Major review IOL in child

MAJOR REVIEW
Intraocular Lens Power Calculation in Children
Maya Eibschitz-Tsimhoni, MD, Steven M. Archer, MD, and Monte A. Del Monte, MD
Department of Ophthalmology and Visual Sciences, Kellogg Eye Center, University of Michigan,
Ann Arbor, Michigan, USA
Abstract. With improving surgical technique and equipment, the acceptable age for placing an
intraocular lens in infants and children is becoming younger. The tools for predicting intraocular lens
power have not necessarily kept up, as current theoretical and regression intraocular lens power
prediction formulas are largely based on adult eyes at axial lengths, anterior chamber depth, and
keratometric values much different than those seen in infants. In addition, the adult eye has matured
and is no longer growing, whereas the eyes of infants and children may continue to note changes in
axial length, keratometric values, and possibly optical characteristics. Another source of error in
intraocular lens power selection that is more likely to occur in pediatric patients than in adult patients
is inaccuracy in measurement of axial length or keratometric power. A review of current tools and
considerations for intraocular lens power prediction in infants and children is presented. (Surv
Ophthalmol 52:474--482, 2007. 2007 Elsevier Inc. All rights reserved.)
Key words. axial length cataract children infants intraocular lens pediatric
I. Introduction
The placement of an intraocular lens (IOL) in
children and infants undergoing cataract surgery is
gaining wider acceptance.33,65 With improved surgi-cal
equipment and technique, the acceptable age for
IOL implantation is becoming progressively younger.
IOL implantation after cataract surgery in children
$2 years of age is now widely accepted,65 although the
implantation of IOLs during infancy is still contro-versial.
31--33,56 A survey of AAPOS members, however,
found that the percentage of responding members
who had implanted an IOL in an infant after cataract
surgery increased from 4% in 1997 to 21% in 2001.33
In this setting, what is the optimal approach for
determining IOL power in children and infants?
II. Refractive Goal
Three major questions arise when determining
the power of IOL to be implanted: 1) Should
a myopic shift be anticipated, and if so, 2) How
much and at what age? 3) What target refraction
should be sought immediately following the implan-tation?
A. NORMAL EYE DEVELOPMENT AND MYOPIC
SHIFT
Most ocular growth occurs in the first few years of
life, and this has significant optical implications.
The normal newborn eye has a mean axial length
(AL) ranging from 16.6 to 17.0 mm and a mean
keratometric power of 51.2 diopters (D).17,35,57,59
O’Brien and Clark demonstrated a mean AL of
15.38 0.25 mm in preterm infants at 33 weeks.45
AL increased at a rate of 0.18 mm/wk until 40 weeks
then slowed to 0.15 mm/week until the age of 3
months. The AL of infants at 3 months was 18.23
mm. The growth rate then slows again, reaching
a mean adult value of 23.6 mm at 15 years of age. As
a child’s eye develops, the refractive changes are
474
2007 by Elsevier Inc.
All rights reserved.
