Prediction error and myopic shift after intraocular lensimplantation in paediatric cataract patients

N E D Hoevenaars,1 J R Polling,1,2 R C W Wolfs1

ABSTRACTAim To determine the amount of myopic shift in childrenafter cataract surgery with intraocular lens (IOL)implantation and to evaluate success in achieving thetarget refraction.Methods The children were assigned into three groupsdepending on age at time of surgery: Group A,0e1 years old; Group B, 1e7 years old; Group C, 7e18years old. Multiple regression analysis was used tocreate a formula for expected myopic shift and to findout which variables were associated with a higherabsolute prediction error.Results Children less than 12 months of ageexperienced higher myopic shifts and a larger mean rateof refractive change per year compared with olderchildren. We found higher myopic shifts in youngerchildren at time of surgery and children with unilateralcataract. Absolute prediction error was significantlyhigher in Group A compared with Groups B and C(p0.022 and p0.037, respectively). Multipleregression analysis showed that corneal radius was theonly variable significantly associated with absoluteprediction error.Conclusion Our data demonstrate the complexity inpredicting the postoperative refraction in children under1 year old and show that age at surgery and laterality arefactors to consider when deciding which IOL power toimplant in children.

INTRODUCTIONDue to advances in surgical techniques, improve-ments in intraocular lens (IOL) materials and betterunderstanding of the growth of the eye, theacceptable age for IOL implantation in children andinfants is becoming progressively younger.1 2

Although IOL implantation in children less than2 years old is becoming an increasingly acceptedprocedure, some surgeons prefer to leave infantsaphakic after cataract surgery and use contact lensesfor optical correction.3 Previous studies showedaphakic eyes display a greater rate of refractivegrowth than pseudophakic eyes.4 5 Children withhigher rate of refractive growth were found to havepoorer long-term visual results.6 This supports theuse of IOL implantation in children and infants.Despite developments in IOL implantations in

younger children, the choice of which implantpower to use remains one of the most difcult andmost discussed aspects in paediatric cataractsurgery. Age at surgery, visual input, presence of anIOL, laterality and inter-ocular axial length differ-ence have all demonstrated an affect on growth ofthe eye.7 8 This leads to complicated IOL powerpredictions in an individual child. Surgeons havevarying opinions as to the optimal postoperative

refractive goal in infants and children. Currentlymost surgeons underpower the lens, resulting ina hyperopia in the years following implantation.9 10

Some authors advise aiming for emmetropia post-operatively. This option does not allow for post-operative myopic shift, but may allow for easiermanagement of amblyopia in the early post-operative period.3

There is still no consensus on the ideal post-operative refraction in infants and children afterIOL implantation. In this study, we analysedmyopic shift and prediction error in children oper-ated in the Erasmus University Hospital,Rotterdam, The Netherlands.

METHODSThe medical records of 82 consecutive paediatricpatients who had undergone cataract surgery at ourclinic between January 2000 and January 2009 werereviewed retrospectively. Both congenital anddevelopmental, and unilateral and bilateral cataractwere included. Excluded patients were those withintra-ocular congenital anomalies such as persistentfetal vasculature (n4), patients without IOLimplantation (n25) and those with a follow-upexamination less than 3 months postoperatively(n3). Four patients were lost to follow-up.Patients were divided into three groups based onage at surgery regardless of whether the cataract(s)were unilateral or bilateral: Group A, 0e1 years old;Group B, 1e7 years old; Group C, 7e18 years old.Preoperative evaluation included slit-lamp exam-

ination, dilated funduscopy, retinoscopy, kera-tometry and biometry. Axial length measurementswere performed using the Alcon Ocuscan (Alcon,Irvine, California, USA).. Keratometry readingswereobtained in the operating room on sedated childrenin supine position with automatic hand-held kera-tometer (Righton Retinomax K-Plus2; Righton,Tokyo, Japan). The SRK-Tand Holladay II formulaswere used to calculate IOL power, which wasadjusted for age and expected myopic shift of thechild. We used the Holladay IOL Consultant &Surgical Outcome Assessment Software package(Holladay Consulting, Bellaire, Texas, USA) tocalculate lens power. In unilateral cataract cases, therefractive error of the fellow eye was taken intoaccount when deciding what power to implant inorder to prevent signicant anisometropia.Phacoemulsication was performed according to

a standard protocol. In brief, a 3.0 mm corneoscleralincision was made. A circular capsulorhexis wascreated followed by hydrodissection. Lens contentswere aspirated and the IOL was placed in thecapsular bag. All wounds were closed with 10-0ethilon sutures. Primary posterior capsulorhexis or

1Department of Ophthalmology,Erasmus University MedicalCenter, Rotterdam, TheNetherlands2Hogeschool Utrecht, Universityof Applied Sciences, Utrecht,The Netherlands

Correspondence toDr R C W Wolfs, ErasmusUniversity Medical Center,Department of Ophthalmology,3000-CA Rotterdam, TheNetherlands;r.wolfs@erasmusmc.nl

Accepted 13 June 2010Published Online First6 August 2010

1082 Br J Ophthalmol 2011;95:1082e1085. doi:10.1136/bjo.2010.183566

Clinical science

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capsulotomywas performed depending on the age of the child. Ananterior vitrectomy was performed when necessary. During therst cases of cataract surgery with IOL implantation, polymethylmethacrylate (PMMA) intra-ocular lenses were implanted; latercases received foldable silicone or acrylic intra-ocular lenses.Postoperatively, all children received dexamethasone 0.1% eyedrops three times a day for 4e6 weeks. All children receivedstringent amblyopia treatment (occlusion) and adequate opticalcorrection with contact lenses or spectacles when necessary.

