The document discusses advancements in optical biometry and intraocular lens (IOL) power calculation, emphasizing their importance for achieving optimal cataract surgery outcomes. It reviews various contemporary biometry devices, their technologies, and the corresponding IOL calculation formulae which help cater to diverse ocular conditions. Additionally, it provides insights into the evolution of these technologies, their advantages, and future prospects in improving patient vision without glasses.

1. Optical Biometry
By
Bareq Mared Thamer
SuperVisor
Ibraheem Jafarzada por

2. Intraocular lens (IOL) power calculation is the single most important
determinant of functionally improved result of a technically precise cataract
surgery. We have discussed recent advances in the field of optical biometry
and IOL power calculation formulae as a means to achieve better
postoperative visual outcome. The use of automated optical biometry
device, the current ‘gold standard’ of IOL power calculation, dates back to
1999. We have highlighted the evolution of newer optical biometry devices
and the technology they are based on, and their advantages and
limitations. We have done technical comparison of contemporary biometers
and have included contextual current review of literature. We have
described newer generation IOL power formulae, IOL power calculation in
high to extreme myopia, toric calculators and intraoperative aberrometry,
and concluded our discussion with a note on future prospects of IOL power
calculation
Abstract

3. Introduction
Cataract surgery is the most common surgical procedure performed worldwide. The goal
of cataract surgery is not just the removal of cataract, but to provide the patien sharp,
clear vision without glasses. Despite the growing popularity of laser-assisted in situ
keratomileusis (LASIK) and the growing interest in phakic intraocular lenses (IOLs)
and other refractive procedures, cataract surgery provides a wider range of refractive error
correction than any other surgical procedure, hence emerged the concept of “refractive
cataract surgery.” For performing refractive catarac surgery, a cataract surgeon now has,
in his armamentarium a host of technological innovations such as femtosecond
laser-assisted cataract surgery and the Zepto capsulotomy device to name a few. To
match patient’s expectations of crisp and spectacle-free vision, premium IOLs, namely
multifocal IOLs, accommodating IOLs and toric IOLs are available. These technological
advancements can help achieve better outcomes after cataract surgery. However,
the improved outcomes are dependent on precise and accurate biometry. Newer biometry
instruments that perform ocular measurements with micron precision and newer IOL
calculation formulae to provide precise IOL power required

4. OPTICAL BIOMETRY
To provide the best possible refractive outcome is the goal of the
surgeon, whether the eye of the patient is normal or short or long or
postrefractive surgery. Accurate measurement of all ocular parameters
to obtain information about the complete geometry of the eye is
required to arrive at the correct IOL prediction for each patient.
Optical biometry is a highly accurate noninvasive automated method for
measuring the anatomical details of the eye. Accurate anatomical
measurements are critical for precise IOL power calculation. For many
years, the gold standard of axial length (AL) measurement was
ultrasound (US) biometry.
The introduction of optical biometry in the late 1990s
revolutionized the precision of IOL power calculation.

5. IOLMASTER500
The IOL Master 500 ( Carl Zeiss Meditec AG, Jena, Germany) [Figure 1] is
an all-in-one biometer which measures AL, K, and other ocular
parameters as well as performs IOL power calculations. It is based on the
concept of PCI and operates as a modified Michelson
Interferometer.[15,18,19] PCI biometry was first developed by Austrian
physicist Fercher and Roth[20] who performed the first in vivo AL
measurement in 1986. The principle involves a dual beam of infrared (IR)
light (780 nm) emitted by a semiconductor laser diode. A signal is
produced as a result of interference between the light reflected from the
tear film and that reflected by the retinal pigment epithelium. The
photodetector receives the interference signal to calculate the optical
distance (OD) between the corneal surface and retina.This OD is used to
derive the other geometrical intraocular distances.

