The contribution of intraocular lens calculation accuracy to the refractive error predicted at 10 years in the Infant Aphakia Treatment Study

PURPOSE

To determine the relative contribution of intraocular lens (IOL) calculation accuracy and ocular growth variability to the long-term refractive error predicted following pediatric cataract surgery.

METHODS

Pseudophakic eyes of children enrolled in the Infant Aphakia Treatment Study (IATS) were included in this study. Initial absolute prediction error (APE) and 10-year APE were calculated using the initial biometry, IOL parameters, postoperative refractions, and mean rate of refractive growth. The cohort was divided into children with a low-initial APE (≤1.0 D) and a high-initial APE ( >1.0 D). The 10-year APE was compared between the two groups using the Mann-Whitney U test. Linear regression was used to estimate the variability in prediction error explained by the initial IOL calculation accuracy.

RESULTS

Forty-two children with IOL placement in infancy were included. Seventeen eyes had a low initial APE, and 25 eyes had a high initial APE. There was no significant difference in APE 10 years following surgery between individuals with a low initial APE (median, 2.67 D; IQR, 1.61-4.12 D) and a high initial APE (median, 3.45 D; IQR, 1.64-5.10 D) (P = 0.7). Initial prediction error could explain 12% of the variability in the prediction error 10 years following surgery.

CONCLUSIONS

IOL calculation accuracy contributed minimally to the refractive error predicted 10 years after cataract surgery in the setting of high variability in the rate of refractive growth.

Effective lens position and pseudophakic refraction prediction error at 10½ years of age in the Infant Aphakia Treatment Study

BACKGROUND

The refraction prediction error (PE) for infants with intraocular lens (IOL) implantation is large, possibly related to an effective lens position (ELP) that is different than in adult eyes. If these eyes still have nonadult ELPs as they age, this could result in persistently large PE. We aimed to determine whether ELP or biometry at age 10½ years correlated with PE in children enrolled in the Infant Aphakia Treatment Study (IATS).

METHODS

We compared the measured refraction of eyes randomized to primary IOL implantation to the "predicted refraction" calculated by the Holladay 1 formula, based on biometry at age 10½ years. Eyes with incomplete data or IOL exchange were excluded. The PE (predicted - measured refraction) and absolute PE were calculated. Measured anterior chamber depth (ACD) was used to assess the effect of ELP on PE. Multiple regression analysis was performed on absolute PE versus axial length, corneal power, rate of refractive growth, refractive error, and best-corrected visual acuity.

RESULTS

Forty-three eyes were included. The PE was 0.63 ± 1.68 D; median absolute PE, 0.85 D (IQR, 1.83 D). The median absolute PE was greater when the measured ACD was used to calculate predicted refraction instead of the standard A-constant (1.88 D [IQR, 1.72] D vs 0.85 D [IQR, 1.83], resp. [P = 0.03]). Absolute PE was not significantly correlated with any other parameter.

CONCLUSIONS

Variations in ELP did not contribute significantly to PE 10 years after infant cataract surgery.

The accuracy of intraocular lens calculation varies by age in the Infant Aphakia Treatment Study

Refraction predictions from intraocular lens (IOL) calculation formulae are inaccurate in children. We sought to quantify the relationship between age and prediction error using a model derived from the biometry measurements of children enrolled in the Infant Aphakia Treatment Study (IATS) when they were ≤7 months of age. We calculated theoretical predicted refractions in diopters (D) using axial length, average keratometry, and IOL powers at each measurement time point using the Holladay 1 formula. We compared the predicted refraction to the actual refraction and calculated the absolute prediction error (APE). We found that the median APE was 1.60 D (IQR, 0.73-3.11 D) at a mean age (corrected for estimated gestational age) of 0.20 ± 0.14 years and decreased to 1.11 D (IQR, 0.42-2.20 D) at 10.60 ± 0.27 years. We analyzed the association of age with APE using linear mixed-effects models adjusting for axial length, average keratometry, and IOL power and found that as age doubled, APE decreased by 0.25 D (95% CI, 0.09-0.40 D). The accuracy of IOL calculations increases with age, independent of biometry measurements and IOL power.