0039-6257/07/$--see front matter
doi:10.1016/j.survophthal.2007.06.010
SURVEY OF OPHTHALMOLOGY VOLUME 52 NUMBER 5 SEPTEMBER–OCTOBER 2007

INTRAOCULAR LENS POWER CALCULATION IN CHILDREN 475
largely due to growth in AL. More than half of this
growth in AL occurs before 1 year of age and most
axial elongation occurs during the first 2 years of
life.17,35,38 The change in mean keratometric power
occurs almost completely within the first 6 months
of life, with only minor changes after that.17,28 As
the AL increases from an average of 16.8 mm at
birth to 23.6 mm in adulthood, the corneal
curvature will decrease from an average power of
51.2 D to 43.5 D. The lens power decreases by more
than 10 D during the first year of life, then drops
only 3--4 D from the age of 2 until the lens power
stabilizes at 10 years of age.17
In aphakic and pseudophakic eyes, the lens power
is static and, if the AL grows normally, decreasing
hyperopia or increasing myopia would be expected
to result. Axial growth after cataract surgery can be
attributed to normal eye growth as well as other
factors, including age at surgery, visual input, the
presence or absence of an IOL, laterality, genetic
factors, and interocular AL difference.30,63 Weakley
et al noted that the rate of refractive growth was
correlated with visual acuity outcome.64
McClatchey and Parks observed aphakic children
into adulthood and found a decrease in refractive
error that followed a logarithmic regression curve
and was very similar to that predicted from Gordon
and Donzis’s data on phakic children.39 In addition,
they calculated the theoretic long-term refractive
effects of pseudophakia in a large group of aphakic
eyes with long-term follow-up and predicted a 6.6-
diopter mean myopic shift (range --36.3 to þ2.9)
over a mean follow-up of 11 years.40 Children aged 2
years and under at the time of surgery had
a significantly greater predicted myopic shift and
a greater variance in the predicted refractive change
than those older than 2 years at the time of
surgery.40 There has been little long-term evaluation
of refractive data in pseudophakic children. Al-though
some authors have shown that removing the
crystalline lens and implanting an IOL may retard
the axial elongation of the eye,18 most authors have
found an overall myopic shift, which was greatest in
the youngest patients and continued until at least
age 8 years as well as a marked variability in
postoperative refraction.5,9,13,16,27,29,37 Vanathi et al
noted a mean myopic shift of 7.35 D in 12 children
(mean age 6.7 years) post-uniocular cataract surgery
followed for a mean of 7.8 years.62 In a study of 52
eyes in 42 patients aged 12 months to 18 years
undergoing cataract surgery with IOL implantation,
Crouch reported a mean myopic shift of 3.66
D in children operated on at 3--4 years of age, 2.03
D in children operated on at 7--8 years of age, 1.88 D
on children operated on at 9--10 years of age, 0.97 D
on children operated on at 11--14 years of age, and
0.38 D on children operated on at 15--18 years of
age.8 Mean follow-up by age group ranged between
4.38 and 6.35 years. Similarly, in a study of 38 eyes in
27 patients undergoing cataract surgery with im-plantation
of a posterior chamber IOL followed for
a mean of 6.1 years, Plager et al reported a mean
myopic shift of 4.60 D in children operated on at
age 2--3 years, a mean myopic shift of 2.68 D on
children operated on at age 6--7 years, a mean
myopic shift of 1.25 D on children operated on at
age 8--9 years, and a mean myopic shift of 0.61 D on
children operated on at age 10--15 years.46 Several
studies have shown that large mean myopic shifts
occur in some infants, although the change in
individual infants was quite variable. Crouch re-ported
a mean myopic shift of 5.96 D after a 6.35-
year mean follow-up of children who underwent
IOL implantation at 1 to 2 years of age.8 Dahan
reported a myopic shift of 6.93 3.42 D after a 7.7-
year follow-up of 34 children (68 eyes) who had
undergone IOL implantation during the first 18
months of life.9 The mean increase in AL in these
eyes was 3.59 1.80 mm. Wilson reported a myopic
shift of 6.22 D after a 21 months follow-up of 16
children (32 eyes) who underwent IOL implanta-tion
during the first year of life.66 After a mean
follow-up of 13 months, Lambert reported a mean
myopic shift of 5.29 D in the pseudophakic eye of 11
children who underwent IOL implantation during
the first 6 months of life.31
Measurements of the ALs in the pseudophakic eye
and the unoperated fellow eye have shown no
significant difference in AL change over time
between the pseudophakic and its fellow eye. These
findings suggest that most pseudophakic eyes grow
normally, and, thus, a significant shift after IOL
implantation is to be expected in these young
patients.13,27 Superstein et al, however, found that
patients with pseudophakia between 2 and 20 years
of age have only a minor trend toward myopia and
show less myopic shift than patients with aphakia.58
Zwaan also found minimal myopic shift in their
series of 306 pseudophakic eyes in patients 2--16
years of age.67 Better understanding of the factors
influencing pediatric eye growth will assist in IOL
power calculation and the prediction of refractive
changes after IOL implantation.
