ARTICLE
Validity of autorefraction after cataractsurgery with multifocal ReZoom intraocular
lens implantationGonzalo Munoz, MD, PhD, FEBO, Cesar Albarran-Diego, MD, Hani F. Sakla, MD, PhD
PURPOSE: To evaluate the clinical utility of spherocylindrical automated refraction (AR) comparedwith subjective manifest refraction (MR) after cataract surgery with implantation of ReZoom refrac-tive multifocal intraocular lenses (IOLs) (Advanced Medical Optics, Inc.).
SETTING: Private Practice.
METHODS: This prospective nonrandomized interventional study consisted of 72 patients with bi-lateral cataract and a potential visual acuity of at least 20/40. Patients had bilateral nonsimultaneouscataract surgery and implantation of a ReZoom IOL. Manifest refraction was performed in all pa-tients followed by 3 consecutive measurements using the Topcon KR-8000 autorefractor with non-dilated and dilated pupils. Assessment of repeatability of multiple consecutive ARs and comparisonof the AR and MR using power vector analysis were performed at the 6-month follow-up. Themain outcome measures were the correlation between AR and MR with sphere, spherical equiva-lent, and astigmatism as well as the repeatability of AR before and after dilation with phenylephrine10%.
RESULTS: Repeatability analysis showed that the initial nondilated AR was not significantly differentfrom the mean of the 3 refractions for nondilated and dilated measurements. The mean differencebetween the initial AR and the MR was�0.84 G 0.62 diopters (D) for sphere (SD),�1.00 G 0.61 Dfor spherical equivalent, and �0.06 G 0.19 D and �0.01 G 0.17 D, respectively, for J0 and J45,the 2 components of astigmatism. Linear regression of AR versus MR data showed poor correlationfor sphere (R2 Z 0.4852) and spherical equivalent (R2 Z 0.5529), whereas the correlation for the2 astigmatic components of vector analysis was excellent (J0, R2 Z 0.8881; J45, R2 Z 0.8640).Correlation was better when the MR residual refractive defect was higher.
CONCLUSIONS: Although autorefraction showed excellent agreement with subjective refractiveastigmatism, correlation with spherical values was poor, with a trend toward more negative values.Autorefraction after ReZoom IOL implantation can be used as a good starting point for subjectiverefraction of astigmatism; however, spherical values should be underestimated.
J Cataract Refract Surg 2007; 33:1573–1578 Q 2007 ASCRS and ESCRS
Multifocal intraocular lenses (IOLs) are designed toavoid or reduce dependence on eyeglasses after cata-ract surgery.1–8 The multifocal IOL takes advantageof the brain’s ability to adapt to far or near vision asthe different elements of the lens are used dependingon what the patient is looking at.
The ReZoom (AdvancedMedical Optics, Inc.) is a 5-zone refractive acrylic multifocal IOL that has been ap-proved for clinical use in the United States and Europe.It has 5 concentric rings of varying optical power. Thepredecessor of this IOL, the refractive silicone multifo-cal Array (Advanced Medical Optics, Inc.), providescomparable distance visual acuity and affords better
Q 2007 ASCRS and ESCRS
Published by Elsevier Inc.
near visual acuity than conventional monofocalIOLs.9–14 In general, patients with multifocal IOLsare less dependent on eyeglasses and enjoy anenhanced quality of life. However, despite an im-provement in uncorrected near visual acuity withmul-tifocal IOLs, loss of clarity and low-contrast acuityand the presence of halos and glare have beenreported.15,16
Automated refraction (AR), especially under cyclo-plegia, is considered a fast and reliable method forevaluating refraction in the general population.17–19
In clinical practice, AR after cataract surgery normallygives a valid starting point that is followed bymanifest
0886-3350/07/$dsee front matter 1573doi:10.1016/j.jcrs.2007.05.024
1574 AUTOREFRACTION AFTER REZOOM IOL IMPLANTATION
refraction (MR), which continues to be the goldstandard for determining refractive error. However,the reliability of AR decreases in some circ*mstances,such as in eyes with media opacities and IOLs, due tothe scattering of the infrared beam used by theseinstruments.20–23
The current study was designed to compare the re-peatability and accuracy of MR and AR in patientswith ReZoom IOLs. To our knowledge, there are noprevious studies of the validity of AR after ReZoommultifocal IOL implantation. This should allow us todetermine whether AR is sufficiently accurate to beuseful as a starting point for subjective refraction afterReZoom multifocal IOL implantation.
