Use of the aphakic refraction in intraocular lens (IOL) power calculations for secondary IOLs in pediatric patients

Intraocular lens power calculation formula in congenital cataracts: Are we using the correct formula for pediatric eyes?

The major challenge these days in pediatric cataract surgery is not the technique of surgery or intraocular lens (IOL) used but the postoperative refractive error. Amblyopia occurring due to postoperative refractive error which the child has; destroys the benefit obtained by a near-perfect and timely surgery. Even if we settle the debate as to what should be the ideal postoperative target refraction, there is a postoperative surprise that is not explained by our conventional insights of an accurate power calculation in children. The role of IOL power calculation formulae in affecting the postoperative refractive error should not be underestimated. Therefore, which age-appropriate formula is to be used for children is unclear. This review is an update on major IOL power calculation formulas used in pediatric eyes. We have tried to define why we should not be using these formulas made for adult eyes and review the literature in this regard.

Comparison of Aphakic Refraction and Biometry-Based Formulae for Secondary In-The-Bag and Sulcus-Implanted Intraocular Lens Power Estimation in Children

PURPOSE

The aim of the study was to compare the accuracy of refractive outcomes in children undergoing secondary in-the-bag or cilliary sulcus intraocular lens (IOL) implantation, using aphakic refraction (AR)-based formulae (Hug and Khan) and biometry-based formulae (Holladay 1, Hoffer Q, SRK/T, and SRK II).

METHODS

In this retrospective study, a total of 65 eyes of 44 patients who underwent secondary in-the-bag or cilliary sulcus IOL implantation were included and divided into 2 groups: 39 eyes of the in-the-bag IOL group and the other 26 eyes of the sulcus-implanted IOL group. Holladay 1, Hoffer Q, SRK/T, and SRK II formulae were employed depending on the biometric data, while Hug and Khan formulae were used based on preoperative AR. The prediction error (PE) and the absolute value of predicted error (APE) were compared between the 2 groups and formulae.

RESULTS

In the in-the-bag IOL group, nonsignificant differences of APE were found among the 6 formulae, while the Holladay 1, Hoffer Q, SRK/T, and SRK II all demonstrated a significant hyperopic shift of median PE value compared to the Hug formula (p < 0.05, all), and Holladay 1 and SRK II also showed a significant hyperopic shift of PE compared to the Khan formula (p < 0.05, both). Higher percentages of eyes with PE <1 D were found using Hoffer Q and SRK/T. In the sulcus-implanted group, the Holladay 1, Hoffer Q, and SRK/T had a significantly smaller median value of APE than the Hug and Khan formulae (p < 0.05, all), and the SRK II had a significantly smaller median value of APE than the Hug formula (p < 0.05), while Holladay 1 had the lowest value of APE. Higher percentages of eyes within PE <1 D were found using Holladay 1, Hoffer Q, and SRK/T, while the highest one was SRK/T. Significantly larger hyperopic shifts of median PE value using all the 6 formulae were found in eyes with sulcus-implanted IOL than eyes with in-the-bag implanted IOL (p < 0.05, all). In the eyes of with in-the-bag implanted IOL, the Hug and Khan formulae had significantly smaller APE values when compared with the eyes with sulcus-implanted IOL (p < 0.05, both).

CONCLUSIONS

Whether IOL was in the bag or implanted in the sulcus, almost all the formulae showed hyperopic shift, SRK/T showed the best accuracy. Biometry-based formulae were superior to AR-based formulae in accuracy of IOL power calculation, especially when IOL was implanted in the sulcus. In-the-bag IOL implantation should always be with higher priorities, especially when using AR-based formulae in IOL power calculation.

Selection of an initial contact lens power for infantile cataract surgery without primary intraocular lens implantation

PURPOSE

To provide guidelines for the selection of an initial contact lens (CL) power based on the preoperative characteristics of the patient in eyes undergoing infantile cataract surgery without primary intraocular lens (IOL) implantation.

DESIGN

Cohort study.

PARTICIPANTS

Eyes were included if cataract surgery was performed without primary IOL implantation before 1 year of age, a SilSoft CL (Bausch & Lomb, Rochester, NY) was placed immediately after surgery, and postoperative refraction data were available within 1 month after surgery.