B. POSTOPERATIVE REFRACTIVE GOAL IN OLDER
CHILDREN
There is no consensus in the literature on the
ideal postoperative refraction in infants and chil-dren
after IOL implantation. Wilson et al surveyed
members of the American Society of Cataract and
Refractive Surgery (ASCRS) and members of the

476 Surv Ophthalmol 52 (5) September--October 2007 EIBSCHITZ-TSIMHONI ET AL
American Association for Pediatric Ophthalmology
(AAPOS) in 2001 to determine prevailing practice
patterns in pediatric cataract surgery.65 Although
a few surgeons targeted emmetropia or even mild
myopia after surgery at all ages, most aimed for
hyperopia until 5 years of age when the consensus
shifted to emmetropia. Enyedi et al recommended
a postoperative refractive goal of þ6 for a 1-year-old,
þ5 for a 2-year-old, þ4 for a 3-year-old, þ3 for a 4-
year-old, þ2 for a 5-year-old, þ1 for a 6-year-old,
plano for a 7-year-old and --1 to --2 for an 8-year-old
and older.13 Other authors recommend that pa-tients
between 2 and 4 years of age have lens
calculations performed to obtain a spherical equiv-alent
refraction equal to that of the fellow eye and
then reduce the lens power by 1.25 D to allow for
ocular growth. These authors suggest patients older
than 4 years of age receive IOLs with powers
calculated to match the spherical equivalent re-fraction
of the fellow eye.7 For older children, it is
recommended that lens power be calculated for
emmetropia, and then adjustments be made to
avoid greater than 3.00 D of postoperative anisome-tropia.
7
C. POSTOPERATIVE REFRACTIVE GOAL
IN INFANTS
For children #2 years old, implantation of IOLs is
still controversial and a 2001 AAPOS members’
survey found that most responding AAPOS mem-bers
still prefer to leave the infant aphakic after
cataract surgery and to use contact lenses for optical
correction.33,34 However, as previously noted, the
percentage of the responding AAPOS members who
implant an IOL in an infant after cataract surgery is
increasing.33 The Infant Aphakia Treatment Study is
an ongoing study that will compare the visual
outcome of children with unilateral aphakia cor-rected
with a contact lens compared with an IOL
implant (Lambert SR et al: Infant Aphakia Treat-ment
Study. www.nei.nih.gov/neitrials/viewStudy
Web.aspx?id5108, 2006).33
For now, there are varying opinions as to the
optimal postoperative refractive goal in infants and
children under 2 years of age. Some surgeons
choose to use an IOL with adult power.6,19 Their
belief is that with growth and the expected myopic
shift, the child will have good visual acuity and
emmetropia in adulthood. This refractive goal
results in significant residual hyperopia in the years
following implantation, a condition that must be
corrected. Near vision is most affected, as the
pseudophakic eye does not accommodate, and even
mild uncorrected hypermetropic anisometropia
may cause severe amblyopia. The residual hyperopia
needs to be corrected with a contact lens or
spectacles that overcorrect by þ2.00 to þ3.00 D to
provide clear near vision and prevent amblyopia. As
the eye grows, contact lens power diminishes and
the contact lenses are slowly phased out.