Refractive growth variability in the Infant Aphakia Treatment Study

PURPOSE

Prediction of refraction after cataract surgery in children is limited by the variance in rate of refractive growth (RRG3). This study compared RRG3 in aphakic and pseudophakic eyes with their fellow, normal eyes in the Infant Aphakia Treatment Study.

SETTING

Twelve clinical sites in the United States.

DESIGN

Randomized clinical trial.

METHODS

Infants randomized to unilateral cataract extraction had RRG3 calculated based on biometric data (axial length and keratometry) at cataract surgery and at 10 years of age, for both the normal and cataract eyes. Subjects were included if complete biometric data from both eyes were available both at surgery and at 10 years. Variance in RRG3 was compared between the groups with Pitman test for equality of variance between correlated samples.

RESULTS

Longitudinal biometric data were available for 103 of the 114 patients enrolled. RRG3 was -15.00 diopters (D) (3.00 D) for normal eyes (reported as mean [SD]), -17.70 D (6.20 D) for aphakic eyes, and -16.70 D (6.20 D) for pseudophakic eyes (P < .0001 for comparison of variances in RRG3 between normal and all operated eyes). Further analysis found differences in the variance in axial length growth (P < .0001) between operated and normal eyes; the variance in keratometry measurement change did not reach significance.

CONCLUSIONS

The standard deviation in the RRG3 of normal eyes in our study was half of that found in eyes that underwent cataract surgery.

Comparison of the rate of refractive growth in aphakic eyes versus pseudophakic eyes in the Infant Aphakia Treatment Study

PURPOSE

To compare the rate of refractive growth (RRG) between aphakic eyes and pseudophakic eyes in the Infant Aphakia Treatment Study (IATS).

SETTING

Twelve clinical sites across the United States.

DESIGN

Randomized clinical trial.

METHODS

Patients randomized to unilateral cataract extraction with contact lens correction versus intraocular lens (IOL) implantation in the IATS had their rate of refractive growth (RRG3) calculated based on the change in refraction from the 1-month postoperative examination to age 5 years. The RRG3 is a logarithmic formula designed to calculate the RRG in children. Two-group t tests were used to compare the mean refractive growth between the contact lens group and IOL group and outcomes based on age at surgery and visual acuity.

RESULTS

Longitudinal refractive data were studied for 108 of 114 patients enrolled in the IATS (contact lens group, n = 54; IOL group, n = 54). The mean RRG3 was similar in the contact lens group (-18.0 diopter [D] ± 11.0 [SD]) and the IOL group (-19.0 ± 9.0 D) (P = .49). The RRG3 value was not correlated with age at cataract surgery, glaucoma status, or visual outcome in the IOL group. In the aphakia group, only visual outcome was correlated with refractive growth (P = .01).

CONCLUSIONS

Infants' eyes had a similar rate of refractive growth after unilateral cataract surgery whether or not an IOL was implanted. A worse visual outcome was associated with a higher RRG in aphakic, but not pseudophakic, eyes.

FINANCIAL DISCLOSURE

None of the authors has a financial or proprietary interest in any material or method mentioned.

Slipping the knot: a comparison of knots used in adjustable suture strabismus surgery

PURPOSE

To evaluate the frictional force created by different knots used in adjustable suture strabismus surgery.

METHODS

To allow the simulation of strabismus surgery suture tying methods a model using 6-0 polyglactin 910 suture was created. Three different knots were evaluated: (1) the sliding noose knot with a double wrap of suture, (2) the cinch knot with a single throw on both sides of the pole suture, (2) and a single-throw square knot. (Bow-tie knots were not included.) A digital force meter was used to measure the force (gram-force [gf]) required to overcome the static friction created by the knot. Each simulation was repeated with new suture material 5 times and the force required after subsequent repositioning was also recorded.

RESULTS

The force to overcome static friction of the sliding noose knot was 240 gf [95% CI, 187-284 gf]; of the cinch knot, 150 gf [95% CI, 123-167 gf]; and of the square knot, 110 gf [95% CI, 95-121 gf]. Subsequent movement of each knot along the same suture required progressively less force, with the sliding noose maintaining the most static friction.