PATIENTS AND METHODS
Study Design
This prospective study comprised 144 eyes of 72 cataractpatients who had bilateral potential visual acuity of at least20/40 and who had cataract surgery with binocular implan-tation of the ReZoom IOL. Potential visual acuity was deter-mined by a dilated near-pinhole test, a good predictor ofpotential visual acuity in patients with vision limited purelyby cataract.24 Exclusion criteria were ocular disease otherthan cataract (eg, uveitis, amblyopia, glaucoma, retinal de-tachment, diabetic retinopathy, macular degeneration, orcorneal, including previous refractive surgery or neurooph-thalmic disease). Written informed consent was obtainedfrom all patients before surgery in accordance with the Dec-laration of Helsinki, and institutional review board approvalwas obtained from the hospital ethics committee.
All the eyes were operated on by 1 of 2 surgeons (G.M.,H.F.S.), and the second eye was operated on within 1 weekof the first. Phacoemulsification using a 2.8 mm clear cornealincision placed on the steepest meridian, capsulorhexis, andsymmetric implantation of the IOL in the capsular bag wereperformed in all the eyes.
Patients were examined 1 day, 1week, and 1 and 6monthsafter surgery. Data for the study, including MR masked toautorefraction, slitlamp examination, andAR,were collectedat the last visit. In all patients, MR was performed using thecross-cylinder technique by the same experienced examiner(C.A.-D) in the same examination unit. All refractions wereperformed to limit variability in equipment or technique,and care was taken to ensure a consistent back-vertex
Accepted for publication May 23, 2007.
From the Refractive Surgery Department (Munoz, Albarran-Diego),Centro Oftalmologico Marques de Sotelo, and Hospital NISA Valen-cia al Mar (Munoz, Albarran-Diego), Valencia, and the RefractiveSurgery Department (Munoz, Sakla), VISSUM Instituto Oftalmolo-gico de Alicante, Alicante, Spain.
No author has a financial or proprietary interest in any material ormethod mentioned.
Corresponding author: Cesar Albarran-Diego, Centro OftalmologicoMarques de Sotelo, Avenida Marques de Sotelo 5, Planta 2a, 46002Valencia, Spain. E-mail: [emailprotected].
J CATARACT REFRACT SURG
distance of 12.0 mm. After MR, AR was performed withthe KR-8000 autorefractor (Topcon), which has shown excel-lent agreement with subjective refraction in normal healthyeyes.25 Three consecutive measurements were taken beforeand after dilation with phenylephrine 10%.
ReZoom Intraocular Lens
The multifocal ReZoom IOL is of soft foldable hydropho-bic acrylic material with an ultraviolet-absorbing filter. Theoptic is 6.0mm and the overall length, 13.0mm. The ReZoomIOL has 5 concentric refractive zones: zone 1 (bright light/distance dominant) is a large, distance-dominant centralzone for bright-light situations when pupils are constricted;zone 2 (large near dominant) provides near vision in a rangeof moderate- to low-light conditions; zone 3 (distance) pro-vides distance vision in moderate- to low-light conditions;zone 4 (near dominant) provides additional near vision inlow-light conditions; zone 5 (low light/distance dominant)provides additional distance-dominant support in low-lightconditions when pupils are fully dilated. The ReZoom IOLuses a near power of C3.50 diopters (D) at the lens plane,which corresponds to approximately C2.40 to C2.80 D inthe spectacle plane. The IOL has a patented OptiEdge tripleedge, which comprises a rounded anterior edge to reduce in-ternal reflections, a sloping side edge tominimize edge glare,and a square posterior edge to reduce the incidence of poste-rior capsule opacification. The edge provides 360-degreecontact between the anterior capsule and posterior capsule.
Statistical Analysis
Manifest and automated refractions in conventionalscript, sphere (S), cylinder (C), and axis (4), were convertedinto power vectors coordinates (M, J0, J45) by the followingformulas according to Thibos and Horner26:
MZSþC=2; J0Zð�C=2Þ cosð24ÞJ45Zð�C=2Þ sinð24Þ
All refractions were expressed in minus cylinder. Vectoranalysis is not sensitive to the sign of the spherocylindricalnotation and yields the same results independently of usinga positive or a negative cylinder notation.