A few authors have recommended targeting
emmetropia postoperatively after IOL implantation
in younger children.36 This approach may assist with
amblyopia management in the early postoperative
period. With ocular growth, the resulting myopic
shift will necessitate the use of a contact lens or
refractive surgery to correct the residual refractive
error and minimize the resultant aniseikonia.38
In Wilson’s survey of ASCRS and JAAPOS
members in 2001, there was wide variation in the
postoperative refractive goal for infants at 6 months
of age, ranging from emmetropia to high hyperopia
(defined as $7 D), with most aiming for moderate
hyperopia (defined as $3 D but !7 D).65 For
infants at 12 months of age, most respondents
aimed for moderate or mild (defined as O0 D but
!3 D) hyperopia. At 2 years of age there was
a prevailing consensus to aim for mild hyperopia.65
This is consistent with Plager et al who assume that
a shift toward decreasing hyperopia (increasing
myopia) will occur at a descending rate throughout
childhood and, therefore, gives children a hyperopic
pseudophakic refractive error.47 The magnitude of
the planned hyperopia increases with decreasing
age and is modified by the AL and refractive error of
the fellow eye. In the Infant Aphakia Treatment
Study, the target refractive error after IOL implan-tation
is þ8 for infants 4--6 weeks of age and þ6 for
infants 6 weeks to 6 months of age (Lambert SR
et al: Infant Aphakia Treatment Study. www.nei.nih.
gov/neitrials/viewStudyWeb.aspx?id5108, 2006).
There remains no study demonstrating a visual
advantage of one approach over the other.
III. Measurement of Axial Length
In addition to the uncertainties of growth after
IOL implantation, the measurements of AL and
keratometry in children can be less accurate than
for adults. Office measurement of AL and keratom-etry
can be difficult in young children and infants
and must often be done under anesthesia in an eye
that is unable to cooperate with precise fixation and
centration. Mittelviefhaus et al have shown that the
lack of fixation in children who have keratometry
under general anesthesia may lead to inaccurate
keratometry readings.43 In addition, in pediatric
patients AL measurement is frequently done in the
operating room under anesthesia where a skilled
technician may not be available.

A-scan ultrasound biometry is the conventional
method for measurement of AL in children.
Ultrasound can be performed using applanation
or immersion techniques. The applanation tech-nique
places the ultrasound probe directly on the
cornea, which slightly indents the surface. This may
introduce a measurement error in recorded AL.
Using the immersion technique, the ultrasound
probe does not come into direct contact with the
cornea, but instead uses a coupling fluid between
the cornea and probe preventing corneal indenta-tion.
When the probe is aligned with the optical axis
of the eye and the ultrasound beam is perpendicular
to the retina, the retinal spike is displayed as
a straight, steeply rising echospike. When the probe
is not properly aligned with the optical axis of the
eye, the ultrasound beam is not perpendicular to
the retinal surface and the retinal spike is displayed
as a jagged, slow-rising echospike.55
The quality of the ultrasound machine and the
average ultrasound velocity may also introduce
errors in AL measurement. The most appropriate
ultrasound velocity is different at different ALs and
some ultrasound machines employ a single average
ultrasound velocity. For example, an axial myope of
29.00 mm is best measured at an average velocity of
1,550 m/sec, while an axial hyperope of 20.00 mm is
best measured at an average velocity of 1,560 m/sec.
A more accurate measurement can be obtained by
setting the velocity of the ultrasound machine at
1,532 m/sec and correcting for the AL.21,24,55 The
human eye is mostly composed of aqueous and
vitreous, both of which have an ultrasound velocity
of 1,532 m/sec. Only the cornea and crystalline lens
have different ultrasound velocities. If the eye is
measured at an ultrasound velocity of 1,532 m/sec,
a corrected axial length factor (CALF) of þ0.32 mm
is added to the apparent AL to obtain the true AL.
As these differences represent a relatively small
percentage of the total AL measurement, a single
CALF of þ0.32 mm can be universally applied for
phakic eyes of all ALs. This method is more accurate
than using an average ultrasound velocity, such as
1,548 m/sec. In aphakia, an ultrasound velocity of
1532 m/sec is recommended.55
Partial coherence interferometry (PCI) has been
used in cooperative children with reliability and
accuracy.26,48 PCI requires patient cooperation and
thus may not be a viable option in infants and young
children. Claimed improvements over conventional
ultrasound techniques include high reproducibility,
contact-free measurement, and observer indepen-dence
of the measurements.26 This technique relies
on a laser Doppler to measure the echo delay and
intensity of infrared light reflected back from tissue
interfaces.