CONCLUSIONS

The sliding noose knot generates the most frictional force and also maintains the most friction after subsequent repositioning. Important consideration should be given to multiple repositioning movements, because the force required for each subsequent repositioning decreases.

A case of familial exudative vitreoretinopathy identified after genetic testing

We report the case of a 21-month-old girl who was found to have familial exudative vitreoretinopathy after genetic testing revealed a genetic deletion at 7q22. She had previously been followed for exotropia; however, fundus examinations in the office were thought to be normal. After the pediatric geneticist identified the link between 7q22 deletions and vitreoretinopathies an examination under anesthesia was performed. Fluorescein angiography during this examination confirmed the presence of avascular areas of the retina.

Intraocular lens power calculation for humanitarian missions based on partial biometry

PURPOSE

To determine whether the correlation between corneal power (K) and axial length (AL) can be used for intraocular lens (IOL) power calculation when biometric data are incomplete.

SETTING

Developing regions served by United States Navy humanitarian assistance missions.

DESIGN

Case series.

METHODS

Measurements of K and AL were collected from all adult cataract surgery charts and used to calculate emmetropic IOL powers. A formula for estimating K or AL was derived by Deming regression analysis. The emmetropic IOL powers were calculated by hypothetical scenarios as follows: (1) K estimated from the formula and measured AL, (2) mean population K and measured AL, (3) measured K and estimated AL, and (4) measured K and mean population AL. The mean absolute refractive error (MAE) was calculated for each hypothetical scenario and an additional scenario (scenario 5) using single IOL power for all eyes. The MAEs were compared with a paired t test.

RESULTS

The formula derived from Deming regression analysis was K = 74.56 - 1.317 × AL. The MAE for the scenarios were (1) 0.90 diopters (D), (2) 1.11 D, (3) 1.91 D, (4) 1.55 D, and (5) 1.22 D. The MAE for scenario 1 was significantly less (P<.01) than that for scenarios 2 and 5. The MAE for scenario 5 was significantly less than that for scenarios 3 and 4.

CONCLUSIONS

The correlation between K and AL can be used to improve accuracy of IOL calculation when K is unavailable. When the AL is unavailable, the mean population IOL power is most accurate.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Predictability of intraocular lens calculation and early refractive status: the Infant Aphakia Treatment Study

OBJECTIVE

To report the accuracy of intraocular lens (IOL) power calculations and the early refractive status in pseudophakic eyes of infants in the Infant Aphakia Treatment Study.

METHODS

Eyes randomized to receive primary IOL implantation were targeted for a postoperative refraction of +8.0 diopters (D) for infants 28 to 48 days old at surgery and +6.0 D for those 49 days or older to younger than 7 months at surgery using the Holladay 1 formula. Refraction 1 month after surgery was converted to spherical equivalent, and prediction error (PE; defined as the calculated refraction minus the actual refraction) and absolute PE were calculated. Baseline eye and surgery characteristics and A-scan quality were analyzed to compare their effect on PE.

MAIN OUTCOME MEASURES

Prediction error.

RESULTS

Fifty-six eyes underwent primary IOL implantation; 7 were excluded for lack of postoperative refraction (n = 5) or incorrect technique in refraction (n = 1) or biometry (n = 1). Overall mean (SD) absolute PE was 1.8 (1.3) D and mean (SD) PE was +1.0 (2.0) D. Absolute PE was less than 1 D in 41% of eyes but greater than 2 D in 41% of eyes. Mean IOL power implanted was 29.9 D (range, 11.5-40.0 D); most eyes (88%) implanted with an IOL of 30.0 D or greater had less postoperative hyperopia than planned. Multivariate analysis revealed that only short axial length (<18 mm) was significant for higher PE.

CONCLUSIONS

Short axial length correlates with higher PE after IOL placement in infants. Less hyperopia than anticipated occurs with axial lengths of less than 18 mm or high-power IOLs. Application to Clinical Practice Quality A-scans are essential and higher PE is common, with a tendency for less hyperopia than expected.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00212134.

Competency checklists for strabismus surgery and retinopathy of prematurity examination

PURPOSE

To evaluate two checklist tools that are designed to guide, document, and assess resident training in strabismus surgery and examination of infants at risk for retinopathy of prematurity (ROP).