6. The employment of optical AL instead of anatomic AL has significantly
improved the refractive results of cataract surgery. The IOLMaster 500 has
been shown to consistently measure AL accurately to within ±0.02
mm.This translates into a 5–10-fold precision in AL measurement. With
>100 million power calculations performed worldwide, the IOLMaster 500
is the current gold standard biometer

8. IOLMASTER 700
IOLMASTER 700 [Figure 2] was the first optical biometer to incorporate SS-OCT
technology.[16,17,28-31] Its advantages over the earlier devices are as follows:
1. It provides full-length OCT image of the eye. The device performs 2000 scans/s. It can
identify unusual ocular geometry (e.g., crystalline lens tilt/decentration)
2. It is more accurate. Measurements can be verified visually
resulting in fewer “refractive surprises”
3. The OCT image provides a fixation check. The biometer’s fixation check feature alerts
the user to a suboptimal scan if the image captured does not show the foveal pit. The
fixation check also helps identify macular pathologies such as macular holes and age-
related macular degeneration, though the findings need to be verified with a dedicated
retina OCT
4. Unique telecentric K and distance-independent K: The unique software of IOLMaster
700 allows highly accurate distance-independent corneal surface measurements,
independent of PS and even in restless patients
5. Better cataract penetration rates: the IOLMaster 700 can perform biometry even
through dense cataracts
6. Software includes “Haigis Suite” (which includes Haigis, Haigis-T for torics, and
Haigis-Lfor postrefractive surgery eyes) and other IOL power calculation formulae (SRK/T
formula:
Sanders-Retzlaff-Kraff formula; T for theoretical, Hoffer
Q, Holladay 1 and 2, and Barrett Universal II)
This device is especially suited for Toric IOLs. IOLMaster 700 contains inbuilt toric
calculator (Barrett Toric calculator and Haigis-T for toric IOLs), and there is no need to
use a separate online toric calculator

9. LENSTAR LS 900
LENSTAR LS 900 [Figure 3] uses the principle of OLCR. Apart from the
parameters measured by IOLMaster, the Lenstar also measures LT. Use of LT,
in conjunction with the latest state-of-the-art IOL calculation formulas
(Barrett, Olsen, Holladay 2), translates into more accurate biometry. The
latest version of Lenstar LS900 is equipped with the Hill-radial basis
activation function (Hill-RBF), Barrett Universal II, Barrett True-K, and Barrett
Toric calculator. Some of its other features are
1.Automated positioning system allows for dynamic eye tracking of patient.
2.Dual-zone K (at 1.65 and 2.3 mm) and T-cone topography (allows true
Placido topography of the central cornea)
3.Contains EyeSuite IOL which is a comprehensive set of premium IOL
calculation formulae for cataract surgery patients and patients
postkeratorefractive surgery. Table 2 compares the technical specifications
of IOLMaster 500 and Lenstar LS 900.

10. EYESTAR 900
The new device based on SS-OCT was launched in October 2017. The device
contains EyeSuite software and provides elevation-based topography maps
of both front and back of cornea and provides biometry data of the entire
eye from cornea to retina. In addition, it provides two-dimensional (2D) and
three-dimensional (3D) images of anterior segment as well as crystalline
lens. Data acquisition process is smooth and fast, ensuring patient comfort.
The device contains the latest IOL power calculation formulae such as Hill-
RBF and Barrett Universal 2.
Various authors have reported excellent agreement between AL
measurements by IOLMaster and the Lenstar.[16,33-36] Epitropoulos
compared AL acquisition and other parameters by IOLMaster 500 (version
7.1 software) with those from Lenstar LS 900 in 105 cataractous eyes of 63
patients.[37] AL was acquired by the composite mean value of five
measurements (composite-5 IM) and 20 measurements (composite-20 IM) of
IOL Master 500 version 7.1 software and the standard mean of the first five
measurements on standard-5 LS Lenstar LS900. He observed

13. ARGOS ADVANCED OPTICAL BIOMETER (MOVU)
The Argos [Figure 5] uses a 1060-nm and 20-nm bandwidth SS-OCT technology to
collect 2D OCT data of the eye. The fast image reconstruction algorithm of the
instrument is used to provide real-time 2D imaging of the eye. The 1050 nm light
cause less scatter than shorter wavelengths leading to more photons being available
to make measurements and hence better penetration through dense cataract.
Equipped with Video K with IR light-emitting diode ring illumination, Argos measures
AL, CCT, ACD, LT, PS, aqueous depth, WTW, K, and astigmatism. The biggest
advantage of Argos is its ability to image through very dense cataracts through an
“Enhanced Retinal Visualization” mode [Figure 6] that increases imaging sensitivity of
the retinal area by 100 times (without increasing laser power).
The Argos uses a propriety swept laser source specifically designed for deep imaging
(>50 mm) at fast 3000 lines/s A-line rate. The Argos also features an “Analysis
mode” which allows the surgeons to verify the results obtained.
Shammas et al. reported good repeatability and reproducibility and comparability of
measurements obtained by Argos biometer, IOLMaster 500, and Lenstar LS900.[31]
The study was performed on 107 eyes. AL was correctly measured in 96% of cases
with the Argos compared with 79% for Lenstar and 77% for IOL Master 500.

