Olsen Thomas, Thorwest Martin
University Eye Clinic, Aarhus Kommunehospital, Aarhus, Denmark.
J Cataract Refract Surg. 2005 Jul;31(7):1345-50. doi: 10.1016/j.jcrs.2004.12.066.
To study the conditions for consistent axial length measurements with partial coherence interferometry (PCI) performed with the Zeiss IOLMaster.
University Eye Clinic, Aarhus, Denmark.
A consecutive, unselected series of 1289 cataractous eyes were measured with the optical technique of PCI according to the IOLMaster as well as with conventional (contact) A-scan ultrasound (US) for the measurement of axial length. For each PCI reading, the signal-to-noise ratio (SNR) was recorded and used for comparison with the US measurement. All patients had routine phacoemulsification with implantation of an intraocular lens (IOL). In 284 cases, the patients were reexamined 2 to 3 months after surgery and the axial length was again measured using PCI. The readings of the IOLMaster, which had been calibrated against immersion US from the manufacturer, were recalculated to represent the true optical length and used in the analysis of the consistency of the measurements.
Not all readings obtainable with the IOLMaster were of good quality, and large differences with conventional US were found. The error between US and PCI decreased significantly with increasing SNR, showing a minimum error at an SNR value above 2.1. The SNR correlated significantly with the visual acuity with considerable scatter, however. Excluding readings with a poor quality (SNR <2.1), the postoperative PCI measurements showed a high correlation with the preoperative measurement (r = 0.99), showing a mean difference of 0.08 mm +/- 0.12 (SD). The difference was highly significantly different than zero (P < .001) and may be explained by a higher refractive index of the biological lens than assumed in the original calibration of the IOLMaster.
The quality of the axial length readings of the IOLMaster was influenced by the SNR value. However, with proper SNR evaluation and recalibration of the PCI measurements, it is possible to achieve consistent PCI readings with little variation between preoperative and postoperative measurements. These results are promising for a higher accuracy of the IOL power calculation.
研究使用蔡司IOLMaster进行部分相干干涉测量法（PCI）时获得一致眼轴长度测量值的条件。
丹麦奥胡斯大学眼科诊所。
采用IOLMaster的光学PCI技术以及传统（接触式）A超（US）对连续入选的1289例白内障患眼进行眼轴长度测量。每次PCI测量时，记录信噪比（SNR）并与US测量值进行比较。所有患者均接受常规超声乳化白内障吸除联合人工晶状体（IOL）植入术。284例患者在术后2至3个月接受复查，再次使用PCI测量眼轴长度。已根据制造商的浸没式US进行校准的IOLMaster测量值重新计算以代表真实光学长度，并用于分析测量的一致性。
IOLMaster并非所有可获得的测量值质量都良好，且与传统US测量值存在较大差异。US与PCI之间的误差随SNR增加而显著降低，在SNR值高于2.1时误差最小。然而，SNR与视力显著相关，但存在较大离散度。排除质量较差（SNR<2.1）的测量值后，术后PCI测量值与术前测量值高度相关（r = 0.99），平均差异为0.08 mm±0.12（标准差）。该差异与零有极显著差异（P<.001），可能是由于生物晶状体的折射率高于IOLMaster原始校准中假设的值。
IOLMaster眼轴长度测量值的质量受SNR值影响。然而，通过适当的SNR评估和PCI测量的重新校准，可以实现一致的PCI测量值，术前和术后测量值之间变化很小。这些结果对于提高IOL屈光度计算的准确性很有前景。
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