AIM: To provide guidance for more accurate measurement of axial length(AL)of difficult measuring eyes by comparing the differences in the AL of the patient's difficult measuring eye with three methods of the sitting position, supine position A-scan and Lenstar 900(Lenstar, LS900).

METHODS: Clinical case-control study. We selected 102 cases(102 eyes)including cataract patients with combined silicone oil filled, vitreous hemorrhage or retinal detachment and patients with dislocation of the lens or IOL in Zhengzhou Second Hospital from May 2019 to September 2020. AL were measured using LS900 and A-scan on sitting position and supine position respectively, and the results of the three methods were statistically analyzed.

RESULTS: The detection rates of LS900 and A-scan axial measurement were 83% and 100% respectively. Three methods of A scan in sitting position, supine position and LS900 to measure the overall AL, silicone oil group, lens dislocation group and vitreous hemorrhage group, the differences were statistically significant(P<0.001), The mean values of AL measured by overall A-scan, supine positions of silicone oil group, supine position of lens dislocation group and vitreous hemorrhage group were statistically significant differences with LS900 measurement(all P<0.05), while there was no statistical difference between the results of the overall sitting position and the difficult measuring eye groups' sitting position compared with the LS900 measurement of AL. The three measurements showed good consistency within the 95% consistency range, but the result of A-scan on sitting position was closer to LS900.

CONCLUSION: Changing the conventional decubitus position to the sitting position can improve the accuracy of the measurement results and provide clinicians with more reliable guidance for the treatment of patients with difficult measuring eyes of A-scan axial measurement, especially in diseases with altered ocular structure.