Validating e-norms methodology in ophthalmic biometry

Harnessing historical data to derive reference limits - A comparison of e-norms to traditionally derived reference limits

Objective

Nerve conduction studies (NCS) require valid reference limits for meaningful interpretation. We aimed to further develop the extrapolated norms (e-norms) method for obtaining NCS reference limits from historical laboratory datasets for children and adults, and to validate it against traditionally derived reference limits.

Methods

We compared reference limits obtained by applying a further developed e-norms with reference limits from healthy controls for the age strata's 9-18, 20-44 and 45-60 years old. The control data consisted of 65 healthy children and 578 healthy adults, matched with 1294 and 5628 patients respectively. Five commonly investigated nerves were chosen: The tibial and peroneal motor nerves (amplitudes, conduction velocities, F-waves), and the sural, superficial peroneal and medial plantar sensory nerves (amplitudes, conduction velocities). The datasets were matched by hospital to ensure identical equipment and protocols. The e-norms method was adapted, and reference limit calculation using both ±2 SD (original method) and ±2.5 SD (to compensate for predicted underestimation of population SD by the e-norms method) was compared to control data using ±2 SD. Percentage agreement between e-norms and the traditional method was calculated.

Results

On average, the e-norms method (mean ±2 SD) produced slightly stricter reference limits compared to the traditional method. Increasing the e-norms range to mean ±2.5 SD improved the results in children while slightly overcorrecting in the adult group. The average agreement between the two methods was 95 % (±2 SD) and 96 % (±2.5 SD).

Conclusions

The e-norms method yielded slightly stricter reference limits overall than ones obtained through traditional methods; However, much of the difference can be attributed to a few outlying plots where the raters found it difficult to apply e-norms correctly. The two methods disagreed on classification of 4-5% of cases. Our e-norms software is suited to analyze large amounts of raw NCS data; it should further reduce bias and facilitate more accurate ratings.

Significance

With small adaptations, the e-norms method adequately replicates traditionally derived reference limits, and is a viable method to produce reference limits from historical datasets.

Refractive Predictability of a Swept Source Optical Coherence Tomography Biometer in Long and Short Eyes Implanted with Extended Depth of Focus Intraocular Lenses

Purpose

To determine the refractive predictability of Argos (Movu, a Santec company) measurements and the Barrett Universal II formula in long and short eyes implanted with an extended depth of focus (EDOF) intraocular lens (IOL).

Methods

This retrospective, non-interventional study included 86 eyes (55 long and 31 short) of 55 patients. Preoperative biometry was performed using the Argos. Preoperative IOL power formulas were the preprogrammed Barrett Universal II (BUII). Data were collected for refractive outcomes, postoperative prediction error (directional and absolute), and monocular corrected distance visual acuity (CDVA, Snellen).

Results

The mean absolute prediction error for BUII was 0.27 ± 0.26 D overall, 0.24 ± 0.20 D in long eyes, and 0.33 ± 0.33 D in short eyes. Overall, the percentage of eyes with ≤ 0.5 D prediction error was 84% for BUII. In long eyes, the percentage of eyes with ≤ 0.5 D prediction error was 90% for BUII. In short eyes, the percentage of eyes with ≤ 0.5 D prediction error was 74% for BUII. The percentage of eyes with ≤ 0.5 D of MRSE was 89% for long eyes and 94% for short eyes. Visual acuities were excellent in both long and short eyes, with > 90% of eyes 20/25 or better in each group.

Conclusion

The prediction error of Argos using BUII was low in long and short eyes at one month after EDOF IOL implantation.

Comparison of the new Hoffer QST with 4 modern accurate formulas

PURPOSE

To investigate the new Hoffer QST (Savini/Taroni) formula (HQST) and compare it with the original Hoffer Q (HQ) and 4 latest generation formulas.

SETTING

I.R.C.C.S.-G.B. Bietti Foundation, Rome, Italy.

DESIGN

Retrospective case series.

METHODS

Refractive outcomes of the HQST, Barrett Universal II (BUII), Emmetropia Verifying Optical (EVO) 2.0, HQ, Kane, and Radial Basis Function (RBF) 3.0 formulas were compared. Subgroup analysis was performed in short (<22 mm) and long (>25 mm) axial length eyes. The SD of the prediction error (PE) was investigated using the heteroscedastic method.

