2023.08.04.28
Files > Volume 8 > Vol 8 no 4 2023
Comparison of ocular biometry and intraocular lens power using a novel biometer and a traditional biometer
Makarem Ali Hussain Alshammari
1* Siham sabah Abdullah Al
Muhammad2
1
Al-Imam al-Sadiq Hospital.Iraq
2
Al-Nahrain Medicine Hopital. Iraq
*Corresponding authors: Email [email protected]
Available from: http://dx.doi.org/10.21931/RB/2023.08.04.28
ABSTRACT
The implantation of an
intraocular lens (IOL) is the gold standard in today's cataract surgery.
Calculating the power of the intraocular lens (IOL) has emerged as a central
concern in cataract surgery over the last decade. The study aims to investigate the relationship between
optical biometry and applanation
ultrasound measurement of the eye's axial length.
This prospective cohort study was done on 60 eyes from sixty patients
undergoing phacoemulsification with primary intraocular lens implantation and
scheduled for cataract surgery in the Ophthalmology Department of al-Imam
al-Sadeq Hospital. Thirty eyes of patients were measured by ultrasound measurement
(by A-Scan, Group 1) and the other thirty eyes by optical biometry (by IOL
Master, Group 2). In Group 1There were 14 eyes of 14 males (47%) and 16 eyes of
16 females (53%) with a mean age was 71.6 ±4.33years. In Group 2, there were 16
eyes of 16 males (53%) and 14 eyes of fourteen females (47%), and the mean age
of the patients in this Group was 66.13±8.61 years. The mean IOL of the patient
in Group I was (19.96±1.81). At the same time, the mean IOL potent ion of the
patient in Group II was (22.96±1.66).
Keywords:
Optical Biometry, Ultrasound Biometry, Intraocular lens (IOL),
IOL Master
partial coherence interferometry (PCI)
INTRODUCTION
Calculating the intraocular lens (IOL) is an essential step in
getting the precise aim that includes the refractive outcome and is a vital
objective in recent cataract surgery1.
Modern cataract surgery is a refined procedure that enables most patients to
achieve high-quality postoperative vision. However, postoperative refractive
outcomes remain a significant area of concern for surgeons due to advancements
in surgical technique, new lOL technologies, improved biometric methods, and
advanced methods of IOL power calculation 2.
Refractive error is no
longer acceptable following cataract surgery due to improvements in technology
for cataract surgery and the launch of distinctive intraocular lens implants.
Consequently, precise biometric readings must be obtained for undistorted
vision following surgery3.
Innovations like intraocular lens (IOL) power prediction
algorithms, phacoemulsification, and ocular biometry have significantly
improved the refractive result of cataract surgery during the last fifty years4.
This result depends on precisely predicting the implanted IOL's power, which
relies primarily on preoperative biometry data, IOL power calculation methods,
and manufacturer IOL power quality control. The most critical step for
accurately calculating the IOL power is the preoperative measurement of the
ocular axial length (AL)5.
A-scan
ultrasonography, with a reported longitudinal resolution of approximately 200
μm and an accuracy of approximately 100–150 μm, is routinely employed to
measure the ocular axile length AL. However, due to varying pressures
the transducer exerts on the eye during applanation ultrasonography, which is
often employed for ocular biometry, ultrasound biometry necessitates physical
contact between the transducer and the eye 6. A postoperative refractive error of 0.28 diopters (D) is caused
by an AL shortening of 0.1 mm in ultrasound biometry, and measurement errors in
the AL have been shown to account for 54% of the expected refraction errors
following IOL implantation.7 Recently, the IOL Master optical
biometry device was created for commercial use based on the dual beam partial coherence interferometry (PCI) concept. The optical AL is measured using short-coherence
infrared light (= 780 nm), and the geometric AL is then calculated using the
group refractive index8. Additionally, it evaluates the corneal
curvature, the anterior chamber depth, and the corneal diameter. Then, it
determines the best IOL power using the biometry data it has collected and
several IOL power calculation algorithms that are part of its computer
software. The IOL master's AL measures have exceptional precision, resolution,
accuracy, and consistency 9.