IV. Intraocular Lens Power Calculation
Once the decision has been made to implant an
IOL and the desired postoperative refractive goal is
determined, what intraocular lens power calculation
formula should be used to reach that refractive
goal? Several formulas can be used to predict the
IOL power needed to achieve the desired refractive
goal. To date, formulas for IOL lens power
calculation have been largely derived from studies
in adults.
Intraocular lens power calculation formulas fall
into two major categories; empirically determined
regression formulas and theoretical formulas. The
regression formulas, such as the Sanders-Retzlaff-
Kraff (SRK) formula, are based on mathematical
analysis of a large sampling of postoperative results
in adults. In adult eyes, the SRK formula (first
generation linear regression formula) is most
appropriate for eyes in the average AL range
(22.5--25.0 mm). The formula does not work well
for long (O25 mm) or short (!22.5 mm) eyes.50
The formula generally undercorrects short eyes and
overcorrects eyes with long ALs, because it attempts
a linear fit to a hyperbolic relationship.
The first-generation theoretical IOL formulas
assume a constant position of the IOL, or post-operative
anterior chamber depth (ACD) in all eyes,
regardless of their AL. Since the measured post-operative
ACD was found to be directly proportional
to the AL of the eye (longer eyes had larger ACDs),
these formulas were less accurate for long or short
eyes.22 Several second-generation theoretical formu-las
emerged, such as the Hoffer formula, that
replaced the constant ACD with one that included
a correction for AL.25
The SRK formula was also modified to improve
accuracy for short and long eyes and reemerged as
the SRK II formula. This was a simple modification
of the original SRK formula in which the ‘‘A’’
constant is modified according to the AL of the
eye.54 In addition to the SRK II formula, a number
of other modified empirical formulas have been
developed in an effort to attain even better
predictive accuracy. These include the Gills,15
Axt,3 Thompson-Maumenee,60 and Donzis-Kastle-
Gordon10 formulas. All divide the range of AL and
use two or three regression lines for a better fit of
each segment of the curve.11 Holladay and col-leagues
have noted that the AL versus calculated
power graphs for second-generation formulas, of
both theoretic and regression derivation, converge
to the same general result.25
Thus, with second-generation formulas, ACD was
no longer a constant in all eyes but rather varied
with AL. Holladay and associates were the first to

consider that the ACD might vary not only with the
AL but also with the corneal curvature.25 Their
formula modified the ACD based on the AL, and
also based on the corneal height (distance from the
cornea to the IOL’s first principal plane). This
formula was shown to be significantly more
accurate than previous theoretic formulas and the
SRK II.23
Hoffer also developed a third-generation IOL
formula.22 He speculated on the relationship
between ACD and AL and developed an expression
that resulted in an S-shaped curve that fit his
impression of what this relationship should be. This
formula deepened the ACD with increasing AL and
with increasing corneal curvature. This modification
of the ACD, added to his previous Hoffer formula,
has become known as the Hoffer Q formula.
