Positional accommodative intraocular lens power error induced by the estimation of the corneal power and the effective lens position

Purpose:

To evaluate the predictability of the refractive correction achieved with a positional accommodating intraocular lenses (IOL) and to develop a potential optimization of it by minimizing the error associated with the keratometric estimation of the corneal power and by developing a predictive formula for the effective lens position (ELP).

Materials and Methods:

Clinical data from 25 eyes of 14 patients (age range, 52–77 years) and undergoing cataract surgery with implantation of the accommodating IOL Crystalens HD (Bausch and Lomb) were retrospectively reviewed. In all cases, the calculation of an adjusted IOL power (P_IOLadj) based on Gaussian optics considering the residual refractive error was done using a variable keratometric index value (n_kadj) for corneal power estimation with and without using an estimation algorithm for ELP obtained by multiple regression analysis (ELP_adj). P_IOLadj was compared to the real IOL power implanted (P_IOLReal, calculated with the SRK-T formula) and also to the values estimated by the Haigis, HofferQ, and Holladay I formulas.

Results:

No statistically significant differences were found between P_IOLReal and P_IOLadj when ELP_adj was used (P = 0.10), with a range of agreement between calculations of 1.23 D. In contrast, P_IOLReal was significantly higher when compared to P_IOLadj without using ELP_adj and also compared to the values estimated by the other formulas.

Conclusions:

Predictable refractive outcomes can be obtained with the accommodating IOL Crystalens HD using a variable keratometric index for corneal power estimation and by estimating ELP with an algorithm dependent on anatomical factors and age.     

Comparison of the Astigmatic Power of Toric Intraocular Lenses Using Three Toric Calculators

Purpose

To compare the astigmatic power of toric intraocular lenses (IOLs) obtained from the AcrySof, TECNIS, and iTrace toric calculator in patients with preoperative with-the-rule (WTR) or against-the-rule (ATR) corneal astigmatism.

Materials and Methods

Fifty eyes with cataract and corneal astigmatism greater than 0.75 diopters were enrolled in each group (WTR and ATR). Keratometric values were measured using autokeratometry, an IOLMaster, and an iTrace, which incorporated corneal topography and ray-tracing aberrometry. Based on measured keratometric values, the astigmatic power of each toric IOL was calculated using three toric calculators.

Results

Bland-Altman plots showed good agreement between six pairwise corneal astigmatism values in both groups. The TECNIS calculator tended to suggest a higher astigmatic power of the toric IOL than the AcrySof calculator. With the higher astigmatism and keratometric values from the IOLMaster, in both groups, calculations from the AcrySof and TECNIS calculators resulted in higher calculated astigmatic powers than those from same calculators with autokeratometry-measured values, demonstrating good agreement. With the higher calculated astigmatic power values, the values from the iTrace toric calculator using keratometric values obtained from iTrace ray tracing wavefront aberrometry or iTrace simulated keratometry showed fair to moderate agreement with those from the other calculator-keratometry pairs in both groups.

Conclusion

To achieve the best refractive outcome after toric IOL implantation, understanding the differences in keratometric values between instruments and in calculated astigmatic power among toric calculator programs is necessary. Moreover, systemic analysis of each toric calculator in conjunction with postoperative data is required.     

Interchangeability of corneal curvature and asphericity measurements provided by three different devices