In
our study. We will look at the main factors that may affect the accuracy of
refractive error prediction, how this residual error affects outcomes after
surgery, and whether refractive outcomes improve with the new intraocular lens.
All
the patients underwent the following procedures: The information was gathered
throughout the history-taking process: age, gender, domicile, and particular
habits of the patients or their families. Relations, major complaint (painless
progressive loss of eyesight), and examination of the complaint (onset, course,
and duration). The Snellen visual acuity chart was completed for every patient
before surgery. Preoperatively, patients received autorefraction, keratometry
(K) and axial length measurement. Ultrasound B scans were performed on patients
with dense media opacity and obscured fundus visibility. Non-cycloplegic
autorefraction and fundus inspection were also performed. Assessment from the axial
length of the eye included: Group I (Ultrasound A scan group, 30 eyes) had
axial length measurements by A-scan ultrasound and K readings by manual
keratometer. An optometrist does a scan-guided biometry. An accurate
keratometric measurement is the first step in predicting IOL power. Next, the
axial length was measured using the contact A-scan biometry. The patients were
prepared by instilling one drop of tropicamide (mydriacil) 1%, then one drop of
surface anesthesia in the form of benoxinate hydrochloride 0.4% was dropped
into the patient's eye. The data, including two keratometrics (K1, K2) and the
average axial length plus a constant of IOL, were introduced in the calculating
program of the optometrist. The intraocular lens power was based on the SRK/T
formula, and all patients underwent uncomplicated cataract surgery by
phacoemulsification within the bag IOL implantation through an interim precise
corneal incision.
Statistical Methodology
Data analysis was carried out using the statistical package of
Statistical Package for Social Sciences- version 25 (SPSS-25). Data were
presented in simple percentages, mean, and standard deviation measures. The
significance of the difference of different means (quantitative data) was
tested using the student's test for the difference between two unpaired tests.
Scattering distribution curve used for correlation. Statistical significance
was considered whenever the p-value was equal to or less than 0.05
RESULTS
Group 1 (A-scan ultrasound biometry group) Included 30 eyes subjected
to biometry with A-Scan ultrasound biometry. There were 14 eyes of 14 males
(47%) and 16 eyes of 16 females (53%). The mean age was 71.6 ± 4.33 years.
Group 2 (Optical biometry (IOL Master group)) Included 30 eyes subjected to
biometry with IOL Master Optical biometry. There were 16 eyes of 16 males (53%)
and 14 eyes of fourteen females (47%), and the mean age of the patients in this
Group was 66.13 ± 8.61 years. Also, a total of 60 eyes of 60 patients were
enrolled in our study (eyes in 30 females (50%) and eyes in 30 males (50%).
Group I: 14 eyes of 14 males (47%) and 16 eyes of 16 females (53%), and Group
II: 16 eyes of 16 males (53%) and 14 eyes of fourteen females (47%), as shown
in (table 1).
Table
1. Characteristics of Patients
The mean axial length of the patient in Group I was (22.55 ± 0.83
mm)
while II was (23.021 ± 0.71 mm) Also, the mean k1 reading of the
patient in Group I was (44.1 ± 1.71) Diopter. While Group II was (44.68 ± 0.88)
Diopter. Additionally, group I had a mean k2 reading of the patients as (44.81
± 1.76) Diopter, and Group II had a mean k2 reading of the patients (45.45 ±
0.83) Diopter. Group I had a mean k reading of the patient of (44.45 ± 1.72)
Diopter, whereas Group II had a mean of (45.07 ± 0.82) Diopter, as shown in
(table 2).
Table 2. The Axial Length and K reading distribution parameters
between Ultrasound (US) and optical Biometry (OB)
Figure 1. Comparison between
ultrasound (US) and optical biometry (OB) for Axial Length (AL).
