[Accuracy of immersion B-scan ultrasound biometry in high myopic patients with cataract]

To compare the accuracy of axial length measurement with three methods, that is, immersion B-scan, contact A-scan, and IOLMaster in high myopia with cataract.

To analyze the data of the 40 patients (66 eyes), who were all high myopia with cataract and accepted the phacoemulsification and fold-able lens implantation surgery in our hospital from Jan 2012 to May 2012. The measurement of axial length was performed respectively in 66 eyes by immersion B-scan, contact A-scan and IOLMaster. Keratometric power was measured preoperatively by IOLMaster. The IOL power calculation was carried out according to SRK/T formula in the basis of IOLMaster. Their refraction outcome was follow-up three months after operation.

The axial length was (27.91 ± 1.96) mm, (27.71 ± 2.15) mm, (27.88 ± 2.04) mm respectively by immersion B-scan, A-scan and IOLMaster. There was no significant difference between immersion B-scan and IOLMaster method (t = 0.726, P = 0.473). But the axial length measured by contact A-scan was shorter than that tested by immersion B-scan(t = 2.223, P = 0.003) and IOL Master (t = 2.614, P = 0.014) significantly. There was significant difference between immersion B-scan and contact A-Scan method in those patients whose mean absolute refractive error (MARE) was within ± 0.50 Diopter three months after operation (χ(2) = 5.67, P < 0.05) , while there was no significant difference between immersion B-scan and IOLMaster measurement (χ(2) = 0.06, P > 0.05). The same situation happened in those patients whose MARE was within ± 1.00 Diopter. That means, there was significant difference between immersion B-scan measurement and contact A-scan measurement (χ(2) = 4.19, P < 0.05) , while there was no significant difference between immersion B-scan and IOLMaster measurement(χ(2) = 0.36, P > 0.05).

The immersion B-Scan measurement is better than A-scan, and it is as accurate as the IOL Master measurement, which is another good choice for the axial length measuring in high myopia with cataract cases.