Clinical & Experimental
Mesa-Gutierrez et al. J Clinic Experiment Ophthalmol 2011, 2:1
Ophthalmology
http://dx.doi.org/10.4172/2155-9570.1000126
Review Article
Open Access
Intraocular Lens Power Calculation after Myopic Lasik with no Previous
Data: A Review of Available Methods
Juan Carlos Mesa-Gutierrez*, Antonio Rouras-Lopez, Jose Porta-Monnet, Vicente Amias-Lamana, Isabel Cabiro-Badimon and Laura Solanas-Garcia
Hospital Esperit Sant, Barcelona, Spain
Introduction
power is used in the Shammas post-LASIK (Shammas-PL) formula and
in this formula the effective lens postion (ELP) does not vary with the
Intraocular lens (IOL) power calculation after keratorefractive
corneal curvature, which has been altered by the LASIK procedure [22].
surgery has been a major challenge for the ophthalmic community and
has generated numerous scholarly works and efforts trying to optimize
Seitz/Speicher/Savini + Double-K SRK/T formula
current formulas and tailor new methods to better predict the correct
intraocular lens (IOL) power [1-8]. Aramberri's work on the double-K
The method of separately considering the anterior corneal
adjustment of third-generation IOL formulas significantly improved
curvature and posterior corneal curvature, first described by Seitz and
the hyperopic results stemming from inaccurate estimation of the
Langenbucher and later reviewed by Speicher, could be considered the
effective lens position by those formulas [9].
most accurate, at least when coupled with the double-K SRK/T formula
[2,23]. If the preoperative corneal power is unknown, the Seitz/Speicher
IOL power calculation can lead to unexpected refractive outcomes
method can be modified according to Savini et al., who suggest using
for 2 primary reasons. The first is that the surgical y induced corneal
a mean value of -4.98 D for posterior corneal curvature [21,24]. The
power change, as measured by keratometry or corneal topography, is
Seitz/Speicher/Savini method:
underestimated because the standard keratometric refractive index
(usual y 1.3375) is not valid once the laser modifies the anterior to
K = simulated K x 1.114 - 4.98
posterior corneal curvature ratio [10-13] The second reason is that the
is similar to other methods like the one proposed by Maloney [25]:
IOL position is erroneously predicted by third-generation theoretical
K = central corneal power x 1.114 - 4.9
formulas (eg, Hoffer Q, Hol aday 1, SRK/T) that derive the prediction
and the modified version developed by Wang (4):
from the corneal curvature [13-17]. A third reason may be partial y
K = central corneal power x 1.114 - 6.1
responsible for the inaccuracy of IOL power calculation for eyes with
equation 6 of Awwad (11, 26).
a small optical zone and large correction; in this case, the difference
SimKadj no history = 1.114 x SimK - 6.062
between the paracentral corneal area (where keratometry [K] and
and, to a lesser extent, the Shammas et al. no-history method [22]:
simulated K readings are taken) and the central cornea area (where the
K Shammas = simulated K x 1.14 - 6.8
visual axis passes) can be clinical y relevant [11,18-20].
Ho et al.found that the Seitz/Speicher method modified according
When no previous data are available the calculations are more
to Savini et al. is highly accurate [27, 28]. Obviously, this method
misleading as no double-K adjustment can be done, unless an average
(developed for eyes for which the preoperative corneal power is not
value (eg, 43.13 D) is presumed to be the preoperative corneal power.
known) must be used in conjunction with double-K formulas, which
Various formulas have been described, and surgeons can now choose
require entry of the preoperative corneal power. There are 3 possibilities
from many methods. This can easily generate confusion rather than
to solve this contradiction: (1) calculate the preoperative corneal power
accuracy. The aim of the present study was to provide with various
by adding the refractive change to the postoperative corneal power, (2)
methods of calculating IOL power in patients with no pre-refractive
use a mean value such as 43.13 or (3) estimate the effective lens position
surgery data available.
(ELP), as suggested by Ho (27-29). The good results obtained with the
We address two possible scenarios with no preoperative corneal
Seitz/Speicher method (with or without the Savini modification) could
power known. When neither preoperative corneal power nor refractive
be related to its total independence of the surgical y induced refractive
changes are available the lowest mean absolute error is achieved with
change (a likely source of errors) [27].
the methods of Masket, Seitz/Speicher/Savini, Shammas, and Camellin/
Rosa method + Single-K SRK/T formula
Calossi. When preoperative corneal power is unknown but the
surgical y induced refractive change is known the lowest mean absolute
Refraction with Rosa method (Rrosa) = R x (0.0276 AL + 0.3635)
error is achieved with the Masket method followed by the the Savini
method, Speicher/Seitz method modified by Savini, and Shammas no-
history method. Good results can also be obtained with the Awwad
*Corresponding author: Juan Carlos Mesa-Gutierrez, Servicio de Oftalmologia,
and Camellin/Calossi methods when the calculated corneal power is
Hospital Esperit Sant Avda Mossen Pons i Rabada, s/n 08923 Santa Coloma de
entered into the double-K Hol aday 1 formula instead of the double-K
Gramenet, Barcelona, Spain, Tel: 34 93 3864241; Fax: 34932607981; E-mail:
SRK/T [21].
juancarlosmesa@excite.co.uk
Preoperative corneal power and refractive change unknown
Received December 16, 2010; Accepted January 19, 2011; Published January
20, 2011
According to a recent paper these are the most reliable methods
Citation: Mesa-Gutierrez JC, Rouras-Lopez A, Porta-Monnet J, Amias-Lamana
[21].
V, Cabiro-Badimon I, et al. (2011) Intraocular Lens Power Calculation after Myopic
Lasik with no Previous Data: A Review of Available Methods. J Clinic Experiment
Shammas no-history method + Shammas-PL formula
Ophthalmol 2:126. doi:10.4172/2155-9570.1000126
Copyright: (c) 2011 Mesa-Gutierrez JC, et al. This is an open-access article
KShammas = 1.14 x K - 6.8
distributed under the terms of the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided
The main advantage of this method is that the corrected corneal
the original author and source are credited.
J Clinic Experiment Ophthalmol
Volume 2 * Issue 1 * 1000126
ISSN:2155-9570 JCEO an open access journal