The mean ACD of the patient in Group I was (2.93 ± 0.29) while, in
Group, it was (3.21 ± 0.51) Also, the mean IOL of the patient in Group I was
(19.96 ± 1.81) Whereas the mean IOL strength of the patient in Group II was
(22.96 ± 1.66) Also, the mean lens thickness in Group I was (3.76 ± 0.78) While
in Group II was (4.31 ± 0.41).
The spherical desired refraction of the patient in Group I was (-0.74 ± 0.04), and in
Group II was (-0.91 ± 0.058) and achieved
refraction of the patient in Group I
(-1.12
± 0.02) Moreover, in Group II, it was (-1.05 ±0.01), as shown in (table 3).
Table 3. The Anterior Chamber Depth (ACD), Lens Thickness (LT), and
the intraocular lens (IOL).
Intraocular lens (IOL) measuring is crucial
in modern cataract surgery to achieve the desired refractive outcome. The
primary goal of cataract surgery is to restore clear vision by removing the
cloudy lens and replacing it with a clear artificial lens. The correct power of
the IOL is essential to achieve the desired refractive outcome and provide the
patient with optimal visual acuity.
Various technologies and formulas are available to accurately estimate
the IOL power required for the desired refraction. Scan ultrasonography is the
most commonly used method for measuring the ocular axial length (AL)14.
However, modern technology and optical biometry have significantly improved our
ability to accurately measure visual axial length (AL). The study included 60 eyes of 60 patients,
with cataracts as the only ocular pathology and axial lengths less than 24.50
mm. The study group comprised 30 females (50%) and 30 males (50%). The patients
were divided into two groups, with 30 patients implanted with an IOL calculated
by the IOL master and 30 patients by ultrasound. The postoperative visual and refractive
outcomes were evaluated in both groups. The patients implanted with the IOL
calculated by the IOL master had a postoperative spherical refraction ranging
from 0.01 to 1.05. In contrast, those implanted with an ultrasound had a
postoperative spherical refraction ranging from 0.02 to 1.12. The results
showed that the axial length measurements by optical biometry were 0.47 mm
longer than those by A-scan ultrasonography (P<0.001). These findings are consistent with other
studies that have reported similar differences. The most significant
contributor to this disparity is the pressure the ultrasound probe exerts on
the eye. Therefore, optical biometry is preferred over A-scan ultrasonography,
as it provides more accurate measurements and reduces the risk of error. In conclusion, accurate IOL measurement is
essential for achieving the desired refractive outcome in cataract surgery.
Advances in technology and formulas have improved our ability to measure ocular
axial length accurately. Optical biometry is the preferred method for measuring
axial length over A-scan ultrasonography due to its accuracy and reduced risk
of error. When measuring the length of
the eye, there are two main methods: ultrasound and optical biometry. Both
methods have their advantages and limitations.
Ultrasound emits sound waves that penetrate the eye and bounce back to
create an image.15 This image can then be used to measure the length
of the eye. However, ultrasound has limitations in terms of accuracy and
resolution. The accuracy of axial length with ultrasound is approximately
0.10–0.12 mm compared to 0.012 mm for optical biometry. This is because
ultrasound is reflected mainly at the internal limiting membrane (ILM), while
the light of the optical biometry is reflected at the retinal pigment
epithelium (RPE). This results in a difference corresponding to the retinal
thickness of the fovea, which is about 130 μm.
On the other hand, optical biometry uses laser light to measure the length
of the eye. Laser light has a very short wavelength compared to sound, which
means it has better resolution.16 The light of the optical biometry
is reflected at the RPE, which allows for a more accurate measurement of the
length of the eye. However, the accuracy
of both methods is limited by retinal thickness variation surrounding the
fovea. A precise preoperative calculation is necessary to attain the most
desirable results, and an exact IOL power formula must be employed. The
refractive power of the human eye depends on the strength of the cornea
keratometry (K) values, the axial length of the eye (AL), and the position of
the lens. Therefore, the best refractive outcomes after surgery depend on
accurately evaluating these factors. Patients
may have a severe refractive error if these biometric measures and computations
are wrong. This is why it is important for eye surgeons to carefully consider
the measurement method and accurately evaluate the factors that contribute to
the eye's refractive power. Doing so can ensure that their patients have the
best possible outcomes after surgery.