METHODS

The target CL power was calculated by using the postoperative refraction at the corneal plane for each eye. A regression formula was derived using the targeted CL power and the axial length (AL). The CL power also was estimated using various formulas. An A-constant was derived to estimate CL power using IOL power calculation formula.

MAIN OUTCOME MEASURES

Contact lens power.

RESULTS

Fifty eyes of 50 patients were analyzed. Age at the time of cataract surgery was 2.4 ± 1.7 months. Refraction at the corneal plane was 29.6 ± 4.4 diopters (D). Regression analysis revealed that CL power=84.4 - 3.2 × AL (R(2) = 0.82; P<0.001). Contact lens power can be estimated using an A-constant of 112.176 in the IOL power calculation formula. If a CL power of 32 D had been used, 22 (44%) of 50 eyes would have needed a replacement of CL.

CONCLUSIONS

We devised guidelines on selecting the initial CL power based on preoperative AL. The IOL power calculator also can help to estimate CL power. Refraction at the conclusion of surgery in infants may be difficult, and preoperative biometry can be used to estimate CL power.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Comparison of aphakic refraction formulas for secondary in-the-bag intraocular lens power estimation in children

PURPOSE

Intraocular lens (IOL) formulas based on aphakic refraction alone have been proposed as an alternative to biometry-based formulas. The purpose of this study was to determine the relative accuracy of these simplified formulas.

METHODS

Records of patients who received secondary in-the-bag (IOL) implants and for whom aphakic refraction was obtainable were retrospectively studied. The formulas for IOL power calculation by Hug (J Pediatr Ophthalmol Strabismus 2004;41;209-11) and Khan and by AlGaeed (Br J Ophthalmol 2006;90:1458-60; modified to account for greater K values in our population) were compared with the biometry-based Holladay 1 formula by calculating the absolute prediction error for each.

RESULTS

Twenty eyes met the inclusion criteria. The average age at IOL implantation was 4.8 ± 3.4 years. The mean of the absolute value of the prediction error when we used the Hug's formula was 2.4 ± 2.1 D; with Khan's formula, 2.4 ± 2.0 D; and with biometry, 1.6 ± 1.4 D. None of these differences was statistically significant (paired t test: Hug vs Khan, P = 0.9; biometry vs Hug, P = 0.3; biometry vs Khan, P = 0.2). The absolute prediction error was more than 2 D in 8 of 20 eyes (40%) when we used Hug's formula, 11 of 20 eyes (55%) with Khan's formula, and 5 of 20 eyes (25%) with biometry.

CONCLUSIONS

Although the 0.8 D reduction in accuracy of the refraction-based formulas was not statistically significant, we recommend continued use of biometry-based formulas for IOL power calculation. Aphakic refraction may be used to confirm IOL power prediction when biometry is difficult.

The relationships among cycloplegic refraction, keratometry, and axial length in children with refractive accommodative esotropia

PURPOSE

To explore the relationships among cycloplegic refraction, keratometry, and axial length in children with refractive accommodative esotropia and to evaluate the feasibility of axial length estimation from the other 2 parameters.

METHODS

This is a prospective case series of children ages 4-12 years who were diagnosed with refractive accommodative esotropia, cooperative for keratometry and optical biometry by the IOLMaster, and without amblyopia in the right eye. The right eyes of the first group of patients were used to generate a linear regression formula from cycloplegic refraction, keratometry, and axial length. This formula was used in the second group of patients to estimate axial length from cycloplegic refraction and keratometry.

RESULTS

A total of 100 children were enrolled. Cycloplegic refraction ranged from +2.25 D to +8.25 D, keratometry ranged from 38.34 D to 48.37 D, and measured axial length ranged from 19.34 mm to 23.66 mm. Estimated and measured axial lengths were strongly correlated (Pearson coefficient = 0.9; 95% CI, 0.83-0.94) with the former values having a greater mean by the paired t test (2-sided P < 0.0001; difference between means, 0.27 mm). Estimated and measured values differed by <0.5 mm for most eyes (33/50, 66%) and were within 1 mm for all eyes.

