Accuracy of Various Intraocular Lens Power Calculation Formulas in Steep Corneas

Accuracy of intraocular lens power formulas in patients with average keratometry greater than 46 diopters

OBJECTIVE

To compare the accuracy of Kane, Barrett Universal II, Haigis, and SRK-T formulas in eyes with average keratometry greater than 46 diopters (D).

METHODS

A retrospective analysis was conducted on 101 eyes of 101 patients with average keratometry greater than 46 D. The absolute prediction error (EA) was obtained for each patient one month after surgery. The mean absolute prediction error (MEA), median absolute prediction error (MedEA) and the percentage of patients with absolute refractive error less than 0.25 D, 0.50 D, and 1.00 D were calculated for each formula analyzed.

RESULTS

The Kane formula achieved the lowest MEA (0.53 ± 0.43) and the lowest MedEA (0.41), followed by Barrett Universal II (MEA: 0.56 ± 0.42, MedEA: 0.49), SRK-T (MEA: 0.59 ± 0.44, MedEA: 0.54), and Haigis (MEA: 0.77 ± 0.47, MedEA: 0.69), showing a significant difference in the results. It was also observed that the Kane formula was the most accurate, with the highest percentage of patients, with EA less than 0.25 D, 0.50 D, and 1.00 D (30.7%, 54.4%, and 86.1%, respectively), while the Haigis formula was the least accurate (12.9%, 33.7%, and 69.3%, respectively).

CONCLUSION

In eyes with corneas having average keratometry greater than 46 D, the Kane formula proves to be a useful tool in intraocular lens (IOL) power calculation and demonstrates higher precision compared to the Barrett Universal II, SRK-T, and Haigis formulas.

Efficacy of corneal curvature on the accuracy of 8 intraocular lens power calculation formulas in 302 highly myopic eyes

PURPOSE

To investigate the effect of corneal curvature (K) on the accuracy of 8 intraocular lens formulas in highly myopic eyes.

SETTING

Eye Hospital and School of Ophthalmology and Optometry, Wenzhou Medical University, Wenzhou, China.

DESIGN

Retrospective consecutive case series.

METHODS

302 eyes (302 patients) were analyzed in subgroups based on the K value. The mean refractive error, mean absolute error (MAE), median absolute error (MedAE), root-mean-square absolute prediction error (RMSAE) and proportions of eyes within ±0.25 diopter (D), ±0.50 D, ±0.75 D, ±1.00 D were statistical analyzed.

RESULTS

Emmetropia Verifying Optical (EVO) 2.0, Kane, and Radial Basis Function (RBF) 3.0 had the lower MAE (≤0.28) and RMSAE (≤0.348) and highest percentage of eyes within ±0.50 D (≥83.58%) in the flat (K ≤ 43 D) and steep K (K > 45 D) groups. Hoffer QST had the lowest MedAE (0.19), RMSAE (0.351) and the highest percentage of eyes within ±0.50 D (82.98%) in the normal K group (43 < K ≤ 45 D). When axial length (AL) ≤28 mm, all formulas showed close RMSAE values (0.322 to 0.373) in flat K group. When AL >28 mm, RBF 3.0 achieved the lowest MAE (≤0.24), MedAE (≤0.17) and RMSAE (≤0.337) across all subgroups.

CONCLUSIONS

EVO 2.0, Kane, and RBF 3.0 were the most accurate in highly myopic eyes with a flat or steep K. Hoffer QST is recommended for long eyes with normal K values. RBF 3.0 showed the highest accuracy when AL >28 mm, independent of corneal curvature.

Best fit formula approach in delayed sequential bilateral cataract surgery

BACKGROUND

We evaluated whether the best-fit intraocular lens (IOL) power formula for the first operated eye (BF1) was also the most accurate formula for the second eye.

METHODS

This was a retrospective study of 152 patients who underwent uncomplicated delayed bilateral cataract surgery with a minimum delay of 3 weeks using only one 1-piece IOL (HOYA, Vivinex) at the Medical University of Vienna, Austria. Seven different formulae (Barrett Universal II, Castrop, Haigis, Hoffer Q, Holladay 1, Kane, and SRK/T) were investigated to test the formula selection approach with regard to the calculated mean and median absolute prediction errors (MAE/MedAE).