Data collectionThe target refraction (desired postoperative refractive error) andthe IOL calculation formula were both selected by the operatingsurgeon. Generally, the younger the patient at time of surgery,the more hyperopic the target refractive error was chosen toanticipate for the myopic shift. All children were reviewed 1 day,1 week and 4 weeks postoperatively; further check-ups werebased on individual patient needs. Refraction at 3 months aftersurgery was used as the postoperative refraction (when thecorneoscleral incision was stable). The spherical equivalent ofthe postoperative refractive error was used in the analyses(spherical equivalent: spherical power + ( 3 cylindricalpower)). Using target refraction, prediction error for eachsurgical outcome was calculated with the followingformula11 12: prediction error (D) desired postoperativerefraction (D)eactual postoperative refraction (D).

StatisticsThe ManneWhitney U test was used to analyse differences inprediction errors between groups (A, B and C), differences inprediction error in axial length (

eyes with corneal radii 2 years old at time of IOL implantation.18 Our data arecompatible with these ndings, showing larger myopic shift andwider ranges in target refraction under the age of 7 years, andmore so under the age of 1 year. We feel that this can be

explained by the fact that in pseudophakic eyes the lens power isstatic, so that increase in axial length results in a decrease inhyperopia or an increase in myopia.3 The effect of vertexdistance is another optical phenomenon that inuences thechanges in refraction in growing pseudophakic eyes. As the eyegrows, the IOL moves farther from the retina, causing a myopicshift.5

A greater myopic shift in children with unilateral pseudo-phakia versus children with bilateral pseudophakia has alreadybeen documented.1 8 Our results conrmed these ndings, as wealso found a signicantly greater rate of change in the unilateralgroup than in the bilateral group. Poorer quality of the retinalimage in unilateral cataract cases and deprivation amblyopiacould be a trigger for accelerated growth in the affected eye. Thiswould be explained by a decrease in retinal proteoglycansynthesis that leads to an increased rate of scleral growth inthese patients.19

At the moment there is no agreement in the literature on theideal target refraction in infants and children after IOLimplantation. A majority of surgeons choose to underpower theIOL, resulting in hyperopia, in anticipation of the myopic shiftin the years after surgery.20 21 Enyedi et al suggested under-powering by +6 D at 1 year of age and decreasing 1 D per year,up to 1 D at 8 years and older.17 Astle et al supported theserecommendations except for that they recommended under-powering the IOL by as much as 7.0e8.0 D at age 1e2 years and5.0e7.0 D at age 2e4 years.10

We found a wide variation in myopic shifts (8.13 to 0 D)among our patients less than 1 year of age. Both laterality andage at time of IOL inuenced the myopic shift, comparable withprevious ndings.1 9 Hence, we recommend underpoweringmore in younger children than older children and almost +1 Dmore in unilateral cases than bilateral cases. According to theexpected myopisation formula yielded by multiple regressionanalysis, we recommend underpowering by +7.8 D in childrenwith unilateral cataract at age of 3 months at time of IOLimplantation.

Prediction errorThe mean absolute prediction error found in our patient groupwas 1.14 (range 0.01e3.53) D. This is comparable to theprediction error in previous studies in children, varying from1.08 to 1.16 D.12 22 Although the absolute prediction error in ourstudy was not higher than ndings in research based on children,it remains much higher than that found in adults. For compar-ison, in a study by Olsen using the latest generation IOL powercalculation formulas the mean prediction error was 0.47 D.23

There are several possible reasons for the higher prediction errorobserved in children. Most importantly, the measurement ofaxial length and keratometry in infants is usually done undergeneral anaesthesia in an eye that is unable to cooperate withprecise xation and centration.3 In addition, the desired residualhyperopia necessary to compensate for the myopic shift causesa higher prediction error. Furthermore, axial lens positions based

Table 2 Calculated postoperative refractive goalaccording to age and laterality

Age (months)

Underpowering intra-ocular lens(D)

Unilateral Bilateral

3 7.8 6.9

6 7.7 6.7

12 7.4 6.4

24 6.8 5.8

48 5.6 4.6

Table 3 Results by age

AgeTargetrefraction (D)

Implantpower (D)

Absolute predictionerror

Follow-up(years)

Change (D) at lastfollow-up

Rate of change(D/year)

Group A: 0e12 months old +3.70 (+0.49 to +8.5) +26.9 (20e30) 2.09 (0.95 to 3.53) 3.0 3.18 (8.13 to 0.0) 1.05

Group B: 1e7 years old +1.22 (0.52 to +4.78) +24.39 (8e37) 1.08 (0.14 to 2.39) 2.7 1.06 (6.51 to +1.63) 0.40

Group C: 7e18 years old +0.06 (0.78 to +1.53) +20.39 (8e29) 0.88 (0.01e2.90) 1.3 0.06 (1.38 to +0.5) 0.05Values are means with ranges.

1084 Br J Ophthalmol 2011;95:1082e1085. doi:10.1136/bjo.2010.183566

Clinical science

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on anterior chamber depths have been obtained from studies inadult populations. These data might not apply to the shalloweranterior chambers in paediatric eyes.24

Our multiple regression model showed that only cornealradius was signicantly associated with prediction error; age attime of surgery, axial length, surgeon, IOL power and lateralitydid not appear to play a role. Greater prediction errors in eyeswith smaller corneal radii have also been found in previousliterature. Moore et al showed that age at time of surgery andcorneal radius were the only two variables signicantly associ-ated with mean absolute prediction error.22 Tromans et al foundgreater prediction errors in 12 eyes with corneal radii

doi: 10.1136/bjo.2010.1835666, 2010

2011 95: 1082-1085 originally published online AugustBr J Ophthalmol

N E D Hoevenaars, J R Polling and R C W Wolfs

cataract patientsintraocular lens implantation in paediatric Prediction error and myopic shift after

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