METHODS

A panel of staff surgeons from several teaching institutions evaluated the checklists and provided constructive feedback. All former residents who had been trained via the use of these checklist tools were asked to take self-assessment surveys on competency in strabismus surgery and ROP examination. A Likert 5-point scale was used for all evaluations, with 1 being the lowest rating and 5 the highest rating.

RESULTS

Six experts in strabismus and seven in ROP rated the checklists. Their comments were used to revise the checklists, which were sent to the same group for reevaluation. The mean Likert score for the final checklists was 4.9 of 5.0 for both checklists. Of 16 former residents, 9 responded to the self-assessments with a mean overall score of 4.1 (of 5.0) for strabismus surgery and 3.9 for ROP examination.

CONCLUSIONS

These checklist tools can be used to assess the quality of a resident's training and experience in these specific ophthalmology skills. They are complementary to other curriculum and assessment tools and can serve to organize the educational experience while ensuring a uniformity of training.

Theoretical strategy for choosing piggyback intraocular lens powers in young children

INTRODUCTION

The normal growth of a young child's pseudophakic eye can result in a large myopic shift. Temporary polypseudophakia using piggyback intraocular lenses (IOLs) has been proposed as a means to reduce the amount of myopic shift by removing the anterior IOL when the eye becomes sufficiently myopic. Since the rate of refractive growth can be used to predict the refractive curve over time in pseudophakic children, we used this knowledge to develop a theoretical strategy for choosing IOL power combinations for temporary polypseudophakia.

METHODS

We used a novel Pediatric Piggyback IOL Calculator to develop a strategy for choosing the powers of the anterior and posterior IOLs. We graphed the predicted results for several combinations of piggyback IOL powers and chose the combination of IOL powers that appeared to give the best results, based on the known rate of refractive growth (5.4 D) and its standard deviation (2.4 D). We aimed for a combination to minimize the hyperopic or myopic refractive error during the first 6 years of life to facilitate amblyopia management and minimize the refractive error at age 20 years.

RESULTS

We found optimal results when the initial postoperative goal refraction with polypseudophakia was moderate hyperopia and the anterior IOL had approximately 20% of the total required IOL power.

CONCLUSIONS

This theoretical strategy can be used to determine piggyback IOL powers to use in children.

Intraocular lens power requirements for humanitarian missions

PURPOSE

To develop a generalized method to determine an optimum set of intraocular lens (IOL) powers for humanitarian missions.

SETTING

Humanitarian missions to Central America, South America, and Southeast Asia.

METHODS

Biometric data of adults who had cataract surgery on 2 humanitarian missions were reviewed, and the ideal emmetropic IOL power for each eye was calculated. Using statistical modeling, the number of extra IOLs required at each power to account for natural variation inherent in random population samples was calculated. To limit the total number of IOLs and maximize availability of suitable IOLs for each patient, a tolerance strategy for choosing IOL powers was developed and the ideal proportion of extra IOLs required at each power was empirically determined.

RESULTS

Data of 103 patients were reviewed. The mean IOL power was 20.38 diopters (D) +/- 2.32 (SD). Applying a tolerance strategy to accept IOLs with powers 0.5 D below or 1.0 D above the emmetropic IOL power, the number of extra IOLs required at each power was decreased to a fraction of the fourth root of the number of eyes anticipated to require that IOL power. The model predicted that with this strategy, fewer than 2% of all patients would be rejected due to lack of an IOL with a suitable power.

CONCLUSIONS

The spreadsheet-based IOL power prediction model calculated an ideal distribution of IOLs to order for humanitarian cataract surgery. It is generalizable to missions of any size and should help planners minimize costs while ensuring excellent refractive outcomes.

The association between myopic shift and visual acuity outcome in pediatric aphakia

PURPOSE

The advent of intraocular lens implantation after pediatric cataract surgery necessitates an increased understanding of refractive development. The significant variation in rate and amount of refractive change among eyes, both aphakic and pseudophakic, is well recognized, although the causes of such variation remain unclear. The purpose of this study was to determine if a correlation exists between the rate of refractive growth (RRG) and visual acuity outcome in pediatric aphakia.

