ARTICLE

Influence of spher

ical intraocular lensimplantation and conventional laser in situ

keratomileusis on peripheral ocular aberrationsAnkit Mathur, PhD, David A. Atchison, DSc

Q 2010 A

Published

SCRS an

by Elsev

PURPOSE: To measure the effect of spherical intraocular lens (IOL) implantation and conventionalmyopic laser in situ keratomileusis (LASIK) on peripheral ocular aberrations.

SETTING: Visual and Ophthalmic Optics Laboratory, School of Optometry, and Institute of Healthand Biomedical Innovation, Queensland University of Technology, Brisbane, Australia.

METHODS: Peripheral aberrations were measured using a modified commercial Hartmann-Shackaberrometer across 42 degrees � 32 degrees of the central visual field after spherical IOLimplantation and after conventional LASIK for myopia. The results were compared with those inan age-matched emmetropic group and an age-matched myopic control group, respectively.

RESULTS: The rate of quadratic change in spherical equivalent (SE) refraction, higher-order root-mean-square (RMS) aberrations, and total RMS aberrations across the visual field was greater andthe amount of spherical aberration higher in the IOL group than in the emmetropic control group.However, coma trends were similar in the 2 groups. The rate of quadratic change in SE refraction,higher-order RMS aberrations, and total RMS aberrations was greater across the field and theamount of spherical aberration higher in the LASIK group than in the myopic control group. Thetrend in coma across the field in the LASIK group was opposite that in the other groups.

CONCLUSIONS: Spherical IOL implantation and conventional myopic LASIK increased ocular pe-ripheral aberrations, causing a significant increase in spherical aberration across the visual field.Laser in situ keratomileusis reversed the sign of the rate of change in coma across the field relativeto that in the other groups.

Financial Disclosure: No author has a financial or proprietary interest in any material or methodmentioned.

J Cataract Refract Surg 2010; 36:1127–1134 Q 2010 ASCRS and ESCRS

Refractive procedures, such as intraocular lens (IOL)implantation and laser in situ keratomileusis (LASIK),are the most commonly performed ophthalmic surger-ies. Intraocular lens implantation is the only refractivetreatment for cataract, whereas LASIK is the mostpopular corneal correction for myopia. In LASIK, thecorneal stroma is ablated with an excimer laser,altering the corneal shape to correct refractive errors.1

Improvements in instruments and surgical techniqueshave rendered both procedures safe with few postop-erative complications.

An IOL with a spherical surface, no matter what itsshape, has positive spherical aberration that adds tothe generally positive spherical aberration of thecornea.2–4 The situation is somewhat similar to thatin the older eye; in young eyes, corneal sphericalaberration tends to be partially compensated for by

d ESCRS

ier Inc.

negative spherical aberration of the lens; however,with increasing age, the balance is lost as the sphericalaberration of the older lens tends to become positive.5,6

Spherical aberrations in eyes with spherical IOLs arehigher than those in age-matched phakic eyes.7–9 Intheory, spherical aberration can be reduced by IOLswith appropriate aspheric surfaces,10,11 as foundwith the aspheric IOLs produced in recent years.12

Aspheric IOLs provide some improvement in spatialvision over that obtained with spherical IOLs.12

Although the effects of IOL design and the natureof corneal ablations on axial aberrations and imagequality have been considered, attention should alsobe given to their effects on peripheral vision, whichis important for movement13 and detection tasks,both of which are affected by peripheral refractiveerrors.14,15 Also, these factors may affect diagnostic

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1128 REFRACTIVE SURGERY AND PERIPHERAL ABERRATIONS

and therapeutic procedures performed in the periph-ery, such as fundus imaging and photocoagulation.

