Optimization of biometry for intraocular lens implantation using the Zeiss IOLMaster

Comparison of IOL power calculation formulae for pediatric eyes

PurposeTo evaluate and compare the accuracy of modern intraocular lens (IOL) power calculation formulae in pediatric eyes and compare prediction error (PE) obtained with manufacturer's vs personalized lens constant.Patients and methodsAn observational case study was conducted in 117 eyes (117 patients) undergoing pediatric cataract surgery with IOL implantation. PE was calculated as predicted refraction minus actual postoperative refraction, and absolute PE as absolute difference independent of the sign, (APE)=predicted refraction minus actual postoperative refraction. This was done for each formula using manufacturer's and personalized lens constant. Further, PE and APE were evaluated according to axial length (AL).ResultsMean age of children was 2.97 years. About 66/117 eyes (56.4%) were below 2 years of age. Using Holladay 2, Holladay 1, Hoffer Q, and SRK/T formulae with manufacturer's lens constant, mean PE was 0.36, 0.41, 0.69, and 0.28 diopter (D), respectively. With personalized lens constant, it was 0.16, 0.15, 0.50, and -0.12 D, respectively. Difference in mean PE between the formulae was statistically significant (P<0.0001). SRK/T and Holladay 2 formulae had the least PE, both with manufacturer's and personalized constant. For eyes with AL<20 mm, SRK/T and Holladay 2 formulae gave the least PE. Personalizing the lens constant led to a decrease in mean PE in all formulae, except the Hoffer Q formula. However, personalizing the lens constant did not significantly improve the APE. At least 21% eyes had an APE of >2 D with all formulae, even with personalized lens constants.ConclusionIn pediatric eyes, SRK/T and the Holladay 2 formulae had the least PE. Personalizing the lens formula constant did reduce the PE significantly for all formulae except Hoffer Q. In extremely short eyes (AL<20 mm), SRK/T and Holladay 2 formulae gave the best PE.

Factors Affecting the Accuracy of Intraocular Lens Power Calculation with Lenstar

This retrospective study was performed to compare refractive outcomes measured by conventional methods and by use of the Lenstar biometer and to investigate the factors affecting intraocular lens (IOL) power calculation with Lenstar with and without IOL-constant optimization. The study included 100 eyes of 86 patients who underwent cataract surgery. Corneal curvature was measured with a manual keratometer (MK), automated keratometer (AK), and the Lenstar biometer, and axial length (AL) was measured by A-scan and Lenstar. Mean numerical error (MNE) and mean absolute error (MAE) were compared between AK and MK with A-scan, and Lenstar with and without optimization. Factors affecting the accuracy of the IOL power calculation by use of Lenstar with and without optimization were analyzed. No significant differences were observed in the MNE or MAE among the devices. The proportion of MAE within 0.5 D was higher for Lenstar with optimization (62.7%) than without optimization (46.2%). The proportion of MAE within 0.5 D was 62% and 58% for MK and AK with A-scan, respectively. Without optimization, the MAE was smaller in eyes with ALs between 23 mm and 25 mm (p=0.03), whereas it was smaller at higher corneal powers when the IOL constant was optimized (>44 D, p=0.03). The IOL power calculations showed no significant differences among the devices, but the results of MAE within 0.5 D by use of Lenstar without optimization were worse than those of conventional methods. The AL influenced the accuracy of refractive outcomes determined by using Lenstar without optimization, and corneal curvature was shown to affect the accuracy of refractive measurements using Lenstar with optimization.

Accuracy of biometry for intraocular lens implantation using the new partial coherence interferometer, AL-scan

Purpose

To compare the refractive results of cataract surgery measured by applanation ultrasound and the new partial coherence interferometer, AL-scan.

Methods

Medical records of 76 patients and 104 eyes who underwent cataract surgery from January 2013 to June 2013 were retrospectively reviewed. Biometries were measured using ultrasound and AL-scan and intraocular lens power was calculated using the SRK-T formula. Automatic refraction examination was done 1 month after the operation, and differences between the ultrasound group and AL-scan group were compared and analyzed by mean absolute error.