RESULTS

The mean intraindividual difference in axial length was 0.2 mm (±0.3 mm). BF1 coincided with the best-fit formula for the second eye (BF2) in 56% of patients (p < 0.05). Using BF1 for the second eye led to a lower MedAE (0.22 dioptre, D) than using a formula at random (0.33 D) and was less accurate than using the best-fit formula for each eye separately (0.1 D). The MedAEs of all formulae were generally low, ranging from 0.28 to 0.35 D.

CONCLUSION

Using BF1 for the second eye led to a lower MedAE than the random selection of a formula. Therefore, BF1 can be used for the second eye if the surgeon is unsure of the choice of formula.

Accuracy of Intraocular Lens Power Calculation Based on Total Keratometry in Patients With Flat and Steep Corneas

PURPOSE

To analyze the accuracy of the current intraocular lens power calculation formulas using standard keratometry (K) and total keratometry (TK) data in patients with flat and steep corneas.

DESIGN

Retrospective consecutive cross-sectional study.

METHODS

An optical biometer with swept-source optical coherence tomography was used in this retrospective study. The standard deviation (SD), mean absolute error (MAE), median absolute error (MedAE), and the proportion of eyes with prediction error (PE) within ±0.25 diopter (D), ±0.5 D, ±0.75 D, and ±1.00 D were calculated to evaluate the refractive outcomes of each formula.

RESULTS

A total of 231 eyes from 231 patients were included. In the entire study cohort, the Emmetropia Verifying Optical (EVO) formula using TK data showed the lowest SD (0.383) and MAE (0.30) and the highest percentage of cases with a PE within ±0.5 D (81.4%). In the flat keratometry group, the EVO (P = .042), Haigis (P = .043), Hoffer Q (P = .038) and Holladay 1 (P = .013) formulas using TK data had significantly lower SD than using K data. The EVO formula using TK data showed the lowest SD (0.357) and MAE (0.28). In the steep keratometry group, the Hoffer Q (P = .036) and SRK/T (P = .029) formulas using TK data had significantly lower SD than using K data. The BUII TK formula showed the lowest SD (0.431), MedAE (0.26), and MAE (0.32).

CONCLUSION

The TK data set showed a better trend of refractive outcomes, especially in the flat and steep keratometry groups. EVO (TK) and BUII TK formulas were suggested for eyes with K values lower than 42 D and K values higher than 46 D, respectively.

Assessment of the influence of keratometry on intraocular lens calculation formulas in long axial length eyes

PURPOSE

Hyperopic surprises tend to occur in axial myopic eyes and other factors including corneal curvature have rarely been analyzed in cataract surgery, especially in eyes with long axial length (≥ 26.0 mm). Thus, the purpose of our study was to evaluate the influence of keratometry on four different formulas (SRK/T, Barrett Universal II, Haigis and Olsen) in intraocular lens (IOL) power calculation for long eyes.

METHODS

Retrospective case series. A total of 180 eyes with axial length (AL) ≥ 26.0 mm were divided into 3 keratometry (K) groups: K ≤ 42.0 D (Flat), K ≥ 46.0 D (Steep), 42.0 < K < 46.0 D (Average), and all the eyes were underwent phacoemulsification cataract surgery with Rayner (Hove, UK) 920H IOL implantation. Prediction errors (PE) were compared between different formulas to assess the accuracy of different formulas. Multiple regression analysis was performed to investigate factors associated with the PE.

RESULTS

The mean absolute error was higher for all evaluated formulas in Steep group (ranging from 0.66 D to 1.02 D) than the Flat (0.34 D to 0.67 D) and Average groups (0.40 D to 0.74D). The median absolute errors predicted by Olsen formula were significantly lower than that predicted by Haigis formula (0.42 D versus 0.85 D in Steep and 0.29 D versus 0.69 D in Average) in Steep and Average groups (P = 0.012, P < 0.001, respectively). And the Olsen formula demonstrated equal accuracy to the Barrett II formula in Flat and Average groups. The predictability of the SRK/T formula was affected by the AL and K, while the predictability of Olsen and Haigis formulas was affected by the AL only.

CONCLUSIONS

Steep cornea has more influence on the accuracy of IOL power calculation than the other corneal shape in long eyes. Overall, both the Olsen and Barrett Universal II formulas are recommended in long eyes with unusual keratometry.

Predictability of combined cataract surgery and trabeculectomy using Barrett Universal Ⅱ formula

PURPOSE

To compare the predictability of intraocular lens (IOL) power calculation using the Barrett Universal II and the SRK/T formulas in eyes undergoing combined cataract surgery and trabeculectomy.