Although theoretical studies have predicted periph-eral image quality for IOLs of different shapes,16–18 asyet there are no experimental studies. It has been pre-dicted that peripheral image quality is considerablyworse in pseudophakic eyes than in phakic eyesbecause of the large amount of astigmatism.17 Tendegrees from the center of the field, the IOL positionrelative to the pupil should not influence sphericalaberration but would have a significant influence oncoma.16,19 Coma increases linearly with the IOL shapefactor when the IOL is positioned at the pupil andshows a quadratic change with the IOL shape factorwhen the IOL is moved away from the pupil.16,19

The ablation profile in LASIK and related cornealrefractive surgeries is important in aberrations. Con-ventional LASIK increases higher-order aberrations(HOAs), particularly spherical aberration.20–22 Theincrease in spherical aberration occurs because the an-terior cornea, generally prolate (negative asphericity)before surgery, becomes oblate (positive asphericity)after surgery.23–25 The exact form of the surface, andhence the aberrations, is influenced by several factors,including hinge position, flap and bed thickness,decentration, optical zone diameter, wound healing,stromal regression, and corneal biomechanics.26–34

Wavefront-guided LASIK has been applied to custom-ize corneal ablation and minimize postoperativeaberration.35,36 Although the results have been prom-ising,36,37 many factors (eg, corneal hydration duringsurgery and postoperative healing) can influence theoutcomes.34,38

Theoretical studies39,40 indicate that peripheralimage quality after corneal refractive surgery is worsethan in emmetropic eyes. The image quality worsensconsiderably as the pupil becomes larger than the

Submitted: January 27, 2009.Final revision submitted: January 6, 2010.Accepted: January 7, 2010.

From the Visual and Ophthalmic Optics Laboratory, School ofOptometry, and Institute of Health and Biomedical Innovation,Queensland University of Technology, Kelvin Grove, Australia.

Supported by Australian Research Council Discovery grantDP0558209.

Lee Lenton, FRANZCO, Frank Howes, FRCOphth, Julie Albietz, PhD,and Andrew McCormack helped recruit patients.

Corresponding author: Ankit Mathur, PhD, Q528C, Institute ofHealth and Biomedical Innovation, Q-Block, Queensland Universityof Technology, 60 Musk Avenue, Kelvin Grove QLD 4059, Australia.E-mail: a.mathur@qut.edu.au.

J CATARACT REFRACT SURG

ablation zone. Ma et al.41 found greater peripheralmyopic shifts and greater astigmatism along thehorizontal meridian in eyes treated with conventionalLASIK than in untreated myopic eyes. PeripheralHOAs were measured in 2 LASIK patients; the ratesof change in spherical aberration were greater thanin the control group, and the rates of change in hori-zontal coma were of the opposite sign in the centralG25 degrees of the visual field than in the controlgroup.24 The changes in coma and spherical aberrationwere predictable on the basis of simple eye modelswith positive corneal asphericity.

The success of IOL implantation and LASIK is basedon the level of axial aberrations, visual acuity, andcontrast sensitivity function, without considerationof peripheral vision or peripheral optics. To betterunderstand the effects of these surgical interventions,we evaluated their effects on peripheral aberrations.

PATIENTS AND METHODS

The study comprised patients from a private ophthalmologyclinic in Brisbane and Queensland University of Technologywho had IOL implantation or laser in situ keratomileusis(LASIK) for myopia. The study complied with the tenetsof Declaration of Helsinki and was approved by theuniversity’s human research ethics committee. Afterreceiving written and verbal explanations of the proceduresand risks involved, all patients provided informed consent.

The IOL group had phacoemulsification with implanta-tion of an AcrySof SN60AT IOL (Alcon, Inc.). The IOL isspherical and biconvex; the front surface is more curvedthan the back surface. The patients had surgical scars at11 to 12 o’clock on the right corneas with clear posteriorcapsules. In the LASIK group, surgery was performed using1 of several laser platforms.