AIM: To evaluate the interchangeability of keratometric and asphericity measurements provided by three measurement systems based on different optical principles. METHODS: A total of 40 eyes of 40 patients with a mean age of 34.1y were included. In all cases, a corneal curvature analysis was performed with IOL-Master (IOLM), iDesign 2 (ID2), and Sirius systems (SIR). Differences between instruments for flattest (K1) and steepest (K2) keratometric readings, as well as for magnitude and axis of corneal astigmatism were analyzed. Likewise, differences in asphericity (Q) between SIR and ID2 were also evaluated. RESULTS: Mean differences between devices for K1 were 0.20±0.21 (P<0.001), -0.12±0.36 (P=0.046) and -0.32±0.36 D (P<0.001) for the comparisons IOLM-SIR, IOLM-ID2 and SIR-ID2, respectively. The ranges of agreement for these comparisons between instruments were 0.41, 0.70, and 0.70 D. For K2, mean differences were 0.31±0.33 (P<0.001), -0.08±0.43 (P=0.265) and -0.39±0.38 D (P<0.001), with ranges of agreement of 0.65, 0.84, and 0.74 D. Concerning magnitude of astigmatism, ranges of agreement were in the limit of clinical relevance (0.49 D, P=0.011; 0.55 D, P=0.386; 0.43 D, P=0.05). In contrast, ranges of agreement were clinically relevant for astigmatic axis (26.68o, 33.83o and 18.37o, P≥0.121) and for Q between SIR and ID2 (0.16, P<0.001). CONCLUSION: The keratometric corneal power, astigmatic axis and asphericity measurements provide by the three systems evaluated cannot be considered as interchangeable, whereas measurements of corneal astigmatism obtained with SIR and ID2 can be considered as interchangeable for clinical purposes.     

不同角膜仪测量的角膜曲率值的一致性分析

目的：比较测得后三种不同角膜仪测量的角膜曲率，以评估其测量值之间的一致性。

方法：前瞻性研究。252例患者(252眼)使用IOL Master(IM)，Bausch & Lomb手动角膜仪(Man)以及TOPCON KR-8800自动角膜仪(Top)进行角膜曲率测量。记录并对比平均角膜曲率值。使用Bland Altman统计方法进行仪器间的一致性分析。

结果：1)IOL Master 和 手动角膜仪：IOL Master平均角膜曲率为44.62±1.52 D，手动角膜仪为44.60±1.52 D。 t-test显示差异具有统计学意义(P=0.001)； Bland-Altman图显示两种仪器间95%一致性区间(LOAs)为-0.22～0.22； 2)IOL Master 和自动角膜仪：IOL Master平均角膜曲率为44.62±1.52 D，自动角膜仪为44.46±1.53 D。t-test显示差异具有统计学意义(P<0.0001)。Bland-Altman图显示两种仪器间95%LOAs为 -0.24～0.55； 3)自动角膜仪和手动角膜仪：自动角膜仪平均角膜曲率为44.60±1.52 D，手动角膜仪为44.46±1.53 D。t-test显示差异具有统计学意义(P<0.0001)。Bland-Altman图显示两种仪器间95%LOAs为-0.30～0.57。

结论：使用不同的仪器获得的角膜曲率数据是不可替换的，这对于白内障外科医生在外科手术计划和结果评估方面具有重要意义。     

VERION数字导航系统测量角膜曲率和散光的可重复性及其与iTrace、Lenstar LS900、手动角膜曲率计检测结果的一致性研究

目的 分析VERION数字导航系统测量角膜曲率和散光的可重复性及其与iTrace、Lenstar LS900、手动角膜曲率计检测结果的一致性.方法 对62名年龄相关性白内障患者分别用上述四种仪器进行角膜生物测量,记录并分析陡峭轴角膜曲率(steep keratometry,Ks)、平坦轴角膜曲率(flat keratometry,Kf)、散光幅度、散光轴位、矢量参数J0和J45.分析VERION测量的可重复性,并比较VERION与其他三种仪器测量结果的一致性.结果 用组内相关系数(intraclass correlation coefficient,ICC)和克隆巴赫系数(Cronbach's alpha,α)分别对Ks、Kf、散光幅度、散光轴位、J0以及J45做出分析,结果均大于0.9(均为P＜0.001),提示VERION测量角膜曲率及散光的可重复性极好.VERION测量的Ks、散光幅度均高于iTrace(均为P＜0.05),其余指标的差异无统计学意义(均为P＞0.05).Bland-Altman分析显示J0、J45及散光轴位的95％ LOA分别为(-0.31 ～0.35)D、(-0.25～0.31)D、-13.5°～12.3°.二者测量的散光轴位差小于10°者占总体的77％ (48/62),在合并角膜散光大于1D的患者中占91％ (42/46).VERION与Lenstar LS900测量结果仅J45差异有统计学意义(P＜0.05),其余指标差异无统计学意义(均为P＞0.05).Bland-Altman分析发现J0、J45及散光轴位的95％ LOA分别为(-0.25 ～0.31)D、(-0.27 ～0.36)D、-13.5°～11.0°.二者测量的散光轴位差小于10°者占总体的85％(53/62),在合并角膜散光大于1D的患者中占93％(43/46).VERION与手动角膜曲率计检测的Kf、散光幅度差异有统计学意义(均为P＜0.05),其余指标差异无统计学意义(均为P＞0.05).Bland-Altman分析显示J0、J45及散光轴位的95％ LOA分别为(-0.38 ～0.35)D、(-0.41 ～0.42)D、-12.6° ～16.4°.二者测量的散光轴位差小于10°者占总体的81％ (50/62),在合并角膜散光大于1D的患者中占91％(42/46).结论 VERION在测量角膜曲率及散光方面具有良好的可重复性.其与iTrace、Lenstar LS900和手动角膜曲率计在角膜曲率、散光幅度的测量方面一致性较好,但对散光轴位的测量差别较大.     