Statistical analysis was performed using SPSS for Win-dows (version 12.0, SPSS, Inc.). Three consecutive AR mea-surements were averaged (after power-vector conversion)before dilation and after dilation with phenylephrine 10%.One-sample t tests were used to check for differences be-tween themeans of the 3 ARmeasurements in each eye (non-dilated and dilated) comparedwith the initial AR nondilatedmeasurement for M, J0, and J45 to consider a proper repeat-ability of AR measurements. Two-sample t tests were usedto look for differences between AR and MR. Differences int tests were considered statistically significant whenP!.05. For all t tests, the calculated statistical power washigher than 0.8 using Sample Power (version 2.0, SPSS, Inc.).
RESULTS
Data were collected for 144 eyes of 72 patients (31 menand 41 women). The mean age of the patients was 69.8years G 9.4 (SD) (range 31 to 87 years). The best cor-rected MR visual acuity ranged from 20/15 to 20/40.
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mailto:[emailprotected]
1575AUTOREFRACTION AFTER REZOOM IOL IMPLANTATION
Repeatability of Automated RefractionMeasurements
The mean differences between the initial nondilatedARmeasurement and themean of the 3measurementsbefore dilation was 0.02 G 0.14 D for M, �0.02 G0.13 D for J0, and 0.01 G 0.08 for J45 and after dilation,0.02 G 0.15 D for M,�0.01 G 0.07 D for J0, and 0.01 G0.09 for J45. No significant differences (1-sample t test)were observed, suggesting the initial measurementwas similar to the means of the 3 AR measurements(nondilated and dilated). Because no systematic differ-ences between the initial values and the means of the3 values were observed, initial nondilated AR mea-surements were used in all subsequent analyses.
Agreement Between Automated Refractionand Manifest Refraction Measurements
Figure 1 shows the mean values of the difference be-tween AR andMR for all the components of refraction.
Sphere Themean difference between the first AR andtheMR sphere was�0.84 G 0.62 D; 84.7% of the differ-ences were greater than 0.25 D.
Spherical Equivalent The mean value of the differencebetween the first AR compared with the MR sphericalequivalent was �1.00 G 0.61 D; 90.3% of the differ-ences were greater than 0.25 D.
Cylinder The mean value of the difference for the2 components of the astigmatism J0 and J45 betweenthe initial AR cylinder and the MR cylinder was�0.06 G 0.19 D and �0.01 G 0.17 D, respectively;7.6% and 6.2% of the differences, respectively, weregreater than 0.25 D.
Correlation Between Automated Refractionand Manifest Refraction Measurements
Figure 2 shows the scatterplot of the differences inrefractive data between AR and MR for the sphereand the 3 components of vector analysis: M, J0, andJ45. Correlation between J0 and J45 determined by ARversus MR was excellent, with coefficients of correla-tion (R2) of 0.8881 and 0.8640, respectively. The corre-lation for sphere and spherical equivalent between ARand MR was poor (R2 Z 0.4852 and R2 Z 0.5529,respectively).
Two-sample t tests showed statistically significantdifferences between AR andMR for sphere and spher-ical equivalent (P!.0001), whereas J0 (P Z .3083) andJ45 (0.9039) showed no statistically significant differ-ences between AR and MR.
An analysis including only eyes with a sphericalequivalent value determined by AR to be higherthan 2.00 D (n Z 47) yielded improved correlation
J CATARACT REFRACT SURG
coefficients (Figure 3). Conversely, when the analysisincluded only eyes with a spherical equivalent valueof 2.00 D or less (n Z 97), the correlation coefficientsworsened (Figure 4).
Figure 5 shows a scatterplot of the difference be-tween AR and MR compared with the MR. The figureshows that the difference was not a function of the sizeof the MR for sphere and spherical equivalent.
Auto
refra
ctio
n- M
anife
st R
efra
ctio
n (D
)-2,0
-1,5
-1,0
-0,5
0,0
0,5
J0
J45
S M
Figure 1. Box plot of the difference between AR and MR for S(sphere), M (spherical equivalent), and J0 and J45 (vector componentsof astigmatism).