In this study, only right eyes were tested. All patients hada detailed slitlamp examination and corneal topographymeasurement with an E300 corneal topographer (MedmontInternational Pty. Ltd). The anterior corneal vertex radiusof curvature and asphericity were estimated from cornealheight data from the central 6.0 mm cornea, as describedpreviously,42,43 using the formula

X2 þ Y2 þ ð1þQÞZ2 �2ZR Z0

where X and Y are distance in the horizontal direction andvertical direction, respectively; Q is the asphericity; Z is thedistance along the visual axis; and R is the anterior cornealvertex radius of curvature.

The data in the IOL group and LASIK group were com-pared with data in age-matched control groups. The controlgroup for IOL patients consisted of emmetropic patients. Thecontrol group for LASIK patients consisted of myopicpatients.

Peripheral aberrations were measured with a modifiedCOAS-HD (Wavefront Sciences, Inc.) Hartmann-Shackaberrometer, which uses a wavelength of 840 nm. Patientsplaced their head on the aberrometer’s chinrest and througha 45-degree beam splitter fixated on a 6-row, 7-columnmatrix of targets projected sequentially on a rear projectionscreen across the 42 degree � 32 degree central visual field.The screen was 1.2 m from the eye. The center of the target

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1129REFRACTIVE SURGERY AND PERIPHERAL ABERRATIONS

matrix was aligned with the internal fixation target of theaberrometer. Before measurements were taken, the pupilcenter was aligned with the measurement axis of the aberr-ometer and the cornea (rather than the entrance pupil) wasmade conjugate with the lenslet array with the help of theaberrometer’s pupil camera. Two measurements were takenat each visual field location, and the aberration coefficientswere averaged. Detailed descriptions of the methods havebeen given.44

Axial aberrations were measured using the internalfixation target of the aberrometer and the manufacturer’s in-structions. The internal target was fogged by 1.50 D to limitthe influence of accommodation on axial aberrations. Axialaberration coefficients in the refractive groups and controlgroups were compared using independent sample t tests.Aberrations were described using Zernike coefficients upto the 6th order at a 555 nm wavelength for a 5.0 mm pupilin accordance with the International Organization for Stan-dardization aberration standard.45 Zernike coefficients forelliptical pupils resulting from eye rotation relative to theaberrometer were estimated with the aberrometer softwareand a purpose-designed MatLab-based algorithm (TheMathWorks, Inc.), which compensated for the ellipticalshape of the pupil by stretching it by the inverse of thecosine of the viewing angle.46 Peripheral refractions weredetermined in terms of spherical equivalent (SE) M, regularastigmatism J180, and oblique astigmatism J45 from Zernikecoefficients as previously described.46

RESULTS

The IOL group consisted of 6 patients with a meanage of 62 years (range 55 to 68 years) and a meanpostoperative SE refraction of 0.12 diopter (D) (range�0.2 D to 0.9 D). The LASIK group consisted of6 patients with a mean age of 32 years (range 25 to39 years). Table 1 shows the surgical details and refrac-tion in the LASIK group. No patient had postoperativecomplications, and all had high-contrast visual acuityof at least 6/7.5 (Bailey-Lovie chart).

The emmetropic control group (for IOL patients)comprised 7 patients with a mean age of 63 years(range 50 to 71 years) and a mean SE of 0.1 D G 0.6(SD). The myopic control group (for LASIK patients)comprised 10 patients with a mean age of 27 years(range 22 to 35 years) and a mean SE of �3.8 G 1.9 D.

Table 1. Operative data and refraction in the LASIK group.

Pt Time Since LASIK (Mo) Optical Zone (mm) Preop

1 12 6.5 �6.50 �0.502 28 6.4 �3.25 �0.503 43 5.0 �2.25 �0.504 5 6.5 �5.75 �2.755 48 6.5 �2.25 �0.256 36 6.8 Not know

LASIK Z laser in situ keratomileusis

J CATARACT REFRACT SURG

Intraocular Lens Versus Emmetropia

The mean anterior corneal radius of curvature was7.6 G 0.2 mm in the IOL group and 7.7 G 0.3 mm inthe emmetropic control group and the mean aspheric-ity, �0.08 G 0.15 and �0.16 G 0.08, respectively.The difference between groups was not statisticallysignificant in either parameter (P Z .48 and P Z .30,respectively).