Intraocular lens implantation is a common surgical procedure used to
replace the natural eye lens with an artificial one. The success of this
surgery depends on accurate measurements of the eye's dimensions, including
axial length and keratometry readings. These measurements help determine the
appropriate size and power of the intraocular lens to be implanted, which
affects the patient's postoperative vision.
Unfortunately, these measurements can lead to significant refractive
errors after surgery, negatively impacting the patient's visual acuity and
quality of life. According to recent studies, errors in assessing the
influential lens position (ELP) are responsible for most of these postoperative
refractive errors. Incorrect ELP assessment accounts for 38% of these errors,
while keratometry error accounts for only 8%. This highlights the importance of
accurate ELP assessment in achieving optimal refractive outcomes after intraocular
lens implantation.17 One way to improve the accuracy of these
measurements is through optical biometry, which measures axial length using
light instead of sound waves. Studies have shown that optical biometry is more
accurate than traditional A-scan ultrasound measurements, with the IOL Master
measuring axial length 0.47 mm longer than A-scan measurements. This difference
was statistically significant, indicating that optical biometry may be a more
reliable method for measuring axial length.
However, not all studies have shown a significant difference between
optical biometry and A-scan ultrasound measurements. In a recent study, GAD et
al. found that the difference in axial length measurements between these two
methods was only 0.34 mm, which was not statistically significant. This
suggests that the choice of measurement method may depend on individual patient
factors and the surgeon's preference.
Similarly, studies have shown varying results when comparing keratometry
readings obtained through different methods. In our study, we found that the
mean average K reading (Kav) measured by a keratometer used with A-scan was
44.45±1.72 D, while the mean Kav measured by the IOL Master was 45.07±0.82 D.
This difference was statistically significant, indicating that the choice of
keratometry method may also affect postoperative refractive outcomes. In conclusion, accurate assessment of axial
length and keratometry readings is crucial for achieving optimal refractive
outcomes after intraocular lens implantation. While optical biometry may be a
more accurate method for measuring axial length, the choice of measurement
method may depend on individual patient factors and surgeon preference.
Similarly, the keratometry method may also affect postoperative refractive
outcomes. Further research is needed to determine the most reliable methods for
these measurements and to improve the success rate of intraocular lens
implantation surgery. Corneal power
measurement is a crucial step in determining the appropriate intraocular lens
(IOL) power for cataract surgery. In recent years, there has been a shift
towards using optical biometry, such as the IOL Master, to measure corneal
power rather than traditional ultrasound techniques. This is due to the greater
accuracy and precision of the IOL Master, which measures corneal power using a
six-point measure on a smaller diameter circle than traditional ultrasound
techniques. The bell-shaped cornea is a
unique feature that must be considered when measuring corneal power. As the
cornea flattens towards the eye's periphery, measurements taken with an
auto-keratometer using a ring 3 millimeters in diameter centered on the cornea
may not provide the most accurate results. The IOL Master's more central
measurement approach better accounts for the cornea's shape and produces more
clinically relevant results. A recent
study found that the IOL power measured by the IOL Master was significantly
more substantial than ultrasound techniques. This difference was statistically
significant and highlights the importance of using optical biometry for
measuring corneal power. However, other studies have found discrepancies
between the IOL Master and other measurement techniques, such as the A-scan,
which provided more extraordinary IOL powers.
Despite these discrepancies, the SRK-T formula remains widely used and
reliable for calculating IOL power. More accurate and precise methods for
measuring corneal power will likely emerge as technology advances. In the
meantime, using the most reliable and clinically relevant techniques available
to ensure successful outcomes for cataract surgery patients is essential. The anterior chamber depth (ACD) measurement
has long been a crucial step in ocular biometry. Traditionally, this
measurement was taken using actual measurements of the ACD, which were based on
assumptions that short eyes would have shallower ACDs and long eyes would have
deeper ACDs. However, this method was not entirely accurate and often resulted
in errors in estimating intraocular lens (IOL) power, leading to poor
postoperative refractive outcomes.