RESULTS

1259 eyes of 1259 patients divided in a White group (n=696), implanted with the AcriSof SN60AT (Alcon Labs), and an Asian group (n=563), implanted with the SN60WF (Alcon Labs), were investigated. In the Asian group, the heteroscedastic method did not disclose any significant difference among the SD of the 4 modern formulas (range from 0.333 to 0.346 D), whereas the SD of the HQ formula (0.384 D) was significantly higher. Compared with the original HQ formula, in both White and Asian groups, the HQST formula avoided the mean myopic PE in short eyes and the mean hyperopic PE in long eyes.

CONCLUSIONS

The new HQST formula was superior to the original HQ formula and reached statistical and clinical results comparable with those achieved by the BUII, EVO, Kane, and RBF formulas.

Evaluation of biometric formulas in the calculation of intraocular lens according to axial length and type of the lens

To compare the accuracy of the modern biometric formulas in cataract surgery according to axial length and lens type. It is a Cross-sectional design from 365 patients who underwent cataract surgery. The SRK/T, Hoffer Q, Haigis, and Holladay I formulas were extracted from the IOLMaster 500 biometer. Barret formulas and the Kane were obtained from the online calculator. Patients are classified according to axial length (AL) into three groups: AL ≤ 22 mm, 22 < AL < 25 mm, and AL ≥ 25 mm. In addition, implanted intraocular lenses are classified as Monofocal, extended focus, and Multifocal. There are no significant differences between the formulas. In short, the Kane formula was more accurate than the other biometric formulas. Kane and SRK/T were the most accurate in monofocal lenses, with the lowest residual refractive error. The Holladay I formula obtained the lowest mean absolute error with the highest number of eyes with minimum residual ± 0.5Dp in the multifocal lenses in the 22 < AL < 25 mm eyes. In the long AL eyes, SRK/T and Kane's obtained the lowest mean absolute error and the best percentage of eyes with ± 0.5Dp of residual refractive error. There are no significant differences between the formulas. However Kane's formula has shown high accuracy, especially in short and long eyes with monofocal lenses.

Accuracy of newer intraocular lens power formulas in short and long eyes using sum-of-segments biometry

PURPOSE

To analyze the accuracy of newer intraocular lens power formulas in long and short eyes measured using the sum-of-segments biometry.

SETTING

Private practice, Lynwood, California.

DESIGN

Retrospective observational study.

METHODS

595 patients scheduled for cataract surgery had their eyes measured using the sum-of-segments biometry. The expected residual refractions were calculated using Barrett Universal II (B II), Barrett True Axial Length (BTAL), Emmetropia Verifying Optical (EVO), Hill-RBF, Hoffer QST, Holladay 2, Holladay 2-NLR, K6, Kane, Olsen, PEARL-DGS, T2, and VRF formulas and compared with the traditional Haigis, Hoffer Q, Holladay 1, and SRK/T formulas.

RESULTS

In the 102 long eyes, all new formulas had a mean absolute error (MAE) equal or lower than the traditional formulas, ranging from 0.29 to 0.32 diopter (D). In the 78 short eyes, BTAL, EVO, Hoffer QST, K6, Olsen, and PEARL-DGS formulas had the lowest MAE (0.33 D, 0.33 D, 0.31 D, 0.36 D, 0.32 D, and 0.32 D, respectively), whereas all traditional formulas exceeded 0.36 D.

CONCLUSIONS

All new formulas performed equal or better than the traditional formulas with the sum-of-segments biometry. The best overall results in the short and long eyes as well as in the very short and very long eyes were noted with the BTAL, EVO, Hoffer QST, K6, Olsen, and PEARL-DGS formulas, closely followed by the B II and Kane formulas.

Body mass index changes: an assessment of the effects of age and gender using the e-norms method

Background

To validate e-norms methodology in establishing a reference range for body mass index measures. A new method, the extrapolated norms (e-norms) method of determining normal ranges for biological variables is easy to use and recently was validated for several biological measurements. We aimed to determine whether this new method provides BMI results in agreement with established traditionally collected BMI values.

Methods

We applied the e-norms method to BMI data from 34,384 individuals and compared the ranges derived from this method with those from a large actuarially based study and explored differences in the normal range by gender, and age.

Results

The e-norms derived range of healthy BMI in adults is from 22.7 to 30.6, and showed that BMI is consistently higher in men than in women and increases with age, except in subjects aged 80–98 years in whom healthy BMI appears to be lower.

Conclusions

Our e-norms derived healthy BMI ranges agree with traditionally obtained actuarially based methods, supporting the validity and ease of use of our method.