Figure 1 shows the mean axial HOA and higher-order root-mean-square (RMS) aberrations in the IOLgroup and emmetropic control group. The IOL grouphad statistically significantly greater positive sphericalaberration C(4,0) (mean difference C0.10 G 0.04 mm;t Z 3.1, P Z .01) and higher-order RMS (mean differ-ence C0.18 G 0.03 mm; t Z 5.1, P!.001) than thecontrol group. There was no significant differencebetween the 2 groups in any other axial HOAcoefficient.

Figure 2 shows the mean higher-order wavefrontmaps across the pupil at each visual field location.The wavefront maps in the IOL group were domi-nated by spherical aberration and those in the emme-tropic control group by coma across most of thevisual field. Coma increased away from the center ofthe field in both groups so its orientation approxi-mately matched the visual field meridian.

Figure 3 shows the mean refraction and aberrationvalues as a function of visual field position in theemmetropic control group and IOL group. The astig-matic terms J45 and J180 increased quadraticallyaway from the center of the visual field along the135- to 315-degree meridian and 90- to 270-degree me-ridian, respectively, and decreased along the perpen-dicular meridians. The SE (M) decreased ina quadratic manner away from the center of the fieldin both groups. The rate of change in J45, J180, andM across the field was greater in the IOL group thanin the control group; the between-group difference inthe change in M was greater (approximately 0.0020 D/degrees2 higher in IOL group) than the difference in

Refraction

Postop Laser Platform

� 160 �0.25 �0.75 � 15 Bausch & Lomb Z100� 180 �0.25 �0.75 � 31 Carl Zeiss AG MEL 80� 10 C0.25 �0.25 � 120 Nidek EC-5000� 180 Plano �0.25 � 115 WaveLight Allegretto 400 Hz� 90 C0.25 �0.50 � 155 Not knownn Plano �0.25 � 35 Not known

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Figure 1.Mean axial trefoil C(3,�3), vertical coma C(3,�1), horizon-tal coma C(3,1) coefficient, spherical aberration C(4,0), and higher-order RMS (HO RMS) aberrations in the emmetropic control groupand IOL group. The error bars represent the standard deviation ofthe mean aberration. The asterisks above the IOL group results indi-cate significant differences between groups (IOL Z intraocular lens;RMS Z root mean square).

1130 REFRACTIVE SURGERY AND PERIPHERAL ABERRATIONS

the changes in J45 and J180. Trefoil C(3,�3) was morenegative in the IOL group than in the control group,although the difference was not statistically significant(P Z .47). Vertical coma C(3,�1) and horizontal comaC(3,1) had similar magnitudes and linear dependen-cies along the vertical field meridian and horizontalfield meridian, respectively, in both groups. Sphericalaberration C(4,0) was significantly more positive(mean difference C0.15 G 0.03 mm; t Z 5.8, P!.001)across the field in the IOL group than in the controlgroup. Higher-order RMS aberration was higheracross the visual field in the IOLgroup,mainly becauseof the differences in spherical aberration. Total RMSaberrations excluding defocus changed at a greaterrate in the IOL group, mainly because of differencesin the rates of change in astigmatism.

J CATARACT REFRACT SURG

Laser In Situ Keratomileusis Versus Myopia

The mean anterior corneal radius of curvature was8.5 G 0.4 mm in the LASIK group and 7.7 G 0.2 mmin the myopic control group and the mean asphericity,C0.6 G 0.1 and �0.2 G 0.1, respectively. Both werestatistically significantly higher in the LASIK group(P Z .005 and P!.001, respectively).

Figure 4 shows the mean axial HOA coefficients andhigher-order aberrations in the LASIK group and themyopic control group. The LASIK group had statisti-cally significantly greater positive spherical aberrationC(4,0) (mean difference C0.09 G 0.04 mm; t Z 3.5,P Z .004) and greater negative horizontal coma (meandifference �0.11 G 0.04 mm; t Z 2.8, P Z .014) thanthe control group. There was no significant differencebetween groups in any other axial HOA coefficient.