Fortunately, advancements in technology have significantly contributed
to simplifying the ocular biometry procedure. One such advancement is the
IOLMaster, a non-contact approach that does not require topical anesthetic.
This provides comfort to the patient and reduces the risk of corneal abrasions
and spreading infections. Optical
biometry, using Swept-source OCT, like the IOLMaster, provides a measurement
based on an image that enables the operator to observe a whole longitudinal eye
segment. The operator can monitor the fovea's picture and be warned if the
patient is not appropriately fixating. This alerts the operator to any
irregular eye geometries, such as lens tilt, allowing for more precise
estimations of the IOL power and ultimately resulting in improved postoperative
refractive conditions. In addition to
measuring the ACD, the IOLMaster is now taking the place of ultrasonography in
measuring the axial length (AXL). It offers rapid data capture and the ability
to measure the AL along six distinct axes, making it a more efficient and
accurate biometry method. Despite technological
advancements, however, ultrasonic biometry cannot be ruled out entirely, as
some eyes, anywhere from 8% to 10% of cases, continue to require it. Therefore,
a combination of various biometry methods may be necessary to ensure accurate
and reliable measurements for successful cataract surgery outcomes. Various factors can often hinder the
collection of accurate optical AXL data. One such factor is corneal scarring,
which can cause opacity in the cornea, making it difficult to obtain clear
measurements. Similarly, opaque cataracts can impede the collection of optical
AXL data, as they can obstruct the visual axis and prevent the instrument from
accurately measuring the length of the eye.
Another factor that can lead to erroneous AXL measurements is poor
fixation, particularly in cases where the patient suffers from age-related
macular degeneration. In such cases, the patient may be unable to maintain
optimum fixation, leading to inaccurate readings. 18 Moreover,
positioning disabled patients on the IOL Master machine can be a challenging
task that requires special consideration. Such patients may have physical
limitations that make it difficult to assume the required position for the
instrument to take accurate measurements. As such, special measures must be
taken to ensure that these patients are comfortably and safely positioned on
the machine without compromising the accuracy of the AXL measurements. In conclusion, collecting optical AXL data
can be a complex process that requires careful consideration of various factors.
By understanding the potential challenges during the process, medical
professionals can take the necessary precautions to ensure that accurate
measurements are obtained and that patients receive the best possible
care.
The
IOL Master is a cutting-edge technology that has revolutionized the field of
ophthalmology. With its simple and easy-to-use interface, the IOL Master has
become a favorite among eye care professionals for its ability to measure the
eye's axial length precisely, which is crucial for accurate intraocular lens
(IOL) power calculations. Unlike
traditional methods of measuring the eye, the IOL Master does not require the
patient to make eye contact, which is especially helpful for those with
difficulty with eye movements or limited mobility. Additionally, the IOL Master
is entirely safe and eliminates the risk of transmitting diseases through
contact, making it an ideal tool for use in any healthcare setting. One of the most significant advantages of
the IOL Master is its ability to provide more accurate IOL power calculations.
By taking precise measurements of the eye's axial length, the IOL Master helps
ensure that the IOL selected for a patient has the correct power and size,
resulting in improved postoperative refractive conditions. This means patients
can enjoy better visual acuity and enhanced quality of life after cataract
surgery. Overall, the IOL Master is a
powerful tool that offers numerous benefits for patients and eye care
professionals. Its ease of use, safety, and accuracy make it an invaluable
asset in diagnosing and treating eye conditions. As technology continues to
evolve, the IOL Master will remain at the forefront of ophthalmic innovation
for years.
1. Committee MSA. Optical Biometry Using Partial Coherence
Interferometry Prior to Cataract Surgery. Canberra Dep Heal Aging. 2005;
2. Abdelghany AA, Alio JL. Surgical options
for correction of refractive error following cataract surgery. Eye Vis.
2014;1(1):1–7.
3. Olsen T. Calculation of intraocular lens
power: a review. Acta Ophthalmol Scand. 2007;85(5):472–85.