-3 -2 -1 0 1 2
Man
ifest
Ref
ract
ion
(Dp)
-3
-2
-1
1
2
Autorefraction (Dp)
y = 0,7867x - 0,0096R2= 0,8881
-6 -5 -4 -3 -2 -1 0 1-4
-3
-2
-1
1
y = 0,4925x + 0,0862R2= 0,5529
M
J0
-1,5 -1,0 -0,5 0,0 0,5 1,0-1,5
-1,0
-0,5
0,0
0,5
1,0
y = 0,7100x - 0,0086R2= 0,8640
J45
-5 -4 -3 -2 -1 0 1-3
-2
-1
1
2S
y = 0,4306x + 0,1787R2= 0,4852
Figure 2. Scatterplot of refractive data for the whole group (n Z 144)(autorefraction [x] versus manifest refraction [y]) for S (sphere), M(spherical equivalent), and J0 and J45 (vector components of astigma-tism). The solid line shows the linear regression and the dashed line,the 95% confidence interval.
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1576 AUTOREFRACTION AFTER REZOOM IOL IMPLANTATION
DISCUSSION
Subjective or manual refraction remains the method ofchoice for determining the refractive status after cata-ract surgery; however, it can be time consuming andrequires trained technicians. Several techniques, in-cluding AR and retinoscopy, can be used to determineat what point to start with subjective refraction. In thegeneral population, retinoscopy is superior to AR asa starting point to noncycloplegic refraction27; how-ever, retinoscopy requires experienced clinicians,while AR does not. The popularity of autorefractorsis attributable to their ease of use, availability, and
-6 -5 -4 -3 -2-4,0-3,5-3,0-2,5-2,0-1,5-1,0-0,50,0
-3 -2 -1 0 1 2
Man
ifest
Ref
ract
ion
(Dp)
-2,0
-1,5
-1,0
-0,5
0,00,5
1,0
Autorefraction (Dp)-1,5 -1,0 -0,5 0,0 0,5 1,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
y= 0,6844x + 0,6665R2= 0,5798
y = 0,7752x - 0,0515R2= 0,9272
y = 0,7505x - 0,0075R2= 0,9532
M
J0
J45
-5 -4 -3 -2 -1 0-3,0-2,5-2,0-1,5-1,0-0,50,00,5
S
y = 0,5922x + 0,5818R2= 0,5252
Figure 3. Scatterplot of refractive data for eyes with AR sphericalequivalent greater than 2.00 D (autorefraction [x] versus manifest re-fraction [y]) for S (sphere), M (spherical equivalent), and J0 and J45(vector components of astigmatism). The solid line shows the linearregression and the dashed line, the 95% confidence interval.
-2,5 -2,0 -1,5 -1,0 -0,5 0,0 0,5-2,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
-2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 0,5
Man
ifest
Ref
ract
ion
(Dp)
-2,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
Autorefraction (Dp)-1,5 -1,0 -0,5 0,0 0,5 1,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
y= 0,4126x + 0,0469 R2= 0,2775
y = 0,7896x - 0,0093R2= 0,8515
y = 0,6801x - 0,0071R2= 0,7996
M
J0
J45
-2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0-2,0-1,5-1,0-0,50,00,51,01,52,0
S
y = 0,4280x + 0,1321R2= 0,3952
Figure 4. Scatterplot of refractive data for eyes with AR sphericalequivalent 2.00 D or less (autorefraction [x] versus manifest refrac-tion [y]) for S (sphere),M (spherical equivalent), and J0 and J45 (vectorcomponents of astigmatism). The solid line shows the linear regres-sion and the dashed line, the 95% confidence interval.
J CATARACT REFRACT SURG
patient acceptance. They are now present in nearlyall ophthalmology and optometry offices. However,it is widely accepted that AR is not sufficiently accu-rate to be a substitute for subjective refraction to deter-mine the best corrected visual acuity after surgery orfor prescribing eyeglasses.28 Autorefractors are mostcommonly used to provide a starting point for subjec-tive refraction.28,29
To our knowledge, the validity of AR after multifo-cal IOL implantation (including the ReZoom IOL) hasnot been reported. Multifocal refractive IOLs provideprojection onto the retinal plane of images set at vari-ous distances using concentric rings of varying opticalpower. This may cause scattering of the infrared beamused by the autorefractor, giving false values in eyeswith multifocal refractive IOLs. In fact, the sheet ofinstructions for the ReZoom IOL states that autore-fractors may not provide optimum postoperativerefraction. It is well known that the accuracy of AR de-creases in other clinical situations (eg, media opacities,previous corneal refractive surgery).22,23,30–33
We evaluated the repeatability of AR in eyes withthe ReZoom IOL and found that the first AR measure-ment and the means of the 3 AR measurements fornondilated pupils and dilated pupils were not signifi-cantly different. We also found that multiple measure-ments did not improve the agreement between ARmeasurements and MR measurements. Our resultssuggest there is no significant variability across con-secutive AR measurements in the presence of a Re-Zoom IOL with nondilated pupils and dilated pupils.