Results

Mean axial length measured preoperatively by the ultrasound method was 23.53 ± 1.17 mm while the lengths measured using the AL-scan were 0.03 mm longer than that of the ultrasound group (23.56 ± 1.15 mm). However, there was not a significant difference in this finding (p = 0.638). Mean absolute error was 0.34 ± 0.27 diopters in the ultrasound group and 0.36 ± 0.31 diopters in AL-scan group, which showed no significant difference (p = 0.946) in precision of predicting postoperative refraction.

Conclusions

Although the difference was not statistically significant, intraocular lens calculations done by the AL-scan were nearly similar in predicting postoperative refraction compared to those of applanation ultrasound, however more precise measurements may be obtained if the axial length is longer than 24.4 mm. Except in the case of opacity in the media, which makes obtaining measurements with the AL-scan difficult, AL-scan could be a useful biometry in cataract surgery.

Optimization of intraocular lens constant improves refractive outcomes in combined endothelial keratoplasty and cataract surgery

PURPOSE

To evaluate the accuracy of intraocular lens (IOL) power calculations with A-constant optimization in Descemet's stripping automated endothelial keratoplasty (DSAEK) combined with cataract extraction and intraocular lens implantation (DSAEK triple procedure).

DESIGN

Retrospective case series.

PARTICIPANTS

Thirty eyes of 22 patients with Fuchs' endothelial dystrophy who underwent the DSAEK triple procedure performed by a single surgeon.

METHODS

Prediction errors were calculated retrospectively for consecutive DSAEK triple procedures. These prediction errors then were used to determine an IOL constant for this cohort of patients. The new optimized IOL constant subsequently was compared with the manufacturer's IOL constant, allowing evaluation and quantification of refractive benefits of optimization.

MAIN OUTCOMES MEASURES

The error in diopters (D) of the predicted refraction with the manufacturer's and optimized IOL constants.

RESULTS

Optimization of the A constant decreased the mean absolute error (MAE) from 1.09 ± 0.63 D (range, 0.12-2.41 D) to 0.61 ± 0.4 D (range, 0-1.58 D; P = 0.004). Comparing the intended and final postoperative refractions calculated with the original manufacturer's constant and the optimized constant, 20% versus 43% of all eyes were in the less than 0.5-D range and 50% versus 83% of all eyes were in the less than 1.0-D range of the target refraction. Furthermore, optimization decreased the number of eyes that were more than 1.0 D from the target refraction from 50% to 17%.

CONCLUSIONS

Optimization of the IOL constant showed significantly improved accuracy of predicted postoperative refraction compared with the manufacturer's IOL constant, which may help improve the postoperative refractive outcomes in patients undergoing the DSAEK triple procedure.

Keratometry obtained by corneal mapping versus the IOLMaster in the prediction of postoperative refraction in routine cataract surgery

BACKGROUND

To establish whether simulated keratometry values obtained by corneal mapping (videokeratography) would provide a superior refractive outcome to those obtained by Zeiss IOLMaster (partial coherence interferometry) in routine cataract surgery.

DESIGN

Prospective, non-randomized, single-surgeon study set at the The Royal United Hospital, Bath, UK, District General Hospital.

PARTICIPANTS

Thirty-three patients undergoing routine cataract surgery in the absence of significant ocular comorbidity.

METHODS

Conventional biometry was recorded using the Zeiss IOLMaster. Postoperative refraction was calculated using the SRK/T formula and the most appropriate power of lens implanted. Preoperative keratometry values were also obtained using Humphrey Instruments Atlas Version A6 corneal mapping.

MAIN OUTCOME MEASURES

Achieved refraction was compared with predicted refraction for the two methods of keratometry after the A-constants were optimized to obtain a mean arithmetic error of zero dioptres for each device.