14. ALADDIN
Aladdin [Figure] combines OLCR biometry with anterior
topography, Zernike corneal wavefront analysis, and
pupillometry in one instrument. Following are its important
advantages:
1.It provides information about corneal asphericity [Figure 8]
by mapping 24 Placido rings (on cornea) and analyzing 1024
data points using its real corneal radii technology. It provides
extensive information on status of anterior surface of cornea
including presence of corneal irregularities, common signs of
keratoconus, and information about higher-order aberrations
2. Dynamic pupillometry allows better assessment of lens
centration, constriction, and dilation of pupil in photopic
and mesopic conditions to assist in premium IOL selection.
3. Zernike wavefront analysis allows evaluation for higher-
order aberrations and corneal surface anomalies like
keratoconus
It contains inbuilt toric calculators – Barrett IOL Suite
and Abulafia–Koch regression formula
The 850-nm superluminescent diode allows the Aladdin to
penetrate even high-density cataracts

16. AL-SCAN(NIDEK)
This easy to use PCI-based biometer [Figure 9] uses an 830 nm IR laser diode for
AL measurement. It has following features:
1.It contains “3D autotracking” to track patient’s eye movements along the X, Y,
and Z planes. The “autoshot” feature allows device to capture the scan as soon as
it senses correct alignment
2.Topography and K with double mire rings help evaluate for aberrations. It
measures K at 36 points
3.It employs Scheimpflug imaging to measure CCT and ACD (a Scheimpflug
system images the anterior segment with a camera perpendicular to a slit beam,
thus creating an optical section of cornea and lens). It also provides data about
pupil position

17. GALILEIG6 LENSPROFESSIONAL
The Galilei G6 [Figure 10] combines OLCR optical biometry, dual-Scheimpflug
imaging, and Placido-disc topography. Some of its features are as follows:
1.It provides high-definition pachymetry and 3D anterior
chamber analysis
2.It measures total corneal wavefront, curvature, and K data of anterior as well as
posterior cornea, that is, provides complete data to plan cataract or refractive
surgery
3.Ray-traced posterior corneal surface data to detect bulging or asymmetry in late
stages
4.The combination of Scheimpflug imaging with optical biometry makes Galilei G6,
especially suitable for IOL selection in postkeratorefractive surgery eyes and also
(including keratoconus screening) of refractive surgery candidates. It is also helpful
in devising corneal implants and in planning and follow-up of keratoplasty patients
5.It includes newer IOL power formulas including Shammas No-History, Barrett
Universal, and Barrett True-K Toric calculator.
The comparability of biometric measurements and IOL power calculation between
IOLMaster 500 and Galilei G6 was studied by Ventura et al. They found similar
results

18. Figure 9: A Nidek AL Scan (AL-Scan, Nidek Co., Aichi,
Japan) biometry and phakic intraocular lens power
printout. AL = axial length, ACD = anterior chamber
depth, R1 = flattest radius of corneal curvature; R2 =
steep radius; 90° apart from r1
Figure 10: The Galilei G6optical biometer (Galilei G6, Ziemer. Port, Switzerland)

19. INTRAOCULAR LENS POWER FORMULAE
The first IOL power formula was published by Fyodorov andKolonko in 1967 and was based on schematic eyes.[45]
Several
IOLpower formulae are available at present.[46]
Important onesare tabulated below [Table 4].
Recently, Koch et al. suggested a new classification of IOL power formula (see below) based on (a) method of calculating
IOL power and (b) the data used for these calculations.[51]
1. Historical/refraction based
2. Regression analysis based: SRK, SRK-II
3. Vergence formulae (based on Gaussian optics)
a. Two variable
i. Holladay 1
ii. SRK-T
iii. Hoffer Q
b. Three variable
i. Haigis
ii. Ladas Super Formula
c. Five variable
i. Barrett Universal II
d. Seven variable
i. Holladay 2
4. Artificial Intelligence based
a. Hill-RBF
b. Clarke neural network
5. Ray tracing
a. Okulix
b. PhacoOptics.