---

Citation: Mesa-Gutierrez JC, Rouras-Lopez A, Porta-Monnet J, Amias-Lamana V, Cabiro-Badimon I, et al. (2011) Intraocular Lens Power Calculation
after Myopic Lasik with no Previous Data: A Review of Available Methods. J Clinic Experiment Ophthalmol 2:126. doi:10.4172/2155-
9570.1000126
Page 2 of 5
K(Rrosa) = 337.5/Rrosa
preventing the cusp phenomenon which may happen using SRK/T
AL = Axial length; R=k/337.5
formula.
Another method proposed by Rosa is as follows [30]
- Automatic adjustments for extreme axial lengths.
KRosa = (1.3375-1)/((K x RCF)/1000).
- Contribution of corneal wavefront (espherical aberation) from
RCF: Rosa Correction Factor based on axial length (mm)
Pentacam.
22 - <23: 1.01
- It has two separate algoriths: one for myopia and other one for
23 - <24: 1.05
hyperopia.
24 - <25: 1.04
According to his author BESSt2 is more accurate than BESSt1 in
25 - <26: 1.06
hyperopia and more accurate than Haigis-L in myopia (34, 35).
26 - <27: 1.09
Awwad method + Double-K Holladay I
27 - <28: 1.12
28 - <29: 1.15
In the absence of information about the change (D) in spherical
29:1.22
equivalent (SE), a regression based solely on average corneal
central power (ACCP) in the central 3.0 mm area (ACCP3mm)
Ferrara method [31]
should be used (26):
K = ((-0.0006 x AL
ACCPadj no history = 1.151 x ACCP3mm - 6.799
2 + 0.0213 x AL + 1.1572) -1) / (Kr/1000).
AL: Axial lengh.
In the absence of topographic data a regression based on SimK is to be
Kr: Keratometry (radius of curvature in mm).
used:
SimKadj no history = 1.114 x SimK - 6.062
Rosa and Ferrara method may easily lead to postoperative myopia
[32].
Quantitative area topography (Orbscan II) and Total corneal
power (Galilei)
BESSt method + Double-K formula
In 2004, Sonego-Krone et al reported that the refractive change
The formula takes into account anterior and posterior corneal
at the corneal plane after myopic LASIK had a difference of -0.08+/-
radii and pachymetry (Pentacam, Oculus) and does not require pre-
0.53 D with the corneal power change determined by quantitative area
keratorefractive surgery information [33].
topography in a 4-mm-diameter central zone of Orbscan II total-mean
Input Variables
postoperative maps (36).
rF: Front corneal radius (mm)
Quantitative area topography is distinct from quantitative point
rB: Back corneal radius (mm)
topography, which assesses the average of only two single steeper and
CCT: central corneal thickness (microns)
flatter values. The total-mean power maps represent the spherical
Formula
equivalent refraction of both corneal curvatures with regard to the
n.air =1
corneal thickness and are comparable to the equivalent power of the
n.vc = 1.3265
cornea assessed by the thick lens formula. The total-optical power
n.CCT = n.vc + (CCT x 0.000022)
maps represent the ray tracing of light through the whole cornea. The
K.conv = 337.5/rF
advantage of this method is that the final total corneal powers to be
n.adj:
used in IOL calculation may be obtained directly from the topographic
if K.conv <37,5 n.adj = n.CCT + 0.017
maps, as measured after the previous corneal refractive surgery without
if K.conv <41,44 n.adj = n.CCT
depending on regression formulas, artificial refraction indices, contact
if K.conv <45 n.adj = n.CCT - 0.015
lens over-refraction, aphakic intraoperative refraction, previous
ELSE; n adj EQUALS n CCT
refractive or topographic data, algorithms, or correction factors [36,37].
n.acq = 1.336
It has been applied in a multicenter study using the total mean
d = d.cct /n.vc
power (equivalent power) and the total optical power [38,39].Total
d.cct = CCT /1000000
optical power maps by the Orbscan Topography System appear to be
Fant = 1/rF x (n.vc - n.air)
relatively accurate in detecting the changes in corneal power measured
Fpost = 1/rB (n.acq - n.vc)
by refraction after LASIK. The correlation is highest when averaging
Using the BESSt formula, 46% of eyes were within +/-0.50 D of the
within the central 4.0 mm zone. The corneal power change derived
intended refraction and 100% were within +/-1.00 D.
from axial power maps correlates less well than that derived from the
TOP maps, as expected. Total optical power maps appear to provide an
Output
accurate measure of corneal power change in LASIK [37-39].
KBESSt (corneal power after keratorefractive surgery, D) =
{ [1/rF x (n.adj - n.air)] + [1/rB x (n.acq - n.adj) ] - [d x 1/r x (n.adj -
This same method has been applied with success using the Galilei's
n.air) x 1/rB x (n.acq - n.adj) ] } x 1000.
total corneal power (TCP) by ray tracing from a central zone of 0 to
BESSt formula has been replaced by the BESSt2 algorithm. Corneal
4 mm diameter. Similar to the Orbscan II total-optical power, the
power is still estimated with gaussian optic formula as with BESST1
Galilei uses a 4-mm diameter central zone for the TCP derived from
but some improvements can be found:
ray tracing. Galilei TCP represents the average total corneal power fot
- prediction of preoperative anterior radius from postoperative
the central 4 mm diameter of the cornea. This TCP is calculated using
posterior radius measurements.
the ray tracing method, which takes the actual refractive indices of the
- automatic application of double-K adjustment to the the predicted
cornea into account. The post-LASIK corneal power is estimated using
preoperative anterior radius.
the following formula [40,41]:
- It uses a modified 3rd generation formula for IOL power calculation,
post-lasik adjusted corneal power = 1.057 x tcp - 1.8348
J Clinic Experiment Ophthalmol
Volume 2 * Issue 1 * 1000126
ISSN:2155-9570 JCEO an open access journal