METHODS

Multicenter, retrospective observational case series. One hundred and twenty-five eyes of 85 patients with cataract surgery before 1 year of age and a minimum of 3 years of follow-up were analyzed. RRG was calculated for each eye using the logarithmic model of ocular growth and compared with final logMAR acuity using linear regression.

RESULTS

The correlation of RRG with final logMAR acuity was statistically significant (r(2) = 0.10; P <.01), ie, 10% of variance in RRG is related to acuity outcome. The correlation was higher in unilaterally aphakic patients (n = 44; r(2) = 0.19; P <.01) than in bilaterally aphakic patients (n = 81; r(2) = 0.08; P <.01). Eyes with visual acuity of 20/60 or better had a significantly lower RRG than those with poorer acuity (4.1 v 5.4 diopters (D); P <.01).

CONCLUSIONS

RRG in aphakia is correlated with visual acuity outcome. Eyes with poorer acuity have a greater RRG.

A comparison of the rate of refractive growth in pediatric aphakic and pseudophakic eyes

OBJECTIVE

To compare the rate of refractive growth in pseudophakic children's eyes to that of aphakic eyes.

DESIGN

Multicenter, retrospective observational case series.

PARTICIPANTS

83 patients with pseudophakic eyes (100 eyes) and 74 patients with aphakic eyes (106 eyes), with an age of surgery between 3 months and 10 years and a minimum follow-up time of 3 years or more, depending on the age at surgery.

METHODS

A logarithmic model was used to analyze the rate of refractive growth for each eye.

MAIN OUTCOME MEASURES

Age at surgery, intraocular lens power, intraocular lens A-constant, initial postoperative refraction, final refraction, and final age.

RESULTS

Overall, pseudophakic eyes showed a lesser rate of refractive growth than aphakic eyes (-4.6 diopter vs. -5.7 diopter, P = 0.03). This trend was also present but less significant when the eyes were grouped into those less than 6 months of age at surgery (-3.3 diopter vs. -4.6 diopter, P = 0.09) and older patients (-5.0 diopter vs. -6.1 diopter, P = 0.07). However, the mean quantity of myopic shift was greater in pseudophakic eyes than in aphakic eyes (-5.26 diopter vs. -4.54 diopter), despite shorter follow-up times in the pseudophakic eyes. This is due to the optical effects of a constant intraocular lens power in a growing eye.

CONCLUSIONS

Pediatric pseudophakic eyes have a slightly lesser rate of refractive growth than aphakic eyes. The new rate values should be used for predicting future refractions in these eyes.

Intraocular lens calculator for childhood cataract

PURPOSE

To evaluate a computer program to predict the pseudophakic refraction of a child at any age.

SETTING

A pediatric ophthalmology practice.

METHODS

A computer program was written for Windows 95 that calculates the initial postoperative pseudophakic refraction of a child using Holladay's formula, given the axial length and keratometry readings. The logarithmic model was used to predict the ultimate refraction at age 20 years and chart the predicted curve of refractive error with standard deviations.

RESULTS

The program provided a graph of a child's predicted pseudophakic refraction versus age that would allow the surgeon to dynamically view the effects of changing the intraocular lens (IOL) power.

CONCLUSIONS

If pseudophakia and aphakia have the same effect on the growth of the eye, this program should accurately predict the myopic shift of a pseudophakic child. This could help guide the surgeon's choice of IOL power.

Theoretic refractive changes after lens implantation in childhood

OBJECTIVE

Children with aphakia tend to have decreasing hyperopia as they grow older. No large study of the long-term refractive changes in children with pseudophakia has been published, although myopic shifts of greater than 10 diopters (D) have been reported. The authors used the refractions of children with aphakia and long follow-up to calculate the theoretic long-term refractive effects of pseudophakia.

DESIGN

The study design was a chart review of eyes that underwent cataract surgery before age 10 with documented refractions for more than 7 years.

PARTICIPANTS

Ninety-three eyes were studied.

INTERVENTION

The initial aphakic refractions of the study eyes were used to calculate the intraocular lens (IOL) powers that would have been required to give emmetropia at cataract removal. The aphakic refractions at last follow-up were used to calculate the final pseudophakic refractions, and these were compared with the predictions of a logarithmic model of myopic shift.