20. BARRETT UNIVERSAL II (BARRETT U2)
The formula is called Universal because it is suitable for all types of eyes: short, medium, or long and also for different
lens styles. This formula is based on a theoretical model of eye in which ACD is related to AL and K.[53]
In this formula,
ELP is characterized by ACD and LF (lens factor). The LF isinfluenced by K, AL, ACD, LT, and WTW in that order. This
formula also takes into account the negative value of LF in calculating ELP in the presence of negative-powered type of
IOL. The Barrett U2 formula can be openly accessed on www.apacrs.org. Following are the features of Barrett Universal II
formula:
a. Accurate for all eyes regardless of AL
b. Essential variables required for calculation are AL, K, optical ACD, and desired postoperative refraction.
Optional variables required are LT and WTW
c. Lens factor or “A constant” of the selected IOL is required.If not available, ULIB “A constant” of SRK/T formula is
recommended (ULIB is the User Group for Laser Interference Biometry)
d. AL and K data from optical biometer (for example, IOLMaster, Lenstar) is required for calculation. However,
immersion biometry data may also be used. Since optically measured AL is different from the US measured AL,
acoustic A constant will fail to give optimum results when used with optical biometry. Therefore, when AL
obtained by US biometry is usedin Barrett formula, an appropriate A-constant must be used (This requires pre‑ and
post‑operative clinical data and is done on a spreadsheet form in MS Excel format which can be downloaded from
the ULIB website ocusoft.de/ulib/)
e. Barrett U2 is able to predict for highly myopic eyes and
negative powered IOLs without specialized constants or
AL modification.

24. HOLLADAY 2
In 1993, Dr. Holladay led a worldwide study involving 34 cataract surgeons to determine which of the 7 variables were
relevant as predictors of ELP.[52]
Surprisingly, horizontal WTW measurements emerged as the next most important variable
after AL and K. It was also proved that there is almostno correlation between AL and size of anterior segment in 80%–90%
of the eyes [Table 6]. This led to the concept of nine types of eyes – not just three (short, medium, or long).
These results led to the formulation of Holladay 2 formula, aneasy‑to‑use program, in which 7 variables (AL, K, ACD, LT,
WTW, age of patient, and previous refraction) are inserted forcalculation of ELP and appropriate IOL power.
This newer formula is a great choice for nearly every eye.[54]
It is a complete software package that not only allows
IOL powercalculation in many different types of eyes but also honing ofindividual results by personalizing theA-
constant.This formulais available as part of Holladay IOL Consultant/Surgical OutcomesAssessment Program
(HIC‑SOAP, available at www.hicsoap.com). It is a paid software.
HILL‑RADIAL BASIS ACTIVATION FUNCTION (RADIAL BASIS ACTIVATION FUNCTION ONLINE
CALCULATOR)
The new Hill-RBF method [Figure 11] is an advanced, self-validating method for IOL power selection. It was
launched in 2016. It is purely “data driven,” independentof ELP and has no data bias. RBF method uses
artificial intelligence-driven pattern recognition and sophisticated data interpolation. RBF algorithms are used
globally in a variety of technologies such as facial recognition software and thumbprint security scanners. A
special feature is that it

25. the user the reliability of result, that is, the software can tell whether it is likely to be correct or whether it is unsure about
the calculated IOL power. The older version of Hill RBF online calculator used data from 3400 eyes with a wide rangeof
preoperative ocular parameters. The RBF calculator has been updated in 2017 and includes data from 12400 eyes. The data
for normal eyes have been increased by about 7000 eyes.Atotal of 1000 exceptionally short eyes and axial myopia withIOL
power up to -5D have now been included in the latest version. In addition, a target other than plano can be set (e.g.,
surgeon can aim for slight myopia and calculate the requiredIOL power accordingly).
The Hill-RBF is the product of the efforts of Dr. Warren Hilland his team which included engineers from
MathWorks, and 39 investigators from over 17 countries. The Hill‑RBFis incorporated in Lenstar Eye Suite
and is also availableto ophthalmologists globally as an open access web-based calculator
(rbfcalculator.com/online). The uniqueness of Hill-RBF lies in the fact that greater the number of surgical
outcomes that are fit into the model, greater the accuracy
Figure 11: The new Hill‑RBF method is an advanced, self‑validatingmethod for IOL power selection