---

Citation: Mesa-Gutierrez JC, Rouras-Lopez A, Porta-Monnet J, Amias-Lamana V, Cabiro-Badimon I, et al. (2011) Intraocular Lens Power Calculation
after Myopic Lasik with no Previous Data: A Review of Available Methods. J Clinic Experiment Ophthalmol 2:126. doi:10.4172/2155-
9570.1000126
Page 3 of 5
Preoperative Corneal Power Unknown and refractive Hamed-Wang-Koch method + double-k formula
change known
This method requires knowledge of the refractive change from the
Masket method
surgery and the postoperative Sim-K from the topography unit. This
group modifies the effective reftactive power (EffRP) of the EyeSys:
The equation was determined to be as follows:
IOL Power Adjustment = LSE x (-0.0.326) + 0.101
K = EffRP - (0.15 x SE) - 0.05
They also offered a second method to calculate true corneal power by
Where LSE is the total prior laser treatment, adjusted for vertex
substituting 0.15 by 0.19
distance, in spherical equivalent (SE).
[43,44].
Clinical example is as follows:
Jarade method + double-k formula
Previously myopic eye:
- SRK/T formula suggests 14.0 D for emmetropia after cataract surgery
Requires knowing the surgical y induced refractive change at the
- Prior laser correction (SE) = - 4.0 D
corneal plane (SEcp) and the average radius of curvature of the cornea
- Adjustment calculation: -4.0 D x (-0.326) + 0.101 = + 1.405 D
now (Kr) [45]:
- IOL power adjusted by adding +1.4 D to the original + 14 D = +14.5
KJarade = ((1.3375 + 0.0014 x SEcp) - 1)/(Kr/1000)
D for emmetropia
The Masket method had a great advantage in that it omits the
Haigis-L method
double-K step required by the Savini and Seitz/Speicher/Savini methods.
KHaigis = -5.1625 x Kr + 82.2603 - 0.35
The latter methods can be significantly influenced by the choice of the
preoperative corneal power to be entered into the double-K formulas.
This method requires only the postoperative K reading form the
In contrast, the Masket method (like the Shammas no-history method)
Zeiss IOLMaster in radius of curvature (or converted to diopters using
does not have this drawback [5].
the index of refraction setting in the IOLMaster) [46].
Savini + Double-K SRK/T
Maloney Central Topography method + double-k formula
Ksavini = ((1.338+ 0.0009856 x SEsp) -1) / Kr/1000)
Central power = (central topographic power x [376/337.5]) - 4.9
SEsp: Change in spherical equivalent at spectacle plane
Koch and Wang obtained the best results using the Maloney
Kr: Keratomety (radius of curvature in mm). [20,21,24]
method using -6.1 instead of -4.9.
Camellin + Double-K Holladay 1
[4].
KCamellin = ((1.3319 + 0.00113 x SEsp) - 1) / (Kr/1000).
They also offered a second method to calculate true corneal power
SEsp: Change in SE at spectacle plane.
if SE is known [44]. The formula is:
Kr: Keratometry (radius of curvature in mm).
K = EffRp - (0.19 x SE)
When entered into the double-K SRK/T formula, the corneal power
calculated with the Camellin/Calossi method results in a positive
Feiz-Mannis method
arithmetic error in IOL power prediction, with a subsequent myopic
This method utilizes the change in refractive error to offset the
outcome. The suboptimal results are probably due to the fact that this
calculated target IOL power [47].
method was developed to be used with the Camellin/ Calossi formula
for IOL power calculation, which is a modified Binkhorst II formula,
P = PTARG - 0.595 x SEcp + 0.231