Automated refraction showed a tendency towardmore negative sphere and spherical equivalent valuesthanMR, with a mean difference of�0.84 D for sphere
-4
-3
-2
-1
1
2
-2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 -2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5
Diff
eren
ce A
utor
efra
ctio
n-M
anife
st R
efra
ctio
n (D
)
-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
Manifest Refraction (D)
-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
M
J0
J45
-4 -3 -2 -1 0 1 -4 -3 -2 -1 0 1-4
-3
-2
-1
1
2S
Figure 5. Scatterplot of the difference between AR and MR com-pared with MR for S (sphere), M (spherical equivalent), and J0 andJ45 (vector components of astigmatism).
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1577AUTOREFRACTION AFTER REZOOM IOL IMPLANTATION
and�1.00 D for spherical equivalent. Overall, approx-imately 85% of sphere measurements and 90% ofspherical equivalent measurements were at least0.25 D different from the MR values. Some automatedrefracting devices show so-called instrument myopia,which is an overall trend toward excessive near-objectaccommodation.34 Accommodation no longer playsan important role in a pseudophakic eye, and the in-strument myopia observed in the eyes with ReZoomIOLs should be explained by the presence of themultifocal refractive IOL itself. The ReZoom IOLuses 5 concentric refractive zones alternating distantand near zones that may interfere with the infraredbeams of the autorefractor, causing this kind of instru-ment myopia.
Few patients had hyperopic subjective refractionsafter surgery. In these cases, AR was less positivethanMR, which means that even in the cases with pos-itive MR sphere, AR tended to show a degree of pseu-domyopia (or less hyperopia).
Surprisingly, astigmatic AR measurements showedexcellent agreement with MR astigmatism in the pres-ence of the ReZoom IOL. Less than 10% of cylindermeasurements by AR were more than 0.25 D differentfrom the MR values.
Eyes with the ReZoom IOL with MR emmetropiatended to show a degree of spherical or astigmatic er-ror in AR. In other words, AR worked worse in eyeswith a low MR postoperative refractive defect, whileit was more accurate in eyes with a high MR postoper-ative refractive defect. The ReZoom IOL providessimultaneous projection of images onto 2 different ret-inal planes; in this situation, the presence of a low re-fractive optical defect may be compensated for bythe cortical process of vision and the cortical process it-self may not be able to compensate for larger opticaldefects. The cortical process of vision ultimately playsa role that makes subjective refinement of any availablemethod of AR necessary. Even with highly sophisti-cated automated techniques such aswavefront-derivedAR, which accurately reflects the eye’s physical opticalsystem, agreement between AR and MR is not alwayscomplete.35
When sequential bilateral cataract surgery isplanned, the postoperative result in the first eye mayhelp refine the power of the IOL to be implanted inthe second eye. In the presence of a ReZoom IOL, theresidual postoperative spherical component of the re-fraction in the first eye should always be determinedby MR, not by AR alone, because of the tendency to-ward false-negative spherical values. From a practicalviewpoint, it would be interesting to be able to imple-ment a regression formula in the autorefractor to ob-tain a more accurate automatic measurement of therefractive error in the presence of a ReZoom IOL.
J CATARACT REFRACT SURG
Unfortunately, the correlation between sphericalvalues determined by AR or MR was low, making itimpractical.
In summary, AR showed excellent agreement withMRastigmatism, but notwith spherical values.Autore-fraction after ReZoom IOL implantation can be usedas a good starting point for subjective refraction ofastigmatism, although spherical values may beunderestimated.
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First author:Gonzalo Munoz, MD, PhD, FEBO
Refractive Surgery Department,Centro Oftalmologico Marques de Sotelo,and Hospital NISA Valencia al Mar,Valencia, Spain
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