27. INTRAOCULAR LENS POWER CALCULATION IN HIGH TO
EXTREME MYOPIA
High myopia is one of the most prevalent refractive conditionsglobally with a high risk of other associated eye conditions.[55-57]
Patients of axial myopia (AL >25 mm) are at risk of suboptimalrefractive outcome after cataract surgery.[58]
The single most
important consideration in this setting is to avoid unanticipatedpostoperative hyperopia. Several authors have reported that
AL measured by the optical biometry is more precise than theUS in an eye with posterior staphyloma.[59,60]
Second, the use
of third-generation formulae may lead to incorrect IOL powercalculation resulting in unsatisfied patient postoperatively.
In their landmark article, Wang et al. suggested that modification of AL is required to calculate IOL power with the
SRK-T, Holladay 1 and 2, Haigis and Hoffer Q formulas in eyes with AL >25.2 mm.[61]
They looked at IOLs (IOL
power thatwas required to be implanted) in 2 groups – power >5D and power 5D or less. In both the groups, it was
found that adjustingAL significantly reduced the incidence of postoperative hyperopia. The idea behind the AL
modification is that whenthe original AL is fed into the Wang-Koch’s formula [Table 7],a value lower than the
original AL value is calculated. Whenthis lower AL value is reinserted into the formulae, an IOL power of higher
dioptric value is obtained. This, in turn, eliminates the risk of postoperative hyperopia. However, theWang‑Koch
modification may be less accurate in very low power/negative lenses.
FULLMONTE INTRAOCULAR LENS 2.0
The FullMonte IOL software system is a new adaptive, optimizing process based on Markov Chain Monte Carlo
process. It is nota formula, rather a computing process which combines moderntheoretical formulas (SRK/T,
Holladay I, Haigis etc.) with surgeon’s own postoperative refractive record to provide not asingle value of IOL
power for emmetropia but expected refraction as a graph of probability distributions. The software continuously
optimizes itself, adapting to several factors such as short eye/long eye, cases of unique anatomy, or postrefractive
patients.

28. INTRAOPERATIVE WAVEFRONT ABERROMETRY
One of the latest developments in the field of cataract surgery is intraoperative wavefront aberrometry. It can
perform aphakic and pseudophakic refractive measurements in the operating room on the eye being operated,
thus providing real-time intraoperative refractive information. This allows surgeon to confirm or revise the IOL
power (calculated through preoperative biometry), optimize the lens location, and tailor arcuate corneal incisions
to the eye’sastigmatic requirements

29. OPTIWAVE REFRACTIVE ANALYSIS SYSTEM WITHVERIFEYE
ORange wavefront aberrometry system (WaveTec Vision Systems, Inc.) was the first commercially available
intraoperative wavefront aberrometer. It has now been replaced by the Optiwave Refractive Analysis (ORA) system
[Figure 12]. ORA utilizes IR light and Talbot Moire interferometry, a system in which two gratings are set at a specific
angle and distance to produce a fringe pattern as wavefronts are diffracted through the grates.[74]
This fringe pattern is then
analyzed to provide information on sphere, cylinder, and axis to guide proper IOL selection (including premium IOLs) as
well as placement. ORange is attached to asurgical microscope and aphakic, and pseudophakic refractionsare performed in the
operating room. It takes 40 measurementsin less than a minute.
It has a special role in toric IOL implantation. The device shows promise particularly in postrefractive surgery eyes and
eyes at the extremes of AL spectra. By providing real-time data to surgeons during cataract surgery, the intraoperative
aberrometer allows an unprecedented precision.
ORA has revolutionized premium cataract surgery practice, and some surgeons use it in all their toric, multifocal, and
accommodative IOLs in addition to using it as a guide for intraoperative astigmatic keratotomy. Another situation where
ORA is useful is in postrefractive surgery patients.
However, there are some drawbacks as well. It has a learningcurve. Dr. Mahdavi conducted a survey which
revealed that it took 20% of the 101 respondents >100 cases to feel comfortable with ORA. It also prolongs the
surgical time by up to 5–6 min