The originators of the SRK formulas brought
their retrospective analytic approach to develop
a third-generation IOL formula. The SRK/T for-mula
is a nonlinear theoretical optics formula
empirically optimized for postoperative anterior
chamber depth based on axial length, retinal
thickness correction for AL, and corneal refractive
index.51 It thus combines advantages of theoretical
and empirical analysis. For extremely long eyes
(O28 mm), the SRK/T seems to be significantly
more accurate than regression formulas.53
To improve accuracy in short, hyperopic eyes,
Holladay further modified his formula by includ-ing
consideration of white-to-white corneal diame-ters,
preoperative anterior chamber depth, lens
thickness measurements, as well as the patient’s
age and preoperative refractive error to create the
Holladay 2 formula (Holladay JT: Holladay IOL
Consultant Computer Program. Houston, TX,
1996).20
In adults, the Holladay formula is considered to
be most accurate for eyes with an axial length
between 22 and 26 mm. The Hoffer Q formula is
considered to be most accurate for short eyes
(!24.5mm). The SRK/T formula is considered
optimal for long eyes (O26mm).53
A. THE SRK FORMULAS
1. IOL Calculation Using the SRK
Formula49,50,52,53
D15Al0:9 Km2:5 Am
Al IOL constant in diopters
D1 Primary implant power predicted by the SRK
II formula
Am Axial length in millimeters
Km Average K reading
2. IOL Calculation Using the SRK II Formula54
D15Al0:9 Km2:5 AmRsg
Al IOL constant in diopters
D1 Primary implant power predicted by the SRK
II formula
Am Axial length in millimeters
Rs Desired postoperative refraction in diopters
Km Average K reading
Where
Al 5 A þ 3 for Am ! 20.0 mm
Al 5 A þ 2 for 20.0 # Am ! 21.0
Al 5 A þ 1 for 21.0 # Am ! 22.0
Al 5 A for 22.0 # Am ! 24.5
Al 5 A 0.5 for Am $ 24.5
and
g51.00 for Al0.9Km2.5Am#14.00mm
g51.25 for Al0.9Km2.5AmO14.00mm
B. IOL CALCULATION USING THE HOFFER
Q FORMULA22
D25f1336 = ðAmd0:05Þg
f1:336=½1:336=ðKmþRsÞ
½ðdþ0:05Þ=1000g
D2 Primary implant power predicted by the Hoffer
equation
d Chamber depth (ACD) in millimeters
Where
ACD 5pACDþ0:3Am23:5
þðTan KmÞ2þ0:1Mð23:5AmÞ2
Tan 0:1 ðGAmÞ20:99166
If Am # 23, M 5 þ1 G 5 28
Am O 23, M 5 --1 G 5 23.5
The personalized ACD (pACD) is set equal to the
manufacturer’s ACD-constant, if the calculation was
selected to be based on the ACD-constant. In case
the A-constant was chosen, pACD is derived from
the A-constant according to (from Holladay et al25)
pACD5ACDconst 50:58357
A-const 63:896
Personalization of the pACD is the process whereby
one enters the IOL power actually used and the
resultant spherical equivalent refractive result and
back-calculate what ACD would have produced an
error of zero. If one calculates this ‘‘perfect ACD’’
for a whole series of eyes (using same surgeon and
IOL style), average the number and that becomes
the personalized factor for that surgeon and IOL.

C. THE HOLLADAY FORMULA
1. IOL Calculation Using the Holladay
Formula24,25
D351336
br acor 0:001 Rs
½v ðbracorÞþa acor r
ðacordSFÞ fbrdSF0:001Rs
½v ðbrdSFÞþaðdþSFÞ rg
D3 Primary implant power predicted by the Holla-day
equation
acor Corrected axial length in millimeters
v Vertex distance in millimeters
SF Holladay’s surgeon factor in millimeters
Where
r 5 337.5 / Km
b 5 nv / (nc
1) with nv 5 1.336 and nc 5
1.333333
a 5 1.0 / (nc 1)
Rag 5 r for r $ 7 mm
Rag 5 7 mm for r ! 7 mm
With
AG 5 0.533 Am for AG # 13.5 mm
AG 5 13.5 mm for AG O 13.5 mm
d5ACD50:56 þ Rag qffiffiffiRffiffiffiaffiffigffiffiffi2ffiffiffiffiffiffiffiffiffiAffiffiffiGffiffiffi2ffiffi=ffiffiffi4ffiffiffiffi
acor 5 Am þ Tr where Tr 5 0.200 mm
with SF5xxx Aconst þ yyyy
Although the surgeon factor represents a measur-able
distance (anterior iris plane to the effective
optical plane of the IOL), the optimal way to arrive
at this factor is to solve the formula in reverse for the
constant, using as input variables the preoperative
Am and keratometry measurements, the IOL power
implanted, and the stabilized postoperative refrac-tion.