4. Findl O,
Drexler W, Menapace R, Heinzl H, Hitzenberger CK, Fercher AF. Improved
prediction of intraocular lens power using partial coherence interferometry. J
Cataract Refract Surg. 2001;27(6):861–7.
5. Steinert RF.
Cataract surgery: Expert Consult-Online and Print. Elsevier Health Sciences;
2009.
6. Byrne SF,
Green RL. Ultrasound of the eye and orbit. Mosby Incorporated; 2002.
7. Santodomingo-Rubido
J, Mallen EAH, Gilmartin B, Wolffsohn JS. A new non-contact optical device for
ocular biometry. Br J Ophthalmol. 2002;86(4):458–62.
8. Gaballa SH,
Allam RSHM, Abouhussein NB, Raafat KA. IOL master and A-scan biometry in axial
length and intraocular lens power measurements. Delta J Ophthalmol.
2017;18(1):13.
9. Eleftheriadis
H. IOLMaster biometry: refractive results of 100 consecutive cases. Br J
Ophthalmol. 2003;87(8):960–3.
10. Elsaadani AEI,
Badawi NM, Elterawy AZA. Optical biometry versus ultrasound biometry. Egypt J
Hosp Med. 2020;81(5):2088–92.
11. Alpins NA,
Walsh G, Optom В. accurate biometry and intraocular lens power calculations.
Refractive Surgery Nightmares-Conquering Refractive Surgery Catastrophes. Slack
Inc; NJ; 2008. p. 581–5.
12. 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(4):524–34.
13. Iyamu E,
Osuobeni E. Age, gender, corneal diameter, corneal curvature and central
corneal thickness in Nigerians with normal intraocular pressure. J Optom.
2012;5(2):87–97.
14. Gad MN, Mourad
MS, Rehan RA, Mustafa MM. Intraocular lens Master optical biometry vs
conventional ultrasonic biometry in intraocular lens power calculations in
highly myopic vs emmetropic eyes. J Egypt Ophthalmol Soc. 2020;113(2):39.
15. Moon SW, Lim
SH, Lee HY. Accuracy of biometry for intraocular lens implantation using the
new partial coherence interferometer, AL-scan. Korean J Ophthalmol.
2014;28(6):444–50.
16. Meena DS,
Sukhadia H, Goyal S, Kumar V. Compare the Accuracy of IOL Power Calculations
Using Ultrasound Biometry and Partial Coherence Laser Interferometry based
Optical Biometry. Indian J Forensic Med Toxicol. 2021;15(2):120–6.
17. Shajari M,
Kolb CM, Petermann K, Böhm M, Herzog M, de’Lorenzo N, et al. Comparison of 9
modern intraocular lens power calculation formulas for a quadrifocal
intraocular lens. J Cataract Refract Surg. 2018;44(8):942–8.
18. Ferrer-Blasco
T, Domínguez-Vicent A, Esteve-Taboada JJ, Aloy MA, Adsuara JE, Montés-Micó R.
Evaluation of the repeatability of a swept-source ocular biometer for measuring
ocular biometric parameters. Graefe's Arch Clin Exp Ophthalmol. 2017;255:343–9.
Received: 28 September 2023/
Accepted: 15 November 2023 / Published:15 December 2023
Citation. Hussain Alshammari, Siham M A, Al Muhammad S A. Comparison
of ocular biometry and intraocular lens power using a novel biometer and a
traditional biometer. Revis Bionatura 2023;8 (4) 28. http://dx.doi.org/10.21931/RB/2023.08.04.28
Additional information Correspondence should be addressed to [email protected]
Peer review information. Bionatura thanks anonymous reviewer(s) for their
contribution to the peer review of this work using https://reviewerlocator.webofscience.com/
All articles published by Bionatura
Journal are made freely and permanently accessible online immediately upon
publication, without subscription charges or registration barriers.
Bionatura ISSN.
13909355. Scopus coverage years:
from 2016 to the Present
Publisher's Note: Bionatura stays neutral concerning
jurisdictional claims in published maps and institutional affiliations.