目的：评估B超在不同性质眼后段异物大小测量中的准确性。

方法：回顾性分析2016-01/12在我院被诊断为眼后段异物的患者13例13眼。异物在取出后用直尺测量实际大小，并同术前B超所测数值进行比较，同时计算相关系数(B超测量值/实际大小)。为了排除手术操作损伤异物对真实大小测量的影响，选定长度为5mm的不同材质物体(分别为金属、玻璃和木质)放入直径约20～30mm的水囊中模拟眼内异物，同样进行以上的测量，测量重复4次。

结果：选取13眼内异物均经玻璃体手术完整取出，其中金属磁性异物12眼，玻璃异物1眼。12个金属异物术前B超所测长轴和实际长度的平均值分别为3.65±1.30和2.45±0.94mm，所有测量值均大于实际值(P=0.016)。相关系数的平均值为1.49。体外实验中，金属、玻璃和木质三种不同性质异物B超的平均测量值分别为6.76±0.15、6.55±0.04和6.02±0.07mm，相关系数分别为1.35、1.31和1.20。

结论：B超用于眼后段异物测量时，其所测量值会大于真实大小，尤其是对于金属和玻璃异物。因此在术中制作异物取出切口时需要进行考虑。

METHODS: IOFBs from a total of 13 eyes collected in our hospital from January 2016 to December 2016 were analyzed retrospectively. Immediately after IOFBs being taken out, their actual sizes were measured with a ruler. The difference between the pre-operative B-ultrasound measurements and the actual size were compared, and the correlation coefficient was calculated(B-ultrasound measurement/actual size). In order to exclude the possibility that any damage to the IOFB during an operation may interfere with the actual size measurement, different kinds of 5mm long objects(metal, glass and wood)were put into a water sac which was about 20mm-30mm in diameter to mimic IOFB in the eyes respectively. Same measurements for each kind of objects were then preformed and repeated for 4 times.

RESULTS:All the 13 cases of IOFBs, including 12 cases of magnetic metal and one case of glass were removed intact via vitrectomy. Of all metal IOFBs, the average axle length by B-mode ultrasound and the average actual axle length were 3.65±1.30mm and 2.45±0.94mm respectively. All measurements were larger than actual sizes(P=0.016). The average correlation coefficient was 1.49. For the water sac experiment, the average measured values of metal, glass and wood objects were 6.76±0.15mm, 6.55±0.04mm and 6.02±0.07mm, and the average correlation coefficient were 1.35, 1.31 and 1.20 respectively.

CONCLUSION:The measured size is larger than the actual size when B-mode ultrasonographic scan is used to evaluate the posterior segment IOFB, especially for metal and glass objects. Therefore, it is necessary to take into consideration when making incisions for operational IOFB removal.