Figure 5 shows the mean higher-order wavefrontmaps across the pupil at each visual field location.The wavefront maps in the LASIK group were domi-nated by spherical aberration near the center of thefield, whereas coma was the predominant aberrationaway from the center. The wavefront maps in the my-opic control groupwere dominated by coma across thewhole field. The orientation of coma in the LASIKgroup matched the visual field meridian but wasopposite the orientation in the myopic control groupas well as in the other 2 groups (Figure 2).

Figure 6 shows mean refraction and HOA terms asa function of visual field position in the myopic controlgroup and the LASIK group. The astigmatic termsJ45 and J180 were similar in the 2 groups. The M valuechanged little across the field in the control group butbecamemore negative into the periphery in the LASIKgroup by a rate of approximately 0.0020 D/degrees2.Trefoil C(3,�3) was more positive and had greaterrates of change in the LASIK group than in the controlgroup. However, the difference between the groupswas not statistically significant (P Z .12). For verticalcoma C(3,�1) and horizontal coma C(3,1), the slopes

Figure 2. Higher-order wavefrontmaps across the pupil (5.0 mm diame-ter) at each visual field location in theemmetropic control group and theIOL group (I, S, N, and T Z inferior,superior, nasal, and temporal visualfield, respectively; IOL Z intraocularlens).

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Figure 3.Mean refraction and aberration coefficients across the visual field (5.0 mm pupil) in the emmetropic control group and the IOL group.A: Oblique astigmatism. B: Spherical equivalent. C: Regular astigmatism. D: Trefoil. E: Vertical coma. F: Horizontal coma. G: Spherical aberra-tion.H: Higher-order RMS. I: Total RMS excluding defocus. The SE (M) has been shifted for each group so it is zero at the center of the field. Thecolor scales represent the magnitude of aberration coefficients (mm) and are common for a given aberration coefficient between the 2 groups. Thedotted black lines are the visual fieldmeridians in 30-degree steps (HORMSZ higher-order rootmean square; I, S, N, and T Z inferior, superior,nasal, and temporal visual field, respectively; IOL Z intraocular lens; RMS Z root mean square).

1131REFRACTIVE SURGERY AND PERIPHERAL ABERRATIONS

were in opposite directions in the LASIK group andcontrol group. Spherical aberration C(4,0) was signifi-cantly higher across the field in the LASIK group(mean difference C0.11 G 0.03 mm; t Z 3.7, P Z.003) than in the control group but was not as highas in the IOL group (Figure 3). Higher-order RMSand total RMS changed at greater rates in the LASIKgroup than in the control group.

Figure 4.Mean axial trefoil C(3,�3), vertical coma C(3,�1), horizon-tal coma C(3,1) coefficient, spherical aberration C(4,0), and higher-order RMS (HO RMS) in the myopic control group and the LASIKgroup. The error bars represent the standard deviation of themean aberration. The asterisks above the LASIK group results indi-cate significant differences between the groups (LASIK Z laser insitu keratomileusis; RMS Z root mean square).

J CATARACT REFRACT SURG

Figure 7 shows the differences between the LASIKgroup and the myopic control group in the verticalcoma C(3,�1) slope along the vertical visual fieldand in the horizontal coma C(3,1) slope along the hor-izontal visual field. The mean slopes in the LASIKgroup were approximately 50% higher and of the op-posite sign than those in the control group (P!.001).The coma slopes in the IOL group and emmetropiccontrol group were comparable to those in the myopiccontrol group (17% to 32% greater).