This surgeon factor is therefore a number
representing a particular surgeon’s previous experi-ence.
25
V. Intraocular Lens Power Calculation in
Pediatric Patients
Because all intraocular lens power calculation
formulas were derived from considerations regard-ing
the adult eye, it is yet unclear whether they can
be applied in children with the same degree of
confidence, especially with short ALs and high
keratometry values and a target refraction that may
be significantly different from plano.
There are only five publications reporting on
outcome post IOL implantation in children with
respect to the prediction formula used.1,2,42,44,61 A
spectrum of ALs with specific keratometry values is
missing. Recent work by Mezer et al suggests that
none of the current prediction formulas, including
Hoffer Q, Holladay, SRK/T, SRK, and SRK II provide
adequate outcomes in patients between 2 and 17
years of age.42 Only the mean error for all patients
was reported. Differences as a function of ALs and
keratometry values were not defined. The average
differences ranged between 1.06 0.79 to 1.79
1.47 D. Andreo et al stated that there was little
difference between SRK II, SRK/T, Holladay, and
Hoffer Q formulas in short, medium, and long eyes
in providing adequate predicted refraction.1 The
mean error was between 1.23 to 1.33 D in long eyes,
0.98 to 1.03 D in medium eyes and 1.41 to 1.8 D in
short eyes. However, only the mean of a small
number (n 5 17) of patients with AL ! 22.0 mm
(as short as 18.6 mm) was evaluated in the group with
short eyes. Neely et al showed that the SRK II, SRK T,
and Holladay I formulas had no significant differ-ence
in lens power predictability in children.
However, there was increased variability in post-operative
refractive outcome in patients younger
than 2 years of age with all formulas. The Hoffer Q
formula had a tendency to overestimate the IOL
power and showed the greatest degree of variability.44
Even in the adults, only a small number of
patients with short ALs have been reported. For
example, in a study by Hoffer of 500 eyes, only 36
eyes were less than 22 mm with an average of 21.43
0.69 mm.22 In a study of 100 eyes by Barrett, only
25 eyes were less than 22.5 mm.4 Nevertheless, in his
article Hoffer suggests that the Hoffer Q formula is
superior in eyes shorter than 22.0 mm. In addition,
it may be inaccurate to extrapolate conclusions from
short adult eyes to the pediatric population.
Newer formulas such as the Holladay II formula
were designed to increase the accuracy of the IOL
power calculation. The Holladay II formula in-corporates
measured anterior chamber depth, lens
thickness, and corneal diameter and is purportedly
helpful in adults requiring at least 30 D of power for
emmetropia.25 In a study by Fenzl et al, the
refractive and visual outcomes of hyperopic cataract
cases whose IOL power calculation was made using
Holladay I and Holladay II formulas were com-pared.
14 The mean absolute deviation from pre-dicted
(target) refraction was nearly equivalent in
the two groups; however, the standard deviation of
the mean absolute deviation was smaller in the
Holladay II group. Hoffer also reported on his
clinical results using the Holladay II intraocular lens
power formula in adults. He found that although
the Holladay II formula reduced the mean absolute
error in short eyes (! 22.0 mm) (n 5 10), it was not
more accurate than the Hoffer Q.20

In an analytical prediction of implant power
prediction equation discrepancies, the average
primary implant power discrepancy was reported
for the modified Binkhorst, modified Colenbrander,
Holladay, Hoffer, and SRK II equations. Only
a general discrepancy as a function of three ALs
and three chosen keratometry values was provided,
with the shortest AL being 21 mm.41
In recent work by Eibschitz et al, an analytical
comparison of predicted implant power using
keratometry values up to 55 D and axial length
values as short as 16 mm was performed for two
different refractive goals using the optimized in-traocular
lens constants for the SRK II, SRK/T,
Holladay I, Hoffer Q, and Haigis equations.