METHODS

We retrospectively reviewed the clinical charts of 56 consecutive eyes undergoing cataract surgery and trabeculectomy. IOL power calculations were performed using the Barrett Universal II and SRK/T formulas. We compared the prediction error, the absolute error, and the percentages within ± 0.5 D and ±1.0 D of the targeted refraction, 3 months postoperatively, and also investigated the relationship of the prediction error with the keratometric readings and axial length, using the two formulas.

RESULTS

The prediction error using the SRK/T formula was significantly more myopic than that using the Barrett Universal II formula (paired t-test, p<0.001). The absolute error using the Barrett Universal II formula was significantly smaller than that using the SRK/T formula (p = 0.039). We found significant correlations of the prediction error with the axial length (Pearson correlation coefficient, r = 0.273, p = 0.042), and the keratometric readings (r = -0.317, p = 0.017), using SRK/T formula, but no significant correlations between them (r = 0.219, p = 0.167, and r = -0.023, p = 0.870), using the Barrett Universal II formula.

CONCLUSIONS

The Barrett Universal II formula provides a better predictability of IOL power calculation and is less susceptible to the effect of the axial length and the corneal shape, than the SRK/T formula. The Barrett Universal formula, rather than the SRK/T formula, may be clinically helpful for improving the refractive accuracy in such eyes.

Influence of Posterior Corneal Asphericity on Refractive Error of SRK-T and Barrett Formulas for Lucidis IOL

PURPOSE

To evaluate the influence of posterior corneal asphericity on the refractive error using SRK-T and Barrett formulas for the intraocular lens (IOL) power calculation for Lucidis Extended Depth of Focus (EDOF) IOL.

SETTING

This study was carried out at a tertiary ophthalmology center in Geneva, Switzerland.

DESIGN

A retrospective study. Medical records from all enrolled patients were analyzed and the following information was extracted retrospectively, over 1 month following surgery.

METHODS

We retrospectively reviewed 75 eyes that underwent cataract surgery and were implanted with a Lucidis EDOF IOL. We measured the posterior corneal asphericity (Q value), axial length (AL), and anterior chamber depth (ACD) and then calculated the IOL power using SRK-T and Barrett formulas.

RESULTS

Seventy-five eyes were included, all of which had 1-month postoperative data. In the cohort, 32 eyes were from females (43%) and 43 from males (57%). The mean age of the study population was 73 ± 8.8 years. The mean AL was 23.5 ± 0.98 and the mean ACD was 3.13 ± 0.3. The mean posterior Q value was - 0.35 ± 0.2. In a regression analysis, we found a statistically significant relationship between the error in refraction prediction and the posterior Q value, irrespective of the formula used. The relationship between posterior corneal asphericity and the refraction prediction error was stronger for the Barrett II Universal formula than for the SRK-T formula.

CONCLUSIONS

Posterior corneal asphericity was correlated with the refractive error of calculation of both SRK-T and Barrett formulas, with a stronger correlation to the latter formula.

Comparison between SRK/T and Haigis Formulas on Visual Acuity of Patient with Senile Cataract Post-Phacoemulsification

BACKGROUND: Cataract contributes to the most common cause of blindness worldwide. Cataract surgery is the most performed surgery in the world. To achieve optimal results, pre-operative biometric must be accurate and the use of a formula for measuring the strength of the intraocular lens (IOL) accurately must be used. SRK-T and Haigis are formulas applied in the calculation of IOLs. AIM: The objective of the study was to determine the evaluation of visual acuity after phacoemulsification using the SRK/T and Haigis formulas. METHODS: This was an observational prospective analytic study at Medan Baru Eye Hospital from June 2019 to August 2019. Following the examination, patients were required further follow-up on 7–30 days post-phacoemulsification. RESULTS: The number of subjects was 122 patients (122 eyes), 84 patients were observed, and 38 patients did not come back for control. This study was within the value of p = 0.053. Prediction of refractive errors after phacoemulsification for myopia identified using SRK/T formula was more common, resulting in 3 eyes (75.0%) compared to the Haigis formula. On contrary, the prediction for emetropia was mostly discovered on Haigis formula which amounted to 41 eyes (51.25%) compared to the SRK/T formula. CONCLUSIONS: There was no significant difference in predicting post-phacoemulsification visual acuity between SRK/T and Haigis formula.

The impact of cataract progression on accuracy of intraocular lens power measurement

Purpose

The aim of this study was to assess the impact of cataract progression using the Haigis formula-calculated intraocular lens (IOL) power and investigate the accuracy of IOL power measured at different time points.

