AIM: To evaluate the accuracy of B-mode ultrasonography in the measurement of different kinds of posterior segment intraocular foreign body(IOFB).

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.