Significant differences in intraocular lens power
prediction were found among the Hoffer Q, Holla-day
I, and SRK II formulas in the pediatric range of
axial length and keratometry values. The Holladay I
and Haigis formulas were found to be similar in
their IOL prediction. The SRK/T was comparable to
the Holladay I and Haigis formulas but still differed
in the high keratometry values.12
When determining individual ACD constants in
the Hoffer Q formula for short, medium, and long
eyes, the results in the short eye (!22.0 mm) series
are less accurate using the personalized pACD
derived from the 36 short eyes examined than when
using the pACD derived from the entire 450 eye
series.22 The same is true for the long eye (O 24.5
mm) series. This illustrates that developing a per-sonalized
ACD for AL subgroups at the extremes is
of no value for the Hoffer Q formula and actually
makes the results clinically less accurate in short
eyes. A similar analysis performed for the Holladay
and SRK/T formulas in short eyes showed no
statistically significant benefit to a subgroup of short
or long ALs using personalized SF or A-constant
compared with using the overall 450 eye personal-ized
pSF or A-constant.22
VI. Conclusion
Refractive growth after IOL implantation in
infants and children cannot be predicted accurately
(large standard deviation) and current IOL formu-las
vary in their predictive outcomes. If the target
refraction goal is emmetropia, amblyopia treatment
will be easier but may result in myopia later in life. If
the target refraction goal is hyperopia, amblyopia
treatment may be more difficult but emmetropia
later in life is more likely. Although placement of an
IOL in children has gained acceptance and place-ment
of an IOL in infants is gaining favor among
some AAPOS members, there remains no IOL
power calculation formula derived primarily on
the basis of characteristics of the child’s eye or the
historical outcome from IOL implantation in
children. With the trend towards implanting IOLs
in infants with shorter ALs, there will likely be
a greater need to understand the accuracy and the
differences between prediction formulas at the
lower extremes of AL and keratometry values. Using
current formulas and refining the A-constant and
surgeon factor may reduce postoperative refractive
error, but unlike adults, most pediatric ophthalmol-ogists
only perform a few, if any IOL implants in
infants and children with a wide range of AL and K
values rendering adjustment of A-constants and
surgeon factors problematic. Any modern IOL
formula can be used on children but more error
should be expected. Use immersion A-scan instead
of contact and repeat K-readings to make sure they
are reproducible. As for multifocal IOLs in children,
given the need for highly accurate biometry,
astigmatism control, and no refractive growth,
caution should be used in considering the use of
multifocal IOLs in infants and children.
VII. Method of Literature Search
This article was prepared by using the database of
National Library of Medicine by using the search
words intraocular lens, lens power calculation, lens power
formula, myopic shift, cataract, infants, children, axial
length, pediatric, and refractive error from 1975 up to
April 2006, our own published papers, and manual
searches based upon articles cited in the texts of
other articles. The Cochrane Collaboration and
Embase were also searched using the search terms.
Relevant textbooks were cited as referenced sub-sequently.
Articles were included if they emanated
from peer-reviewed journals. Clinical studies were
selected if they were randomized controlled trials,
single- or double-blind, or interventions with phar-macological
therapy compared to placebo or some
other pharmacological agents. Abstracts were used
in the case of non-English articles, if available.
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The authors reported no proprietary or commercial interest in
any product mentioned or concept discussed in this article.
Reprint address: Maya Eibschitz, MD, 1000 Wall St. Ann Arbor,
MI 48105.
Outline
I. Introduction
II. Refractive goal
A. Normal eye development and myopic shift
B. Postoperative refractive goal in older chil-dren
C. Postoperative refractive goal in infants
III. Measurement of axial length
IV. Intraocular lens power calculation
A. The SRK formulas
1. IOL calculation using the SRK formula
2. IOL calculation using the SRK II formula
B. IOL calculation using the Hoffer Q formula
C. The Holladay formula
1. IOL calculation using the Holladay for-mula
V. Intraocular lens power calculation in pediatric
patients
VI. Conclusion
VII. Method of literature search

Major review IOL in child

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