RESULTS

The mean follow-up time was 11 years. The median calculated pseudophakic refraction at last follow-up was -6.6 D with a range of -36.3 to +2.9 D. Children who underwent surgery in the first 2 years of life had a substantially greater myopic shift than older children (P < 0.001) and a larger variance in this myopic shift (P < 0.001). The logarithmic model accurately predicted the final refraction within 3 D in 24% of eyes undergoing surgery before 2 years of age and in 77% of eyes undergoing surgery after this age.

CONCLUSIONS

Pseudophakia in children is predicted to result in a large quantity of myopic shift, particularly in very young children. An IOL power chosen to leave a child initially hyperopic should lessen both the quantity of myopic shift and the extreme myopia that can result with growth. The surgeon who implants IOLs in young children must be prepared for a wide variation in long-term myopic shift.

Myopic shift after cataract removal in childhood

BACKGROUND

Children who have had cataract removal tend to have decreasing hyperopia (myopic shift) as they grow older. We wondered if the rate of myopic shift could be determined by age at surgery, cataract type, glaucoma, or other factors.

METHODS

We studied 156 aphakic eyes of children who had cataract surgery before age 10 and documented refractions for more than 3 years. Refraction was corrected with contact lenses and spectacles; glaucoma was managed with medicine and surgery. Stepwise multiple regression was used to analyze differences in the rate of myopic shift between subgroups.

RESULTS

The average refraction tended to follow a logarithmic decline with age (P < 0.01, R2 = 0.97). The average rate of myopic shift (the slope of spectacle plane refraction vs log of age, where age is in years and log is base 10) was -5.5, with a standard deviation of 3.8. Age at surgery had a small but statistically significant effect on the rate (P < 0.01, R2 = 0.04). No other studied factor reached statistical significance. However, among the 86 eyes with cataract removal after age 6 months, age at surgery was not as significant (P = 0.21), and unilateral cataract eyes tended to have a greater rate than bilateral cataract eyes (-7.7 vs -5.7; P = 0.05, R2 = 0.05).

CONCLUSIONS

Aphakic refraction tends to follow a logarithmic decline with age. The rate of myopic shift is determined partly by age at surgery and whether the cataract was unilateral or bilateral, although the effects are small. A wide variation in the rate of myopic shift exists. The following factors made little difference in the rate: cataract type, glaucoma, sex, side, and best corrected visual acuity.

Intranasal visualization for nasolacrimal duct intubation

PURPOSE/METHODS

To improve intranasal visualization of nasolacrimal procedures we use a self-retaining nasal speculum with or without a sinuscope.

RESULTS/CONCLUSIONS

Placement and retrieval of silicone stents can be accomplished with less trauma than with a blind sweep technique. Additionally, the valve of Hasner can be seen and the creation of false passages avoided.

Dissociated horizontal deviation

Despite the emphasis placed on the vertical aspect of the deviation by its currently accepted clinical label, dissociated vertical deviation is well known to include movements in both the torsional and horizontal planes. When the horizontal component is very prominent, dissociated horizontal deviation is suggested as an appropriate label. We report the clinical characteristics and surgical treatment of six patients with a dissociated horizontal deviation that was marked enough to be the reason for seeking medical attention. All patients underwent lateral rectus recession unilaterally or bilaterally, alone or in combination with superior rectus recession. In addition, we report the use of the darkening wedge test to demonstrate the Bielschowsky phenomenon in the horizontal plane. This phenomenon, a dissociated exotropia spontaneously moving toward and crossing the midline to become an esotropia under cover when a progressively darkening filter is placed over the fixing eye, has not to our knowledge been previously reported.

Rhabdomyosarcoma of the ciliary body

Rhabdomyosarcoma is the most common malignant orbital tumor of childhood. It has twice been reported to arise within the globe from the iris. In addition, teratoid medulloepithelioma, a tumor arising from the ciliary epithelium, can contain a rhabdomyoblastic component, often in combination with other heteroplastic elements. The authors report what may be the first recorded case of an embryonal rhabdomyosarcoma of the ciliary body, possibly representing a one-sided differentiation of a malignant teratoid medulloepithelioma.