30. HOLOS
Another intraoperative aberrometer is HolosIntraOp [Figure 13a and b] by Clarity. It utilizes rapidly
rotating microelectromechanical mirror and quad detector to measuremagnitude of wavefront displacement. Like
the ORA, Holosgathers optical wavefront and refraction data intraoperativelyto verify the preplanned IOL
power and helps choose thesize and location of incisions to correct astigmatism.[77]
Upto 90 measurements
second are taken per second. Like the ORA, it is attached to operating microscope for intraoperativerefractive
measurements

31. THE FUTURE OF INTRAOCULAR LENS POWERCALCULATION
TheUniversintraocularlenscalculator
TheUniversIOLwasdevelopedbyDr.SamirSayeghetal.[78]
Itisaweb-basedcalculatorwhichcombinesallthe
high-qualitythird and fourth generation formulae with a toric IOL calculator.Itdoesnotproposeanew
formula.ThesurgeoncanuseoneoracombinationofformulaforIOLpowercalculationtoachieveoptimum
results.Thecalculatoralsotellshowmuchtheformuladiffersfromeachothersothatthesurgeonhasanidea
howcloses/hewillbetothetarget.Thecalculatoralso

32. OKULIX
OkulixisanewerIOLformulacalculationprogramthatisbasedontheprincipleof“ray-tracing.”Itintroduces
theconceptof“truegeometricalposition”ofIOLandusesanteriorandposteriorcentralcurvatureradii,
asphericityofIOLsurfaces,centralIOLthickness,andindexofrefractiontodescribeIOLposition.[79]
Itmayfind
particularuseintoricandphakicIOLsandIOLpowercalculationinpostkeratorefractivesurgeryeyes

33. CONCLUSION
IOLpower calculation in normal and complex eyes has evolved significantly in the last two decades. With ever‑evolving lens
designs and increasing patient expectations, performing the best possible measurements is the key for successful surgery
with good refractive results and a satisfied happy patient. The latest biometry technologies armed with newer IOLpower
calculation formulae have become necessary tools forthe refractive cataract surgeon. With current biometers and newer
formulae expecting outcomes in the range of ±0.50D has become a reality in majority of the patients. However, attainment
of target postoperative refraction is still not a reality in all cases (such as irregular corneas and postkeratorefractivesurgery
eyes) and further research is required in this direction.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.