Toric工晶状体治疗白内障合并角膜散光疗效观察

目的：应用角膜曲率联合角膜地形图检查测量角膜曲率,采用个性化手术源性散光值,计算人工晶状体型号及轴位,在白内障手术中植入散光型人工晶状体来矫正角膜散光并观察疗效。 方法：收集白内障并伴有角膜规则散光的病例43眼,手术中采用白内障超声乳化术植入AcrySof Toric IOL,并放置IOL于目标轴位,观察术后屈光结果。 结果：术后随访3mo,33眼使用T5以下人工晶状体,85%患者裸眼视力＞0.5,70%患者裸眼视力＞0.8术后角膜散光由术前的1.64±0.53D降至0.63±0.32D,10眼应使用T6,T 7,但使用T5裸眼视力均＞0.5,残余散光接近预测值。术后3mo观察,43眼术后第1d平均轴位偏离465°±4.21°,84% IOL轴位偏离＜10°,3mo平均旋转116°±184°,100% IOL旋转＜10°。 结论：应用角膜曲率联合角膜地形图检查测量角膜曲率,采用个性化手术源性散光值,计算人工晶状体型号及轴位,植入AcrySof Toric IOL能有效地矫正角膜散光,并具有良好的囊袋内稳定性。     

A new, pachymetry-based approach for diagnostic cutoffs for normal, suspect and keratoconic cornea

Purpose

To analyze whether an association exists between keratometric and pachymetric changes in the cornea, and whether it can be used to create pachymetric cutoff criteria secondary to keratometric criteria.

Methods

In this cross-sectional study, 1000 candidates presenting to the refractive surgery services of a tertiary care hospital underwent bilateral Orbscan IIz (Bausch and Lomb) assessment along with other ophthalmic evaluation.

Results

Stepwise regression analysis-based models showed that simulated keratometry (simK) astigmatism was significantly predicted by the minimum corneal thickness (MCT) and difference between central and MCT (δCT), mean SimK by the MCT and δCT, and maximum keratometry in the central 10-mm zone by the MCT and δCT (P<0.001). The mean MCT values were 542.5±39.6, 539.9±39.2, 524.2±49.5, and 449.3±73.7 μm for flatter normal (<44 D), steeper normal (≥44 D), keratoconus suspect and keratoconic eyes, respectively (P<0.001). The mean differences between central corneal thickness and MCT (δCT) were 12.2±7.1 μm, 12.4±7.4 μm, 14.4±8.9 μm and 23.2±10.1 μm for the flatter normal, steeper normal, keratoconus suspect, and keratoconic eyes, respectively (P<0.001). Mean and 2SD cutoff were used to suggest that a cornea having MCT<461 μm or δCT>27 μm has only a 2.5% chance of being normal and not a keratoconus suspect or worse.

Conclusion

Pachymetric diagnostic cutoffs can be used as adjuncts to the existing topographic criteria to screen keratoconus suspect and keratoconic eyes.