

92. AXL length measurement instruments in our
hospital
• Ascan :
• Biomedix echorule pro
• Applanation and immersion
• IOL formulae available

93. • Optical biometer
• OA 2000 (TOMEY GmbH , Nagoya, Japan )
• SSOCT based (product description- dense cataract can also be measured)
• Auto alignment - auto shot
• Placido disc 9 rings
• 5.5 mm cornea is measured
• CCT is measured at 9 points
• K , ACD, LT, PACHYMETRY, pupil size, WTW
• SRKT , Haigis, HOFFER Q, holladay 2, Olsen,
• Oculix, barretts
• IOL models details can be downloaded

94. • Low reliability mark
• Low reliability data sets have exceeded the majority: !
• When reliability of all data is low: !
• When multiple higher peaks are detected in AXL measurement: !
• When all data returns as error : error

95. OA 2000 video

98. Thank you