34. REFERENCES
1. Drexler W, Findl O, Menapace R, Rainer G, Vass C, Hitzenberger CK, et al. Partial coherence interferometry: A novel approach to biometry in
cataract surgery. Am J Ophthalmol 1998;126:524‑34.
2. Chen YA, Hirnschall N, Findl O. Evaluation of 2 new optical biometry devices and comparison with the current gold standard biometer.J
Cataract Refract Surg 2011;37:513-7.
3. Rohrer K, Frueh BE, Wälti R, Clemetson IA, Tappeiner C, Goldblum D. Comparison and evaluation of ocular biometry using a new noncontact
optical low‑coherence reflectometer. Ophthalmology 2009;116:2087‑924.
4. Németh J, Fekete O, Pesztenlehrer N. Optical and ultrasound measurement of axial length and anterior chamber depth for intraocular lens power
calculation. J Cataract Refract Surg 2003;29:85‑8.
5. Holladay JT. Ultrasound and optical biometry. Cataract Refract Surg Today Europe 2009 (November/December); Mini Focus on Diagnostics; p.
18‑19.
6. Murphy GE, Murphy CG. Comparison of efficacy of longest, average, and shortest axial length measurements with a solid-tip ultrasoundprobe in
predicting intraocular lens power. J Cataract Refract Surg 1993;19:644‑5.
7. Haigis W. Pseudophakic correction factors for optical biometry. Graefes
Arch Clin Exp Ophthalmol 2001;239:589‑98.
8. Khurana AK. Intraocular lenses: Optical aspects and power calculation. Theory and Practice of Optics and Refraction: 2nd
ed, Ch. 9. Elsevier
publications.
1. Naeser K, Naeser A, Boberg‑Ans J, Bargum R. Axial length following implantation of posterior chamber lenses. J Cataract Refract Surg
1989;15:673‑5.
2. Pitault G, Leboeuf C, Leroux les Jardins S, Auclin F, Chong-Sit D, Baudouin C, et al. Optical biometry of eyes corrected by phakic intraocular
lenses. J Fr Ophtalmol 2005;28:1052-7.
3. Ikuno Y, Tano Y. Retinal and choroidal biometry in highly myopic eyeswith spectral-domain optical coherence tomography. Invest OphthalmolVis
Sci 2009;50:3876‑80.
4. Yasuno Y, Miura M, Kawana K, Makita S, Sato M, Okamoto F, et al. Visualization of sub-retinal pigment epithelium morphologies of exudative
macular diseases by high-penetration optical coherence tomography. Invest Ophthalmol Vis Sci 2009;50:405‑13.
5. Pierre Kahn V, Quoc EB, Chauvaud D, Renard G. Axial length measurement in silicone oil filled eyes using optical biometry. Invest Ophthalmol
Vis Sci 2005;46:5543.
6. Wilson ME, Trivedi RH. Axial length measurement techniques in pediatric eyes with cataract. Saudi J Ophthalmol 2012;26:13-7.
7. Kielhorn I, Rajan MS, Tesha PM, Subryan VR, Bell JA. Clinicalassessment of the Zeiss IOLMaster. J Cataract Refract Surg 2003;29:518‑22.
8. Hoffer KJ, Shammas HJ, Savini G. Comparison of 2 laser instruments for measuring axial length. J Cataract Refract Surg 2010;36:644-8.
9. Akman A, Asena L, Güngör SG. Evaluation and comparison of the newswept source OCT-based IOLMaster 700 with the IOLMaster 500. Br J
Ophthalmol 2016;100:1201-5.
10. Sheng H, Bottjer CA, Bullimore MA. Ocular component measurement
using the Zeiss IOLMaster. Optom Vis Sci 2004;81:27‑34.
11. Connors R 3rd
, Boseman P 3rd
, Olson RJ. Accuracy and reproducibility of biometry using partial coherence interferometry. J Cataract Refract Surg
2002;28:235-8.
12. Fercher AF, Roth E. Ophthalmic laser interferometer. Proc SPIE
1986;658:48‑51.
13. Haigis W, Lege B, Miller N, Schneider B. Comparison of immersion ultrasound biometry and partial coherence interferometry for intraocularlens
calculation according to Haigis. Graefes Arch Clin Exp Ophthalmol2000;238:765-73.
14. Hill W, Angeles R, Otani T. Evaluation of a new IOLMaster algorithm
to measure axial length. J Cataract Refract Surg 2008;34:920‑4.
15. Packer M, Fine IH, Hoffman RS, Coffman PG, Brown LK. Immersion A-scan compared with partial coherence interferometry: Outcomes analysis.
J Cataract Refract Surg 2002;28:239‑42.
16. Bhatt AB, Schefler AC, Feuer WJ, Yoo SH, Murray TG. Comparison of predictions made by intraocular lens master and ultrasound biometry. Arch
Ophthalmol 2008;126:929‑33.
17. Tehrani M, Krummenauer F, Blom E, Dick HB. Evaluation of the practicality of optical biometry and applanation ultrasound in 253 eyes.J Cataract
Refract Surg 2003;29:741‑6.
18. Freeman G, Pesudovs K. The impact of cataract severity on measurement acquisition with the IOLMaster. Acta Ophthalmol Scand
2005;83:439‑42.
19. Vogel A, Dick HB, Krummenauer F. Reproducibility of optical biometry using partial coherence interferometry: Intraobserver and interobserver
reliability. J Cataract Refract Surg 2001;27:1961‑8.
20. Srivannaboon S, Chirapapaisan C, Chonpimai P, Loket S. Clinicalcomparison of a new swept-source optical coherence tomography-basedoptical
biometer and a time-domain optical coherence tomography-basedoptical biometer. J Cataract Refract Surg 2015;41:2224-32.
21. Rohrer K, Frueh BE, Wälti R, Clemetson IA, Tappeiner C, Goldblum D,et al. Comparison and evaluation of ocular biometry using a newnoncontact
optical low‑coherence reflectometer. Ophthalmology 2009;116:2087‑92.
22. Holzer MP, Mamusa M, Auffarth GU. Accuracy of a new partial coherence interferometry analyser for biometric measurements. Br J Ophthalmol
2009;93:807‑10.
23. Shammas HJ, Ortiz S, Shammas MC, Kim SH, Chong C. Biometry measurements using a new large-coherence-length swept-source optical
coherence tomographer. J Cataract Refract Surg 2016;42:50-61.
24. Srivannaboon S, Chirapapaisan C, Chonpimai P, Koodkaew S. Comparison of ocular biometry and intraocular lens power using