and not with the double-K SRK/T formula. The Camellin/ Calossi
P = IOL Power
formula calculates the ELP from the preoperative anterior chamber
PTARG = the target IOL power to produce the postoperative
depth. Considerably better results can be obtained by entering the
desired refractive error.
calculated corneal power into the double-K Hol aday 1 formula [8,42].
The historical K method, although theoretical y considered the gold
Awwad method + Double-K Holladay 1
standard, is misleading in practice because myopic or hyperopic errors
Two variables, ACCP3mm and SE, were shown to be vital and
in post-LASIK refractions can easily translate into errors of the same
sufficient for accurate refractive power prediction. The multiple
magnitude in the final post-cataract surgery refraction. In addition,
regressions based on these 2 independent variables successful y
early occult cataractous stage can produce myopic shift and potential y
predicted corneal refractive power (26):
lead to a falsely over-minused post-LASIK refraction result, introducing
an error in corneal power estimation. We recommend against using the
ACCPadj = ACCP3mm - 0.16 x (SEpostLASIK - SEpreLASIK)
historical K method [48].
Adjusting for the fact that the measured ACCP3mm overestimates
This method is based on the fact that the final change in refractive
the true value by about 0.16 D for every diopter of myopic laser
error the eye obtains from surgery was due only to a change in the
correction [26].
effective corneal power. If this refractive change the patient experienced
In ACCP is not available, SimK and SE are to be used:
is algebraical y added to the presurgical corneal power, we will obtain
the effective corneal power the eye has now. Obviously this requires
SimKadj = SimK - 0.23 x (SEpostLASIK - SEpreLASIK).
knowledge of the K reading and refractive error prior to refractive
As the measured SimK overestimates the true value by about 0.23 D
surgery (48).
for every diopter of laser correction [26].
K = KPRE + RPRE - RPO or [K = KPRE + RCC]
J Clinic Experiment Ophthalmol
Volume 2 * Issue 1 * 1000126
ISSN:2155-9570 JCEO an open access journal

---

Citation: Mesa-Gutierrez JC, Rouras-Lopez A, Porta-Monnet J, Amias-Lamana V, Cabiro-Badimon I, et al. (2011) Intraocular Lens Power Calculation
after Myopic Lasik with no Previous Data: A Review of Available Methods. J Clinic Experiment Ophthalmol 2:126. doi:10.4172/2155-
9570.1000126
Page 4 of 5
KPRE = refractive surgery preoperative corneal power
calculation methods in eyes that have undergone LASIK. Ophthalmology 111:
RPO = refractive surgery PO refractive error (spherical equivalent)
1825-1831.
RPRE = refractive surgery preoperative refractive error (spherical
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J Clinic Experiment Ophthalmol
Volume 2 * Issue 1 * 1000126
ISSN:2155-9570 JCEO an open access journal

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Citation: Mesa-Gutierrez JC, Rouras-Lopez A, Porta-Monnet J, Amias-Lamana V, Cabiro-Badimon I, et al. (2011) Intraocular Lens Power Calculation
after Myopic Lasik with no Previous Data: A Review of Available Methods. J Clinic Experiment Ophthalmol 2:126. doi:10.4172/2155-
9570.1000126
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J Clinic Experiment Ophthalmol
Volume 2 * Issue 1 * 1000126
ISSN:2155-9570 JCEO an open access journal

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