CONCLUSIONS

In children with refractive accommodative esotropia, there exists a constant mathematical relationship among cycloplegic refraction, keratometry, and axial length. This relationship allows reasonable estimation of axial length from the other 2 parameters.

Emmetropization after lensectomy and anterior vitrectomy for persistent hyperplastic primary vitreous cataract

PURPOSE

To report the case of a 2-year-old boy whose aphakic eye became emmetropic 15 months after lensectomy with anterior vitrectomy for a classic persistent hyperplastic primary vitreous cataract.

METHODS

Retrospective case report.

RESULTS

Emmetropization of the aphakic eye was caused by corneal steepening and axial elongation. At 2 years old, the child would fixate and follow with either eye.

CONCLUSIONS

In this patient, the fortunate combination of axial elongation and corneal steepening resulted in the aphakic eye's developing a plano refraction and thus becoming more amenable to amblyopia treatment.

Paediatric secondary intraocular lens estimation from the aphakic refraction alone: comparison with a standard biometric technique

AIM

To compare the following two methods of paediatric secondary posterior chamber intraocular lens (PCIOL) determination with the Holladay formula: (1) estimation from the aphakic refraction alone (using assumed keratometry (K) of 44 diopters); and (2) calculation based on preoperative measured biometry.

METHODS

(1) Retrospective medical record review in a referral eye hospital of children with aphakia aged < or =12 years who underwent secondary PCIOL implantation with an Alcon MA60BM lens; (2) PCIOL determination for a plano refraction by the above two methods (estimation and calculation); and (3) prediction of pseudophakic refraction for the PCIOL actually implanted by the above two methods compared with the actual pseudophakic refraction.

RESULTS

50 eyes of 30 children with aphakia were studied. The estimated (mean, 95% confidence interval (CI)) secondary PCIOL values (25.81, +/-1.65 D) and the calculated secondary PCIOL values (26.35, +/-1.50 D) were not significantly different (mean absolute value of the difference 1.86 D, 95% CI +/-0.41 D) by the two-tailed paired t test at alpha = 0.05 (p = 0.11). For each eye, the pseudophakic refractions predicted by the two methods for the PCIOL that was actually implanted differed, both from each other and from the actual pseudophakic refraction (repeated-measures analysis of variance, p<0.001; Tukey test, p<0.01).

CONCLUSIONS

The method of PCIOL estimation from the aphakic refraction alone provides values similar to those obtained by a standard technique and can be useful if biometry is unavailable. Targeting a pseudophakic refraction in paediatric aphakia is prone to error.

Retinoscopic (refractive) estimation of axial length in paediatric aphakia: a comparison with ultrasonic measurement

AIM

To compare paediatric axial length values estimated from the aphakic refraction alone with axial length values measured by ultrasound.

METHODS

Retrospective institutional medical record review of paediatric aphakic patients 12 years of age and younger with documented ultrasonic axial length and objective refraction (retinoscopy) within 3 months of each other. An estimate of axial length was made from the aphakic refraction alone (with an assumed average keratometry value of 44 dioptres) for all patients.

RESULTS

149 eyes of 102 paediatric aphakic patients were identified. The ultrasonic axial length values (mean 22.47 mm, SD 1.69, 95% confidence interval (CI) 0.27) and estimated axial length values (mean 22.41 mm, SD 1.53, 95% CI 0.25) had an average difference of 0.05 mm (SD 1.04, 95% CI 0.17) and were not significantly different (p = 0.56) by the two tailed paired t test. A histogram of the differences that did exist between the two values resembled a normal distribution. The nine eyes with the largest differences between the two values had either low hyperopic aphakic refractions or abnormal average keratometry values.

CONCLUSIONS

There was no significant difference between the two groups of axial length values, and the distribution of differences that did exist seemed random. The greatest differences between the two values occurred in longer (less hyperopic) eyes and in eyes with abnormally steep or flat keratometry. Estimation of axial length from the aphakic refraction alone seems to be a useful technique in the average paediatric eye, especially if biometry is unavailable.