Methods

This prospective study was performed on 75 eyes of 75 patients who underwent uneventful cataract surgery. Preoperative ocular parameters including axial length (AL), keratometry (K), anterior chamber depth (ACD), corneal astigmatism, corrected distance visual acuity (CDVA) and uncorrected distance visual acuity (UDVA) examined at the two time points, more than 3 months preoperatively and preoperative 1 day were compared. The ocular parameters measured in the two time points were used to calculate the predicted implanted IOL power and the actual IOL power was chosen on the basis of parameters measured earlier before surgery using the Haigis formula. The mean numerical error (MNE) and mean absolute error (MAE) predicted by the two time points were also compared.

Results

There were significant differences in the ACD, IOL power, UDVA and CDVA (P<0.01), but no statistical differences in AL, mean K and corneal astigmatism (P>0.05) during the average of 5.6 months before surgery. No statistically significant difference was detected in MNE (P>0.05), while the MAE had a significant difference in the two time points (P<0.05).

Conclusion

The IOL power measured earlier before surgery might result in a higher accuracy and the postoperative refractive outcome tended towards emmetropia.

Intraocular Lens Power Formulas, Biometry, and Intraoperative Aberrometry: A Review

The refractive outcome of cataract surgery is influenced by the choice of intraocular lens (IOL) power formula and the accuracy of the various devices used to measure the eye (including intraoperative aberrometry [IA]). This review aimed to cover the breadth of literature over the previous 10 years, focusing on 3 main questions: (1) What IOL power formulas currently are available and which is the most accurate? (2) What biometry devices are available, do the measurements they obtain differ from one another, and will this cause a clinically significant change in IOL power selection? and (3) Does IA improve refractive outcomes? A literature review was performed by searching the PubMed database for articles on each of these topics that identified 1313 articles, of which 166 were included in the review. For IOL power formulas, the Kane formula was the most accurate formula over the entire axial length (AL) spectrum and in both the short eye (AL, ≤22.0 mm) and long eye (AL, ≥26.0 mm) subgroups. Other formulas that performed well in the short-eye subgroup were the Olsen (4-factor), Haigis, and Hill-radial basis function (RBF) 1.0. In the long-eye group, the other formulas that performed well included the Barrett Universal II (BUII), Olsen (4-factor), or Holladay 1 with Wang-Koch adjustment. All biometry devices delivered highly reproducible measurements, and most comparative studies showed little difference in the average measures for all the biometric variables between devices. The differences seen resulted in minimal clinically significant effects on IOL power selection. The main difference found between devices was the ability to measure successfully through dense cataracts, with swept-source OCT-based machines performing better than partial coherence interferometry and optical low-coherence reflectometry devices. Intraoperative aberrometry generally improved outcomes for spherical and toric IOLs in eyes both with and without prior refractive surgery when the BUII and Hill-RBF, Barrett toric calculator, or Barrett True-K formulas were not used. When they were used, IA did not result in better outcomes.

Comparison of Predictability Using Barrett Universal II and SRK/T Formulas according to Keratometry

Purpose

To compare the predictability of intraocular lens (IOL) power calculation using the Barrett Universal II and the SRK/T formulas, according to the keratometry.

Methods

We retrospectively reviewed the clinical charts of 335 consecutive eyes undergoing standard cataract surgery. IOL power calculations were performed using the Barrett Universal II and the SRK/T formulas. We compared the prediction error, the absolute error, and the percentages within ±0.25, ±0.5, and ±1.0 D of the targeted refraction, 1 month postoperatively, and also investigated the relationship of these outcomes with the keratometric readings, using the two formulas.

Results

The prediction error using the SRK/T formula was significantly more myopic than that using the Barrett Universal II formula (the paired t-test, p < 0.001). The absolute error using the SRK/T formula was significantly larger than that using the Barrett Universal II formula (p=0.006). We found a significant correlation between the prediction error and the keratometric readings using the SRK/T formula (Pearson correlation coefficient, r = −0.522, p < 0.001), but there was no significant correlation between them using the Barrett Universal II formula (r = −0.031, p=0.576).

Conclusions

The Barrett Universal II formula provides a better predictability of IOL power calculation and is less susceptible to the effect of the corneal shape, than the SRK/T formula. The Barrett Universal formula, instead of the SRK/T formula, may be clinically helpful for improving the refractive accuracy, especially in eyes with steep or flat corneas.