RESULTS

The mean absolute prediction error was 0.39 dioptres (standard deviation 0.29) for IOLMaster and 0.48 dioptres (standard deviation 0.31) for corneal mapping (P = 0.0015). Keratometry readings between the devices were highly correlated by Spearman correlation (0.97). The Bland-Altman plot demonstrated close agreement between keratometers, with a bias of 0.0079 dioptres and 95% limits of agreement of -0.48-0.49 dioptres.

CONCLUSIONS

The IOLMaster was superior to Humphrey Atlas A6 corneal mapping in the prediction of postoperative refraction. This difference could not have been predicted from the keratometry readings alone. When comparing biometry devices, close agreement between readings should not be considered a substitute for actual postoperative refraction data.

Comparison of intraocular lens power prediction using immersion ultrasound and optical biometry with and without formula optimization

PURPOSE

Comparison of postoperative refraction results using ultrasound biometry with closed immersion shell and optical biometry.

PATIENTS AND METHOD

Three hundred and sixty-four eyes of 306 patients (age: 70.6 ± 12.8 years) underwent cataract surgery where intraocular lenses calculated by SRK/T formula were implanted. In 159 cases immersion ultrasonic biometry, in 205 eyes optical biometry was used. Differences between predicted and actual postoperative refractions were calculated both prior to and after optimization with the SRK/T formula, after which we analysed the similar data in the case of Holladay, Haigis, and Hoffer-Q formulas. Mean absolute error (MAE) and the percentage rate of patients within ±0.5 and ±1.0 D difference in the predicted error were calculated with these four formulas.

RESULTS

MAE was 0.5-0.7 D in cases of both methods with SRK/T, Holladay, and Hoffer-Q formula, but higher with Haigis formula. With no optimization, 60-65 % of the patients were under 0.5 D error in the immersion group (except for Haigis formula). Using the optical method, this value was slightly higher (62-67 %), however, in this case, Haigis formula also did not perform so well (45 %). Refraction results significantly improved with Holladay, Hoffer-Q, and Haigis formulas in both groups. The rate of patients under 0.5 D error increased to 65 % by the immersion technique, and up to 80 % by the optical one.

CONCLUSIONS

According to our results, optical biometry offers only slightly better outcomes compared to those of immersion shell with no optimized formulas. However, in case of new generation formulas with both methods, the optimization of IOL-constants give significantly better results.

Value of dual biometry in the detection and investigation of error in the preoperative prediction of refractive status following cataract surgery

PURPOSE

To report the value of dual biometry in the detection of biometry errors.

METHODS

Study 1: retrospective study of 224 consecutive cataract operations. The intraocular lens power calculation was based on immersion biometry. Study 2: immersion biometry was compared with optical coherence biometry (OCB) in terms of axial length, anterior chamber depth, keratometry readings and the recommended lens power to achieve emmetropia. Study 3: prospective study of 61 consecutive cataract operations. Both immersion and OCB were performed, but lens power calculation was based on the latter.

RESULTS

Study 1: 115 (86%), 101 (75.4%), 90 (67.2%) and 50 (37.3%) of postoperative spherical equivalents were within +/-1.5 dioptres (D), +/-1.25 D, +/-1 D and +/-0.5 D of the target, respectively. Study 2: excellent agreement between axial length readings, anterior chamber depth readings and keratometry readings by immersion biometry and OCB was observed (reflected in a mean bias of -0.065 mm, -0.048 mm and +0.1803 D, respectively, in association with OCB). Agreement between the lens power recommended by each technique to achieve emmetropia was poor (mean bias of +1.16 D in association with OCB), but improved following appropriate modification of lens constants in the Accutome A-scan software (mean bias with OCB = -0.4 D). Study 3: 37 (92.5%) and 23 (57.5%) of operated eyes achieved a postoperative refraction within +/-1 D and +/-0.5 D of target, respectively.

CONCLUSION

Systematic errors in biometry can exist, in the presence of acceptable postoperative refractive results. Dual biometry allows each biometric parameter to be scrutinized in isolation, and identify sources of error that may otherwise go undetected.