Total keratometry for toric intraocular lens calculation: comparison from two swept-source optical coherence tomography biometers

Purpose

To compare the astigmatism prediction accuracy of total keratometry (TK) from the IOLMaster 700 and total corneal power (TCP) from Anterion based on swept-source optical coherence tomography (SS-OCT) technology in toric intraocular lens (toric IOL) calculation.

Design

A retrospective observational study.

Methods

Total corneal astigmatism (TCA) were obtained using IOLMaster 700 and Anterion. Z CALC 2.0 was used to calculate the expected postoperative refractive astigmatism in conjunction with TCA. Prediction errors (PE) in refractive outcomes was analyzed 1 month postoperatively using the vector analysis by the Holladay method, including the mean vector PE magnitude, percentage of cases with vector PE in certain intervals, and the centroid PE.

Results

A total of 56 eyes from 56 patients were enrolled in the study with an insertion of an AT TORBI 709 toric IOL. The difference in mean vector PE of postoperative refractive astigmatism between TK and TCP was not statistically significant (0.48D versus 0.46D, P = 0.281). TK and TCP yielded 27.3 and 40.0% of eyes with vector PE ≤ 0.25D, and 58.2 and 63.6% with vector PE ≤ 0.5D (both P > 0.05), respectively. TK and TCP resulted in similar ATR centroid PE of 0.10D@35° ± 0.60D and 0.15D@22° ± 0.57D, respectively, and there were no significant differences between x-PE component and y-PE component.

Conclusion

IOLMaster 700 and Anterion provided comparable astigmatic predictability in toric IOL implantation using total keratometry and Z CALC 2.0.

Comparison of total corneal power measurements obtained with different devices after myopic keratorefractive surgery

AIM

To analyze the differences, agreements, and correlation among total corneal power parameters generated by different instruments after myopic keratorefractive surgery.

METHODS

The prospective cross-sectional study included patients who underwent myopic keratorefractive surgery and received measurements of corneal power 3mo after surgery. Automated keratometer was used for the measurement of simulated keratometry (SimK), swept-source optical coherence tomography (SS-OCT) based biometer for total keratometry (TK), anterior segment-OCT for real keratometry (RK), and Scheimpflug keratometer for the true net power (TNP), the total corneal refractive power (TCRP) and equivalent K-readings (EKR). The differences among these parameters were analyzed, and the agreements and correlation between SimK and other total corneal power parameters were investigated.

RESULTS

A total of 70 eyes of 70 patients after myopic keratorefractive surgery were included. The evaluated corneal power parameters were as follows: SimK 38.32±1.93 D, TK 37.54±2.12 D, RK 36.64±2.09 D, TNP 36.56±1.97 D, TCRP 36.70±2.01 D, and EKR 37.55±2.00 D. Pairwise comparison showed that there were significant differences (P<0.001) among all parameters except for between TK and EKR, RK and TNP, RK and TCRP (P=1.000, 1.000, 1.000, respectively). The limits of agreement between SimK and TK, RK, TNP, TCPR, and EKR were 1.08, 1.08, 1.43, 1.48, and 1.73 D, respectively. All parameters showed good correlation with SimK, and the correlation coefficients were 0.995, 0.994, 0.983, 0.982, and 0.975.

CONCLUSION

Among the corneal power parameters after myopic keratorefractive surgery, the value of SimK is the largest, followed by TK and EKR, with TCRP, RK, and TNP being the smallest. The differences among the parameters may be attributable to the different calculation principles. Correct understanding and evaluation of corneal power parameters can provide a theoretical basis for taking advantage of the total corneal power to improve the accuracy of intraocular lens calculation after keratorefractive surgery.

Keratometric indices for detecting the type of keratoconus: a combined discriminant analysis

BACKGROUND

This study sought to determine the diagnostic ability of anterior, posterior and total keratometric indices in discriminating keratoconus (KCN) stages 1 to 4 from normal corneas.

METHODS

Anterior and posterior simulated keratometry (sim-Ksteep and sim-Kflat), maximum keratometry (Kmax), Kmax y co-ordinate, anterior and posterior radii of curvature centred on the thinnest point (ARC-3 mm and PRC-3 mm), and anterior, posterior, and total asphericity (Q-value) measured by Pentacam were extracted from electronic medical records of 200 KCN and 200 normal cases. Stepwise leave-one-out cross-validation and areas under receiver operating characteristic curves (AUROC) were used to detect the best set of indices for differentiating normal from low-grade (stages 1-2, Kmax ≤ 53.00 D) and high-grade (stages 3-4, Kmax > 53.00 D) KCN.

RESULTS

Mean age in KCN and normal groups was 33.10 ± 7.48 and 32.24 ± 9.00 years (p = 0.332), respectively. In the low-grade KCN group, PRC-3 mm (AUROC = 0.986), Kmax (AUROC = 0.979), and Kmax y co-ordinate (AUROC = 0.824) performed best, and the difference in AUROC between PRC-3 mm and Kmax was not significant (p = 0.153). In the high-grade KCN group, Kmax (AUROC = 1.000), PRC-3 mm (AUROC = 0.998), posterior Ksteep (AUROC = 0.970), posterior Q-value (AUROC = 0.940), and posterior Kflat (AUROC = 0.894) performed best, and there was no significant difference in AUROC values between Kmax and PRC-3 mm (p = 0.307) or between posterior Ksteep and posterior Q-value (p = 0.113).

CONCLUSIONS

Among the studied keratometric indices, PRC-3 mm and Kmax appear to have the best ability for detecting mild to severe KCN. The next best factors which showed good discrimination ability were Kmax y co-ordinate in low-grade cases and posterior Ksteep and Q-value in high-grade cases.

Post-small incision lenticule extraction phacoemulsification with multifocal IOL implantation: A case report

A 54-year-old patient presented with cataract, 5 years after undergoing SMILE for high myopia in both eyes. He was motivated in achieving spectacle free vision and his post SMILE-induced aberrations were minimal, due to which he was found suitable for a trifocal IOL implant. Of the various methods considered, the IOL power predicted by a novel combined telecentric keratometry and swept source OCT-based method was finally selected. One month post-operatively, the patient achieved a binocular UDVA of 20/20p and near vision of N.6, suggesting that newer IOL formulae could be superior in providing satisfactory outcomes in post refractive patients.