DISCUSSION

Similar to earlier studies of aberrations after IOL im-plantation47 and LASIK,20–22 we found greater axialhigher-order RMS aberrations in the IOL and LASIKgroups than in the 2 control groups. Spherical aberra-tion was more positive across the field in the IOLgroup than in the other 3 groups and was more posi-tive in the LASIK group than in its control group.The signs of coma slopes in the LASIK group werethe opposite of those in the other groups.

Our LASIK results support those in a study by Atch-ison,24 in which the LASIK patients had horizontalcoma slopes with signs opposite those in untreatedeyes within about G25 degrees of fixation. Beyondthis angle, Atchison found that the slopes changedsign. We did not measure out far enough to test this.Atchison found that spherical aberration decreasedinto the peripheral visual field; again, we may nothave measured far enough to confirm this.

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Figure 5. Higher-order wavefrontmaps across the pupil (5.0 mm diame-ter) at each visual field location in themyopic control group and the LASIKgroup (I, S, N, and T Z inferior, supe-rior, nasal, and temporal visual field,respectively; LASIK Z laser in situkeratomileusis).

1132 REFRACTIVE SURGERY AND PERIPHERAL ABERRATIONS

In the IOL group and its emmetropic control group,the anterior corneal radius of curvature and aspheric-ity were similar, whereas both were higher in theLASIK group than in the myopic control group. Thechanges in peripheral spherical refraction equivalentin spherical aberration and in peripheral coma afterLASIK can be largely explained by these differ-ences.24,41 Similar effects have been found in myopicorthokeratology.43,48 One orthokeratology study43

showed the influence of treatment zone, with the eyewith the smaller zone having a reversal in coma slopeout to approximately G15 degrees only.

Zhou et al.37 found that increases in cornealasphericity, on-axis coma, and on-axis sphericalaberration were significantly smaller after wavefront-guided LASIK than after conventional LASIK. Because

Figure 6.Mean refraction and aberration terms across the visual field in theB: Spherical equivalent.C: Regular astigmatism.D: Trefoil.E: Vertical comaTotal RMS excluding defocus. The SE (M) has been shifted for each groupmagnitude of aberration coefficients (mm) and are common for a given aare the visual field meridians in 30-degree steps (HO RMS Z higher-ordtemporal visual field, respectively; LASIK Z laser in situ keratomileusis; R

J CATARACT REFRACT SURG

of the way in which corneal asphericity influencesaberrations, we predict that the peripheral myopicrefraction would be smaller with wavefront-guidedLASIK than with conventional LASIK and that thedifferences in coma slope and in spherical aberrationacross the field would be smaller than in the controlgroup.

In conclusion, spherical IOL implantation and con-ventional LASIK produced considerable changes inperipheral ocular aberrations. Both procedures in-creased the rate of change in higher-order RMS aberra-tions toward the periphery of the field. Both alsoincreased spherical aberration across the field, al-though the increase was higher after IOL implanta-tion. Laser in situ keratomileusis reversed thedirection of change in coma across the field.

myopic control group and the LASIK group.A: Oblique astigmatism.. F: Horizontal coma.G: Spherical aberration.H: Higher-order RMS. I:so it is zero at the center of the field. The color scales represent theberration coefficient between the 2 groups. The dotted black lineser root mean square; I, S, N, and T Z inferior, superior, nasal, andMS Z root mean square).

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Figure 7. Vertical coma C(3,�1) along the vertical visual field andhorizontal coma C(3,1) along the horizontal visual field in the myo-pic control group and LASIK group (5.0 mmpupil). The coma slopeswere estimated by least-squares linear fits. The horizontal coma co-efficient for a given horizontal field angle was the mean of the hori-zontal coma coefficients with the same horizontal field angle butwith vertical field angles of G3 degrees. The error bars representthe standard deviation of the coma coefficient (LASIK Z laser insitu keratomileusis).

1133REFRACTIVE SURGERY AND PERIPHERAL ABERRATIONS

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OL 36, JULY 2010

First autor:Ankit Mathur, PhD

Institute of Health and BiomedicalInnovation, Queensland University ofTechnology, Kelvin Grove, Australia